2 replies to this topic

[UP4014Fan]

Here's a new image of M101, cropped from the master, combining what I captured the other night with what I captured last night.  After culling in Blink, where I only lost about 20 subs due to star trails, thanks to my new mount, I ran them through Subframe Selector, assessing for the first deviation for number of stars and FHWM.  The result was that I retained 139 subs from Saturday and 361 from last night. 

 

One of the things I did when imaging last night was to turn the voltage on the dew ring down - that killed the corrector plate spikes in the run last night.  Those remaining are from Saturday.  I have to thank the CN member who suggested that technique.

 

I do want to add another couple of hours to this because I imaged this with a nearly full Moon and had to deal with the sky glow, but overall I'm real pleased.  

 

Thanks for everyone here who shares their expertise and experiences!

 

 

[VMan]

What are these "corrector plate spikes" you are referring to?

[UP4014Fan]

It's been noted here and on the Celestron fora that there's an issue with using the Celestron dew ring without some sort of environmental control (that is, just plug it into a 12-volt source and just letting it run on its own), the corrector plate on their SCT gets slightly distorted, causing a spike or "Saturn's Ring" artifact on brighter stars.  Celestron sells two different control units that monitor temperature/dew point that control the heating of the dew ring.  These run between $299 and $499, IIRC.  People have also made their own units.

 

One member here suggested simply lowering the voltage to the dew ring, which I did by using a variable output transformer.  Not nearly as elegant, but it seemed to work.  If you look at this detail from an image I took of the Pleiades, you'll see the "Saturn's Ring" or the spike artifact to which I'm referring.