100mm Macro and exension tube !!

[Sendide]

Hi everubody,
what would be the effect of an extesion tube EF-25 on a canon macro lens 100mm USM? I read somewhere online that it gives 1:1.36 or so. but wil you have this ratio at the same distance from the subject or will you have to be closer?
has anyone experienced this setting or equivalent please?

thanks for your help
Khalid

[DaveG]

Hi everubody,
what would be the effect of an extesion tube EF-25 on a canon macro lens 100mm USM? I read somewhere online that it gives 1:1.36 or so. but wil you have this ratio at the same distance from the subject or will you have to be closer?
has anyone experienced this setting or equivalent please?

thanks for your help
Khalid

The lens is still a 100 mm and will retain the magnificatiion of a lens of that length, even with an extension tube. The only way to increase the size of the subject - without changing the lens's focal length - is to get closer. That's what the tube does, it lets you get closer and still allow focusing.

If you used an extender (teleconverter) then the focal length would change depending on which one you chose, the 1.4X or 2X. This would change the magnification size without changing the minimum focusing distance. If you keep the lens/camera in the same in the same "focused as close as we can get" position introducing the an extender would increase the magnification and the subject image would be larger on the groundglass.

But I think that the previous "extender" paragraph, is a solution in theory rather than in practice. You lose two stops (2X extender) and it will not be the sharpest tool in the box. An extension tube is a better solution, if in fact you need anything solved. The 100 macro will focus down to 1:1 now and if you are using it on a 10D it's effectively a 160 mm lens. That should let you stand off from the subject and still get 1:1.

Where greater than 1:1 is important is when your subject is quite small or if you need to make huge prints and want to use all of the capture that you can. But the downside of the tube is that you get even shallower depth of field and will lose even more light to the bellows factor than the lens naturally will lose when focused to 1:1. You also lose your ability to focus to infinity while the extension tube is aboard and this can be a bit of a pain.

If you have access to this tube I'd suggest that you try it out to see if you like it. It may well cure one problem while introducing a few new ones.

[Sendide]

Thanks Dave,
your explanation is very helpful.
just in case you have experienced onther trick or have an idea about it : using the canon 100mm MAcro USM with the canon 50 mm f:1.4 USM inverted on the top of it : will that interfere with the distace to the subject on focus, cause that is very important to me (small bugs and insects)?
regards
Khalid

[DaveG]

Thanks Dave,
your explanation is very helpful.
just in case you have experienced onther trick or have an idea about it : using the canon 100mm MAcro USM with the canon 50 mm f:1.4 USM inverted on the top of it : will that interfere with the distace to the subject on focus, cause that is very important to me (small bugs and insects)?
regards
Khalid

I have no idea how that would work. But reversing a lens usually means that
you've gone to magnifications well beyond macro into micro ranges.

I wonder how you would control the aperture in reversed lens like a 50? In the
old days you would take lens like a 20, reverse it and have a neat little micro
lens. But the lens would either stay at the aperture you selected, or you could
flick the aperture lever over. I don't see how you'd do this with a reversed
Canon AF 50mm lens. Perhaps you just rely on the conventionally mounted 100's
aperture to do the work, with the 50 wide open, if you can tie them together.

If you do have a lens to lens adapter it's worth a try just to see what kind of
trouble you can get into :P But I don't think that I'd spend lots of money before
I saw how it'd work.

If you plan on doing a lot of this kind of shooting you might want to have a look
at the Canon MP-E 65mm f2.8 lens. It will offer up to a 1:5 magnification. It isn't
cheap - $820US from B&H - but it should do the job.

[Scottes]

A couple of differences between extension tubes and extenders like the 1.4x and 2x is that the extenders will still allow you to focus at infinity and do not change the minimum focus distance. With an extension tube you will be able to focus closer, you lose some light but not as much a TC. Extension tubes have no glass - they're hollow tubes - so do not distort the image like TCs will.

With the 100mm Macro you will not be able to use either of the Canon TCs - they have a protrusion so they just will not fit on the 100mm. Third party TCs, like Kenko, will fit but they are not as good as the Canon in either optics or build quality. They are much cheaper, though.

If you're looking for insects then a kenko TC may be your best bet. Since it won't change the focus distance you don't have to get closer to achieve 1:1- in fact with the 10D you could max at 1.96:1 with a 1.4 TC. Since the 100mm has a fairly close focus distance to achieve 1:1 the TC will actually allow you to back off and still achieve 1:1. I don't like the idea of putting Kenko glass in front of the great Canon 100mm though.

However, take a look here (http://www.bobatkins.com/photography/eosfaq/closeup.htm) for a chart from Chuck Westfall comparing magnification and working distances using extension tubes or the Canon Close-Ups lenses (diopters) models 250D and 500D.

If you thought about a Close-Up lens the 250D would be the one for the 100mm Macro. But I wouldn't recommend it since it allows (ie; forces) you to focus much closer. Not good for insects.

Putting the Canon 25mm extension tube on your 100mm Macro would yield up to 1.38x magnification - the same as the 1.4 TC without but without any inferior optics in the way, and less light loss. Your minimum focus distance is changed slightly - from 1' to about 9" - and with the 10D you're at almost 2:1 - which is a fly filling the frame. So if you're looking for bees, fo example, you can back off quite a bit and still have it fill the frame. For dragonflies or butterflies you can be back several feet and still fill the frame.

I'd recommend getting a set of Kenko tubes - you'll get 3 tubes (12, 20, and 36) for the same price as a Canon EF25 II. I've never heard of anyone complaining about the Kenko tubes, or ever having problems with them. You'll get much more flexibility with a set like this.

[karusel]

Excellent link, Scottes! :wink:

[Sendide]

Thanks Scottes, it's worth it to check the kenko tubes, the 65mm Macro from canon is very tempting too, even its relatively expensive price.... :cry: ,
any experience with that?
I know I'm asking a lot , sorry , but in this forum at least, you get the answer from experienced people, not dealers .... who try just to sell ....

regards

Khalid

[karusel]

Quite incidentally I ran across this thread (http://www.fredmiranda.com/forum/topic/80925) at fredmiranda. Check it out.

[jyrgen]

With 50mm reversed on top of another lens, the working distance is very small, few centimetres. Since it works reversed to it's normal way, your subject is at the distance where usually film or sensor is. Which means it's difficult, but not impossible, to work with insects and other subjects that tend to fly away.

As for aperture and focusing, usually you leave it wide open as it is and focus to infinity, and use your main lens to determine aperture and focus of the combination. 50 f/1.4 is so bright though, that you can stop it down somewhat, if you wish (to improve sharpness?), without getting vignetting. I have used 17-40 f/4 as reversed part and it was possible to get vignetting-free combinations, too.

The reversing method is certainly worth trying, you can reach great magnifications. But short working distance renders it impracticable for moving things, I'm afraid. However, looking at Mark Plonsky's work (http://www.mplonsky.com/photo/article.htm), I am obviously wrong :roll: