Collmination & mirror temperature

#1 30-12-2009, 02:31 PM

Hi Guys & Girls,
I'm still waiting for my Laser Collimator to arrive two weeks now so I'm still suffering with fuzzy images.

I know my mirrors are out of alignment but just how much does the collimation change due temperature variations, because things seem worse. When I get this problem fixed is this going to be a re-adjustment issue from Winter to Summer?

I hope Santa came good for some of you, I got a lump of coal.....

barx1963 (Malcolm) · #2 30-12-2009, 03:52 PM

Hi Doug
Temperature shouldn't affect alignment too much on a small scope. The "getting worse" simply means it is getting bumped as you move it and it is getting further out of alignment. On my 12" I find collimation stays pretty well on through an observing session as long as I don't bump the tube and I regularly have temperature changes of 15-20deg over the course of a session. I know as I have a temp sensor attached to the scope.
You should be able to get it pretty well collimated without a laser. The first time I did it I just put my eye to the focuser tube and tried to line everyhing up so my pupil that I could see was in the centre.
First adjust the secondary mirror so you can see all 3 retaining clips on the primary and the image of the primary looks round. Then adjust the primary so your eye is in the middle. Thats all I did and for a small scope (8" or smaller) most people will be hard pressed to see the difference.
Just be carefull if using tools to adjust the secondary, have them tyed to a bit of string around your wrist, or have the tube pointing down so you don't drop anything on the primary.

Malcolm

#3 30-12-2009, 05:10 PM

Hi Malcolm,
Good advise & thanks, I had visualy adjusted the secondary & the primary much to your discription two weeks ago. It's fairly good looking at stars with a 30mm EP, However turn it on to the Moon or Jupiter & it looks awful. Go to a smaller EP 20<>4mm forget it all crap.

The focus seems uneven, sharper on the edges than in the centre. This is why I bought the Collimator.

Also very good advice using string to prevent an accident with the primary mirror.

Thanks for the advice,

Doug

barx1963 (Malcolm) · #4 30-12-2009, 05:47 PM

How do stars look in the shorter EPs? If they are still crisp, I'd suggest collimation is not the prob. Jupiter is very low so the seeing is poor with it at the moment. The moon is often difficult because of its sheer brightness. I find I can only get really good views of the moon using a filter.

barx1963 (Malcolm) · #5 30-12-2009, 05:49 PM

Oh also, improve the accuracy of your allignment by using a collimation cap. Bintel sell em for I think about $2.50 or just punch a hole in an old film canister, if you can find one!

#6 30-12-2009, 06:05 PM

I tried that too! didn't work that well either. I have a good quality polarising filter for the moon made it much more comfortable but...

I should point out the I carry the barrel very carefully & don't bump it around at all, the tripod is a differant matter at 28 kg.

I feel my scope was either knocked around in transit or the factory wingnut didn't do his or her job properly.

mswhin63 (Malcolm) · #7 30-12-2009, 10:04 PM

Have a look inside the tube to the focuser barrel. Can you see if there is a lense inside on the end of the focuser tube?

#8 31-12-2009, 12:53 PM

MSWhin63
I'm not sure where your going with this..There is no lens in the focus tube once the EP is removed. Are you suggesting I may have left a barlow in place. Not the case if that's what your suggesting.

barx1963 (Malcolm) · #9 31-12-2009, 01:19 PM

I think what he is saying is some reflecters have a built in barlow in the focuser to provide more magnification with a shorter tube. These are often not very high quality barlows and cause some problems.

#10 31-12-2009, 01:37 PM

You know I just discovered that on the rear of the spider web are some evenly spaced grooves. I just did a realignment using these marks. The primary mirror moved a lot to make these marker lines equally placed while looking down the focus tube. I then re did the secondary, now it looks striaght.

There is no mention of these marker lines in the instuction manual. Now I need some stars to test out this new adjustment

hickny (Peter) · #11 31-12-2009, 01:57 PM

Doug, Not sure if you've seen this sight or not. I found it very helpful.
http://www.andysshotglass.com/Collimating.html

#12 31-12-2009, 02:02 PM

Thanks peter however it will take awhile to download the movie as we only have dialup out here. I just discovered that on the rear of the spider web are some evenly spaced grooves. I just did a realignment using these marks. now it looks better to the eye.

#13 07-01-2010, 04:37 PM

Quote:

Originally Posted by hickny

Doug, Not sure if you've seen this sight or not. I found it very helpful.
http://www.andysshotglass.com/Collimating.html

Hey Peter that internet lesson was very helpful. Iceman should include it somewhere on the site as a sticky. Thanks for sending it to me.

StarGazing (Alex) · #14 13-01-2010, 09:55 PM

Hi Doug has your scope have a fan for the primary, that usually helps keep the air stable with the outside atmosphere. Hope this help

Alex.

#15 22-01-2010, 10:42 AM

No it doesn't, I let the scope cool down about 30-60 minutes before I start.

Does a fan cause any vibration when viewing or doing images?