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11-17-2013, 12:43 AM   #1
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Extension tubes questions

I have lately acquired two sets of tubes. First I bought the Asahi Pentax Auto tubes, then this last week I got a set of the Kenko tubes with electrical contacts. While I really like the automated metering with the Kenkos, there is one thing that they won't do as compared to the Pentax ones: Catch-in-Focus. The camera keeps trying to focus the lens. I guess there is no way around this with my FA 50mm f1.4. It seems that the only combination to achieve both auto metering and CIF would be with an A series lens. Is this the case or is there a way to use CIF with FA lenses? Also, another question: The Kenkos' aperture levers are not spring loaded, the Asahis' are. Do the Kenkos put too much strain on the FA lens as its spring does all the work?

I am trying to see which ones I should keep. I would appreciate any input from you all. Thank you.


Last edited by pixie; 11-17-2013 at 01:51 AM.
11-17-2013, 03:04 AM - 1 Like   #2
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Didn't test this but at least you can achieve catch in focus with any lens if you isolate all contacts. For testing purposes a thin foil or paper will do.
If you isolate all the contacts except those for aperture you could probably achieve catch in focus with your FA 50 while retaining auto metering.
11-17-2013, 06:01 AM   #3
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Yea, you can use catch in focus even with plain cheap tubes. If they are painted or coated you will have to scrape/sand the paint off where the camera mount meets the lens. I just took a knife and scraped it off.
11-17-2013, 08:14 AM   #4
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How many pins/contacts (excluding the "Ricoh pin") does the Kenko tube have? The body might want the 7th (data) pin for catch in focus to work.

11-19-2013, 04:34 PM   #5
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If it is a question of cif being related to the electrical contacts, just take the lens out of A mode. That will isolate the aperture contacts. Catch in focus is possible with manual focus also, by putting the camera in manual focus i believe. It should be possible
11-19-2013, 07:45 PM   #6
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Thanks all for chipping in. Here's a picture of the tubes' contacts. The manual says that if CIF is set to [ON] in Custom Settings, if the focus mode is set to AF.S and one of the following types of lenses is attached, CIF shooting is enabled and the shutter is released automatically when the subject comes into focus.
- Manual focus lens
- DA or FA lens that has an AF and MF setting on the lens (the setting on the lens must be set to MF before shooting)

So this isn't really an issue with the tubes, but the lens itself. The FA 50mm f/1.4 has no AF/MF switch and therefore will not support CIF. The only way this could be achieved would be to fool the camera into thinking that an A type lens is mounted, and I don't believe that is possible. Like I mentioned in my OP, CIF works just fine with the very same lens when on the manual tubes. So it's either automated metering when on the Kenkos or CIF on the Asahis, for my FA 50mm f1.4. BTW, are there Pentax AF lenses with an AF/MF switch?

Last edited by pixie; 08-24-2014 at 12:08 AM.
11-19-2013, 10:40 PM   #7
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QuoteOriginally posted by delegopa Quote
Didn't test this but at least you can achieve catch in focus with any lens if you isolate all contacts. For testing purposes a thin foil or paper will do.
If you isolate all the contacts except those for aperture you could probably achieve catch in focus with your FA 50 while retaining auto metering.
Thanks. It sounds like there is a way of persuading the camera that an A lens is mounted when, in fact, it is an FA lens. Would you happen to know which contacts to isolate?


Last edited by pixie; 11-19-2013 at 11:15 PM.
11-20-2013, 03:51 AM   #8
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QuoteOriginally posted by Pentaxpixie Quote
BTW, are there Pentax AF lenses with an AF/MF switch?
Yes there are. I am not 100% sure if each and every Pentax lens with built-in SDM focusing motors have this switch, but all of those SDM-lenses that I have seen, including my own DA* 200mm, have it. So with the lens in MF and the body in AF.S mode you can indeed have automated meetering and CIF together. Very convenient!

So, rather than your FA 50mm, you might consider the DA 55/1.4?: SMC Pentax-DA* 55mm F1.4 SDM Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database
11-20-2013, 07:02 AM   #9
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QuoteOriginally posted by Pentaxpixie Quote
Would you happen to know which contacts to isolate?
My guess would be the data pin, the 7th pin from the right in your photo. The tube has a "Ricoh" contact where the screw-drive shaft would normally be.
11-20-2013, 10:15 AM   #10
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Sry, but I found no current pin layouts. Would be interested in this too.
Old layout is here: Features and Operation of the Ka Mount
But it should work. When I set my Sigma 70-300 to MF catch in focus is possible. Isolating all AF related contacts should therefore be enough. Currently dont have time to test this by myself.
11-20-2013, 06:54 PM   #11
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There will be more discussed in this post than asked for, but it has links on how to short the A pin.
PK/A extension tubes? - PentaxForums.com

If after reading the text, you want pictures of what I did, scroll down a couple posts.
11-20-2013, 08:16 PM   #12
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QuoteOriginally posted by Not a Number Quote
Originally posted by Pentaxpixie
Would you happen to know which contacts to isolate?
My guess would be the data pin, the 7th pin from the right in your photo. The tube has a "Ricoh" contact where the screw-drive shaft would normally be.
I tried sticking a tiny piece of electrical tape on the 7th pin, but the tube would not turn to lock when being mounted. I could get a cheap A 50mm that would keep automation and CIF, but after some first handheld tries at macro shots with the FA 50mm on the full set (67mm) of Kenko tubes, I doubt CIF would be much help. I really had a hard time managing focus even at f/11 or f/16. There was quite a bit of wind, but I still have to work on my technique, and build some DIY diffuser for the onboard flash.
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Last edited by pixie; 11-21-2013 at 12:09 AM.
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