collimation woes

blink138 (Pat) · #1 02-09-2015, 04:13 PM

hello members i hope i can get some advice needed here
i have finally hit "bravery status" last night and decided that i really need to be able to collimate my sct
i will go directly to the last step (to cut a short story long ha ha!), so i had my c11 at f10 with a 2" 2 times powermate, 2 times cannon adaptor, 60da.............. well bugger me it seemed to be working fine at that magnification, and all observations through EOS utility on my computer
it all seemed to be really good until i put my 0.63 reducer back in and my 60da to get a sample shot of nice pinpoint stars, and as i was getting the focus of a brightish star the bloody doughnut was sitting close to the bottom, completely misaligned!
any idea how this is so?
i have had to refocus stars after changing adapters many times and the hole has always been roughly central, i hope i have not mucked up anything more serious?
please help as it is getting me down!
pat

glend (Glen) · #2 02-09-2015, 04:32 PM

In imaging you need to collimate with your camera view in many mind, in other words with all the gear onboard that you use to image - then do a star test for final tweaks.

Bench collimation might look good visually but the weight of the camera, and other gear may flex the image train and take it out of collimation. Ideally check te camera view of collimation in various scope attitudes.

AlexN · #3 02-09-2015, 04:59 PM

Yep. Also with an sct you really need to tweak your collimation with the scope in similar orientation to where you are imaging as the primary mirror can flop and this can throw out your alignment.

blink138 (Pat) · #4 02-09-2015, 05:18 PM

thanks guys i hear what you are saying, however i have changed adapters and such like before and still managed to see a central doughnut regardless, and i thought i had very good collimation on maximum magnificatio at f40 and upon changing it down to f6.3 found the collimation way out!
do you guys think it should be that far out changing adapters and such? if yes i shall just have to put up with it, however i thought it should be good if i managed to collimate it at the f/40, but as i said did not look good at f/6.3
pat

Atmos (Colin) · #5 02-09-2015, 05:36 PM

May be a bit of a silly question but do you have your spacing correct with the 0.63x reducer? As a guess, incorrect spacing could throw a lot of things out.

On that vein, could there be a different differential flexure on the imaging train between having the powermate/reducer?

blink138 (Pat) · #6 02-09-2015, 05:45 PM

thanks colin and yes the reducer is correct as i have it inside my moonlite focusser
the train i guess is quite heavy and long colin, but what could be the answer to that i wonder, it is that it seemed collimated at the high power and uncollimated at the lowest power i cannot get my head around it, and it goes against everything i have read, low power first and then the highest achievable power for fine collimation
i also obviously need to focus the mirror in the normal sct manner between adapter changes as their is no where near enough just in the moonlite
i wonder if i take the moonlite off and just use the normal focus method for the sct?
pat

Atmos (Colin) · #7 02-09-2015, 05:55 PM

Quote:

Originally Posted by blink138

thanks colin and yes the reducer is correct as i have it inside my moonlite focusser
the train i guess is quite heavy and long colin, but what could be the answer to that i wonder, it is that it seemed collimated at the high power and uncollimated at the lowest power i cannot get my head around it, and it goes against everything i have read, low power first and then the highest achievable power for fine collimation
i also obviously need to focus the mirror in the normal sct manner between adapter changes as their is no where near enough just in the moonlite
i wonder if i take the moonlite off and just use the normal focus method for the sct?
pat

What I had in mind is that, theoretically, the reducer will have a lot more in the way of extensions than what you'd get with the 2x powermate which in itself is a solid piece of equipment. I am wondering whether there could be a very slight flex with the extensions.

blink138 (Pat) · #8 02-09-2015, 06:35 PM

quite possibly colin and perhaps at the f40 discussed it would show up even more perhaps?
even so this is how i have read it to be done on all SCT's so i am a little stumped at whether or not to do a collimation at the f6.3, as supposedly inaccurate as it is, and image like that?
pat

blink138 (Pat) · #9 10-09-2015, 06:40 PM

well after a lot of trial and error i think i have got my head around this collimation thing, in fact it was quite enjoyable!
i had not heard about any one using backyard eos and attaching the dslr to do a live view but it seemed to work for me anyhow
i could just turn the computer around to the front of the scope without going to the eyepiece constantly
admittedly i spent the first half hour trying to find the focus of the target even though the c11 cap was on ha ha!
i managed to attach my 2 times powermate and my brother loaned me a 2 times cannon thingy
i took some test shots of m17 and all seems well
necessity forced me to eventually try collimation as i mucked about with it months ago and ruined what i had
pat