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09-13-2009, 07:32 AM   #1
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Teleconverter Help

If been out trying to shoot birds, and I'm frustrated with the limited reach on my current long lens. So I'm considering a teleconverter to use with my Sigma 70-300mm f/4-5.6 APO DG Macro. Can anyone comment on if a Pentax SMC 2x-S Rear Converter-A would work with my Sigma, or would a Kenko 2X MC7 DG be a better choice. Or am I just wasting money?

09-13-2009, 07:43 AM   #2
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QuoteOriginally posted by brett Quote
If been out trying to shoot birds, and I'm frustrated with the limited reach on my current long lens. So I'm considering a teleconverter to use with my Sigma 70-300mm f/4-5.6 APO DG Macro. Can anyone comment on if a Pentax SMC 2x-S Rear Converter-A would work with my Sigma, or would a Kenko 2X MC7 DG be a better choice. Or am I just wasting money?
From my limited experience with slow lenses and teleconverters I'd say you will get unsatisfying results from that combination due to the fact that your widest aperture will be F11.
09-13-2009, 07:57 AM   #3
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I'd agree with Spock. A very good TC coupled with a very good lens can produce very nice results. I have no personal experience with that Sigma but, in addition to the speed issue, I'd have my doubts as to whether it's good enough optically to support a TC.
09-13-2009, 08:01 AM   #4
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If you use a 2x converter with a lens such as the Sigma you will lose some IQ and 2 stops as Spock points out.

The effect of this is the auto-focus will really struggle, if it works at all.

I have read on some forums that using a 1.5x converter with this type of lens does yield some auto-focus success in favourable light as the loss is around 1 stop. Most AF systems are designed to work with apertures of f5.6 or faster.

I have not tried this myself but have been curious as there are time when 300mm isn't long enough for me either and I can't justify the expense a longer AF lens at the mo.

My advice would be to try it out at a local camera store if this is possible then you will be able to make an informed decision.

Good luck and if you do go down this route post some images as I might follow.

Cheerz MZ

09-13-2009, 08:51 AM   #5
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Thanks for confirming what I thought might be the case. Unfortunately I'm not in the position to spend big bucks for a long, fast lens. I guess I'll go with plan B and get an inexpensive 500mm mirror lens to play with.
09-13-2009, 12:08 PM   #6
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That would be my vote too - and check out the Mirror Lens Club thread if you haven't already for inspiration. But I'd also be realistic here - while a basic consumer like your 70-300 won't work very well with a TC - you'll almost always do better by simply cropping the results from the 70-300 without a TC - the mirror lens might not beat the results of cropping by very much either. See my blog article on the Vivitar (=Phoenix, =Opteka, =Samyang, =Quantaray, probably others) 500/8 mirror:

Marc Sabatella: The Vivitar 500/8 Mirror Lens

Last edited by Marc Sabatella; 09-13-2009 at 04:47 PM.
09-13-2009, 01:01 PM   #7
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If its more reach that you want, and your budget is small, I am in agreement with Marc on the mirror lens. For a few $s more, you might find a 4-500mm pentax or takumar manual lens.
09-13-2009, 01:59 PM   #8
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Definitely forget any 70-300 buddying up with any TC.
Not worth it.
Just look for a good MF 400-500mm prime or mirror lens.
You can't beat those for value for money.

09-13-2009, 03:19 PM   #9
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I read up and looked around, and settled on a Vivitar 500mm F6.3 Mirror Lens 1:6.3 DX. $175 shipped with a T-mount. I considered a long used prime, but I didn't want to carry around the bulk. I also thought about trying to find a Tamron, but I think this will do for the time being. I know focusing is a challenge, but I hope to get the hang of it with some practice. Thanks all.
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