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Comparison Prime focus Moon 150mm F8 Achromat and ED

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About this observation
Observer
Peter Anderson
Time of observation
04/04/2020 - 15:00
Object
Moon
Observing location
Brisbane, Australia.
Equipment
150mm F8 standard achromat and ED
Exposure
Both 100 ISO - 1/100sec achromat, 1/125 sec ED
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These are part of my comparison tests between a Celestron 150mm F8 achromatic refractor and a Skywatcher ED of the same specifications. The size of the images do not display the fine detail on each image. Perhaps the ED is marginally better in this regard.

The Celestron image was taken on 7th January 2020 with the Moon at 40 degrees altitude. The Skywatcher ED on 5th April 2020 with the Moon at 37 degrees altitude. Conditions were comparable. Apart from reduction in size and cropping, the images were unadjusted in any way. The same camera, a Canon 70D was used in each case.

Firstly it is obvious from the relative size of the image that the Moon was closer on 5th April and that the libration in the north-south direction had changed considerably. The April date was chosen to replicate the phase of the earlier images - though libration has played a part in producing some significant differences.

I would comment (as I did for the stellar images I posted on this site), that the colour balance of the ED images are different, and the light transmitted is also greater because the exposure was 1/125 second and not 1/100 second  at the same ISO speed of 100.

Spurious colour on the limb and bright features, readily encountered with the achromat are not apparent at this scale except for a subtle yellow-green shading on the southern limb and a faint trace around the rest of the bright limb. These colourations generally become more apparent at higher magnification when bright objects and features are involved, particularly at sharp contrasty boundaries..

These are just two of the comparison images. I am in the process of preparing a more detailed account.

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