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04-08-2010, 01:49 PM   #1
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Extension Tubes

I have purchased a set of QualShot extension tubes and am having trouble getting them to work. I have the pentax adaptor and everything seems to fit together good, however, i just get a very very dark blurry screen on the viewfinder. I am in full manual mode..............just not working.............??????????????

04-08-2010, 02:06 PM   #2
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Is the lens attached set to wide open? The tubes can't be controled (or the lens) by the camera. If it's a screwmount (you said adapter) then set the lens to auto which will open it up fully. It should be bright through the VF assuming you are in decent light. Tubes will dimisnish the light a fair amount depending on the length.

If in Auto it's bright, then switch back to manual and turn the aperture to the widest setting (IE F1.4 etc). It should be equally bright. Then focus on the subject and stop the lens down to where you want it. Meter and shoot.
04-08-2010, 03:08 PM   #3
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Darkness & Blurriness

I tried those things -- i am stopped down on the ring to 2.8...........i do see some light coming in and out when using the ring on the Pentax 100 DFA.....but i still can't focus on anything.............very blurry???????????
04-08-2010, 03:22 PM   #4
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I assume the "QualShot extension tubes" don't have electrical contacts, worse yet, they don't have aperture coupling lever.

If that's the case, and if you use them with a lens that doesn't have aperture ring, the lens will be at its smallest aperture. That is probably f/22 or even f/32. Coupling with the extension tubes, the effective aperture can be something like f/64.

No wonder the viewfinder is so dark.

To use with lenses that don't have aperture ring, or have aperture ring set at A, you need extension tubes that have electrical contacts. In this case, the camera can control the aperture.

Extension tubes with electrical contacts can be hard to find. It's easier to buy teleconverters with electrical contacts and remove the optics to use as extension ring.

Or you can buy an inexpensive manual lens (e.g. Pentax-M 50mm f/2) to use with the existing extension tubes. In this case, you can open up the aperture, focus, then close down the aperture using the lens's aperture ring before hitting the shutter release.

04-08-2010, 04:41 PM   #5
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Ring

I am attempting to use these ext. tubes with the Pentax SMC DFA that does have a aperature ring.............
04-08-2010, 04:57 PM   #6
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With extension tubes, the focus ring on the lens has limited effect. You will need to focus by moving the whole setup back and forth.

Try the shortest tube in the set and see how it goes. Extension tubes make the viewfinder dark. F/2.8 on the lens is not really F/2.8 anymore. The effective aperture can be 1 - 2 stops slower.

You will get more helpful answers if you perform a simple test and provide clearer descriptions of your test.
04-08-2010, 05:09 PM   #7
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The effect can be quite significant and bring the focus point in really close. Put the lens really close to your subject and move the whole camera/lens assembly back to establish focus from there.
As SOldBear says start with the narrowest ring first and go from there. Stacking rings will make the view finder very dark and the point of focus extremely close.
04-08-2010, 05:34 PM   #8
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When you said "adapter" I incorrectly assumed that the entire setup was screwmount. But the subsequent posts have given you the right information. Your focus distance on the lens is 30CM (12 in) without tubes, so you are going to be much less than that, maybe half the distance to the subject.

Plus usually extension tubes are used with a non macro prime that is faster than 2.8 to allow more light in. As posted above, you may be loosing 2 stops, making the lens act like an f5.6. So combined with being close to the subject and shading the light, it will be dim in the veiwfinder.

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