Eyepieces for Collimation

[joe4444]

I bought a 1970's Celestron C8 SCT on eBay, and it only came with a 26mm eyepiece. This was not a problem for me at first because my only intended use for the C8 is astrophotography. Then I realized that precise collimation is critical for astrophotography. I think I'm collimating very well with the 26mm eyepiece, but it's difficult to make the final adjustments when a slightly defocused star is so small in the field of view. Most guides suggest starting at low power and working up to higher power eyepieces in steps. Others say to go straight for a 400-500X eyepiece. Is there any benefit to going from 26mm to 20mm to 15mm to 9mm to 4mm rather than straight from 26mm to 4mm? Also, would a less expensive house brand, such as this OPT 4mm be sufficient for collimation?

[rowan46]

Hi joe I use a hartmann mask variant for collimaing my sct it works a treat and costs very little to make here's the link it's very simple

Duncan's Decorating and Repair Services

It will get your focus right as well if you use it do let me know how you get on with it

[rowan46]

sorry! I forgot to answer your question the main reason for going in steps is so that you don't lose your target star I only have three eyepieces. I use a 25mm to find a star (usually polaris as it doesn't move much) recentre on a 10mm and barlow that one as it's my highest power eyepiece and then collimate.

[joe4444]

I start out using polaris, too, since I'm already on it from polar alignment. So as long as I can find the star there is no problem with jumping from 26mm to 4mm?

I may give that mask a try. My attempt to make my own Bahtinov mask was a disaster. This one looks much easier to cut

[rowan46]

I start out using polaris, too, since I'm already on it from polar alignment. So as long as I can find the star there is no problem with jumping from 26mm to 4mm

that's about right. About the mask most imagers appear to agree that for focussing the bahtinov is the most accurate. But the advantage of this mask is it makes collimating very easy I have bobs knobs on my scope and with the mask I can have it collimated within aprox 30 secs after putting my high power eyepiece in.

[Moonshane]

Hi joe I use a hartmann mask variant for collimaing my sct it works a treat and costs very little to make here's the link it's very simple

Duncan's Decorating and Repair Services

It will get your focus right as well if you use it do let me know how you get on with it

this is very cool. would it work with a newt too?

[rowan46]

this is very cool. would it work with a newt too?

I doubt it as there are 2 mirrors to align. but I may be wrong I have certainly never heard of it being used to collimate a newt