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06-27-2009, 03:46 AM   #1
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Adaptall Ka mount

I would be interested to hear about anyones experience with the adatpall KA mount on the older series one adaptall lenses.
Having seen the price of an adaptall KA mount (more than I have paid for any of my adaptall lenses) and having found all of the required information about the pentax ka mount system and electrical contacts on the web (Welcome to Bojidar Dimitrov's Pentax K-Mount Page) and being a keen model engineer, I decided to have a go at modifying a normal pk mount to a ka mount. The lens I modified the mount for is an adaptall 35-80 f/2.8-3.5 zoom (model QZ-35M). Modifying the mount was fairly straightforward but when I tried it I was a little disapointed with the results. It workes OK at either end of the aperture range but in the middle it overexposes considerably (about 1.5-2 stops at F/8). At first I though that this was just because the mecghanism for the ka mount must be fundamentally different to ensure that the aperture area opening is linear with the displacemnt of the actuator and I started wondering about further modifying the mount to compensate for this. However I subsequently got hold of an adaptall 2 28mm f/2.5 (model 02B) and this workes fine over the whole aperture range. I would very much like to know if anyone else has experiences similar exposure problems using a proper adaptall ka mount on the older ka lenses. If so these lenses were just not designed to work with with a ka mount, otherwise there is something else wrong with my lens.
In spite of the exposure problem the modification is deemed to be worthwhile as it means that I can frmae and focus at full aperture and the camera does the stoppuing down when I release the shutter. I just have to remember to dial in the required amount of exposure compensation when I set the aperture.

06-27-2009, 08:09 AM   #2
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I am not sure the mechanism of the KA mount adaptall adaptor is the same as the K mount in controlling the aperture.

the K mount has (for pentax lenses) aperture diameter change with the linear movement of the lever, the KA has the area change with the linear movement of the lever.

The same may hold true for the tamron adaptall mounts.

I have not compared mine, I have the KA on a 28mm F2.5 and the K on a 24mm F2.5 lens.

the result you posted sound suprisingly like the results I got converting a 50mm F2 K mount to KA mount, by adding a spring loaded pin at the A position and drilling the mount to get the aperture coding.

Look closely as to how your K mount adaptor moves.
06-27-2009, 08:40 AM   #3
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Original Poster
I have modified / converted a couple of other lenses with similar ressults but these are definately due to that fact that the diameter and not the area changes linearly with the movement of the lever. However the fact that my modified adaptall mount workes with an adaptall 2 lens but not with a searies 1 adaptal lens indicates that the searies one lenses (or at least the one I have) were not designed with the ka adapter in mind. Have you tried the ka adapter on the older searies 1 24mm f/2.5?
06-27-2009, 01:38 PM   #4
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QuoteOriginally posted by MattGunn Quote
I have modified / converted a couple of other lenses with similar ressults but these are definately due to that fact that the diameter and not the area changes linearly with the movement of the lever. However the fact that my modified adaptall mount workes with an adaptall 2 lens but not with a searies 1 adaptal lens indicates that the searies one lenses (or at least the one I have) were not designed with the ka adapter in mind. Have you tried the ka adapter on the older searies 1 24mm f/2.5?
I can't answer about origonal adaptall lenses all I have are adaptall 2

06-27-2009, 02:12 PM   #5
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I have tried something similar with a Rikoh (RI) adaptall-2 mount. I was hoping that it is linear in the same way as the PKA- It is not. I used tape and a little piece of alu foil to shorten the A contact. Whatever I set for largest and smallest aperture with the contacts I never got the aperture to close correctly- it always stayed open to far.

The biggest differences between the PKA and the PK and Rikoh is that the lever on the Ricoh and PK is hinged while it runs parallel (without hinge) on the PKA. I believe the hinge prevents it from being linear since the lever point (or length) gets shorter towards medium apertures and than longer towards the end.

I have three PKA adapter- and 2 of them were quite a bid off when I got them. The widest aperture was fine, but than they did not stop down for the first 1-2 stops. Their design is quite bad- if you take them apart you can see that they can get easily out of adjustment. All 3 I have have slightly different designs, and only one has a special hole on the side which allows easy adjustment. I would only pay $90 if it is really in excellent condition.
06-27-2009, 02:48 PM   #6
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An ol' f@rt's opiunion

QuoteOriginally posted by Lowell Goudge Quote
I can't answer about origonal adaptall lenses all I have are adaptall 2
I have three - 2's and two "-1's" from way back when . . .

Given that I mainly use Manual-mode anyway, I can't find a significant optical difference in them that I can't attribute to personal technique or modern digital coatings (which rarely appear in real use). I frequently use a P/K rather than a P/KA adapter just because that's the way I work and A/F isn't a factor anyway.

Tamron's Adaptall-2 and most Adaptall (1?) lenses were pretty darn good glass any way you look at 'em -- the technology was refined by then and they were trying hard to produce lenses with optical qualities that overcame the marketing hoopla of A/F in the early '80s. Some compromises were obviously subsequently made in the bodies but the optics weren't degraded so as to keep up market presence and reviews. IMO, they really should be considered along with the (somewhat over-rated?) Vivitar Series 1 glass.

Mechanically and optically speaking, my Tamron Adaptall's are both consistent and satisfactory, given that I know how to work around the Di-issues in the few instances they arise.

I know technology is a factor. If you don't believe that, just try to teach someone to drive an 'old fashioned' manual shift automobile. But once you learn to shift gears (or set aperture/shutter speed) for yourself it's just another machine to get you from here to where you wanna be.

Some old glass, like some new glass is really fine no matter the age if you just take into consideration that the modern amenities aren't critical.

H2
06-27-2009, 04:00 PM   #7
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QuoteOriginally posted by pacerr Quote
IMO, they really should be considered along with the (somewhat over-rated?) Vivitar Series 1 glass.

Actually I think they are mostly superior the the Vivitar series 1 lenses, my 70-210mm f3.5 19AH is better than the 2 different Vivitars I have had and the 01A 35-80mm f2.8-3.8 is also a superb performer.
I do think the Series 1 Macro is better than the 90mm 55B and 72B lenses I have though.
06-28-2009, 10:15 AM   #8
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I too have owned a series 1 Viv. It was the most desirable version 3 Komine, with the added bonus of being an A lens. Not all Version 3 komines were built in the A version.


I now own the 19H, and it cost me less than half what i sold the Viv series V3 for, and everything they say about this lens is true. It has to be one of the best in its class

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