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07-01-2010, 11:10 AM   #1
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2X Tele-Converter

Can someone inform me what 2x tele-converter would fit a SMC Pentax-A 400mm 5.6 lens and be able to use it on a K10d? Thanks

07-01-2010, 11:55 AM   #2
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As long as the tc is a Pentax K mount piece, it will perform with that lens. Some have autofocus features some do not but the P K mount teleconverter is of course what you look for.
I have old Focal and Star -D tc that work very well for Pentax K mount lenses but neither interact with autofocus connections.
07-01-2010, 02:33 PM   #3
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Pentax made two "A" type 2x TCs; the 2xS and the 2xL. Because the 2xL extends almost 2cm into the lens, only certain lenses are listed as compatible. I can't put my finger on that document at the moment but its something you need to be aware of. For example, the 2xL will physically NOT fit the DA*300/4.
07-01-2010, 03:02 PM   #4
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Since this is more a lense question than a camera question, I'm moving it to the more appropriate forum.

07-01-2010, 03:14 PM   #5
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I have a Vivitar PK-A/R-PK 2x TC that fits and works perfectly with A lenses passing the aperture info and control. On the tele end of things it's a little soft but I love it for macro work.

I found mine on eBay.
07-01-2010, 08:48 PM   #6
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Here it is:
http://www.pentax-manuals.com/manuals/accessories/converter_a_s.pdf
The Pentax 2X-L teleconverter will fit the SMC Pentax-A 400mm 5.6 - and is a designed / matching teleconverter for that lens. I would highly recommend the 2X-L above any other, as it will provide the best quality by a long shot. Trouble is, it can be hard to find and doesn't come cheap. The Pentax 2X-S teleconverter would also be suitable. Note - the manual states that the Pentax 1.4X-S teleconverter is not suitable for the SMC Pentax-A 400mm 5.6 lens. Reason being "vignetting at each corner". Hmm - I wonder if that still holds true on a cropped sensor though...? The Pentax-F 1.7X AF adapter is the another Pentax teleconverter. Not only is it a decent teleconverter - it will also add autofocus functionality to a manual focus lens such as the SMC Pentax-A 400mm 5.6. However, my experience with this teleconverter is mixed. I find it doesn't play nice with exceptionally sharp lenses - as it doesn't seem to be able to pass the sharpness though. There are various non-Pentax K teleconverters out there. Some good, and some better used as paperweights. The better ones seem to be of a 7-element construction. I have used a Vivitar x2 (made by Kiron / Kino) that was pretty awesome.
07-01-2010, 09:04 PM   #7
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QuoteOriginally posted by tumbleguts Quote
Thanks for the manual. This is not the one I have seen though and although it has a lot more information it does include all the long glass for the 2xL. Maybe they weren't released yet...like the A*400/2.8.

Very true about even finding the 2xL as the only one I remember seeing for sale was bundled with an A*400/2.8

EDIT: Found my reference and it is for the Pentax lenses and which TC they are most compatible with. Unfortunately it does not include the A400/5.6 in the charts.

Last edited by imtheguy; 07-01-2010 at 09:17 PM.
07-01-2010, 09:14 PM   #8
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QuoteOriginally posted by mattb123 Quote
I have a Vivitar PK-A/R-PK 2x TC that fits and works perfectly with A lenses passing the aperture info and control. On the tele end of things it's a little soft but I love it for macro work.

I found mine on eBay.
To turn a lens into a macro lens, especially a fine fifty (my A50 f1.2), you're right, it's a fantastic unit. For a Teleconverter however, it does tend to soften things a little bit. It does have the advantage of being adjustable but it comes at a small cost. Still quite usable but you want the lens you use with it to be tack sharp. Any error in the lens will be multiplied with the 2x Macro Focusing TC.

That isn't to say it isn't useful. I know that this is a way off of 400mm but here is a sample from a Pentax M135 f3.5 mounted on that converter.. Go ahead and click the image to pixel peep..






07-02-2010, 05:34 PM   #9
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QuoteOriginally posted by imtheguy Quote
EDIT: Found my reference and it is for the Pentax lenses and which TC they are most compatible with. Unfortunately it does not include the A400/5.6 in the charts.
In one of the Pentax lens booklets I have (Pentax 35mm SLR Lenses, L-1204) has a comprehensive table with color dots representing which teleconverters can be used with which lenses.

It has the A 400/f5.6 accepting the long versions 1.4x and 2x (and the short version 2x but not the short version 1.4x).
07-02-2010, 08:48 PM   #10
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QuoteOriginally posted by mattb123 Quote
I have a Vivitar PK-A/R-PK 2x TC that fits and works perfectly with A lenses passing the aperture info and control. On the tele end of things it's a little soft but I love it for macro work.

I found mine on eBay.
I have one of those and it works brilliantly with, say, the M50 1.7. Even using it as a TC I find works fine but it does ruthlessly expose the limitations of the lens you are using it with. That means you generally have to stop down a couple of clicks: that combined with the loss of two stops-worth of light can lead to lighting challenges, slower-than-ideal shutter speeds or higher-than-ideal ISOs.
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