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  #21  
Old 11-07-2021, 05:33 PM
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mental4astro (Alexander)
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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.

And don't forget DSOs and the Moon!

Alex.
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  #22  
Old 11-07-2021, 05:35 PM
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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.

https://www.nakedeyeplanets.com/mars-oppositions.htm
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  #23  
Old 11-07-2021, 06:32 PM
daz (Darren)
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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.


Once again, thanks for everyone's help.
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  #24  
Old 11-07-2021, 06:34 PM
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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.
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  #25  
Old 12-07-2021, 12:17 PM
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No spider vanes, Astro744.
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  #26  
Old 12-07-2021, 12:24 PM
daz (Darren)
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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 12:25 PM. Reason: clarification
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  #27  
Old 13-07-2021, 04:49 PM
daz (Darren)
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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).
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  #28  
Old 13-07-2021, 06:41 PM
daz (Darren)
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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.
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  #29  
Old 13-07-2021, 08:55 PM
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Sent you a PM regarding the EPs as it is beyond the scope of this thread.

Alex.
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  #30  
Old 13-07-2021, 10:05 PM
daz (Darren)
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Apparently, the rear end plate screws off:


https://stargazerslounge.com/topic/3...-or-knackered/


however it seems plenty tight, so not sure how to. Shouldn't need to screw it all the way off, just enough to pull the rest of the o-ring out.
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  #31  
Old 14-07-2021, 07:41 AM
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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.
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  #32  
Old 19-07-2021, 09:08 PM
daz (Darren)
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Alex,


Seems like I can't pm atm. In regards to the Vixen SSW's, the 82 deg fov is probably ideal for a mak, yes?
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  #33  
Old 22-07-2021, 10:30 PM
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If it is super tight and has a gap part way round, maybe it is cross threaded,
which wouldn't do much for the quality of your images.
raymo
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  #34  
Old 23-07-2021, 04:18 PM
daz (Darren)
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I'm pretty sure it's threaded o.k. Raymo, but the o-ring has been somehow caught in the threading, leaving a gap where the o-ring should sit.

I've contacted Saxon, & have an o-ring on the way, but no eta.
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  #35  
Old 27-07-2021, 03:57 PM
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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.
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  #36  
Old 27-07-2021, 05:44 PM
daz (Darren)
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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.
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  #37  
Old 28-07-2021, 05:07 PM
daz (Darren)
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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.
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  #38  
Old 14-08-2021, 06:21 PM
daz (Darren)
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Well, I've opened the mak, taking the front off (which needed a special spanner), to have a look at whatever it is that is reflecting.



Turns out to be a round, metallic aberration in the tube. I'm not sure if this is normal, or not. Possibly an artifact of the manufacturing process.


The problem is, it is highly reflective, so I'm thinking the solution is to paint the inside of the tube.


Next step is to get a hold of some Black 3.0.


Speaking of which, does anyone know if it can be sourced in Australia?
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  #39  
Old 14-08-2021, 06:53 PM
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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
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  #40  
Old 14-08-2021, 07:29 PM
daz (Darren)
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Might as well do it properly seeing as I've gone to this much trouble, Raymo.
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