When do the differences between APS-C and full frame sensors matter, and why?

  • I'm trying to decide on a higher-end digital SLR, and I'm down to choosing between an APS-C model and a full-frame model.

    I understand that the sensors are of different sizes, and as such have an effect on the perceived magnification of the lens, with the smaller APS-C sensor having an effective focal length greater than what it otherwise would be with a full frame sensor. But why does this matter?

    • What things should drive my choice between one or the other?
    • In which situations is one better than the other, and why?

    Have spent hours researching aps-c Vs FF. I would appear for taking group photos of 50 people I would be better off with a APS-C camera as they would sharper at the corners as well as less vigenetting. Any thoughts?

    @Allen: good question — I think worth asking as a new question.

    See also: Roger Cicala of lensrentals.com on "The Full Frame Move".

  • Matt Grum

    Matt Grum Correct answer

    11 years ago
    • One major difference is that a FF camera produces a depth of field that's around 1.3 stops shallower than an APS-C camera for the same subject & framing. This is most important when you have the aperture as wide as possible, e.g. for portraiture. To replicate the look of a 50 f/1.4 lens you'd have to use something like a 31 f/0.9 lens, which doesn't as far as I know exist!

    Quick and dirty comparison image, APS-C Canon 30D left, FF Canon 5D right, same lens (FF image was zoomed in, however to give the same field of view), same composition, both f/2.8

    • Another difference is that if you're using a lens designed for a full frame camera (like all Canon EF lenses) you are making full use of the image circle, which is less demanding of the optics and so you can expect a sharper image for the same number of megapixels. It's true that some lenses get softer toward the edge of the image, but you will still get higher average sharpness with most lenses, and telephotos will be sharper right across the frame. The crop factor of APS-C cameras takes the middle out of the lens and blows it up, losing sharpness in the process in a similar manner to a teleconverter.

    • Larger formats allow for sharper optics. One of the driving forces for larger formats (other than the relatively constant resolving power per unit area of film) has been that it allows lenses to be produced which resolve a greater number of line pairs per picture height. Going full frame on a DSLR benefits from this to an extend - see: With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

    • A bigger sensor means bigger pixels, which in turn means you capture more light usually achieving lower noise levels in the process. Greater dynamic range goes hand in hand with this.

    • You get a larger, brighter viewfinder on a full frame camera, which can be helpful composing shots. Having said that, I personally find the 5D viewfinder too large, I've not used a 7D but it has a very high spec 'finder.

    • You have more mirror to move on a full frame camera. The larger mirror used to mean shooting speed is limited (the mirror on my 5D moves so slowly I can actually see the world slide sideways/up for an instant) however high speed full frame models are now available.

    • Likewise the mirror box, focussing screen and pentaprism are larger, meaning the camera is larger and heavier.

    • Lens hoods are designed for FF image circle and are therefore slightly more effective on FF cameras. This mostly applies to prime lenses, as zoom lens hoods are designed cut to accommodate the widest zoom setting, so everything else is already non optimal. If you're using an EF lens on a crop camera you ideally want the hood tighter (since the extra shading will lie outside the smaller sensor, a tighter hood won't vignette).

    I have nothing against APS-C cameras but for any format it makes sense to use lenses designed for your sensor size. The range of EF-S lenses is smaller than the range of EF lenses. However for some uses (sports etc.) the smaller sensor size is helpful for the extra reach and speed it allows. Also the better noise characteristics of a FF sensor don't quite make up for the higher ISO you need to use get the same exposure when stopping down to match the DOF as a crop. So if you have to maximise DOF crop has a slight edge.

    If there are EF-S lenses available for what you want to shoot then it won't be noticeably worse choosing this camera. However I feel full frame gives you more flexibility (speed aside) - as you can get the same deep DOF as a crop, but go narrower if you need to.

    Matt, I like your answer, thoughtful and complete. Given the obvious advantages of the FF sensor I nevertheless find that I get outstanding quality on my APS-C DSLR. To me, at least, it seems the improvements are merely incremental. I suspect that some important advantages accrue not from the sensor but from the fact that FF bodies have in general more advanced specifications.

    **@labnut** The area where you really notice the difference is with fast wide lenses, there's simply nothing available for APS-C that can match the 24 f/1.4L for speed and field of view. The ability to get nice blurred backgrounds when shooting wide is pretty much exclusive to full frame. But yeah you can still get amazing results in 90% of cases with a crop. Look at how long Nikon went without FF in their lineup. I disagree that the difference can be accounted by FF cameras being higher spec, the 7D beats the 5DmkII on pretty much everything but sensor size and MP and the 50/60D are close.

    Some other points, perhaps harder to quantify: increased micro-contrast, or fine tonal transitions. The smaller you go, the more you seem to lose. Then, all else equal, low light performance simply due to more photons, dynamic range and color depth.

    The viewfinder on the 7D is a 1:1/100% viewfinder, however since that is an APS-C sensor, it is smaller than the 5D's. The 7D's finder has some pretty advanced active display stuff since it uses an LCD to display information across the whole surface of the viewfinder.

    +1 as I 100% agree with you and, until today, you missed one: dynamic range. On this day, an APS-C camera blew past FF and medium format: http://www.dxomark.com/index.php/en/Camera-Sensor/Compare-sensors/%28appareil1%29/676|0/%28appareil2%29/485|0/%28appareil3%29/579|0/%28onglet%29/0/%28brand%29/Pentax/%28brand2%29/Nikon/%28brand3%29/Phase%20One :)

    **@John Cavan** Actually I mentioned DR in the 4th point. As for the K-5, it's an excellent sensor, for sure, but it only wins in the DR stakes at low ISOs (where the noise floor will dominate the DR reading) at higher ISOs FF sensors such as the 5D have greater DR. Given a perfect electonics (i.e. a sensor with zero light loss that simply counts photons) a bigger sensor will yield greater dynamic range *every time*.

    ultimate question: how much do these advantages worth? do they worth $1300 (difference btw 5d markII and 50d)?

    @spinodal it doesn't have to be expensive to get into FF, you can pick up a 5D mkI for $700, and you could save money on lenses too. If you wanted a wide prime you could pick up the EF 20mm f/2.8 for $539 whereas with a crop body you'd have to get the EF 14mm f/2.8L which wouldn't give as wide a field of view and cost you an extra $1700! Yeah the build quality of that lens is better but still. The same is true of the Canon 35mm f/1.4 and 50mm f/1.4

    @Matt - looking at the two images, it looks like both have an identical perspective (i.e, shot from the same point) and hence same FoV (as far as I can tell, all the elements in the frames have the same size). However, you mention the same lens on both bodies. How come?

    @ysap it was a zoom lens, I used two different focal lengths to achieve the same field of view

    @Matt - ok, that explains it (but it is not quite the same lens per-se?). It would be nice also to demonstrate how you can get the same DoF with a smaller aperture on the FF.

    @ysap It's the same lens in the sense that I didn't take anything off the camera, I don't think most people consider zooming to be "changing lenses". When I have time I'll shoot some better examples, including one where a different fstop is used to get the same DOF.

    @MattGrum - I'd dare to say that for the specific purpose of explaining this topic, most people actually *do* consider that as a lens change (maybe we should conduct a poll?). However, once you mentioned that in the comment, then the situation became clear.

    I think the fact that the focal length of the lens was changed should be mentioned in the answer.

    Yes, there are ifs and buts. Changing the lens for the same field of view simply means the smaller sensor must be enlarged more to view it enlarged to compare at same size. That greater enlargement reduces both resolution and depth of field of the smaller image. If instead using the Same lens, the field of view is of course different, but THEN a larger sensor will compute greater DOF, not less, because of the first point, the smaller senor must be enlarged more to view the image as same size (DOF calculation numbers assume enlargement a default 8x10 inch print).

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Content dated before 7/24/2021 11:53 AM