Why no FF equiv. to EF-S 17-55/2.8?

Started Jan 11, 2013 | Discussions thread
MAC
MAC
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Re: What has been confusing to me in this thread...
In reply to Donald Duck, Jan 13, 2013

Donald Duck wrote:

MAC wrote:

I think schmegg may have made a small calculation error - and actually it helps the FF

In going from F2.8 to F4.5 - once must multiply by 1.6.... 1.6 x iso400 = iso 640 which means he loses 2/3 stop in the iso noise calculations

No, you multiply by 1.6^2 (the area ratio), so ISO 400 is equivalent to ISO 1000 or so. That is about 1.35 stop higher.

ISO 100 on crop is like ISO 250 on FF, etc.

ah, thanks for that.  I was thinking incorrectly in one dimension.  I know now to use ^2

so then at least to me, it ain't worth changing his zoom on a crop camera for 24-105 on FF

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