Newbie's FOCUS problem

cloudyseattle

The Problem:

I can focus the camera through my beginner scope when viewing terrestrial objects, but I am unable to obtain good focus on lunar or planetary objects- The focuser is mid-range with Terrestrial, but can't seem to focus on more distant objects (ie, focuser is racked all the way "in" and images are still not in focus). Without the camera, images are easy to focus through the scope with usual eye pieces.

I assume I will need some attachment to shift the reflector telescope's focus into range of the ASI camera's imaging plane. It seems I need to either bring the camera closer, or shift the focus point farther out. What type of adapter would I need?

Telescope: Mead Starfinder DS-114 (4 1/2" Reflector) D=114mm F=910mm f/8

Focuser: 1.25" Meade rack/pinon focuser (replacement for original 1" Meade focuser)

Collimation: Confirmed with Orion LaserMate Deluxe II

Camera: ASI 120MC attached directly to focuser using included ZWO 1.25" adapter

Newbie from Seattle-

I'm just beginning to understand telescope and camera optics

ken_t

Hi,

You should be able to obtain focus if you use a 2X barlow lens in front of the camera.

You are correct, you need to move the focal point of the camera to the same position as the eyepiece was when in focus. You can always use the 2X barlow with your eyepieces for visual work afterwards.

Have Fun, Ken

cloudyseattle

Thanks Ken-

I thought Barlow 2x were for simply increasing magnification... I didn't think of it as also shifting the focus point. Appreciate the help.

My other thought was to replace the current focuser with a shorter focus unit (a little more work than simply adding a barlow).

Now I just need a clear night to try it-

ken_t

Good Luck with the clear night thing

If you were to fit a shorter focuser, would your eyepieces still attain focus ? :?

Buy a cheap barlow (ebay etc.) if it works for you then look for a better quality one.

Money, Money, Money...

Enjoy, Ken

cloudyseattle

Option #1 - Barlow 2x (ordered, will be here in a few days)

Option #2 - Replace long focuser with shorter focuser (JMI reverse Crayford focuser -RCF Mini1)

The JMI site mentions that Meade Starfinders use a longer focuser on their Newtonians. The standard JMI RCF-Mini1 uses a short 3" drawtube. When mounted for StarFinders, they suggest ordering it with their longer 4.6" drawtube (for direct viewing)... OR, order their standard 3" draw for astrophotography imaging and simply add an extension tube when switching back to eyepieces. This would solve part of the difficulty switching between focal lengths for eyepieces vs cameras.

see JMI website for details on using these focusers on Meade Starfinders

http://www.jimsmobile.com/buy_rcf.htm

ken_t

Hi,

Try the barlow first.

The Focuser's you linked to will not fit a 114mm scope, the smallest radius quoted is a 3.75", which would be for a 7.5" scope. ( i think, maths?)

Save the money, try the barlow, see what you want to do next.

Have Fun, Ken