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02-08-2011, 01:09 AM   #46
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QuoteOriginally posted by excanonfd Quote
Does the AF work at all with the Kenko tubes in macro mode, and to what degree - not that I see myself getting one anytime soon but I am curious about Kenko's own recommendation to use manual focus in macro mode.
I have the Kenko Uniplus Tube 25.
It is the only one I know that works.
It works without problems with SDM lenses. SDM-AF works.



02-08-2011, 11:38 PM   #47
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Thanks blende8 for the pictures - $80.00 for one 25mm extension tube, pretty expensive!
02-09-2011, 02:24 AM   #48
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QuoteOriginally posted by excanonfd Quote
Thanks blende8 for the pictures - $80.00 for one 25mm extension tube, pretty expensive!
That's actually amazingly cheap for a full function tube that really works. Especially considering it's so rare.
Try begging your dealer or Pentax for such an accessory for their own cameras at any price.

Otoh; walk into just about any store and you'd get a 3-tubes set of full autos for Canon, Nikon or Sony for similar money, and for C/N you could even have a choice of tube brand.

.R.
02-09-2011, 03:25 AM   #49
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in reflecting back on this, and a couple of other threads, it occurred to me that most people are probably happy with the current AF macto lenses, which are internally focused and can go to 1:1 without tubes.

Little do they know that the internal focusing really converts the lens to something shorter, probably half the nominal focal length at min focus.

02-09-2011, 08:18 AM   #50
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Can I get that again in English ?
02-09-2011, 08:53 AM - 1 Like   #51
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QuoteOriginally posted by spystyle Quote
Can I get that again in English ?
the focal length doesn’t stay the same at the full 1:1 magnification. say you have a 100mm 1:1 macro with IF. at 1:1, it will most likely be 50mm in focal length. you need 100mm extension to get a 100mm lens to magnify to 1:1. you only need 50mm for a 50mm lens. with internal focusing its easier to drop the focal length down to 50 to achieve the 1:1 than it is to extend the 100mm to a true 1:1. because, well it should be obvious that internal focus only has so much room inside the lens to achieve this, and its usually not enough to gain 1:1 at the stated focal length. how all this is done though is beyond me, im not an engineer by any stretch of the imagination.

Last edited by séamuis; 02-09-2011 at 08:58 AM.
02-09-2011, 02:52 PM   #52
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Interesting
02-09-2011, 04:53 PM   #53
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QuoteOriginally posted by spystyle Quote
Can I get that again in English ?
Actually seamuis Is close but not quite right

There are two types of macro, internal focus and focus through lens extension. Focusing by lens extension requires the lens be capable of extending to twice it's focal length I.e. A 100 mm macro needs to extend out from it's infinity position which is 100 mm from the focal plane to 200 mm or to grow by 100 mm in length. This is mechanically difficult and most 100 mm macros that focus by extension of the entire lens group only extend 50mm and give 1:2 magnification.

Internally focused macros change the focal length to focus, with the front element staying fixed. The net result is that while a 100 mm macro which is internally focused may go to 1:1 you will find the effective focal length at 1:1 is only 50mm. You can confirm this by checking the workin distance: 1:1 is always at a distance of 2x the focal length and an internally focused macro will donthis at 100 mm away from the subject where as a true 1:1 100mm macro will do this with a working distance of 200mm

02-09-2011, 06:01 PM   #54
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QuoteOriginally posted by Lowell Goudge Quote
...

Internally focused macros change the focal length to focus, with the front element staying fixed. The net result is that while a 100 mm macro which is internally focused may go to 1:1 you will find the effective focal length at 1:1 is only 50mm. You can confirm this by checking the workin distance: 1:1 is always at a distance of 2x the focal length and an internally focused macro will donthis at 100 mm away from the subject where as a true 1:1 100mm macro will do this with a working distance of 200mm
Thanks, I was going to ask you to explain all that, and now you have.

Can I presume the famous Zeiss 100mm to be a good example of a fully internal close [re]focuser, because they only push it to 1:2?

The working distance calc is the bit that always intrigued me, it's worth chasing and I've been meaning to do some serious measure tests with my Tamron 90, a well known lens for it's tromboning, v stock 50mm plus tubes setup.
I just don't know the bloody formulae for that.

Also I take it DoF alters respectively under these rules? That's one of important concern too, even though it's always small in this territory even little bit matters.

You raise a very interesting point, because we often get to read reviews and owner comments on such as the Canon 100 macro, with claims of its biggest "merit" over others being that it doesn't trombone (much), saying that to be better for user-convenience grounds - that it can't accidentally extend and strike the subject on AF, with zero mention of any real distance to subject or other tech differences in the comparison against others.

Yeah I ack that the Canon is a pretty sharp blade too, but I've never really seen telescoping-extending of a lens as a serious disadvantage myself (or can't Canon users physically adjust ), so long as acceptable IQ is possible, but DoF and working distance are always very valid areas for concern.

I suspect all this is not a universally understood principle, if known at all.

So to get to the point; what's your take on the mad_tromboner v full_internal shootout of designs, which is the natural better, or preference, for maximising DoF and W.D advantage?

.R.

Last edited by Hypocorism; 02-09-2011 at 10:32 PM.
02-09-2011, 08:16 PM   #55
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QuoteOriginally posted by Hypocorism Quote
So to get to the point; what's your take on the mad_tromboner v full_internal shootout of designs, which is the natural better, or preference, for maximising DoF and W.D advantage?

.R.
I can't be considered as unbiased here as I have 2 macro lenses, an SMC-M 100F4 and an SMC Takumar-Macro 50mmF4. Both lenses extend to focus and provide only 1:2 without extension tubes.

The pro's is that for example, the 100F4 with a 50mm Extension tube can give 1:1 at a working distance of 200mm, but also the image in the viewfinder gets dimmer ecause of the enlargment. An internal focusing 100mm lens will give 1:1 at a 100mm working distance, but will offer a brighter image in the viefinder making focusing easier. That is critical for AF lenses because lenses generally cant AF if the aperture (effective at focusing distance is much smaller than F6.7 therefore one could argue internal focusing is a mandatory requirement of AF

The con is loss of working distance.

For me AF is not important, my macros are all MF and since the focus sensors are much larger than the critical point you are focusing on, my take is that AF is not needed for macro any way and can as often as not, focus on the wring thing anyway.
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