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06-04-2010, 11:11 AM   #1
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Strange behavior from Tele-Takumar 300mm

I just picked up a Tele-Takumar 300mm f6.3 as the latest fix in my Takumar LBA. I got out my genuine finest kind Pentax M42 to K adapter and screwed it onto the lens without problem. However when I went to mount the lens onto my K10, the lugs on the adapter would line up with the slots in the mount (as they should) but I could not turn the lens/adapter combo to secure it. Of course I did not try to force it as that's usually a recipe for disaster. After a couple of attempts I carefully inspected the lens/adapter and everything was fine, no protrusions or anything and nothing in the camera mount to block it. I took the adapter off the 300 and attached it to a SMC 50 f1.4 and tried to mount that on the K10. Worked fine the first time, just as Pentax advertises. Then I unscrewed the 50 leaving the adapter in the mount, also as advertised and tried mounting the 300 that way. No problem, screwed right into the adapter. But no matter what, when that adapter is on the lens first, I cannot mount it on my K10. Anybody have any ideas why?

Oh I did find one other thing out about that lens. If you've had your shoulder rebuilt, it's not a good lens for use without a support of some kind.

CW

06-04-2010, 11:48 AM   #2
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is it possible that the aperture activation pin is hitting something which blocks the lens from mounting?

Look at the back of the lens or perhaps attach a photo of the rear

there are several known interference issues between lenses and pentax DSLR bodies, the most notable is the Vivitar extended "protective shield around the aperture activation lever being too long and interfering with the components inside the body
06-04-2010, 05:17 PM   #3
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Lowell, this one is a preset lens so there are no activation pins, levers or anything else on the back.

CW
06-04-2010, 08:07 PM   #4
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Not to be a smart alec but is your rebuilt shoulder causing the problem? The bayonet is a precise fit. With the 50, you are pushing the lens/adapter combo square from the front of the lens while turning. With the heavy 300, the adapter may not be perfectly aligned to turn it as you are holding from one side of the lens. I'm a mechanic and I deal with fastners for a living. As I have grown older, they are more and more becoming a problem. It's possible the adapter is somehow becoming warped on the 300, but you should be able to notice that right off as the threads would not feel right threading the lens to the adapter. I have had problems mounting my 200/4 Tak. It's me, not the lens.

06-05-2010, 10:34 PM   #5
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Issue Solved

When you are trying to mount the 300mm lens with the adapter, the flat steel rear end of the Tele-Takumar is coming into contact with the AF Coupler and trying to force it down while you turn the lens. This causes the lens to line up at an angle. When the M42 to K mount is already mounted in the camera and you try to screw the lens into the adapter, it begins with the flat steel back of the lens above the AF Coupler and as the threads tighten the lens down, it makes gradual contact with the Coupler pushing it out of the way. Don't know how good that is for the AF Coupler but it does work.

CW
06-06-2010, 02:04 AM   #6
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Hi, I have one too. I use it with the original adapter, which I leave attached to my camera most of the time. Never had issues. So, I screw it into the adapter which is first fitted to the cam. But as it is a rather long lens, screwing it into the adapter needs a careful "screw start". Sorry about your shoulder. I'm a 55 year old woman and manage to use this lens with good (sharp) results handheld. I'm really happy with it, because it is so light and transportable. So I can use it. It gives me better results than the 55-300 at the far end. Hope you like this lens, it has such beautiful colors and lovely performance. Good luck with your shoulder.
06-06-2010, 05:56 AM   #7
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QuoteOriginally posted by straightshooter Quote
When you are trying to mount the 300mm lens with the adapter, the flat steel rear end of the Tele-Takumar is coming into contact with the AF Coupler and trying to force it down while you turn the lens. This causes the lens to line up at an angle. When the M42 to K mount is already mounted in the camera and you try to screw the lens into the adapter, it begins with the flat steel back of the lens above the AF Coupler and as the threads tighten the lens down, it makes gradual contact with the Coupler pushing it out of the way. Don't know how good that is for the AF Coupler but it does work.

CW
The af coupler is spring poaded and should retract, however if this is causing the problem simply use the lens release button when you mount the lens. It retracts the AF coupling.

The other thought I had is that the rear of the lens may be slightly recesses, and when the k-mount adaptor is on the lens you do not have the ability to incert the adaptor fully into the body.

Note the af drive should not interfere in any way with the lens going fully in place unless the drive in the middle is catching a screw head and many M42 lenses do not correctly allign vertically on the cameras
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