NGC253 - first guided image

[browndog (Ian)]

This is my first attempt at auto-guiding. I used a Celestron 8" SCT with a 6.3 Meade Focal reducer on a CG-5 mount, auto-guided through 80mm refractor using an unmodded Toucam, PHD Guiding and GPUSB, and Canon 350D.

I also tried to focus using DSLRFocus. Not sure if I got the focus correct, but it is easier to use than manual focus using the viewer on the camera.

10 x 300sec @ ISO800
Processing in DSS and then Photoshop.

I currently have a 1.25" T-adaptor and I get a lot of Vignetting. Does any know if a 2" T-adaptor would help to reduce this?

Any comments or ideas of how to improve greatly appreciated.

[[1ponders] (Paul)]

Great first effort Ian.

There are a couple of ways you can try to connect. One is to use this SCT to T adapter
https://www.bintelshop.com.au/Images/Stock/5439X.jpg

Alternatively you can use a prime focus adapter, remove the silver end screw the FR into the body of the adapter and then screw the silver bit back into the FR. This works but doesn't give the recommended distance from FR last element to imaging surface. You will get less than the stated .63 reduction.
https://www.bintelshop.com.au/Images/Stock/7182X.jpg

BTW these are available from Bintel, MyAstroShop, York Optical, Sirius etc. Most shops should carry them.

[[1ponders] (Paul)]

Check out the images in this thread. http://www.iceinspace.com.au/forum/s...hlight=adapter

[browndog (Ian)]

Hi Paul

Thanks for this information. I may have a problem with my setup. I don't have the SCT "T" adaptor..???

My Setup:
Telescope --> Focal Reducer --> 10:1 Bintel Focuser --> "T" mount --> Camera

Would this setup make my camera (image surface) too far away from the Focal Reducer?

[[1ponders] (Paul)]

Ok then part of your problem is that maybe your FR is to far from your camera. From memory the optimum distance from last element of the FR to imaging surface of the Meade and Celestron FR is 105mm. How do you get your T mount (which I am assuming is your T ring to connect to the focuser?

[Dr Nick (Nick)]

Nice, I wish I could get images like that one

[browndog (Ian)]

Paul - I have a 1.25" Camera Adaptor that connects to the "T" ring - and slides into the focuser (like an eye-piece). Bintel Camera Adapter 1.25" https://www.bintelshop.com.au/Product.aspx?ID=6384

Your comments about an optimal distance from the last element of the focal reducer to the image surface is a concern for me. I will have measure my setup to see how long it actually is. I think that my setup may be a bit too "long". Do you know what the optimal distance should be? You mentioned 105mm - is this an exact distance or is there a preferred range?? Are there any written references that you are aware of?

What about a 1.25" adaptor compared to a 2" adaptor - Does this makes any difference? Does anyone else use a 1.25" adaptor and a 350d?

****
Thanks for the positive comments Dr Nick - I still feel I have a long way to go. Practice, Practice, Practice...

[[1ponders] (Paul)]

The 2" prime focus adapter will make a lot of difference compared to the 1.25" adapter in relieving vignetting. I have something similar to your adapter but I unsrew the 1.25" part from the tube to use. I rarely use it for DSO imaging with the DSLR though.

As for the focal length of the adapter, the image of my Canon attached to the back of the Meade focuser with the FR and T adapter is probably a bit long but not by much.

The thing is the further away from the imaging plane the FR is, the greater the amount of focal reduction. Unfortunately the further away the greater the FOV but the smaller the usable lens area. In other words at the correct distance you ge 0.63x focal reduction with the largest usable FOV. The further away you get the greater the reduction, but the small the FOV without distortion.

The best thing I can suggest is to get the 2" Prime Focus adapter and try that and see how you go with vignetting. At this stage leave the FR at the front of the focuser.