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04-19-2007, 01:41 PM   #1
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2X Teleconverter

Can you chaps steer me right here? I have a 1.4X and a 2X teleconverter. The 1.4 works great and gives quite satisfactory results. However, the 2X just continually wanders and will not Autofocus at all.
I have been mainly using on my Pentax 50-200 lens. K10d camera.
The Telecons are Kenko ( I know, a cheapr version.)
Would it be worth seeking out a Pentax or similar quality brand 2X or does the same problem still arise.
Is it just me missing something in the operation here?.

04-19-2007, 01:54 PM   #2
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You're missing something: light! The 2x converter spreads the available light over a much larger area. What hits the sensor is 2 or more stops less than what the aperture is set at/what it is without the converter. You need a brighter scene or manual focus.

QuoteOriginally posted by Bramela Quote
Can you chaps steer me right here? I have a 1.4X and a 2X teleconverter. The 1.4 works great and gives quite satisfactory results. However, the 2X just continually wanders and will not Autofocus at all.
I have been mainly using on my Pentax 50-200 lens. K10d camera.
The Telecons are Kenko ( I know, a cheapr version.)
Would it be worth seeking out a Pentax or similar quality brand 2X or does the same problem still arise.
Is it just me missing something in the operation here?.
04-19-2007, 04:18 PM   #3
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i'm surprised that the 1.4 works in AF with the 50-200.
04-19-2007, 05:47 PM   #4
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Just manual focus?

04-19-2007, 06:19 PM   #5
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Manual focus is way easier with these teleconverters. Even if these tele works, AF is always lousy anyway - inaccurate and hunting a lot.

Surprised you are trying that with 50-200mm as the images would be very soft and the view finder would be soooo dark. If you could focus on the spot and stopping down to get a great picture. I am impressed.
04-19-2007, 06:58 PM   #6
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I found that the 1.4 has been quite workable in AF mode. However not the 2 X.
Have been using in Manual focus in most instances.
I am finding, as you say, the results are not all that great really. Takes a lot off the quality of the50-200 lens.
I am doing a bit of looking into a longer reach lens,(400 or 500).
I have added a picture showing the 1.4 on the 50-200. Distance of about 250 mtrs. Not too bad I reckon,
Thanks guys for your thoughts and help much appreciated.

Last edited by Bramela; 10-06-2007 at 04:32 PM.
05-01-2007, 10:17 PM   #7
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try a vivitar macro x2. it's very cheap price and works not too bad

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/6438-macro-lenses-2.html
cool:
05-02-2007, 02:46 AM   #8
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I think the message as someone else pointed out is light!

I have found most pentax autofocus SLRs and DSLRs will work all the time if the lens is faster than f5.6 effective maximum apature

By effective maximum apature I mean that the lens apature, AND the reduction in stops by the TC combine to f5.6

In fact, by practice I find that this can be pushed a little. the 1.7x autofocus TC works on primes up to F4, yeilding an effective maximum apature of F6.8, yet is only specified to work on F2.8 lenses and faster. This has held true for my PZ-1, *istD and K10D. On an F5.6 prime it can't focus, and ranges continously as you ave noted.

This may also be why the 1.4x TC works, you are just at the limit. but the 2x costs another Fstop and probably your performance also.

I would ignore anyone suggesting another maker of 2x TC, light is light and all will perform the same. If you want to use autofocus with a 2x TC, you will need a faster lens first.

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