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03-13-2016, 10:09 AM - 2 Likes   #2956
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PKA mounts testing: Part 3 Review, summary and conclusions.

PART ONE - Post 2888.
PART TWO - Post 2891

My usage of the PKA mount has been afflicted with exposure inconsistency. I have used a number of them and pretty much my experience has been the same with both the K-r I used to have and with my current K5, and with the variety of adaptall lenses in my collection.

Well, as I asked: Is it the camera? Is it the mount? Is it the lens? Or perhaps a combination..?

First thing I can say is that as remarked upon in the first part post 2888 the shutter speeds the camera is recorded as delivering are mostly consistent with the stopping down of the aperture, with just a few minor discrepancies. This is as it should be - the camera is after all simply calculating a shutter speed in proportion to the measured wide open exposure reading.
Second thing I can say is that the mounts which showed the most variation tended to do so with all the lenses I tried them on. And conversely the mounts which showed relatively consistent exposures tended to so with all the lenses.
The first point concentrates our attention on the closing down of the lens iris. On Pentax, the operation of the aperture is as follows. Putting the lens into AE position on the PKA mount closes the iris fully, but on camera the camera aperture control pushes the aperture lever on the mount down, which pushes the aperture lever on the lens down, opening the iris fully. When the shutter is pressed the camera aperture control moves an amount corresponding to the selected aperture, the return spring in the mount moves the mount aperture lever in sync and the return spring in the lens moves the lens aperture lever in sync closing the iris the requisite amount. So if the pic ends up overexposed the suspicion must be that the iris has not closed as much as it should have.
The second point concentrates our attention on the operation of the mount ahead of the camera mechanics and the lens mechanics. So I had a closer look at a couple of the mounts that showed a lot of exposure variation - no's 3 and 5, and took the cover off to examine the internals. There was nothing I could see suggestive of a fault or a problem. But I did try a bit of judicious lubrication. This however had little effect, and a technician at Luton Camera Repairs responded to a request for advice like this:

QuoteQuote:
These do not require lubrication. The parts that rub together are coated (grey). This is a dry luticant bonded to the metal surface during manufacture. If the mechanism is sluggish it will need cleaning (which is what the WD40 is doing, but then it will go sticky).
I have tried some cleaning (toothbrush and meths), results are only suggestive of improvement.

So what might cause imprecision in the closing down of the iris?

Hypothesis 1. The mount has aged/acquired wear and tear which has meant it has lost the necessary precision. Or it never had it due to manufacturing inconsistencies.
Hypothesis 2. Dirt etc. is just making the mount "sticky".
Hypothesis 3. The springs that move the aperture lever in either the lens and mount or both , and therefore the iris, on shutter release, have aged/weakened/aren't strong or effective enough.
Hpothesis 4. A combination of factors, including the above, the lens, the camera (eg low battery?).

There is another thing: I have a general impression that exposure variation tends to be more with shorter focal length lenses. Why might that be? Well the physical movement of the iris in a shorter focal length lens is less than that of a longer focal length lens simply because the iris is simply smaller. So this suggests that inaccuracies in its movement might be more noticeable, more significant in comparison to longer focal length lenses with larger iris's. This ties in to some extent with another impression: mounts that show a lot of variation tend to show it the most over the first stop down, second stop down. For example if you refer back to my film strip for the CT105 in post 2891 that is a good example. I should mention that this is only an impression and I have had example mount + lens combos that have shown au contraire more exposure discrepancy at the f11/f16 end of things (and even in a couple of instances a reversal of the anticipated overexposure to underexposure at f11, f16).

These impressions do tend to focus my suspicions on hypothesis 2, however the current state of play is simply that I don't really know! I did try to use my 300mm f2.8 to see if the change in depth of field would be indicative, but because this lens has suffered from dropping onto its end accidentally which has affected the automatic stopping down in Av, I couldn't draw any conclusions.
My usage of these PKA mounts has meant that I now habitually chimp a sequence of shots at successive f-stops on mounting lens + PKA on the camera. With a perspective from that I can automatically and quickly adjust the exposure compensation to match the selected f number. As a common rule of thumb, 2 compensatory clicks (= +2/3 stop) for first stop down, down one click for the next, and one click for the next, exposures then tend to be relatively consistent over the next middling f5.6/8/11 stop or two.

Any further insight, info or ideas for more diagnostic experimentation appreciated. If there is a conclusion it is perhaps that you may need to try a few to find a good one, and if/when you find a good one that seems to work particularly well - hang on to it!

03-21-2016, 09:58 AM   #2957
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Rear caps to fit Tamron Adaptall lenses

As mentioned on my info page old canon cfd mount caps work well on lenses like the 03A, 103A, 17A, 09A, .... most of the ones with a protruding rear baffle. I have just noticed this particularly cheap offer:

Auction no. 201542212462
03-22-2016, 03:23 PM   #2958
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Disassemble 200mm f3.5 04B

Anyone have any insight into getting the main front elements out? I have separated the main optical unit from the helicoid but its not clear what should unscrew to access the lens elements.
04-22-2016, 01:49 PM - 1 Like   #2959
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K-3 with Tamron Adaptall 2 02B - 28mm f2.5



04-29-2016, 12:18 PM   #2960
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Either I'm totally discombobulated today . . . quite possible . . . or the Adaptall-2 site has reverted to the ---.COM address again. My bookmark for ---.ORG no longer connects to the site.

Anyone else?

(Just change .org/ to .com/ in the bookmark properties.)
04-29-2016, 12:49 PM   #2961
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QuoteOriginally posted by pacerr Quote
Either I'm totally discombobulated today . . . quite possible . . . or the Adaptall-2 site has reverted to the ---.COM address again. My bookmark for ---.ORG no longer connects to the site.

Anyone else?

(Just change .org/ to .com/ in the bookmark properties.)
Yes, appears so. (And copyright date updated to include 2016)
04-29-2016, 01:20 PM   #2962
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Maybe they'll being adding more new content then?
04-29-2016, 02:53 PM   #2963
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QuoteOriginally posted by pacerr Quote
Either I'm totally discombobulated today . . . quite possible . . . or the Adaptall-2 site has reverted to the ---.COM address again. My bookmark for ---.ORG no longer connects to the site.

Anyone else?

(Just change .org/ to .com/ in the bookmark properties.)
Yes, this was discussed earlier this week. The site owner changed the domain.

04-29-2016, 08:02 PM   #2964
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QuoteOriginally posted by monochrome Quote
this was discussed earlier this week.
Really? Here? Gosh, some one wake me up next time.
04-30-2016, 08:03 AM   #2965
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Attila, who also runs mflenses.com, said:

QuoteQuote:
First I couldn't get com , so I did took .org , later Google was smart enough to take off .com due was spam only and I could buy .com. It wasn't too smart to pay both so I let .org to go.
adaptall-2.com it is!
(now i have to update the links on my pages)
05-03-2016, 06:33 AM   #2966
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K-3 with Tamron Adaptall 2 72B - 90mm f2.8

new-to-me 72B:



05-05-2016, 07:41 PM   #2967
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K-3 with Tamron Adaptall 2 72B - 90mm f2.8

where has this lens been all my life?



05-05-2016, 08:07 PM   #2968
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Probably hiding right behind a 52BB. And it holds up nicely with either of the Tamron 1.4x TC's if you need a little more reach.
05-06-2016, 07:45 PM   #2969
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K-3 with Tamron Adaptall 2 72B - 90mm f2.8

05-08-2016, 05:37 PM - 1 Like   #2970
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K-3 with Tamron Adaptall 2 72B - 90mm f2.8

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