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08-14-2012, 06:25 PM   #91
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QuoteOriginally posted by vonBaloney Quote
Why are you out of luck with a DA lens? If it has contacts, then you control the aperture with the body as usual. And the TC version has the advantage of actually having AF gear-drive pass-thru (on some of them), which I don't think any of the dedicated tubes have.
If it is a plain A-type tube (6 electrical contacts), you get mixed results with DA-type lenses. Some will give the correct aperture range, but others won't. With a DA-type tube, AF may work, sort of.

08-14-2012, 06:32 PM   #92
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QuoteOriginally posted by baro-nite Quote
If it is a plain A-type tube (6 electrical contacts), you get mixed results with DA-type lenses. Some will give the correct aperture range, but others won't. With a DA-type tube, AF may work, sort of.
Is there a difference between a "DA-type" tube and any AF-supporting tube that might predate digital? The seventh contact came with autofocus, right? (Ignoring the first try at AF, which was abandoned.) I have a TC that has 7 contacts, a gear-drive and the additional SDM contacts.
08-14-2012, 06:41 PM   #93
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QuoteOriginally posted by JimJohnson Quote
Correction- It's a great way to get a 25mm tube. If all you want/need for extension is a multiple of 25mm and A-series support, it's not a bad way to go. However, if you want to extend a DA lens, you are out of luck; or if you want something other than a multiple of 25mm, it can be more difficult/expensive finding the lower and higher power teleconverters to get the other tube lengths.
I only care about auto aperture, not AF. There are AF TC's too, but usually more expensive. A 2X TC is normally around 25mm. A 1.4X is less, and a 3X is more. The 3X TC's are normally inexpensive. It was a good solution for me.
08-14-2012, 06:46 PM   #94
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QuoteOriginally posted by baro-nite Quote
If it is a plain A-type tube (6 electrical contacts), you get mixed results with DA-type lenses. Some will give the correct aperture range, but others won't.
Do you mean that with the TC mounted, the wrong aperture is reported in the exif? That's true for some TC's but there's no practical disadvantage that I can see. I can control aperture electrically and my exposures are dead on with the A tube mounted.

08-15-2012, 04:56 AM   #95
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QuoteOriginally posted by vonBaloney Quote
Is there a difference between a "DA-type" tube and any AF-supporting tube that might predate digital? The seventh contact came with autofocus, right? (Ignoring the first try at AF, which was abandoned.) I have a TC that has 7 contacts, a gear-drive and the additional SDM contacts.
No difference AFAIK, but I've never seen a definitive answer to this.

QuoteOriginally posted by audiobomber Quote
Do you mean that with the TC mounted, the wrong aperture is reported in the exif? That's true for some TC's but there's no practical disadvantage that I can see. I can control aperture electrically and my exposures are dead on with the A tube mounted.
My findings are based on a small number of lenses, given in detail here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/176775-da-lens...rious-tcs.html

Wrong aperture value is not just in EXIF, also in camera displays. Just did a quick test with the A400/5.6 on a DA-type TC. It shows an aperture range of f/2.4 to f/45; the lens has an actual range of f/5.6 to f/45. On the KA mount, the 6 pins encode the minimum aperture (correct here) and the size of the aperture range (incorrect here). My test exposures show no difference between "f/2.4" and "f/2.8"; both seem to be actually f/5.6 (exposure slightly different but the tube of course eats some light). Haven't tested at the other end of the range, but for me this is not usable anyway. I can't explain what's happening with this or any other combination I've tested; I can only say that I've found no TC/tube that gives full compatibility with all mount types. I suspect this is one of the reasons Pentax has yet to produce a TC for F-series and later lenses.
08-15-2012, 06:20 AM   #96
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QuoteOriginally posted by baro-nite Quote
Wrong aperture value is not just in EXIF, also in camera displays. Just did a quick test with the A400/5.6 on a DA-type TC. It shows an aperture range of f/2.4 to f/45; the lens has an actual range of f/5.6 to f/45.

I can only say that I've found no TC/tube that gives full compatibility with all mount types. I suspect this is one of the reasons Pentax has yet to produce a TC for F-series and later lenses.
I don't have any DA type TC's (I assume by DA that you mean a TC with auto aperture and screw-drive-only AF). I have two A TC's and one PZ AF TC. All three behave the same way. The camera screen and exif data report uncorrected aperture. In other words, if my lens is electronically set for f4, that's what I see in the screen and in the exif. I have to mentally add one stop for a 1.4X or stops for a 2X TC. I don't see this as any sort of problem. I've not heard of what you are discussing, where a lens shows an impossible range of apertures.

I'm reasonably certain the Pentax AF 1.7X TC shows corrected aperture values.
08-15-2012, 07:14 AM   #97
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QuoteOriginally posted by audiobomber Quote
I don't have any DA type TC's (I assume by DA that you mean a TC with auto aperture and screw-drive-only AF). I have two A TC's and one PZ AF TC. All three behave the same way. The camera screen and exif data report uncorrected aperture. In other words, if my lens is electronically set for f4, that's what I see in the screen and in the exif. I have to mentally add one stop for a 1.4X or stops for a 2X TC. I don't see this as any sort of problem. I've not heard of what you are discussing, where a lens shows an impossible range of apertures.
I'm using the term "DA-type" rather loosely, meaning it has the 7th (data) pin and screw drive, but even with the units I have there is variation within that (PZ contacts or not, all 7 pins go through the TC or not). So I guess I should say "crippled KAF/KAF2" instead.

Re incorrect aperture values I'm not talking about whether or not they are corrected for the TC; none of the units I have attempt that AFAIK. I get just plain wrong values with certain lens/TC combinations. I'm sure I could figure out what indicated value corresponds to what actual value for each case, and if I had to I would, but I'd rather figure out which combinations work correctly. Out of curiosity, which lenses have you tried?
08-15-2012, 07:25 AM   #98
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QuoteOriginally posted by baro-nite Quote
Out of curiosity, which lenses have you tried?
Mostly the A*300mm f4, but also DA 18-135, D FA 100mm and Sears A 135mm macro. Is there some combo you would like me to test? My gear is listed in my profile.

PS Why would an auto TC behave any differently than auto tubes? If one is wonky, the other should be too. But as I said, I haven't seen the behaviour you describe.

08-15-2012, 07:48 AM   #99
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QuoteOriginally posted by audiobomber Quote
Is there some combo you would like me to test?
Thanks for the offer; at this point I don't even have a theory for what's happening here, so I'd be wasting your time to have you do this.
08-15-2012, 07:20 PM   #100
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QuoteOriginally posted by vonBaloney Quote
Why are you out of luck with a DA lens? If it has contacts, then you control the aperture with the body as usual. And the TC version has the advantage of actually having AF gear-drive pass-thru (on some of them), which I don't think any of the dedicated tubes have.
note to Jim- repeat after me. Do NOT post advice when you are tired....

Okay, let me clarify. What I meant is I have yet to see a reasonably priced TC with all the contacts AND AF where the price justified pulling the glass. And yes, I know I said nothing of the sort. My bad. I will stand by my statement that it will likely be unreasonably pricey if your goal is to build a set of various sized extension tubes out of TCs.
08-15-2012, 07:31 PM   #101
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QuoteOriginally posted by JimJohnson Quote
note to Jim- repeat after me. Do NOT post advice when you are tired....

Okay, let me clarify. What I meant is I have yet to see a reasonably priced TC with all the contacts AND AF where the price justified pulling the glass. And yes, I know I said nothing of the sort. My bad. I will stand by my statement that it will likely be unreasonably pricey if your goal is to build a set of various sized extension tubes out of TCs.
But tubes with contacts are also unreasonably pricey if you can even find them, so you do what you can...
08-16-2012, 06:37 AM   #102
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I'm cheap. I would find a set of M-type tubes (aperture stopdown linkage, but no contacts), tape in the appropriate insulator spots to communicate the lens' min & max aperture, short the 'A' contact on the body, and manually focus. These tubes cost very little, and other than focus, I still get full automation. I assure you you will get images equal to finding and dismantling an auto-focus or auto aperture teleconverter. And the modifications won't take any more time.

While none of the above modifications are permanent, many folks shooting macro tend to use the same lens, so the modifications are often a one-time thing.
08-16-2012, 09:55 AM   #103
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QuoteOriginally posted by JimJohnson Quote
I'm cheap. I would find a set of M-type tubes (aperture stopdown linkage, but no contacts), tape in the appropriate insulator spots to communicate the lens' min & max aperture, short the 'A' contact on the body, and manually focus. These tubes cost very little, and other than focus, I still get full automation. I assure you you will get images equal to finding and dismantling an auto-focus or auto aperture teleconverter. And the modifications won't take any more time.

While none of the above modifications are permanent, many folks shooting macro tend to use the same lens, so the modifications are often a one-time thing.
This sound interesting, can you please post pictures of your current macro set up with modified M-type tubes?
08-16-2012, 10:15 AM - 1 Like   #104
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QuoteOriginally posted by excanonfd Quote
This sound interesting, can you please post pictures of your current macro set up with modified M-type tubes?
I use an M-type macro converter matched for a 50mm lens rather than fixed length tubes, but the setup would be the same.
Here are the photos:
https://www.pentaxforums.com/forums/pentax-camera-field-accessories/113756-pk-extension-tubes.html#post1965895

If you scroll up a couple posts from the photos, you'll have complete instructions.

For what it's worth, I also have a Pentax K bellows unit. The same principles apply, but as it has no mechanism to stopdown the lens at exposure, I have to meter, lock exposure, stop the lens down manually, then release the shutter. I never have to put up with that lovely "F - - -" in my K-r's metering display.
08-17-2012, 04:54 PM   #105
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QuoteOriginally posted by JimJohnson Quote
I use an M-type macro converter matched for a 50mm lens rather than fixed length tubes, but the setup would be the same.
Here are the photos:
https://www.pentaxforums.com/forums/pentax-camera-field-accessories/113756-pk-extension-tubes.html#post1965895

If you scroll up a couple posts from the photos, you'll have complete instructions.

For what it's worth, I also have a Pentax K bellows unit. The same principles apply, but as it has no mechanism to stopdown the lens at exposure, I have to meter, lock exposure, stop the lens down manually, then release the shutter. I never have to put up with that lovely "F - - -" in my K-r's metering display.
Thank you, that worked very well. Following the instructions you've provided, I was able to get my Tamron Adaptall-2 02B 28/2.5 with a PK/M adapter to work like an A lens. No green button to meter and no "F--" to worry about, an excellent modification!
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