Quote:
Originally Posted by jwoody
Hello Anthony.
So in the end what was the magic number you came up with?
I am in a similar boat to you having just cleaned my primary in the RC10 and want to get it perfect.
Thank you
Keremy
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Hi Jeremy,
To be honest I have let this one sit for a while, I just made an adjustment and recollimated but also got a new Esprit120 so ended up playing with that instead.
I believe 1970mm is about right but need to confirm. I did reach out to Lucas many moons ago and this is what he suggested I try.
I will aim to get this set up next weekend to have a test and play. The easy part is that now thw primary morror is straight it doesn't take long to adjust the secondary and recollimate, in fact I can do this at the mount out the back to get it exact.
Once I have I will get you the Astrometry details.
Re: GSO RC10 Help
Hi Anthony,
I have a quick and easy method for getting the spacing right for the GSO RC10. I know for a fact that the back focus distance from the end of the GSO focuser (with the 1.25" adapter inserted) is 123.33mm. I have a schematic diagram from GSO which shows this. As I use the 2" barrel when using the focuser I remove the 1.25" adapter (which from memory is 10mm thick) so the back focus becomes 133.33mm from the 2" barrel on the focuser. Obviously 133mm is close enough.
What I do then is use the live view mode on a DSLR to focus. I use the large 50mm spacer and my DSLR with t-ring is 55mm. So with 105mm spacing from the DSLR and large spacer I know the focuser needs to rack out 28mm to equal the correct back focus.
Now the rule is for each 1mm the secondary is brought closer to the primary the back focus increases by 10mm.
For example with my DSLR and 50mm large spacer (105mm), if the focuser only racks out 18mm to reach focus on the live view I need to move the secondary 1mm closer to the primary to create another 10mm of back focus. I then do a quick cheshire alignment of the secondary after moving it and hopefully the focuser racks out to 28mm when focusing again with the DSLR.
If the opposite occurs and the focuser racks out too far then the secondary needs to move away from the primary.
When you have this sorted and your back focus is 133mm from the 2" barrel you can then fine tune by using plate solving with MaximDL to calculate the focal length. You will find the focal length of the GSO RC10 is approximately 1970mm.
When you use ccd inspector with the correct spacing you will still see a very slight hump in the centre of the field but not like the one you have currently.
I hope I have explained this so it is understandable? Let me know if you have any questions. I will try and post the RC10 diagram I have or if you send me your email i will send it direct.
Kind Regards,
Lucas