Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Third Quarter Moon with an Astro-Tech AT72ED and ZWO ASI183MM

  • Please log in to reply
2 replies to this topic

#1 james7ca

james7ca

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7342
  • Joined: 21 May 2011
  • Loc: San Diego, CA

Posted 29 December 2018 - 08:38 PM

Taken on the morning of December 29, 2018 using a Astro-Tech AT72ED (72mm aperture, f/6), a Tele Vue 2X Powermate, a ZWO ASI183MM Pro camera, and a stacked set of Baader Semi-APO and 610nm Long Pass filters (to limit the bandwidth to between 610nm and 675nm). Best 20% of 1000 frames using Autostakkert!, sharpened with Registax, and finished with Photoshop CC2017.

With the Powermate the AT72ED was working at about f/12 and an effective focal length of 860mm. The original image scale was thus near to 0.6 arc seconds per pixel (critical sampling for the camera/scope combination).

This was a test to see how much detail I could obtain by matching the moon's full disk to the frame bounds of the ASI183 camera. To do so you need to use a focal length of about 820mm, so at 860mm I was a little over the maximum. At full scale the moon was 3370 pixels high which is still a little under the height of the ASI183 sensor (3672 pixels). However, on occasion the moon will be larger than on last night, so that's why my target focal length is closer to 820mm.

 

I'd rate the seeing conditions when this image was taken as poor as we are currently having a weak Santa Ana condition (and the image on the liveview during capture looked very turbulent).

 

In addition to the image of the moon, I've included a picture of the AT72ED with the extensions used to mount the Powermate and the ASI183MM camera. The actual "stack" when imaging was a little longer than shown here, since in this picture the dew shield was retracted and the focus was fully inward (when imaging the focuser drawtube was extended by 17mm, so I probably need to add another half inch to the extension tubes).

 

You can see an image of the gibbous moon that I took a few days ago using a smaller Stellarvue SV50ED at a similar image scale using the ASI183MM:

 

  https://www.cloudyni...m/#entry9037374

 

I had better seeing when using the SV50ED so both scopes seemed to have produced about the same limiting resolution. Actually, at higher reproduction scales the image from the session with the SV50ED looks better than what I got last night with the AT72ED, but I think almost all of that was from the differences in the seeing conditions. Also, the images taken with the AT72ED were done well after the start of dawn, in fact the sky was already blue although the sun hadn't yet risen (sunrise was at 6:53AM, this image was taken just after 6:30AM).

Attached Thumbnails

  • Last Quarter Moon with AT72ED and ZWO ASI183MM (Small).jpeg
  • AT72ED with Powermate and ASI183 Camera.jpg

Edited by james7ca, 29 December 2018 - 09:21 PM.

  • Carol L, zjc26138, jim kuhns and 8 others like this

#2 Tom Glenn

Tom Glenn

    Surveyor 1

  • -----
  • Posts: 1903
  • Joined: 07 Feb 2018
  • Loc: San Diego, CA

Posted 29 December 2018 - 09:23 PM

This looks nice James.  I didn't even bother setting anything up last night, as the seeing forecasts (which are hopelessly optimistic anyway) were among the worst I have seen, with Meteoblue saying 2 arcseconds and Clear Sky rating it as "Poor".  I have little doubt that in these conditions you probably have a good bit of resolution left in the tank, even with a 72mm aperture.  



#3 james7ca

james7ca

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 7342
  • Joined: 21 May 2011
  • Loc: San Diego, CA

Posted 30 December 2018 - 12:15 AM

Tom, thanks.

 

Here is a detail from the AT72ED shot that can be compared to the image I did a few days ago with the SV50ED. The phase of the moon is obviously different and the processing was not matched, but it looks like both sessions recorded about the same amount of detail. I think the AT72ED may look better in some spots while the SV50ED is better in others, a bit difficult to tell because of the differences in the lighting and processing. However, both are starting to look a little "strained" at this reproduction ratio which is near to 60% of the capture scale. I'd actually like to be closer to 80% or even full scale on the best nights when not having to use a red or near IR filter.

Attached Thumbnails

  • AT72ED Detail.jpg

  • Carol L, roelb and aeroman4907 like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics