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08-11-2009, 10:16 AM   #1
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2x converter, worth it or just get longer lens?

I recently purchased the Pentax 18-250 lens for my K10D, and I must say its a great every day lens. However we were out on a canoe trip the other evening and I was trying to get some closeups of some Pelicans and found I could not get as close as I wanted without spooking them.

I am thinking about getting a 2X converter, but a quick search brought up a Sigma for about $300. I''m wondering if this is worthwhile or should I just put the $$ towards a longer lens. I've never used a converter before, can I expect decent pictures from it, do I lose much speed etc.? Do I need to spend $300 or can I pick up a decent one for less?

I'm looking at one on ebay for about $90 - anyone here have experience with these?


thanks!

08-11-2009, 10:22 AM   #2
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Don't buy cheap AF converters.
Search for 7 element versions, use strings like "7 MC teleconverter pentax", "7 elements teleconverter pentax".
I have recently tested not very widely known non-AF old Telemore95 II by Komura.
To be short - no go with my modern lenses, and pretty good with my old fast zoom.
Each teleconverter must be matched to perticular lens, so it can work ok with one and very bad with another.
08-11-2009, 10:23 AM   #3
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I use a 1.7X converter with my DA* 300mm F4 and get good results.

I don't think I'd advise using a 2X with the 18-250mm that would make it a 500mm F11 so you would need really bright light and up the ISO to use it.

Converters are best used on fast prime lenses.
08-11-2009, 10:26 AM   #4
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QuoteOriginally posted by Glen_S Quote
I recently purchased the Pentax 18-250 lens for my K10D, and I must say its a great every day lens. However we were out on a canoe trip the other evening and I was trying to get some closeups of some Pelicans and found I could not get as close as I wanted without spooking them.

I am thinking about getting a 2X converter, but a quick search brought up a Sigma for about $300. I''m wondering if this is worthwhile or should I just put the $$ towards a longer lens. I've never used a converter before, can I expect decent pictures from it, do I lose much speed etc.? Do I need to spend $300 or can I pick up a decent one for less?

I'm looking at one on ebay for about $90 - anyone here have experience with these?
thanks!

I have a Kenko 1.5X TC and the 18-250mm Tamron, the combination has lost of problems with focusing on my K10D. Manual focus is fine.

- Bert

08-11-2009, 11:05 AM   #5
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I'd stay away from 2X converters not unless you have very good fast lens to compensate for the light loss of using these.
A 1.5X or 1.7X usually is better.
The Kenko 1.5X costs $99 I think at Amazon.
08-11-2009, 11:52 AM   #6
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I have a kenko 1.5x and use it with my longer teles. It clearly does have focusing problems as in low light it hunts more. However, the manual clearly says that below f4 this will happen and it does. I use it with my DA 55-300 and have used it with my DA 17-70 SDM just fine. As was said above, in manual focus it's just fine.

Frankly, I haven't tried in on my Tamron 18-250 but that seems like too much range for a t/c.
08-11-2009, 11:52 AM   #7
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QuoteOriginally posted by mille19 Quote
I use a 1.7X converter with my DA* 300mm F4 and get good results.

I don't think I'd advise using a 2X with the 18-250mm that would make it a 500mm F11 so you would need really bright light and up the ISO to use it.

Converters are best used on fast prime lenses.
If I may interject a semi-related question to this thread, which 1.7x TC do you use with the DA*300? The SDM works ok? How would you rate the IQ impact? thanks.
08-11-2009, 11:59 AM   #8
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I have both the Tamron-F AF Tele-converter (2X Pz-AF BBAR MC7) and the Vivitar 2X Macro Focusing Teleconverter with electrical contacts but no AF. I've tried each with a variety of lenses, from modern zooms to old fast primes, and as far as I'm concerned the loss of IQ is too great to justify using them.

The *only* times I've gotten as good or better images by using a 2X teleconverter instead of just cropping or blowing up an image taken without one is when focusing on really distant small objects. I'm fairly certain the only reason for that is the added magnification allowed for more accurate focus, certainly with my eyes, maybe with the autofocus.

Of the two, the Tamron performs more consistently and provides better images. That surprised me based on what many say about the vivitar. Of course the Tamron doesn't help for close focusing and the Vivitar will let you get very close with a 50mm on it.

08-11-2009, 01:02 PM   #9
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Not only do you lose two stops of light with a 2X TC - thus making the lens f/11 at best, and effectively disabling AF - you also lose quite a bit of IQ with most TC's. You're usually better off just cropping. You could also try a 500/8 mirror lens as an alternative, although with these, it's usually only *somewhat* better than cropping.
08-11-2009, 01:28 PM   #10
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I have a Tamron 18-250mm (essentially the same as the Pentax counterpart).

I also have 3 AF teleconverters: Tamron 1.4X, Pentax 1.7X, and Tamron 2X, all considered high quality.

The only TC that sort-of works with the 18-250mm is the Tamron 1.4X. Even then, at 250mm lens setting (350mm effective), the AF hunts a lot. It needs something contrasty to lock on.

There's not enough light for the 1.7X and the 2X to work.

In terms on IQ, it's better to take the photo without the TC and crop a bit more during post processing.

Teleconverters do have their place, it's just not with the 18-250mm.
08-11-2009, 01:52 PM   #11
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what camera are you using and what size will you be printing at? All those megapixels are there for some significant cropping.
08-11-2009, 02:20 PM   #12
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QuoteOriginally posted by KyPainter Quote
The *only* times I've gotten as good or better images by using a 2X teleconverter instead of just cropping or blowing up an image taken without one is when focusing on really distant small objects. I'm fairly certain the only reason for that is the added magnification allowed for more accurate focus, certainly with my eyes, maybe with the autofocus.
That's a great observation, and actually has a lot to do with why I think I can get somewhat better results from my cheap Samyang-made Vivitar 500/8 mirror than I can by simply cropping an image from my DA50-200.

Of course, sometimes - as when birds - it's just *fun* to be able to see things bigger / "closer" in the viewfinder. I don't necessarily *need* better results than cropping to find it worthwhile. But most 2X TC's are likely to give results *worse* than cropping.
08-11-2009, 04:28 PM   #13
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QuoteOriginally posted by Marc Sabatella Quote
But most 2X TC's are likely to give results *worse* than cropping.
I agree 200%. I had a 2X Vivitar Macro Focusing Teleconverter for a while, but sold it. It was OK for macro use, but as a teleconverter, my results were always inferior to just cropping -- less sharp, less contrasty.
08-11-2009, 11:51 PM   #14
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It's the Pentax 1.7x AF converter I use.
The SDM does not work because the AF is done in the converter.
The IQ is very good, I only use it in good light and stop down to F8.
The image attached was taken with this combo.
Attached Images
 
08-12-2009, 12:23 AM   #15
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I don't aggree that cropping is better.
With Telemore 2x converter (as far as I remember about $20 :-) ) I have it is not so.
I use it with 80-200m F3.5 lens. Manual focusing is pretty good.

Look here: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/69025-telemore...converter.html

Usable at F3.5 and F4, but be warned about abberations.
At F5.6 it is very-very good. At F8 it is razor sharp, and no, you can't get same results but cropping. I checked this.
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