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12-13-2011, 01:03 PM   #1
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Catch-in-focus with Tamron Adaptall 2 mirror lens

Hey all,

I just picked a 500mm mirror lens up off eBay and have been playing around with it a bit. I pooh-poohed the idea of difficulty focusing because, after all, I'm a real photographer from back when we had to mix up our own emulsions from the caribou we hunted with our stone hand-axes...anyway, after decades of work with manual-focus lenses, I figured, how hard could it be?

Hard, as it turns out. Of the 50 or so images I shot the first time out, I had maybe 5 in focus without undue shutter blur. You would not think that ducks bobbing on little foot-high waves would move around enough to muck with your mind, focus-wise. (But if you would not think that, clearly you've never tried to hand-focus a 500mm f/8 catadioptric!)

With other lenses, I'll sometimes use the trick of setting the autofocus point, then using catch-in-focus while I slowly rack the focus ring. Here, though, the shutter was firing the instant I pressed, even when things were WAY out of focus. I seem to recall C-I-F working with M lenses. Am I missing something?


TIA,

rw

(Here's one of the few keepers.)

12-13-2011, 01:13 PM   #2
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Check the mount of the lens - is it plastic or painted? If so, it's not shorting the data pin. If not, is it at least covering the pins? If it is painted, are you willing to scratch some paint to bare metal so that it will short the data pin?

Looking in the link, it looks like it's either painted, or not actually making contact with the pins. Without the data pin shorted, the camera doesn't realize there's a lens attached and won't engage CIF.
12-13-2011, 01:47 PM   #3
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As an owner of the shorter sibling, the Tamron SP 350mm f/5.6 I can confirm that these lenses ARE difficult to focus - but practicing will bring you a long way (after some time...).

What I cannot confirm is you observation that a Pentax DSLR in catch-in focus mode would fire instantly and when way out of focus. At least not when used with the original (blank) metallic Adaptall-2 P/K or P/KA Cutom Mount.

If, on the other hand, you are using the black anodized M42 Adaptall adapter you may get the result you describe.

So, what camera model and what aAdaptall mount have you been using?
12-13-2011, 01:49 PM   #4
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QuoteOriginally posted by Stone G. Quote
original (blank) metallic Adaptall-2 P/K or P/KA Cutom Mount.
Ah yes, I conveniently ignored the adaptall part. I'd place a bet that you're right, Stone G., that fewayne's adapater is the culprit and is what's preventing that data pin short.

12-13-2011, 02:02 PM   #5
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Aha! I bet you're right. It's a bare-metal adapter (I think it's actually a Tamron brand), but it's for a Nikon -- I've got a cheapie Pentax one on order, but meanwhile I've just been hanging the thing on the mount and handling it very carefully. And I wouldn't be surprised in the least if it's not touching the pins to short them.

Which means that I should ensure conductivity on the aftermarket one when it arrives, because IIRC it's painted.

Thanks ever so -- one problem solved. (And a shout-out to a fellow Madison Pentaxian, too!)
12-14-2011, 01:37 AM   #6
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Some Nikon mounts short the pins, some don't. Any Pentax adapter should cover the pins. With adapted lenses, we often use metal tape on the lens base to short the pins. That's fine with lenses, not so fine with adapters. All the T-T2, macro, wide-flange M42-PK and other adapters I've used have a tight fit on the camera mount. Tape causes them to jam onto the mount -- its thickness is just enough for that. So, sanding or filing away the black paint is a must.

If trying to use CIF with a mount that doesn't short the pins, the camera just fires. That's my signal that I haven't scraped away enough paint, or I haven't got the lens lined up right, or I've otherwise focked up, like setting AF.C. That signal says, HAY DUMMY! TRY AGAIN!

I use a Sakar 500/8 mirror on my K20D. It's T2 with a sanded mount. I *always* use CIF and SR with that lens, handheld. With CIF, I nail the focus on contrasty centered subjects. Even with SR, it's best to shoot with a shutter of 1/1000 sec or faster, handheld, and let ISO float where it will. High-ISO noise can be fixed in PP; motion blur can't. And that little Sakar is nifty in urban environments, since it just doesn't look like a long tele. Just gotta watch the light...
12-14-2011, 10:54 AM   #7
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Remember that Catch-in-Focus is using the AF sensor, which is trying to squint through an f8 lens. Sometimes it will not get enough light to work.
12-14-2011, 11:59 AM   #8
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As Just1MoreDave said, I can confirm that CIF will not work with 55B except under very bright conditions, Stone G's 06B will work in most situations because it's one-stop faster. I wonder what the threshold is for the Pentax AF sensor, f6.3?


Last edited by excanonfd; 12-14-2011 at 12:03 PM. Reason: add
12-14-2011, 12:02 PM   #9
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QuoteOriginally posted by Just1MoreDave Quote
Remember that Catch-in-Focus is using the AF sensor, which is trying to squint through an f8 lens. Sometimes it will not get enough light to work.
While that's no doubt true, he said that it just fires, rather than doesn't fire. That leads me to believe the pins idea, rather than a light issue. If it was a light issue, it wouldn't fire, right?
12-14-2011, 12:11 PM   #10
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QuoteOriginally posted by Just1MoreDave Quote
Remember that Catch-in-Focus is using the AF sensor, which is trying to squint through an f8 lens. Sometimes it will not get enough light to work.
I find on my K20D that the CIF aperture cutoff is generally between f/8-f/11 for longer lenses, and between f/11-f/16 for very short lenses. I have not yet had CIF fail with any lens at f/8 when the subject is adequately lit, and have not had CIF succeed with any lens stopped-down to f/16 no matter how well-lit. CIF works with my 500/8 and 1000/10 mirrors. I do not know if the cutoff is the same with other Pentax cameras. In any case, CIF works when the subject is lit and contrasty.
12-14-2011, 03:44 PM   #11
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Mirror Lenses and Catch-In-Focus

It may be counterintuitive to most, but I believe that a (good) 500mm f/8 lens would behave better in repect of CIF than my faster 350mm f/5.6 lens.

Here are my findings and here is why:

Using CIF on my 06B is all but impossible. I hardly ever get a "beep" just a fleeting flash of the red focus point when I approach correct focus. Long time ago, during night shots of the Moon, I noticed that with my Tamron 01F 2X teleconverter - as well as with my Tamron F-series SP 2X TC - I got focus confirmation more frequently.

And there is nothing wrong with my lens. It is as sharp as catadioptric mirror lenses go: I use it frequently for astro photography and stars are pin-point sharp without any distrotions over the entire field --- when the lens is properly focused. But give the barrel a sligt twist and stars turn into blobs with the shaddow of the central obstruction in the middel of each blob.

This took me into a more systematic "research" trying out my 06B with and without TC on well-lit daylight subjects and results were the same: Hardly ever would CIF work with the "bare" lens but frequently (in well lit, good contrast situations) with the TC on. I should add that we are mostly talking hand-held shots - SR works, even at 700mm FL!!!

Recently then, I acquired the Kenko Pz-AF 1.5X Teleplus SHQ converter and now things got really interesting: With this combination (effectively a 500mm f/8 system) I can use CIF even under much less than optimum ligthening and contrast situations!!!

Why this???

Well, my layman's explanation is that my 06B lens has a comparatively very large central obstruction This is the price that you have to pay to get a compact, fast catadioptric lens. But that also means that you are really dependent upon the outer beams of the light cones to form your image and hence, correct focus becomes truly critical.

With the use of TCs the light rays arrive at a steeper angle at the sensor and hence, small deviations from "exact" focus become less critical.

OK, as said: This is a layman's speculations. Take them for what they are...

But no doubt and no matter what: My 350mm f/5.6 system works better than ever before - as far as CIF is concerned - in combination with my 1.5X TC.

Last edited by Stone G.; 12-14-2011 at 03:49 PM. Reason: missing point
12-15-2011, 11:02 AM   #12
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Pentax adapter has arrived. Anodized. Emery paper in my future! :-) I might try a fragment of foil first, just to test the concept.

Here's a question: Does anybody know specifically which pins need to be shorted? I suppose it's not that big a deal to just sand the whole area. The Wikipedia page gives some guidance but it's not entirely clear. This page does give the pinouts, so I can puzzle it out on my own.
12-15-2011, 11:34 AM   #13
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QuoteOriginally posted by fewayne Quote
Pentax adapter has arrived. Anodized. Emery paper in my future! :-) I might try a fragment of foil first, just to test the concept.

Here's a question: Does anybody know specifically which pins need to be shorted? I suppose it's not that big a deal to just sand the whole area.
It is indeed no big deal to scrape the entire area. I use the file blade on my Leatherman tool for that, just because I don't keep sandpaper at my desk. Be careful about sticking foil in there. Some adapters have a tight fit, and metal tape or foil can cause them to jam on the mount. Have fun!
12-15-2011, 08:57 PM   #14
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OK, I've got at least some success with sanding off the paint -- thanks! Sometimes I would get a fire, others not, but I suspect it may have been due to somewhat dim light not allowing the focus sensor to lock. And I got some sharpies that way, too. Especially once I thought to turn down the ISO, hang a big flash on the camera, and get an effective shutter speed of 1/5,000 or thereabouts.
12-21-2011, 10:41 AM   #15
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It may also be an idea to use some acetone on a q-tip or a dust-free rag. The idea being to dissolve the paint, rather than abrade it and the underlying metal. Just be careful of ventilation, and be careful not to drip any into the lens. You'll be less likely to introduce metal particles into your lens/camera or to create a rough surface on the lens mount that would, in turn, wear the camera mount.
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