Here are some elementary questions. I have a 35-70 f/2.8.
1. How, mechanically, does the lens maintain the constant f/2.8?
2. Does the image projected onto the sensor plane always just contain the FX rectangle, or is there waste (wasted photons) outside that rectangle (other, of course, than the photon wastage becasue of the circular projection outside the inscribed rectangle)?
1 -- As the focal length gets longer, the aperture is made bigger to maintain the constant ratio to the focal length.
2 -- From an engineering point of view, there will be a little extra light spilled beyond the inscribed rectangle because coming up short would be a bad thing. However, I would expect that spillage to be very small given the abilities of today's manufacturing tolerances.
---------+---------+---------+---------+---------+ Joseph K Seattle, WA, USA
1) as the optical elements move in the zoom, so does the diaphragm. At least I think that's how it works in this lens.
2) I've never actually seen the image circle of this lens, but given that its corner falloff is relatively minimal, I think that the projected image circle is relatively large compared to the 35mm frame. Not huge, but bigger than the lenses that have 2+ stops of corner falloff.
_____ Brian... a bicoastal Nikonian and Team Member
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