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06-16-2011, 09:54 AM   #1
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tele converter math check or help

Im a little lost on the math but i think I got it.


Lens 200 f4 plus 2X TC = 400 f8---------------------- I think Im ok
Lens 200 f4 plus 3X TC = 600 f12 ---------------------""""""""""""


Lens 200 f4 plus 1.4X TC = 280 f5.6-------------------- does that look right?

Thanks

06-16-2011, 10:01 AM   #2
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It does for 1,4x and 2x TC.

For 3x TC maybe it is f11 since that is the next level, but i'm not shore.
06-16-2011, 10:01 AM   #3
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You got it all right - all three of them!
06-16-2011, 10:11 AM   #4
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Original Poster
Thanks

Now I under stand why my 3x pics are usually (bleep)y

06-16-2011, 07:30 PM   #5
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Yes, the math is right.
For 'fun', try stacking some TC's.
I can put two each 2x and 3x on my Rubinar 1000/10.
Then I have a 10,000mm f/100 mirror!
Yeah, the images are (bleep)y.
But it's pretty cheap.
06-17-2011, 01:06 AM   #6
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Stacking TC's

QuoteOriginally posted by RioRico Quote
Yes, the math is right.
For 'fun', try stacking some TC's.
I can put two each 2x and 3x on my Rubinar 1000/10.
Then I have a 10,000mm f/100 mirror!
Yeah, the images are (bleep)y.
But it's pretty cheap.
So, a 350mm f/5.6 lens with two 2XTCs stacked will be a 350*2*2 mm f/(5.6*2*2), in round numbers = 1400 mm f/22 system - and that might look like this:



(bleep)y pictures? Need not be so:



Un-cropped lunar picture taken with the equiment above on a simple tripod.

Of course, with a lunar picture like this there is quite a bit of processing involved, (first of all stacking of 16 exposures), but sharp pictures can be obtained with stacked teleconverters.
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