secondary adjustment on a 10" gso dob

[GrahamL]

hi all

well i picked up a 10 " dob a week or two back and am a little lost on the secondary adjustment screws .. which does what.. I watched that good
video link thats been posted round here and it is great ..but his adjusters look a little differant to mine ?. pictured below is what I see through the barrell, things are all square but just a touch off, in that i can see a
little of the secondary holder on one side ... do you think it needs a tweak ?which screws do I loosen to adjust ?

Thought I'd better ask someone after my little "incident " this
morning with the primary .. it was a little off centre so i thought i'd have a shot at a fine adjustment of it ... I had read a lot and was still a little
apprehensive about it all and was definately thinking way to far ahead as i started .. slackened off locking screws ..(insert brain meltdown )
and decided the first adjusting screw i came to after doing this was also
a locking screw and happily started unwinding it as well
seeing the mirror cell moving markedly in the tube while doing this!!
Realiseing what i done I left the room in dissgust to make a cuppa
and when i came back couldn't remember which screw i had wound out:screwy:
So what was an easy fix of just winding it back in was gone now
In the hour or so i spent trying to find my way back to the centre again
was loads of fun ..at one point i even had one of the adjusting screws completely undone so as to lose the spring on the floor ..A long time later I got close enough to slip the chesire back in and actually was getting
very good at moving the cell where i wanted it .. its perfect now :rofl:
And I learned a lot .. noteably primary out of the box was only about 1/16th of a turn on one screw away from alignment.

any advice on what not to screw up with the secondary mucho appreaciated:P

[Jupiter]

I feel your pain, sounds a bit like my story this week, doing the same job, my first collimation, being the sort of person I am I stuck to the task and with the wonderful help of google I found a great page which once printed helped solve my problems, I also bought a laser collimater which is excellent.
If I can find the original site where I found the instructions i will post the url.

[Jupiter]

(http://www.iceinspace.com.au/forum/www.cloudynights.com)

[Nordo]

Hey, big J, where's the URL?

[Jupiter]

Sorry about that I pm'ed him the url because it wouldn't allow me to post it here for some reason, here goes:- http://www.cloudynights/document/primer.pdf best collimation advice I could find.
Yet when you click on the link it says irl could not be found but I have it up on screen here at home, dang intranets.

[Jupiter]

Another idea is type 'John Crilly collimation' into google and dl the pdf file which is the second listing which comes up, good luck.

[Nordo]

Thanks mate:hi:
I think there is meant to be a "s" at the end of "/document/ " ?

[bojan]

Hi Nightstalker,
Very good article aoput colimation can be found here:

http://www.atmsite.org/contrib/Carlin/collimation/kolli.html#Step5


When I was doing mine recently, I was using a TV monitor to watch what is happening, through my digital camera - mounted co-axially on the eyepiece holder (without eyepiece, of course). This way it is relatively easy to centre the image of the primary mirror, you can see immediately the effect of every move.

The important part is to mark clearly the centre of the mirror with marker (this part of the mirror is obstructed by secondary anyway, so a mark is not a problem).

Good luck, Bojan

[Nordo]

Bojan
Sounds like a great idea when your wife/girlfriend doesn't share your interest. How do you know you have the camera's axis co-incident with the focuser's tube axis?

[bojan]

I have the camera adapter machined (with threads), so it has to be :-)

[Jupiter]

Spend 70 bucks on a laser collimator then make it work, I did.

[Nordo]

Oh, I didn't realised you had it attached. I thought you were merely just pointing the camera down the tube:doh:
Have you ever tried viewing through it and/or capturing video through it?

[Nordo]

Don't forget, many laser collimators need aligning before you can use them;)

[bojan]

Hi Nordo,
yes, and I obtained some pretty good Moon images so far (I haven't got enough time to do much more but I will, someday :-)
Actually, this adapter was made because I wanted good afocal images.
Colimation was just another application :-)

[astronut]

Hi NS, You won't have to adjust the secondary very often, but to make it easier when you do I suggest that you get rid of those secondary screws and replace them with hand operated ones. It makes the job infinately better and there's no tool to drop on the primary mirror.
I would recommend a Cheshire/sight tube, Bintel sell them for $69 and there made by Orion.
If it helps I'll post the instructions that came with the collimator.
Here is a image of the new knobs. Cheers, John.:)

[GrahamL]

thanks all:)

thats a good idea john ,so where do you get those screws ?

so those three are adjusters for the tilt of the secondary ?
whats the centre one a locking screw?

I have this chesire i just bought for $30 is there any way i can modify it to do both,I have access to a lathe and engineer to make most little things i might need;). As near as i can see with the secondary it is awefull close to being right.. but I'm not adverse to messin with something that aint broke.

again all thanks for your help

[Starkler]

Nightstalker, that looks like the cheshire sold by Andrews. Thats a cheshire only, but the orion one is a combination cheshire and sight tube.
The difference is that the orion one is longer, enabling you to set it so that you can sight the secondary against the inside edge of the sight tube.

If you want to make a sight tube, get a length of 1.25" outer diameter tubing thats [f-ratio of your scope] x [inner diameter of the 1.25' tube] long, with a peephole in the centre of one end.

See this page (http://www.philharrington.net/tube.htm)for the general idea

[astronut]

Thanks Geoff, You beat me to it:lol: the Orion Cheshire/Sight tube is very easy to use.
NS I bought the new knobs from www.Astronomy-Shoppe.com (http://www.Astronomy-Shoppe.com) Tony Costanzo is the owner and he is very helpful.
I have a Meade 12" Lightbridge, they are all based on the G.S.O. scopes and share quite a lot of hardware. If you go to the site and click onto http://www.astronomy-shoppe.com/_derived/Kits.htm_cmp_copy-of-network-blitz110_vbtn_a.gif (http://www.astronomy-shoppe.com/Kits.htm)it will show you all the improvements that can be made to just about any dob sold in OZ. It's worth every cent:thumbsup: Cheers, John.
P.S. Delievery is about 10 days.

[Hotkey]

My 10 inch Dob is proving very difficult to collimate. I spend hours adjusting then when I take it out at night I find I can just split easy doubles. I have read heaps of articles but must be doing something wrong still. But I won't let it beat me, no siree. So Nightstalker keep at it and it will all fall into place finally and be worth the effort. The people here can give excellent advice.
Evan

[astro_nutt]

G'day hotkey,
Have you checked to see if the focuser is collimated..ie..if you removed the secondary mirror and inserted a cheshire crosshair or laser that it should show the point EXACTLY opposite the centre of the EP holder of the focuser!
Use the old paper ribbon wrapped around the tube along side the focuser....mark the centre of the EP holder on the ribbon and the tube..mark the ribbon where joined..remove the ribbon then crease where the centre mark is...then fold it flat and crease the other end..replace ribbon back on tube in excactly the same spot..you should have a crease on the opposite of the focuser..measure from the centre of the EP holder to the ribbon next to the focuser...put a piece of masking tape on the spot where you'll mark the point...then measure from the edge of the ribbon and mark the point on the masking tape..drill a 3mm hole..(tube should be horizontal)..vacuum any drill filings then insert your collimator and see if the hole is opposite..if you can..adjust it..then re-insert the seconday mirror.
Also..check to see if the focuser or the 1.25" adapter is loose.
Cheers!

[Starkler]

Have you checked your scope (http://www.iceinspace.com.au/index.php?id=63,206,0,0,1,0)for pinched optics ?

Is the scope properly cooled when you observe? This time of year it should be outside for an hour at least before its anything like cooled close to ambient assuming you dont have a fan.

[Starkler]

If you have a laser, the easy way is to adjust the secondary so that the laser dot falls into the middle of the secondary donut. This ensures that the focuser is square to the optical axis and your focal plane is not tilted at the focuser.