M106

[Dmack1]

This was one of my last images with the SW Evostar 80 ED before I pulled out the LX200 for Galaxy Season.

 

I struggled with the background on this one and the stars sem to be showing what I think is a "pinched optics" - can anyone confirm that? It seems strange because my images on nights before and after are not showing the same anomaly and it was not particularly cold that night.

 

This is 55 X 180s SW Evostar 80ED, ASI2600mc

 

[AstronomyUkraine]

1 hour ago, Dmack1 said:

I struggled with the background on this one and the stars sem to be showing what I think is a "pinched optics" - can anyone confirm that? It seems strange because my images on nights before and after are not showing the same anomaly and it was not particularly cold that night.

The stars don't look to have pinched optics, they look to be elongated slightly, maybe poor guiding on those images. If you are running Pixinsight, put the offending files in subframeselector, and check the eccentricity.

[Dmack1]

19 minutes ago, AstronomyUkraine said:

The stars don't look to have pinched optics, they look to be elongated slightly, maybe poor guiding on those images. If you are running Pixinsight, put the offending files in subframeselector, and check the eccentricity.

Thanks Brian, there is definately a bit of eccentricity and I'm sure I can tighten up guiding.

But my concern is the star shape shown in this tight crop which is a STF of the unprocessed image. This is the area around the brightest star in the lower left quad of the image above.

 

I'd be delighted if its NOT pinched optics as i have not the first idea how to deal with that.

[TerryMcK]

Some of the larger stars have strange shapes but I can't see too well as the png isn't that high res so when I zoom in with PixInsight it just goes blocky. Possible to upload the image as a tiff or xisf (I know they can be big though so you might be able to use a free service like wetransfer.com)

[TerryMcK]

Now that you have zoomed in it reminds me of an issue I had with the flattener on one of my scopes. It had a slight burr that was sticking up on the inside of part of the machined internals. I had to file off the burr as it appeared to be creating a slight optical funny within the imaging train that was creating "the lighthouse effect" as somebody on another forum mentioned.

If it is lens pinching that is generally created when the lens cell is expanding or contracting due to very cold weather creating a stress point and can be alleviated by carefully slackening off one or more of the lens screws.

Hopefully it isn't lens pinch and it may just be a burr.

[Dmack1]

 

8 minutes ago, TerryMcK said:

Now that you have zoomed in it reminds me of an issue I had with the flattener on one of my scopes. It had a slight burr that was sticking up on the inside of part of the machined internals. I had to file off the burr as it appeared to be creating a slight optical funny within the imaging train that was creating "the lighthouse effect" as somebody on another forum mentioned.

If it is lens pinching that is generally created when the lens cell is expanding or contracting due to very cold weather creating a stress point and can be alleviated by carefully slackening off one or more of the lens screws.

Hopefully it isn't lens pinch and it may just be a burr.

Thanks terry, I'll have a look in the FR but since the nights immediately before and after were OK I'm not sure about that. But i'll take a close look at the whole imaging train because the temperature was not significantly different that night - certainly not as cold as other nights recently and no warmer than others which have been fine - so pinching seems unlikely.

 

I really appreciate your input.

[AstronomyUkraine]

7 hours ago, Dmack1 said:

Thanks Brian, there is definately a bit of eccentricity and I'm sure I can tighten up guiding.

But my concern is the star shape shown in this tight crop which is a STF of the unprocessed image. This is the area around the brightest star in the lower left quad of the image above.

 

I'd be delighted if its NOT pinched optics as i have not the first idea how to deal with that.

Be interesting to see the shape of the star out of focus, but you might never get it to replicate again. The concensus seems to be, the number of diffraction spikes corresponds to the number of collimation grub screws on a refractor, if it is pinched optics. I wouldn't recommend messing about with those, you could end up with way more problems than you have now. I have noticed on some of my images, I have 6 diffraction spikes, but they don't worry me, I'm leaving well alone.

 

Brian