Pixies

Sounds like Tele Vue Dioptrx. Anyway, I checked the view through my OVL Aero 70 tonight. Afraid it does look like astigmatism.

Well, I thought this single thread would save me posting lots of different ones for each sketch! It's been 4 weeks now, but at last a good night for observing! Mostly done at x150. It appeared calm but didn't really take much more magnification. Seeing wasn't too bad, with plenty of opportunity for fine detail - although it did appear to be degrading as time went on. Afterwards I tried a quick stacked video with my phone, but it wasn't great.

My lowest powered EP has an exit pupil of 5mm. I know it suffers from field curvature slightly, which is why I haven't been too critical with its performance. Next time I use it I'll pay more attention to exactly what is going on with the star-shapes, and compare with the view with my specs on.. Is it the often-mentioned 'seagull' shape that would be visible?

Ever thought of a RACI finder?

Well, well. Just back from the opticians and I have mild astigmatism. It's been many years since I've been, as my short-sightedness prescription has hardly changed. It's only mild astigmatism - and he said that it was on my prescription before, so I just hadn't paid attention (or remembered)! Luckily my viewing eye is the one with less astigmatism: -0.5 horizontal. The thing is - I've never used my specs to observe (unaware that they have some cylindrical correction for my astigmatism) and can't say that I have ever been aware of any problems with what I can see. I know what stars look like when an EP suffers from astigmatism, but is the effect the same when one suffers with it in one's own eyes.

Thanks all. I had found an Altair 2" Dielectric with 1.25" adapter going secondhand for not too much. Thought it would work here with 1.25" EPs but also a keeper for future scopes. The diagonal with the scope is the cheapy plastic one that everyone recommends is replaced.

Hi, Now I've become familiar with Newtonians, I get a Mak to start the learning process all over again. It's only a wee one - Skymax-90. A quick look at Mars last night between the clouds and I'm hoping to get a little more use out of it this weekend (weather permitting). I have the eyepieces from the current 8" dob. I believe it has a M44.5x1.0 Maksutov thread on the back plate and a visual back that allows for a 1.25" star diagonal to be fitted. The actual hole in the back plate is only 18mm diameter (the internal circumference of the end of the baffle tube): Now - I realise that this is a small Mak, but the thread on the back isn't much different from an SCT thread size, I understand, and adapters are available. I have the chance to get a reasonable 2" star diagonal. Is this appropriate for a little Mak like this? Would it just be a waste and would 2" EPs just suffer from vignetting? I know it might be overkill, 2" attachments on this scope. But I would hope that anything I get would transfer to other scopes later. Perhaps the 2" diagonal with a 1.25" adapter and stick with 1.25" EPs would be fine? Cheers

Telrad and RACI. Did someone above say they had a Telrad going spare?

Do you find you need an RDF to go with it? I have trouble aligning my dob's RACI without the Telrad.

Hi, A question for anyone with a 90 Mak. Wide angle EPs aren't possible, so the available FoV through the scope is limited with a slow f13.8 3.5" scope. It has an RDF, but is a straight 6x30 a better option as the finder? Anyone with any experience of using both types of finder with a small slow scope? Cheers

I love how they intend to measure the mass of the sample they've taken, once back orbiting the asteroid. Osiris-Rex will extend the sample arm and then go into a spin, measuring its angular momentum. They'll compare this figure with one taken when they did this earlier with no sample, and the difference will give them the mass of the sample. If they haven't got enough, they'll get some more in another TAG.

Managed to get it as close as I can do with the hubble artificial star. I bought that ages ago (from here) but have never been able to use it as my other scope's minimum focus distance is just too great. But at about 10m it's fine with the wee Mak. It's so odd seeing the diffraction rings with no disturbance. I'll do a proper star test when there's a clear night (hopefully in 2020 sometime). So thanks everyone for all your help. I now have a working Skymax-90 for very little cash. I love this forum!

Oh - it was so far out, I needed something to get it close. I've got an artificial star, so just about to fish it out of the man drawer.

It's proving hard to collimate with the o-ring being as hard as bakelite! I'll have to get it done roughly until I can get a new o-ring. Just checking - it's a case of using a cheshire to get the cross-hairs over the eye hole? Then a star-test. I'm doing it without the star-diagonal in place. Is that OK?

Thanks both of you, It's all gone back together fine. Now time to collimate it. That star diagonal. It is pants, isn't it? And I wonder why the gold parts on this Mak? Perhaps it's quite an early one.