I was doing some optical tests with my small APO triplet refractor, the one I am hoping to use for a General Relativity test during the Solar eclipse in April 2024. The telescope is a 80mm f6 APM refractor with a LOMO lens (slightly masked to reduce the aperture to 76mm). I am using a Tele Vue 0.8x flattener/reducer and a Baader Red CMOS filter. The camera is currently a ZWO 183MM planetary camera (I am hoping to eventually use a ZWO 294MM). I was surprised how good the resolution was with such a short focal length and small aperture.
The exposure was 4.5ms; 50sec; best 10% stacked in AS3!. Some sharpening with ImPPG and a little Photoshop for levels.
Here is the full field of the camera at 25%:
During the eclipse, exposures of around 0.5sec to 1.0sec would be taken in order to record the star positions near the Sun and to look for deflections caused by gravity. The 294MM camera has a larger field but approximately the same size pixels.
Here is a 100% view of the moon, which shows how much even a small refractor can resolve. Open in a new tab to see at full resolution.
Finally, here is a 100% crop taken with a 1sec exposure a little bit away from the moon. This is a single frame, unstacked. I think the ultimate processing technique will be to chose approximately the best 50% of the frames and stack them. The precise star locations will then be determined and deflections from their ideal positions will be indicative of gravitational deflection of starlight.
Full moon, 5 Feb 2023, with a small refractor
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Re: Full moon, 5 Feb 2023, with a small refractor
This is a fantastic observational project. Please keep us posted
Pedro Re'
https://pedroreastrophotography.com/
https://pedroreastrophotography.com/
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Re: Full moon, 5 Feb 2023, with a small refractor
A full description of the project can be found here: viewtopic.php?t=39027
A question for Pedro: I noticed an interesting focusing issue that I had never noticed before. At first I focused on a bright star using a William Optics Bahtinov mask. I then looked at the moon and noticed that the lunar image was not perfectly focused. I needed to move the focus outward very slightly (by 100 steps on my ZWO EAF and Feather Touch focuser). When I went back to a bright star and saw that the Bahtinov mask pattern was no longer perfectly aligned, so I had to move the focus back in by 100 steps.
I assume this has something to do with lunar/solar light coming from an extended object (corresponding to angles of approximately f/100) while stars are perfect plane waves. The focal movement required is really like the moon is "not really at infinity". Did you or anyone else ever notice this focusing effect? Does my interpretation make sense?
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Re: Full moon, 5 Feb 2023, with a small refractor
These are absolutely wonderful images this is a fantastic project, but I think I would be more interested in the eclipse and corona and get too distracted to image the stars
Have you decided where to go yet?
I wonder whether prominences are slightly out of focus compared to the disc centre sometimes or it could be me being fussy
Alexandra
Have you decided where to go yet?
I wonder whether prominences are slightly out of focus compared to the disc centre sometimes or it could be me being fussy
Alexandra