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help to adjust focus of a RMC TOKINA 35-105MM 1:3.5-4.3
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PostPosted: Tue May 10, 2022 12:19 pm    Post subject: help to adjust focus of a RMC TOKINA 35-105MM 1:3.5-4.3 Reply with quote
Hello, I bought this RMC TOKINA 35-105MM 1:3.5-4.3 lens (Olympus mount), it had a little fungus on a glass of the rear group, before disassembling a lens I check its image quality and if the focus is correct. In this case the focus was off, it was different focus to infinity on 35mm and 105mm, on 35mm the focus was more than an inch before the infinity mark, and on 105mm it was pretty close to the infinity mark.

Checking the internet I found a manual: https://allphotolenses.com/public/files/pdfs/73ad8c581b0e006ecb9214f3cec4fe87.pdf

In which you can read regarding the focus: "Once you have your subject in focus at a given focal length, refocusing as you zoom is unnecessary", therefore this lens seems not to be a varifocal.

Normally when I adjust focus on zooms, the longer focal length is set with the front group and the shorter focal length is set with the rear group. But I have not observed in this lens any way to adjust the rear group, I need it to go deeper into the lens (away from the sensor), in the front group there are 3 small screws that allow the front group to be moved away or closer but with this I cannot cause focus at all focal lengths to be reached at the infinity mark.

In some telephoto zooms in the intermediate area they have slots with screws or threaded rings that allow the groups to be moved away or closer. In this lens I have not seen that type of mechanism either.

Please has anyone done the focus adjustment on this lens model that can help me?


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PostPosted: Tue May 10, 2022 12:42 pm    Post subject: Reply with quote
Did you make sure the close focus mode (silver button) is completely disengaged?


PostPosted: Tue May 10, 2022 1:04 pm    Post subject: Reply with quote
D1N0 wrote:
Did you make sure the close focus mode (silver button) is completely disengaged?


Yes, in close focus mode it engages and disengages correctly, currently disengaged.


PostPosted: Tue May 10, 2022 2:21 pm    Post subject: Reply with quote
If you have adapted this lens, there may be a slight back focus distance problem due to the adapter. In that case a more precise adapter might help. This can also be caused by a, slight shift in element spacing or wear/misadjustment of the internal cams. Even if you could find someone to adjust this, it would cost many times what the lens is worth.


PostPosted: Tue May 10, 2022 2:26 pm    Post subject: Reply with quote
It might be a relatively simple operation if it is like this Tokina
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/309272-tokina-rmc-80-200mm-f4-pk-mount-infinity-focus-adjustment-long-end.html


PostPosted: Tue May 10, 2022 2:51 pm    Post subject: Reply with quote
kymarto wrote:
If you have adapted this lens, there may be a slight back focus distance problem due to the adapter. In that case a more precise adapter might help. This can also be caused by a, slight shift in element spacing or wear/misadjustment of the internal cams. Even if you could find someone to adjust this, it would cost many times what the lens is worth.


Thanks kymarto, but I have also verified with an analog Olympus OM10 camera and the focus looks the same or very similar to the adapter that I use with the micro four thirds, it also shows that in 35mm it reaches infinity near the 10 foot / 3 meter mark

I know from experience that some cheap adapters may not have the exact measurements for the register distance or that some lenses begin to have a certain feeling of being "a little loose" due to wear of parts and that gives some problem to focus, but in this case such a big difference does not seem to be due to wear of mechanical parts but rather that it had previously been adjusted in the wrong way or poorly assembled.


PostPosted: Tue May 10, 2022 2:57 pm    Post subject: Reply with quote
D1N0 wrote:
It might be a relatively simple operation if it is like this Tokina
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/309272-tokina-rmc-80-200mm-f4-pk-mount-infinity-focus-adjustment-long-end.html


Thanks D1N0, but that infinity focus adjustment was required for the long end of the lens (200mm), in my case I require infinity adjustment for the short end (35mm), normally they are very different.


PostPosted: Tue May 10, 2022 3:14 pm    Post subject: Reply with quote
In my experience, Tokina often uses a set of slim spacer rings on the back group to adjust back focus. You can check by unscrewing the lens group in the back with a special tool. BTW, my sample of the Tokina 35-105 mm f/3,5-4,3 doesn't use any spacer rings, (i've just checked) and the back focus/infinity stop is perfect all the long between the shortest and the longest focal length. You might check if the front and back lens groups are firmly screwed in or somewhat a little bit loose.


PostPosted: Tue May 10, 2022 3:49 pm    Post subject: Reply with quote
Alsatian2017 wrote:
In my experience, Tokina often uses a set of slim spacer rings on the back group to adjust back focus. You can check by unscrewing the lens group in the back with a special tool. BTW, my sample of the Tokina 35-105 mm f/3,5-4,3 doesn't use any spacer rings, (i've just checked) and the back focus/infinity stop is perfect all the long between the shortest and the longest focal length. You might check if the front and back lens groups are firmly screwed in or somewhat a little bit loose.


Thanks Alsatian2017, but it does not have spacer rings on the rear group, and if it had I would have to remove them because I need to move the rear group away from the sensor, I already did the test unscrewing the rear group (as if it had a spacer ring) and it could not focus to infinity at 35mm


PostPosted: Tue May 10, 2022 3:58 pm    Post subject: Reply with quote
The name ring also looks like it's partially unscrewed sitting at the top of the lens barrel. Probably somebody has been at it already.


PostPosted: Tue May 10, 2022 5:03 pm    Post subject: Reply with quote
Mauro wrote:
kymarto wrote:
If you have adapted this lens, there may be a slight back focus distance problem due to the adapter. In that case a more precise adapter might help. This can also be caused by a, slight shift in element spacing or wear/misadjustment of the internal cams. Even if you could find someone to adjust this, it would cost many times what the lens is worth.


Thanks kymarto, but I have also verified with an analog Olympus OM10 camera and the focus looks the same or very similar to the adapter that I use with the micro four thirds, it also shows that in 35mm it reaches infinity near the 10 foot / 3 meter mark

I know from experience that some cheap adapters may not have the exact measurements for the register distance or that some lenses begin to have a certain feeling of being "a little loose" due to wear of parts and that gives some problem to focus, but in this case such a big difference does not seem to be due to wear of mechanical parts but rather that it had previously been adjusted in the wrong way or poorly assembled.


I had a long Tokina ATX (150-500mm) that had the same non-pan focus problem, that was sent back to Tokina in the day. I believe that it had to do with the cams that change the element spacing when zooming. The cams have plastic bushing which can wear, or a drop can mess with the mechanical setup.


PostPosted: Tue May 10, 2022 7:05 pm    Post subject: Reply with quote
D1N0 wrote:
The name ring also looks like it's partially unscrewed sitting at the top of the lens barrel. Probably somebody has been at it already.


I did that myself, when I checked all the possible focus adjustment mechanisms... I didn't screw it all the way back in, so I could easily remove it to complete any necessary adjustments to the front group.


PostPosted: Tue May 10, 2022 7:21 pm    Post subject: Reply with quote
kymarto wrote:
Mauro wrote:
kymarto wrote:
If you have adapted this lens, there may be a slight back focus distance problem due to the adapter. In that case a more precise adapter might help. This can also be caused by a, slight shift in element spacing or wear/misadjustment of the internal cams. Even if you could find someone to adjust this, it would cost many times what the lens is worth.


Thanks kymarto, but I have also verified with an analog Olympus OM10 camera and the focus looks the same or very similar to the adapter that I use with the micro four thirds, it also shows that in 35mm it reaches infinity near the 10 foot / 3 meter mark

I know from experience that some cheap adapters may not have the exact measurements for the register distance or that some lenses begin to have a certain feeling of being "a little loose" due to wear of parts and that gives some problem to focus, but in this case such a big difference does not seem to be due to wear of mechanical parts but rather that it had previously been adjusted in the wrong way or poorly assembled.


I had a long Tokina ATX (150-500mm) that had the same non-pan focus problem, that was sent back to Tokina in the day. I believe that it had to do with the cams that change the element spacing when zooming. The cams have plastic bushing which can wear, or a drop can mess with the mechanical setup.


when the problem occurs with the plastic bushings, in analog lenses it is observed that the zoom/focus ring feels a little loose with some play in both directions, in this lens it feels quite firm.
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