M3 / NGC 5272

[rjbokleman]

Here's my first 'test' image using the new C8 EdgeHD, Celestron OAG, w/ZWO ASI1600MC-Cool @ 1422mm w/.7x focal reducer.

It's only 1.6 hours from Friday night, so not a lot of time on this one. As I mentioned in the thread containing Chuck's images, I used a Bahtinov Mask here for the C8 to get my initial focus on Vega. Slewed to M3 and left things as they were for 2 hours.

There are NO Bias, NO Dark, or Flat frames here. Just a PixInsight 1.8 debayer (GRBG), Star Alignment, and then some histogram work with a little saturation tossed in.



PHD2 was used and I was able to guide under 0.50" of total error. Sometimes as low as 0.44 and sometimes as high as 0.67.

Once I get around to building the Bias / Dark library, it will be off to look for a new Flats setup for the C8. My existing home made unit isn't big enough to handle 203mm in aperture. If anyone has a suggestion...I'm all ears.

[Apollo XX]

Hey Ron,

Great first image! Looking forward to seeing what the future holds with this setup.

[AndyG]

Looking good Ron. Guiding and focus are perfect, and the scope optics are giving nice round stars right to the edge. Awesome!

[rjbokleman]

Thanks, Mike.

Andy was privy to the earlier test images and how bad they were.

I was looking for that exact feedback on the stars. As Bill L. mentioned - back focus - is key on the SCT for a flat field to the edges. You need to do the math for your scope and then attempt to fit everything in the image train as closely as you can.

The C8 EdgeHD requires 133.35mm of back focus @ 2032mm and 105mm @ 1422mm. This can be complex because in order to be able to rotate the camera and/or guide scope you really need to use an Off Axis Guider (OAG). Rotating the guide camera help you locate a nice star to guide on. Rotating the camera lets you frame your target. Then there's the issue of wanting to use a 2" filter...which requires M48 threads.

The Celestron OAG has two adapters T2/M42 and M48 (2") threads both male and female of different lengths (12.5mm/4.5mm respectively).

In this case I had the .7x Focal Reducer --> Celestron OAG w/Female 48mm --> Blue Fireball 1mm Male/Male converter --> IDAS Filter --> ZWO M48/M42 changer --> 6mm M42 spacer --> ASI1600MC. All totaled this was 106.8mm. 1.8mm over the desired 105mm.

To fix this, I ordered a Stellarvue SFE-M48-005, 5mm M48 spacer. That will bring me down to 105.8 shaving off another 1mm. That means I can now remove the 6mm M42 spacer and replace it with the new M48 5mm and try this again.

[rjbokleman]

This can be complex because in order to be able to rotate the camera and/or guide scope you really need to use an Off Axis Guider (OAG).

I found this out quickly attempting to use my 50mm Orion / QHYCCD combo with even the .7x Focal Reducer @ 1422mm...tracking was impossible.

I also tried to mount my Stellarvue 60EDS (3lbs) on top for 330mm of guide scope and failed because of two things:

The QHYCCD guide camera didn't have enough back focus in the SV60EDS to obtain focus. I would have had to buy yet another extender to make that work.

The bigger issue turned out to be weight. The iEQ45 Pro with all that on it just didn't have the counter-weights to handle it. I would have had to add another 5lbs probably or gotten some kind of counter weight rod extension for the mount. When you get into this territory...you've probably exceeded the mounts capabilities...so I punted and went back to the OAG.

[rjbokleman]

Here's a screen capture of PHD2 while guiding during the capture of M3.

[Ronald Z]

Really great capture, Ron!

Ron Z