As the title says. I received my Apex-L and wanted to do initial testing even though the moon was 98.9% full.
Physical inspection. The included documentation is well written and covers what the user needs to know. The Apex-L and Sky-Watcher adapter plate both come with 2ea 1mm spacer rings. I had one area of concern when inspecting the Apex-L and Sky-Watcher adapter plate. The male M42 threads on the Apex-L and male M48 threads on the Sky-Watcher adapter plate were only 3mm high. Adding 1mm spacer rings on either to obtain the 58mm back focus was a concern. That would give me 2mm to screw on the next link in the chain. Starizona said this shouldn’t be a concern. I disagree and think there should be more thread. The ZWO Filter Drawer and ZWO 16.5mm spacer thread height is 4mm so I added the needed 1mm spacers there.
Configuration of the optical train was as follows:
Apex-L + SW Adapter Plate (1mm) + ZWO Filter Drawer (21mm) + 1mm Spacer Ring + ZWO Spacer (16.5mm) + 1mm Spacer Ring + ASI2600MC Pro (17.5mm Back Focus) = 58mm
I centered on Deneb to do 4-corner testing using the recommended 58mm back focus. The figure below shows the results (screen grab). I plan to do retesting using a back focus of 57.8mm and 58.2mm to see if the stars improve.
The figure below shows the vignetting of the above optical train (screen grab). I am disappointed with the vignetting. I expected much less. The figure doesn’t show an inner vignetting ring between Deneb and the start of the dark vignetting. I realize this is a 0.65x FR/FF on a F/5.5 scope but my other FR/FF’s never showed this much vignetting for my APS-C sensors. I am not sure if the moon being 98.9% full is a factor here. The scope was pointed ~90 degrees away from the moon. I will have to wait until the moon isn’t up to do more testing. There’s too much light pollution and noise in the processed image below to come to a conclusion.
Processed Deneb Image – 60ea 30 second subs including Darks, BIAS and Flats. Basic PixInsight processing. Very small crop because of Dithering.
I need to do more testing and adjusting the spacers but it looks like the Apex-L does an OK job producing acceptable stars in the corners. I am disappointed with the vignetting using my ASI2600MC Pro. Using the Apex-L with a 4/3 sensor or less will produce very good results... I need to do more testing in 1 week when the moon rises later. Lastly, its 'my opinion' that the thread height on the Apex-L and the Sky-Watcher adapter plate are too short.
I would like to get feedback from users that are using the Apex-L with the Sky-Watcher 100ED APO on the above vignetting.
Edited by Jim Waters, 29 November 2020 - 06:20 PM.