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I tried imaging Sirius last night and found I was getting concentric ellipses radiating out from the star.


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Hi, 

As above I was trying to image Sirius and was getting strange ellipses radiating out from the star.

I was using a Celestron 127SLT on a GOTO mount and a 20mm eyepiece. I took the picture with my phone, with ISO 3600 and 32s exposure.

Can anyone tell me why I might be seeing this and how I might be able to fix it. I have never noticed this before doing similar exposures of Arcturus.

Thank you

IMG_20220929_041239077.dng

IMG_20220929_041441866~3.jpg

Edited by 8abu_Frik
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Was there stray light hitting the objective? The pattern looks similar to an obstruction on the front of a Newtonian or SCT, anything like that will present itself as some sort of diffraction spike around the star(s).

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6 hours ago, 8abu_Frik said:

Is there anyway I can correct for / fix it?

I also think this is lens flare. Sirius is the brightest star in the sky and your using ISO 3600 and 32s exposures? I think that might be OTT.

Try reducing the ISO and/or the exposure duration. 

The cause is the cover glass in front of the very small sensor on your phone. I've had  similar reflections of bright objects in the night sky just using the phone on its own, never mind concentrating then through an eyepiece. 

Experiment and see what makes a difference. 

 

Mike

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5 hours ago, Stickey said:

I also think this is lens flare. Sirius is the brightest star in the sky and your using ISO 3600 and 32s exposures? I think that might be OTT.

Try reducing the ISO and/or the exposure duration. 

The cause is the cover glass in front of the very small sensor on your phone. I've had  similar reflections of bright objects in the night sky just using the phone on its own, never mind concentrating then through an eyepiece. 

Experiment and see what makes a difference. 

 

Mike

Thank you so much for the suggestion, I'll see if it helps next time I'm out.

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The larger ellipses (up/down/left/right) are caused by microlens diffraction, sometimes erroneously called microlensing.  It's a property of the sensor and many dedicated astro-cameras have the same problem. There's really nothing you can do to prevent it.

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