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06-03-2010, 04:10 AM   #1
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macro, macro

I've found the Tamron 90mm F2.8 macro combined with a 25mm Kenko uniplus tube (extension tube with electrical contacts) is a good combination for 1:1+ macros. Not sure on how much greater than 1:1 it is, but since the Tammy is already 1:1 it has to be greater. Unfortunately the combo isn't suitable for hand holding, the DOF is so thin that you need a tripod. Here are a few samples, all taken with the K20D.



popup flash used as a fill flash on this one




NaCl(for my next trick, I'll try adding a Raynox 250 to the mix)H2O

06-03-2010, 11:59 AM   #2
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Great shots
06-03-2010, 12:08 PM   #3
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Great shots
i can not find 25mm Kenko uniplus tube in the market
06-03-2010, 12:44 PM   #4
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QuoteOriginally posted by koper Quote
Great shots
i can not find 25mm Kenko uniplus tube in the market
Koper, it's not an easy part to find, I searched e-bay and here and keh etc for months, and then found it around the corner on craig's list. But it's very nice because it has the electrical contacts, not that I use the AF, but being able to adjust aperture from the thumbwheel is very nice.

NaCl(keep looking, also check for extension tubes with contacts)H2O

06-03-2010, 01:28 PM   #5
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Love the shots! Want to try the combination myself after seeing your work.
Wish the Kenko tube was easier to find.
06-03-2010, 01:32 PM   #6
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QuoteOriginally posted by Thrasis Quote
Wish the Kenko tube was easier to find.
It's been said before, but worth repeating: it's easier to find a teleconverter with electrical contacts (pK-A mount). You can then remove the glass to make it an extension tube.

06-03-2010, 02:51 PM   #7
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QuoteOriginally posted by NaClH2O Quote
I've found the Tamron 90mm F2.8 macro combined with a 25mm Kenko uniplus tube (extension tube with electrical contacts) is a good combination for 1:1+ macros. Not sure on how much greater than 1:1 it is, but since the Tammy is already 1:1 it has to be greater.
IIRC, MAG = (TL-FL)/FL where MAG is magnification, TL is total length, and FL is lens focal length. So here you have a 90mm lens; at 1:1, its extension is also 90mm so the total length is 180mm. Your 25mm Kenko extension gives at total length of 205mm, so magnification= (205-90=115)/90 = 1.28:1 -- a slight boost.

For significantly greater magnification, you either need much more extension, or reverse-stack a shorter lens onto a longer one... but if the Tammy 90 is anything like my Viv 90M/2.8, that's not really feasible. But the Raynox 250 clipped onto the Viv macro sure makes a difference! That puts it in the neighborhood of 2:1.
06-04-2010, 04:30 AM   #8
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QuoteOriginally posted by RioRico Quote
IIRC, MAG = (TL-FL)/FL where MAG is magnification, TL is total length, and FL is lens focal length. So here you have a 90mm lens; at 1:1, its extension is also 90mm so the total length is 180mm. Your 25mm Kenko extension gives at total length of 205mm, so magnification= (205-90=115)/90 = 1.28:1 -- a slight boost.

For significantly greater magnification, you either need much more extension, or reverse-stack a shorter lens onto a longer one... but if the Tammy 90 is anything like my Viv 90M/2.8, that's not really feasible. But the Raynox 250 clipped onto the Viv macro sure makes a difference! That puts it in the neighborhood of 2:1.
Thanks for that RioRico, was not sure how to calculate the magnification. 1.28:1 doesn't sound a lot greater than 1:1 but there sure seems to be a pretty big difference when looking thru the camera viewfinder. When I get my Raynox 250, I'll do another "experiment".

NaCl(any more macro than that would have to be a microscope)H2O

06-04-2010, 04:34 AM   #9
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QuoteOriginally posted by SOldBear Quote
It's been said before, but worth repeating: it's easier to find a teleconverter with electrical contacts (pK-A mount). You can then remove the glass to make it an extension tube.
Thanks SOldBear, hadn't thought of that! And there being a bunch of "auto" t/c's available, they'd be a lot cheaper too. Is there any tube constriction?

NaCl( get a handful of then and have a macro, macro, macro, macro, macro Macro!)H2O
06-04-2010, 11:24 PM   #10
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I haven't had a chance to muck around with my M42 gear for a bit.

But I managed to get an extension tube set cheap ... and also managed to get a reversing ring as well ... pretty much more of the Taks available are the same filter ring size as well.

I just got a Macro Tak 50/4 .... so now I am tempted to reverse the 28/3.5 on it and see waht I can get.

But so far I have reversed the 28/3.5 on the 35/3.5 ... and the magnification was a lot more than I thought. I took a shot of earphones ... and I could get it all in the frame ... I need to find something a lot smaller with detail to get it in frame.

I had a thread a while back ... but I can't remember what I called it ... and where I posted it.
06-05-2010, 04:08 AM   #11
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A convenient way to do the math is:

Magnification_change=Extension_change/focal_length

In this case,
Magnification_change = 25/90 = 0.28

This is fundamentally no different than the earlier posting, just easier to do mentally.
06-05-2010, 10:16 AM   #12
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QuoteOriginally posted by Mechan1k Quote
But so far I have reversed the 28/3.5 on the 35/3.5 ... and the magnification was a lot more than I thought.
The strength of magnification is in terms of diopter, which is the inverse of focal length (in meter). Thus the 28mm is 1/028 = 35 diopters and the 35mm is 1/0.035 = 29 diopters.

For comparison, the Raynox 150 is 4.8 diopters and the Raynox 250 is 8 diopters.
06-05-2010, 11:39 AM   #13
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new focal length

QuoteOriginally posted by SOldBear Quote
The strength of magnification is in terms of diopter, which is the inverse of focal length (in meter). Thus the 28mm is 1/028 = 35 diopters and the 35mm is 1/0.035 = 29 diopters.

For comparison, the Raynox 150 is 4.8 diopters and the Raynox 250 is 8 diopters.
That is correct.

A way to understand what's going on in general is that stacking 2 lenses, focal length f'+focal length f", creates a new lens with a focal length of:

f = f'*f"/(f'+f")

This and the distance of the "new lens" from the image plane is sufficient to estimate magnification, which is

M = (lens_to_image_distance/lens_focal_length) - 1

These two formula are sufficient to estimate magnification etc with complex arrangements of extension tubes, preliminary magnification, multiple combined lenses, etc.

There are many other short cut relationships for special cases like when the primary lens is on the camera and focused at infinity, but the above two equations cover all such special cases.

Dave

The next level of precision is a usually small correction for distance between the stacked lenses, d, and isn't much more complex, simply:
f=f'*f"/(f'+f"- d)

http://en.wikipedia.org/wiki/Lens_(optics)

Last edited by newarts; 06-05-2010 at 12:08 PM.
06-05-2010, 03:46 PM   #14
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QuoteOriginally posted by Mechan1k Quote
I just got a Macro Tak 50/4 .... so now I am tempted to reverse the 28/3.5 on it and see waht I can get.
My MacTak 50/4 arrived a couple days ago. I just now reverse-stacked a SMC-M 28/2.8 on it and I got... an image circle, because the MacTak's objective is inset so far. For stacking, you need lenses' objectives as close together as possible.

QuoteQuote:
But so far I have reversed the 28/3.5 on the 35/3.5 ... and the magnification was a lot more than I thought.
Your magnification there is 35/28 = 1.25x. If I stack my 28 onto my SuperTak 55/1.8 the magnification is ~2x. Oooh, it's great to have many lenses with 49mm front threads! I now use a Hanimar 135/3.5 or Meyer 100/2.8 as a primary, and Takumars 55, 35 or 28 as secondaries -- 135/28 = 4.8x. If I put the 135 on 90mm extension for a total 225, magnification is ~8x. And the effective aperture is somewhere past f/100. Eat your heart out, Ansel!

Let's see, how extreme can I go without a bellows? My SuperTak 200/4 with 58-49 reducing ring, on 120mm of tubes, stacking a Vivitar 24/2 with 55-49 step-down ring, should have magnification of 320/24= 13.3x -- that should be enough to see reflections in an ant's eye, eh?
06-12-2010, 01:42 PM   #15
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Bugger about that with the Macro-Tak ... oh well ... back to reversing my other Taks ... or use my M42 extension tubes on the Macro-Tak.
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