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09-28-2007, 04:12 PM   #1
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AF Ext Tubes

If these Ext tubes at Adorama are AF, how come the normal contacts are not at the bacl of the lense? Are they or not AutoFocus.

AEXTUBEPK Kenko Auto Extension Tube Set for the Pentax AF Mount.

Thanks

09-28-2007, 04:31 PM   #2
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i'd ask adorama..
these are not listed as AF according to the review. i doubt that AF could be achieved with EX tubes because of the amount of light fall off. AF with macro is more of a PITA than using MF. iwould ask them about the listing tho.
09-28-2007, 05:22 PM   #3
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Auto doesn't mean autofocus.

It means that the tubes have the stop down lever, so that you meter at full aperture, and the camera can stop the lens down during exposure.

This implies that any lens attached would work as if they were "M" or "K" lenses.
09-29-2007, 05:08 AM   #4
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Thank you Roy and Ole

09-29-2007, 05:19 AM   #5
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Ole is correct and they would have to have the drive screw and some contacts to be AF. But with extension tubes there would be little point. The best focus is manual anyway. I have a set of Vivitar tubes from Ebay that cost $38. They are basically the idential tubes and work great. If you look around you can save yourself at least $90-100 from that price. The other thing you can do is buy a cheap K mount 2x converter and remove the glass. It would give you one extension around 40-50mm for about $10-20. Add a 50mm lens and you're shootin macros! Works just the same.
09-29-2007, 02:13 PM   #6
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Damnnnnnnnnnnnnnnnnnnnnnnnnnnn Why didn't I remember that. Just got rid of a worthless TC.
09-30-2007, 06:59 PM   #7
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The Kenko Uni-plus 25 extension tube has the screw drive for af, and all the A lens contacts. Af isn't much use for macro, but is very useful for bigger af tele lenses. It reduces the min focus by a few feet in that case. Thinking birds and other small animals here.
Taking the glass out of a teleconverter doesn't always work as an extension tube. Some converters use pretty small glass elements and without them there is a chance of vignetting. Try to pick a converter with large glass elements all the way through.
thanks
barondla
09-30-2007, 07:06 PM   #8
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QuoteOriginally posted by Peter Zack Quote
Ole is correct and they would have to have the drive screw and some contacts to be AF. But with extension tubes there would be little point. The best focus is manual anyway. I have a set of Vivitar tubes from Ebay that cost $38. They are basically the idential tubes and work great. If you look around you can save yourself at least $90-100 from that price. The other thing you can do is buy a cheap K mount 2x converter and remove the glass. It would give you one extension around 40-50mm for about $10-20. Add a 50mm lens and you're shootin macros! Works just the same.
yup,
got mine for $19.03 delivered.

10-01-2007, 05:53 AM   #9
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I don't get it and am a little confused - what can I do, got a small brain.

Here's a another link - Kenko Pentax AF Automatic Extension Tube Set Macro - (eBay item 180162934697 end time Oct-04-07 08:36:25 PDT)

The seller says "Yes, they are AutoFocus; hence AF".
Is this the uni-plus of which Baron speaks?

Roy, what did you get for 20 bucks delivered - the TC or the Tubes?

Thanks
jc
10-01-2007, 06:26 AM   #10
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QuoteOriginally posted by barondla Quote
The Kenko Uni-plus 25 extension tube has the screw drive for af, and all the A lens contacts. Af isn't much use for macro, but is very useful for bigger af tele lenses. It reduces the min focus by a few feet in that case. Thinking birds and other small animals here.
Taking the glass out of a teleconverter doesn't always work as an extension tube. Some converters use pretty small glass elements and without them there is a chance of vignetting. Try to pick a converter with large glass elements all the way through.
thanks
barondla
Barondla is right about the element size on a converter so if you go that route just look for one with a larger glass element. A lot of pawn shops etc have them so you can see it for yourself.

QuoteOriginally posted by JCSullivan Quote
I don't get it and am a little confused - what can I do, got a small brain.

Here's a another link - Kenko Pentax AF Automatic Extension Tube Set Macro - (eBay item 180162934697 end time Oct-04-07 08:36:25 PDT)

The seller says "Yes, they are AutoFocus; hence AF".
Is this the uni-plus of which Baron speaks?

Roy, what did you get for 20 bucks delivered - the TC or the Tubes?

Thanks
jc
Here's a link to the correct version with all the right contacts and drive screw:

Pentax Forum: Extension tubes with K10 - photo.net

If you compare the 2 you'll see that they look like different versions.
10-01-2007, 08:21 AM   #11
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Many companies say af meaning it will work with af camera. Not meaning it will actually af. Only tube I have seen that does af is the Uni 25. Wish they made a set of them. Tried two uniplus 25 tubes together. They don't af well. To much friction between all the drive screws! Not built to the same level as drive screw in good lens.
thanks
barondla
10-02-2007, 08:18 AM   #12
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Thanks a lot guys. Your input and suggestions are ALWAYS helpful.

I really don't know why I got it in my head for AF tubes but collectively you have definately sail "manual focus" is the way to go.

You may not see immediate results for your efforts but they definately will come.

Thanks again.
jc
10-03-2007, 05:06 PM   #13
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It also mentioned in the link on Adorama this about the extension tubes

Kenko's Auto Focus extension tubes are designed with all the circuitry and mechanical coupling to maintain auto focus and TTL auto exposure with most Canon, Nikon, and Minolta lenses given there is enough light to activate the cameras AF system properly.

So by the looks of it ... nothing for Pentax to allow AF.
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