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12-28-2015, 07:03 AM   #1
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Tamron SP 17mm - infinity focus

Hi,

i bought an old lens second hand. Some helpful forum members identified it as a Tamron SP 17mm f3.5 Adaptall (https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/304582-what-lens.html).

Taking some shots outside showed that the lens doesn't focus to infinity. I. e. if i turn the focus ring from near to infinity the image of a far landscape gets sharper and sharper till the ring reaches the limit stop (using live view 10x zoom). Attached you find a sample (with detail) and some pictures of the mount and adapter.

It seems to me that the lens is just a tiny bit too far from the sensor (< .05mm, if i observe the movement of the rear lens element). is there a possibility to adjust the Adaptall adapter? e. g. i spotted some tiny screws at the side of the mount (attached picture upper left third).

Any advice?

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12-28-2015, 07:29 AM   #2
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The mount can't be adjusted. This is a lens issue.
First thing I would do is examine the lens closely, looking (listening) for eg loose elements, and signs that the lens has been tampered with like slight scratching of screws, the lens spanner slots on the nameplate.

I don't have this particular lens. I posted in the adaptall club thread about adjusting infinity focus on the 28A. In fact I later noticed that the problem was a loose front element. in any case pulling off the rubber and seeing if there is an easy adjustment is a first recourse. Have a look and post a pic or two and we can try to advise...
12-28-2015, 09:07 AM   #3
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Thanks for your first hint. Seems to me there is no easy adjustment. There are 6 screws under the rubber, but no one with a slotted hole. If i loose them a bit the focusing ring has less resistance to move.
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12-28-2015, 09:26 AM   #4
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One of those lil screws is for the infinity adjustment stop. I haven't played with this exact setup, but it looks similar to other lenses I've had to adjust. Typically the focus ring is adjustable so that the distance markings can be lined up to grab an interior ring that actually does the focusing. That interior ring can be moved independently with a small screwdriver. But before you go loosening make sure that your PKA mount is seated properly as designed. Sometimes the adaptalls get tweaked by previous owners/abusers. You could also try swapping with another mount if possible or even using an M42 mount (plus K ring) to see if that makes a difference.

12-28-2015, 09:55 AM   #5
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Thank you, too. The six screws are uniformly distributed around the ring. In addition there are three little holes, also equally arranged. So i can't spot a single screw for a stop. Should i loosen all of them a bit? Or unscrew? ... as you see i've no idea what i'm doing - but let's try

Unfortunately i don't have another mount.
12-30-2015, 04:14 AM   #6
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Thank you a lot marcusBMG and digital029art! That was indeed quite easy to do Just had to loosen all the screws a bit till the focusing ring rotates without moving the lens elements. Then screw the focusing ring on again so that the scale is a bit before infinity. When the ring and lens elements are connected again they can be moved to infinity.

Didn't even now there are screws under the rubber and that this can be done without disassembling the lens

Thanks!
12-30-2015, 07:39 AM   #7
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Well done, and you're welcome.
12-30-2015, 11:52 AM   #8
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QuoteOriginally posted by chochichaeschtli Quote
Thank you a lot marcusBMG and digital029art! That was indeed quite easy to do Just had to loosen all the screws a bit till the focusing ring rotates without moving the lens elements. Then screw the focusing ring on again so that the scale is a bit before infinity. When the ring and lens elements are connected again they can be moved to infinity.

Didn't even now there are screws under the rubber and that this can be done without disassembling the lens

Thanks!
There's no reason to take anything apart just for infinity adjustment. Most old school lenses adjust in a similary easy way. Glad it worked out for you!

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17mm, 17mm f/3.5 adaptall, adaptall, adapter, focus, infinity, infinity focus, k-mount, lens, mount, pentax lens, slr lens, sp, sp 17mm infinity, tamron, tamron sp 17mm
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