Starburst? Why?

[gnomus]

This is a 100% crop from an image I took a few days ago.  The star shown is the largest/brightest star in the image.  

My telescope is an ED-80.  I have only taken a few images through it so far.  I have a couple of questions.  

1) Firstly, there is quite a large halo around the star.  This was a 5 minute exposure.  Do I just have to accept that I am going to get large haloes around the brightest stars when imaging?  

2) There appears to be a 'starburst effect' coming from the star.  I had understood that you only got this if you had vanes in the tube (like in Dobs) or if one stretched threads or wires across the objective.  These 'bursts' are not at 90 degrees to one another, and there was nothing in front of the objective.  Again, is this something I am going to have to live with?

3)  The 'bursts' themselves appear to be a bright line flanked by two dark lines.  Is this normal or is it an indication that I had not nailed focus?

I'm not that 'troubled' by these artifacts - I am simply trying to understand what is going on.

Thanks in anticipation

[Leveye]

My Stellarvue SV80ED gives me the same spikes and halos. Typical of what to expect from a scope for under 1K

Here's an example..

I was told by Stellarvue that it could be pinched optics. I just deal with it for a replacement would most likely have the same issues in this price range.

[happy-kat]

If pinched optics you might see none round defocused stars I think, do you get round stars or slightly triangle stars?

Monday night the seeing was awful my camera lens did this and it doesn't usually.

[MattJenko]

I get these as well and I think it is a reflection from the internal filter in the dslr. There is a formula for calculating how far from the sensor the reflection is coming from on the Astrodon site. Your halos look a lot like mine and the calculation goes like this:

The halos look a fairly uniform 170 pixels wide. In my example, my Canon 450D has pixels which are 5.4 microns. This means the image size is 0.884mm across on the sensor. The reflection distance is given by the size of the reflection artifact * the focal ratio, which in this case is (600 * 0.85) / 80- if you also are using the Skywatcher flattener/reducer on the ED80. Putting the maths together, unless I am mistaken, this is a reflection at a distance of 5.6mm from the sensor, which all points to the internal IR/Filter.

My thoughts are to do a full spectrum mod and then use an IR filter much further away from the sensor of my dslr, but I may just bite the bullet and go full CCD

[gnomus]

I get these as well and I think it is a reflection from the internal filter in the dslr. There is a formula for calculating how far from the sensor the reflection is coming from on the Astrodon site. Your halos look a lot like mine and the calculation goes like this:

The halos look a fairly uniform 170 pixels wide. In my example, my Canon 450D has pixels which are 5.4 microns. This means the image size is 0.884mm across on the sensor. The reflection distance is given by the size of the reflection artifact * the focal ratio, which in this case is (600 * 0.85) / 80- if you also are using the Skywatcher flattener/reducer on the ED80. Putting the maths together, unless I am mistaken, this is a reflection at a distance of 5.6mm from the sensor, which all points to the internal IR/Filter.

My thoughts are to do a full spectrum mod and then use an IR filter much further away from the sensor of my dslr, but I may just bite the bullet and go full CCD

Matt

Thanks for the detailed response, especially the various calculations. The only problem is, I have an astro-modded camera with no internal filter! In addition I was using an IR filter further down the chain - one of those IDAS thingies. I'd be interested to hear if you can get rid of these by going the CCD route. It's not a huge issue. I had one (and a half) affected stars in my M42 pic (from which the crop was taken); I didn't have any issues in my M33 shot.

[MattJenko]

Interesting. Mine is modded, but still has the IR filter in it, and I was pretty sure that was the source of my halos. If you don't have anything at that distance, I am wondering if I am wrong then . Save me taking my camera apart to take the filter out to find it hasn't stopped my halos!

Mine also only appear on bright stars on fairly long exposures, like Orion, Pleiades, Altinak etc and I have gotten used to them now and they don't bother me much. If and when I get a CCD, we'll really see!

[lensman57]

This is a 100% crop from an image I took a few days ago.  The star shown is the largest/brightest star in the image.  

Starburst.jpg

My telescope is an ED-80.  I have only taken a few images through it so far.  I have a couple of questions.  

1) Firstly, there is quite a large halo around the star.  This was a 5 minute exposure.  Do I just have to accept that I am going to get large haloes around the brightest stars when imaging?  

2) There appears to be a 'starburst effect' coming from the star.  I had understood that you only got this if you had vanes in the tube (like in Dobs) or if one stretched threads or wires across the objective.  These 'bursts' are not at 90 degrees to one another, and there was nothing in front of the objective.  Again, is this something I am going to have to live with?

3)  The 'bursts' themselves appear to be a bright line flanked by two dark lines.  Is this normal or is it an indication that I had not nailed focus?

I'm not that 'troubled' by these artifacts - I am simply trying to understand what is going on.

Thanks in anticipation

I have posted about this many times I think. There is nothing wrong with the scope or the optics. These are diffraction spikes caused by either the spacer clips or what ever is used to keep the lenses at the required distance to each other. Some scopes show more prominent  spikes than others even in the same class of scope . The more elements you have the more the spikes and it can and does affect even the expensive TAKS. I have been told that scopes that use oil spacing rather than air do not show diffraction spikes as much but have you looked at the price of an oil spaced triplet recently? Just enjoy the views and images. here is a link to my image of IC63 taken with my 5 element Star71, now that is a diffraction spike in a major league.http://www.astrobin.com/125980/

Here is a Synthesized image of a refractor of 80mm of Aperture and 600mm of FL with 3 clips each of 1 mm, done in the Synth module of StarTools, the other parameters are irrelevant for a refractor and only apply to Newts. Note the now  familiar diffraction spikes.

A.G

[Leveye]

Again I was only going by what Stellarvue themselves told me It could be after viewing some examples. Pinched optics was the issue they said it most likely was. They did also mention off centered spacers but there is nothing protruding in my scope at all. I've Inspected it thoroughly. It's for sure not my Camera. I've a few different refractors and non of the other ones give me these spikes using the same camera. 

[lensman57]

Again I was only going by what Stellarvue themselves told me It could be after viewing some examples. Pinched optics was the issue they said it most likely was. They did also mention off centered spacers but there is nothing protruding in my scope at all. I've Inspected it thoroughly. It's for sure not my Camera. I've a few different refractors and non of the other ones give me these spikes using the same camera. 

I think that pinched optics usually manifest themselves in triangular stars sort of equilateral in shape. Both your stars and the OPs seem to have a perfectly round core. I have asked WO for an explanation in my case but I am not holding my breath for an answer.

A.G

[gnomus]

I have posted about this many times I think. There is nothing wrong with the scope or the optics. These are diffraction spikes caused by either the spacer clips or what ever is used to keep the lenses at the required distance to each other. Some scopes show more prominent  spikes than others even in the same class of scope . The more elements you have the more the spikes and it can and does affect even the expensive TAKS. I have been told that scopes that use oil spacing rather than air do not show diffraction spikes as much but have you looked at the price of an oil spaced triplet recently? Just enjoy the views and images. here is a link to my image of IC63 taken with my 5 element Star71, now that is a diffraction spike in a major league.

Here is a Synthesized image of a refractor of 80mm of Aperture and 600mm of FL with 3 clips each of 1 mm, done in the Synth module of StarTools, the other parameters are irrelevant for a refractor and only apply to Newts. Note the now  familiar diffraction spikes.

.......

A.G

Thank you for this detailed response.  You have described exactly what I am seeing.  As I said, I was not troubled too much by it, just interested to know what it was.  Your image has a spectacular version of this effect right enough!

Regards

Steve