Full Frame vs. APS-C Sensors vs Prints

[Johnny]

Bob,

I have just been reading two of your excellent articles. This one http://www.bobatkins.com/photography/digital/full_frame_vs_aps-c.html and this one http://www.bobatkins.com/photography/digital/size_matters.html

You wrote...larger sensors work on the upper part of the MTF curve of a lens, while smaller sensors work on a lower part of the curve...and you compared a 12" x18" print from the 20D and the 5D and said PPI would be respectively 195 and 243.

I understand this is about pixel size and enlargement factor.

I don´t understand all the math beneath this so how do I compare the (original) 5D vs the 50D? Will I see any difference in resolution and contrast in an A4 print or do I need to make a larger print, say A3, to see any difference?

Having your articles fresh in mind I again took a closer look at dxomark´s new camera/lens measurement tools. According to them the 50D / 85mm f:1.8 combo should give me 42 lp/mm and a "score" of 12. ( According to dxomark a "score" of 10 correspond to a 30x20cm optimal print )

The 5D / 85mm f:1.8 combo should give me 59 lp/mm or a "score" of 25. ( A "score" of 20 gives an optimal 45x30cm print ) This should give an optimal A3+ print according to dxomark.

What do you think about these numbers? Are they realistic? Will I be able to make larger prints that has better resolution and contrast using the 5D compared to the 50D?

How do I calculate print resolution by the way? In one of the articles you mentioned a 4.8 lp/mm print from the 5D vs 3.85 lp/mm print from the 20D.

[bmpress]

What do you think about these numbers? Are they realistic? Will I be able to make larger prints that has better resolution and contrast using the 5D compared to the 50D?

Are you asking this question for the same lens on each camera? and the prints will be of the same image?

[Johnny]

Yes.

[Bob Atkins]

I'm not ignoring the question, I'm just thinking about it!

You can get print resolution by dividing sensor resolution (in lp/mm) by magnification. So, for example, if the sensor can resolve 80 lp/mm and you make a print that's 10x the size of the sensor, the print resolution would be 8 lp/mm.

I'll reply further when I've looked at the issue in a little more detail

[Johnny]

Bob,

I am not in a hurry.

Roger N. Clark at clarkvision has also written about the subject. He did not go into details though, like you did.

Thanks for the clarification about print resolution.


- Johnny