Understanding Crop Factor

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There is a great deal of confusion surrounding crop factor, and it is particularly difficult to explain, but let’s give it a try, shall we?

Before we dive in, let me dispel two vicious rumors related to crop factor that are circulating through the photography (Internet) world today:

  1. Crop factor does NOT affect a lens’s focal length.
  2. Crop factor does NOT affect a lens’s aperture.

Before you scroll to the bottom of the screen to leave a comment to the contrary, let me explain why I am stating these facts…

Focal Length The focal length of a lens, expressed in millimeters, is the distance along the lens’s optically central axis (beginning at the rear nodal point) to the image plane in the camera (often illustrated by a "Φ" on the top plate of a camera body) when the lens is focused at infinity. The image plane in the camera is where you will find your digital sensor or film plate.

Therefore, a 50mm lens can measure 50mm from the point where light rays begin to exit the lens in the same direction as they entered the lens until they arrive on the image plane. Some “pancake” lenses and mirror lenses have optical tricks to shorten them, but in general, the focal length is that physical measurement.

A zoom lens can change the physical focal length of a lens. Sometimes this movement is contained inside the lens—the lens body does not physically change length—and other times the lens does change its size.

However, regardless of what kind of camera or sensor you place behind the lens, the focal length will not change just because you have a larger or smaller sensor or frame of film. I will explain later how sensor size (or film size) changes the equivalent focal length—not the true focal length of the lens.

Aperture  is the size of the opening in the lens. Some lenses have fixed apertures that cannot be changed, but most photographic lenses have variable apertures to control the amount of light entering the lens. This opening is regulated by a diaphragm comprising blades that can be adjusted to vary the size of the hole (aperture) through which the light passes.

In photography, aperture is expressed as a ratio of the focal length to the diameter of the aperture opening. The ratio is commonly referred to as an f/number, f/stop, focal ratio, f/ratio, or relative aperture.

This ratio is based on physical measurements and is completely independent of the size of the camera’s sensor or the size of the film you are shooting. Sensor size has an effect on depth of field, but not because it changes aperture. Aperture is independent of film frame or sensor size.

35mm Format

The first thing to know about crop factor is that, as with all “factors,” we need to have a base reference from which to work. In the photography world, this reference is a piece of 135 film. In the digital photography world, “full-frame” sensors are the same size as this film; a film frame with a width of 35mm. Cameras of this photography format are collectively known as “35mm cameras.”

A 35mm film strip measures 35mm across
 

One source of crop factor confusion is the use of “35mm” when discussing the reference. The value in this case is used not as a focal-length measurement, but as a measurement of the dimensions the frame of film. The film image area measures 24 x 36mm, but the strip is 35mm wide. So, when you think of “35mm” when it is used in reference to film or the size of a camera sensor, know that you are not referring to lens focal length. You can mount a lens of any focal length, even a 35mm lens, on a 35mm camera. The focal length is the focal length. Film and sensor dimensions are different.

For years, the 35mm camera has been, by far, the world’s most popular camera format. Because of this, for those of us who grew up in the world of 35mm cameras, when we think of the field of view given by a lens of a certain focal length, we can visualize what the photograph should look like. In the 35mm camera world, a lens with a focal length of around 50mm will provide a “normal” view with its human-eye-like field of view. Lenses with shorter focal lengths will provide a wider view and lenses with longer focal lengths will provide narrower or telephoto views.

Digital Sensors

Life was simple back when almost everyone was shooting 35mm cameras and 35mm film. Sure, there were those making magic with medium format and large format cameras, and there were point-and-shoot cameras that took specially made smaller films. My first camera, handed down from my grandmother, was a Kodak Instamatic 30, with its 13 x 17mm 110 film. Back then, no one really paid attention to “crop factor,” even though it existed. I’d bet most photographers didn’t know the dimensions of their 110 film, nor did they know the focal length of the tiny lenses! You just looked through the camera and took the picture it gave you.

Then, digital photography arrived. In its early days, most sensors were smaller than 35mm film, and a virtual can of worms was opened. Why? Because the sensors were smaller than 35mm film, the images seen through a lens of any particular focal length had a different field of view than that of the same lens on a 35mm film camera. Suddenly, a 50mm lens no longer had a “normal” field of view; it was a bit more of a telephoto.

The cropped sensor “sees” a narrower field of view
 

If you never shot 35mm film, this was no big deal because your mind’s eye did not have a 35mm film reference for different lenses. But photographers entering digital imaging decided that they needed to know the “35mm equivalent” field of view of various lenses when attached to a camera with a digital sensor smaller than 35mm film. The reality of it is, “crop factor” serves to translate a measurement into a language in which many of today’s photographers were never fluent to begin with. And, because of this, many of you out there have been very confused and frustrated by the mention of crop factor. Hopefully this article will end your confusion!

Crop Factor

A round lens produces a circular image circle—not rectangular. The sensor, or film, at the back of the camera captures a rectangular portion of this image circle. When we use 35mm film as a standard, any camera with a sensor smaller than a frame of 35mm film will cover a smaller portion of the image circle produced by a given lens and will thereby change the field of view of that lens. This is the “crop” part of the crop factor.

However, because traditionally, the field of view produced by a given lens has been described not as a measurement of degrees, but by the focal length (kind of the “name”) of the lens, we need to translate the cropped field of view into an equivalent lens focal length.

For example, if you attach a 50mm lens to a camera with a smaller-than-35mm film sensor, you will have to multiply the focal length of that 50mm lens by a factor derived from the size differential of the sensor to calculate the 35mm equivalent focal length. This will then give you the means to figure out the lens’s field of view based on that new equivalent focal length. This is the “factor” part of crop factor.

This multiplication factor is the ratio of the size of the digital sensor to the dimensions of the 35mm film negative.

Formula: The diagonal of a rectangle can be determined by a2+ b2 = c2

Full Frame: 24mm2 + 36mm2 = c2

576 +1296 = 1872

Square root of 1872 = 43.3mm

Full-Frame or 35mm Diagonal / Crop Sensor Diagonal = Crop Factor

So, if you have a camera with an APS-C-sized sensor (circa 15.6 x 23.5mm or 14.8 x 22.2 on Canon), plug in the numbers and you will get a crop factor of 1.5x (or 1.6x for Canon).

Then, to find the equivalent focal length of the new field of view afforded by the smaller APS-C sensor, multiply the true focal length of the lens by 1.5x to get the 35mm equivalent focal length of the lens. A 50mm lens on a camera with a 1.5x crop factor APS-C sensor gives a field of view equivalent to that of a 75mm lens on a full-frame or 35mm film camera.

Remember, the actual focal length of the lens is unchanged, as is its aperture.

In our example, if you weren’t familiar with a 50mm lens’s field of view in the first place, this doesn’t really matter. But if you were familiar with the 50mm lens’s field of view, you will know that this same lens, when placed in front of the smaller sensor, has a narrower field of view than your normal vision has.

A comparison of relative sensor sizes.

 

If you have a zoom lens on a smaller-than-full-frame camera, you can figure out the effective focal-length equivalent by multiplying both focal length numbers by the crop factor. For example, a 70-200mm lens becomes a virtual 105-300mm lens on a 1.5x APS-C sensor.

Cameras with sensors or films larger than a 35mm frame will have sub-one crop factors. For instance, a medium-format Pentax 645Z’s sensor measures 33 x 44mm. This gives it a crop factor of 0.78x. A 50mm lens on this Pentax camera gives an equivalent field of view of a 39mm lens.

Full-frame versus The Rest

The crop factor discussion inevitably leads us to the full-frame versus smaller-sensor debate. For my take, click here.

So as not to drive down the well-trodden path here, in summary, full-frame cameras are ideal for landscape images because there is no crop factor and wide-angle lenses maintain their wide-angle field of view. Smaller-sensor cameras give lenses a virtual telephoto effect that is ideal for some sports, wildlife, and macro work. Both formats have advantages and disadvantages.

Another thing to mention: there are “regular” lenses and there are lenses specifically designed to operate on smaller-sensor cameras. These small-sensor lenses may not work well on their full-frame cousins. On a 35mm film or full-frame digital camera, you may experience heavy vignetting. If the small-sensor lens does work on a full-frame digital camera, the camera might simulate the smaller sensor the lens was designed for and automatically provide the crop factor field of view. A regular lens will work happily on a full-frame digital, 35mm film, or smaller-sensor camera. The crop factor will only apply to a lens if it is used on a small-sensor camera. Today, some manufacturers refer to their “regular” lenses as “full-frame lenses” to emphasize that they are not designed specifically for smaller-sensor cameras. But, before digital photography, all 35mm format lenses were “full-frame.”

The Final Word

Crop factor is really quite simple. The confusing thing is that, as I said earlier, it exists to translate an angular measurement (degrees of field of view) virtually into a linear measurement (millimeters of lens focal length) so that old-school 35mm photographers can figure out the real field of view of a lens based on an equivalent focal length resulting from using sensors smaller than 35mm film. Get it? Got it. Good!

I suppose that is useful in many ways, but I have seen many frustrated photographers over the years try to understand and explain this concept. Sprinkle in some bogus information on the Web about magically changing focal lengths and apertures, and everything has become a mess!

I hope this has cleared things up for those who are new to photography or who were confused a few minutes ago. If not, I stand by to take your questions! And, in case you were wondering, the Instamatic 110 film camera has a crop factor of 2x. 

For more information about the theory behind crop factor, be sure to watch this engrossing video.

 

303 Comments

If you mount a full frame EF mount lens on APS-C camera with an EF to EF-M adapter is it still subject to the crop/multiplication factor? I'm trying to figure out what prime EF lens would be 35mm equivalent on my Canon M50.  

It would still be subject to the crop factor, in this case 1.6x. Crop is dependent on sensor size, though some very specialized adapters referred to as Speedboosters or focal reducers can actually counteract this. 

To get a 35mm equivalent on the M50 I would actually recommend the native EF-M 22mm f/2 Lens. No adapter required. If you do want a full-frame EF lens for other reasons I would recommend the EF 24mm f/2.8 IS USM. If you don't need a full-frame lens, the EF-S 24mm f/2.8 STM is another option dedicated to APS-C.

That answers my question perfectly, thanks. I understand that the diagonal of a different sized sensor is proportional to a standard sized sensor, but wouldn’t the width of the adapter increase the focal length causing more surrounding area of the image to hit the sensor (like a wider angle shot)? I'm curious how this works, but I really started this because I want to try a Cine lens on the M50.

Great question! So if you compare a DSLR (with the Canon EF mount) and a mirrorless (with the Canon EF-M mount) you will notice that the DSLR is a lot thicker. The reason is that the optical system in the DSLR has to account for a mirror, so the distance from the mount to the sensor is longer.

What an adapter does is basically make sure that the DSLR lens is the same distance from the mount to the sensor as it would be if it was mounted natively on a DSLR. Make sense? So the lens is designed to work at the distance the adapter puts it at, meaning no change compared to if it was on a DSLR.

Here's an article that goes into way more detail on mounts and adapters: https://www.bhphotovideo.com/explora/photography/tips-and-solutions/introduction-to-lens-mounts-and-lens-adapters

Please let us know if you have any more questions!

I get it now! In my train of thought, I was mistakenly putting an APS-C lens to an APS-C sensor with an extension tube in between.

Is there any advantage in terms of image quality for the smaller sensor to crop the image, compared to a full frame, versus cropping a full frame image down using photo editing software? 

Maybe. It would be on a case-by-case basis. If you find yourself always using a crop mode or cropping in you may want a 24MP APS-C camera instead of a 24MP full-frame sensor since you'll have more resolution to work with in the end. However, that extra resolution may come with more noise in low-light conditions. So there is always a trade-off.

So how would using an APS-C sized lens on a Full frame camera affect aperture? I want to get the Kipon 40mm f/.85 mark ii lens for my Panasonic S1 which is full frame, but am mostly getting it for that f/.85 aperture (as well as the dreamy look it gives wide open). Will the lens perform at f/.85 or will it be effectively something like f/1.2,4?

Using a lens that is optimized for an APS-C sensor on a camera with a full frame sensor would only crop the image significantly and would cause a reduction in your resolution. The aperture would be independent of this.

So how do you go about determining the ideal lens replacement when moving from an APS-C/DX sensor with a lens designed for that to a full frame sensor?

I'm currently running an old Nikon D7000 with the great Tamron 18-400mm f/3.5-6.3 Di II VC HLD lens, with plans to upgrade to a Z6 and eventually native Z mount lenses and am trying to understand how my current lens will behave on the Z6 and how to determine what the proper native replacement would be when I get to that point.

If adapting a Tamron 18-400mm with the Nikon FTZ adapter, this lens would give you heavy cropping and cut the resolution in half, since the lens only covers a DX sensor effectively and the Z6 has a full frame sensor. Essentially, a full frame equivalent to this lens in a direct Z mount is the Nikon NIKKOR Z 24-200mm f/4-6.3 VR Lens, B&H # NIZ24200.

https://bhpho.to/2YwuSMO

Thanks!  I'll add that to my list.

If I'm using an 18-35mm aps-c lens on an aps-c camera,  Is it an 18-35mm or 28.8-56mm on that camera?  (Canon 80d) 

A lens like the Sigma 18-35mm f/1.8 would keep that focal length on the Canon 80D.  However, the angle of view is similar to using a 28.8-56mm lens on a full frame sensor.

Hi, I just wanted to double check on something. The article refers to adapting non-native full frame lenses to smaller sensors. An f1.4 50mm focal full frame lens would have a 2x cropped 100mm field of view on Micro Four Thirds, but the actual focal dimensions and aperature still remains 50mm f1.4. 

Question 1:  a  .64x speedbooster /focal reducer would only affect field of view, but not actual focal length and aperature?

Question 2: when it comes to native focal lenses for Micro Four Thirds, 25mm f1.2 is an actual full frame 50mm f2.4 in focal length, since they have been designed that way from scratch? Because the subject focal dimension look and bokeh on my 25mm f1.2 MFT  lens apears to be 50mm and f2.4.

Thank you.

Hi Anselm, hopefully I can help simplify this a bit. No matter how you adapt any lens to any camera, the lens will always remain what it is. A 50mm f/1.4 will always be a 50mm f/1.4 no matter which camera it is used on- the differences in fields of view has to do with the camera and sensor size. We use this idea of "crop factor" to help explain how the differences in sensor size are related to using different focal length lenses. Many people have an understanding of how a 50mm lens looks on full-frame, but if this lens is used on a smaller sensor (like Micro Four Thirds) the field of view will be closer to how a 100mm lens would look on full frame, but only in terms of field of view. The lens still would have the same 50mm focal length and the same aperture.

And for the second question, a 25mm f/1.2 lens, which has been designed for Micro Four Thirds, is a 25mm f/1.2 lens no matter how you look at it. If you could manage to put that lens on a full-frame camera, it'd still be a 25mm f/1.2. The catch is that a lens specifically designed for Micro Four Thirds won't have a large enough image circle to cover the larger full-frame sensor...but the field of view and aperture won't change.

Just came across this article while I was doing some research into whether I should get the Fuji XF 90mm/2. After reading this, I my wallet can thankfully say whew...impulse purchase averted (found one used for 50% of original price). My adapted Nikkor 85mm/1.8 AI thanks you.

Hello Alwin,

Glad we were able to help you out.  Stay tuned for more helpful and interesting articles.

Stay safe!

Sorry, Alwin's wallet, but that Fujifilm XF 90mm f/2 is an amazing lens. Your Nikkor 85mm is a great lens, too, but that Fujfilm is crazy fun to use!

WOW! I really needed this. I took my first pix with my older sisters Kodak Brownie 620 in December 1949 and have been snapping away ever since with more cameras than I can remember. I entered the digital world with a Finepix S5000 taking my first pic. with it Xmas Day 2006. There have been several digital cameras since then but am content with my current Nikon D3200.

Like many of us oldies I still think in 35mm film reference terms and wanted to know the equivalent standard 50mm film lens would be for my Nikon DX. I have the kit lens but would be happier to use it if it had a metal mount, also the 55-300mm zoom and the 35mm f1.8 lens. I am mainly interested in people photography, with a bit of Aussie wildlife and macro flowers, beasties, etc. A bit of video and have the external stereo mic. Not all that interested in the 55-300mm zoom though.

So, I get from your article my excellent little AF-S 35mm DX lens is pretty close to a 50mm film camera lens and looks like it will be my primary lens. I mean, after all, some 65 years of film photography does leave me with a 50mm frame --- of mind!

Great forum and some great s/h cameras at great prices from B&H (is that the old Bell and Howell movie camera firm?)

Gayle,

Western Australia

Hello Gayle,

We're happy that you enjoyed the article!  By the way, the "B" and "H" in B&H stands for 'Blimie & Herman' the stores founders :)

Keeping reading our blog for the latest news on new products and helpful tutorials and hands-on reviews.

Cheers,

Hi Gayle,

You are correct...a 35mm lens (DX or non-DX) will get you a 50mm-like field of view that you are familiar with from your film days, so you are good to go! And, that Nikon DX 35mm f/1.8 is a fantastic little lens!

Best,

Todd

It is interesting to see how technology has changed since the article was written! Samsung and Nikon1 are long gone, Fuji isn't mentioned, nor are there any Sony FX, or Pentax FX! L Mount is naturally nowhere to be seen, nor the Sigma FX.

I shoot CX (only Nikon use that name for the 1" sensor cameras, I think, and they don't make any cameras using it now, do they), DX and FX, foremost.

I am often surprised that people claim that an f/2.8 shot with my Sigma 135/1.8 is not the same when I change the sensor format, while in reality, it is the DOF and FOV that changes, nothing else. I love using the old Nikon1 V1, but the last model, the J5, has 20MP on that tiny chip, just as my newest DX!  

Thanks again, Tord! Good stuff!

Great explanations about the crop factor and the 35 mm - equivalent focal length.  My question.  One of T Northrup's videos states that the crop factor must also apply to the f-stop of the DX lens, so he states that a Nikon DX 50mm f/1.8 is actually equivalent to an FX 75mm f/2.7 on a full frame camera.  Yet, in one of the posts below, it's stated that the aperture is the same whether DX or FX.  Which is correct?  Thank you.

Hi Wayne,

Thanks for the kind words!

You aren't the first to bring up that video from Mr. Northrup and, with all due respect to him, the short answer is that he is correct when the f-stop is looked at from the viewpoint of depth of field. Nevertheless, I will try to clarify things for you here:

The formula used to assign an f-stop number to the lens opening is: f-stop = focal length / diameter of effective aperture (entrance pupil) of the lens. Note that sensor size (or film size) does not appear anywhere in that formula. Therefore, the f-stop number of a lens is completely independent of the size of the sensor of the camera. [See https://www.bhphotovideo.com/explora/photography/tips-and-solutions/understanding-exposure-part-2-aperture for more info, if you dare! :)]

This is an important "constant" as, if sensor size changed f-stop in regards to exposure values, we would have to program our hand-held light meters with a sensor size input and exposure math, in general, would get all wonky. But, because the f-stop is independent of sensor size, f/8 at 1/500th of a second and ISO 200 is, for all intents and purposes, f/8 at 1/500th of a second and ISO 200 on an APS-C, full-frame, medium format, large format, smart phone camera, etc.

What Mr. Northrup is alluding to is that sensor size changes the depth of field of a lens. This is true and you can prove it mathematically. What he is saying is that a 50mm f/1.8 lens, when placed in front of a DX sensor, gives the equivalent field of view of a 75mm lens on a full-frame camera AND gives you a depth of field that is mathematically the equivalent of an f/2.7 aperture. [If you want to run the numbers, check out the formulae in this article: https://www.bhphotovideo.com/explora/photography/tips-and-solutions/depth-field-part-3 ...or, use a depth of field calculator that has an input for sensor size.]

So, before you run to the B&H sales counter demanding a full-frame camera, know that it is entirely possible to do shallow-DOF photography with DX (and even Micro Four Thirds) cameras—I do it all the time. The visual difference on most images between f/1.8 and "f/2.7" might not even be noticeable depending on your subject and subject-to-lens distance.

Please let me know if you have follow-up questions and thank you, again, for the kind words, and thank you for reading Explora!

Thanks for the detailed explanation , I also came here from his video and after going through your post , it's all starting to make sense . I just have one question , is there any particular benefits to buying an APS-C lens for an APS-C sensor vs full frame lenses , apart from the huge price disparity ?

The main advantage will be that an APS-C format lens would already be optimized for an APS-C sensor, being that it is at the proper focal length.  One might purchase a full frame lens for an APS-C sensor camera if they intend to upgrade to full frame at some point and are not considered with the crop factor involved.

Hi Ask,

Also, in general, APS-C lenses are lighter and smaller than their full-frame counterparts!

I agree with Todd, but, for instance, Nikon has very few DX lenses compared to the huge number of F Mount FX lenses out there. Some DX lenses work well on FX bodies (in FX mode), some are very soft along the edges, and some vignettes a lot, and a few just isn't very useful.

For Z cameras there are just a couple of DX lenses as yet (which gives essential VR to the Z50). The Z6 and Z7 have in-body-image-stabilization (IBIS), which the Z50 sadly lacks.  

A well-written article, by the way.

Yours,

Tord

Thank you, Tord! I appreciate the kind words!

Can you help? So I have a full frame Nikon 750, purchased 2nd hand, and have just tried a DX 18-200mm lens (which I use on a Nikon D90) on it. To cut out the vignette edges, I had to set the camera to  "crop". Does this mean that the full frame sensor is now behaving like a non-full frame cropped sensor and I may as well not have a full frame camera body? ie. do I now need to purchase a full frame lens!Thanks, (Mr) LB.

Hi Lalit,

Great question.

Yes, when the camera is set to "crop" mode when using a DX lens, it basically is only capturing the same area of the image that an APS-C/DX camera would. You still get the same sensor performance as far as ISO and noise characteristics, but you are getting smaller resolution files as not all of the sensors are recording data.

There are no rules against what you are doing, and there is nothing wrong with it, but I am sure some folks will tell you that you are doing the equivalent of putting old tires on a new race car.

Do you need to purchase a non-DX lens? No. Will you get the subtle (and subjective) benefits of your full-frame camera with non-DX lenses? Yes.

Bottom line: If you like the lens and the images you are getting with it, there is no need to rush to get a non-DX lens.

Thanks for the questions and thanks for reading Explora! Please let me know if you have follow-ups!

Some DX lenses I have work great in FX mode, like the old Sigma 30 Art, as long as you crop to 16:9 format (or why not 5:4, or square, as it is the extreme corners that are bad.

Thanks for sharing your experience, Tord!

OK, long wanted answer to a question..... So if a ff 50mm lens is on a ff camera... its a 50mm true lens...... if you buy an apsc camera (say a6400 Sony) and an apsc lens labeled 50mm.... is the apsc lens a true 50mm as well? and will both images from both cameras take the same 50mm image?  Or is a 50mm apsc lens still a 75mm on a apsc camera. Thanks 

Hey Aussie J,

I hope I can end your long wait for an answer!

So, a 50mm lens is a 50mm lens regardless of what size sensor it sits in front of...or if it is mounted on a camera at all. A 50mm lens cannot be anything but a 50mm lens.

So, on a full-frame camera, the 50mm lens gives an angle of view that gets associated with a classic 50mm lens. If you put a 50mm lens or an APS-C-specific 50mm lens in front of an APS-C sensor, you will get an angle of view similar to that of a 75mm lens on a full-frame camera. The APS-C camera's angle of view will be different than the full frame camera with any 50mm lens mounted...even an APS-C 50mm lens.

If you want to simulate the field of view of a 50mm lens on a full-frame camera, you have to use a 35mm (focal length) lens on the APS-C camera.

I hope this answers your question, Aussie!

G'day and thanks for reading Explora!

Hi Todd, 

Thanks for responding to all the questions many of us have regarding the crop factor and the effects on FOV and DOF.  I'm have the same question as Aussie, but I'm still confused after your answer. The way I understand the question is the following: 

50mm Full Frame Lens on Full Frame Camera = 50mm FOV 

50mm Full Frame Lens on Super 35 or APS-c = Approx. 75mm FOV 

But what is the field of view of the following: 

50mm APS-C Lens on a Super 35 or APS-C Camera = ?  

Above you wrote: 

The APS-C camera's angle of view will be different than the full frame camera with any 50mm lens mounted...even an APS-C 50mm lens.

So is the crop factor of a full frame lens and Super 35/APC-C lens the same on Super35/APS-C cameras?  I know the smaller image circle will not cover a full frame sensor, so doesn't that impact the FOV? 

 When looking for lenses for Super 35 cameras I'm seeing the Equivalent FOV stats listed with a roughly 1.5 crop factor.... this is where I get confused since the way I understood that the Super 35 lens is targeting the smaller sensor in order retain the 50mm FOV?  In other words a Super 35 18-55 cine lens on a super 35 camera would give you the same equivalent FOV as a 18-55 Full Frame lens on a full frame camera. 

Thanks in advance for you response!  

[quote=William P.]

Hi Todd, 

Thanks for responding to all the questions many of us have regarding the crop factor and the effects on FOV and DOF.  I'm have the same question as Aussie, but I'm still confused after your answer. The way I understand the question is the following: 

50mm Full Frame Lens on Full Frame Camera = 50mm FOV 

50mm Full Frame Lens on Super 35 or APS-c = Approx. 75mm FOV 

But what is the field of view of the following: 

50mm APS-C Lens on a APS-C Camera = ?  

For years I was under the assumption that a APS-c Lens targeted the APS-c sensor in a way that emulated a full frame lens/Full Frame sensor combination... so a 50mm APS-c lens on a APS-c Camera would have the same field of view as a Full Frame Lens on a Full Frame Camera.  Since as I understand that not to be the case, wondering why we even have APS-c Lenses?  Why not just use full frame glass and apply the crop factor?  Also... why is the image circle on the APS-c Lens smaller and therefore not work on the full frame camera without vignetting?  It's for this reason I thought the field of view was affected. 

Thank you for any light you can shed on this!  

Bill P.]</p> <p>[quote=William P. wrote:

Hi Todd, 

Thanks for responding to all the questions many of us have regarding the crop factor and the effects on FOV and DOF.  I'm have the same question as Aussie, but I'm still confused after your answer. The way I understand the question is the following: 

50mm Full Frame Lens on Full Frame Camera = 50mm FOV 

50mm Full Frame Lens on Super 35 or APS-c = Approx. 75mm FOV 

But what is the field of view of the following: 

50mm APS-C Lens on a APS-C Camera = ?  

For years I was under the assumption that a APS-c Lens targeted the APS-c sensor in a way that emulated a full frame lens/Full Frame sensor combination... so a 50mm APS-c lens on a APS-c Camera would have the same field of view as a Full Frame Lens on a Full Frame Camera.  Since as I understand that not to be the case, wondering why we even have APS-c Lenses?  

Thank you for any light you can shed on this!  

Hi Bill,

Sorry for the delay in replying! I was busy all week welcoming a new baby boy into this world!

You understood my reply correctly. Any 50mm lens on an APS-C (1.5x) camera will have virtually the same FOV as a 75mm lens on a full-frame/135 format/35mm camera.

It is easy for photographers to get wrapped around the numbers and "crop factor" made everything worse!

Why do we have APS-C-specific lenses? Basically because the lenses can be smaller, lighter, and usually less expensive because they do not have to create an image circle as large as a full-frame sensor. Think about tiny point-and-shoot lenses, or the lenses on your smartphone...smaller sensor to cover, smaller lens required.

Another thing that might help: If you look at, for instance, the Fujifilm X lens line up, you will see that a bunch of primes (and zooms) have focal lengths that, when multiplied by 1.5, end up right at popular full-frame focal lengths. 23mm=35mm. 35mm=50mm. 56mm=85mm. 90mm=135mm. Because the Fujifilm X system only has APS-C lenses, Fujifilm shooters are less confused than Sony, Nikon, Pentax, etc, because they don't have a full-frame lens line-up or full-frame cameras.

I hope that helps! Again, sorry for the delay in replying. Please let me know if you have follow-up questions and thanks for reading!

This is a great helpful article and discussion, but there remains one thing I don't understand.  Let me outline my equipment first, as it is relevant to my question.

I've got a Canon APS-C camera (M6) with EF/EF-M adapter and Canon 70-300mm zoom telephoto lens.  Applying the 1.6 crop factor, this should give an "effective" equivalent maximum telephoto of 480mm.

I also have an EF-S 55-250mm lens.  Apparently, even though it's designed for APS-C (crop sensor) cameras only, the crop factor still applies, so it should be an effective equivalent of 400mm at the long end.

I've also got a Panasonic ZS200 point-and-shoot camera.  The Panasonic's actual focal length is 8.8 - 132 mm.  It has a 1-inch sensor.  Panasonic claims an effective equivalent range of 24-360mm.

So, quality issues aside, in theory my M6 with either of the above lenses should give me a greater effective telephoto (narrower field of view) at the long end of the lens, as compared to the Panasonic ZS200, but it does not.  The field of view in the Panasonic at 360mm equivalent is tighter on the subject than either of the Canon lenses.  That does not make sense to me, based on my understanding of this topic.  Why would that be?

I appreciate any guidance you can offer.

Most likely, you are probably using digital zoom.  While the Panasonic Lumix DC-ZS200 Digital Camera does indeed have a 8.8-132mm lens, which is the 35mm full-frame equivalent of a 24–360mm lens, the camera also has 2x digital zoom.  As indicated on page 140 of the Panasonic Advanced Features for the DC-Z200mm instruction manual states, the camera has Optical Zoom, [i.Zoom] (which stands for "Intelligent Zoom), and [Digital Zoom].  As indicated in the illustration on the bottom of page 140, when viewing the zoom bar on your LCD screen when adjustiong , when the zoom bar is white, you are in the optical zoom range where the lens is actually moving back and forth to adjust zoom, similar to the two lenses you own for use with your Canon cameras.  When in the light-blue range, you are using the Intelligent Zoom feature, and when in the dark blue range, you are fully using Digital Zoom (when combined, i.Zoom and Digital Zoom gives you a combined zoom ratio of 4x).  This is why it appears you have more zoom when using the Panasonic DC-ZS200, as the Canon lenses are purely optical and have no digital zoom capability.  The yellow bar and the focal length reading on the right-hand side of the zoom bar indicates your current zoom position and the current focal length.  You can turn the Digital Zoom feature off by going to MENU → [Rec] (Camera symbol)/[Motion Picture] (Movie camera symbol) → [Digital Zoom] and set [ON]/[OFF] to [OFF].

Hi Todd -

   So if I use a Nikon AF-S DX NIKKOR 35mm f/1.8G Lens on a APS-C camera (D500) and take the same image with a Nikon AF-S NIKKOR 35mm f/1.4G Lens on the same APS-C camera (assuming I use the same f stop for both pictures) I should get an image that looks the same?  I think I understand the crop factor scenario, I just get confused with selecting a DX vs Full Frame lenses....If I'm understanding things correctly, they should both perform the same with regard to field of view....my understanding is the primary differences between the two lenses are full frame uses better glass and tend to weigh more because they are built to cover the bigger sensor size.  I hope I didn't add to the confusion.

Thanks

Doug

Hi Douglas,

Yes, you will get an almost-identical image from the DX 35 and the non-DX 35mm lens assuming the camera has not moved and the aperture is the same.

Remember, there are only DX lenses and non-DX lenses. The advantage to the DX lens is that it can be smaller and lighter as it does not need to produce an image circle as large as the non-DX lenses. But, focal length is focal length...a 50mm lens is a 50mm lens no matter what camera you put it in front of.

I hope I didn't add to the confusion either! :) Let me know if you have more follow-up questions.

Todd - thanks very much for your response and for confirming what I thought to be the case.  Your article on understanding crop factor was really helpful to me....and not confusing at all like many of the other explanations I've read.  I really appreciate such a clear explanation of an otherwise confusing subject.  Thanks again!

Doug

No worries, Doug! I am glad to help clear up the muddy waters of the interweb! :)  Please let me know if you have any other questions and thanks for reading Explora!

Hey Todd,

I would like to discuss the following scenarios:

I shoot pic 1 using a 50mm f2 lens on a full frame camera for a peach 10 meters away.

Then I shoot pic 2 using the same 50mm f2 lens on an APS-C camera for the same peach 10 meters away. Now pic 1 should have a bigger field of view than pic 2. But if we crop pic 1 to the same field of view of pic 2, they should be exactly the same in terms of exposure and depth of field. The reason being the second shoot has the exact condition of the first shoot, only the APS-C sensor captures a smaller view of field. They should have the same light energy per unit area.

To be able to capture the same field of view of pic 1 using an APS-C camera and 50mm f2 lens, I need to move away from the subject. Say I move away to 15 meters toward the peach. Now I take the 3rd shoot, producing pic 3.

Pic 3 has the same field of view as pic 1, but because the distance has changed, the depth of field definitely changed between pic 1 and 3. Now the question is, does pic 3 have the same exposure condition comparing to pic 1? Since pic 1 is taken at 10 meters away and pic 3 taken 15 meters away, the light energy per unit area reaching the lens must be different. I think because of that, the light energy per unit area reaching the sensor would be different too. Like, if we have a square meter of solar panel, having it on Mercury would capture more light than having it on Earth. When further away, we need a bigger aperture to capture the same amount of light than when we are closer.

So in all, sensor size should affect exposure, if we would like to capture the same field of view as a full frame, right?

Thank you!

Hi Feng,
 
Great question(s)!
 
Scenario 1: Full frame, 50mm, subject-lens distance 10m.
Scenario 2: APS-C, 50mm, subject-to-lens distance 10m.
 
Yes, Photo 1 will have a wider field of view.
 
When you crop in, the exposure will be the same, but the depth of field will be slightly different (very slightly) due to the change in reproduction ratios. It might not be visually noticeable, but, mathematically, it happens.
 
Scenario 3: APS-C, 50mm, subject-to-lens distance increased to simulate full-frame field of view.
 
Different exposure? In theory, maybe. Your question actually was very thought-provoking and I had to do some research. And, there is a lot of conflicting information out there!
 
As you are alluding to, transmitted light follows the inverse square law…when transmitted from a point source radiating in all directions—a light bulb without a shade or, the sun.
 
If your light source is the sun, the peach will be pretty much the same brightness regardless of your distance from it. This is why mountains, buildings, etc. are not noticeably darker as you get further away from them. If this was the case, a photo of objects on the horizon would require lots of exposure compensation whereas objects in the foreground would be relatively bright—think of photographing down a road that stretches to the horizon—the pavement in the foreground isn’t noticeably brighter than the distant background road surface. Outdoors, unless in shadow, the sun pretty much evenly lights the world when overhead.
 
If the peach is illuminated by a spot light, it will remain virtually the same brightness regardless of the distance. It reflects the same amount of light regardless of the distance to the camera. As you move further away, the peach gets smaller, but not noticeably dimmer.
 
If the peach is illuminated solely by a light mounted on the camera, you will see a more profound effect in darkening as you move away from the peach due to the inverse square law and the fact that the distance between the light source and the peach is changing.
 
A good example of this in a different scenario:
 
Imagine a street with a tiny house placed at one end. It is nighttime and the house has one window and a light bulb hangs in the center of the room and the light from that bulb and room shine through the window.Regardless of the distance from that window, when you look at that window (or light bulb), the brightness is fairly consistent (unless you get a great distance away). The window does not change its distance from the light source as you move away. Its illumination is fairly constant. Now, think of taking a photo of an object outside of that window using the light from the window as the light source. The further you get from the window, the darker the object is because of its distance from the light source.
 
The inverse square law applies, kind of. It is a very specific law to a specific type of light source. In the real world we have light reflecting from all over out of doors, or in a studio, we control all the light.
 
I could meander around a bit, but I do think I knew what you were getting at…does a smaller sensor mean that there is a change in exposure? And, the answer is that, if there is a change in brightness, it is so minuscule that it is not measurable by a camera meter. This is why handheld exposure meters do not have settings for sensor or film size nor is there a separate set of exposure math for smaller (or larger) sensors.
 
I hope this helps!
 
Let me know if you have more questions.
 
Thanks for reading Explora!

Hi, can you suggest me a DSLR? I'm 16 and just starting photography. I have a great interest in photography. I'm confused between the wide range of DSLRs. I've used shoot and point cameras earlier but now I want to upgre? 

Hi alax!

Thanks for writing in! For a beginner DSLR and some other thoughts, check out this article: https://www.bhphotovideo.com/explora/photography/buying-guide/what-is-the-best-camera-for-beginners

Inside the article is a list of beginner DSLR cameras, but also some thoughts about other cameras that might work well for you.

Please let me know if you have questions after reading the piece.

Thanks for stopping by!

If you are looking for a recommendation for a entry-level DSLR camera that would be a good option for your first DSLR camera purchase, I would recommend the Nikon D3500 DSLR Camera with 18-55mm Lens, B&H # NID35001855B, as a good option for your usage needs.  The camera has full automatic control so you can begin using the camera as you would with any point-and-shoot camera, but as you learn more about photography, you would be able to use the camera in full manual mode, taking full control over all exposure settings and giving you full creative control.  The camera has an easy-to-navigate menu system, has a good five (5) frames-per-second continuous burst rate, HD video recording capability, and has a large library of lenses that are compatible for use with the camera.  While it is a DSLR camera, it is one of the smallest and lightest options currently available.  It also has built-in wireless Blutetooth capabilities which would allow you to wirelessly pair your Bluetooth-enabled smartphone or tablet to transfer images from your camera to your smartphone, and/or to wirelessly control your camera.  It would be a good and flexible first DSLR camera purchase.  If you have any other inquiries, you may contact us directly at askbh@bhphoto.com

I absolutely agree with the camera body choice. I myself am a Nikon user and my first camera was D3200. Excellent value for money! I guess that D3500, as its successor, is also a great choice for a beginner.

However, having this experience, if I were buying my first kit today, I would opt for a lens which could provide me a bit more range, for example 18-105mm. Same as with 18-55, you won't get the best quality in the world, but it is a budget option which you could use until you decide if you really want to do photography and to start investing more. It will give you a wide-angle capability, but also a larger telephoto focal lenghts, so you can experiment more.

When you find out which focal lenghts (or ranges of lenghts) you use the most, consider investing in a higher-quality (and more expensive) lens(es) which will give you much better quality. But whatever you do, try to avoid getting G.A.S. (Gear Acquisition Syndrome) and try to invest more in your education and in learning the techniques than in your equipment.

Hi Vladimir!

Solid advice there! Thanks for stopping by and sharing your experience!

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