Orquid "Phoenix"

Orquid "Phoenix"

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I do mostly handheld macro photography and I currently own a Canon 40D. I want to buy a new camera and I don't know what is the best choice.

My goal is to get the best of my lens. So I'm not sure if full-frame 21mpx 5D MkII or III will give better results than the 18mpx 1.6-crop canon 7D. (Also taking in to account the ISO quality for faster shutter speed pixel density and the resolution of the 180mm.)

Can the 5D get better details then the 1.6 crop?

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Going "full frame" isn't the only thing effecting the results you get: dynamic range, pixel pitch, compression, and post processing can play just as important a role in this scenario. –  Dan Wolfgang May 8 '12 at 15:48
    
i agree, but what is the best choice? What will yield better results shooting with that lens. What camera will give me more details of the bug. –  Daniel May 8 '12 at 17:59
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I suspect the answer is that the 5D will give better results, but I don't know. My point is that the two answers below discuss the merits of lenses and I'm pointing out that the non-lens differences are the most significant contributors to the difference you would see. –  Dan Wolfgang May 8 '12 at 18:02
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I would be interested in seeing actual comparisons instead of opinions. :) My guess is that any difference will be visible at the pixel-peeping level. For normal sized prints or reproductions on the screen, you wouldn't be able to differentiate quality. That's my guess, though, because I haven't done controlled studies. All else being equal, larger pixels on the sensor should produce better results. Resolution isn't everything. Sensor generation also plays a role. My money would be on the best photos coming from the 5D III, followed by a 7D, followed by 5D (original). –  Eric May 8 '12 at 22:03
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2 Answers

up vote 6 down vote accepted

Yes

The 5D will get better details than the 1.6 crop. A macro lens will resolve a certain number of line pairs per millimetre. Image sharpness is measured in line pairs per picture height, by using the same lens but with physically bigger sensor you will get more line pairs per picture height, hence more detail in your image.

Another way to look at it is that using a smaller sensor is like making an enlargement, or viewing a portion of an image close up - it's never going to look as sharp under those circumstances.

Now on some lenses corner performance can drop off to the extent that you get better average sharpness (but lower peak sharpness) by using a crop sensor and simply avoiding the extreme corners. Here is an example of such a lens, the Canon 35mm f/2.0:

APS-C corners occur at 13.5mm, where sharpness at f/8.0 (fine blue line) remains above 0.8. On full frame sharpness takes a nose dive starting at 18mm, which corresponds to middle of the left or right edge of the frame. Now compare that to the Canon 180mm f/3.5L Macro:

Sharpness is extremely high right across the frame, there is no notable drop off, meaning your full frame image will be sharper everywhere, even in the extreme corners.

However if both cameras have a similar same number of megapixels then a crop sensor can be very useful for macro photography as it allows you to photograph smaller objects. A true macro lens on full frame will let you fill the frame with an object only 36mm across, whearas with a crop camera you can fill the [1.6x smaller] frame with an object only 22.5mm across. This can be very useful for um, photographing really small things!

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+1 - This was my thought too - that macro lenses tend to be sharp enough the whole frame. –  rfusca May 8 '12 at 14:59
    
So, if i understand correctly, a fly shot with the 5D image will be sharper but the 7D will fill more of those 18mpx with it, resulting in more details of the fly? Can that compare with the 5D being sharper? –  Daniel May 8 '12 at 17:48
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The full 5D image will always be sharper but as soon as you start cropping that advantage so if you are regularly limited by the minimum focus distance a crop sensor is a better choice. –  Matt Grum May 8 '12 at 22:56
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Oddly, no.

Lenses often have more aberrations towards the edges, so most them do not perform as well on a full-frame. By using a DSLR with a cropped sensor, you use the best performing part of the lens.

To get the most out of it, you need high pixel density, so all the 18 MP Canon cropped DSLRs will do. The 7D among those is top-of-the line with a 100% coverage viewfinder and a weather-sealed body but the 60D is smaller and will give you the same quality.

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This is only true of wide to normal lenses. Telephotos and especially telephoto macro lenses are designed to be aberration free corner to corner, so you will get a noticeably sharper image on a fullframe. Look at the MTFs of the 180 macro the questioner mentions - values stay high even in the extreme corners: usa.canon.com/CUSA/assets/app/images/lens/ef_180_35mtf.gif –  Matt Grum May 8 '12 at 13:55
    
I'd hope most lenses are designed to be aberration free from corner to corner but that does not mean the necessarily manage :) In the MFT chart you linked too, there is clearly a drop in contrast towards the edge of the frame which would not been since using an APS-C sensor. –  Itai May 8 '12 at 14:06
    
The corollary is that the lens must be good enough in the center portion for the crop-sensor camera to take advantage. That is, a lens may perform fairly on a full frame camera, but on a crop camera it performs less well because the center portion of the lens isn't good enough. This is certainly less true with modern lenses (maybe even false?) but there are plenty of older Nikon glass where this is true. –  Dan Wolfgang May 8 '12 at 14:35
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You found a worse example... I knew those existed too :) That does not mean sharpness does not drop. Plus with a denser sensor you can get much more details out of the center area as well. –  Itai May 9 '12 at 0:51
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The point is macro lenses are the main exception to the rule you state in your answer! Even if there is a drop it wont be anywhere near enough to make up for the 1.6x loss in resolution you get from a smaller sensor. Yes you lose the advantage of a bigger sensor if you crop the image, that should be obvious. –  Matt Grum May 10 '12 at 11:55
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