8" EDGE HD or 8" RC?

[that_guy (Tony)]

At the moment, I've started imaging with my C8 evolution with f6.3 reducer on it. Trying to get a flat field has been a nightmare. I've been thinking of getting a separate RC8 for dedicated galaxy imaging and leaving the C8 for visual use as it was intended. Another option is to sell the C8 and get the EDGE version for "around" the same price as buying a separate RC8. Which of these options would be preferable?

[benklerk]

I'll just add my 2 cents as I do own a RC 6.

You need to spend a bit of money to get the RC collimated.
You need to replace the stock focuser as its crap.
You need to get a collimation tilt ring
You need a good pin point laser like a Howie.
You need a tak collimation scope.
Depending on what size camera you are going to use, you need a field flattener if you use a APS or larger sensor.

And also read up on how to collimate GSO RC scope.

[that_guy (Tony)]

How often do you find you needed to collimate? If i buy second hand already calibrated I feel like Id save myself a few headaches.

[UniPol]

Originally Posted by that_guy

How often do you find you needed to collimate? If i buy second hand already calibrated I feel like Id save myself a few headaches.

I bought a GSO RC8 with the tilt ring here on IIS last year and the collimation was and still is spot on. I think far too many people are paranoid about collimation, I've never found it a difficult chore provided it is done carefully and methodically. Over the years I've come to the conclusion that a lot of people just aren't tech savvy and end up getting into all sorts of bother by fiddling with things they have little knowledge about as evidenced by the number of posts that have appeared on IIS. The RC8's et al seem to have copped the brunt of criticism owing to so called collimation issues and to the detriment of sales. After attending quite a number of star parties and events over the years it is obvious to me that some people just don't look after their expensive equipment choosing to throw and stuff things in the back of the whatever and it is no wonder they become damaged and out of whack. Doesn't both me, it's not my equipment. I'm sure there are plenty of others out there that are very happy with their RC's and perhaps don't choose to comment but I'm certainly very impressed with my example. By the way, the focuser is pretty ordinary and adequate for visual but something better is needed for AP, trouble is ends up costing as much as what I paid for the scope second hand.

[benklerk]

Originally Posted by that_guy

How often do you find you needed to collimate? If i buy second hand already calibrated I feel like Id save myself a few headaches.

As Unipol has said, they do hold collimation if you look after the scope. But every now and then you do need to align the optics. I last did mine in Spring 2018, and its still good.

[simon_rl (Simon)]

Originally Posted by UniPol

I bought a GSO RC8 with the tilt ring here on IIS last year and the collimation was and still is spot on. I think far too many people are paranoid about collimation, I've never found it a difficult chore provided it is done carefully and methodically. Over the years I've come to the conclusion that a lot of people just aren't tech savvy and end up getting into all sorts of bother by fiddling with things they have little knowledge about as evidenced by a number posts that have appeared on IIS. The RC8's et al seem to have copped the brunt of criticism owing to so called collimation issues and to the detriment of sales. After attending quite a number of star parties and events over the years it is obvious to me that some people just don't look after their expensive equipment choosing to throw and stuff things in the back of the whatever and it is no wonder they become damaged and out of whack. Doesn't both me, it's not my equipment. I'm sure there are plenty of others out there that are very happy with their RC's and perhaps don't choose to comment but I'm certainly very impressed with my example. By the way, the focuser is pretty ordinary and adequate for visual but something better is needed for AP, trouble is ends up costing as much as what I paid for the scope second hand.

I second all of Unipol's comments. To collimate an RC you just need the Tak scope (which are way over priced for what they are) and you mostly only adjust from the secondary mirror. Actually I have only ever needed to adjust the secondary.


As far as SCT or RC, these arre totally different sccopes and it depends what you want to achieve SCT are more versatile, but not the best for astrophotography. Where as RC arre great astrographs, most will say no good for visual, but I have used mine for visual and while it is not a Dob, I very happy with it.

[trent_julie]

My RC8 was a waste of of my money. I cared for my unit, I even sourced external assistance to have it collimated to no avail. I might add that the scope was not above my skill grade either. I purchased and borrowed the numerous tools listed earlier. That RC had its life ended with a hammer through the mirror in the skip bin. That was the most enjoyment that the RC had brought to me and i didn’t want it causing problems for anyone else.

I moved on to the C9.25, that scope has helped me enjoy astrophotography again. I find the C9.25 easy and quick to deal with, at a later point I will buy a hyperstar for it.

If you want plug and play for for the C925 otherwise if you have the time and dedication go for the RC8.

Trent

[that_guy (Tony)]

could you tell me what the issues were with your rc trent?

[multiweb (Marc)]

Originally Posted by that_guy

could you tell me what the issues were with your rc trent?

Not hammer proof.

[LewisM]

Originally Posted by multiweb

Not hammer proof.

I haven’t laughed so hard in yonks. Merci mon ami!

[The_bluester (Paul)]

Tony, I was using my C925 with the Celestron 0.63 reducer/corrector but I found that you had to have the spacing quite a bit closer than the specified 105mm to have good correction. Spectacularly poor correction and vignetting was the result at the recommended spacing. I ended up significantly closer and with about 0.7 reduction instead of 0.63 to be reasonably happy with mine. It also had real internal reflection issues so I am using the C925 without it now and bought an ED72 for the wider end of the spectrum.

If I had the money I would buy an Edge HD either 8 or 9.25" to replace it but that is not going to be happening for a good long while I think. The off the shelf C925 does show visible coma though it actually comes with an advantage built in. I was going to buy CCD Inspector to help with collimation as I did it using defocused stars as well as I could and then checked it with a trial version of CCD inspector and it was well off. I have since discovered that I can do it very nearly as well in focus using frame and focus images as I can with CCD Inspector. If I use about 10 second exposures and an auto histogram stretch the coma is visible at the edges of the field, so long as stars out in the corners all have the coma induced "Tails" pointed into the corners then the collimation is good. If it is off then they will be pointed all one way, or some corners will have visible tails and the others not etc. I got it within 5 pixels according to CCD Inspector. Longer exposures show slightly elongated stars pointed at the corners which I crop out now. The stuff I am imaging with that scope all works pretty well using about 80% of the available image space.

Having seen someone have a long battle with an RC8 collimation wise with people who really know how to do them helping him out and still never being happy with it's sharpness I wonder if it is difficulty in collimation or variable optical quality between examples that has given them the reputation they have.

[tvandoore (Tim)]

If you're happy with the C8 and are just chasing a flat field, I'd suggest to just go with what you know - stay in C8 land and buy the product that does exactly what you've said you're trying to achieve. I say just get the edge hd.

[Ukastronomer (Jeremy)]

Never looked back great scope

Edge HD especially with mirror lock when imaging