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04-15-2019, 07:00 AM   #3706
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QuoteOriginally posted by stevebrot Quote
It might jam. The PK/A adapter is very strange about how its tabs are moved and when.

More... If I forget to unlock the "A" position and take the adapter off with the aperture ring in other than the max aperture position, it will be difficult to get it to a state where it can be mounted again.


Steve
So, mismounting or misunmounting a PKA adaptall-2 ring can permanently jam tiny internal objects? I've got two of them, and one misbehaves. If I want to shoot an adaptall-2 lens in Aperture Priority, I'm more likely to put an M42 adaptall ring on the lens, than to fool with a PKA and worry that it's going to give me trouble.

04-15-2019, 07:16 AM - 1 Like   #3707
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QuoteOriginally posted by goatsNdonkey Quote
So, mismounting or misunmounting a PKA adaptall-2 ring can permanently jam tiny internal objects? I've got two of them, and one misbehaves. If I want to shoot an adaptall-2 lens in Aperture Priority, I'm more likely to put an M42 adaptall ring on the lens, than to fool with a PKA and worry that it's going to give me trouble.
You should dismount it properly of course, but if they get in a weird state it is just a matter of releasing the black button on the mount so that it can move freely again. The PKA mounts can definitely be fiddly and somewhat fragile, but they aren't as fiddly and fragile as one would believe reading about them online. It just takes a little bit to figure them out and that seems to be all people talk about. For the faster Adaptalls, they are great. One true limitation that is built-in to them is they don't read properly with lenses slower than f/4 -- so like on the 300/5.6 the aperture mapping (what is displayed vs reality) is a bit wonky and non-linear, which can make it troublesome if you are not shooting at a constant aperture. But in general I like to get 'A' ability where I can with full metering and camera aperture control and EXIF data, so it is worth having a PKA mount for use with most of these lenses.
6 Days Ago - 1 Like   #3708
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QuoteOriginally posted by goatsNdonkey Quote
So, mismounting or misunmounting a PKA adaptall-2 ring can permanently jam tiny internal objects?
Unless forced, the jam is not permanent, just difficult to unravel, sort of like one of those sliding wood puzzle balls. That is why it is good to make it a general practice to follow the rules and always move the aperture ring to its widest position prior to swapping Adaptall mounts. As for using M42 in preference, remember that there is no A/M switch on the M42 adapter. For use on a Pentax dSLR, the PK adapter in M mode is my personal preference despite my owning two PKA adapters.

Back to "the jam". It happens because the position of the two index tabs have limited movement relative to each other when the "A" position is engaged and will remain so when adapter removal is attempted (only possible if the aperture ring on the lens is allowed to rotate with the adapter...do not force)*. This locked position initially places the tabs in furthest opposition with the tab near the "A" contacts fixed and the other tab having only limited movement. The adapter can be functionally attached to a lens but may not attach cleanly such that either the adapter will not rotate fully onto the lens or that the aperture ring will be fixed in a position other than the true "A" position. Releasing the "A" lock at this point will free the ring, but sometimes without full range of movement to f/22. This last state may persist even if the adapter is properly removed and reattached.

Note that I have not given full instructions on how to fully reproduce. I was able to do so prior to typing the above using a junk PK/A adapter (stiff actuator) from my parts box, but would not do this sort of play with an adapter I was planning on using again.

To correct:
  • With aperture ring at its widest setting, remove adapter from lens
  • With the mount contacts facing you, rotate both tabs clockwise to their stops
  • While pressing the "A" lock move the tab nearest the base contacts further and release "A" lock button. This approximates the tab positions for a proper lock when on-lens. One tab should be locked and the other with limited and stiff movement.
  • Press the "A" button again and rotate the locked tab counter-clockwise to allow free movement of both tabs. The adapter should now be in proper state.
Prevention? Take care to always have the aperture ring at widest position when attaching/detaching a lens. Check to see if the tabs are locked; if so, perform the steps above to reset the adapter before attaching to the lens.


Steve

* There is also some sort of mechanical interlock between the silver adapter release button and the "A" position lock that creates the errant adapter state.

Last edited by stevebrot; 6 Days Ago at 11:14 AM.
6 Days Ago   #3709
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QuoteOriginally posted by vonBaloney Quote
One true limitation that is built-in to them is they don't read properly with lenses slower than f/4 -- so like on the 300/5.6 the aperture mapping (what is displayed vs reality) is a bit wonky and non-linear, which can make it troublesome if you are not shooting at a constant aperture.
I was aware of the f/4 limitation, but suspect that the wonky part may be avoided by following the advice from the PK/A package insert to not let the camera set apertures outside the lens' actual range. From the "K-mount Page":
QuoteQuote:
The Tamron KA Adaptall Mount

When Joachim Hein read the above discussion, he immediately understood the roots of the exposure problems that some Adaptall lenses have. These are all “slow” lenses with minimum aperture setting of f/22 and an “AE” setting or f/32 and no “AE” setting In the latter case, f/32 is converted to “AE”). “AE” is the Tamron equivalent of the Pentax “A” setting. Looking in the second column of the table above, we see that there is no contact pattern for lenses with apertures ranging between f/4.5 or slower and f/22. Tamron solves this by making the Adaptall mount indicate a maximum aperture of f/4 and warning in the mount manual that the photographer must watch the aperture read-out in the view-finder (not available with P30/P50!) to ensure that only values within the true aperture range are used.
See Features and Operation of the KA Mount | The K-Mount Page for the full discussion as well as the table referenced in the quoted text.

Of course, taking that advice sort of negates the reason for buying the PK/A adapter. It also does not help that most of us bought our adapters used and without the original packing and inserts having the instructions for proper attaching/detaching the adapters and limitations in use.


Steve

(...does have the insert for one of my PK/A adapters...lucky me...)

6 Days Ago   #3710
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QuoteOriginally posted by stevebrot Quote
I was aware of the f/4 limitation, but suspect that the wonky part may be avoided by following the advice from the PK/A package insert to not let the camera set apertures outside the lens' actual range.
It is still wonky in my testing. f/8 is not f/8, and differences of 1-stop are not 1-stop, etc. It could just be down to the lens I suppose -- auto-aperture lever placement is somewhat approximate in all cases (except wide-open) compared to manually setting the aperture, ain't it? (The slower lenses I had were/are the SP 200-500/5.6 and the SP 300/5.6 macro.)
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QuoteOriginally posted by vonBaloney Quote
auto-aperture lever placement is somewhat approximate in all cases (except wide-open) compared to manually setting the aperture, ain't it? (The slower lenses I had were/are the SP 200-500/5.6 and the SP 300/5.6 macro.)
Yep, the movement of the actuator on the body is relative to its home and it is assumed that the lever on the lens will be deflected to its exact maximum aperture when fully mounted and the retention pin engaged; as such, 1/3 stop upward travel of the body's actuator should result in 1/3 stop less light through the lens iris opening. The truth of that last phrase depends on the mechanical precision and calibration of the iris diaphragm mechanism as well as mechanical resistance.


Steve
6 Days Ago   #3712
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I've had about a score of PKA mounts pass through my hands now (currently about 7 or 8 in the box/on lenses inc couple of duds), and my experience is that the majority of them show exposure inconsistency as you go through the f-stops, typically showing increasing overexposure as you stop down. Why this is I haven't been able to determine.
There are links to the write ups I did in this thread here:

https://www.pentaxforums.com/userreviews/tamron-adaptall-mount-adapter.html
6 Days Ago - 3 Likes   #3713
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I have 7 PKA adapters, and all of them have at least a little inconsistency with exposure and aperture (when set from the camera). For example, when I shoot a burst of, say, 7 shots with my 360B, the exposure and DOF reflects a difference of up to one stop among those 7 shots. It only bothers me a little, as I know to expect it and it's kinda like aperture bracketing! When I want greater reliability I just use the aperture ring.

A quartet with the 19AH... first 3 are shot wide open, #1 is at 70mm, the rest are at 210mm









3 Days Ago   #3714
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nice with the 19AH ... very nice ... i gotta get mine out of the hospital ... spring is near !! ...
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QuoteOriginally posted by luftfluss Quote
I have 7 PKA adapters, and all of them have at least a little inconsistency with exposure and aperture (when set from the camera). For example, when I shoot a burst of, say, 7 shots with my 360B, the exposure and DOF reflects a difference of up to one stop among those 7 shots. It only bothers me a little, as I know to expect it and it's kinda like aperture bracketing! When I want greater reliability I just use the aperture ring.

A quartet with the 19AH... first 3 are shot wide open, #1 is at 70mm, the rest are at 210mm






Ohhhhh....nice! I must confess to owning a 19AH and to not actually done any work with it. While I know it is an amazing lens, I also own the much more svelte and much underrated Pentax-A 70-210/4 that has developed a close relationship with my bags...both of them

Clearly, this must change: particularly since I picked up the 19FH hood and a suitable neoprene bag.


Steve

(...given more self-encouragement, I may yet talk myself into this...)
3 Days Ago - 3 Likes   #3716
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QuoteOriginally posted by stevebrot Quote
Ohhhhh....nice! I must confess to owning a 19AH and to not actually done any work with it. While I know it is an amazing lens, I also own the much more svelte and much underrated Pentax-A 70-210/4 that has developed a close relationship with my bags...both of them

Clearly, this must change: particularly since I picked up the 19FH hood and a suitable neoprene bag.


Steve

(...given more self-encouragement, I may yet talk myself into this...)
Yes, do it!

Although, the 19AH is rather large and heavy. But it is sharper throughout its range than the Pentax F 70-210 f/4-5.6 - a lens I like a bunch - and I love lenses with close-focusing capability.





3 Days Ago   #3717
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QuoteOriginally posted by luftfluss Quote
Yes, do it!

Although, the 19AH is rather large and heavy. But it is sharper throughout its range than the Pentax F 70-210 f/4-5.6 - a lens I like a bunch - and I love lenses with close-focusing capability.




Do you fit your 19AH with a tripod foot or do you support it some other way?


Steve
3 Days Ago   #3718
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QuoteOriginally posted by stevebrot Quote
Do you fit your 19AH with a tripod foot or do you support it some other way?
No tripod, but when I'm shooting in or near my yard I tote either a little resin stool or a sheet of plastic so I can sit easily while shooting... elbows and knees do a fair job of stabilizing.

I've only had a couple hundred snaps with my 19AH since acquiring it last August, so haven't fully explored the lens yet.
3 Days Ago   #3719
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QuoteOriginally posted by fuzzyphoton Quote
nice with the 19AH ... very nice ... i gotta get mine out of the hospital ... spring is near !! ...
Oh dear, what sidelined it?
3 Days Ago   #3720
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ooops .... i almost threw this away ... but it made me wonder if my cockatiel really thinks i cannot find her ? tammy 01a ... lots of flash ...
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