guided imaging

[blink138 (Pat)]

hello members..... a question
can somebody please list EVERYTHING needed to begin guided imaging no matter how obvious it may seem from guidescope down
i have a c11 / g11 combo
thanks in advance
pat

[whzzz28 (Nathan)]

Two options, and as you have the C11 i would suggest going with option 1;

Option 1:

• Off-axis Guider (OAG). There are many different types. The Starlight Xpress is rather cheap, around $300. Australian distributor for SX gear is here: http://members.ozemail.com.au/~aeccl...ght_xpress.htm
• Guide camera (Starlight Xpress Lodestar, QHY5 etc)
• Cable to connect camera to mount (unless guiding through software). This is normally included with the camera.
• Adapters to fit the OAG to your camera (varies depending on other adapters and items you have)
• Software to perform guiding. PHD is free and used a fair bit: http://www.stark-labs.com/phdguiding.html

Option 2:

• Guide scope. Most common is a small refractor or finderscope. Something like this is a good starter: http://www.bintel.com.au/Astrophotog...oductview.aspx
• Guide camera (Starlight Xpress Lodestar, QHY5 etc)
• Cable to connect camera to mount (unless guiding through software). This is normally included with the camera.
• Adapters (1.25" extension tube). The guide scope package listed above includes an extension tube.
• Mounting adapters. The package above includes a vixen bar and rings to hold the guidescope, but you need some way to attach it to your scope.
• Software to perform guiding. PHD is free and used a fair bit: http://www.stark-labs.com/phdguiding.html

I mentioned before that Option 1 is better for you. This is because with Option 2 there is a chance that you will get flexure between your C11 and the guide scope which will result in poor images (star trails or fuzzy images). The OAG does not suffer flexure, nor mirror slop.

[blink138 (Pat)]

thanks for your quick reply nathan....... that is a very interesting way to look at it
i was deffo going down the guidescope route because i have an achro refractor i could use
do you think the flexure would be a big problem? what are the factors that cause it or make it worse?
very helpful nathan thanks
pat

[whzzz28 (Nathan)]

Originally Posted by blink138

thanks for your quick reply nathan....... that is a very interesting way to look at it
i was deffo going down the guidescope route because i have an achro refractor i could use
do you think the flexure would be a big problem? what are the factors that cause it or make it worse?
very helpful nathan thanks
pat

A guidescope will work, however SCT's are heavy and often move (very slightly, but enough that it will destroy images) in general operation. Compound the problem by adding another scope ontop of the SCT and you end up with poor images, even if tracking seems to be OK.
An OAG moves the tracking to the SCT. So if the SCT does move in any way during operation, the tracking software won't try to correct for it and your images turn out ok.

Factors that affect flexure:
- mounting between the mount and scope. Either a vixen or losmandy style mount, but this can "bend" ever so slightly.
- The OTA. Aluminum expands and contracts with temperature, although this doesn't normally account for flexure as it normally affects focusing; however it can cause the scope to move slightly. More importantly, aluminium isn't the strongest material. As weight goes up, so does flexing as you move the center of gravity and rotate the mount. This is why a guide scope is generally bad as flexure when the mount is sitting horizontal to the ground (picture the scope pointing straight up) is very strong on the guidescope. Of course flexure is a result of the compounds used to make the scopes, adapters and mounting fixtures. Get high quality stuff and flexure is reduced. Also some OTA's are carbon fibre which reduces flexure even more.
- Weight. A heavy guidescope will be more prone to flexure than a lighter scope. And i doubt your C11 is a light scope.

If your not going too serious into imaging then a guide scope might be ok for you. You can always grab an OAG later if needed - the camera will work with an OAG and guidescope.

[Peter.M]

SCT's also have mirror flop to worry about if you use a guidescope

[blink138 (Pat)]

nathan......... you know your stuff by the sounds! have you had bad
experiences with a guidescope?
i thought an OAG was a purely manual "old school" system whereby you need your eye permanently glued to it for manual adjustment!
when i purchase an accessory i do make sure not get something "just for now will do"as it often does become a false economy and ends up surplus to needs
i have a losmandy top rail and my c11 is CF

peter....... i have an aftermarket very beautiful moonlite focuser but no mirror lock
i have not noticed any focus differences changing meridian...... should i have?
thanks you two..... i have learned a lot..... any more suggestions or advice please?
pat

[Peter.M]

I am no expert, but I think for long exposure deep sky photos (what I assume you want to do because your talking about guiding) the mirror will still move. It may not cause a focus shift, but the stars will still move. I would ask though what you want to do with your photos?

Unfortunately the scope you have is probably not suited to DSO imaging. Its focal length is far too long. At these lengths people usually have to use adaptive optics, and need excellent seeing.


EDIT: i just saw you are using faststar ( i dont think you can use an OAG with it)

[blink138 (Pat)]

hello peter and thanks for hanging in there....... i suppose i want what everybody else wants.... i look at our best astro imagers here on IIS and think how is that possible?
i am starting at the bottom rung testing the waters and putting my limited money to hopefully where it will be best served, and yourself and nathan are helping me to achieve that
for instance i have told my wife honestly, that i have bought a minimum five year plan with my setup at present so i need to learn as much as possible in that time
at this point i dont think it is unfortunate i have a c11 and i find it quite extraordinary on dso compared to my 102mm achro ha ha!
pat

[blink138 (Pat)]

ooh i didnt think that worked peter...... but the above pic was one of the first i have ever done and it was one of the first times i have ever used a dslr!
that is what is so exciting!
pat
i have never used the fastar but i purposely purchased my c11 for that feature so that i could do it later if the mood was taken

[Peter.M]

Well that image is quite good actually, you have a decision to make now though. If it were me and you were going to do more prime focus photography an OAG and autoguider is the way to go. But if you were going to use fastar eventually I dont think you will be able to use it, and an external guidescope would need to be used.

[blink138 (Pat)]

thanks peter i will now seriously look at the OAG setup which i had never considered because as i mentioned i thought it was old school and you needed your eye continually on the object being photographed and needed "manual" guiding
am i wrong?
pat

[Peter.M]

You are indeed, you can connect an autoguider to the OAG to watch the star for you

[blink138 (Pat)]

fantastic! i will seriously look into this.... well done peter and nathan!
pat