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01-25-2011, 01:24 PM   #16
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QuoteOriginally posted by Digitalis Quote
presumably in the middle of 2011 - Sigma added an optical stabilizer to it.
So they blocked the non-OS version to release the OS version for a system that has in-body OS? I assume optically it wasn't improved. Strange move.

01-25-2011, 07:48 PM   #17
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I've put an old pre-set Talumar 200/5.6 on a bellows, and while it won't go quite to 1:1 (I think) it gives me a heck of a lot of working space. But it needs a lot of light.
01-25-2011, 08:00 PM   #18
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QuoteOriginally posted by Laurentiu Cristofor Quote
Strange move

bear in mind sigma don't just make lenses solely for pentax, they produce lenses for their own and many other manufacturers and not all of them have in body IS. From and economic point of view it makes sense, instead of having to manufacture parts for two different lenses( Is and non-IS version) they are consolidating into making just one lens.
01-26-2011, 01:46 AM   #19
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QuoteOriginally posted by Nick Siebers Quote
I've put an old pre-set Talumar 200/5.6 on a bellows, and while it won't go quite to 1:1 (I think) it gives me a heck of a lot of working space. But it needs a lot of light.
Yup, that TeleTak takes a bit of daylight. Put a couple cheap sets of tubes behind it too, and you'll get to 1:1, with an effective aperture of f/11. The TeleTak is a good piece for this, because it's so light (410g) and sharp. Hmmm, maybe I'll try my Enna 240/4.5 on extension -- it's only 300g. But it won't have the same crispness as the TeleTak. It's hard finding sharp longer lenses that don't weigh a ton.

01-26-2011, 01:57 AM   #20
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QuoteOriginally posted by Digitalis Quote
The pentax SMCP-FA* 200mm f/4 ED IF Macro is excellent for both 1:1 macro and distant subjects. However the Sigma 180mm f/3.5 suffers from image quality degradation when subjects approach infinity on the distance scale. At infinity, my sigma 100-300mm f/4 Zoom can beat the sigma 180mm f/3.5 at any aperture.
I find the bokeh of the FA200/4 Macro to be a bit busy (double image bokeh) at longer than macro distances, but it is truly stellar close up.

01-26-2011, 02:05 AM   #21
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QuoteOriginally posted by Wheatfield Quote
I find the bokeh of the FA200/4 Macro to be a bit busy (double image bokeh) at longer than macro distances, but it is truly stellar close up.
I agree the effect is most prominent at f/5 and f/6.3 but nisen bokeh is in my opinion much more acceptable than a lens like the sigma 180mm f/3.5 which suffers from astigmatism at longer focus distances.
01-26-2011, 04:09 AM   #22
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QuoteOriginally posted by Digitalis Quote
I agree the effect is most prominent at f/5 and f/6.3 but nisen bokeh is in my opinion much more acceptable than a lens like the sigma 180mm f/3.5 which suffers from astigmatism at longer focus distances.
You present your assessment about the Sigma 180mm as if it were accepted wisdom. Do you have any other evidence other than your own copy of which you cannot entirely be sure of whether or not it is OK? I know that your copy is great when close focusing but that doesn't prove the absence of a problem when focusing at something near infinity.
01-26-2011, 04:23 AM   #23
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QuoteOriginally posted by newarts Quote
For a 1:1 magnification (image size = subject size) the distance from the subject to the image is always four times the focal length.
Small typo. That should be "twice the focal length".

01-26-2011, 04:56 AM   #24
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Thank you all for this info.
I just ordered the book (Alfred A. Blaker).
I m happy, cheers.
01-26-2011, 05:56 AM   #25
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QuoteOriginally posted by Class A Quote
You present your assessment about the Sigma 180mm as if it were accepted wisdom.
fair call, a sample size of one doesn't hold much water statistically speaking. But I am prepared to be proven wrong, I do know a few people who own the 180mm f/3.5 in different mounts..perhaps I can propose a temporary exchange.
01-26-2011, 06:17 AM   #26
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QuoteQuote:
QuoteQuote:
For a 1:1 magnification (image size = subject size) the distance from the subject to the image is always four times the focal length.
Small typo. That should be "twice the focal length".
No, the distance from the image plane (sensor) to the subject plane (called focus distance) at 1:1 is four times the focal length. The distance from the lens to subject (working distance) and lens to sensor are each 2 times the focal length at 1:1.

The minimum focus distance is always four times the focal length and it always occurs at 1:1 magnification.

The focus distance equation is:

Focus.distance = focal.length(1+m)^2/m ...........which is minimum at m=1

Dave

PS the above neglects the effective lens thickness which is the (positive or negative) distance separating front & rear principal planes.

Last edited by newarts; 01-26-2011 at 06:51 AM.
01-26-2011, 05:44 PM   #27
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QuoteOriginally posted by newarts Quote
No, the distance from the image plane (sensor) to the subject plane (called focus distance) at 1:1 is four times the focal length.
Your right, sorry.

I didn't pay attention to the distance you were defining and assumed you were talking about the "working distance", not the "focus distance". Hope your clarification didn't help only me.
01-26-2011, 05:45 PM   #28
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QuoteOriginally posted by Digitalis Quote
...I do know a few people who own the 180mm f/3.5 in different mounts..perhaps I can propose a temporary exchange.
That would be useful, thanks in advance for considering this.

I googled a bit, trying to find support for your statement, but couldn't. Doesn't prove anything, but at least it doesn't seem to be an obvious and common problem.
01-27-2011, 01:32 AM   #29
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QuoteOriginally posted by Class A Quote
I googled a bit, trying to find support for your statement, but couldn't. Doesn't prove anything, but at least it doesn't seem to be an obvious and common problem.
When I am dealing with distant subject matter, grabbing my macro lens is the last thing on my mind - It's nice to see my biases are shared by the consensus.
In years past it was not uncommon for macro lenses to be poor at distant focus settings. I will point out that mine is the non-DG version, but even that fails to explain the poor performance at great distances.

though I have to say, does this look like an image from a defective lens? I'm not sure if you can tell by looking at this image, but you can see the stomas in the leaf. Stomas are cellular respiration holes that are practically invisible to the unaided human eye unless viewed under a microscope, or a very good camera lens.

Last edited by Digitalis; 05-09-2011 at 02:14 AM.
01-27-2011, 01:45 AM   #30
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QuoteOriginally posted by Digitalis Quote
In years past it was not uncommon for macro lenses to be poor at distant focus settings.
Yes, but floating focusing designs put an end to that and the one in yours could be responsible for causing trouble at infinity focus. In other words, with a moving group that is meant to adjust its position depending on focusing distance it could very well be that the lens excels at the MFD but is poor near infinity focus.

Of course this is just speculation but I think it is fair to say that great close focusing performance doesn't prove that the lens is completely in order with floating focusing designs.

P.S.: Nice image and great lens performance!
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