The Most Arduous Telescope to Collimate.

[Renato1]

I have a 4" Meade DS-2102Mak OTA that is out of collimation. I spent hours last night trying to collimate it, but have still not finished because the process is so painfully longwinded.

Normally, most telescopes have three screws or three sets of two screws for collimation, and they are directly accessible. But on this telescope, they are behind the combined back cover and mounting block, which has to be removed for every adjustment of the collimation screws.

So after looking at a star and deciding which direction needs adjusting, I have to take the tube off the mount, hold it between my legs, unscrew the grub screw on the focusing knob and remove the knob, remove four screws from the back cover, and take the back cover off, adjust the collimation screws, reassemble the whole unit, put it back on the mount, and then go back outside and find a star (which is difficult, as the finder is either no longer aligned with the telescope (or I've nudged it)) and see which direction the next adjustment to collimation has to be, and then repeat the whole process again.

Has anybody come across a telescope with a collimation process worse than this?
Regards,
Renato

[casstony]

Sounds like it's time to buy a different telescope :)

I've avoided buying some scopes because they sound difficult to collimate, including some maksutovs and the GSO RC's. Schmidt Cassegrains and Newts are very easy to collimate, and refractors are easy too provided the lens elements don't need recentering.

[Renato1]

Thanks, but I already have too many telescopes. I just consider this one a real challenge.

The chap who sold me my Vixen APO stongly advised me never to be tempted to tinker with the collimation screws on the lens. So I never have.

Cheers,
Renato

[casstony]

If the elements are all in one cell there's nothing to fear from tilting the cell to collimate; the newer Vixens with a third element towards the rear of the tube that might be a different story.

[Wavytone]

Yes there are a couple harder to collimate:

- a tri-schiefspiegler, you can google that;
- the Loveday folded Newtonian which uses 3 mirrors plus diagonal. You'll find this in Sky & Telescope June 1981 issue.

Refractors pose two added twists - it isn't just the tilt of the mirrors, you also have to find an optimum combination of the rotations of the elements to minimise the collective wedge error, as well as adjusting the separation of the elements. There will be a sweet spot with respect to the monochromatic aberrations as well. These added degrees of freedom make an airspaced 3 or four element refractor the most difficult, IMHO.

[Exfso]

The TOA130 is a nightmare to collimate as well, that is why only Takahashi should do it. I found out the hard way by sending mine to a so called reputable company that Claude suggested. They trashed it and it had to be re built by Takahashi. Just a note it was my fault it got out of collimation in the first place, the dew shield collided with my roll off roof rather solidly and put the collimation out slightly. All in all a very expensive exercise:(

[Renato1]

Harder? Definitely yes, but but I suspect the collimation screws would be accessible - so perhaps still not as arduous.

A 3 element refractor I wouldn't touch in the manner you've described because I remember the three years of frustration I had with a simple doublet. I bought a University Optics 80mm refractor many years ago. All I had to do was assemble it. The spacers were on the glass, and the glass had markings for alignment. Despite following their instructions, and every conceivable variation of putting the optics into the tube and screwing it up - I had astigmatic images. Finally, in frustration, I bought new ED glass optics for it. First attempt at inserting it, and I had astigmatic images. Second attempt trying something different, and I had perfect images.

Puzzled, I took it apart and reinserted the old optics in the exact same way I'd put in the ED glass - and I had perfect images. Turned out I had owned a superb achromat all that time. Anyhow I reinserted the ED glass and had perfect images. And a year later I spent $60 buying a tube and focuser, into which I installed the old optics, and again had very good images. As I've forgotten exactly what I did to finally get those optics working correctly in that University Optics refractor, I have dared pull it apart since.
Regards,
Renato

[Renato1]

Amazing. I think the term "nightmare" is an understatement.
Regards,
Renato

[tlgerdes]

Sounds like you could benefit from an artificial star, that way you don't have to keep assembling it to test.

[brian nordstrom]

:D Easy , my beautiful ( now sold) Takahashi Mewlon 210 , but once it was on ,,, man you knew it was ON :eyepop: !! awesome views and it stayed on for as long as I had it and that's for over 12 months of transporting on the back of my Ute , so touchy , but worth it in the end .

Stick with it as the finished views are worth it .
.
Brian.

[Renato1]

Well, to tell you the truth, I've never seen an artificial star, but I don't think it would help because I'd still have to aim the telescope with an eyepiece at it. And seeing the error in the bullseye pattern, would still have to take the back cover off to get to the screws. I need a special adapter for connecting the eyepiece to the telescope when the screws are accessible, and I don't have it.

I was clouded out last night, so made no progress, and I may get a chance later tonight to continue this long winded process.
Cheers,
Renato

[Renato1]

Thanks Brian,
I'm almost there.
Regards,
Renato

[Renato1]

Well, I started the collimation on the night of 1 April, and finally got the Bullseye pattern very close to concentric at 6.30 am 5 April. Saturn and then Venus looked quite good compared to what it was like before.

What actually hampered me was clouds and lack of stars to test each adjustment. I kept having to wait hours before I noticed some break in the clouds, so that I could go out see what had happened with the previous adjustment.

Anyhow, the next part starts tonight, seeing how a star's diffraction rings look at high power (as the clouds stopped me doing it this morning).

I'm still annoyed that where I've gotten to so far, I could have done in around 10 minutes with a regular telescope.
Regards,
Renato