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12-08-2009, 03:46 AM   #1
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Was I right to castrate my lens?

Moin,

Yesterday I got a lens off the bay, some less expensive 50mm 1/1.4 Auto Revuenon with K-mount. Aperture blades were working smoothly on inspection, but mounted into my brand new K-x, it always stayed open. Tried all menus including optical preview, but still open, and lens does not have a 'M' setting like most M42 lenses.

So I figured out the camera prevents aperture from closing using this pin that stuck out from the underside of the lens, and I decided to cut it off. After lens castration, everything worked fine for me.

Now I wonder, did I do the right thing?

Of course I searched here and googled there, but could not find any reference to neither my problem nor my solution, so just tell me if I did something stoopid.

Stefan

12-08-2009, 04:06 AM   #2
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Could you post some pics of the lens?
12-08-2009, 04:27 AM   #3
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Sure. Note the shortened pin, unfortunately no pre-op picture:
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12-08-2009, 05:50 AM   #4
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When I have non-A lenses mounted, I have only three shooting modes, Av, Manual, and Bulb. The camera keeps keeps the aperture wide open in Av no matter what. I could have the dial set to f22 and it won't do squat. But in Manual mode, it will stop down when I take a shot, or use the green button, or optical preview.
If that's the case, I believe this is normal behavior. It keeps the aperture wide open for more accurate focusing, stopping down only to take the shot.

Whether it's right or not is up to you. I myself have done a similar mod to my M50/1.7, but I disassembled the lens and took out the whole ring, so the mod was reversible. You may have some trouble reattaching the tab if you wanted to undo your mod. :P

12-08-2009, 06:13 AM   #5
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Thanks Kryosphinx.

Actually it did not stop down in manual mode for taking any shot - and I don't think it would have made any sense, as there is no way the camera knows what F-stop to use for proper exposure. So I am fine like this, and the solution with pliers is the best for me, as I rarely manage to reassemble what I once took apart.

Stefan
12-08-2009, 06:24 AM   #6
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unless you set the function "Use Aperture ring" the camera will not stop down the lens.

if the lens is fully functional, i.e. aperture opens and closes smoothly, both using the rig, and when stopped down, it opens using the lever, then you should have the camera checked because it Should work.

there was another thread about this a few weeks back.
Having said that, except for loss of wide open focusing, the lens will now behave like an M42 lens and you can use Av mode.,

Spme people prefer it this way
12-08-2009, 06:45 AM   #7
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Moin,

Just checked, with the kit lens, the aperture closes when I check optical preview using the green button - but that did not work on the above lens. I would have heard if the camera had tried, but nothing, both with "Using Aperture Ring" on and off.

It might be nice if the same optical preview and an exposure metering could be added thru firmware, as it seems that the hardware would allow this. Would perhaps be more elegant than using pliers.

Stefan
12-08-2009, 07:30 AM   #8
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every other pentax camera functions with K mount lenses as you describe with optical preview, and stopping down the lens and metering using the DOF preview and with green button setting the shutter to match aperture.

12-08-2009, 08:50 AM   #9
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Got it now - only in 'M' mode of camera this works, in all other modes the camera refuses to stop down the lens. I expected it to stop down in Av mode and set shutter speed automatically, but it does not, as statet in the manual. Still I wonder about this restriction, it should be possible. So for me it was either manual exposure or the pliers, and I made my irreversible choice.

Stefan
12-08-2009, 08:54 AM   #10
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QuoteOriginally posted by 16N64 Quote
Got it now - only in 'M' mode of camera this works, in all other modes the camera refuses to stop down the lens. I expected it to stop down in Av mode and set shutter speed automatically, but it does not, as statet in the manual. Still I wonder about this restriction, it should be possible. So for me it was either manual exposure or the pliers, and I made my irreversible choice.

Stefan
Hey, as long as it works and the lens is not mine!
12-08-2009, 09:02 AM   #11
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QuoteOriginally posted by 16N64 Quote
Got it now - only in 'M' mode of camera this works, in all other modes the camera refuses to stop down the lens. I expected it to stop down in Av mode and set shutter speed automatically, but it does not, as statet in the manual. Still I wonder about this restriction, it should be possible. So for me it was either manual exposure or the pliers, and I made my irreversible choice.

Stefan
This restriction exists because in Av mode the camera needs to know what aperture is set to calculate exposure with the lens wide open.,

If you want the camera to meter in Av mode then the sequence would be meter, stop down the lens, meter again then flip up the mirror and open the shutter. In this sequence the shutter lag would be unacceptable.

This is how it has always been, and there is no way to improve upon it because the camera control mechanism cannot control the aperture of non A lenses as they are really more of an on off switch for the aperture as opposed to A series lenses where the aperture area is linear with the lever movement,

As I said earlier, some people prefer the approach youo took any way. FOr me, with manual lenses, I just meter off something "approximately grey" in manual mode and then shoot with that setting, and use the advantage of a wide open lens for focusing, because it has the lowest DOF and you can therefore have the most accurate focus.
12-08-2009, 09:18 AM   #12
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Ummmm...I don't know if it came through in the above comments, but you did wrong.



I feel for your poor Revuenon! To pay the ultimate price for a misconfigured camera!

Steve
12-08-2009, 09:37 AM   #13
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QuoteOriginally posted by Lowell Goudge Quote
This restriction exists because in Av mode the camera needs to know what aperture is set to calculate exposure with the lens wide open. [...]
I disagree - even with manual lens attached and camera showing F---, Av mode works fine. I still miss automatic shutter setting based on measurement of incoming light while doing optical preview. If this shutter speed is memorized, there should be no additional latency when taking the actual shot.

Will try more once I got a manual step down lens again.

Stefan
12-08-2009, 09:38 AM   #14
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Just in case somebody has a similar problem in the future: sometimes the aperture might not work bacause the aperture lever is bent, so the camera misses it.
12-08-2009, 01:16 PM   #15
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Just use it like a manual m42... you did 'wrong' but I dont think it's that big of a deal if it's gonna be used and not resold. I personally prefer stop down m42 metering than M/K lenses metering with green button.
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