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01-25-2011, 10:20 PM   #1
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Variable aperture, M-series film bodies question

I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in.

But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird?

I'm confused lol.

01-25-2011, 10:53 PM   #2
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QuoteOriginally posted by Cinders Quote
I have a Quantaray 100-300mm f4.5-6.7. When I used it on my K-x, the aperture would close up the more I zoomed in.

But now I've been using it on my ME Super. It has an aperture ring, but I can zoom in to 300mm and keep it on 4.5. Will it let me take a picture? Will it turn out weird?

I'm confused lol.
The question is whether the meter reads the same. Your lens is not variable aperture per se...rather it is variable maximum relative aperture (f/stop). The absolute aperture stays the same, but the focal length increases resulting in a higher f-number and less light to the film/sensor/meter. Apparently the lens is able to communicate this fact to your K-x. The ME Super, on the other hand, has a much more simple mount and has no idea what focal length the lens is set at or even what the actual aperture is. All the camera is aware of is the offset of the aperture ring from maximum.


Steve
01-26-2011, 01:39 PM   #3
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Will work fine
01-26-2011, 08:54 PM   #4
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QuoteOriginally posted by titrisol Quote
Will work fine
Yeah...that too!

01-26-2011, 09:21 PM   #5
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With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?
01-26-2011, 10:35 PM   #6
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QuoteOriginally posted by Cinders Quote
With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?
Cuz at 300mm your lens is f/6.7...

The f-number formula goes like this: f(ocal length)/n = physical aperture diameter. The "slash" notation reflects this. This is the case regardless of what the aperture ring is set at.


Steve


(I know...the next question is why the DA* 50-135 is constant f/2.8...will let someone else answer that one...)
01-27-2011, 02:27 AM   #7
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Vignetting should be a problem in wide-angles
teles in general can cover areas way larger than 35mm.

You can shoot at 4.5 but it will be a different "effective" aperture (6.7) and the difference in luminosity will be metered by the camera.

Constant f/lenses are very special I guess.... some floating elements maybe?

QuoteOriginally posted by Cinders Quote
With no vignetting, or anything?

Weird, so why can't I shoot at f4.5 at 300mm on a DSLR?
01-27-2011, 02:53 PM   #8
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Ok, I think I get it now. Thanks guys.

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