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07-06-2013, 04:15 PM - 1 Like   #1
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Tamron 90mm f2.5 52BB - a few questions and lots of photos

As some of you may remember I bought the Tamron 90mm f2.5 52BB listed here:
https://www.pentaxforums.com/forums/sold-items/224630-sale-sold-tamron-90mm-f...pic-added.html

It arrived some time ago but it took much longer for the Adaptall > EOS (I shoot Canon 60D) big_is adapter, so the lens was just sitting on the shelf, waiting for its turn. Yesterday I finally got to test it. It fitted nicely with the adapter, focus ring works pretty smooth, maybe there is a bit more CA wide open than I expected but pictures look sharp and tasty. Anyways, after I've done some testing, I'm stuck with several concerns.

Given that I'm an absolute beginner in MF lenses, and not so experienced photographer either, I decided to ask for some expert opinion to solve this puzzle.


1. Irregular aperture shape:



What could have caused it? Bad servicing, manufacturer's error? Don't know if it really affects the image in any way but it's there: a bit out of center and out of the shape it should probably have.




2. There are 13 stops on the aperture ring. Moving the ring only affects the iris between f/2.5 and f/13. Apertures: f/13, f/16, f/22, f/32 look pretty much the same to me:

f/2.5


f/3.3


f/4.0


f/4.8


f/5.6


f/6.7


f/8.0


f/9.5


f/11


f/13 (from now on, you can see the the aperture ring moving but no effect on the iris)


f/16


f/22


f/32





3. There is a slight play on the focusing ring. It would be nothing to write home about if moving the focus ring wouldn't affect the aperture iris. As I said, I'm an absolute beginner in MF lenses but I guess it shouldn't work that way. Even if I didn't care that, let's say: f/4.0 is really f/4.0, such behavior affects light repeatability in a series of photos.

Here is a short video to demonstrate what I'm talking about:





4. Don't know what am I doing wrong but I can't get the lens to work with the 1:1 extension tube. I'm installing it the same way I do the adapter: aligning the aperture tabs and screwing the tube in, until the silver button clicks. When I'm using the lens solo it seems to focus correctly, however with the extension tube I get about 10cm of the effective focusing range:

MFD at 4.0



∞ at 4.0 (the blurred gray area to the bottom of this photo is the black stripe from the photo above)




I'll appreciate every comment on why the things are the way they are Am I doing something wrong, am I overreacting or does this lens have some issues? If so, what illness are the symptoms pointing to and can it be cured?

Here are some more shots:

f/2.5



f/5.6



f/11 (the famous blue spot starting to show up)



f/16



f/32




f/2.5



f/5.6


07-06-2013, 07:02 PM   #2
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With the Adaptall extension tube the lens is close focus only, that's just how extension tubes work - you give up focus at longer distances in order to focus closer. Shorter tubes will let you focus further towards infinity, but they don't let you focus as close. The matched Adaptall tube for 1:1 gives something like 25mm of extension (I have one around here somewhere that I forgot to sell with my 52BB). I believe that the Adaptall 2x teleconverter does give you 1:1 macro with the ability to focus all the way to infinity, but at 180mm and with an equivalent aperture of f/5.6.

Having aperture blades stop down unevenly at smaller apertures isn't unusual, even with some newer lenses. Sometimes the blades bind a bit, sometimes one of the springs that closes an aperture blade is a bit weak. There are probably other causes too.
07-06-2013, 08:40 PM   #3
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QuoteOriginally posted by Steinback Quote
With the Adaptall extension tube the lens is close focus only, that's just how extension tubes work - you give up focus at longer distances in order to focus closer.
Thank you Steinback for your input. I've kind of suspected that's the case since the extension doesn't have any optical elements. I believe this one is matched for the lens since it's Tamron made and it says "for SP 90/2.5 1:2 1:1" on it. The focusing range is pretty narrow but images are really sharp so apparently it does its job.

I've also purchased th 2x TC, still waiting for it to arrive.

QuoteOriginally posted by Steinback Quote
Having aperture blades stop down unevenly at smaller apertures isn't unusual, even with some newer lenses. Sometimes the blades bind a bit, sometimes one of the springs that closes an aperture blade is a bit weak. There are probably other causes too.
I'm not really that concerned about the iris shape. More so about the iris reacting when the focus ring is moved (you can perceive a slight dimming in the viewfinder while you're focusing) and the iris not reacting to the aperture ring between f/13 and f/32.

I provided all the detail I thought of as relevant. Maybe someone will be able to come up with a suggestion as to what needs to be fixed. Who knows, since I already started the whole adventure with MF lenses (last month I bought 6 as my starter kit ), maybe this one will be the first one I'll tinker with.
07-06-2013, 09:13 PM   #4
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One possible cause of the blades not closing fully is the adapter. I don't have one of the Adaptall lenses right now and no experience with the EOS adapter, so I'm just guessing. Maybe try removing the adapter and then using the aperture ring to stop down the blades? Or, the focus ring issue could be related and something isn't tight inside. I had a 52BB and it fidn't change the aperture diameter when focused.

Macro lenses are unusual construction because of the long focus. Taking one apart might be a bit more involved than an ordinary lens.

07-07-2013, 09:36 AM   #5
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I pm you about the issue

Thanks

Randy

Last edited by slip; 07-08-2013 at 09:30 AM.
07-07-2013, 08:47 PM - 1 Like   #6
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QuoteOriginally posted by Just1MoreDave Quote
One possible cause of the blades not closing fully is the adapter.
That's it, mystery solved! It's the adapter, not the lens. Thanks for pointing that out.

In case this could help someone else, here are the details:

The original P/K => Adaptall adapter that came with the lens is equipped with a spring loaded aperture lever:





Moving the lever causes this tab (located on the lens side of the adapter) to go up and down:





The tab from the photo above pushes another spring loaded lever located inside the lens. This causes the aperture to open/close:




It's a precise mechanism so every mm counts. The big_is Adaptall => EOS adapter has no spring loaded anything:




It's just a piece of metal that exerts a constant pressure on the lever inside the lens. This alone should keep the aperture closed at the set value. Don't know if that's a design flaw or they couldn't make the flange any higher without running into some kind of trouble. All I know by now is that the pressure coming from the adapter dimensions alone is not enough to make the aperture fully close, hence the aperture effective range of f/2.5-f/13.

In a spare time I'll do some experiments stacking masking tape on the adapter and checking if that changes anything. The lever inside the lens goes up and down a bit as you turn the aperture ring. The first permanent solution that occurred to me was a tiny leaf spring in the right place on the adapter... but it may as well be that the masking tape will become my permanent solution



QuoteOriginally posted by Just1MoreDave Quote
Or, the focus ring issue could be related and something isn't tight inside. I had a 52BB and it fidn't change the aperture diameter when focused.

OK, so the extension tube issue was my lack of knowledge and the aperture not fully closing is caused by the adapter. I'm glad I started this thread The only issue left is the focus ring causing the aperture diameter to change.


I did another video showing what effect this issue has on light (filmed the live view screen on my camera since it's more readable than filming VF) :



It doesn't make the lens unusable but it's a bit annoying. Two more things I've noticed:

- when you turn the lens upside down, sometimes one of the blades seems to fall off a bit. Not by much but it's different from all the others. After moving the aperture ring it gets back in line.
- when you manipulate the lens a delicate sound can be heard, like if some tiny piece was rolling inside. Difficult to guess from the sound alone but it could very well be a tiny screw or spring

Does it help with the diagnosis or nothing will be certain until opening the lens?



QuoteOriginally posted by Just1MoreDave Quote
Macro lenses are unusual construction because of the long focus. Taking one apart might be a bit more involved than an ordinary lens.
After I've done some reading I imagine it can be indeed. Well, as I wrote before, for now I'd like to know what the illness is. This doesn't necessarily mean I'll start playing the doctor right away In the meantime I'll just try not to pay too much attention to the focus ring/aperture issue, practice my MF skills and enjoy this great lens.



The first attempt on my cat's whiskers

Last edited by kido; 07-07-2013 at 09:47 PM.
07-08-2013, 09:28 AM   #7
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good to hear some of the issues are sorted out
It really is a very sharp lens

thanks

randy
07-08-2013, 10:04 AM   #8
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That is a sharp lens. Sounds like you got most of it sorted out.
Seems like the focus affecting the aperture may mean something has come apart or a screw is not tightened down where it should be internally.
If you are not into taking it apart perhaps you can just set your camera to take bracketed exposures when using this lens, one of them is bound to be close if not correct
At some point whatever is not right in the lens could eventually cause a blockage of the helicoids - at that point you can decide if you love it enough to get it professionally fixed.
https://www.pentaxforums.com/forums/pentax-film-slr-discussion/105296-pentax-...ndrickson.html he may be able to do a repair on this lens as well.

07-08-2013, 11:58 AM   #9
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Regarding the change in aperture when focusing, this can be a problem with the attachment of the aperture to the lens barrel. My Tammy does the same thing, as did my kiron 24/2 and 28/2 lenses. The fix for the kirons was easy, three screws that hold the aperture to the lens barrel, and easy to access when the rear mount is pulled. On the Tammy I never fixed it but I am sure if I tear it down enough I will get to the same type of solution
07-13-2013, 04:26 PM   #10
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QuoteOriginally posted by crewl1 Quote
That is a sharp lens.
Indeed. This thing is so much fun. Didn't expect that a MF macro lens will serve me well even for action shots Of course I'm usually front- or back-focusing a bit, but who cares, I love the final result.

Handheld, 1/250, f/2.5, flash bounced off ceiling:




QuoteOriginally posted by crewl1 Quote
Seems like the focus affecting the aperture may mean something has come apart or a screw is not tightened down where it should be internally.
QuoteOriginally posted by Lowell Goudge Quote
Regarding the change in aperture when focusing, this can be a problem with the attachment of the aperture to the lens barrel.

OK, so now at least I have purpose in life: tighten these damn screws. After a week of playing with this lens the dimming_while_focusing thing turned out to be really annoying. Especially while focusing for the shots like the one above. It's quite possible that I might play the doctor much sooner then expected. I've found this helpful site where someone shares his experiences from opening his Tamron 52BB:

Category: Adaptall 2 - wiratama.net

Maybe it'll help someone else so I'm sharing.


Anyway, the thing I haven't mention before is that shortly after buying this lens I purchased a second copy. Mostly because of the price ($100) and because of the bundled items. It came here few days ago and turned out to be issue-free. So, for now I'll just shoot with this one and when in the right mood I'll think about cracking open the one from Slip.

Two observations:

- the second copy also has irregular aperture iris shape. This thing doesn't seem to affect the image in any way, even the bokeh shape looks pretty regular to me

- the aperture not stepping down past the f/13 is definitely adapter's fault. Right now I have 2 genuine Tamron Adaptall mounts: for P/K and for Olympus (that came on the other lens). On both the aperture works fine.
I've contacted big_is (the seller/manufacturer on eBay) and they promised they'd send me a different copy to test and see if the issue persist. Because of a busy week I still haven't tried the trick with masking tape but one more idea came to my mind. If I succeed in any way, I'll share the solution here.


QuoteOriginally posted by crewl1 Quote
If you are not into taking it apart perhaps you can just set your camera to take bracketed exposures when using this lens, one of them is bound to be close if not correct
I thought of that too. Then I realized this would require the auto-aperture compatibility on both (camera and lens) sides and I'm pretty sure that this Tammy has no idea what are those electric contacts on the camera side
07-13-2013, 05:07 PM   #11
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QuoteOriginally posted by kido Quote
I thought of that too. Then I realized this would require the auto-aperture compatibility on both (camera and lens) sides and I'm pretty sure that this Tammy has no idea what are those electric contacts on the camera side
Oops, I forgot this is not a Pentax camera. My bad.
FYI with a Pentax K-5 you can use a manual lens in bracketed mode and the camera will vary either shutter speed or ISO to get the over/under/correct exposures (you decide which.)
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