IQ of 7d w 15-85mm Vs 6d w 24-105mm?

Started Mar 8, 2013 | Questions thread
qianp2k
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Re: What about The Digital Picture.com tests?
In reply to MAC, Mar 12, 2013

MAC wrote:

ultimitsu wrote:

MAC wrote:

we're talking equivalence across formats . Did you read GB's white paper. The distance from the sensor to the subject when comparing across formats must remain the same.

who is this and what authority does this person hold?

Great Bustard has been with the forum a long time and wrote a great white paper over a long period of time. You were in the thread - see link below. Do you challenge this excellent equivalence white paper? If so, why? I'm sure those of us who agree with Great Bustard on the distance parameter being held the same would like to hear why?

http://forums.dpreview.com/forums/post/51012476

it's maybe your bible but I count on DXOMark, DPR, Photozone, etc well known creditable test sites. I don't count on individual opinions as not well recognized in photography industry. I have respect to GB and to be honest I even don't read his article (funny thing is that sometime he pointed to his own article), someone just has his personal opinion, that's it, nothing more or less. In history something I agree with him something not such as I have to shoot at eq DOF that is totally rubbish.

now we introduce an even more complex subject -- resolution of systems across formats.

dxo messes it up

No they did not.

so you've unfairly penalized crop as well by moving the crop sensor farther away

Sigh. Do you understand if you shoot from the same distance between you/camera and subject (a resolution chart for example), 15mm on 7D has the same AOV of 24mm on 5D? Where the moving crop sensor farther away is from?

photozone says -- you can't use their numbers to compare across formats

You misunderstood what photozone meant. What they are saying is you cannot say "Lens EF X which is tested on 5d2 is sharper than Lens EF-S Y which is tested on 50D". Precisely because since Y was tested on 50D it inherently will show less resolution. This goes directly proving Peter's point. There is no discrepancy between DXO and Photozone's view.

No, they said it because moving a sensor backwards to compare different formats is unfair to the format -- see GB's equivalence white paper

it's only fair to test under the same AOV by either a) Using different focus length lens to achieve the same AOV or FOV on the respective sensor crop format; b) or adjusting distance; or c) both to have the same AOV. That simply reflects how we use cameras to take real world photos such as in portrait. With the same 85mm lens on 5D I have perfect half body photo, you will only have shoulder above photo from the same distance. So you will only have 3 options to have the same photo either by a) using a shorter-focus length such as 53.33mm lens; or b) adjust distance and moved 1.6x away; c) by both such as using 50mm lens and move up a little bit. Otherwise what you are comparing, half body vs shoulder above, apple vs orange?

but to automatically move the crop camera backward -- when the crop sensor cannot magnify like a lens can -- is just wrong when it comes to comparing across formats

No, you keep saying it is wrong yet you cannot explain why. I already explained to you twice that there is no photo loss due to entropy within 1.6 times distance difference so there is no basis to say it is unfair. You have not provided any counter argument.

I explained it. GB got it right. 1.6 is not a lens magnifier. The sensor is cropped off. Keep the sensor position in the same place to be fair since it is not a lens, it is not a 1.6 lens extender -- it is a sensor. Photozone recognized the unfairness, and got it right with the disclaimer

I believe DXOMark and Photozone got both right, and the vast real world photos vividly prove that.

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