Dumb-ass question of the day

[merciful]

As some of you may remember, incompetent online retailer Don Chatterton shipped me a 90/2.8 lens hood rather than an M-spool a few months ago. My credit-card company hasn't straightened him out yet, and it occured to me today that my hood might fit on my new 50/2: and it does. The dumb-ass question is: "will it vignette?" The answer, I strongly suspect, is: "of course, you fool, otherwise it would say 50mm on the side." But I thought I'd ask before wasting a few frames of Tri-X.

[FrankS]

You could place the hood on the camera, open the back, set the camera to B and with a wide-open aperture look to see if the hood is visible in the corners of the film-gate. That way you wouldn't lose any film, although 1 test shot on a roll with the hood on the lens, doesn't seem to be such a waste.

[merciful]

Thanks, Frank: great idea. I don't really mind the frame, of course, I just though I'd see if anyone knew.

[denishr]

Frank is right - this is a good test, although I found it somehow easier/better to look from the front - i.e. through the lens - it's the same thing, just viewed from the opposite side. If the hood obstructs/covers the edge of negative opening (i.e. back) before the edge disappears from view, it will vignette. It's easier to do than explain, I'm afraid. Just look from the front, and tilt the whole camera up, looking through the lens. You'll see the lower edge of the frame in the back rising. It should not be obstructed by the hood at any time...

Denis
PS: edited a few typos... early morning...

[Pherdinand]

I would expect that it's vignetting - there's quite a large difference in the angles of view of a 90 and a 50mm lens. The aperture might compensate somewhat for this... I tried to do the same check myself with another combination of hood/lens, as Frank suggests; however, it was rather difficult to judge if there's light falloff towards the corners, so I went for wasting one frame - i pointed the camera at an evenly lit (white) wall, focused to infinity (which should give the most vignetting, i think, the image circle being the smallest)and checked the gray negative frame after it was developed.