Try aiming the scope at a bright star closer to zenith & look for the same aberrations. Better still would be Jupiter but only with it high in the sky (which right now means around 1am). This will ensure as much as possible less stray light getting in - & try to set up somewhere without strong lights impinging on your scope.
If these strong spikes keep on appearing it will mean looking at things more carefully. I have not seen any such spikes in my 127 Mak. Could also be the eyepiece. Is it very modest in cost? This isn't a certainty as a source, just part of the investigation.
Oh yes, Mars is flaming tiny right now. Earth is leaving it very far behind now in our orbit around the Sun. It won't be a good target for another 18 months or so. Jupiter and Saturn are coming up to opposition next month. Uranus and Neptune later on again, and they present their own challenges to identify.
Mars is 3.8 arcs at present, almost as small as it will appear. Saturn is about to rise on the opposite side of the sky with Jupiter soon after. Next Mars opposition will be Dec 8, 2022 at 17 arcsec. The last one was 22 arcsec so it’s going to be quite a few years before Mars will be approx 25. Very close oppositions are 15-17 years apart. Oppositions are 26 months apart.
Thanks for your advice, Astro744, hopefully will get a chance to do some daytime observing.
Alexander, I'm pretty sure you're right about the spikes being stray light. There are a couple of highrise not to far from the viewing angle, one of which has a big blue neon sign on top. The yellow could be apartment lights.
Seems the most obvious explanation.
You mentioned 4 cardinal spikes in your Mak. Does it have a 4 vane spider? I thought the secondary was on the back of the thick primary front element but I understand there are many different Mak designs.
You shouldn’t be seeing 4 cardinal spikes at all through a central obstructed telescope unless there are some vanes in place or square obstruction (unlikely). An SCT with a huge central obstruction produces no spikes but changes the Airy disk in terms of which rings are brighter.
Alexander, I saw the vixen eyepieces you have for sale, I'm not really in the market for an eyepiece atm, but out of curiosity, would you recommend the 10mm or 14mm?
Looking through the 10mm plossl last night seemed a step up in magnification to what I was using, but have read that often comes with a tradeoff in sharpness?
Last edited by daz; 12-07-2021 at 01:25 PM.
Reason: clarification
Rained out last night, but o.k. tonight. Managed to bodgie up a shield to keep out stray light. Vast improvement.
Using 10mm plossl, I'm still seeing diffraction spikes on Venus, but nowhere to the same extent. Same colours, blue & yellow.
The Moon, no diffraction spikes, but some aberrations around the illuminated area, best guess is scope needs more collimating. (haven't done star test yet, as no bright stars visible to the naked eye in the west, and currently sans finder).
Seems there is a small problem with the scope. The rubber o-ring that fits between the back plate and the tube isn't sitting properly. There is a gap for about 1/3 the circumference where the o-ring should be.
Having second thoughts about attempting this. I'm assuming the o-ring's main function is to stop dust from entering the ota via the thread, so might just tape it up in the interim.
Finally loosened the back plate and pulled the o-ring out, the o-ring was covered in a black, sticky substance which I managed to get on quite a large portion of the back plate.
The o-ring, surprisingly, was in tip-top condition; I was expecting a mangled mess.
Unfortunately, despite having gotten the collimation pretty close, still have massive diffraction pattern.
When I defocused on Venus tonight, I had a perfectly round object thingy, with a dot right in the centre, the way it is supposed to be.
Really don't have a clue as to what's causing the diffraction.
Well, I think I may have found the culprit. In the image just to the left and below centre is a highly reflective object that appears to protrude approximately 1mm from the surface of the tube.
Now to open the bugger up and see if it is easily detached.
Before going looking for special paint I suggest that you paint the protuberance matt black and see if that fixes the problem. There is probably no need to paint the whole tube interior.
raymo