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03-19-2008, 12:39 PM   #1
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Teleconverter for new DA* 300mm???

What teleconverters are available for the new Pentax DA* 300mm lens? Any limitations other than loss of stops?

Thanks

03-19-2008, 01:46 PM   #2
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A new rear converter is on the Pentax lens roadmap. Everybody hopes it will be out soon after the 300mm but nobody knows. Even its x-factor in unknown.

With existing converters, you may loose AF and you definitely loose shake reduction.

The Tamron 1.4x seems to be best but you won't be able to find one new anymore.

The Sigma converters will most likely not fit, because they don't allow for a flush rear lens.
03-19-2008, 02:30 PM   #3
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Did they stop making the Tamrons?
03-19-2008, 03:20 PM   #4
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QuoteOriginally posted by falconeye Quote
[...]
With existing converters, you may loose AF and you definitely loose shake reduction.
[...]
Why is that? I would think that with a SR implemented in the body, it would be immune to TC's?

03-19-2008, 03:24 PM   #5
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SR still functions, but since the increased focal length isn't transmitted to the body, it's only functioning at the lenses original value. So on a 300mm with a 2x TC, instead of SR for a 600mm lens, it's still only 300mm.
03-19-2008, 03:35 PM   #6
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QuoteOriginally posted by Jodokast96 Quote
SR still functions, but since the increased focal length isn't transmitted to the body, it's only functioning at the lenses original value. So on a 300mm with a 2x TC, instead of SR for a 600mm lens, it's still only 300mm.
Got it, thanks!
03-19-2008, 06:10 PM   #7
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The Kenko Teleplus 1.5x SHQ has the power contacts for for the old power zoom system. I believe those are the same contacts used for SDM. It should work (no guaranties though). The bonus is it is a very good TC, and is pretty cheap.

Kenko | 1.5x DG AF Tele-Converter for Pentax AF | K15AFDGPK
03-20-2008, 07:24 AM   #8
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QuoteOriginally posted by roscot Quote
The Kenko Teleplus 1.5x SHQ
Read all about it here:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/19694-tamron-t...rter-pics.html

Seems like people are disappointed about the Kenko Teleplus 1.5x.

And as for SR: If a 600mm becomes 300mm, only 50% of shake will be reduced. So, rather than gaining 4 f-stops, you only gain 1 f-stop anymore. With an ALL-MANUAL TC though, you can enter the focal length and keep SR

03-20-2008, 07:55 AM   #9
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I recently bought a Kenko Teleplus 1.5x with a view to combining it with the 300 DA when it becomes available. I was prepared to buy a Pentax, Tamron or Sigma one. I didn't want to skimp. However, Pentax and Tamron ones were not available new as others have said and in short supply used. There can be issues with the Sigma TCs as people have mentioned. I may well get a Pentax one when it comes out but in the meantime it had to be Kenko. I would have gone for the Kenko Pro range if these had been in a Pentax fit. I have been satisfied with the images to date bearing in mind that I am only using it with a Sigma 70-300 DL Macro and any TC is only going to exagerate weaknesses in the lens you are using it with. I have only tried it hand held in pretty poor light so far so I can't expect crisp sharpness, but the colours/contrast of the images I think on the whole have been good. There are images on the forum with Kenko TCs which are good quality IMO.

The common wisdom is to use matching lenses and TCs, but I have read a number of reports where occasionally people have found that another brand of TC produced better results. It seems it's desirable to try out a lens with different TCs to discover which particular combination works best, but of course that can be expensive.

Paul
03-20-2008, 12:43 PM   #10
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Last month I dropped my Sigma 1.4 TC on the beach, and had to send it to Sigma for a CLA. In the mean time I pulled out my Kenko, and tested it on both my Sigma 70-200 EX and 100-300 EX DG. I was very surprised at the quality of the results. Here is the 70-200 test. I have not uploaded the 100-300 to my Pbase account but they are very similar. You are correct about the SR though. Until the camera can recognize the TC, it is something we will have to live with.

Lens Tests Photo Gallery by Alan H. Glassman Photography at pbase.com
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