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11-04-2014, 03:41 PM   #1
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Two tele-converters?

Can you put multiple tele-converters together?
Like a 1.4x and a 1.4x to get around a 2x (1.4 * 1.4 = 1.96).
So a sequence of tele-converters and lense two get just under 600mm (588mm):
[1.4x][1.4x][300m]
Is this possible?
I wasn't going to do this but, just out of interest, would this work?
Would you lose much IQ?

11-04-2014, 03:47 PM   #2
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It can be done, lots of folks use stacked converters to get longer reach out of their telephoto lenses.
Keep in mind each time you add a TC you lose a stop of light.
There is also a chance of reduced image quality depending on the quality of the lens itself and the TC's.

Feel free to try it, but don't expect miracles unless you have very expensive lenses and TC's that can maximize the available light and image quality.
11-04-2014, 03:54 PM   #3
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If you're using cheap teleconverters, stacking them will quickly ruin your image quality. However, stacking decent ones is feasible as long as the light loss doesn't overwhelm you.

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11-04-2014, 05:09 PM   #4
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Double teleconverters can help in only a limited number of circumstances. You lose so much light that a fast lens is almost essential. Some experiments have been posted on the board. You might want to search for teleconverter photos.

11-04-2014, 06:44 PM   #5
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Even good TCs cause some image loss; it seems to be more noticeable at long focal lengths because the image fills the frame. What is more problematic is the loss of light. Even with live view and magnification, it is hard to pinpoint the focus because the DoF decreases significantly and the darkness of the image leads to increased amplification, which increases noise, which obscures detail.

You'll likely find that the results are no better than just cropping.
11-05-2014, 07:06 AM - 2 Likes   #6
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QuoteOriginally posted by First Poster Quote
I wasn't going to do this but, just out of interest, would this work?
Would you lose much IQ?
Yes, it may work - sometimes. But as already said:

QuoteOriginally posted by Mikesul Quote
Double teleconverters can help in only a limited number of circumstances.


Just to show that it can be done, here's a special example:


A 350mm catadioptric lens plus two 2X teleconverters stacked.
That makes a 1400mm system that......


....may produce this under good atsmospheric conditions.
(non-cropped, downsized image)


100% non-resized crop of the above
(click on images to see larger versions)

Here cropping of a 350mm image would produce much less detail, because in THIS situation, the sensor resolution (: the spatial resolution) is the limiting factor. But it's definitely not a setup I would recommend for birding.........
12-10-2014, 01:39 PM   #7
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You can stack, each stack will reduce the effective amount of light coming into the lens as well as narrow down the image quality.
12-11-2014, 12:54 PM   #8
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Just as a note....

That lens (as well as even my old Sigma 18-200mm) does better with a teleconverter than my Rokinon 500mm f/8 with and without a TC.
Unfortunately, the 500mm (or at least my copy) is not very good near infinity.

Yes, I have tried stopping it down, and I do use a tripod and a 2 second timer delay


Last edited by formercanuck; 12-11-2014 at 01:00 PM.
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