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# Thread: What is the biggest, perfectly sharp format you can get from your sharpest negatives?

1. Originally Posted by RalphLambrecht
Edward

Nicely followed through! How did you calculate the CoCs? I get 0.022 mm where you've got 0.011 mm.
Ralph,

For the 0.011mm value I used:

c = (1/60)/57.3 x 10 x 25.4 / 7

i.e. converting 1/60 of a degree to radians and converting 10 inches to mm. But it's quite possible that I've slipped a factor of two somewhere by not allowing for line pairs or something.

Then I used:

(vn - v) / vn = c / d

from the Wikipedia page to get vn for the near focus point, and found the corresponding object distance 'u' using the thin-lens formula:

1 / f = 1 / u + 1 / v

as you will of course realise. Then I repeated the process for the far focus point etc.

Even if the standard viewing distance for a 10x8 print is of order ten inches or so, I might view such a print in a gallery from a distance of six feet, say, and I certainly wouldn't look at a postcard print from six inches. So DoF turns out to be a bit of a slippery customer!

2. Originally Posted by Edward_S
... But it's quite possible that I've slipped a factor of two somewhere by not allowing for line pairs or something. ...
That's it!

There is another minute error in there, because the viewing angle should be halved first, to calculate the tangent, and that value should be doubled again afterwards, but with tiny angles, such as these, it's negligible.

None of this changes your point, though.

Nice job!

3. Ralph, A friend of mine offered me to purchase a copy of your book for me. Honestly, I'm quite thrifty and I told him to wait until I check his copy in detail. Today passing by a bookstore I pulled a copy from the shelf and spent 5 minutes with it. I have to say that I don't remember any other book in the past few years bringing together so many interesting, important and ignored topics in photography. I'm sure most readers will feel encouraged to read more on each subject and debate it.
Thanks for the work!

4. Originally Posted by onnect17
Ralph, A friend of mine offered me to purchase a copy of your book for me. Honestly, I'm quite thrifty and I told him to wait until I check his copy in detail. Today passing by a bookstore I pulled a copy from the shelf and spent 5 minutes with it. I have to say that I don't remember any other book in the past few years bringing together so many interesting, important and ignored topics in photography. I'm sure most readers will feel encouraged to read more on each subject and debate it.
Thanks for the work!
Thanks for the nice words! I'm really happy to hear that you like it. We've spend more than 10 years pulling this all together. Quite a few people (including a few APUGers) contributed thought, text and images. If it helps, it was worth it.

5. Originally Posted by RalphLambrecht
That's it!

There is another minute error in there, because the viewing angle should be halved first, to calculate the tangent, and that value should be doubled again afterwards, but with tiny angles, such as these, it's negligible.
I'm more accustomed to hand-waving, order-of-magnitude type stuff...

Originally Posted by RalphLambrecht

None of this changes your point, though.

Nice job!
Thanks!

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