Fast lenses, and High ISO

Started 5 months ago | Discussions thread
bobn2
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Re: "fast" is relative
In reply to Albert Silver, 5 months ago

Albert Silver wrote:

EinsteinsGhost wrote:

bobn2 wrote:

Albert Silver wrote:

tko wrote:

Remember that F4.0 is considered kind of slow on FF, but is equal to F2.0 on M43rds, which is considered "fast."

That's not entirely accurate. You are describing the depth of field equivalence, from one sensor to the next, not the light. f/2 on a m43rds may have the depth of field of f/4 on a full-frame, but the light will still be f/2.

The 'light' of a FF f/2 and a FT f/4 will be the same, which is the point he is making. In the end, given equally efficient sensors, you can achieve the same result at the same shutter speed using an f/4 on FF as you can on FT. The density of the light of the f/4 is one quarter but there is a sensor four times the area to collect it, so it ends up the same.

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Bob

The point tko is making is wrong. DOF equivalence applies, exposure equivalence does not (for the reason you state above).

That was my point, though I think Bob missed it.

I didn't miss anything. 'Exposure' doesn't mean the same as 'the light'. It doesn't make much sense to base your assessment of what is 'fast' on exposure in cross format comparisons.

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Bob

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