Old 18-12-2013, 09:58 PM
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rogerg (Roger)
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2x Barlow, 2x Teleconverter not equal

Hi all,

See attached JPG for an interesting comparison.

Large moon has the following optical train:
  • Megrez 90 -> 2" diagonal -> Celestron Ultima 2x Barlow -> small adaptor for 1.25" to Canon mount -> Canon 6D
  • Megrez 90 -> 2" adaptor with T-ring -> Kenko 2x Teleconverter (canon mount 2x) -> Canon 6D

The image shown is full frame, not cropped.

Do people agree with me that the difference in apparent size of the Moon when photographed through he two different methods is a result largely due to the difference in spacing from telescope to barlow/teleconverter, and barlow/teleconverterto camera?

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Old 20-12-2013, 10:31 PM
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Shiraz (Ray)
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hi Roger. if the two negative lenses have the same fl (not necessarily the case though), then the different magnifications depend on the positions of the negative lenses relative to the prime focus of the main optics and the different spacings between the negative lenses and the camera chip. ....which basically agrees with your statement.

Worth a read if you have not already come across it...http://www.brayebrookobservatory.org...BarlowLens.pdf

Last edited by Shiraz; 20-12-2013 at 10:41 PM.
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