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02-26-2007, 04:27 PM   #1
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Screwmount lens

I did some searching and I am still a little cloudy about something.

I picked up a 400mm screwmount lens that I intend on using on my k100d.

The part I don't understand is the correct sequence to set the lens up.

Say I want to shoot at f/8.

I would assume that I would set the the aperture to f/8, press the AE/L button to find the correct shutter speed and snap the picture.

However I have read that with a manual K-mount lens the camera would stop down, meter and set the shutter speed. Obviously the screwmount lens cannot be stepped down via the body so I would need to do that myself.

To my understanding "stopping down" means to move to a smaller aperture (higher number)

Why in the world would I want to do that? Or am I misunderstanding something? If I do stop down, what do I stop down to?

Another interesting tidbit is that the lens has 2 aperture rings. One operates normally and the other will rotate freely between the largest setting (f/5.6) and the number set with the normal ring. Any particular reason for this?

Sorry if this is a total n00b question.

02-26-2007, 04:33 PM   #2
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To stop down, set the diaphragm clutch from auto to manual, and then select the desired aperture.

"Stopping down" simply refers to the closing of the aperture diaphragm. When using an automatic lens, you set the aperture via the aperture ring (or internally through the camera) and a lever on the camera "stops down" the lens to the desired aperture when you take the picture. You have to stop screwmount lenses down manually because they lack the coupler that K-mount lenses otherwise have.

Edit: it looks like you have a very old takumar with two silver aperture rings. It doesn't have the diaphragm clutch, but I'm pretty sure that one ring stops the lens down while the other is just used as a guide for the other.

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02-26-2007, 05:01 PM   #3
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that's a preset lense. what you do is set the ap you want to take at and focus wide open. just before you trip the shutter you spin the actual ap ring down. the preset ring will stop the other ring at the preset ap. you do all of this in Av mode. you do not need to press the AE-L button as the cam is measuring the actual light that the lens is passing..
02-26-2007, 06:24 PM   #4
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So what you guys are saying is that I should focus the camera when the aperture is at its lowest numerical number and "stopping down" is just setting the aperture to the desired size for the picture?

I am still waiting on my K-mount adapter to arrive so I can test everything out.


Thanks for clearing this up guys. I must say that that second ring will make this whole stopping down thing super easy since you won't need to double check that you put the ring back into the correct position.

02-26-2007, 06:30 PM   #5
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that's exactly what the 2nd ap ring is for.. i wish my 500 had it, altho i'm getting good at hitting the ap i want..
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