f/1.8 on m4/3, ASP-C, FF; are they the same?

Started Nov 1, 2010 | Discussions
nugat
Contributing MemberPosts: 699
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DOF is subjective and conventional
In reply to digifan, Nov 3, 2010

DOF is a subjective phenomenon and depends solely on:
--eyesight
--watching distance
--print magnification
--allowed size of circle of confusion

Lens DOF markings (and strangely enough on-line calculators) date back to Barnack's 1912 assumptions based on 19th century CoC standards.

On a 10x8 inch contact print looked upon from one foot a circle of 1/100 inch was considered the "sharpness" limit. This roughly translates to today's 36x24mm frame CoC of 0.03mm magnified 8x to ca A4 print (0.03 mm x 8= 0.24 mm or ca 1/100 inch).

The 19th century assumptions of eyesight strength are rather inadequate, many 20/20 vision individuals (and correction glasses wearers) will see double or triple the detail. Computer pixelpeepers demand a "pixel-level sharpness", etc etc. Therefore many believers in zone DOF and relying on lens markings and DOF calculators are deeply disenchanted with results. In fact to get at the 20/20 vision level sharpness expectations those suggestions must be tightened 2-3 times and aperture closed 2-3 stops to make CoC that much smaller (eg. 0.01mm on full frame).

All that assuming that the lens resolution is good (40lp/mm), camera perfectly steady, focus ideal and diffraction not a factor.
Good reading:
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

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h00ligan
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Re: f/1.8 on m4/3, ASP-C, FF; are they the same?
In reply to Joesiv, Nov 3, 2010

Agreed. If the gf1 had ine stop better iso performance it would be a monster.

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Everdog
Senior MemberPosts: 4,837
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Re: FYI
In reply to Joesiv, Nov 3, 2010

Joesiv wrote:

btw, it also seems like the GH2 "fixed" the underrated ISO values... that might also contribute to the "cleaner" higher ISO's that people are seeing. We'll have to take that into account.

I agree. I am sure they did it for marketing reasons. Some thought the GH1 was not very good at higher ISOs because they were comparing apples to oranges. I just happen to own a T2i and a GH1 and know the truth.

The other thing that hurts Panasonic is the difference in quality in these sensors. I have seen some GH1s with terrible banding at ISO 1600, and other that were perfectly clean. If anyone wants to find "bad" GH1 pictures, they are out there.

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h00ligan
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But...errr..uhmm...
In reply to Gao Gao, Nov 3, 2010

Wouldn't f-stop be the same but T-stop be different?

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