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07-23-2012, 01:27 AM   #1
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Issue with Sigma 180mm f/3.5 [IF] APO EX Macro

Hey guys, I have been experiencing a particularly annoying problem lately. I have been using my sigma 180mm f/3.5 APO [IF] EX with a Pz-AF Uniplus 25mm extension tube* and at focus settings approaching 1:1 I get a rather nasty hotspot:


Sigma 180mm f/3.5 [IF] APO EX - 1/180th ISO 100 f/16 1:1.5 with 25 mm extension - wireless AF540 with sto-fen diffuser - lens hood used, No filters.

It only seems to show up on occasion - it is easier to see when I am using flash, even using ring flash can cause the hot spot to rear its ugly head. The Hotspot doesn't appear when I use my Pentax FA*200mm f/4 ED Macro lens so I'm thinking it is an issue specific to this particular lens/extension tube combination. As more than a few of us are aware Sigma's lenses aren't exactly well known for being resistant to flare. I have used this extension tube with the FA77 and a loaned Carl Zeiss 100mm f/2 Macro for Pentax K mount without issue.

* The reason why I use this particular extension tube is because it transmits lens focal length correctly, as well as aperture information and it also allows for full P-TTL flash functionality.

07-23-2012, 02:27 AM   #2
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I own and I have used the exactly same combination without any apparent problem. But anyway, 25mm tube doesn't extend the lens magnification a lot. It yields something like 1,2:1 so why bother? Better to combine the lens with macro focusing TC.

Now to the problem: Maybe the matt paint in your extension tube is flaking, I can't think of any other explanation.
07-23-2012, 03:03 AM   #3
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QuoteOriginally posted by elho_cid Quote
I own and I have used the exactly same combination without any apparent problem. But anyway, 25mm tube doesn't extend the lens magnification a lot. It yields something like 1,2:1 so why bother? Better to combine the lens with macro focusing TC.

Now to the problem: Maybe the matt paint in your extension tube is flaking, I can't think of any other explanation.

No, it doesn't extend things that much. But it is better than simply cropping and it doesn't lose as much light or compromise the optical performance of the lens as much as a 2X TC does. I have some adhesive flocking that I will place in the tube - it is just time consuming to cut it to the right dimensions, I'll see if that makes any improvement, I have an older K series Helicoid extension tube that I should try with this lens - but it has no lens information contacts.
07-23-2012, 03:41 AM   #4
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Check your extension tube for some internal reflective parts. What you see here's either reflection off the parts of the tube or off the rear element

07-23-2012, 08:54 AM   #5
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Well after some exhaustive flare testing I know what the problem is - and it's a common one. Though I still went through the trouble of Installing temporary flocking in the Extension tube, but I had a hunch that it wouldn't change anything. Though I always like to see the glass as half full...



these were all taken with the Sigma 180mm f/3.5 APO EX Macro at the 1:1 setting with the 25mm Extension tube with a strong halogen light source 3 feet away at a 35 degree angle from the front element.

As you can see in the above picture the hot spot changes its size with aperture - which is indicative of internal reflections. If this hot spot was caused by the extension tube it would have been the same size regardless of the aperture used. This lens has always had this problem, only this time the extension tube increased the flange distance between the sensor and the optical centre of the lens and therefore made the internal reflection more obvious. My 180mm f/3.5 APO EX MACRO lens is not the DG version. The DG version would in all likelihood have the necessary optical coatings to reduce if not eliminate this kind of internal reflection.

Well now I have one more excuse to use my FA*200mm f/4 ED Macro - not that I really needed one.

Last edited by Digitalis; 07-23-2012 at 10:07 PM.
07-23-2012, 08:56 AM   #6
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QuoteOriginally posted by elho_cid Quote
I own and I have used the exactly same combination without any apparent problem. But anyway, 25mm tube doesn't extend the lens magnification a lot. It yields something like 1,2:1 so why bother? Better to combine the lens with macro focusing TC.

Now to the problem: Maybe the matt paint in your extension tube is flaking, I can't think of any other explanation.
It does allow for closer focusing with some lenses. I have used the Kenko af 25mm tube with my DA* 300 to get closer focusing and retain af.
07-23-2012, 09:02 AM   #7
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Yet another example of why I won't buy any Sigma product...

QuoteOriginally posted by Digitalis Quote
well after some exhaustive flare testing I know what the problem is - and it's a common one. Though I still went through the trouble of Installing temporary flocking in the Extension tube, but I had a hunch that it wouldn't change anything.

As you can see in the above picture the hot spot changes its size with aperture - which is indicative of internal reflections. If this hot spot was caused by the extension tube it would have been the same size regardless of the aperture used. This lens has always had this problem, only this time the extension tube increased the flange distance between the sensor and the optical centre of the lens and therefore made the internal reflection more obvious. My 180mm f/3.5 APO EX lens is not the DG version. The DG version would in all likelihood have the necessary optical coatings to reduce if not eliminate this kind of internal reflection.
QuoteOriginally posted by Blue Quote
It does allow for closer focusing with some lenses. I have used the Kenko af 25mm tube with my DA* 300 to get closer focusing and retain af.
Sorry about your experiences, but I've been against Sigma since discovering the taped-on front element on my friend's 300 F2.8 WAY back in the film days.

Get rid of it. Lots of good lenses out there that are carefully designed.

Cheers,
Cameron
07-23-2012, 11:15 AM   #8
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QuoteOriginally posted by Digitalis Quote
Well now I have one more excuse to use my FA*200mm f/4 ED Macro - not that I really needed one.
BTW how would you compare these two? I never had a chance to try out the FA*200/4 Macro and I'm very curious what am I actually missing having the Sigma 180mm lens. Thanks.

07-23-2012, 11:27 AM   #9
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I have an old lens that does that same thing -- makes an aperture shaped hotspot in the image if stopped down more than f/8, especially when focused at certain distances. In my case I can see little bubbles that appear to be on the edges of the inner lens barrel, but since I'm looking through the glass they are highly distorted and I can't really tell where they are. I think it is element separation and it picks up light and bounces it around. But some sort of internal reflection, yeah. Sucks on a macro where you are stopping down to get DOF (on mine it is a 55/1.4 so I just live with it).
07-23-2012, 12:31 PM   #10
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I have the non-DG too, but haven't seen hot spots on mine. Perhaps because I do not have any extensions. And I do not use flash with macro often.

Seb.
07-23-2012, 10:02 PM   #11
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QuoteOriginally posted by elho_cid Quote
BTW how would you compare these two? I never had a chance to try out the FA*200/4 Macro and I'm very curious what am I actually missing having the Sigma 180mm lens. Thanks.
The Pentax FA*200mm f/4 ED [IF] Macro is simply the best macro lens above 100mm that money can buy. The only lens that I have for any other camera system that comes close to matching its performance it is the Voigtlander 125mm f/2.5 APO SLII Macro - which I have in Nikon F mount. The Pentax FA* 200mm f/4 Macro is perhaps one of a handful of modern autofocus lenses that are diffraction limited. The Sigma 180mm f/3.5 APO EX isn't a bad lens optically (apart from this internal reflection issue) it does have rather high amounts of chromatic abberration for an apochromatic lens though, which isn't much of a surprise Sigma has been playing fast and casual with the term "APO" for YEARS.
07-24-2012, 06:11 AM   #12
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If I had the FA* 200/4, I would sell the Sigma 180 so fast it would think it was in orbit with the Hubble Telescope.
07-25-2012, 09:31 AM   #13
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QuoteOriginally posted by Digitalis Quote
The Sigma 180mm f/3.5 APO EX isn't a bad lens optically (apart from this internal reflection issue) it does have rather high amounts of chromatic abberration for an apochromatic lens though, which isn't much of a surprise Sigma has been playing fast and casual with the term "APO" for YEARS.
I agree, Sigma has always been more fast with labels like "macro" or "APO". So the FA*200/4 is better regarding apochromatic treatment? Any other advantage, besides I assume, higher contrast?
07-25-2012, 08:21 PM   #14
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The Pentax FA*200mm f/4 ED Macro Has significantly higher contrast and it is a genuine apochromat. the Sigma 180mm f/3.5 has an odd filter thread (72mm Vs 67mm on the FA* lens) And the image quality seems to take a dive at more distant focus settings, the Pentax FA* lens is perfectly usable as a telephoto - though the focus throw is a bit off putting. And of course, the Pentax lens is significantly more resistant to flare - even though it is optically based on a legacy lens design that pre-dates digital photography.


Pentax FA*200mm f/4 ED [IF] Macro A 1:5 - AF160FC Ring flash and Wireless AF540FGZ used
07-26-2012, 12:54 AM   #15
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Thanks for the answer. Now I just don't understand why you still use the Sigma...
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