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09-09-2012, 09:55 PM   #1
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Macro: Extension tubes vs teleconverterd

I understand you can achieve closer focusing with either but how do they work differently? Is on or the other better? Different circumstances for use?

09-09-2012, 11:06 PM   #2
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Teleconverters will not let you focus closer per se, but the lenses inside will change the angle of the light. Teleconverters will let you focus closer, while also increasing the circle of projection.

The key difference is that with a teleconverter, you put extra glass between the motive and the sensor/film, and that often has a bad impact on IQ. On the other hand, with the bigger projection, extension tubes will give a sensor of fixed size less lens surface area to play with, resulting in a decrease in resolution. My recommendation is, if you have a good teleconverter and a macro lens that's sharp corner-to-corner, use that teleconverter. If, on the other hand, you have a center sharp lens and a bad teleconverter, use extension tubes instead.

Last edited by topace; 09-09-2012 at 11:07 PM. Reason: Edited to say what I actually meant
09-09-2012, 11:39 PM   #3
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QuoteOriginally posted by topace Quote
The key difference is that with a teleconverter, you put extra glass between the motive and the sensor/film, and that often has a bad impact on IQ. On the other hand, with the bigger projection, extension tubes will give a sensor of fixed size less lens surface area to play with, resulting in a decrease in resolution. My recommendation is, if you have a good teleconverter and a macro lens that's sharp corner-to-corner, use that teleconverter. If, on the other hand, you have a center sharp lens and a bad teleconverter, use extension tubes instead.
Isn't it the other way around? A teleconverter only use the center part of the image circle, and extension tubes use full image circle but let you focus closer.
09-10-2012, 02:07 AM   #4
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Extension rings don't use the entire lens surface. It's easy to test. Just shine a light (motive) through a lens so that you get a circle on the other side (image). Now, move the lens closer to the light (extension tube) and watch the circle grow.

On the subject of teleconverters, however, I'm not quite as sure of my earlier statement. I do know some systems with teleconverters work better than the same system with the corresponding extension, so there must be some merit to putting all that glass in there. Maybe someone who knows more about optics than I do can explain it.

09-10-2012, 02:41 AM   #5
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can i know what is the suggested focal length of the lens for it to be paired with TC or/and tubes?or it doesnt really matter?
09-10-2012, 02:47 AM   #6
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QuoteOriginally posted by topace Quote
Extension rings don't use the entire lens surface. It's easy to test. Just shine a light (motive) through a lens so that you get a circle on the other side (image). Now, move the lens closer to the light (extension tube) and watch the circle grow.
Is't that just a sign of focus shifting when extending the lens further from the camera?
http://en.wikipedia.org/wiki/Circle_of_least_confusion
09-10-2012, 10:15 AM   #7
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Here's my take on this. It's uniquely Pentax because no other system has the F1.7x Auto Focusing Adapter (yeah, I know that Nikon had a version, but it's very fussy and often needs modification to even work) so the general common wisdom on this subject isn't really relevant in this very specific case.

I use the 1.7x AFA with my dedicated macro lenses (D FA 100 f2.8, A 50 f2.8, and Sigma EX 180 f3.5 APO DG) more than not. I will admit to being pretty much a dilettante in my macro shooting, but I enjoy it. I shoot critters mostly -- Jumping Spiders are my favorite.

The AFA apparently does allow closer focusing. Rough measurements show that the extra magnification is closer to 1.9x instead of the expected 1.7x, suggesting that the AFA allows a slightly shorter MFD in addition to the optical magnification. Instead of shortening the working distance, it actually allows greater working distance at the same magnification or greater magnification at close to the same working distance as the lens alone. Both of these are desirable situations IMO. By allowing greater working distance (subject distance from the fron element) live critters are less likely to become intimidated and on-camera flash angle is reduced, allowing even the pop up flash to sometimes be used without a lot of bouncing and contortions. The extra magnification is self explanatory. . . but shooting at a greater distance allows for deeper DOF with the same magnification as the bare lens.

Another advantage of the AFA is that AF-C becomes a viable focusing technique. The AFA has a limited focusing range on telephoto lenses since it was primarily meant as a means to allow AF with MF lenses once AF was introduced in Pentax bodies, and the most common lens at the time for SLRs was the normal (50mm) lens which does allow full range of focus with the AFA if the lens is set to infinity. At macro distances, the range becomes very limited -- only a few mm with the 100 and even less with the 180. This acts as a very effective focus limiter, and the full lock to lock focusing range is often within the length of a very small (4mm) subject. AF is very fast with the very light focusing elements in the AFA, and for me at least, I have a much higher keeper rate for walking subjects than any other technique. Jumping spiders don't stand still very often, as they are hunters, always looking for prey, and for me, handholding with AF-C and flash is my best bet for shooting them.

Argue the esoteric technical merits all you want, this works for me. . .

All of these were with the Sigma EX 180 + the AFA. Notice the DOF (length of the spiders estimated at between 3 and 4mm) and that in the last two, the spiders were walking (at least 3 of the feet are off the surface)







Maybe, since the AFA is so unique (and the market has made it so expensive) this might not be a consideration for most, but I think it's valid to add this to the discussion.

Scott
09-18-2012, 01:44 AM   #8
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Scott,

Nice shots! My own success with Pentax and macro hasn't been that good, though.Haven't given up, but ...

I have had some success with a Nikon V1, the FT1 adapter and the glorious AF-S 70-300 VR, plus a Canon 500D close-up lens. Auto-focus works great, and it is a small, easily handled package! The Canon screw-on lens converts infinity to 1/2 meter's distance, and has superb optical quality. Mostly shot ants, and flies, but spiders looks like a great subject! The Nikon lens on the V1 will roughly equal a 120-540 mm lens on my K-5, a dramatic save in price, bulk, and weight!

I've tried using my K-5 with a Tamron 70-200/2.8 (a lovely lens, if a bit noisy), with a similar close-up lens, and even that is not for fainthearted!


Last edited by Tord; 09-18-2012 at 02:26 AM.
09-18-2012, 05:08 AM   #9
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QuoteOriginally posted by Javaslinger Quote
I understand you can achieve closer focusing with either but how do they work differently? Is on or the other better? Different circumstances for use?
to be clear, as many of the explanations are somewhat misleading

Teleconverters are magnifying lens sets that go between the camera and lens to double the magnification of the image before it hits the sensor. Teleconverters DO NOT allow you to focus closer, that is a property of the lens itself, not the teleconverter. When you use a teleconverter you give up F Stops in proportion to the square of the magnification, i.e. a 1.4x converter costs 1 stop, a 2 x costs 2 stops etc. Also, as some have noted, teleconverter quality is highly variable, there are a lot of cheap ones out there. but there are also some good ones.

Extension tubes allow you to focus close, by moving the entire lens group away from the sensor. As they do this the image gets bigger because you can get closer. you also have light loss due to the increased magnification, but as you are not adding any optical elements image quality is usually better. all you see are the lenses' own flaws, not flaws multiplied by the TC. extension tubes are a little harder to use because you cannot focus to infinity, and each extension tube you put behind the lens has a different range of effective use.

there is a third, but rarer option. A macro focusing teleconverter. Vivitar made one, which combines a high quality teleconverter with a focusing helix, such that when used with a 50mm lens, yeilds 1:1 reproduction.

ALso note that when using a non macro lens for macro, you will not necessairly get high edge to edge sharpness. Macro lenses are specifically optimized to focus close and have a flat field behavior which is good for copying small flat objects, most normal lenses have a curved field of focus, so the enges are not always sharp when used in macro. this is not necessairly a bad thing, depending on the effect you are looking for. know about it and use it to your advantage creatively
09-18-2012, 08:54 AM   #10
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To add to what Lowell said:

A teleconverter will increase the focal length of the setup. To use an example, the SP Tamron 90mm Adaptall 2 macro was 0.5 to 1 macro. With a matched extension tube it was 90mm 1:1 macro. With a matched flatfield 2x converter, it was 180mm/5.6 1:1. That is the other issue. Flat field tc are better for use in macro work.
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