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200P - colimation or poor optics


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Nigel, sorry to hear you have a similar issue - I presume that to is with a 200P ? - If so that makes 4 of us affected, which IMO is more then just a co-incidence. OK there has been some discussion that if I wanted to do imaging then the PDS should of been purchased, but as already stated, the stock 200P is marketed as being a fast scope with a direct SLR connection, and doesn't state anywhere in the material that you should expect artifacts when doing so because the scope is being pushed beyond it's potential.

To follow up on the suggestions that some posted favor twisted / bent spider or some other alignment issue then this too would be strange that 4 scopes all have bent spiders (even though I've changed mine three times now and still gave the additional spike). - Even so, that has to be more than co-incidence.

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Sorry Malc, I think that you mis-read my post. The image in the post I linked to was taken by Ernesto Guido & Nick Howes with the Faulkes Telescope North, a 2.0 meter F/10 Richey-Chretien.

I do not have a commercial Dobsonian, I made my own 16" Dob.

Nigel

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No probs.

I just thought that it was interesting that a totally different, and very expensive, telescope should show what appears to be the same effect. I wonder if it is connected with the ccd chip and not the telescope at all? We do see some linear smearing on very bright objects from some of the Solar Space Observatories which are artefacts of the readout from the ccd chip.

Nigel

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You know there must be a strong case for Murphy's law here. For the past month I waited for the new mirror to be made as part of a batch run, and we've had some of the clearest summer skies for ages. Today the new mirror arrived and we have thick cloud here in the south !!

Anyway the new mirror is in and hopefully collimated. I say hopefully as I was so used to seeing the reflections produced by the small stock mirror it took me a while to get used to seeing more of the primary reflected in the secondary. For once I've seen all three primary clips centralized in the reflection. I've now just got to sit and wait for a clear enough session to tweak collimation on a star test and take a 20s sub of Vega to compare the results. Hopefully the rouge spikes will be no more.

post-10726-0-99396800-1374319881_thumb.j

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:hello2: :hello2: OK, confitions not fantastic, but Vega is out and has enabled me to take a test shot. Collimation needs a slight fine tune, but the first result concludes the matter IMO

Attached is a 15s exposure of Vega, the centre section been cropped to 1000 pixels, and then inverted - I HAVE NO ADITTIONAL SPIKES :grin: :grin:

I've done nothing else to the scope - I simply removed the secondary that was shipped from China, and installed the new secondary from Orion optics and then did a collimation.

This proves to me at least that the issue has been poor optics all along. Nothing to do with obstructions in the light path, nothing to do with bent spider veins etc - just a badly made sondary's.

Not sure if I will take this further and try and recover my costs through the retailer, or simply put a line under it and move on.

So now we can finally put what must be the longest running thread on SGL to bed once and for all :)

post-10726-0-39137300-1374442768_thumb.j

post-10726-0-44153500-1374442784_thumb.j

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Yep...it's looking good. I think you can rest assured that it's finally sorted.

I agree with drawing a line line under the whole issue and get on with enjoying your astronomy. Good luck with what you choose.

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Tony,

I think out of curtsey I should inform the retailer and the importer that I've resolved the issue, and let them make any gestures of good will as they may seem fit. My concern is that like Aenima and a few other SGL members there may be lots more 200P's that have this issue of flat edges on the minor axis which doesn't become noticeable until their learning curves evolves and they progress into taking images with a dSLR as per the advertising on in the literature.

I'm just pleased that I now have a scope that performs to my expectations and I can look forward to some nice dark nights this winter progressing with my imaging learning curve

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So Malcom it would appear it was down to a badly coated secondary all along as suggested ? almost a year to resolve Malc but now you can get out there again & enjoy the hobby once more. As it would appear a lot of those scopes suffer the same problem a refund would have been a better course of action I feel as faulty products are all too common these days. Glad it's solved though well done.

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Of course Malcolm you have to do what you deem best. I'm unaware of your relationship with the retailer/importer, so if you feel you and others can benefit from furthering it, then you have to go for it.

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Tony,

I think out of curtsey I should inform the retailer and the importer that I've resolved the issue, and let them make any gestures of good will as they may seem fit. My concern is that like Aenima and a few other SGL members there may be lots more 200P's that have this issue of flat edges on the minor axis which doesn't become noticeable until their learning curves evolves and they progress into taking images with a dSLR as per the advertising on in the literature.

I'm just pleased that I now have a scope that performs to my expectations and I can look forward to some nice dark nights this winter progressing with my imaging learning curve

Hello Malcolm,

First, congratulation for the issue resolution.

I suggest you wait for a while to ensure the issue does not re-surface before contacting any vendor.

Keep in mind that you have resolved this issue back in April and many members congratulated you.

http://stargazerslou...00#entry1907205

Somehow you have resolved the issue with the "problematic" secondary mirror. But after a while, the issue re-surfaced.

At one point you have even correlated the issue to the spider vanes

http://stargazerslou...00#entry1627649

I am curious to know how prevalent is this issue with 200P owners?

Jason

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Jason,

Agreed, I need more testing, probably with the scope at different target stars to rule out any issue with mirror movement or flexing. Looking back I still can't explain the previous results, nor why the issue re-occured some days later, other than the reasons later mentioned by some other SGL members.

As for how common this issue is, well we've had three members report similar issues, and all three stock secondary's I've had from SW have had a non-eliptical profle, so I'm reasonably confident that this issue affects a lot of Explorer 200P's. My guess is that, like me, the issue doesn't become a problem until the user starts using the scope for imaging. It maybe that a lot of 200P owners may even take it that any additional spike on their first images is "meant" to be there and are thus not concerned.

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As I've said before, the 250P secondary I have in my 10" dob also has two uncoated areas similar to Malc's so I wonder if the "defect" is a direct result of the process by which the mirrors are coated and if secondaries across their range of newts might be affected.

James

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Congrats, Malc. Glad you have sorted it.

I expect that all the secondaries from this manufacturer will be the same. They probably employ the same technique for holding the mirrors for coating as did VCSM when I first visited them back in the 90's: they used an angle iron frame to support the mirror in the coating chamber resulting in small areas at the edge not being coated. VCSM then put a second coating on after rotating the mirror and this then gives a full 100% coat. It would appear that the SW manufacturers do not do this second coating thus leaving the edged uncoated. I can just imagine rows of flats in an angle iron channel pushed through the coating chamber, once :rolleyes:

Nigel

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Fingers crossed it's sorted Malc I'm sure you'll keep us all updated. I never really noticed the additional spike on mine until my recent image of the dumbbell so I thought of this long running post straight away. I've fiddled with the collimation checked the vanes & will give it another go the next time I manage to go out to image something & will post the results accordingly.

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