Setting myself up for Astrophotography

[jeepster93]

Hey all! I am new here so forgive the duplicatation of any of my questions.
First off, my equipment:
Celestron C-8 on a go-to eq mount with an F-5.6 reducer.
Orion Short tube 80
several eyepeices and standard accessroies.

I have decided to enter the world of CCD cameras for the scope. The scopes are many years old and have been USED. I have pretty much seen what can be seen without timed exposures.

I am trying to mount the 80 mm ota to the 8 inch ota, and use one or the other as an autoguider, and the other as a photo taking platform.

To this I have accumulated these parts:
(Mostly from Orion telescopes)
a set of mounting rings that fit around the C-8
a mounting rail that mounts to those rings
a set of autoguider mount rings for the 80 mm ota that fits that mounting rail
a starshooter autoguider
a usb to serial cable
a serial to hand paddle cable(both cables from Celestron)
Celestron telescope control software
a laptop computer

Now this should mount the two ota's together...
Is there something that is overlooked?

The real questions I have are:
1. Is there some software that is free(or shareware) that is a better control for the mount than the Celestron software I have?
2. CCD cameras...I am thinking of going with the Orion Starshooter color ccd(4.3 mp)HOWEVER there is the monochrome ccd camera with a filter wheel.
What are the advantages and disavantges of going with a color CCD over a monochrome one and use the filter wheel?

[RickJ]

While using a separate guide scope can be made to work it isn't as easy as it sounds. The problem is flex between the two systems. It's amazing how solidly they must be connected. A C8 has some to a lot of mirror flop depending on its age. In any case this can make using a separate guide scope almost impossible as the mirror can "flop" during an exposure. Off axis guiding is usually preferred with scopes that have moving mirrors unless you have a way of locking the mirror down so it can't flop.

I can't answer 1 as I don't use tha scope or mount. There are many planetarium programs both free and pay that will control a C8. Watch out for wire wrap. For some reason the connection is on the fork so it rotates with the scope. Why they did this I've never understood. There is a wireless adaptor to avoid this problem. I have no idea how well it works.

The question of camera depends on what you want to image. For planetary work a good USB2 web cam is far superior to a deep sky CCD as it takes a 30 frame per second AVI file that free software such as Registax can sort through, find the sharp images, stack them for best resolution then give you the tools to process the image. A CCD can at best take only one frame every few seconds greatly limiting the number of frames you have to work with. While it is possible to catch those perfect seeing instants with such a camera its far easier with the web cam and its software that does much of the sorting work for you.

For deep sky color images the one shot color camera is a good choice as it is simplier and cheaper as well as slightly faster. Since you take colors all at the same time it can somewhat reduce your exposure time. But you must be sure your sampling rate is sufficient. You need to know the average seeing (long term) in your area. It likely runs 2 to 3 seconds. As long as the CCD pixel size is one fourth of your typical best seeing your sample rate is probably sufficient for one shot color. Mono camera can get by with larger pixels and thus collect more photons per pixel. The starshooter would greatly oversample the C8 at f/10 but be a fairly good match with a f 6.3 compressor on the scope You don't mention one in your parts list and it would help greatly.

In fact I'd reverse things at first. Use the 80mm scope for imaging. The far shorter focal length makes guiding and tracking much easier. Starting with the C8 is like starting to learn mountain climbing half way up the face of El Capitan without a safety harness. The 80mm would be a bit undersampled with the OSC you mention but the learning curve so much reduced and great images far easier to achieve for this reason I'd start there then think about the C8 once you get tracking and guiding down along with everything else.

As to mono it is more versital but more expensive as you have the filters to deal with. This compounds the number of flats needed as well. Complications you may not want to deal with, especially at first. You can use larger pixels and still get full resolution of your image however. It makes narrow band imaging far easier and faster. With a one shot color camera H-alpha registers on only one pixel rather than all of them in the color grid so the mono camera builds a higher resolution H-alpha image far faster than the OSC can But you can do it. So if narrow band imaging isn't that important then the OSC route would save money and is easier as you don't have to manage the filter wheel along with everything else. That said I use mono myself.

Rick

[jeepster93]

Thanks for the help, Rick!

Mirror flop, I heard this term before.
How does one tell if his telescope is afflicted with this before spending the money for photography and finding out the telescope he has will not work? My C8 is about 7 years old.
Is there anything that can be done to "fix" mirror flop?(providing I have it) A touch of glue or silicone? Tightining something down tighter? Tape?

My C8 ota is in the shop right now for internal cleaning. It somehow, over the years, got a bit dusty inside(took it out over the 4th and the trees were COVERED in pollen). It is hauled around in the back of a fairly modified jeep also. My major hobby is Jeeping back country trails, the scopes go with me many times. Can I ask the shop to do something to the mirror to insure the eliminatation the flop before it is re-colminated(sp?)?

I guess I should ask...Internal cleaning? It has some dust on the glass and mirror, not a lot, but some. Clean it profesionally or live with it? I try not to clean the glass often as it is coated and I don't want to trash the coatings.

I am taking what you wrote to heart, and am in the process of looking into the web cam option. I was aware of useing the 80mm scope as a photo platform and guiding through the 8 incher.

[RickJ]

All moving mirror scopes without a mirror lock have it to some extent. Off axis guiding easily compensates. You may lose one frame occasionally when a large flop happens but that's a minor issue. You lose them to airplanes and other factors as well. It's just that guiding with a separate scope can't see the mirror slowly tilting and doesn't guide correctly. Off axis guiding through the scope sees and corrects the problem as it happens.

Lately (I don't know when) Celestron has greatly reduced the flop problem. Mainly it means less problem focusing as the object doesn't bounce back and forth in the field much as you focus compared to the past. Any flop is bad for deep sky astrophoto work however. I've seen some third part add ons for some Celestron models to lock the mirror. Not having one I don't pay much attention. Maybe someone will jump in with that info.

Mirror flop also will hit the 80 mm if you guide through the C8 as now the guider sees that flop and compensates when it shouldn't. The shorter focal length of the 80mm will lessen the problem but not eliminate it. Also, when you use a second scope for guiding it is always an issue to get rid of all flex between the two. Good solid rings as you seem to have are a good way to eliminate flex if everything else is very solid as well.

Again, not having a Celestron I can't help you one the internal cleaning issue. The one we have at Hyde has been there over 30 years but has never had an internal dirt problem. Sounds like it was subjected to a very dusty enviornment with the eyepiece open. Normally you keep a film can or some other cover over the eyepiece hole so that can't happen. You can always contact Celestron and ask them about it.

Rick