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06-28-2017, 07:19 PM   #1
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A decent cheap teleconverter?

I've been looking at teleconverters on eBay. I can't imagine you get much for $30?? but I could be wrong.
Thinking about photographing the solar eclipse. Totality is too far away to drive, and I don't want to take my telescope on a plane So I'm down to wondering about sticking a teleconverter on my 100-300 lens. They don't have to be fabulous photos, but enough to say "I was there" and remember the moment. (Yes, I have solar film. I figure I can make a filter out of a step-up ring with a big enough rim.)

So I need a K-mount for a Kx camera, & all the lenses are Pentax bayonet K mounts. I don't care if it isn't autofocus.
The eBay listings include makes I've never heard of, like Beroflex, Sakar, Komura... and JC Penney makes them?
What about the Vivitar ones? Is that still a decent brand? Advice about what to look for?
Thanks.

06-28-2017, 07:46 PM - 1 Like   #2
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Cheap and good is not something you would find in a tele-converter.

A decent 2x TC would be something like the Pentax Rear Converter A 2x-S. Can be found for less than $100...

Rear Converter-A 2x-S Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database

You might find a good third party adapter, I have a Vivitar Series 1 1.4x AF TC that is ok.

Miscellaneous Lenses for Pentax: Teleconverters (All Brands) - Pentax Lens Review Database

Also keep in mind that many TCs aren't compatible with lenses that don't have recessed rear elements.
06-29-2017, 02:02 AM - 2 Likes   #3
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The best cheap teleconverter is cropping in post processing. Good teleconverters (which aren't very cheap) only work well on very sharp and bright expensive lenses. That is because they magnify the center area of the glass. They also magnify unsharpness. Add to that the questionable quality of the glass used in cheap converters and you will and up with worse quality than just cropping out a piece of the frame.
06-29-2017, 04:25 AM   #4
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At $30 probably not; under $100, maybe

I have the Kenko Pz-AF 1.5X Teleplus SHQ Teleconverter which I bought for US$70 on ebay. Both the built quality and IQ are really good. I would highly recommend it

There are some reviews here:

Kenko (?Promaster et al..) AF/Pz-AF 1.4x/1.5x Teleplus.... Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

Some discussion here using it with with the DA*300 lens:

Kenko Pz-AF 1.5X Teleplus SHQ Teleconverter on pentax DA*300 lens any good? - PentaxForums.com

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06-29-2017, 05:19 AM   #5
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Any suggestions for the K1?
06-29-2017, 05:35 AM   #6
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QuoteOriginally posted by gerardbaron Quote
Any suggestions for the K1?

The K-1 has a built in 1.5 tele convertor. It is called crop mode.
06-29-2017, 05:55 AM   #7
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QuoteOriginally posted by gerardbaron Quote
Any suggestions for the K1?
Most of the third-party teleconverters should be full frame.
06-29-2017, 06:33 PM   #8
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Thanks for the comments.
I'll keep looking around... Will have a look at some Vivitars & Kenkos.

QuoteOriginally posted by boriscleto Quote
Also keep in mind that many TCs aren't compatible with lenses that don't have recessed rear elements.
Even if it says K mount? None of my lenses have stuff sticking out the back, so... I don't know about non-recessed elements.

QuoteOriginally posted by D1N0 Quote
The best cheap teleconverter is cropping in post processing. Good teleconverters (which aren't very cheap) only work well on very sharp and bright expensive lenses. That is because they magnify the center area of the glass. They also magnify unsharpness. Add to that the questionable quality of the glass used in cheap converters and you will and up with worse quality than just cropping out a piece of the frame.
Hmmm. Maybe don't really need one then. It's just for "IF" I get to see the eclipse, basically just to have a pretty-good photo to show for the expedition.

As far as magnifying unsharpness etc., I take it the higher the magnification, the more degraded the image, so should I be looking at just 1.5 rather than 2x or higher?

06-30-2017, 01:00 AM   #9
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QuoteOriginally posted by Alliecat Quote
I take it the higher the magnification, the more degraded the image, so should I be looking at just 1.5 rather than 2x or higher?

This is correct. Sharpness of the lens and brightness because of the longer focal distance you have to use higher shutter speeds and the convertor also reduces the amount of light captured forcing a higher ISO, quality of the tele convertor. all affect IQ. I don't really think a 100-300 zoom will benefit from a tele convertor. Just money down the drain.
07-06-2017, 09:17 PM   #10
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QuoteOriginally posted by D1N0 Quote
I don't really think a 100-300 zoom will benefit from a tele convertor. Just money down the drain.
Good to know; don't want to waste money... I guess the question I have to decide is whether to spend a bit to have an alternative to my telescope to see the eclipse... even just to watch through the lens. With all my zooms and the photography I do, I've never needed a teleconverter otherwise.
07-07-2017, 04:05 AM   #11
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07-07-2017, 01:22 PM   #12
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I haven't had good luck with shooting a Q for lunar or solar purposes - having tried several times. Not sure why, as I take all the proper precautions in terms of using a quality prime, solid tripod and self timer. Perhaps the sensor density (pixel pitch) and high magnification from a small sensor are the issues.

It really does depend on the quality of the 100-300 lens used. On my old Tokina 100-300 f/5.6, using a tele-converter would degrade quality significantly. With the Tokina 100-300 f/4 and Pentax 100-300s - you can gain more advantage on a crop sensor with a quality TC. Be sure to stop down and increase exposure for best resolution.

The Pz-AF SHQ works OK in good light with the Pentax in AF, and is good optically. For the eclipse, I plan to use the Vivitar seven-element 2x macro TC for the eclipse on the Pentax lens, live view focusing. (Take the proper ND filtering, as always.) It isn't perfect, but it is adequate overall. That yields 900mm 35mm equivalence - which is fine for a straight eclipse shot. Less than that effective focal length requires a lot of cropping. Environmental factors are likely to contribute as much IQ degradation as the optical comprises of not shooting a prime. For very occasional use, spending a lot more on the set up probably isn't going to be worth the expense, but certainly spending more will yield somewhat better results - as would be expected.
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