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Strange effect around bright stars....


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Sounds like a good plan, not going to do it tonight though as I'm really eager to get a nice photo from my new gear.

Just swtiched to 8min exposures, no wind and sub 1 pixel total error in PHD...I am liking this new scope :) I must admitt I am a little worried about the secondary misting up but I think the hunidity is lowish tonight as it was warm and dry all day

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I think just get the rear of the primary covered, and straighten that wire that feeds the dew heater on the secondary and you'll be good to go. 

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1 minute ago, Daz69 said:

I think just get the rear of the primary covered, and straighten that wire that feeds the dew heater on the secondary and you'll be good to go. 

I hope so, I ordered a black shower cap off ebay so hopefully that's the end solution.

So is the idea for the wire to get it as straight as possible and in line with the vane? Is the straightness more imprtant than the thickness? If so, I'd probably be best sticking it to the top of the vane instead of trying to hide behind it. These vanes are extremely thin so the wire is around double the thickness.

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The 4 points to your stars in the photos are the vanes, so anything between your view (camera lens) and the star, will have some effect to the captured image. Getting the wire as thin and as straight as feasibly possible is the important part IMO. 

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1 minute ago, Daz69 said:

The 4 points to your stars in the photos are the vanes, so anything between your view (camera lens) and the star, will have some effect to the captured image. Getting the wire as thin and as straight as feasibly possible is the important part IMO. 

If you had to choose, would thin or straight be the higher priority?

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Just now, Peje said:

If you had to choose, would thin or straight be the higher priority?

Both! If you can anchor the wire at each end tightly, that's an anchor around the secondary mirror boss and the other anchor being outside the OTA, before both ends of the vane, then you get a straight wire easily. How thin you go is dependant on the power draw the strap uses, and the amperage of the wire used. You could probably get as low as using 1-2 amp wire to feed the heat strap. If a pair of wires are still too thick, split them and have one wire going along one vane and the other wire going along another. 

Do a Google search for wire gauge size in accordance to amp rating to see how thin you can go. Technically, If you have metal vanes and they are isolated from each other and the metal OTA (if it is metal or other conductive material), then you could use the vane as your wire. 

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1 minute ago, Daz69 said:

Both! If you can anchor the wire at each end tightly, that's an anchor around the secondary mirror boss and the other anchor being outside the OTA, before both ends of the vane, then you get a straight wire easily. How thin you go is dependant on the power draw the strap uses, and the amperage of the wire used. You could probably get as low as using 1-2 amp wire to feed the heat strap. If a pair of wires are still too thick, split them and have one wire going along one vane and the other wire going along another. 

Do a Google search for wire gauge size in accordance to amp rating to see how thin you can go. Technically, If you have metal vanes and they are isolated from each other and the metal OTA (if it is metal or other conductive material), then you could use the vane as your wire. 

I'm a hardware engineer so the wire sizing isn't a worry lol. I pull 1w to the heater as I just want to provide enough heat to keep mist at bay. I do like the idea of using the spider vane as a conductor, especially feasible given the carbon tube. The hard bit would be measuring the power draw as that'd mean either taking the scope into work or bringing a very expensive PSU home...you have got me thinking though

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1 minute ago, Daz69 said:

Don't forget though that carbon IS conductive! 

Didn't know that, I'll do a continuity test between some of te points and see what I'm working with, if they are isolated then it should be realitively simple to hook it up

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2 hours ago, Peje said:

Heater removed, scope fully recalibrated including secondary to focuser alignment to make sure it was a good as possible...effect is still there, allbeit slightly different now.

Any other ideas?

Procyon2.png

Looking at this image and then the image taken down your tube, the orientation of the diff spikes relative to the dark stripes matches the orientation of your spider vanes relative to your mirror clips.

You could try putting a paper masking ring around the edge of your primary, just enough to mask off the mirror clips, see if this occurs then.

 

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2 hours ago, Peje said:

Didn't know that, I'll do a continuity test between some of te points and see what I'm working with, if they are isolated then it should be realitively simple to hook it up

That's why we don't use our fishing rods under power lines or in a storm. 

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OK heater refitted, no real change to effect  with the cable kept more straight. I have noticed something else that's a bit odd, I am getting what looks like coma in only one corner of the image, this being the lower left. All other areas are fine, any ideas? I am using a Baader MPCC mk3.

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On 24/03/2017 at 23:38, CraigT82 said:

Looking at this image and then the image taken down your tube, the orientation of the diff spikes relative to the dark stripes matches the orientation of your spider vanes relative to your mirror clips.

You could try putting a paper masking ring around the edge of your primary, just enough to mask off the mirror clips, see if this occurs then.

 

Do you mean the front face or the side? I'm going to enquire with FLO about how much rework I am allowed to do as they have stated they are happy to replace the scope. I am hesitant to send it back as 1) I've spent time getting all my kit migrated and setup & 2) Mirror clips sounds like a design flaw so a replacement scope would like have the same problem

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Looks like I've got to the root of the problem. Today in work I fired over some of the photos to our Video Quality Engineers, he had an interesting theory. He thought that the mirror clips were not actually the problem, he stated they could be a clued to the solution. His theory was that the flare was not present in the places where the clips, meaning they were preventing it. An interesting theory which I had no rebuttle for...I had one of the CAD guys print me out a ring that was 205mm O/D & 195mm I/D

So I went home and looked down the focuser and sure enough there was a silver ring visible around the edge of the primary. The attached photos show the silver ring from both the focuser and the end of the tube. This ring seems to be due to the mirrored surface stopping short of the edge of the glass, this causes a visible silver ring as shown in the photos. The mirror clip looks really good to me, all black and the bit that touches the mirror is rubber so it's not causing any reflections.

03r - Down Focuser.jpg

04r - Down OTA.jpg

05r - Primary Mirror.jpg

06r - Mirror Clip.jpg

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So then I loosened the screws that clamp down on the clips, this allowed me to slide my paper ring underneath before clamping it down, shown in the first two photos I've attached. Paper is certainly not perfect as it rose up in places, also it needs to have a larger outter diameter and nothces for the rear of the rubber parts to allow better coverage. I'm going to get another paper one made that has the right diamters then I'll cut the required slots and get these transfered back into CAD land so I have a profile that I can get printed / cut on a more suitable material.

The third and forth mages show the reduction in the silver ring, it's still present at one side from the cameras perspective but that's due to the poor sizing (not bad for a guess though).

In a spot of good luck the sky cleared at sunset just as I finished reassembling the scope so I fitted it onto the mount and grabbed some test shots of Procyon. It wasn't fully dark and there were clouds coming but I was able to grab an image that I believe shows that this is almost certainly the solution.

Any other thoughts would be greatly appreciated.

07r - Mask Ring Fitted.jpg

08r - Mask Ring Fitted.jpg

10r - Down OTA Ring Fitted.jpg

12r - Through Focuser Ring Fitted.jpg

No Ring vs Ring.JPG

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1 minute ago, ollypenrice said:

Your colleague is very smart!

Olly

He sits in an optics lab all day evaluating all manor of strange effects under obscure lighting for our range of cameras...he lives for this stuff LOL

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On 3/27/2017 at 10:05, Peje said:

Do you mean the front face or the side? I'm going to enquire with FLO about how much rework I am allowed to do as they have stated they are happy to replace the scope. I am hesitant to send it back as 1) I've spent time getting all my kit migrated and setup & 2) Mirror clips sounds like a design flaw so a replacement scope would like have the same problem

Yes mask around the edge of the front of the mirror...exactly as you've done!  The edges of a primary mirror are often a problem area.

Congrats on getting it sorted out :)

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At least the theory is proven, now comes the fun of fine tuning the profile and figuring out how to sort a more permanent solution. My scope has to withstand lots of long nights in high humidity so paper is not a viable solution.

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Hi

The thing is, though, should you have to do all this with a new scope? Haven't you effectively cut down your aperture? Have other users of the same scope had the same problems or is it just your particular scope? If many other users have had the same problem then surely it must be a design defect or a manufacturing/quality control problem.

Other than that, well done for putting so much effort in!

Louise

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Just now, Thalestris24 said:

Hi

The thing is, though, should you have to do all this with a new scope? Haven't you effectively cut down your aperture? Have other users of the same scope had the same problems or is it just your particular scope? If many other users have had the same problem then surely it must be a design defect or a manufacturing/quality control problem.

Other than that, well done for putting so much effort in!

Louise

I should have said this before but FLO offered to replace the scope almost immediately and they have given me permission to do this work without affecting my ability to return the scope, brilliant service as always.

There was a new stock delivery of these scopes due around the time I bought mine so if mine is one of the new ones (I suspect it is) then I may have discovered a design issue with the latest manufacturing run that hasn't been seen before, something they can fix fairly easily with a mask ring.

Previous versions of this scope are rumoured to have wildly unstable collimatiom (something I can't confirm) but my one seems insanely stable, more stable than my previous f/6 Newtonian.

As for cutting down my aperture, yes I guess that's possible but I'm hopeful it would be negligible as I doubt every last mm of the mirror is being used, that would leave no room for error in terms of alignment or manufacturing tolerances.

You are correct that I shouldn't have to go through this with a new scope so hopefully my hard work will be rewarded somehow but at the very least I hope that it'll feed back to Skywatcher and they will release a proper solution that can be applied to my scope to resolve the issue permanently.

 

Pete

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On 24/03/2017 at 21:07, Peje said:

Heater removed, scope fully recalibrated including secondary to focuser alignment to make sure it was a good as possible...effect is still there, allbeit slightly different now.

Any other ideas?

Procyon2.png

I am on holiday, rain on the roof of the caravan woke me and I couldnt resist a quick peek at SGL... I saw your thread, now I know I won't be able to go back to sleep until I have posted! :smile: 

I think you have discussed two seperate unrelated things.

Your first photo (not the one above) showed an aberration that you successfully adjusted out. 

Now you are noticing aberrations caused by your Newtonian's mirror clips. This isn't uncommon and is not related to your first concern. The three dark spikes will coincide precisely with the position of the mirror clips. They are normally only visible around bright stars and the severity depends how large the mirror clips are in relation to the mirror diameter. This is why this aberration is most often noticed on smaller diameter Newtonians - their mirror clips are larger in relation to the mirror diamater.

As far as I know there are only two solutions, one is to render them invisible by covering the remainder of the mirror edge (i.e. if the mirror clips protrude 4mm into the mirror then mask/blacken the entire mirror edge with a 4mm sup-aperture mask, as you have done). The other is to remove the clips and fix the mirror to the cell using silicone-glue (the type of glue used in the making of fish-tanks, I think). No clips - no aberration. 

Hope that helps, 

Steve

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Btw, this aberration is almost identical to one that can be seen when using refractors that use metal spacing tabs to set the lenses, they can also protrude into the light path. 

Will try to get back to sleep now -_-

Apologies in advance if I don't respond again until next week when I am back at my desk. 

Steve

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PS: If you remain concerned you are welcome to accept my colleague's offer of a replacement telescope, though the replacement will also have mirror clips. Almost all Newtonian telescopes use them. 

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