Image for collimation testing - Page 2

acropolite (Phil) · #21 16-09-2005, 10:12 PM

I would guess that the vanes being not aligned with the light path as BD suggests would be the cause of the double spike.

ballaratdragons (Ken) · #22 16-09-2005, 10:15 PM

Thanks Phil!

[1ponders] (Paul) · #23 16-09-2005, 10:21 PM

David, I just had a thought.

Before you go twisting spider vanes have a good look at your avie frame by frame in registax to see if there is any up and down movement in the image. If you don't know how to do that, click and hold on the right hand side of the slider at the bottom (just like a scroll bar) and it'll scroll through all the images. What may have happened is that registax might not have lined all the images up correctly. It's simple enought to check the images and untick some from the frame list and run the prog again. If you don't know how do untick them from the frame list, use the space bar. The unticked frame will show up beside the scroll bar as a red square.

Rather that first than trying structural deformation on your vanes. If you do and accidentally stuff it up you might pop one of your own veins.

davidpretorius · #24 16-09-2005, 10:27 PM

i will definately wait for a new vid that i will take first before any structural changes.

i have collimated since, so i hope to have the motorized focussing happening so i can take a vid for collimation for noobies to show them what to look for and sort out if it is registax or the veins

astro_south (Andrew) · #25 16-09-2005, 11:47 PM

Quote:

Originally Posted by acropolite

I would guess that the vanes being not aligned with the light path as BD suggests would be the cause of the double spike.

If the veins are angled to the light path they will only produce a wider spike - not a double spike. I also noticed the curve in the vanes in Dave's photo but assumed it could have been due to the camera lense. On closer inspection I think your right Laurie - certainly something to look at. The clear double spikes on the left of the star in Dave's original image don't exactly match the oposing spikes on the right - in that the ones on the right seem to converge together. Perhaps this is strong support for the curved vane that Laurie interpreted. There is still something not aligned to produce those dominant double spikes on the left though - I don't think Registax could missalign them like that in a stack.

Remember that with a four vane spider there are actually 8 diffraction spikes that eminate from the airy disc - it is just that they pair up giving the illusion of only 4 diffraction spikes. A 3-vane spider will have the impression of 6 diffraction spikes eminating from the airy disc.

slice of heaven · #26 17-09-2005, 12:21 AM

Dave,moving away from whats causing the double spikes, have you checked the 'secondary' for pinching??????

davidpretorius · #27 18-09-2005, 01:29 AM

Ok, i have taken a video of Rigel Kent. I am wondering if i did not do this before and confuse it with Canopus. Anyway, Rigel is a double star.

So tonight i got some video and have stacked it.

Of course i will get double diffraction if i have two stars????

[1ponders] (Paul) · #28 18-09-2005, 08:29 AM

Quite likely David. Check out this link about focusing with a hartmann mask. It covers a similar issue. http://www.iceinspace.com.au/forum/s...highlight=mask

davidpretorius · #29 18-09-2005, 08:33 AM

thanks, my next project is a hartmann mask i may get the kids involved today in some scissor work

acropolite (Phil) · #30 18-09-2005, 09:04 AM

Dave, you should be able to easily split Rigel Kent @ around 75x mag and it will appear as two distinct stars with noticeable separation. Whether you can accomodate that mag with your combination of ToUcam and EP's I'm not sure. If you can, bump up the mag to around that value and see if you can image the two; if not call Houston as I would say you have a problem...One other thought, I seem to remember that you're using the ToUcam afocally and the double spikes could be simply reflection between the EP and Toucam lens surfaces....

pmrid (Peter) · #31 28-09-2009, 09:50 AM

Quote:

Originally Posted by [1ponders]

The double spikes indicate that the image is still not quite in focus. Why only the horizontal one are double I don't know???

Hi Paul. This is an old thread I know but more or less on topic for the question I'm asking.
In the attached image, the diffraction spikes are not double but split. Does this suggest collimation and/or tracking to you?
It's a single 5 min sub at ISO 200 - I was trying to do some short exposures of Alnitak so I could layer them into some brighter images taken a few nights back.

Peter