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06-01-2011, 12:15 AM   #1
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? about extension tubes

Hi all,
I have bought some Pentax extension tubes. They have the single contact for stop down metering.......which one day I will work out how to use

I have 2 A lens that I would like to use with them, 50mm 1.2 and a 35-105 ( 1/3.5 ). Now I have put them together and put the 50mm on but should I be able to focus with the focus ring? I can twirl that little ring both ways in and out and it seems to make diddly squat difference? Am I missing some thing? some thing very basic

Should I be using the A setting ( all I get is ---F ) or the aperture ring? I have the setting in the menu set cause I can use both lens without a hassle.

Any advice?
cheers
Jan

06-01-2011, 01:03 AM - 1 Like   #2
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QuoteOriginally posted by ricstew Quote
I have bought some Pentax extension tubes. They have the single contact for stop down metering.......which one day I will work out how to use
I'm not sure what you mean by "single contact for stop down metering." Stop down metering (required for pK-mount lens with no electrical contacts) does not require any contact. An extension tube that supports pK-A mount should have 6 or 7 contacts as in this photo:



From what I know, Pentax has never made any extension tube with pK-A mount.

For now, I assume your extension tubes have pK mount.

QuoteOriginally posted by ricstew Quote
I have 2 A lens that I would like to use with them, 50mm 1.2 and a 35-105 ( 1/3.5 ). Now I have put them together and put the 50mm on but should I be able to focus with the focus ring? I can twirl that little ring both ways in and out and it seems to make diddly squat difference? Am I missing some thing? some thing very basic
An extension tube + lens combo does NOT focus to infinity. The point of using an extension tube is to focus at short (macro) distance. The lens's focus ring can be used, but it has very limited range. It's easier to focus by moving the whole camera setup back and forth.

QuoteOriginally posted by ricstew Quote
Should I be using the A setting ( all I get is ---F ) or the aperture ring? I have the setting in the menu set cause I can use both lens without a hassle.
A pK-mount extension tube can be used only with lenses with aperture ring. In this case, the combo lens acts as a pK-mount lens. You have to use it in stop-down metering mode: set camera mode to M, use the lens's aperture ring to control the aperture, and use the green button or the AE-lock button (depending on the camera) to meter (note: if the camera is of K series, exposure will be off big time).

If you use a pK-mount extension tube with a lens without an aperture ring (or with a pK-A lens with the aperture ring set at A), there is no way to control the aperture. It's always at the smallest aperture.
06-01-2011, 01:37 AM   #3
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QuoteOriginally posted by ricstew Quote
Hi all,
I have bought some Pentax extension tubes. They have the single contact for stop down metering.......which one day I will work out how to use

I have 2 A lens that I would like to use with them, 50mm 1.2 and a 35-105 ( 1/3.5 ). Now I have put them together and put the 50mm on but should I be able to focus with the focus ring? I can twirl that little ring both ways in and out and it seems to make diddly squat difference? Am I missing some thing? some thing very basic

Should I be using the A setting ( all I get is ---F ) or the aperture ring? I have the setting in the menu set cause I can use both lens without a hassle.

Any advice?
cheers
Jan
Are they Pentax or another brand? Do they have any pins? I have a set of King A rings with pins but needed to create another contact (from 6 to 7) to get A to work.
06-01-2011, 01:55 AM   #4
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QuoteOriginally posted by Bill_R Quote
I have a set of King A rings with pins but needed to create another contact (from 6 to 7) to get A to work.
No you don't.

All you need to do is to ground the seventh contact. If the flange of the extension tube is painted or anodized metal, you can just sand off the black paint to expose the bare metal surface. See this one (tip of red arrow):



In fact, 6 contacts (7th is grounded) is better than 7 contacts. SDM lenses don't work with extension tubes that have 7 contacts. You'll have to ground the 7th contact for SDM lenses to work.

06-01-2011, 02:34 AM   #5
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They say Asahi pentax japan, no's 1,2 and 3. There is a single pin that I can push down. I can achieve focus by moving the camera. K mount.....with a K5.
cheers
Jan
06-01-2011, 02:34 AM   #6
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QuoteOriginally posted by SOldBear Quote
No you don't.

All you need to do is to ground the seventh contact. If the flange of the extension tube is painted or anodized metal, you can just sand off the black paint to expose the bare metal surface. See this one (tip of red arrow):



In fact, 6 contacts (7th is grounded) is better than 7 contacts. SDM lenses don't work with extension tubes that have 7 contacts. You'll have to ground the 7th contact for SDM lenses to work.
Yes I did! Exactly what I did! I went from 6 to 7 contacts by creating the 7th by scratching away the paint exactly as you have posted.
I didn't join 6 and 7 if that was your interpretation. I created an additional, or 7th, contact.
06-01-2011, 05:02 AM   #7
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QuoteOriginally posted by ricstew Quote
They say Asahi pentax japan, no's 1,2 and 3. There is a single pin that I can push down. I can achieve focus by moving the camera. K mount.....with a K5.
cheers
Jan
with respect to focusing, using a 50mm lens, the course focus with an extension tube attached is achieved by moving the lens and camera closer to the subject. that is because the lens itself has only about 6mm of travel from infinity focus down to about 30cm (1 foot for the metric impared)

your smallest extension tube is normally aroung 12mm, which puts your focusing range between about 25cm (at infinity) and 200cm at minimum focus.

Extension tubes generally set your magnification,

you will find a macro focusing rail is a must when using extension tubes.

as for the "pins" show us the photo of the base. it sounds like they are K mounts with no contacts. to get focus confirmation you need this base to be conducting, and as others have indicated this may require removing paint, although if they are pentax tubes I doubt it
06-01-2011, 02:07 PM   #8
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Perfect Lowel.....that was the bit I was struggling with. They don't have contact pins just the locking pin ( my mistake in terminology )........now to work out the stop down metering bizzo....
cheers
Jan

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