Modern teleconverter with adapted lens?

[connloyalist]

Perhaps this will turn out to be nothing more than one of my wild ideas, but then again you never know.

I own several adapted 200mm lenses that I like using (my Canon FDn 200m 4.0 comes to mind).

I was thinking: if I wanted to go for something longer, would there be an optical advantage in using a modern teleconverter with an adapted lens over that adapted lens' equivalent longer version? And also better than using a teleconverter from the same period as when the lens was made?

For example the Canon FDn 200mm 4.0 (440 grams) + Olympus 1.4 teleconverter (170 grams) = "300mm 5.6" (610 grams), vs. the Canon FDn 300mm 5.6 (635 grams) (not counting the weight of the Novoflex FD-M4/3 adapter here, 53.8 grams).

I actually do own a Canon FDn 300mm 5.6. It's OK but does tend towards CA and while it is the smallest and lightest of the three "vintage" 300mm lenses I own I wouldn't call it small.

Would using a shorter lens with a modern teleconverter result in better optics? Or, would the extra glass make the optics worse? I am assuming that a modern teleconverter would be optically better than in this example a Canon FDn teleconverter.

Regards, C.

[connloyalist]

It just occurred to me: if you have the setup: lens - adapter - teleconverter - camera, then the gap between the rear of the lens and the front of the teleconverter might cause vignetting, because the front element of the teleconverter was designed to be close to the rear element of the lens?

Regards, C.

[DConvert]

Modern teleconverters tend to be limited to a small range of high quality telephoto lenses while legacy models were often suitable for any lens in that mount.
The dedication of modern TCs enables them to be higher quality, but MAY prevent them from working with adapters. Sometimes the front element of the TC has to sit within the rear of the lens, which obviously causes issues for lenses that have elements in that region!

I've used a number of legacy TCs with adapted lenses, and often find the IQ suffers too much for the combination to be worthwhile. It would certainly be more convenient to have a TC that goes between the camera & the adapter, so it can be used with a wide range of different mounts. I've not yet come across modern TCs that come in my price range for trying this

[Ray Parkhurst]

Better optics? No. It's more likely that purpose-designed longer lens will be better. You can get lucky though with different teleconverters and maybe find a good combo.

The small adapter should not cause vignetting (unless it physically vignettes for some reason). As long as infinity focus still works properly, all should be fine.

[DConvert]

[cooltouch]

I suggest that you do as I've done in the past. Test the lens against the various combinations and compare the results in post. That will give you a factual answer, eliminating opinions.