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Comparison 150mm achromat and ED instruments

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About this observation
Observer
Peter Anderson
Time of observation
05/04/2020 - 00:30
Object
Moon
Observing location
Brisbane, Australia
Equipment
150mm F8 Achromat and ED instrument
Exposure
2000 ISO
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Comparison with 5X Barlow lens of Achromat image (on left) and ED (on right). Images 7th January 2020  for the achromat and 5th April 2020 for the ED. - Each around 09hrs 30min UT.

Comments

Grant Privett's picture

Have you considered doing the same type of test but comparing an achromatic image with an achromatic image taken while using a narrow band filter such as a hydrogen alpha - I wonder if, for a near colourless object like the moon, that might yield as good a result as with the ED as all the light will be brought to a single focus. 

Just a thought.

Peter Anderson's picture

You are quite possibly correct but my filters are limited to the usual range of colours plus a couple extra. I know some owners of achromats get very acceptable results from monochrome images but the blue haze would still be over the brighter features like Aristachus in this instance so would entail tweaking in contrast. (Probably anyone who can afford a Ha filter would likely afford an ED in the first place!)

My main field is lunar occultations and this was a secondary, no tertiary instrument. I am getting too old and crotchety to put up with too much.  So when the price of the ED came down considerably I got management approval, sold the old 150mm and replaced it with the ED. So even if I wanted to perform the experiment.....

But, seriously, thanks for you interest and suggestion. Perhaps other members have some experience in this.

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