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12-31-2011, 02:04 PM   #16
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A 50mm or shorter lens works too close for most living critters unless they're chilled and slow. 90-105mm are about the shortest I'd use for moving bugs. My mantids leave if I use anything shorter than 150mm, but they're smarter than the average bug.

12-31-2011, 03:33 PM   #17
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Back in July/August 2011 I posted a message about the effrect of loss of the reflection absorbing tube at the back of a SMCTak200/4. The effect to watch for in that case was a fogging of the middle of the image, which was visible on the image captured but not obvious through the view-finder. https://www.pentaxforums.com/forums/general-technical-troubleshooting/152972-...-function.html

Last edited by tim60; 12-31-2011 at 03:38 PM.
01-01-2012, 07:39 AM   #18
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RioRico wrote: A 50mm or shorter lens works too close for most living critters unless they're chilled and slow. 90-105mm are about the shortest I'd use for moving bugs. My mantids leave if I use anything shorter than 150mm, but they're smarter than the average bug.

Well... I do have a Pentax-A 35-105 f3.5 zoom. That could conceivably make a flexible macro lens for tube use.
01-01-2012, 08:30 AM   #19
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QuoteOriginally posted by GibbyTheMole Quote
I do have a Pentax-A 35-105 f3.5 zoom. That could conceivably make a flexible macro lens for tube use.
Conceivably, yes. It's an A-type lens so it would be most useful on A-type tubes, or on deglassed A-type TCs (probably cheaper). It will also work with dirt-cheap no-control macro tubes but using flash would be trickier. What you won't get is anything like flatfield sharpness. Center the subject and let the edges go to hell, fine. But don't expect it to do a good job shooting your stamp collection.

Just for ducks, think about this: The A35-105/3.5 has a 67mm front thread. I don't know if PK mount-reversal rings go that big, but a PK-58mm adapter and a 67-58mm step-down ring would let you reverse-mount the zoom. I've reversed an A35-80 and shot macro at all focal ranges. Yes, it gives edge-to-edge flatfield sharpness. A couple tricks: use a short bit of macro tube as a lens hood; and try a little extension on the reversed lens for a bit more magnification.

01-01-2012, 01:27 PM   #20
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QuoteOriginally posted by GibbyTheMole Quote
RioRico wrote: A 50mm or shorter lens works too close for most living critters unless they're chilled and slow. 90-105mm are about the shortest I'd use for moving bugs. My mantids leave if I use anything shorter than 150mm, but they're smarter than the average bug.

Well... I do have a Pentax-A 35-105 f3.5 zoom. That could conceivably make a flexible macro lens for tube use.
Removing the lens from a ~$10 PKA Teleconverter would give a nice macro range & work automatically but would likely have a small working distance at 1:1 - I'd guess a little less than 70mm.

Reversing the lens would result in a flat field lens, completely manual, with a somewhat better working distance at high mag; at 35mm 1:1 the working distance would be about 80mm

PS The working distance formula for a reversed lens is particularly simple. WD = 45 + focal.length/magnification
01-03-2012, 06:24 AM   #21
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QuoteOriginally posted by RioRico Quote
I've reversed an A35-80 and shot macro at all focal ranges. Yes, it gives edge-to-edge flatfield sharpness. A couple tricks: use a short bit of macro tube as a lens hood; and try a little extension on the reversed lens for a bit more magnification.
Hmmmm... I may give that a shot & see what happens. Thanks for the tip! - Bobbo :-)
01-03-2012, 07:16 AM   #22
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This is one area where being a Pentaxian is rather hair-shirty... I see Canonites have an autofocus auto-linkage tube (or tubes) available to them... as do Nikonians, and for God's sake Olympians of the four-thirds variety.

If anyone says the air inside a tube is better with a more expensive tube, don't listen! Except if said air is full of reflections, that is.
01-03-2012, 10:18 AM   #23
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QuoteOriginally posted by Nesster:
. . . being a Pentaxian is rather hair-shirty [lacking an] autofocus auto-linkage tube . . .
Personally, I've never considered the lack of auto-focus a handicap for close-up/macro use and suspect I'd spend more time verifying that AF had picked (auto-guessed?) the correct plane of focus and DoF than I ever did acquiring the intended point of focus the ol' fashioned way. I suspect the economics of shooting with higher ISO's and free "digital film" combined with instant review makes macro AF more attractive than it was when you had to wait to discover you'd missed the shot in the wet darkroom.

OTOH, a PK/A extension tube is convenient under certain conditions but easily fabricated from an inexpensive TC with PK/A pins.

H2

01-03-2012, 01:05 PM   #24
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IMHO macro AF can be somewhat useful when shooting a flat subject field at a right angle. But you'll still get better focus using LiveView. AF in a macro lens is for when the lens is used at non-macro scales. So If I blew my wad on a DFA100WR I'd use the AF when shooting faces, not fungal spores.

Yes, an A-type tube or deglassed A-type TC is quite useful for shooting close|macro with an A-type or AF lens, for open-aperture metering and pTTL flash. And I've elsewhere suggested a MAKE-type project: Get an A-type TC, and any cheap bellows (PK or not) with screw-on mounting plates. Remove all the mounts; put the mounts from the TC onto the bellows. Solder wires between the pins on the A-type mounts. Voila! You now have a rare and valuable A-type bellows! Be the first on your block!
01-03-2012, 05:20 PM   #25
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That sounds like a much more useful trick on a camera system with electronic aperture control. (To be more clear: The camera controls the aperture mechanically on all versions of K mount, your modified bellows won't make that work.)
01-03-2012, 05:20 PM   #26
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I have a 35 year old set 4 screw 12-21-31mm made by Pentax. I have hung a 21/2 lb 70-210 Kiron f4 macro on them and no adverse effect on them. At 210 and all three hooked up about 1/16" to the subject and the DOF is so thin I can only focus on one letter on a silver quarter at 45deg. angle.
01-04-2012, 07:16 AM   #27
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QuoteOriginally posted by pacerr Quote
Personally, I've never considered the lack of auto-focus a handicap for close-up/macro use and suspect I'd spend more time verifying that AF had picked (auto-guessed?) the correct plane of focus and DoF than I ever did acquiring the intended point of focus the ol' fashioned way
I agree with that; however, it seems nearly every other month Pop Photo has an article where someone puts a tube on a long-ish Canon lens in order to get a closer non-macro focus, for birds or leaves or some other stuff. That application isn't available to us.
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