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12-07-2008, 09:21 PM   #1
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pentax 18-250mm with a tele-converter

I just picked up the 18-250mm and wonder if anybody tried to put a tele-converter on it.
I would like to buy one that matches this lens.

12-07-2008, 10:14 PM   #2
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Its a very slow lens to put a teleconverter on.
12-08-2008, 06:09 AM   #3
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faster

would it not be faster than a manual lens though?
12-08-2008, 06:18 AM   #4
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Prolly not worth the try to put a TC onto the 18-250. I would think it may not work at all.

With the price of pentax 18-250 going almost the same price as a Tamron 70-200/f2.8 (well, at least here in Australia), I reckon you might as well get the Tamron.

12-08-2008, 06:42 AM   #5
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SLOW as in aperture. The Tamron is f/6.3 at the long end, so sticking a 1.4x teleconverter would make it around f/9, and a 2x would make it f/13 (ouch!) so unless you're shooting a nuclear explosion, you'll have problems (both exposure wise and with autofocus as very little light would be reaching the AF sensors)
QuoteOriginally posted by djayvo Quote
would it not be faster than a manual lens though?
I have to ask "why bother?" Is 250mm not enough reach, especially when you have the range of 18-250mm in ONE lens? Maybe you should have bought one of those 28-300mm lenses
12-08-2008, 07:20 AM   #6
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For the boat

Just thought it would be nice to have a little longer reach for on the boat. I do have a old 300mm fixed but thought the outo focus would be nice.
12-08-2008, 07:22 AM   #7
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QuoteOriginally posted by egordon99 Quote
SLOW as in aperture. The Tamron is f/6.3 at the long end, so sticking a 1.4x teleconverter would make it around f/9, and a 2x would make it f/13 (ouch!) so unless you're shooting a nuclear explosion, you'll have problems (both exposure wise and with autofocus as very little light would be reaching the AF sensors)
It's not how much light reaches the sensors but rather something to do with how wide the cone of light is... And that depends on aperture alone.
12-08-2008, 08:38 AM   #8
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QuoteOriginally posted by djayvo Quote
I just picked up the 18-250mm and wonder if anybody tried to put a tele-converter on it.
I would like to buy one that matches this lens.
Yes, I've tried a Kenko 1.5 AF TC and a 2.0 Manual focus TC on it.
The AF with the Kenko only works well (but slow with a lot of noise) in strong light conditions, otherwise MF is the only option.
Also, the edges of the pictures become soft.
Of course you will have a lens with a small aperture as a result....

If you are in Africa, in full daylight, it works well if you pump up ISO and slow the lens down at least one stop, if you are in Holland, with grey weather, it is not usefull to mount the combination on the camera.
I've tried both.

- Bert

12-08-2008, 02:04 PM   #9
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QuoteOriginally posted by egordon99 Quote
...so unless you're shooting a nuclear explosion, you'll have problems...
I'd say that even if you were in a nuclear explosion you would still have problems. They would just be of a different kind.

12-08-2008, 05:33 PM   #10
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I get blamed for a lot.

QuoteOriginally posted by Miserere Quote
I'd say that even if you were in a nuclear explosion you would still have problems. They would just be of a different kind.

OK, bad idea I'll stick to my 300mm manuel focus cheaper anyways. Plus this world is in bad shape as it is and I would hate getting the blame for a nuclear explosion.
12-08-2008, 05:45 PM   #11
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I have an 18-250, and bought a Tamron 1.4X for it. what others have said came true. It often was too slow due to the additional 1 stop light loss to be of much use. Plus Tamron told me via an e-mail that their 1.4X was not recommended for their Tamron 18-250. Because of the long chain of AF drive shafts through the two lenses, MF always had a gritty non-smooth feel to it. When there was enough light, aF would work ok.

Now i have a 300mm prime lens and use the 1.4X on it. Much better.

18-250 is a good walk around lens when needing or wanting to take a variety of pictures very quickly.

Best wishes, Phil
12-08-2008, 06:01 PM   #12
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QuoteOriginally posted by egordon99 Quote
SLOW as in aperture. The Tamron is f/6.3 at the long end, so sticking a 1.4x teleconverter would make it around f/9, and a 2x would make it f/13 (ouch!) so unless you're shooting a nuclear explosion, you'll have problems (both exposure wise and with autofocus as very little light would be reaching the AF sensors)


I have to ask "why bother?" Is 250mm not enough reach, especially when you have the range of 18-250mm in ONE lens? Maybe you should have bought one of those 28-300mm lenses

Thank you.
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