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01-18-2011, 07:06 PM   #1
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Why do DA lenses stop down fully on pre-A cameras?

Why do DA lenses stop down fully on older (film) cameras? They are always fully stopped down according to the viewfinder shutter speed indication.

Anybody know?


Last edited by Spock; 01-18-2011 at 10:24 PM. Reason: Re-phrased the question!
01-18-2011, 09:52 PM   #2
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Apparently old lenses with set aperture rings would always have their lever fully pulled during shooting. With A lenses, the lever is pulled according to the aperture setting in the camera.

Therefore, pre-A cameras always fully pull the lever, bring the lens to it's minimum aperture.
01-18-2011, 10:21 PM   #3
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QuoteOriginally posted by paperbag846 Quote
Apparently old lenses with set aperture rings would always have their lever fully pulled during shooting. With A lenses, the lever is pulled according to the aperture setting in the camera.

Therefore, pre-A cameras always fully pull the lever, bring the lens to it's minimum aperture.
That sounds right. Thank you.

I just tried fitting DA lenses to my old ME and what happens is I get an open aperture preview through the viewfinder but the camera meter shows a shutter speed that corresponds with the lens' minimum aperture.

So, it would appear that a DA lens acts just like an A-lens with the aperture ring set to the 'A' position (or a M-lens set to minimum aperture).

It's interesting that the old camera 'knows' what the DA lens' minimum aperture is.

Last edited by Spock; 01-18-2011 at 10:28 PM.
01-19-2011, 10:08 PM   #4
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QuoteOriginally posted by paperbag846 Quote
Apparently old lenses with set aperture rings would always have their lever fully pulled during shooting. With A lenses, the lever is pulled according to the aperture setting in the camera.

Therefore, pre-A cameras always fully pull the lever, bring the lens to it's minimum aperture.
That's what it would do when shooting, but I suspect our Green-blooded Vulcan friend is seeing the lenses stopped down in the viewfinder.

I would suspect something wrong, because when I put DA lenses on my MX they don't stop down on their own.

01-19-2011, 10:25 PM   #5
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QuoteOriginally posted by unixrevolution Quote
That's what it would do when shooting, but I suspect our Green-blooded Vulcan friend is seeing the lenses stopped down in the viewfinder.

I would suspect something wrong, because when I put DA lenses on my MX they don't stop down on their own.
No, a DA lens on my Pentax ME has an open aperture when looking through the viewfinder, but gives a shutter speed that indicates that it would fully stop down for shooting.

(I was a little confused when I first posted - as a bit of time elapsed between experimenting with that camera and lens combination and posting - but I have since edited my original post.)
01-20-2011, 03:17 AM   #6
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Have a look at the picture below, taken from Bojidar's K-mount page.
Top right you can see the lens with the "stop-down indicator".
(This is not the diaphragm actuator!)
The camera can "read" this with the "stop down coupler".
From this it is getting the apperture.
Unfortunately Pentax DSLRs don't have a stop down coupler anymore.


01-20-2011, 03:41 AM - 1 Like   #7
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QuoteOriginally posted by blende8 Quote
Unfortunately Pentax DSLRs don't have a stop down coupler anymore.
Thank you. But the DA lenses do have a 'stop down indicator' - why would they need one if the cameras they are designed to be used on don't have a 'stop down coupler'?
01-20-2011, 04:48 AM   #8
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QuoteOriginally posted by Spock Quote
Thank you. But the DA lenses do have a 'stop down indicator' - why would they need one if the cameras they are designed to be used on don't have a 'stop down coupler'?
Bingo!
That is the 1Mio $ question!

And receive a rep.point for that one.
Welcome to the inner circle.



Now up to the next one:
Why does the position of the 'stop down indicator' of a DA lens not correspond to f22, but more to f11?
And why do we have several plug-in positions here?
DA50-135


01-20-2011, 06:03 AM   #9
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QuoteOriginally posted by blende8 Quote
Bingo!
That is the 1Mio $ question!

And receive a rep.point for that one.
Welcome to the inner circle.



Now up to the next one:
Why does the position of the 'stop down indicator' of a DA lens not correspond to f22, but more to f11?
Hmm, yes - I thought the shutter speeds in the viewfinder were a bit fast for F22...

Also, can anyone tell me why the 'stop down indicator' of my DA*200 lens moves when I move the aperture actuator?
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