Has anyone heard about tele-filters similar to close-up filters. neither I have heard. But wonder whether any such filters are available. Since the effective focal length of a lens depends on the optical (glass) lens, I wonder whether it is possible to make any filters which can increase the effective focal length of the lens, thus without changing the apperture.

Then wonder if IS-filters are possible. Just screw them up on your lens and get the stabilization. May not be as good as the one within the lens but it could be much more versatile as I can use it for a variety of lenses of the same filter size.

-- sajeev (chack74@yahoo.co.in), January 21, 2002

Answers

In the Good Old Days, there were fisheye converters that worked like that - screw them into the filter threads of a 50mm lens and you've got a fisheye. I know there are wide-angle and tele converters that attach to the front end of a camcorder's lens. I don't know of any such devices for regular film cameras but it sounds like it would be possible. Of course, you can get teleconverters that mount between the lens and the body and which therefore work with a variety of lenses; why reinvent the wheel?

A screw-on IS filter might be possible but since IS requires power, it would have to have a power source - either batteries installed in the filter or a connection to an external power source. An IS adapter that fits between the body and the lens would be better in this regard, as it could draw from the power that's already being provided to the lens, just as an IS lens does.

I don't know if there's anything in IS that ties a given implementation to certain focal length(s) or if you could make one that's generic. My guess is that the focal length is tied in there somehow - after all, if the lens deflects down (say) half a degree, it makes a much greater difference to the image with a telephoto lens than it does with a wide-angle lens. I know IS zoom lenses exist (I have one) but since the whole thing is integrated, the computer that controls IS can know the lens' focal length at the time and adjust accordingly.

Another problem with an IS filter that attaches to the front filter thread: what about the angle of view of the lens? You can already have problems with having multiple filters on most lenses, and those are relatively small filters, only a few millimeters thick. An IS filter would have to be much thicker - probably a few centimeters - so it would have to be huge in order to be usable with anything other than a telephoto lens. Yet another reason why it would be better to put it behind the lens instead of in front of it.

-- Steve Dunn (steved@ussinc.com), January 21, 2002.

An IS filter would not be possible, as the IS relies on being between the elements of the lens and the film. This is why IS lenses always have the IS group at or near the back of the lens.

However, I think an IS teleconverter might be possible.

Close-up Filters (also referred to as close-up lenses and Dioptres) are indeed available. Tele filters are not available to my knowledge, except that many digital cameras have such accessories to boost focal length.

-- Isaac Sibson (isibson@hotmail.com), January 21, 2002.

Isaac said, "...except that many digital cameras have such accessories to boost focal length."

And so did old fixed lens rangefinder cameras. It should not be that difficult to fix one of those to a modern lens. The difficulty would be in finding one that is of decent quality and the proper diameter. So yes, this is possible. Image quality would be questionable.

I doubt that you will ever see IS in a filter. I also think that IS is too integrated into a particular lens to work as a TC. Every time you switched lenses you would have to change the parameters of the IS. But this is all speculation, cause it hasn't been done.

-- Jim Strutz (j.strutz@gci.net), January 21, 2002.

Yes, there is an Image Stabilizing accessory that attaches to the front of a lens. And yes, it is even made by Canon.

http://www.usa.canon.com/indtech/broadcasteq/bctv/vaplens.html

There are some minor limitations. Firstly, it is intended for television broadcasting/video surveillance, and requires a serious power supply. Then, it might not fit your lenses very well. And, oh, I nearly forgot, it only costs about $USD12,000

So I'm sure that you will want to use just one for a number of your lenses :-)

-- Julian Loke (elan7e-owner@yahoogroups.com), January 22, 2002.

I for one think it would be a neat idea if canon could introduce the IS into the teleconverter (or someone else for that matter). Its a smart idea, and would make any tele lens that the converter fits a Tele-IS lens. I want to get a 1.4x TC, maybe by then they'll have the IS built in? Granted I intend to also buy a 300 4L IS (some day).

-- Carl Smith (emorphien@mail.rit.edu), January 28, 2002.