Hi Jerry,
I don’t know what camera you’re using but I‘d like to encourage you considering to ditch the reducer. Reducers are fine if you need to increase the field of view and a larger sensor wouldn’t be an option. For sampling, today’s cameras can bin or you do it in post processing (CCD vs. CMOS discussions aside), it’s no longer like analogue photography. This can help you on the OAG w.r.t. finding a guide star. The illumination on the field edges is significantly reduced by the reducer. This often leads to issues with OAGs.
I am not convinced that the OCAL is very helpful. Unless I err completely, it does check alignment by looking at the secondary with a camera and check geometrically if the secondary is centered, right? If so, that might help on a completely misaligned secondary to get it back to somewhere, where serious alignment can be done but not more. A proper collimation is done at a real star, unless you have access to an interferometer ;-)
Personally, I’m aligning my SCT with an eyepiece but I know some people find that challenging for technical or physiological reasons, which is perfectly fine. If you’re using a camera (but also with an eyepiece) my major advice is:
Be patient and gentle!
Don‘t turn the screws too much as this will avoid getting the star out of the field and you might even align too much and overshoot. Figure out what amount of revolution angle is enough to keep the star in the FOV. We might talk about an 8th or 16th of a turn. The initial collimation might take much longer but once you were close subsequent fine-tnings will be a matter of max. 5 minutes.
Be gentle: don’t overturn the screws. Hold the screw driver like an unboiled egg and not like a hammer. That will limit your forces. If you didn’t use enough torque, the worst that happens: you lose collimation and next time you use a bit more torque. The process the other way round wouldn’t be advisable as it always holds: „after snug comes off“.
Hope my little novel here could help.
Björn
Thanks Bjorn. I do notice more vignetting with the Edge and the reducer, I also notice it with my Esprit 100 and the Starizona reducer. With the Askar 130PHQ the reducer doesn't produce any vignetting at all.
As far as the OCAL is concerned, I worked with it all morning and came to the conclusion that the camera must be exactly centered with the center of the secondary mirror before using it to collimate. A star test will reveal if I am right. I replace the screws on the Edge with Bob's knobs, at first I didn't like them but now I see their advantage so I am going to continue to use them. I don't like holding a sharp object near the corrector plate and the knobs seem to tighten enough.
Some SCT owners are having good experiences collimating the Edge with the OCAL. Some are not. I think my discover today about centering the camera first might be the answer, time will tell. If it works, I have no doubt it will be the best way for me to collimate. If it doesn't I'll have to search for another way.
One question: When you collimate, do you use Polaris because it won't move away from the FOV as fast as, say, Vega? I tried Vega the other night because of its brightness, but Polaris may be better, albeit not as dark.
