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03-16-2014, 09:54 AM   #1
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How good is the Pentax 1.7TC

The introduction of the Pentax 1.4 TC led me to see if I could use it for Wildlife photography. My conclusion would be probably if I could use it on stationary subjects with manual focus. So I tested the K-3 using the Sigma 500 4.5 lens and two TC - unfortunately I do not have the new 1.4 Pentax TC to test. I did test a Sigma 1.4 TC and the Pentax 1.7 TC. Amy, thank you, loaned me the Sigma TC.
For this test I set the aperture of the 500MM lens manual to f8 and used Manual Focus using Live View Magnified and a Hoodman to get as good a focus as possible. I used a 2 second shutter delay with Live View (mirror up)
Here are three shots of a neighbor's car at 500mm, 700mm and 850mm followed by a composite picture showing the small upper right hand portion of the rear license plate with the registration certificate with small numbers under the expiration year.
On the composite shot:
A is 500mm lens by itself - cropped
B is the 500mm and 1.4 Sigma TC - cropped
C is the 500mm and 1.7 Pentax TC - cropped
D is the cropped 500 with 1.4 Sigma made to be the same size as the Sigma with Pentax 1.7 TC
E is the cropped 500 by itself made to be the same size as the Sigma with Pentax 1.7 TC

If the new Pentax 1.4 TC is as good as the Pentax 1.7 TC I will probably buy it

The old Pentax 1.7 TC is clearly a very good TC

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03-16-2014, 10:04 AM   #2
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Here's my page of test images, that includes the 1.7 TC....

https://www.pentaxforums.com/forums/16-pentax-news-rumors/250767-hd-teleconve...ounced-17.html

If you like the old TC, the AF on the new TC is simply to die for.
03-16-2014, 10:36 AM   #3
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If it is as good, or very close, in optical performance to the 1.7 I will buy it. From the test I did, as best as I could focus, the 1.7 gives you significantly better reach than cropping when you can use it manually - fairly stationary subjects. For example I plan to use it this week at a eagles nest where I can set up, focus on the nest and wait for the birds. I have not had a chance to try birds in flight with the 500 using the Sigma 1.4TC to evaluate the potential of autofocus on a 500 using a TC.

Norm have you used one of your lenses for BIF with the 1.4TC - is it doable? Is there enough light to focus accurately and fast enough and get some keepers?
03-16-2014, 10:40 AM   #4
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If "A" is the Sigma alone, why is it so blurry compared to "C" (the Sigma w/Pentax 1.7x tc) As good as the Pentax tc may be it can't add sharpness that isn't there to begin with.

03-16-2014, 10:50 AM   #5
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QuoteOriginally posted by RockvilleBob Quote
If it is as good, or very close, in optical performance to the 1.7 I will buy it. From the test I did, as best as I could focus, the 1.7 gives you significantly better reach than cropping when you can use it manually - fairly stationary subjects. For example I plan to use it this week at a eagles nest where I can set up, focus on the nest and wait for the birds. I have not had a chance to try birds in flight with the 500 using the Sigma 1.4TC to evaluate the potential of autofocus on a 500 using a TC.

Norm have you used one of your lenses for BIF with the 1.4TC - is it doable? Is there enough light to focus accurately and fast enough and get some keepers?
BiFs usually mean fairly big slow moving birds.... I don't really have any of those to try on tis time of year. Give another few months , when the seagulls are back.
03-16-2014, 11:09 AM   #6
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QuoteOriginally posted by sandpipe Quote
If "A" is the Sigma alone, why is it so blurry compared to "C" (the Sigma w/Pentax 1.7x tc) As good as the Pentax tc may be it can't add sharpness that isn't there to begin with.
I understand your question but even using Live View with a hoodman and putting Live View into magnification mode, it was difficult to focus. I can only attribute it to focusing. On the other hand the total 850mm provided more to focus on just due to magnification.

There is also the depth of field issue. I should probably stop the 500 by itself to provide the same DOF as the 1.7?

Then there is just the number of pixels the numbers span - with greater magnification the numbers span more pixels.

Either way - the 1.7 is a great TC - those numbers under the 15 plus the MARYLAND to the left of the 15 are really small - really small even when you look at them a foot away with your eyes.

What this showed me is that the 1.7 is a TC that can really extend your reach. Just using manual focus in live view also showed me that a minor touch on the focus can throw things off a lot.

I also feel that for action shots this showed me that a TC may not be helpful at all since it add an extra stop and the focus with a native f4.5 lens may not be quick enough for pictures of BIF.
03-16-2014, 01:37 PM   #7
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this is with the tamron 1.4 adapter and the sigma 500 with autofocus



















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