Originally posted by bdery I certainly hope not!
If someone asks you if changing sensor size will have any practical effect on their ability to control DOF, and your answer is "there is no link between sensor size and DOF, FULL STOP," then I'm sorry to say that you're misleading them by leaving information out. You really are. I fully believe it's not your intention.
It's akin to the question "Is a 50mm lens still a 50mm lens on FF vs. aps-c?" being answered with "a 50mm lens is a 50mm lens. The lens doesn't change. FULL STOP."
That's an extremely unhelpful answer, to the point that it implies something factually wrong - that the photographer will see no difference using a 50mm lens on any format. It's an answer that's not really answering what's being asked. And anyone who isn't suffering from Aspergers should know what's really being asked 95% of the time that question comes up -
does the FOV change, and if so, how?
That question should always be answered with a variation of: "The physical properties of the lens can't change, it's still 50mm, however a 50mm lens of a larger format will give you a wider FOV." (and then you can go into effects on DOF if you have the fortitude...)
Quote:
you are saying exactly the same thing as me.
You very well can think in terms of field of view when discussing composition. However, when discussing optical performances, discussing field of view is the most convoluted road you can take. It creates approximations, inaccuracies, misunderstandings, in short it's a mess.
The reason FOV needs to be tied to it is because it determines what FL is used which determines what the physical aperture will be for that exposure. The physical aperture (not f-stop) is what determines the total light hitting the sensor which is the only reason larger sensors of the same generation realize any advantage in the first place - they are getting more light.
The FOV is one of the grounding parameters the photographer cares about - maybe even the most important parameter, even more than exposure. You start with FOV, with framing.
Perhaps unfortunately, to establish a standard so we know what FOV we're talking about, we use 135mm equivalents.
Otherwise, if you walk into a camera store intending to buy this:
... and you ask the clerk if that 5mm lens will be wide-enough - say if it will look like at least 24mm on your aps-c camera which is your personal requirement for the purchase - the clerk will answer: "
5mm is 5mm is 5mm. It's a 5mm lens. FULL STOP."
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