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Pentax 105/2.8 Super Takumar as a tube lens - big surprise!
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Beatsy



Joined: 05 Jul 2013
Posts: 1349
Location: Malvern, UK

PostPosted: Fri Apr 13, 2018 6:16 pm    Post subject: Pentax 105/2.8 Super Takumar as a tube lens - big surprise! Reply with quote

With the spring frenzy upon us, I'm back to stacking insects more often. However, the combination of an aging PC (replacing soon) and 42 megapixel FF images from my Sony A7rii make for painfully slow image import/export and stacking. So I started mostly using APS-C crop mode because the resultant 18-megapixel images process 5-10 times faster!

I use 135mm tube lenses with my Mitties; an MC Sonnar for marginally better image quality or a Vivitar/Komine to avoid the slight corner clip (vignette) of the Sonnar when running full frame. Both work perfectly on APS-C as the FoV doesn't stray too far outside each Mitty's specified image circle, whereas FF does cause noticeable image degradation toward the corners (albeit still eminently usable).

The down side of APS-C is a significantly reduced FoV compared to using FF. It's irritating when subjects don't quite fit and I either have to revert to the drudge of FF imaging, or drop to the next Mitty down (which is often too big a drop, wasting space in the frame). So I decided to find a shorter tube lens that would compress most of the full-frame FoV onto APS-C, but not quite all of it. My goal was to exclude the FF clipped corners of the Sonnar and not go quite as far into the "out of spec" territory where Mitty images degrade.

None of my existing lenses fit the bill as they either vignetted massively, or were simply too big for the rig. They were all too far from the "just over 100mm" focal length I figured was optimum anyway. So looking around, I came across a Pentax 105mm f/2.8 Super Takumar which is the ideal focal length and has the same filter thread as my existing tube lenses. Despite the one mention on this forum being negative, I decided to buy it anyway. The lens arrived today and I've only had time for a couple of test stacks, but it's looking pretty good.

First the negatives. This lens renders very flat, low-contrast images. Easily fixed in post of course, but it robs some dynamic range meaning contrast can't be pushed quite as aggressively to pull out more detail (when needed). There's a super-multi-coated version that's far better, but it's expensive and more than I wanted to spend on a speculative test. The lens exhibits quite strong field-curvature too, but that's irrelevant when stacking, and may be the cause of the "surprise benefit" (more on that later).

So I put each of my Mitties on it and visually checked general image quality across the frame and into the corners (APS-C mode enabled). Perfect with every one (5x, 10x, 20x and 50x)! Image scale is more to my taste too with far less over sampling at higher powers. Really nice crisp images. I used a random butterfly wing glued to some card as the test target, lit by a single flat panel lamp. It's not the ideal choice as the scales on this one are quite small and tend to be a bit "sparkly" - but good enough for the test.

Here's a stack done with the 50x Mitty - running at 26.25x onto the sensor for a FoV 0.91mm wide in APS-C mode. Sharp enough all the way into the corners - pretty much as expected. The image wasn't cropped at all.



Just for grins, I put the camera back to full frame mode, expecting to see vignetting and complete mush in the extreme corners. That was the big surprise! I couldn't believe how good the corners were - noticeably better than on the 135mm tube lenses! It's a guess, but I wonder if the field curvature is compensating in some way for the aberrations present in the outer (out of spec) image circles of the Mitties. No idea really, but I'll take it! Here's the same butterfly wing taken with a 50x Mitty on full frame (same mag of course, so just a larger FoV). Also not cropped.



More to test yet and I'll add some 100% crops tomorrow - but this is quite encouraging. Final image is just a short stack of the center of a daisy (a few grains of pollen) with the 50x Mitty. Cropped in for composition.

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Beatsy



Joined: 05 Jul 2013
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Location: Malvern, UK

PostPosted: Sun Apr 15, 2018 1:20 am    Post subject: Reply with quote

Follow-up. OK, it seems the 105mm Takumar has nothing to do with getting better corners on a way over sized FoV. It's just that the 50x and 20x Mitties stand being pushed a bit further than 5x and 10x do. I'd never noticed this before as I'd never pushed the image circle that far (until now).

Also - I retract the comment about the Takumar having very low contrast rendering. It doesn't. In fact, it's actually quite good. The problem (again) was specific to the 50x objective and the very glarey subjects I used without proper diffusion. Attached image (grass seeds in the making) was done with a 10x Mitty on the 105mm Takumar using APS-C crop mode (and a crop off the edges for composition). The colours and contrast are "as shot" (DMAP stacking).

Overall - I'm thrilled with how this new arrangement performs. I know most will call it "under sampling" but I really like the near-pixel-level resolution and sharpness with the 5x and 10x Mitties. 100% crops are great with very little apparent softness (see second pic - apologies for 'flare' artefacts, but I wanted to show it 'unedited'). It's pretty much the same with 20x and 50x Mitties though the smallest resolvable distance will cover closer to two and three pixels respectively with those.

Image transfer and stacking times are almost an order of magnitude quicker too. Well happy with that. The lens is a keeper.



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GaryB



Joined: 29 Jul 2016
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PostPosted: Sun Apr 15, 2018 3:01 am    Post subject: Reply with quote

Very nice.
That second set has great colours and contrast.
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mawyatt



Joined: 22 Aug 2013
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Location: Clearwater

PostPosted: Sun Apr 15, 2018 5:45 am    Post subject: Reply with quote

Steve,

Nice find!

I know what you mean about caught between the 135/125mm and 200mm zone for tubes with the Mitty's (just had a mishap due to this). Long ago I tried my Nikon 105mm Macro VR, and it didn't perform well, so I gave up on anything around 100mm thinking the Mitty's were too far off base for the edges to be anything decent.

Any advise on what to look for with the Pentax 105mm Takumar, good price, etc?

Best,
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Beatsy



Joined: 05 Jul 2013
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Location: Malvern, UK

PostPosted: Sun Apr 15, 2018 6:33 am    Post subject: Reply with quote

mawyatt wrote:
Steve,

Nice find!

I know what you mean about caught between the 135/125mm and 200mm zone for tubes with the Mitty's (just had a mishap due to this). Long ago I tried my Nikon 105mm Macro VR, and it didn't perform well, so I gave up on anything around 100mm thinking the Mitty's were too far off base for the edges to be anything decent.

Any advise on what to look for with the Pentax 105mm Takumar, good price, etc?



Lucky really. I have a 150mm Super Takumar I got ages ago but it's awful as a tube lens! It vignettes so badly it's like looking through a porthole on FF and even clips the corners in APS-C crop mode. If I'd remembered I had that lens (stuffed at the back of a shelf) I may have avoided the 105mm! So glad I forgot about it Very Happy

To clarify, the corners (with 105mm tube lens) are not particularly "good" on full frame with any Mitty, but they're tolerable on the higher power ones. But they *ARE* good enough if you want extra space for composition and only have background or blurred stuff in the corners. They're also good enough if you're publishing heavily downsized images, like we do here. Key thing is there is no vignetting from the Takumar. That's on full frame though, which I want to get away from for a bit. On a crop sensor or when running a FF sensor in crop mode, the corners are excellent! This is the mode I'll be mostly using now - until I get my new stonking-spec PC anyway Smile

Prices (in English) range from £45-£110 or so, double that (£90-£240) for the super multi-coated version. I guess $ prices will be the same numbers. They don't seem particularly rare, so it's feasible to wait for a bargain if budget is an issue and you're not in a rush.

Cheers
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ChrisR
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PostPosted: Sun Apr 15, 2018 1:36 pm    Post subject: Reply with quote

Are you fairly sure the SMC version is
(a) better, in normal uses - I'm not a Pentax user
and
(b) the same construction? Sod's law....

Do you have a 100X?
Maybe it works with an 85mm
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Beatsy



Joined: 05 Jul 2013
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PostPosted: Sun Apr 15, 2018 2:06 pm    Post subject: Reply with quote

ChrisR wrote:
Are you fairly sure the SMC version is
(a) better, in normal uses - I'm not a Pentax user
and
(b) the same construction? Sod's law....

Do you have a 100X?
Maybe it works with an 85mm

Good points. (a) Yes, fairly sure from a few glowing reports about the SMC version compared to the normal one. (b) Not so sure about that.

I don't have the 100x nor any temptation to get one. It has 100% more mag (than the 50x) but only 20% more resolution (0.4 microns compared to 0.5). Similar story with the "HR" versions of the M Plan APO Mitties. Shorter (though still useable) working distances for not much extra resolution. I suspect the image circles aren't as "pushable" as the normal M Plan APOs either - but don't know that and would be interested to hear if anyone is using one of these.
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Lou Jost



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PostPosted: Sun Apr 15, 2018 2:17 pm    Post subject: Reply with quote

"It's just that the 50x and 20x Mitties stand being pushed a bit further than 5x and 10x do. I'd never noticed this before as I'd never pushed the image circle that far (until now)."

NathanM posted tests here showing that the 7.5x Mitutoyo also had an unusually large image circle relative to the 5x and 10x. I have that lens and like it very much pushed down. You would surely like it too.
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Beatsy



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PostPosted: Sun Apr 15, 2018 2:32 pm    Post subject: Reply with quote

Lou Jost wrote:
NathanM posted tests here showing that the 7.5x Mitutoyo also had an unusually large image circle relative to the 5x and 10x. I have that lens and like it very much pushed down. You would surely like it too.

I know. Get thee behind me, Lou Jost! Razz
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Smokedaddy



Joined: 07 Oct 2006
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PostPosted: Sun Apr 15, 2018 2:36 pm    Post subject: Reply with quote

ChrisR wrote:
Are you fairly sure the SMC version is
(b) the same construction? Sod's law....

https://jeffandmichelephoto.com/learn/how-can-i-tell-the-differences-between-the-different-pentax-105mm-f24-lenses

-JW:

Edited: wrong link. <duh>
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mjkzz



Joined: 01 Jul 2015
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PostPosted: Mon Apr 16, 2018 4:41 am    Post subject: Reply with quote

I got a Pentax 105mm f/2.8 SMC and just tried it.

ChrisR wrote:
Are you fairly sure the SMC version is
(a) better, in normal uses - I'm not a Pentax user
and
(b) the same construction? Sod's law....


(a) do not know if it is better as I do not have the other one

(b) putting on a generic PLAN 4X 0.1NA and a 10X 0.25NA, surprisingly, very little vignetting for either objective, tried both on a Canon 100mm f/2.9 Macro, both show visible vignetting.




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ChrisR
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PostPosted: Mon Apr 16, 2018 5:35 am    Post subject: Reply with quote

The one Smokedaddy cited is the f/2.4 for large format - an even bigger hole, though harder to adapt to the camera I assume.
One could try multiple LSAs; I have three, but can only find one.
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Beatsy



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PostPosted: Mon Apr 16, 2018 7:23 am    Post subject: Reply with quote

mjkzz wrote:
(b) putting on a generic PLAN 4X 0.1NA and a 10X 0.25NA, surprisingly, very little vignetting for either objective, tried both on a Canon 100mm f/2.9 Macro, both show visible vignetting.


Did you get your SMC version (very) recently, or is it one you already had?

Another minor data point for the lens. The infinity focus position is right on the hard stop. I.e. the lens doesn't focus past infinity. I know a slight focus error won't introduce noticeable issues, but it's nice to know it's set "as good as can be" with a simple twist of the focus ring to it's maximum travel.

I tried my Sony 90mm f/2.8 macro too. Porthole vignetting on full frame and clipped corners on APS-C. Rubbish!
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mjkzz



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PostPosted: Mon Apr 16, 2018 9:51 am    Post subject: Reply with quote

I had one but gave it to a friend only about a month ago, so I just bought another one after reading this post :-) because I tried the Canon 100mm f/2.8 macro and I got almost dark vignetting at corners, so I was curious and, yeah, surprise.
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rjlittlefield
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PostPosted: Mon Apr 16, 2018 10:53 am    Post subject: Reply with quote

mjkzz wrote:
because I tried the Canon 100mm f/2.8 macro and I got almost dark vignetting at corners

Exactly which lens was that, and on what sensor size?

I ask because I routinely use Canon EF 100mm f/2.8L IS USM as tube lens on APS-C, and that combo works very well.

--Rik
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