Quote:
Originally Posted by darkskybondi
A few questions:
1. Can a slightly uncollimated scope cause an awful dim view?
2. Are the people who say laser collimation is useless right?
3. Am I going to burn my darn retinas off if I stare at the alignment dot on my laser collimator (the one on the side)? It so bright!
4. Am I collimating correctly, by the sound of it?
5. Is it possible that I got sold a dud scope? What else could be wrong with it?
6: 
Cheers, disappointment, here's hoping -
- DSB  |
Hi,
You have landed on the right asteroid here at IIS, I got all the assistance I needed when in the same position just starting up. I have a 200mm & 300mm dob, and a 100mm refractor and am only JUST past where you are now. It will work OK.
Now a 250mm dob is a good instrument and when used correctly (you will certainly get this right without too much trouble) from Bondi you will get great views to the East. Velvet darkness!! It will need to be collimated each setup however.
To your questions:
1: No, it will just cause an apparent difficulty focussing and a lack of resolution, say between double stars like Rigel in Orion. You will get past that.
2: No, there certainly is a bit of a dialogue here about it, but barlowed laser collimation is very effective.
3: No, but do not stare directly into the laser itself.
4: No, but nearly so. Keep going. It is not as difficult as it appears just now.
5: No, almost certainly not. See, dobs by their nature are all-adjustable, and so need a bit of fiddling before use. On the other hand you get more aperture for the money, and so more light-gathering power.
Now as to what might be wrong:
- many dobs need stronger springs on the collimation adjustment screws, that was my first move and it saved me much later grief. You can get good springs in Bunnings by matching the originals plus a bit more length, or here
https://www.bintelshop.com.au/Product.aspx?ID=6492
These new springs make the mirror move more predictably and solidly when you adjust the collimation screws.
Your trouble is most likely to be that when you screw up these adjustment screws, the mirror is not moving in concert due to the weak springs. That was my problem also at first. I found that I could tighten and loosen these screws madly all night, and the mirror would not respond.
Then when you replace them, my advice is to get a 2X Barlow lens and do what is described here (now there is much debate about what method is best, but I am a fan of this method, Barlowed Laser Collimation)
http://www.astrosystems.biz/laser.htm
For your GSO laser you will need to attach a little paper disc to the front of the Barlow lens with a small hole in the dead centre to allow the laser through. It looks like this
http://www.cameraconcepts.com/barlow...ollimation.pdf
Then you do this:
1: Use the laser collimator
without the Barlow lens to centre the laser dot on the centre spot of the main mirror, by adjusting the 3 screws on the secondary housing. Actually you will find you can do this easily by rotating the secondary mirror housing a little either way, and adjusting only the right-hand-most screw a small amount. Take care not to stick your greasy thumb on the secondary mirror.
2: Then mount the laser in the Barlow-lens-with-paper-disc-on-the-end, and do not be alarmed by the large fuzzy red blob which appears on the main mirror, even if it is not perfectly central. It just has to cover the centre spot so it produces a reflected image.
3: I like to use a small hand mirror then to see the relected image of the centre spot on the paper disc you put on the end of the Barlow. A dental mirror is good also. This what you want to see (the "after")
http://www.obsessiontelescopes.com/l....html#barlowed
You just adjust your collimation screws to move the reflected image of the main mirror centre spot until it is concentric on the hole in the paper on the end of the Barlow lens. This is not at all sensitive to how much wobble there might be in the laser-to-focusser mounting.
4: Tighten the locking screws on the main mirror cell gently, and you are done.
Hope this assists
Cheers