Tamron SP 500mm (55BB) on Pentax k-50 focus problem

Steppy · 11-22-2021, 03:44 AM

Hello, sorry but can’t find solution anywhere…

I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help!

**yucatanPentax** · 11-22-2021, 04:09 AM

Here are the install instructions for the adapter/mount in case you're concerned that the mount isn't properly in place. However, I'm not sure the mount would affect focusing.

TAMRON ADAPTALL-2 OWNER'S MANUAL Pdf Download | ManualsLib

stevebrot · 11-22-2021, 04:16 AM

Originally posted by Steppy

Hello, sorry but can’t find solution anywhere…

I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help!

Welcome to the Pentax Forums!

Yes, that sounds like the correct adapter and if the two tabs engage cleanly with the aperture scale correct, it is properly mated to the lens and should attain infinity focus as well as minimum focus distance at 1.7m. If infinity focus fails, there is a problem with the lens.

Steve

Steppy · 11-22-2021, 05:03 AM

Ok, that’s kinda bad news but thanks a lot for the quick help!!!

lotech · 11-22-2021, 07:33 AM

I used 2 of this lens and they all focused properly, it sounds like something gets in between the lens and the mount or camera body, adding distance to the focal plane/sensor and turned the lens into close focus only, please recheck the mount is properly fitted.

Just a side track fyi, I got a Russian MTO mirror with M42 (yes not T2), and I do not use the 'flush' type adapter coz it is slow to put on and remove, but that's the only adapter allows infinity focus on K body. I used the 'flanged' type adapter instead and that worked fine on the mirror, coz mirror lens is designed to 'overshoot' infinity, due to expansion of the metallic mirror in temperature the infinity focus point is not locked and slightly over, the added headroom just enough to compensate the added back focus distance due to the adapter flange and I got perfect infinity focus, and I suspect there is something wrong with your adapter, or it does not mount properly, more than the lens problem.

romay · 11-22-2021, 08:17 AM

Can you post a couple of pictures of the lens & the mount so we can make sure it's okay? It would also be interesting to see the back element - maybe the corrective group is missing.

There is a slight chance that the previous owner adapted the lens to fit a different camera with shorter registration distance and adjusted the infinity stop to compensate.

**kiwi_jono** · 11-22-2021, 07:05 PM

Thats a pity. I have one (focuses fine at infinity) and its a very good lens so worth investigating if its possible to adjust (maybe google infinity focus adjustment for it?).

lotech · 11-22-2021, 07:19 PM

Originally posted by kiwi_jono

Thats a pity. I have one (focuses fine at infinity) and its a very good lens so worth investigating if its possible to adjust (maybe google infinity focus adjustment for it?).

Yeah it's the best mirror lens so far I've used, even one with slight oxidation on the coating it still produced excellent image with good color and contrast, I am regretted to have parted with them, and MTO is the 2nd to the best also worth considering.

kypfer · 11-23-2021, 01:18 AM - **1 Like**

If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted?
It'd have to be a Tamron Adaptall tube, obviously, as supplied for the 90mm macro, but weird things happen

Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar?
I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed.

lotech · 11-23-2021, 01:38 AM

Originally posted by kypfer

If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted?
It'd have to be a Tamron Adaptall tube, obviously, as supplied for the 90mm macro, but weird things happen

Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar?
I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed.

A photo of the victim may tell the story !

aldo taddia · 11-23-2021, 01:42 AM

I had a similar problem after disassembling the lens to clean the lenses. But I had reassembled it in the wrong way. I then realized where I was wrong and corrected the error. Now it works great at all distances. That is a good objective.

lotech · 11-23-2021, 02:07 AM

Originally posted by Steppy

Hello, sorry but can’t find solution anywhere…

I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help!

Are there any sights of drop, any dent on the body ? the shock could dislocated the elements to cause focusing problem, you may also see distorted image, just a wild guess.

---------- Post added 11-23-21 at 05:24 PM ----------

Originally posted by Steppy

Hello, sorry but can’t find solution anywhere…

I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help!

This may be too much of asking, but you could do a test to see if the problem is on the mount or the lens itself. Pls put the back of the lens facing to the wall and the front pointing at a far object like building or hill, then use a tape measure to adjust the lens distance (last glass element) to the wall to 45.5mm that's the K mount back focus distance, then try to focus the lens, if the lens is in good shape you will see a clear projected image on the wall, this test completely bypass any adapter mount related problem.

https://en.m.wikipedia.org/wiki/Flange_focal_distance

Steppy · 11-23-2021, 05:30 AM

Wow, guys, you’re EXTREMELY helpful! Thanks for all the suggestions, I’ll do them one by one later today and post the pictures! 👍

stevebrot · 11-23-2021, 07:26 AM

Originally posted by kypfer

If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted?

No...according to the OP, he fit the lens to its PK adapter and the aperture scale lined up to f/8 as expected.

Steve

stevebrot · 11-23-2021, 07:27 AM

Originally posted by kypfer

Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar?
I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed.

The filters were dropped on the BB version.

Steve

11-22-2021, 03:44 AM	#1
Steppy New Member Join Date: Nov 2021 Posts: 3	Tamron SP 500mm (55BB) on Pentax k-50 focus problem Hello, sorry but can’t find solution anywhere… I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help!

11-23-2021, 02:07 AM	#12
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	Originally posted by Steppy Hello, sorry but can’t find solution anywhere… I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help! Are there any sights of drop, any dent on the body ? the shock could dislocated the elements to cause focusing problem, you may also see distorted image, just a wild guess. ---------- Post added 11-23-21 at 05:24 PM ---------- Originally posted by Steppy Hello, sorry but can’t find solution anywhere… I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help! This may be too much of asking, but you could do a test to see if the problem is on the mount or the lens itself. Pls put the back of the lens facing to the wall and the front pointing at a far object like building or hill, then use a tape measure to adjust the lens distance (last glass element) to the wall to 45.5mm that's the K mount back focus distance, then try to focus the lens, if the lens is in good shape you will see a clear projected image on the wall, this test completely bypass any adapter mount related problem. https://en.m.wikipedia.org/wiki/Flange_focal_distance Last edited by lotech; 11-23-2021 at 02:37 AM.

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11-22-2021, 04:09 AM	#2
yucatanPentax Loyal Site Supporter Join Date: Dec 2009 Location: Dallas / Yucatan Posts: 1,839	Here are the install instructions for the adapter/mount in case you're concerned that the mount isn't properly in place. However, I'm not sure the mount would affect focusing. TAMRON ADAPTALL-2 OWNER'S MANUAL Pdf Download \| ManualsLib

11-22-2021, 04:16 AM	#3
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Steppy Hello, sorry but can’t find solution anywhere… I bought on eBay Tamron 500mm mirror lens (55BB) for my Pentax k-50, it came with the original “tamron adaptall 2 for Pentax k” adapter, I’m fairly sure I have it mounted correctly (it clicks on, the two little bits on the side fall into the holes and the dial correctly shows it’s aperture 8) but I can’t focus beyond about 2,5 metre - when I hit the end of focus ring (it should be focused to infinity at that point). Is that the correct adapter at all or is something wrong with the lens? Thanks a lot for any help! Welcome to the Pentax Forums! Yes, that sounds like the correct adapter and if the two tabs engage cleanly with the aperture scale correct, it is properly mated to the lens and should attain infinity focus as well as minimum focus distance at 1.7m. If infinity focus fails, there is a problem with the lens. Steve

11-22-2021, 05:03 AM	#4
Steppy New Member Join Date: Nov 2021 Posts: 3 Original Poster	Ok, that’s kinda bad news but thanks a lot for the quick help!!!

11-22-2021, 07:33 AM	#5
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	I used 2 of this lens and they all focused properly, it sounds like something gets in between the lens and the mount or camera body, adding distance to the focal plane/sensor and turned the lens into close focus only, please recheck the mount is properly fitted. Just a side track fyi, I got a Russian MTO mirror with M42 (yes not T2), and I do not use the 'flush' type adapter coz it is slow to put on and remove, but that's the only adapter allows infinity focus on K body. I used the 'flanged' type adapter instead and that worked fine on the mirror, coz mirror lens is designed to 'overshoot' infinity, due to expansion of the metallic mirror in temperature the infinity focus point is not locked and slightly over, the added headroom just enough to compensate the added back focus distance due to the adapter flange and I got perfect infinity focus, and I suspect there is something wrong with your adapter, or it does not mount properly, more than the lens problem.

11-22-2021, 08:17 AM	#6
romay Senior Member Join Date: Nov 2014 Posts: 113	Can you post a couple of pictures of the lens & the mount so we can make sure it's okay? It would also be interesting to see the back element - maybe the corrective group is missing. There is a slight chance that the previous owner adapted the lens to fit a different camera with shorter registration distance and adjusted the infinity stop to compensate.

11-22-2021, 07:05 PM	#7
kiwi_jono Loyal Site Supporter Join Date: Dec 2009 Location: Christchurch, New Zealand Photos: Gallery \| Albums Posts: 2,437	Thats a pity. I have one (focuses fine at infinity) and its a very good lens so worth investigating if its possible to adjust (maybe google infinity focus adjustment for it?).

11-22-2021, 07:19 PM	#8
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	Originally posted by kiwi_jono Thats a pity. I have one (focuses fine at infinity) and its a very good lens so worth investigating if its possible to adjust (maybe google infinity focus adjustment for it?). Yeah it's the best mirror lens so far I've used, even one with slight oxidation on the coating it still produced excellent image with good color and contrast, I am regretted to have parted with them, and MTO is the 2nd to the best also worth considering.

11-23-2021, 01:18 AM - 1 Like	#9
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,592	If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted? It'd have to be a Tamron Adaptall tube, obviously, as supplied for the 90mm macro, but weird things happen Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar? I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed.

11-23-2021, 01:38 AM	#10
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	Originally posted by kypfer If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted? It'd have to be a Tamron Adaptall tube, obviously, as supplied for the 90mm macro, but weird things happen Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar? I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed. A photo of the victim may tell the story !

11-23-2021, 01:42 AM	#11
aldo taddia Senior Member Join Date: Apr 2020 Location: Ferrara Italia Posts: 139	I had a similar problem after disassembling the lens to clean the lenses. But I had reassembled it in the wrong way. I then realized where I was wrong and corrected the error. Now it works great at all distances. That is a good objective.

11-23-2021, 05:30 AM	#13
Steppy New Member Join Date: Nov 2021 Posts: 3 Original Poster	Wow, guys, you’re EXTREMELY helpful! Thanks for all the suggestions, I’ll do them one by one later today and post the pictures! 👍

11-23-2021, 07:26 AM	#14
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by kypfer If the OP is unfamiliar with what the lens looks like "normally", is there any chance there's an extension tube fitted? No...according to the OP, he fit the lens to its PK adapter and the aperture scale lined up to f/8 as expected. Steve

11-23-2021, 07:27 AM	#15
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by kypfer Alternatively, (grasping at another passing straw), has the internal interchangeable filter, at the rear of the lens, been replaced by a close-up lens or similar? I'm unfamiliar with the #55BB specifically, but on my #55B the rear "element" (the interchangeable filter) is marked 'TAMRON 30.5 NORMAL JAPAN' on it's periphery, only readable with the mount removed. The filters were dropped on the BB version. Steve