Crop Factor. Something to consider when buying a lens when you are shooting other than FF.

Started Jun 6, 2014 | Discussions thread
Mirfak Senior Member • Posts: 1,379
Re: What about medium format or larger?

b0k3h wrote:

forpetessake wrote:

Mirfak wrote:

caerphoto wrote:

The main flaw in your argument is that everything should be based around a 36×24mm frame as the ultimate standard.

If someone shoots APS-C and nothing else (as I do), 'full-frame equivalence' is entirely irrelevant to them. 18mm is moderate wideangle, 55mm is moderate telephoto, and 35mm is roughly 'normal'. I don't think of my Fuji 35/1.4 as a '50mm f/2 equivalent', I think of it as a 35mm f/1.4, a little long for the kind of shooting I like to do, but it renders out of focus backgrounds rather nicely.

Likewise, someone shooting large format film (5×4in) uses a 150mm lens as a 'normal'; there are no mental gymnastics done to convert apertures to their 135 equivalents, and Schneider and Rodenstock don't market their lenses as "150mm f/5.6 (50mm f/2)" (or whatever the actual numbers are; I don't really care).

The manufacturers don't see it that way. They give full frame equivalent numbers because it normalizes the focal length to the FOV of given standard.

Manufacturers lie all the time, it's called advertisement!

When they convert the focal length to the FF equivalent and conveniently forget to convert the f-stop as well they intentionally want to confuse the ignorant buyers into thinking they are getting better deal than they do. People usually have a good understanding of how much the FF lenses should cost, we were buying them for decades. For example, the normal 50mm f/1.4 or f/2.0 were always quite good quality and quite affordable. If the buyers realized that Fuji 35/1.4 is a full equivalent to 52mm f/2.1 FF lens they would be displeased by its MAP. B.t.w. I have that lens and like it, I got it for $450, which is already quite high price for what it offers.

Luckily, the market is moving toward FF anyway so all those games will be over soon.


(1) f-stop has always and forever been a primary an element of control for exposure. and only as as secondary or tertiary control for focus depth. when i was a wee lad learning on a pentax k1000 "f stop" was for light. its this way in every elementary book and magazine. hence "sunny 16" or f4 for shade. NOT '16 for landscape' and 'f4 for portrait.'

(2) now then, an f-stop is an INHERENT property of a lens and its design. as is its focal length. all of which are marked properly on every lens from every optics maker ever. and that TRUE f-stop number is imminently valuable as it provides understanding of exposure capabilities. which is the PRIMARY consideration for any shooter --- see #1.

go back to the koolaid line with the rest of the conspiracy theorists

Couldn't have put it any better. I owned a K1000 BTW.

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