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01-07-2010, 06:21 PM   #1
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Manual focus 'smoothness' question on a macro lens...

So I just bought a used Sigma 50mm Macro 1:1 manual focus lens (with 'A' aperture), and while cosmetically and optically good (apart from some minor bits of dust on the inner elements), the process of manually focussing the lens does not have consistent smoothness or resistance through the range, and since this is my first 1:1 manual focus macro lens, I was wondering if this is normal or not?

Right around 1:2.5 it resistance ramps up quite a bit, stays high until 1:1.3 where it gets a bit higher until 1:1.2 where it starts to drop and is then smooth through 1:1.1 until 1:1 (at which point the lens barrel is fully extended). The reverse trip (compacting the lens back down in size) has resistance variations in the same spots but somewhat less.

And if this isn't normal, is this something that could get worse over time? (i.e. how worried should I be about this?)

01-07-2010, 07:10 PM   #2
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my DA 35 Macro which I believe does 1:1 is perfectly smooth and constant the whole way.
01-07-2010, 09:00 PM   #3
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Your lens may be in need of a little attention in the form of a CLA. Drop by your friendly local camera repair and see what they think.

Steve
01-07-2010, 09:13 PM   #4
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QuoteOriginally posted by stevebrot Quote
Your lens may be in need of a little attention in the form of a CLA. Drop by your friendly local camera repair and see what they think.

Steve
Good idea. Anyone have a recommended camera repair place in the Somerville/Cambridge Massachusetts area?

01-07-2010, 09:32 PM   #5
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I think I have this same lens and it's smooth throughout the focus range. Macro lenses have complex focus mechanisms similar to zooms, because they extend so far. It's possible that one part is binding.

I have actually had focusing problems improve over time, but more frequently they get worse. One sign on a used lens is a loose or missing rubber grip, damaged from someone trying to focus really hard.
01-08-2010, 12:20 AM   #6
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QuoteOriginally posted by nater Quote
So I just bought a used Sigma 50mm Macro 1:1 manual focus lens (with 'A' aperture), and while cosmetically and optically good (apart from some minor bits of dust on the inner elements), the process of manually focussing the lens does not have consistent smoothness or resistance through the range, and since this is my first 1:1 manual focus macro lens, I was wondering if this is normal or not?
1. Your DoF (for a macro lens typically at F8 or smaller aperture) is little.
2. If you want to do a critter or moving subject, you do not focus, use the other common type that is used by manual shooter. Set your camera to burst firing and you fire non-stop meanwhile moving towards or away from your subject. This was how I shot this picture . Tamron 90mm at F8 under natural light





Daniel
01-08-2010, 12:26 AM   #7
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It's possible it has been unused for sometime. You may find that if you 'exercise' the focus ring the damping may become more consistent.
01-08-2010, 07:24 AM   #8
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I am not familiar with this lens, but is it internal focusing? I suspect so.

I have found with some zoom lenses, as zooming occurs, the direction of movement of the elements changes abd the resistance of the focusing changes specifically at the point where the elements change direction. This same issue may take place with internal focusing mechanisms, which effectively modify the focal length as they focus.

01-08-2010, 10:53 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
I am not familiar with this lens, but is it internal focusing? I suspect so.

I have found with some zoom lenses, as zooming occurs, the direction of movement of the elements changes abd the resistance of the focusing changes specifically at the point where the elements change direction. This same issue may take place with internal focusing mechanisms, which effectively modify the focal length as they focus.
Here is the lens in question:

PentaxForums.com Third-Party Pentax Lens Review Database - 50mm f2.8 Macro

(Interesting side note: I contributed that picture/entry when I came across that Sigma 50mm macro on the internet several months ago and didn't see any entry in the database here. I wasn't able to find any additional info at the time, but after thinking about what I was looking for for my first 1:1 macro lens, I recently thought it would be a good choice, despite the lack of info.)

That picture shows the lens in the 1:1 focus position and fully extended. As you twist the manual focus barrel, the entire lens extends/collapses, so at infinity focus it is about 1/2 of it's close focus length (i.e. the parts of the lens barrel before and after the grip are mostly inside the grip cylinder).

I don't have any other prime lenses that focus this way, and it seems somewhat unusual to me, even for a macro (which as I understand it usually just have an inner barrel that extends as you focus, rather than have the focus barrel move while the lens extends in front of and behind the focus barrel).
01-08-2010, 11:22 AM   #10
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QuoteOriginally posted by nater Quote
...I don't have any other prime lenses that focus this way, and it seems somewhat unusual to me, even for a macro (which as I understand it usually just have an inner barrel that extends as you focus, rather than have the focus barrel move while the lens extends in front of and behind the focus barrel).
This focus movement seems more common on 1:1 macros. I have 5, and only the Pentax-M 50mm f4 Macro works like a normal prime. Although it extends quite a bit, it only extends in front of the focus ring. My other macros are this Sigma model, a Vivitar 55mm f2.8 made by Komine, a Panagor 90mm f2.8 made by Kiron and a Kiron 105mm f2.8. The Kirons and Vivitar use the extension behind the focus ring for the magnification scale.

You might expect some sort of informed user opinion on how the Sigma compares to these other lenses, but I am only good at purchasing macros, not actually using them.
01-08-2010, 05:40 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
I am not familiar with this lens, but is it internal focusing? I suspect so.

I have found with some zoom lenses, as zooming occurs, the direction of movement of the elements changes abd the resistance of the focusing changes specifically at the point where the elements change direction. This same issue may take place with internal focusing mechanisms, which effectively modify the focal length as they focus.
Sorry but please don't make half guesses if you don't know. I have the manual focus Sigma 50mm f/2.8 Macro and it is not an internal focus design. It is a 1:1 macro and the lens barrel extends uniformly and smoothly from min focusing distance to infinity. The manual focusing ring is smooth and well damped. Imo it's also better than the A 50mm f/2.8 Macro (1:2) which I had and on par with the FA 50mm f/2.8 Macro (1:1). It is an excellent lens in terms of sharpness and rendition.

Sigma 50mm f/2.8 macro (left), Sigma 90mm f/2.8 macro (right)




A recent shot taken last week

K-7 Sigma 50mm f/2.8 Macro
01-08-2010, 06:02 PM   #12
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QuoteOriginally posted by creampuff Quote
I have the manual focus Sigma 50mm f/2.8 Macro and it is not an internal focus design. It is a 1:1 macro and the lens barrel extends uniformly and smoothly from min focusing distance to infinity. The manual focusing ring is smooth and well damped. Imo it's also better than the A 50mm f/2.8 Macro (1:2) which I had and on par with the FA 50mm f/2.8 Macro (1:1). It is an excellent lens in terms of sharpness and rendition.
Thanks very much for the info, that's good to know. And nice photos, btw!
01-08-2010, 06:53 PM   #13
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QuoteOriginally posted by creampuff Quote
Sorry but please don't make half guesses if you don't know.
That's why I qualified it very clearly.

I have seen change in resistance as the direction of internal elemenst change, and that is what the description sounded like, but I made sure that I a) explained what I was referring to and b) said I was not familiar with the particular lens.

It is important in any post, to state what you think, and differentiate from what you know. I believe I did that clearly
01-09-2010, 02:26 PM   #14
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QuoteOriginally posted by nater Quote
So I just bought a used Sigma 50mm Macro 1:1 manual focus lens (with 'A' aperture), and while cosmetically and optically good (apart from some minor bits of dust on the inner elements), the process of manually focussing the lens does not have consistent smoothness or resistance through the range, and since this is my first 1:1 manual focus macro lens, I was wondering if this is normal or not?

Right around 1:2.5 it resistance ramps up quite a bit, stays high until 1:1.3 where it gets a bit higher until 1:1.2 where it starts to drop and is then smooth through 1:1.1 until 1:1 (at which point the lens barrel is fully extended). The reverse trip (compacting the lens back down in size) has resistance variations in the same spots but somewhat less.

And if this isn't normal, is this something that could get worse over time? (i.e. how worried should I be about this?)
Today arrived ths very same sigma macro lens to diagnose/repair for someone.
It suffers from exactly the same problem.
It was easy to repair (if you are a bit technical and have the right equipment)
I will post pictures later, your lens will very likely have the same fault.

George

The pictures :

The lens showed a heliocoid shaped stripe over half its barrel.




The cause seemed to be some material between the focus ring and the lensbarrel.




To remove the focus ring, remove the focus rubber, make a mark (permanent pen or so) how the focus ring is mounted to the focus mechanism.
Then remove the black tape.
You best set the lens at infinity, when the tape is removed, the focus mechanism can go a little beyond 1:1, and an aperture lever will come loose.




To remove the focus ring, you have to remove also the bayonet (3 phillips screws), the aperture ring, and another ring.
Nothing special, but beware of the small metal ball and spring of the aperture click mechanism.

When removed from the lens, I found this :



The felt, originally glued at A, was now compressed at B.

After stretching and glueing :




Something else I noticed are newton rings (actually stripes caused by interference) :



Two lenses must be really close for this.

George

Last edited by glasbak; 01-09-2010 at 04:27 PM. Reason: added pictures
01-13-2010, 02:16 PM   #15
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I just acquired one of these from fleabay and have a question about the automatic aperture. When set to A the camera does not recognize f2.8. The lowest it will go is f4. Is this normal for this lens or should I send it back?
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