The 1/4000 x 1/8000 issue

Started Sep 14, 2012 | Discussions thread
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rhlpetrus
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The 1/4000 x 1/8000 issue
Sep 14, 2012

I'm from the time when 1/1000 was the standard, the fancy pro bodies topped at 1/2000. I never thought much about it, so, since some are saying that it's a big difference, I just did some quick calculations (professional bias). 1/4000 is 5 1/3 stops faster than 1/100s, correct?

Let's assume one is shooting in full sunlight. Sunlight means basically sunny 16 exposure, so 1/100 and f/16 at ISO 100, let's use that. Move SS to 1/4000, that menas you open your lens to f/3.5. If you were using 1/8000s, that would be f/2.5, so actually you can't use all the speed of a good prime, anyway, but yes for a fast zoom.

I just checked the DOF tables using an 85mm, typical lens that is used to isolate subjects. I used FF CoC as a reference, and 10ft as reference distance. Here are the values (DoF Masters):

f/2.5
Subject distance 10 ft
Depth of field
Near limit 9.7 ft
Far limit 10.3 ft
Total 0.62 ft

f/3.5 (I actually used f/3.6, they don't have f/3.5)

Subject distance 10 ft
Depth of field
Near limit 9.58 ft
Far limit 10.5 ft
Total 0.88 ft

Thus, the difference is 0.12 ft = 3.6cm in front and 0.14ft = 4.2cm behind of plane of focus (I used the totals to compute that, there are round-off effects in the limits figures). Is that a big difference? Will you be able to notice that in a print? I doubt it.

I just think this 1/4000s x 1/8000s is likely one of those specs that may be interesting, but certainly not the big deal many are taking it to be. I think I've never used my cameras above 1/2000s, well, the M3 only went up to 1/1000 anyway, I have to check the dslr shots.
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Renato.
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