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05-10-2011, 08:23 AM   #1
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am i an idiot? - possible k10d, K mount lens hack

Hi All,

I have a Pentax K10d and have recently picked up some old K mount lenses. I'm aware of the restrictions when using K lenses with the K10d's 'crippled' lens mount - in order to use anything other than the fastest aperture, you need to be in manual mode and ether aperture preview then meter manually using the cameras display, or press the little green button which makes the camera perform the aforementioned process automatically over about a second.

Although this is ok, it's a little cumbersome and slow.

As an alternative, I was wondering if it's possible to remove the pin from the lens that allows the camera to control the aperture (the spring loaded one at the side of the mount). This way, surely I can put the camera in AV or full auto mode and use the aperture wheel to control the aperture and the camera will meter properly because essentially the lens will always be in aperture preview mode. The only drawback I can see is that if I set the lens to a slow aperture things will look very dark through the viewfinder. I don't see this as a massive issue though considering I'm only likely to use slow apertures in very bright, outdoor situations.

Will this work, or just break my lens?

thanks

05-10-2011, 08:38 AM   #2
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This will let you use Av mode (as is allowed with M42 lenses), but I don't think it's worth risking breaking your lenses for it.

Adam
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05-10-2011, 08:41 AM   #3
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Have you used the green button for a while yet? As long as the light isn't changing rapidly it does a pretty good job. Set it once and use it until the light changes.
05-10-2011, 08:46 AM   #4
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QuoteOriginally posted by ophillip Quote
Hi All,

I have a Pentax K10d and have recently picked up some old K mount lenses. I'm aware of the restrictions when using K lenses with the K10d's 'crippled' lens mount - in order to use anything other than the fastest aperture, you need to be in manual mode and ether aperture preview then meter manually using the cameras display, or press the little green button which makes the camera perform the aforementioned process automatically over about a second.

Although this is ok, it's a little cumbersome and slow.
true, but you don't need tp press the green button every time you shoot, I use manual lenses and unless you are constantly changing exposure conditions you can shoot over and over without re-setting. Just keep an eye occasionally on the histogram
QuoteQuote:

As an alternative, I was wondering if it's possible to remove the pin from the lens that allows the camera to control the aperture (the spring loaded one at the side of the mount).
some people have gone as far as cutting this off, althoug I see no reason to damage the lens at all. others have drilled a second latching pin location so that the lever (note it is not really a pin) does not contact the camera body lever, achieving the same thing
QuoteQuote:
This way, surely I can put the camera in AV or full auto mode and use the aperture wheel to control the aperture
no, the camera will not control anything without this lever in place
QuoteQuote:
and the camera will meter properly because essentially the lens will always be in aperture preview mode.
yes, like any M42 lens as an example
QuoteQuote:
The only drawback I can see is that if I set the lens to a slow aperture things will look very dark through the viewfinder. I don't see this as a massive issue though considering I'm only likely to use slow apertures in very bright, outdoor situations.

Will this work, or just break my lens?

thanks
It can work, but as I have noted above, I personally think it is a waste of time and effort for very little gain.

What makes it worse, is the K10D is the worst camera there is, with respect to metering with old lenses, and as a result, simply using Av mode, with any stopped down lens will be frustrating at the very least. Manual mode is a much better way to go with the K10D and K mount lenses. Set the aperture where you want to have it, and then press the green button while metering off a medium grey sruface, (tree trunks and paved roads are suitable alternatives) and then look at the hystogram. it should be centered. each vertical line (1/4 scale markings) is about 1 1/2 stops. Adjust exposure by changing shutter speed appropriately and test again. Once it is set, go and shoot until lighting changes or you want different aperture and /or shutter speed, and then repeat the process

It is much better - especially on a K10D

05-10-2011, 09:05 AM   #5
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Hi, ophillip
I removed that lever by unscrewing it on an el cheapo Ricoh while I was removing the ricoh pin
I don't recommend this mod.

The dslr ("crippled") will work on the AV mode by controlling the shutter speed as the aperture is varied manually.

The problems are:
The viewfinder image gets darker as you stop down
The AF does not work properly smaller than about F8

The lens will no longer expose properly on a film slr because the rotary slider is being driven but the camera sensor thinks the lens is wide open.

Much better, in my opinion, to get used to Manual and the exposure button.
05-10-2011, 10:25 AM   #6
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As well as issue with exposure lock. Realize that the light of the scene may shift your shutter speed because of some of your camera settings.
I have a Vivitar lens that has had the aperture lever removed. It was interesting for a brief moment but really less convenient that using the green button.
05-10-2011, 10:34 AM   #7
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Put a piece of aluminium foil over the "A" pin on the body mount while you mount the K-mount lens, set the diaphragm ring to f/22 and that's it, you have an "A" lens, sort of. You will be able to control the f/stop from the body, use all program modes and even the P-TTL flash system will work

(Although there's some deviation because the K-mount diaphragm lever does not work the same way as on a true "A" lens (non-linear vs linear), so you'll have to use a bit of exposure compensation.)
05-11-2011, 04:39 AM   #8
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Wow! what a great forum - thanks everyone.

I think my lens is going to stay intact for the time being and I'll get used to using the green button... although I might reach for the tin foil as Asahiflex suggests. If anyone has any more experience of this mod I would appreciate it, for example how to ensure you don't get bits of tinfoil all over your sensor!

thanks

05-11-2011, 04:55 AM   #9
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QuoteOriginally posted by Asahiflex Quote
Put a piece of aluminium foil over the "A" pin on the body mount while you mount the K-mount lens, set the diaphragm ring to f/22 and that's it, you have an "A" lens, sort of. You will be able to control the f/stop from the body, use all program modes and even the P-TTL flash system will work

(Although there's some deviation because the K-mount diaphragm lever does not work the same way as on a true "A" lens (non-linear vs linear), so you'll have to use a bit of exposure compensation.)
The problem with this is that the camera gets the wroing coding back from the lens contacts, meaning that aside from the non-linear (i.e. linear area control of the aperture with lever movement that a KA has as opposed to diameter linear with lever mopvement onK mounts) the exposure will be all over the map, under at some points over at others. Even with correct coding of aperture, the exposure can go from -2 to +2 stops, over the whole aperture range, and is actually worse than the metering with the green button, so although you can shoot other modes, the trial and error approach to metering is less automated than if you use just the green button in manual

QuoteOriginally posted by ophillip Quote
Wow! what a great forum - thanks everyone.

I think my lens is going to stay intact for the time being and I'll get used to using the green button... although I might reach for the tin foil as Asahiflex suggests. If anyone has any more experience of this mod I would appreciate it, for example how to ensure you don't get bits of tinfoil all over your sensor!

thanks
good idea to leave the lens alone, and forget tin foil unless you really need to do some flash shots, but again, the trial and error approach is slower than just doing the flash calculation manually
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