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malc-c

200P - colimation or poor optics

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I'm a happy bunny :)

Looks like the work paid off. Here's a test shot - 30s exposure of Procyon, and whilst it may not be perfect, it has no rouge diffraction spikes :)

Not 100% sure what resolved this issue. I repeated everything I did previously only this time was more precice with the centering of the spider, but then the old method of using a mark on a strip of card should still be no different - also the draw tube is no further out of the focuser than before - anyway I'm now going to leave the scope well alone

Thanks to Jason and everyone else who gave input to this thread. Your support has kept me going when I might of just given up on the hobby - Cheers guys

post-10726-0-26382200-1366317110_thumb.p

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Glad it's all sorted for you Malcolm. :cool:

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Cool. When you sort out the uneven starburst pattern, it'll be sorted. <runs and ducks for cover>

Russell

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<runs and ducks for cover>

Russell

You can run but you can't hide :)

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That would have been the first thing I checked :) LOL

Seriously very happy its worked out for you after so many trials and tribulations.

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Here's the best "star focus" - not quite sure, but it looks like the colimation is out, or the spider is off axis ?post-10726-0-73725300-1345667538_thumb.j

Hi Malcolm,

I am about 9 months too late but from the photo of the mirror it looked as if the secondary mirror had a tilt, I am glad that you have now sorted it out but for next time may I suggest you watch the video series from astronomy shed on advance collimation , it is apparently possible for the laser to be totally misleading in aligning the secondary to the primary.

Hope you didn't mind the pointer. Happy observing.

A.G

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Not 100% sure what resolved this issue.

Hello Malcolm,

Back in September when I first joined this thread I suggested your issue had to do with misaligned spider veins.

http://stargazerslou...60#entry1624658

Fast forwarding 6 months I still believe this was your issue all along

http://stargazerslou...80#entry1904734

Yet you still do not seem to be 100% convinced.

Regardless, I am happy that things have worked out for you. Now you owe all of us great astrophotos :)

Jason

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it is apparently possible for the laser to be totally misleading in aligning the secondary to the primary.

Unfortunately, Dion from astro shed still have not corrected or removed that video especially after he was shown that his statements about lasers being "misleading" are incorrect.

Jason

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Jason,

To be honest I'm not sure of anything now. Having centred the boss on the spider so many times over the past 6 months I would of thought that the chances of misalignment every time would of been slim. But seeing that I did nothing else to the secondary mirror (like coating the back with black paint) I would have to agree that the issue was something else rather than poor optics, and your theory is the more probable the more plausible.

It's just a shame that as we enter the summer season, I've missed a lot of the dark cold winter night DSO's :( - Oh well there is always next year :)

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great result. the main thing is that it's sorted :smiley: enjoy the scope and use it lots! sometimes, going back to the start and doing everything again is the only way.

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Great news!

Lets pray for some clear nights so you can make the most of it!

Cheers

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yes, it does. I made this point at the start of the thread. ideally a scope should be set up so that the focuser drawtube is less than about 1cm into the drawtube when focused using your eyepiece with least outward travel required. unless doing critical imaging lke Malc it's unlikely to be an issue.

in this pic, the bright stars have what i call the pacman effect. is that caused by the focuser?

Image11_zpsefe7cccd.jpg

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in this pic, the bright stars have what i call the pacman effect. is that caused by the focuser?

How are you connecting the camera to the scope. If you have used an ext tube, you would need to wind the draw tube in somewhat until focus is achieved, which could cause the draw tube to interfere with the light path. But I personally don't think that is the cause of the odd shaped stars

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its connected threw a t-ring that connects directly to the focuser barrel. il bring you up to speed on my setup.

canon eos1000d, konus 8" reflector, eq5 motorised. the scope is well collumated. though i have heard people saying konus has pants optics.

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On my 200P I have a coma corrector attatched to the canon 400D body, which is then placed inside the focus barrel and locked in place by the two thumb screws. The distance from the outside of the scope to the approx position of the CCD in the camera is 130mm. The focuser barrel intrusion inside the scop is approx 11mm, which is approx the gap between the primary mirror and the edge of the scope. If your focuser barrel intrudes further then that could be a possible cause, but then given that this was suggested as a possible cause to the issue I was having, would of thought you too would be having additional spikes rather than indented stars

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just measured. the barrel intrudes 36mm into scope when the dslr is in focus. almost half way to the secondary. that seems like alot.

il give a coma corrector a go tho. sounds like a good plan.

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Well here's the result of a crop from a stack of 16 x 420s images of M51 taken last night (with a very bright Moon I must add !)

I'm pleased with the resolution and how the optics are finally performing. OK the processing could do with tweaking, but that's another story

post-10726-0-79637600-1367146705_thumb.p

Edited by malc-c
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Happy for ya :)

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I'm a happy bunny :)

Looks like the work paid off. Here's a test shot - 30s exposure of Procyon, and whilst it may not be perfect, it has no rouge diffraction spikes :)

Well, seems it was short lived. The other night I used Arcturus as a focus star, and after removing the mask and taking a 30s test exposure the spike was back. The scope and set up had not been touched since the test image on Procyon was taken. This time unlike the test image with Procyon, Arcturus wasn't bang central in the field of view. I mentioned this to a friend who has said all along that this issue is with the optics, namely the secondary mirror and in his mind this proved it. He asked me for some measurements of the offending secondary, and said he would get back to me once he has crunched the numbers.

We met up today and he went through his findings, and using extensive formula showed me the correlation between the angle of the rogue spike and the area where the minor axis is uncoated. He also produced some full sized drawings to back up the maths.

I've asked my friend to type up a report on his findings and I'm intending to pass this on to the retailer / importer with a request for some assistance in resolving this matter once and for all as the scope is still not useable to its full performance. Whilst this can be resolved by installing an over sized mirror (which was what I had originally requested through the retailer / importers back in November of last year), I don't see why I should turn to a third party optical company to get a perfect mirror. The state of these three secondary's does indeed question the quality control Synta have in place as this is the 3rd secondary I've had which has had this uncoated area on the edges of the minor axis. Looking at some other images (including one other SGL member who has posted in this thread) it would seem that there are quite a few Skywatcher reflectors with this same fault. One thing for sure is I'm not prepared to wait another five months for a replacement PDS mirror from China !

Looks like this post might be one of the longest running threads on SGL... I'll keep you posted.

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Sorry. I clicked 'like' but after thinking I'd prefer to just post something that sounds a little more supportive that an unsympathetic 'Like' - Im very interested in the outcome and hope you get to the bottom of the problem once n for all Malc.

All the best

Aenima

ps i have a 'spikey' 200p :D

Edited by Aenima

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Well I've raised the matter with OVL and basically they have now closed the door on this. Whilst they state that they have gone beyond their normal duty of care as the scope is now out of warranty, they didn't accept that there was an issue with the scope whilst it was in warranty, and state that having just supplied a new mirror from china this is all they were prepared to do. I commented that I appreciate what they have done for me, but pointed out that I had, through the retailer requested a 200PDS mirror in a bid to confirm one way or another that there is a problem with the stock secondary, only after five months to receive a standard 200P and not the 200PDS as ordered. This was blamed on Synta making the mistake which was out of OVL's hands. I did suggest OVL pass on my concerns that IMO there is a quality control issue as all three secondary's have this flat area on the minor axis, and even though OVL claim they have sold loads of 200P's they have never heard of this issue before, to which I replied that I know of at least one other person (Aenima) who has reported similar issues.

Anyway, as we were going round in circles we ended the call. I've called the retailer and they too were unhappy with the way OVL have dug their heels in and refused to assist further. However the retailer has offered to see if they can source a suitable secondary from some of their contacts that is less then the £110 One leading optics manufacture wants.

I just want to add that whilst I'm reporting my findings here, and I'm not that happy with the way OVL have now refused to assist me with this anymore, they have been helpful in the past and I can to a degree see their point of view given the age of the scope. As this is a public forum I'm posting my view point, and I don't wish to draw SGL into any litigation. I am simply documenting the developments and my experiences in this ongoing thread. I welcome OVL to comment on the technical aspects if they wish . The conversation I had was civil and business like, and we closed the call in a professional way.

I'll update this thread once I source the funds to replace the secondary with one from a 3rd party.

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You didn't buy your telescope from OVL. You need to discuss this with your supplier, not their supplier.

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