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10-13-2014, 10:21 PM   #1
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focal length input for m42 teleconvertor 3x

I have an M42 Asanuma auto tele converor 3x with a Takumar SMC 50mm f1.5. I need to manually input a focal length for M42 lenses on my Kx body. What focal lenght should I input? Is it just plain 3x, so 150mm, or is there something more.thanks

10-13-2014, 10:23 PM   #2
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QuoteOriginally posted by kangamel Quote
I have an M42 Asanuma auto tele converor 3x with a Takumar SMC 50mm f1.5. I need to manually input a focal length for M42 lenses on my Kx body. What focal lenght should I input? Is it just plain 3x, so 150mm, or is there something more.thanks
150mm would be correct.

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10-13-2014, 11:16 PM   #3
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thanks Adam
10-14-2014, 07:35 AM   #4
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QuoteOriginally posted by kangamel Quote
I have an M42 Asanuma auto tele converor 3x with a Takumar SMC 50mm f1.5. I need to manually input a focal length for M42 lenses on my Kx body. What focal lenght should I input? Is it just plain 3x, so 150mm, or is there something more.thanks
I agree with Adam. But why using a 3x convertor on such a (good) lens? You loose all the light, it stops down your 1.5 (prob. 1.4) to somewhere between 4 and 8 I think..

10-14-2014, 07:46 AM   #5
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QuoteOriginally posted by PenTed Quote
I agree with Adam. But why using a 3x convertor on such a (good) lens?
A converter on a good lens is way better than a converter on a bad lens!
10-14-2014, 04:44 PM   #6
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What is the conversion when it comes to converters in f/stops? I have a 70-200f2.8 and thinking about a converter 2x, because the super zoom I would like to get, is just not going to happen for awhile.
10-14-2014, 05:02 PM   #7
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QuoteOriginally posted by Storm Chaser Quote
What is the conversion when it comes to converters in f/stops? I have a 70-200f2.8 and thinking about a converter 2x, because the super zoom I would like to get, is just not going to happen for awhile.
Stops are about the same -- you lose 1 stop with a 1.4x, 2 with a 2x, etc... actual amount can vary slightly...
10-14-2014, 05:39 PM   #8
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vonBaloney, thanks for the info. I know there is a big difference between makes. I here pentax has a good one?

10-15-2014, 05:21 AM   #9
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QuoteOriginally posted by PenTed Quote
I agree with Adam. But why using a 3x convertor on such a (good) lens? You loose all the light, it stops down your 1.5 (prob. 1.4) to somewhere between 4 and 8 I think..
using it for fun just because it is here and it fits.
t's pretty terrible what it does though, terrible in all the things, except tele conversion, which I don't need anyway
10-15-2014, 01:47 PM   #10
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Bad convertors even don't give a better resolution. In other words, if you enlarge a picture taken with the bare 1.4 3-fold than sharpness could be the same as the picture taken with the 1.4x3.

A good convertor does a lot better, especially in the center. Corners remain a problem because the convertor is not specifically designed for the lens that is put onto it.
10-15-2014, 05:42 PM   #11
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Thanks PenTed. I acquired thic TC with some other stuff so just thought I'd give it a go to see what a tc does, it is consistently soft and fuzzy from corner to corner. I would hope a more expensive unit would give a better result. I am trying to work out how I get closer to the moon when my max focal length is the 55-300, defiantly not with this thing!
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