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04-19-2011, 06:46 AM   #1
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1.4 or 1.7

Can someone point me in the right direction for a teleconverter 1.4 or 1.7 which will work with acceptable results on the DA 300 F4 lens?
Doing a search did not really give any definitive answers.
Thanks
joe

04-19-2011, 06:55 AM   #2
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Assuming you are referring to the Tamron 1.4x PZ-AF TC, or the Pentax 1.7x AF-A TCs, they are both probably the most recommended that you'll be able to find (though neither can be bought new, they are around in the marketplace and on ebay).

You'll have a light loss of 1 (for the 1.4x) and 1.5 (for the 1.7x) stops respectively.

With the high quality of the 300mm F4, you might just be better off cropping from the original though.

The tamron will AF, but only in good light (liveview AF on the K5 is another option that will give consistent results with a slight loss in actual speed). From what I understand of the Pentax 1.7x, it actually has it's own AF module - the lens will need to be relatively pre-focused in the general area, then the TC does the AF rather than the camera itself.
04-19-2011, 07:25 AM   #3
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Everything Paul said except :

a) check this link for comparisons of the DA*300 with and without TCs : https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/139941-lenses-...-x1-4-etc.html

b) You can try EBay or forums but your best bet is the Japanese Amazon (or EBay, I forget which). Costs around US$350 new - however I don't know how the Earthquake & Tsunami there has affected supplies.

c) There are Japanese forwarding companies that for a small fee (around US$20 I think) will buy it for you and then forward it onto the address you have given them. Note that as the AFA contains a minute amount of radioactive material it's somehow managed to get itself banned from direct importation into the USA and Western Europe.
04-19-2011, 09:59 AM   #4
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That is a great round-up of what to expect from different lenses and TCs!

I'm thinking about doing one with my 1.4x and new 2x 7 element tamron, maybe run a compare between the 120-400 and 50-135 with and without TCs at comparable lengths (don't have anything else long made by Pentax at the moment).

The 1.4x Tamron seems to be about the best bet going at the moment based on your test images - crops are pretty comparable to IQ from the lens to which it is attached without the TC.

04-19-2011, 10:00 AM   #5
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The Pentax Rear Converter-A 1.4x-S is good, but you won't get AF. The Pentax-F 1.7x AF Adapter is also good. I have both. My long lenses are K200/2.5 and F300/4.5.

The Pentax Rear Converter-A 1.4x-L would have been the best, but reportedly it doesn't work with the DA*300/4. I would have purchased one, but it won't work with my K200/2.5 without filing some metal down!

I had the latest Tamron 1.4x mentioned above, but prefer the Rear Converter-A. Honestly, however, I don't end up using the TCs much.

Last edited by DSims; 04-19-2011 at 10:07 AM.
04-19-2011, 12:10 PM   #6
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Thanks guys, will search around on ebay.
04-19-2011, 12:50 PM   #7
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I never tried the tamron 1.4x with the power zoom contacts, but tried two different Kenko shq pz 1.5x TC's that people said would work with the DA300 and they would hunt way too much. I worried the focus motor might be damaged and didn't use them. The 1.7x pentax worked very well and is a good match for the DA300.I guess different people have different definitions of "works".
04-19-2011, 03:37 PM   #8
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I don't think the motor will be damaged. All the kenko is doing is providing the electrical contacts. My sigma 70_200 hsm hunts a bit at the long end but its fine with the kenko till about 150. I suspect its more due to light not being sufficient for auto focus than an electrical issue as it was nearly sunset when I had the hunting issue. Probably same with da300 as its only f4.

04-19-2011, 05:43 PM   #9
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QuoteOriginally posted by selar Quote
I don't think the motor will be damaged. All the kenko is doing is providing the electrical contacts. My sigma 70_200 hsm hunts a bit at the long end but its fine with the kenko till about 150. I suspect its more due to light not being sufficient for auto focus than an electrical issue as it was nearly sunset when I had the hunting issue. Probably same with da300 as its only f4.

Sent from my GT-P1000T using Tapatalk
I don't think it was the light affecting my DA300mm and the kenko but the fact the camera probably didn't know the proper distance information. I got the same effect with a TC on a 40D canon body when taping the pins on the TC to get the camera to attempt to focus as non 1 series canon bodies won't even try to AF at less than f5.6.
I wonder if Pentax couldn't find a fix either as the TC they were promising a few years ago (even had a prototype at a show) never went into production. Just a hunch.
04-19-2011, 06:56 PM   #10
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I have posted about it previously, but wanted to mention that hunting is largely absent with the 1.4x TC when used with the K-5 in conjunction with the CDAF in liveview. It is naturally somewhat slower than the normal PDAF but it is quite a bit more consistent.
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