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Galah
02-26-2009, 05:59 PM
They are two different birds built to acheive two different aims.

A teleconverter magnifies the image, but actually reduces close focusing ability. They are used to decrease the angle of view; usually of a lens that is already at least a medium-long lens. They are not made for close-up photography. They contain optics. Infinity focus is maintained.

I have only screwed around with dipoters; never taken a pic with them, so I am not sure if they cut light to a notable degree or not, but I don't think that they do.

Dear 2F/2F,

Thanks for contributing.

As I understand it, the teleconverter retains the original minimum focus distance of the lens to which it is attached and magnifies the image: the net effect is an enlargement similar to that obtained by an extension tube of the same length as the teleconverter, but without loss of working distance. Whether the image quality is the same for both appears to be a moot point. Both result in light loss.

As far as I know, a diopter lens has the advantage of no light loss.

wayne naughton
02-26-2009, 06:12 PM
extension tubes on a close focusing mid tele is perfect for me.....plenty of space between lens and subject, cheap and portable closeup kit, great for flowers and larger insects.cheap and midrange teleconverters are a waste of money IMO.

AgX
02-26-2009, 06:20 PM
...the net effect is an enlargement similar to that obtained by an extension tube of the same length as the teleconverter, but without loss of working distance.


The lenght of the extension ring (or bellows) forms an additional extension of the lens.

The lenght of a tele-converter is of no interest. What is of interest is its magnification factor. This depends on the optics of a tele-conveter, not of its length.
(Today typical factors are 1,4 and 2)

Michel Hardy-Vallée
02-26-2009, 06:26 PM
As I understand it, the teleconverter retains the original minimum focus distance of the lens to which it is attached and magnifies the image: the net effect is an enlargement similar to that obtained by an extension tube of the same length as the teleconverter, but without loss of working distance.

Yes and no: your 50mm lens with a 2x teleconverter will have the angle of view of a 100mm lens. Its close focus and infinity focus distances remain the same.

Tubes or bellows increase the minimum focus distance, so you can get closer to your subject than you could with the lens alone. But the angle of view of your 50mm on extensions remains the same, AFAIK.

The difference between the two, in the range of situation where they can give you the same magnification, is thus one of perspective. So yes, the results are "similar" in terms of magnification, but no, they are "different" in terms of perspective (cf. a portrait shot with a 24mm v. one shot with an 85mm).

With the teleconverter, you could fill up the picture frame with the flower, from a distance of, say, 2m. With the tubes, you could fill up the picture frame with the flower, from a distance of, say, 0,5m.

I suppose that the people those who use both TC and extensions together do so because their subject require to keep a certain working distance, and they do not have the money to buy the more expensive, longer-focal macro lenses (Nikon, for e.g., has a 50mm, a 105mm, and a 200mm).

At least that's how I understand it.

David A. Goldfarb
02-26-2009, 06:48 PM
Another issue with a teleconverter is transmissive light loss. A good 2x converter usually has seven elements, and a cheap one has four elements. A seven element converter will often have a half stop light loss in addition to the two stop loss due to doubling the focal length while maintaining the same physical aperture diameter, and if you use non-TTL auto flash or a handheld meter, you need to account for it. TTL metering will take of it.

One situation where people might combine an extension tube and a teleconverter is bird photography, because you are often photographing small subjects with a really long lens that isn't long enough, and if you're lucky, you can be closer than the near focusing distance of the lens, so if you've got a 600mm lens and want to photograph something the size of a sparrow, you'll need a teleconverter, and if you can get within 12 feet, you'll probably need an extension tube.

Galah
02-26-2009, 06:59 PM
Hi all,

This is terrific folks, just what I was hoping for: a lot of information coming in.

Can someone, please, post in some pics/links illustrating some of the above points?

Keep them coming.

Thanks.:-)

2F/2F
02-26-2009, 06:59 PM
I did not know that the base lens' close focusing distance is maintained when using a TC. You learn something new every day on this forum. I guess if a TC is just magnifying the center portion of what is being projected by the base lens, this makes perfect sense.

glbeas
02-26-2009, 07:20 PM
Some companies built medium to longish focal length lenses on short mounts meant to be used on a bellows so you could focus at infinity as well as in to macro distances. I don't know if there are any recent or current models being made though.

Q.G.
02-27-2009, 04:33 AM
I did not know that the base lens' close focusing distance is maintained when using a TC. You learn something new every day on this forum. I guess if a TC is just magnifying the center portion of what is being projected by the base lens, this makes perfect sense.

That's (almost*) exactly what it does.

(* it magnifies the entire image projected by the prime lens, but since the film size remains the same, and there is a lot of vignetting ... ;) )


It has been mentioned that teleconverters do not affect working distance, and that the physical length of such a thing does not matter.
But they do and it does: the front lens is moved closer to your subject by the length of the converter.
In 'normal' photography not a big deal. But it can be in close-up photography.


The extra loss of light David mentiones should only occur in uncoated converters. Put a decent coating on their elements, and that extra light loss is negligible.


Diopters work by reducing the focal length of the combined optical system. The lens' physical extension obviously is not affected.
And same amount of extension + shorter focal length = closer focussing distance.
The good thing is that they indeed do not lead to a loos of light. The bad thing that the thus changed lens loses its correction.
Diopters are quite usuable when not trying to get too close. But the closer you get, the worse these thingies are.

2F/2F
02-27-2009, 04:49 AM
That's (almost*) exactly what it does.

(* it magnifies the entire image projected by the prime lens, but since the film size remains the same, and there is a lot of vignetting ... ;) )

Indeed; that is what I meant: As far as what the film sees is concerned, the center portion is it.

Good to know. I have only ever used a TC when looking for more reach. Time to experiment.

I want to correct my first post where I state that TCs reduce close focusing ability. I simply assumed this to be the case.

dynachrome
02-28-2009, 09:09 PM
There are some exceptions to the claims made about teleconverters. I have the 90/2.5 Vivitar Series 1 macro lens in Canon FD mount. The lens goes to 1:2 by itself. You can use simple extension tubes to get to 1:1 or you can use the 1:1 converter made for the lens. The converter does not allow the lens to focus to infinity but provides excellent quality at 1:1, with some light loss. I have the Vivitar 2X Macro Focusing Teleconverter in mounts for several different camera types. How well it works depends on the lens you attach it to and your magnification. The Panagor Auto Macro Converter has fewer elements and allows focusing only in the close-up range but also provides decent performance when attached to a 50mm standard lens of moderate speed. If you use an f/1.4 or f/1.2 lens, performance will suffer.

If I use my Canon Bellows FL with the 100/4 Canon FLM bellows lens I can shoot subjects at various distances. For slower work an enlarging lens on a bellows can also give good results. I have used the Vivitar 90-180 f/4.5 Flat Field Series 1 lens with the Konica Hexanon 2X teleconverter to give me 1:1 magnification at the 180mm setting. The performance is not bad if you have enough light to focus what has become a 360mm f/9 lens.

Galah
03-01-2009, 06:45 PM
Thanks all for your interest in this topic and for the benefit of your knowledge of the subject. All this is very informative and helpful.

More of the same (with pictures, if possible) would be appreciated.:-)

Thanks.

jmg1911
03-01-2009, 09:47 PM
So stick an extension tube or tubes behind a longer lens and get the best of both worlds. When I used Leica R3s, my favorite was 180mm Elmar.

Galah
03-02-2009, 06:53 PM
Here is a web-page with an interesting alternative viewpoint to Macro technique:

http://www.digicamhelp.com/learn/macro-close/extreme-macro.php

David A. Goldfarb
03-02-2009, 07:13 PM
The extra loss of light David mentiones should only occur in uncoated converters. Put a decent coating on their elements, and that extra light loss is negligible.

Measure it, and you'll see. You lose some light due to reflections, even with multicoating, and some is transmissive loss due to the glass itself, even with a converter of excellent quality made by one of the major manufacturers. Most people don't notice, because they are using TTL metering, but meter a uniformly illuminated plain surface like a gray card with the lens focused at infinity (the surface should not be in focus) the lens stopped down two stops and no teleconverter, and then with the lens wide open and the teleconverter, and you'll get different readings--up to a half stop in transmissive loss in my experience.

Still photographers often ignore transmissive loss in general, because it's compensated for automatically with in-camera metering. State of the art modern multicoated cine lenses that cost more than a luxury car, though, are often marked in T-stops, rather than f:stops, because there is less room for exposure error and more money at stake on a film set, and handheld metering is the norm.

alanrockwood
03-02-2009, 07:41 PM
An interesting fact that might be relevant: A camera lens is optimized for a specific lens-to-object distance. Even if a lens were perfectly corrected for all aberrations at that one specific distance (which is not possible by the way) it will not be perfectly corrected at other distances. I think there is even a rigorous theorem to this effect that someone proved long ago. I think it might have been Maxwell or someone famous like that.

What are the implications of this? Basically, one should not necessarily assume that using an ordinary camera lens with extension tubes or bellows (i.e. far from its ideal conjugate ratio) will produce better close up results than alternative techniques that use additional optical components, such as tele-converters and/or diopters. It is all going to depend on the specific details of the lens designs.

By the way, if I am not mistaken, spherical aberration and coma tend to be particularly bad actors when one changes the conjugate ratio.

alanrockwood
03-02-2009, 07:47 PM
Here is another interesting link on comparing different close-up techniques.

http://www.waynesthisandthat.com/closeuplenses.html

Q.G.
03-03-2009, 12:40 AM
Measure it, and you'll see.
I do that every time i use my lenses, process the film, and see the results. ;)

The aperture values on them are calculated. F-stops, not T-stops.
I never noticed anything that would make me think it is anything but negligible.



A camera lens is optimized for a specific lens-to-object distance.
That's true.
But not all lens designs are equally sensitive to this. And most do quite well covering a wide range.
Things can get iffy when the conjugate ratio changes from long-short to just about equal, and from just about equal to short-long.
The upshot is that, though their performance does change, most standard lenses are excellent performers from infinity to close-up. Some even still when going beyond 1:1.

alanrockwood
03-03-2009, 09:00 PM
Q.G. You are right that some lenses perform better with change of conjugate ratio than others.

Just for fun I ran some lens trace calculations using WinLens. I tried all 14 lenses in the "double gauss" library that is distributed with the program. This library includes a wide range of lenses, such as biotar types, dogmar, some that look like plasmats, etc. I ran them at conjugate ratios of infinity and at 1:1 and eyeballed the spot diagrams to see how well the lenses did.

Basically all or almost all the lenses gave much better spot diagrams at infinity than at 1:1 conjugate ratio. By eye I would say that most of the lenses were at least twice as bad at 1:1 as at infinity. Some were better than others. For example, one of the lenses described as a "Biotar F/5.6 HFOV 20deg USP 2117252 " wasn't too bad at 1:1. Others, such as the one labeled "DG F/1.5 HFOV 23deg Leica Xenon L" were truly horrible at 1:1. Part of the difference between these extremes two may relate to the aperture used in the simulations. However, the point is that the lenses performed much differently at infinity compared to 1:1.

Interestingly, most of these lenses are based on symmetrical or near-symmetrical types. This general class of lenses is generally considered to be better behaved with respect to changes in conjugate ratios than highly unsymmetrical lenses, yet in general there were big changes in performance when going from infinity to 1:1.

One lesson is that an ordinary camera lens is probably not going to perform particularly well when used with extension for extreme closeups . Of course, there are probably lenses for which this rule of thumb would fail. I think that modern macro lenses using internal focusing would likely fall into this class because the designer could arrange the focusing to adjust for aberrations while it is focusing.

One final note: stopping the lens down should cover a variety of faults, except for lateral color. Most closeups are probably shot at small apertures anyway in order to maximize depth of field, so here is a case where mother nature wants to work with us instead of against us.

Q.G.
03-04-2009, 10:19 AM
Yes.

But then, there are lenses, and lens simulations. ;)

Try a Planar on a bellows, and you will be amazed how well it holds up, even when compared to a Makro-Planar.