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02-28-2017, 05:25 AM - 1 Like   #16
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QuoteOriginally posted by Des Quote
.


@WildMark did a comparison here of a few different model 1.4x TCs. There was one Sigma that he liked, but not all Sigmas will fit all lenses. I have the Kenko 1.5x pz TC, which despite the name is really 1.4x; it is the same as the Tamron 1.4x pz TC. The pz indicates that it will work (theoretically) with lenses that have SDM or DC autofocus; most TCs won't. The Kenko/Tamron is fine, in my experience. The gold standard is the Pentax DA 1.4x WR TC, but it's really expensive.
With respect to the sigma TCs, the sigma APO -EX teleconverters have a protruding front element, the lenses they fit, all have recessed rear elements and a bore diameter in the order of 35mm. In fact the screw drive BIGMA can't zoom out to 50mm with a TC attached because to get to 50mm the rear element moves back into the area occupied by the TC. Pentax made a similar rear converter for their fast telephoto lenses also,

The sigma converter is good, but very limited to fast lenses,

02-28-2017, 06:09 AM   #17
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QuoteOriginally posted by Des Quote
Yes they are optically identical. The F has a tripod collar and a slide out hood, which the FA doesn't, although you can get a cheap aftermarket tripod collar for the FA and the reverse-mounting hood it comes with is very good. The F is a little lighter. But the F is harder to find. Check out the reviews of these lenses - people love them.


@WildMark did a comparison here of a few different model 1.4x TCs. There was one Sigma that he liked, but not all Sigmas will fit all lenses. I have the Kenko 1.5x pz TC, which despite the name is really 1.4x; it is the same as the Tamron 1.4x pz TC. The pz indicates that it will work (theoretically) with lenses that have SDM or DC autofocus; most TCs won't. The Kenko/Tamron is fine, in my experience. The gold standard is the Pentax DA 1.4x WR TC, but it's really expensive.
Des,

I find several several Kenko 1.4 TCs, new, for about $100. Doing an eBay search, I also was shown several Kenko 2.0 TCs. Would these also be appropriate? I think the 1.5 would be just fine. There must be some downside to the 2.0??

I checked out the length and weight for the 300mm w/1.5 TC and it would work out great for me. Like you said, about the same weight as the Tokina. I'm closing in on it, Des, thanks in great part to your recommendations.

Jack

---------- Post added 02-28-17 at 05:16 AM ----------

QuoteOriginally posted by Lowell Goudge Quote
With respect to the sigma TCs, the sigma APO -EX teleconverters have a protruding front element, the lenses they fit, all have recessed rear elements and a bore diameter in the order of 35mm. In fact the screw drive BIGMA can't zoom out to 50mm with a TC attached because to get to 50mm the rear element moves back into the area occupied by the TC. Pentax made a similar rear converter for their fast telephoto lenses also,

The sigma converter is good, but very limited to fast lenses,
Hi Lowell,

Thanks for the info on the Sigma TC. Des turned me on to the Kenko 1.4 and has actually used it with the Pentax 300mm. Since they are available in several major camera stores, I'll probably stick with that one.

Jack.
02-28-2017, 04:38 PM   #18
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QuoteOriginally posted by Setter Dog Quote
Des,

I find several several Kenko 1.4 TCs, new, for about $100. Doing an eBay search, I also was shown several Kenko 2.0 TCs. Would these also be appropriate? I think the 1.5 would be just fine. There must be some downside to the 2.0??

I checked out the length and weight for the 300mm w/1.5 TC and it would work out great for me. Like you said, about the same weight as the Tokina. I'm closing in on it, Des, thanks in great part to your recommendations.

Jack
The 1.4x converters reduce the maximum aperture by 1 stop - eg 300mm f4.5 becomes the equivalent of 420mm f6.3. 2x converters cost two stops, so 300mm f4.5 becomes an effective 600mm f9, which is too limiting. If you were starting with a 300mm f2.8 a 2x converter would be more useful - 600mm f5.6 - but that is a very different beast.

And the greater the magnification the greater the degree of image degradation. A very good 1.4 TC on a very good lens won't affect the image quality too much, but a 2x TC is pushing it more.

See this article:

Pentax K-Mount Teleconverter Guide - Articles and Tips | PentaxForums.com

As for the Kenko 1.4 it's not the same as mine.

My Kenko 1.5 pz cost the equivalent of about $US150 second hand in mint condition. The Tamron counterpart will be around the same price.

Here are the third party TC reviews in PF: https://www.pentaxforums.com/userreviews/pentax-off-brand-teleconverters-c90.html
Be careful with these reviews; there is a lot of variability in TCs with similar names. On some review pages, different models are lumped together (e.g. various Kenko and Tamron 1.4 and 1.5 TCs). Check carefully for reviews of the exact model you are looking at.

BTW here is the comparison by @WildMark I mentioned: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/309566-tel...on-x1-4-a.html The Tamron that Mark tested was the 1.4 pz, which is the same as my Kenko. The Kenko that Mark tested was a different model.

To confuse matters further, it seems that there are even two versions of the Kenko 1.5 pz, one which magnifies 1.4x and the other 1.7x: https://www.dpreview.com/forums/thread/3537477

Note that with any of the third party TCs the camera won't know there is a TC attached for SR purposes and the EXIF will only record the focal length of the lens. It's an inconvenience but I have not found it a significant problem in practice.

Last edited by Des; 02-28-2017 at 05:59 PM.
03-01-2017, 03:37 PM   #19
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For completeness I should add that if money is no object, the combination of a DA*300 f4 and DA 1.4x TC has a number of advantages:
- 1/3 stop faster (300mm f4, or 420mm f5.6 with the TC)
- quiet and possibly more accurate autofocus (not necessarily faster)
- quick shift (manual focus override) (The FA has a clutch to switch to MF which is pretty good for a lens of that vintage, but not as good as QS.)
- more recent coatings
- Weather resistant, both lens and TC
- best quality TC
- EXIF data records correctly
- SR based on the real equivalent focal length

Downsides:
- Cost: about $US1100 for the lens and $500 for the TC. The lens is a little cheaper used; the TC is very difficult to find. (Compare that with about $850 for the F or FA 300 f4.5 + a decent third party TC)
- Some people who have used both argue the image quality from the F/FA lenses is better (probably splitting hairs)
- SDM autofocus is known to fail at times, and the repair may be uneconomic (but the lens can be converted to screw-drive AF). Many of the screw-driven F/FA lenses are still going strong after 25-30 years; you wouldn't expect many SDM lenses to last that long.
- DA weighs about 100g or so more
- A little bulkier

Neutral:
DA*300 uses 77mm filters. same as the DA 12-24, for example
F/FA*300 use 67mm filters, which are a little cheaper. Same size on a number of DA* lenses, and some others like Tamron 17-50.
(This is an indication of the smaller diameter of the F/FA* lenses.)

Theoretically, a third party TC with pz contacts (e.g. Tamron/Kenko pz) will drive SDM autofocus, but people who have tried it report that the AF doesn't work well, or reliably. That's why if you get the DA*300, you should really get the Pentax DA TC.

One more lateral thought, Jack. Since you have a Sony A7ii (24mp?) have you looked at other long tele options for that instead? The 24mp sensor is an advantage for photographing wildlife, where cropping is the norm. Or replace both the Sony and the K-50 with a K-3/K-3ii/K-P, or even a K-1, if you are not heavily invested in Sony gear.


Last edited by Des; 03-01-2017 at 04:11 PM.
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