Here's what I do; maybe it'll help some people;
- Put the Howie Glatter in the eyepiece holder (single dot mode, we're not up to the hologram rings thing just yet). Use the focuser plate to centre the red dot in the secondary donut. Yes, this may not be the optical centre of the secondary, if it's the geometric centre that's enough to align the focuser more or less with the centre axis of the OTA. manipulating the tilt of the secondary doesn't move the donut so we can say that the focuser - donut (and to a reasonably accurate degree the OTA) are aligned, That's all we can say at this point - who knows about the primary and secondary.
- Now for this bit, I prefer an orion cheshire laser. Blasphemy, I know! But look - under the sticker there are three collimating screws and I collimate mine to match the Howie Glatter. Chuck it in the eyepiece holder and adjust until the laser bounces right back into the hole. (fig 1 - you can see I've replaced the grub screws with more accessible tech screws). At this point, you have the focuser aligned with the secondary, both of which are reasonably closely aligned with the tune itself.
- Now for the last part. I read a lot about projecting the Howie Glatter hologram rings (if you have that attachment) onto a nearby wall. The thing is, if you're in the bush, white walls are in short supply. So I just cut a circle of diffusion gel such that it fits over the spider knobs (fig 2). Diffusion gel is plastic and transparent and non-flammable and you can get it from professional film lighting shops like John Barry. I used Lee Filters 216 'White Diffusion'. You should be able to buy it in smaller squares rather than a whole roll. Or, you know, improvise. It really just needs to be translucent like frosted glass - it needs to diffuse the light that hits it. Maybe you could get one cut from some kind of rigid plastic and it'll probably work even better than mine. Anyway, now the projected rings are showing you the projection of the light path through the scope. Use the Primary adjustment screws to centre the rings and you're done. It's best to only use two screws to get it in the right spot so you don't change the focal length of the entire system because that would be a bad and not very good thing.
- Now here's the thing; remember how I said the donut may not be the optical centre of the secondary? If a star test shows this to be the case, you have to revisit the focuser alignment. The secondary doesn't move much - it more 'rotates around a central axis' so if your focuser needs to be looking at a different part of the secondary, you need to readjust focuser tilt. Adjust it in the direction of misalignment, then repeat steps 2 & 3. If it's worse, you adjusted the wrong way (make a note of the correct direction for nest time). Artefacts and reflections in between the rings can help you spot that something isn't right, so keep an eye out for these (fig 3). By far the most critical adjustment is the focuser adjustment. Tiny errors make much larger errors in the Secondary and Primary Mirrors that are difficult to adjust and result in a lot of tail-chasing.
Anyway I hope that helps someone.
Edited by Stonius, 26 July 2021 - 10:04 AM.