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07-29-2015, 02:26 PM   #1
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Using catch in focus on manual lens with macro extension tubes

Hello,
Iím a macro beginner trying to avoid investing in macro lens just yet, maybe a used one at some point. Iíd like to work beyond 1:1 and have a few questions please:

Iíve been experimenting with my Pentax SMC 50mm 1.4 lens (w/ K-5iis) on a set of Pentax auto extension tubes. Catch in focus works pretty well with my autofocus lenses set to manual, also works well with the manual 50, lens only Ė but less well with the extension tubes. I find myself moving back and forth trying to achieve focus confirmation to trip the shutter. I suspected it might be because less light is reaching the sensor, (More extension diminishes light, right?) but the technique becomes frustrating. I realize that focus is more difficult to achieve as such close range. Can anyone help me understand how to more successfully use catch in focus with macro extension? Is there a better way?

Hope these next questions don't sound stupid, but here goes: If the 50mm is mounted on extension tubes, does that alter what focal length I select after turning on the camera? Iíve been selecting 50 for obvious reasonsÖ Does the amount of extension matter here? What if the 50 mm is reversed, still select 50 as its focal length?


Thanks very much!
Bob

07-29-2015, 02:35 PM   #2
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sorry I can't help. Bit was wondering if you could help me. How do you use catch in focus with an auto focus lens. Or do you mean lenses where you can set the lens itself to manual?
07-29-2015, 02:42 PM   #3
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The same thing used to happen to me. There is a point when it is too dark for CIF to work.
07-29-2015, 03:03 PM   #4
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QuoteOriginally posted by sergysergy Quote
The same thing used to happen to me. There is a point when it is too dark for CIF to work.
Ditto, when I was trying this. Tubes make for little light - even though the lens may still be set at f/8 its effective aperture is higher. Which makes CiF fail. See here for a calculator.

07-29-2015, 04:10 PM   #5
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What tubes , ?

Are you using Tubes less aperture levers ? If so , buy some Auto tubes ( Extension Tubes with aperture levers ) ...
The other thing to try , is an eye cup .. The eye cup will block more ambient light so you can see thru the lens better ...
Or a magnified eye cup ? ( Perhaps )
07-29-2015, 04:35 PM   #6
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So CiF doesn't ever get triggered? Try with really good light, just for an experiment. And a contrasty subject. Tubes make you lose some light, but you would have to be using a lot of them for a f1.4 lens to fail CiF.
Because yes, CiF needs enough light. And also contrast. And it only works with centre point. And it needs to be sightly steady - if the frame is shaking too much, it won't find focus.

But I think for macro work, people usually use MF and a high aperture (for DoF), with artificial light. Because ultimately, macro is just really close focus. On macro lenses, you just twist focusing ring all the way to nearest, and then focus by moving closer or further, and only use the focus ring for tiny adjustments.

That said, getting good light, focus and DoF is the hardest part of macro photography.
07-29-2015, 05:26 PM   #7
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QuoteOriginally posted by rob_k20d Quote
sorry I can't help. Bit was wondering if you could help me. How do you use catch in focus with an auto focus lens. Or do you mean lenses where you can set the lens itself to manual?
Yes, the lens itself must be set to manual.

I appreciate all the responses - CiF is a great tool but not a silver bullet in macro. With lower light, complete manual focus seems to work better as long as the subject isn't moving.

Macro = easy to try, hard to master...
07-29-2015, 06:47 PM   #8
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Also think - "my opinion only" it is far easier to get manual focus with after market focus screens - the standard Pentax screens don't seem to help me.

Pity "Katzeye" out of business - I had their screens & they were fabulous with K7 & K5.

08-01-2015, 07:53 AM   #9
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Low light can be a problem with CIF, but I've never had that happen unless it is really dark. The main problem with tubes is if they are painted at the camera side mount you will need to scrape the paint off to get the contacts grounded or the CIF will not work. Had to do this with my vivitar tubes.
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