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Rokunar vs Kenko
Old 02-01-2005, 08:07 PM   #1 (permalink)
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Hi - a quick question conserning Rokunar vs Kenko tele-converters and tele-conveters in general.

Of the two mentioned, is one considered the better of the two?

Tele convertors in general are they good, bad, or indifferent as compared to the lense of equal focal length? ie. a 200mm verus a 100 with a 2x tele-converter.

TIA
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Re: Rokunar vs Kenko
Old 02-01-2005, 09:07 PM   #2 (permalink)
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I don't have experience with either of those.. I have a Tamron 2X that's come in pretty handy but I wouldn't use it to make money..

Some cons of teleconverters are you lose a lot of light and you're adding more lens elements which will bring down overall quality..


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Re: Rokunar vs Kenko
Old 02-01-2005, 09:12 PM   #3 (permalink)
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Rokunar and Kenko I can't address.

I have a 2x teleconverter, made by Sigma, it's matched to my Sigma lenses. While it's a cheap way to get to 400, that magnification comes at a cost: In my experience, with my rig, I lose a stop (from 2.8) within the same ISO rating, and there's a loss in clarity detectable only at the largest sizes.
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Re: Rokunar vs Kenko
Old 02-01-2005, 10:26 PM   #4 (permalink)
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Not sure about either of those you've mentioned. I have a tamron 1.4x, which is nice in that it will work with any Canon EF lens, and it's optics are pretty good.

Generally, what I've heard about teleconverters is that with a 1.4x you only lose a very small amount of optical quality, but with a 2x the quality loss is quite a bit more noticable. Of course this all depends on how picky you are and the end use of the pics.

There's a couple articles/reviews on photo.net that may be of interest to you. They're listed in the index.

Oddly enough, this isn't the sort of thing that comes up much in a glamour forum. [img]/ubbthreads/images/graemlins/smirk.gif[/img]
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Re: Rokunar vs Kenko
Old 02-01-2005, 10:53 PM   #5 (permalink)
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I would think the Kenko one
I have never heard of the other brand [img]/ubbthreads/images/graemlins/confused.gif[/img]

More to the point , you asked about a 100mm with a converter, I would not use a converter on any lens that short
You could just go get something like a 70 to 300 zoom( I have the nikon F4-5.6 not fast but I love that lens)
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Re: Rokunar vs Kenko
Old 02-02-2005, 03:02 AM   #6 (permalink)
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Thanks -

i've heard the same as far as using tele-converters:
- slight degradation of image - depending on the quality of the converter
- vigiting more common depending on focal length of the lense.
- And metering adjustment needed to be calculated.

I wasn't planing on using it specificly for a 100mm lense - that was just an example lense - actual lense is a 90mm - though i hadn't heard of the problems coming in till over 300mm not under? I'll have to look more into this...

tele-conv. cost is about 1/4 the cost of a new lense (depending), just a thought i had - trying to work the budget a little wiser - looking at a KL 250mm or 180mm - hoping for the 250mm [img]/ubbthreads/images/graemlins/wink.gif[/img]. but thought i might get away with a 2x tc. instead. for the moment on the 90mm. (MF) since there are other things i need as well.

Thanks again
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Re: Rokunar vs Kenko
Old 02-02-2005, 08:44 AM   #7 (permalink)
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Generally, a converter plus lens gives noticeably less sharp performance than a prime lens of the same focal length as the combination. As often, the higher quality converters degrade performance less than the bargin brands. The two you mention are probably equivalent, insofar as I know.

I don't know how a prime+converter compares to a zoom of the same length as the combination. I suspect a good zoom beats a cheap converter + decent prime.

FWIW, I used a Vivitar(?) converter with my Pentax system for a while, combining it with the 50/1.8 and 135/2.8 on occasion. Then I got a 200/4 and saw the difference. Personally, unless you're REALLY strapped for cash, I wouldn't recommend it. There's also the (somewhat) minor issue of changing the converter in and out, what with caps and all.
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Re: Rokunar vs Kenko
Old 02-03-2005, 12:17 PM   #8 (permalink)
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I would go with the Kenko. I have a Kenko Pro 300 2x Teleconverter which I use on my Nikkor 70-200 f2.8 AF VR for surfing and other distance shots. It works great. I also use a Nikkor TC-201 with my older lenses.

A converter magnifies any flaws in the lens and reduces the effective f stop. At slower f stops the auto focus may have problems & hunt.

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Re: Rokunar vs Kenko
Old 02-03-2005, 12:39 PM   #9 (permalink)
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I guess i should have been more specific -
- this is in reference to a manual focus Mamiya RB67 medium format camera - 2x tele-converter to be used with a 90mm prime or in the future when i get the newer lense a 50mm wide, 180mm or 250mm KL prime - no zooms for this bad boy yet, just straight thru's.

thanks [img]/ubbthreads/images/graemlins/cool.gif[/img]
 
 
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