I have Canon EOS 2000 with a Sigma 100-300 f/4.5-6.7. I recently bought a Quantaray - 500mm/1000mm Preset Telephoto (T-mt.) f/8 as an inexpensive way to get closer to wildlife. My question is, would I have been better off buying a 1.4 or 2x tele-extender for my 100-300 Sigma lens? Could I use the auto-focus with such a tele-extender? Of the tele-extenders I found, none of them were for the 100-300 lens.

Thanks,

-- P R Ganapathy (pr_ganapathy@yahoo.com), April 04, 2001

Answers

You won't find a dedicated teleconverter (extender) for any 3rd party zoom lens, and I think only one manufacturer zoom.

That said, there are some excellent TC's out there. But I don't think it would do any good.

Issues: 1. You'll lose autofocus with a 2x, and it will be agonizingly slow with a 1.4x or completely shut down due to the multiplication of f- stop. (multiply your widest aperture by the multiplication factor of the teleconverter... At 300mm your lens only opens to 6.7. With a 2x TC it will be 13.4!!!) Your body won't autofocus at all past f8, and your lens' 6.7 is probably the practical limit.

2. Image quality will suffer. Assuming your TC is perfect (and trust me, none are) you will be multiplying the size of any flaws in your main lens by the TC factor. A chip in the glass that causes a tiny flare that's hardly noticible with that lens becomes glaringly obvious. Of course, there will also be softening, chromatic aberration, etc. from using a TC. These vary by the quality of the TC itself.

Now, the lens you bought is basically a low-end telescope. That's not necessarily a bad thing. Just keep in mind that you won't get the absolutely razor sharp and contrasty images you see published. It may, however, allow you to get the shot you need to get!

What I did was purchased a used 300mm f4 along with a high quality 2x TC (looking for a Minolta MD mount high quality 1.4. Anybody know of one?) for my manual focus Minolta body. It is great. I get decent shots with that combo at 600mm. But it's a very excelent lens to begin with.

I say you take the lens you bought and play with it for the 30 days you have from Ritz to return it. Develop some film and see if that's what you were trying to get. You may be very happy! :-)

-- Don Tuleja (durocshark@hotmail.com), April 04, 2001.

I think you did the right thing. A long tele is a very simple design, and some of these inexpensive presets are remarkably sharp. It's likely to produce noticeably sharper images than the best you could have gotten with your zoom and a teleconverter.

rick :)=

rick_oleson.tripod.com

-- rick oleson (rick_oleson@yahoo.com), April 09, 2001.