Modifying Sky watcher 130mm for prime focus

[Zendrix]

Hello all!

Because i can't reach to prime focus in my sky-watcher 130mm f:900mm using a Canon 1000D, im gonna modify it pushing my mirror forward a little bit. I'm following a thread in which they accomplished this successfully (http://stargazerslounge.com/showthre...hlight=mod+130) but, althoug im confortable unmounting stuff, i don't want to commit major mistakes so, for anyone who might give wise advice, i would very much appreciate it.

Here is what i understood the process is about:

1- We replace the original colimation screws with longer (5mm araldite threaded rod, [5cm long?]) ones;

2- We use, instead of the original "O" ring, solid springs (1.2mm);

3- The araldite 5mm threaded rod (which i understood would have about 5cm (2"), would go inside these springs and the spring would be bearing the tension;

4- I suppose because these screws can't go forward and hit the back of the mirror, "geppetto" used this system of the wing nuts, so you will control colimation from there (which apparently makes it easier)

Doubts:

1- What king of caring do i have to have disassembling the mirror cells? What mistakes should i not do, besides breaking the primary mirror, of course? Is the mirror glued to the inside mirror cell?

2- Do the springs have to be really tight against the araldite 5mm or can they have a more comfortable radius, say like 6mm or 7mm?

3- How long should the springs be? I got some from a car shop, while looking for a box with thousands of them, and found 3 equal (2.5cm long and inside radius 5mm, maybe 1.2mm thick, so really solid ones)

4- Can i take the opportunity and try to clean the main mirror? what do you use for that?

5- Did someone here go through this process and maybe could share some pics and tips?

Thanks a lot in advance

Cheers

Rui

[steppenwolf]

1- Is the mirror glued to the inside mirror cell?

The mirror should be ratained with three or four small clips screwed into the mirror cell - no glue.

4- Can i take the opportunity and try to clean the main mirror? what do you use for that?

Only clean the mirror if it is really, really dirty or you risk doing more harm than good. 'Dust OK', 'Scratch NOT OK'!! If you do decide to clean the mirror then

will show you how to do it safely.

[Zendrix]

thank you for your input steppenwolf!

cheers,

Rui

[Zendrix]

Update:

I failed to modify my sky-watcher for tonight... apparently, the structure of the mirror cell has been upgraded, which makes the solution in the other thread obsolete for this kind of arrangement...

I was thinking in solutions for pushing the mirror up:

A- I cut 2 or 3 cm or the tube and replace the whole mirror system again, 3cm further up, maintaining the original mirror structure;

B- I place some higher rubbers where the mirror sits in the mirror cell, but this wont be such a stable solution...

C- I don't use prime focus, only imaging with eyepieces in between.. I wonder what are the disadvantages of this last one, besides loosing some FOV.

[Zendrix]

Finally, i sliced the tube 3cm, placed again the mirror and i can now reach prime focus with my canon.