Bigma internal focus adjustment.

BSell · Jul 7, 2005

steveinvictoria said:
Brian, Thanks for your comments re loosening the rear element.
I'm eventually going to try it with mine, but have been thinking
through this worrisome issue of the ensuing loose element. Someone
suggested removing the element and applying a lock-tight compound
to the threads before reassembly. I don’t like this idea – what if
you (or a Sigma service technician) wants to disassemble it in the
future?

Please see my post above about the different kinds of Locktite available. If you get the right kind, dissassembly is no sweat.

steveinvictoria said:
Sometimes in machinery or electronics, you’ll see a tiny small dab
of what looks like paint or nail polish, applied so it overlaps the
thread and nut, thus holding it in place, and letting you know if
the nut has moved. Maybe that could be used between the element
and threads. Or how about a very small dab of clear silicone.
Either of these could be easily removed if the element eventually
required re-adjustment or removal. Either of these would eliminate
the need to remove the element.

As long as the 'dab' cannot fall into the lens it shouldn't be a big deal. I would rather see something on the threads as once it's put together, there is no place for anything to fall off.

steveinvictoria said:
Also, regarding your comments about a + - tolerance for the factory
setting of the element, Murphy’s Law will insist that an equal
number of these lens will require tightening (clockwise rotation)
to achieve optimal sharpness. If loosening the element does not
improve sharpness, do you think there are shim(s) behind it that
could be removed, permitting clockwise adjustment of the element?

I'm with you on the Murphy's Law thing. I know what my luck is, I would be removing a shim and one shim would be too much! Of shopping for a shim half as thick I would be.

Yes, taking a shim out seems the way to go to move the element forward in the stack. Having not taken my rear element out, I don't know if there is a hazard of putting the rear element too far forward and having something else in the lens strike the rear element because its too far forward. I doubt the tolerances are that tight but it's something to watch for.

steveinvictoria said:
Thanks
Steve

BSell · Jul 7, 2005

gjk said:
This problem might not affect you. Mine is no where near "loose"
and I'm confident it won't move by itself.
--
gjk

You just unscrewed yours a 1/4 turn or something right? I would hazard the guess that any locktite on your threads is doing its job still.

Brian

Fer · Jul 11, 2005

Knackerman said:
My question then is; Is the sharpness caused by the actual turning
of the element, or is it due to the distance to the other elements
of the lens?

I think it's the latter...

Knackerman said:
How can we get the element secured and tightened at the right
position so it dosen't wander away? (I've made a discrete mark on
the black ring, so that I can see if it turns by mistake after
usage.

I would use an appropriate locker. There are purposedly-formulated (and typically colored) "glues" that are meant to secure screws without permanently lock the assembly. Those products come from many manifacturers and are widely used in mechanics.
I haven't done it yet, BTW.

Enjoy your sharper Bigma!

Fernando
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Roy NN7DX · Jul 20, 2005

I thought about what you folks have done to the rear lens slug tuning with BigMa and other Sigma lenses... I'd bought a Sigma 1.4x EX APO teleconverter a year ago and it never seemed to work right...

Hey... Tune Up time... The element "slug" was only hand tight and easy to tune... Big difference! perhaps only 1/4 turn or so movement required... I'll still do an even more critical tuning using my 180mm BugMa macro or my new EF500mm/f4IS lens... When it's as good as can be I'll add a touch of nail polish to hold the slug in position.

Sure, it would have been nice if these lenses and converters were sold in perfect alignment but they are not. Me? I'm very happy doing this final critical tweak myself, on my camera and using my lenses.
--
3 Canon DSLR's... Now the pixels are really hitting the fan...
Regards,
from the Oregon Coast,
Roy NN7DX

noclue · Oct 21, 2005

I am wanting to find out if anyone has had any longterm problems doing this. Or, if anyone has additional info on this topic. I'm baffled why this hasn't gotten more attention with as many pixel-peekers at this forum.

Thanks

Another birder · Oct 21, 2005

noclue said:
I am wanting to find out if anyone has had any longterm problems
doing this. Or, if anyone has additional info on this topic. I'm
baffled why this hasn't gotten more attention with as many
pixel-peekers at this forum.

I just tried on my 105 macro - On mine, the collar will not budge at all, so I guess I might just leave it.
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Another birder · Oct 21, 2005

I was doing this mostly as a test for when I get my bigma, but if you are having a problem with the black colour, then removing the metal mount does allow you to get much better access.

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noclue · Oct 22, 2005

no text

gjk · Oct 22, 2005

I was able to loosen element easily, but after many attempts(with tripod or clamped, using remote) was unable to increase resolve. Lense is currently in for calibration-fingers are crossed. If yours is under warranty, I would recommend sending it in first-let them try. Just my two cents.
--
gjk

Another birder · Oct 22, 2005

gjk said:
I was able to loosen element easily, but after many attempts(with
tripod or clamped, using remote) was unable to increase resolve.
Lense is currently in for calibration-fingers are crossed. If yours
is under warranty, I would recommend sending it in first-let them
try. Just my two cents.

Its probably lens dependant - The bigma is a lens with a LOT of elements, and I guess there is more chance that it will need a tweak. In the case of my 105 macro, its not likely to be that far off. To be honest, Im not sure if I was able to improve the image all that much.

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foggy · Oct 22, 2005

I can't imagine reading a thread like this on Canon L lenses I'm glad you people are getting a fix. But it's a sad reflection on Sigma that people have to do this to a $900.00 lens and it can't or won't be fixed by Sigmas repair facility. I have the 135-400 APO coming and if it is soft or has a like problem I will be sending it back so fast.

Foggy

Steve Fox · Oct 23, 2005

I was able to adjust mine also.

At first, I couldn't turn the element, so I got a thin leather belt and used it as a wrench. Once I got it loose, it turned easily by hand.

I turned it about 1/8" ccw and it got a little better. I turned it another 1/8" and it got better still, so I left it there.

The only problem I had was I dropped one of the screws on the carpet and it took me longer to find it than to make the adjustments and photos.

I thought it was sharp before, but it's a lot better now.

I wonder if they all are off by being too far in. There can't be much cw adjustment potential, even if there is a shim that could be removed. I guess we're lucky in that respect. Since the element is so far from the camera sensor at the 500mm setting, I'm amazed such a small adjustment makes a difference.

I also wonder if the factory position is a compromise between the 500mm and 50mm focal lengths. Since I mostly use it for longer focal lengths, I prefer the sharpness at the longer length. I would also guess that softness wouldn't be as obvious at shorter lengths. I'll try some tests at shorter lengths later.

Geoffrey Kitt · Oct 23, 2005

Has anyone tried this on a Bigma and found that they couldn't improve on the factory setting?

Daniella68313 · Oct 23, 2005

Tim O'Connor said:
I was doing this mostly as a test for when I get my bigma, but if
you are having a problem with the black colour, then removing the
metal mount does allow you to get much better access.

I don't understand...what'S the relation between black colour and getting better access?

Another birder said:
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Daniella68313 · Oct 23, 2005

Foggy said:
I can't imagine reading a thread like this on Canon L lenses I'm
glad you people are getting a fix. But it's a sad reflection on
Sigma that people have to do this to a $900.00 lens and it can't or
won't be fixed by Sigmas repair facility. I have the 135-400 APO
coming and if it is soft or has a like problem I will be sending it
back so fast.

you will be sending it back so fast..this is not the sharpest Sigma lens. it is nice at F8 though..but wide open it is soft and I don't think anything Sigma can do to fix that. adjusting the rear element probably only fix back or front focusing problem, not the native lens softness.

just my guess.

foggy said:
Foggy

--

Please do not start new thread for private message to me but send them to me via email instead! thanks.

foggy · Oct 23, 2005

You might be right, if so they will get it back. Paying $400+ for something that is as sharp as a coke bottle isn't going to cut it. I wonder if the Tokina 80-4004.5-5.6 ATX is any better? I won't send it back till I test it. I believe in giving any piece of equipment a chance. But it is going to have to fly pretty fast out of the box.

Foggy

gjk · Oct 23, 2005

I was unable to improve factory setting. It is currently in for testing(a brief conversation with technician revealed that nothing was out of spec on the tele-end, but they would have another look), but I don't want to get my hopes up.
--
gjk

DIGIC · Oct 23, 2005

I think this tune is great for improving sharpness at the long end (all samples shown here can confirm that), but i wonder how this change will affect sharpness at shorter FLs.

The Bigma is great for it's reach, but also for it's flexibility, so i am really interested to know how sharpness at short and medium FLs is affected.

Thanks so much.

--
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Deorum · Oct 24, 2005

Didnt work for me... No improvement, no deterioration either.
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Fly like an eagle!

Deorum · Oct 24, 2005

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Fly like an eagle!

Bigma internal focus adjustment.

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