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I had a Canon EOS 600D for 6 years but switched now to a Canon EOS 5D Mark II because I faced the limit of my camera. I do a lot of HDR photography and felt kind of limited after all these years.

I got a really good price for a used Canon EOS 5D Mark II, and I tried it out a couple of times. The more and more I dive into the camera and it's settings I am pretty happy but the image quality is not really much better. Yes, the comparison is not fair, because the 5D Mark has a bigger FOV and therefore I had to scale the image down a little bit, still wondering if you have some tips.

Both pictures were shot with a Canon EOS 50mm, f1.8 and the following settings:

ISO 400, f1.8 and ISO 160 (left) and 125 (right). Is it just me or why did I expect a better quality? Thanks a lot for any input!

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    What improvement of quality did you expect? The 5D II has a fullframe sensor and you compare a 100% to a (ca.) 160% zoom in. To compare the quality you have to usw the same framing of the picture. – Horitsu Oct 9 '18 at 4:08
  • Btw. also the lens is a very strong factor. If the lens is shitty and doesn't have the ability to give a crisp sharp image, you will have also a worse photo. – Horitsu Oct 9 '18 at 4:10
  • Thanks for your feedback. I will try to make a new one - btw, in both cases I used the same lens – Daniel Stephens Oct 9 '18 at 4:15
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    The same lens deliver not the same results for APS-C and fullframe if you compare them at the same relative spots in the photo. – Horitsu Oct 9 '18 at 5:07
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    Not necessarily in relation to this specific image, but I do think it would be helpful if you specified exactly what improvements you were expecting. – osullic Oct 9 '18 at 8:19
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You expected it to be better because people tend to think, bigger = better. People talk about how great full frame is without understanding what is really different, and your expectations are too great.

Sensitivity and Noise

Full-frame sensors have larger sensels than crop sensors that produce the same number of megapixels. For sensors of the same generation, full-frame sensors are expected to have an advantage in ISO sensitivity and noise. However:

  • The advantage is reduced on full-frame sensors that use smaller sensels to produce more megapixels.

  • The advantage applies primarily to high-ISO. Noise is minimized at low-ISO, such as those you used to take your test shots.

  • Sensible lens choices, with faster apertures, reduce the need to push ISO.

  • Newer technologies increase light sensitivity and reduce noise. However, Canon tends to develop technologies slower than molasses, and the EOS 5D mk2 was current throughout the 600D life-cycle. (This is why Sony has a 5-year head start on full-frame mirrorless.)

To see the noise difference between crop and full-frame, you need to take multiple ISO-matched images throughout the ISO range. View them at 100% without resizing. You should see noise become unacceptable at lower ISO settings on the crop sensor vs the full frame.

The "Full-Frame" Look

What your test images demonstrate is, when taking photographs from the same position, with the same lens, with the same settings, everything is the same between crop sensor and full frame, except field of view. Changing sensor size just changes the portion of the (exact same) imaging circle that is recorded.

What creates the "full frame look" is what people do to compensate for the different field of view. To fill the frame with the subject on a full-frame sensor, the camera has to be closer or the lens has to have a longer focal length. The difference can be reduced on crop sensors by using faster apertures, when available.

  • Thanks a lot for your detailed explanation. That totally makes sense to me now! – Daniel Stephens Oct 9 '18 at 12:10
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You're comparing an older (2008) full-frame camera to a newer (2011) crop body, so if you expect an improvement by moving backwards a generation, you're probably in for some disappointment. If you can find a used 6D (2012), you'll be a lot happier in terms of image quality than with a 5D Mk II, because the improvement in sensors over those four years was pretty significant.

That said, nothing you're doing in that photo is going to show much of a benefit anyway:

  • You're using the same lens, which means your crop body is using the sharpest center part of the lens, and the full-frame is using the whole lens. Expect some sharpness loss from that alone. Doubly so if you're cropping the full-frame image. Try an 85mm lens of comparable quality on the full-frame body, or else change the distance to match rather than cropping.
  • You're not doing anything that pushes the limits of the sensor. Try under-exposing by a stop and pushing the shadows. See how much more you can bring things up before you lose too much image quality.
  • Take photos in low light and at high ISO. Again, see how high you can crank the ISO before the IQ is too poor to use.

And again, those three years in image sensor technology between the 5D Mark II and the 600D might very well mean that the 600D still wins in the tests above, but at least you'll be giving the 5D Mark II a fighting chance. :-)

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You're using a 50mm f/1.8 at f/1.8, which is well known to be very soft wide open. If you want to compare the resolution limits of each camera, you need to use a lens that isn't softer than what either camera is capable of.

You'll probably see a greater difference if you put the cameras on a tripod, stop the aperture down to about f/2.8, and carefully manually focus using Live View. Being on a tripod will also allow you to expose long enough that the images don't appear to be slightly underexposed.

You're also magnifying the image from the 5D Mark II by 1.6X more than the image from the 600D so that they appear to frame the same subject from the same distance. This is giving up one of the key advantages of a larger sensor camera: a lower enlargement ratio to get to the same viewing size of each camera's respective field of view. You need to shoot from about two-thirds the distance with the FF camera so that the subject is the same percentage of the total width of the frame in each photo.

But beyond all of that, a FF camera will not make you a better photographer than an APS-C camera allows you to be. Yes, there are some advantages to using a FF camera for some situations. There are also advantages to using an APS-C camera for some situations. One is not always "better" than the other. They're both different from the other.

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