Originally Posted by 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.
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.
Originally Posted by Galah
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)
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.
Originally Posted by Galah
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.
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.
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.
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.
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.
That's (almost*) exactly what it does.
Originally Posted by 2F/2F
(* 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.
Indeed; that is what I meant: As far as what the film sees is concerned, the center portion is it.
Originally Posted by Q.G.
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.