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malc-c

200P - colimation or poor optics

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Here's the raw TIF (cropped so it falls below the 20mb file limit) from DSS - please feel free to post process if you want a bit of fun

Thanks, much clearer without that green. The star effected by the five spikes is the only one, so it must only effect brighter stars or when zoomed in.

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Malc can you upload a linear image (unstretched) as colour calibration needs to be done on linear data.

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Malc can you upload a linear image (unstretched) as colour calibration needs to be done on linear data.

I've clicked the reset button in DSS and saved the file as 16bit tif - then cropped in PS to reduce the file size from 51mb to around 12mb - hope this is what you are after ?

m27c.TIF

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Hi Malc its still stretched, can you zip up the subs and host them somewhere?

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One last suggestion. Can you find someone with the same scope and swap the secondary to see if the problem travels with it. Might be worth a try :)

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Sorry its took a while i drifted off to the drum kit for a bash !

I did strugle with background noise, sheathing i need to work on.

post-6688-0-41942800-1347929579_thumb.jp

Edited by Earl

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Wow.... I'm impressed - and the stars have colour too

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I know almost nothing about astro imaging but one thing's for sure, it's in the processing.

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I know almost nothing about astro imaging but one thing's for sure, it's in the processing.

Oh yes I agree.... Now I have a slightly better understanding of DSS here's the result of a re-processing session (an a new PC - 6 core 16GB RAM - :) :) - makes quick work of the processing :) )

Forgot to add:

30 x 180s lights and 30 x 180s darks - no flats !

post-10726-0-87652500-1348779434_thumb.p

Edited by malc-c

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I was still not satisfied with the spike, so tonight I played about with the mirror position, by adjusting just the spider arms - this was the best result. OK it's got other colimation issues but it's indicating that the issue is with colimation rather than optics....

post-10726-0-32249800-1350074802_thumb.j

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Sorry for dragging this up again, but wanted to share my latest effort into try and get to the bottom of this. I jumped in a purchased another MS Lifecam and used the billet part adapter so I could follow Dion's "advanced collimation" video,

First thing I did was remark the focuser center point, using a set square to the edge of the tube, taking a line through the hole where the spider attaches, and crossed with a vertical mark. The focuser was then centred using the laser so that it struck the intersection between the twoi marks. I then tested the centering of the camera using mir-de-collimation and the reticule on sharp cap (see 1st image). However when it was placed in the focuer (I use an Orion self centering eyepiece golder) I noticed that the ring produced by the end of the draw tube was "off centre" when compared to the rings on mir-de-collimation (see 2nd image). Anyway I went ahead and fitted the spider, having confirmed the legs were straight and not bent, and fitted the secondary and proceeded to set it up by aligning the rings with the rings on the overlay. Whilst this was perfect, the reflection from the primary was way out (images 3 and 4). So after some further fuffing about I gave up and stuck the cheshire back in and started all over again... Needless to say I now have it looking as text book as ever.... but now the clouds have rolled in and I'll have to wait to see what the results are like.

I've stuck the web cam back in and captured a short length of video, changing exposure so as to try and pick up the reflections... would welcome comments.... http://www.micro-heli.co.uk/col.avi

post-10726-0-81287600-1350243517_thumb.p

post-10726-0-55014700-1350243576_thumb.p

post-10726-0-35895500-1350243608_thumb.p

post-10726-0-24931300-1350243630_thumb.p

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Ok I'm giving up.... this was the result - now have two spikes !

post-10726-0-42436300-1350246423_thumb.j

Edited by malc-c

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Extra spikes can only and only be caused by intrusions into the light path. Most certainly collimation has nothing to do with it. I am still of the opinion that the extra spikes are caused by misaligned spider vanes. I suspect the two vanes located along the focuser axis. Double check them again. Do not use a ruler. Get a string and stretch it with your hands and place it along opposite vanes. Are they inline?

Jason

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Did you try replacing / swapping the secondary with another scope to see if the problem travels ?

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Do you have a washing line going over or through your obsy? :-)

Sent from my GT-I9100 using Tapatalk 2

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Did you try replacing / swapping the secondary with another scope to see if the problem travels ?

I never received a reply from the importers, and have just raised the request via RVO. On recommendation I've downloaded and installed CCDInspector. ON checking various images with the software the collimation is spot on, with other test suggesting the alignment of the optics is as perfect as you can get with a commercially mass produced scope. One comment was that one set of results were as good as his 10" quattro.

So that leaves something else in the mix.... next option will be to pain the back and sides of the mirrors to reduce the chance of internal refractions... but my guess is that, as others have pointed out, its something else within the optical path. One thing for sure, the scope has had this fault since purchase. I located an image of Sirius taken one month after purchase and it too had the spike.

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Extra spikes can only and only be caused by intrusions into the light path. Most certainly collimation has nothing to do with it. I am still of the opinion that the extra spikes are caused by misaligned spider vanes. I suspect the two vanes located along the focuser axis. Double check them again. Do not use a ruler. Get a string and stretch it with your hands and place it along opposite vanes. Are they inline?

Jason

The spider was set up using graph paper to ensure that the arms were not only straight but at 90 degrees to each other.... On installation I used a strip of plastic and measured off and marked the distance from the centre of the spider to the edge of the tube on both sides, repeating the process over and over again until the mark was centred on both sides without the need to change its position. This was then performed on the other set of arms, thus centreing the boss in the middle.

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Did you give the idea I suggested a go.

It might show when the spikes start and stop. Use discs in 1/2" increments, it may show up something or not.

Nothing to lose at this stage. Good luck.

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A good way to check the spiders/secondary would be to mount a de-focused red laser behind it. With the tube far enough from the wall, it would reveal any​ imperfection (bent, ragged edge etc.) at a basically microscopic level.

I feel it must be something to this effect as your testing has been pretty thorough.

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I have a feeling the focusser needs a shim to set its drawtube square with the telescope tube, the second image above suggests this may be an issue. Although the focusser may be square you need to consider the alignment of the drawtube itself.

Have you got a spot on the opposite side of the tube to the focusser so this can be aligned first without the spider in place, this is a key step but is often overlooked.

The steps you could take are:

  1. Measure the circumference of the outside of the tube and measure half this length around the tube from the centre of the foccuser drawtube - mark this on the tube ( this will be directly opposite to the drawtube opening).
  2. Then measure how far down into the tube the centre of the drawtube is and take the same measurement on the opposite side of the tube.
  3. Where these two points overlap make a mark on the inside of the tube.(stick on a ring binder reinforcing ring).
  4. Then without the secondary fitted use the cheshire to make sure the drawtube is pointing directly at this mark.
  5. Once this is confirmed you can refit the secondary and move on with collimation.

good luck,

Astronymonkey

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Hi, and thanks for the input. Yes, I followed the Astronomy Shed tutorial to find the centre spot of the focuser. Basically I used digital calipers to measure the hole in the tube along the focal length axis, then divided that in half and added it to the measurement of the edge of the hole and edge of the tube. I then used card strip on the inside circumference between the hole and then divided that by 2 to get the intersection. This was then spotted with a gold marker pen (tube is flocked) and a Hotech laser used to position the focuser in that spot.

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Well, I've just got home and checked my e-mail and had some wonderful news. I contacted Ian at RVO requesting prices for a replacement, and detailed at length the issues I've had with links to this thread for further background info (rather than repeating everything). He has been in contact with OVL and has instructed me to return the complete spider and secondary for replacement, with no hint of request for payment... what can I say... Fantastic service not only from Ian, but also backed up by the importers.

This has really picked me up as I received a notification letter yesterday advising me that my position at work is "at risk" of redundancy, so been somewhat down of late. Knowing I might get a scope that should perform better than it has been as a result of RVO /OVL's actions has made me happy again :)

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Sorry I haven't read through all 9 pages so I risk repeating what has been said already. I don't think the problem is the spider. I think it more likely that it is something intruding too much on the light path (e.g. focuser) or an internal reflection. These links might help if they haven't been offered already.

http://spider.ipac.caltech.edu/staff/kaspar/obs_mishaps/images/int_reflection2.html

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3907379/Main/3907022

In itself an extra spike isn't any more of a problem than the 4 you normally get. Nice if you can find a solution but it's not going to spoil the view.

Glad to hear of the good customer service. Good luck with your telescope and with your work situation.

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