Are my stars elongated?

Astro Jeep · Feb 11, 2026, 05:53 AM

📷 IC434_HSS_RGB_30s_Stars.tif📷 IC434_30s_RGB_OnlyStars.tif📷 IC434_30s_Star Mask.tif

Just a quick note: browsers do not render TIFF files natively, and AstroBin does not convert them in the forum. Upload JPEGs to make them visible, or attach as files instead of images.

andrea tasselli · Feb 11, 2026 at 07:39 AM

That's a very unusual rendering of IC432 and surroundings. Why bother with the RGB if you aim at basically a colorized version of a B&W image? But, regardless, you can't post tiff files on the forum, just jpg/png/bmp for straight rendering. Also, if you want a serious analysis you'd need to provide a raw file or its auto-stretched rendering (as an image file, see above) for all to see. ATM I can't see a damn thing.

I used RGB stars because I only shot in Ha and SII to make an HSS palette. I specifically wanted the nebulosity to appear white, as if it were a cloud. Because of that, I decided to shoot RGB stars, because I didn’t want to take OIII images to convert the SHO stars into RGB stars later. I am simply experimenting.

I took the TIFF files down. I didn’t realize that you wouldn’t be able to see the TIFFs, and I will post JPGs soon. Thank you.

Astro Jeep:
I used RGB stars because I only shot in Ha and SII to make an HSS palette. I specifically wanted the nebulosity to appear white, as if it were a cloud. Because of that, I decided to shoot RGB stars, because I didn’t want to take OIII images to convert the SHO stars into RGB stars later. I am simply experimenting.

I took the TIFF files down. I didn’t realize that you wouldn’t be able to see the TIFFs, and I will post JPGs soon. Thank you.
Quote this post in your reply. If you select text, only the selection will be quoted.

andrea tasselli · Feb 11, 2026 at 02:33 PM

Astro Jeep:
I used RGB stars because I only shot in Ha and SII to make an HSS palette. I specifically wanted the nebulosity to appear white, as if it were a cloud. Because of that, I decided to shoot RGB stars, because I didn’t want to take OIII images to convert the SHO stars into RGB stars later. I am simply experimenting.

I took the TIFF files down. I didn’t realize that you wouldn’t be able to see the TIFFs, and I will post JPGs soon. Thank you.
Quote this post in your reply. If you select text, only the selection will be quoted.

From what I can see in the processed image it isn't simply an elongation but rather a bi-axial variation of the stars' shapes (triangular to linear) which might hint to a deeper seated issue with the optics. This is why providing access to a raw file would yield more insights than anything else.

After reading your reply, it occurred to me that I had not performed a sensor analysis to determine whether my sensor was flat. It is probably slightly off. I know it most likely isn’t a guiding issue because PHD2 showed near-perfect guiding that night. I also added the raw .xisf file from PixInsight as you requested. I really appreciate your insight, so thank you!

Astro Jeep · Feb 11, 2026 at 02:34 PM

I tried BlurXterminator, and I would rather always fix the root cause. I have a set of 120-second RGB stars that had much better-shaped stars. I didn’t use them because I was having a difficult time reducing the bloat, but if I used those instead, I am sure I would get stars with a nice Gaussian fall-off. That point you made was worth making the post alone. Thank you, Sir.

If you have PI, just use the FWHMEccentricity tool to actually measure the ellipticity of your stars. As you are learning, there are a lot of factors that can cause elongated stars and guiding is only one factor. You also need to make sure that your optics are good, that they are well aligned and that the sensor is not tilted with respect to the image plane. Mechanical vibration due to wind or other factors can also cause elongation.

The very first thing to do is to learn how to measure the elongation yourself and if you have PI, you already have a number of tools to do that. Then start working through your system to identify problems. FWHMEccentricity can be used to evaluate sensor tilt simply by analyzing a dense star field and looking at the eccentricity contour plots over the whole field. It’s best to start with short exposures to reduce the effects of guiding and vibration. If the field is not symmetric, you might have a problem. Then go to longer exposures to see if things get worse and if they do, then figure out why. Imaging systems are very sensitive to small errors so a huge component to being successful at astro-imaging is learning how to solve problems and to do that you have to learn to be very methodical. You’ve taken the first step—namely asking if your star images are round. The next step is to figure out how to determine that yourself. After that, you have to work to identify potential causes and then tests to confirm or eliminate them. It’s a slow and sometimes frustrating process but it is immensely satisfying when you get things figure out.

Good luck with it!

John

Based on what you’ve presented my opinion is they are not elongated.

I would say soft (out of crisp focus). Maybe overexposed which can make them soft in my experience.

I’d suggest you work with your exposure times by shortening them and increasing the count. And pay attention to your guiding specs. Tighter guiding leads to sharper stars and better details overall.

I use PHD2 for guiding and NINA as my overall control program. My guiding runs 0.2 to 0.3 RMS averages. Well below the coveted 0.5 averages. I believe that is because also I don’t move my mount from day to day. So it retains its Polar Alignment month after month. (Much like having a pier, and not dismounting the telescope.)

You will be able to gage by the tiny stars getting tinier and more numerous. And the larger stars shrinking. Just a matter of fine tuning.