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dealing with reflections and diffraction with ASI1600MM

Posted: Fri Nov 10, 2017 7:02 pm
by thomehm
Currently I'm dealing with an issue in which my images show wide spikes projecting from bright stars at symetric angles, as illustrated in the attached file. I have a Celestron EdgeHD 8, a Celestron .7 reducer, and a ZWO ASI1600MM. So far, in discussions with other people, and reading threads in CN, I have learned that this results from diffraction and reflections within the ASI1600 because the sensor does not have an A/R coating. I see that other people have this problem, especially with the ASI1600, and it is a known issue. But it seems especially severe in this photo. So, I am looking for ways to deal with the problem. This photo was captured with (20) 30 second exposures via Nebulosity, which I then ran through Deep Sky Stacker, and played with the level and stretching tool only within DSS.


Any suggestions would be appreciated.

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Wed Nov 15, 2017 12:52 pm
by Sam
maybe from reducer
you can attach the camera only and try again

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Sat Nov 18, 2017 6:59 pm
by thomehm
Thank you for your reply Sam. Removing the .7 reducer from the optical path will be a good experiment. I will perform this experiment. However, I purchased the .7 reducer for an obvious reason. This reason for this purchase persists and I will not consider it an acceptable outcome to not be able to use the .7 reducer.

I also understand that this known issue is not fully under your control, as the Panasonic sensor is manufactured primarily for non-Astrophotography purposes so does not have the anti-reflective coating. Your company does not have the volume of purchases to demand the the sensor manufacturer add such a coating to the sensor. I also understand that other Astronomy camera manufactures have the same issue. I have also heard that whether these reflection problems present themselves is highly dependent upon the exact nature of the optical train. The best we can do is to try to understand this better.

This forum is a good place to exchange this information. I will do some experiments to try to debug my specific setup, and will publish anything I find here. I would appreciate it if your company could look into this problem further, and publish findings, so as to better advise the users on how to deal with the reflections issue.

thanks,

D.T. Gehm

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Tue Nov 21, 2017 1:57 pm
by Sam
thomehm wrote:Thank you for your reply Sam. Removing the .7 reducer from the optical path will be a good experiment. I will perform this experiment. However, I purchased the .7 reducer for an obvious reason. This reason for this purchase persists and I will not consider it an acceptable outcome to not be able to use the .7 reducer.

I also understand that this known issue is not fully under your control, as the Panasonic sensor is manufactured primarily for non-Astrophotography purposes so does not have the anti-reflective coating. Your company does not have the volume of purchases to demand the the sensor manufacturer add such a coating to the sensor. I also understand that other Astronomy camera manufactures have the same issue. I have also heard that whether these reflection problems present themselves is highly dependent upon the exact nature of the optical train. The best we can do is to try to understand this better.

This forum is a good place to exchange this information. I will do some experiments to try to debug my specific setup, and will publish anything I find here. I would appreciate it if your company could look into this problem further, and publish findings, so as to better advise the users on how to deal with the reflections issue.

thanks,

D.T. Gehm
thanks for your understanding
you are absolutely right :D

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Sat Dec 16, 2017 10:15 am
by je2000
Does this occur more with refractors/reflectors? With or without focal reducer?

I have a Stellarvue 102mm triplet with FPL-53 glass. These reflections seem worrisome and I have not made the ASI1600 purchase yet.

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Wed Dec 20, 2017 12:24 am
by rockstarbill
je2000 wrote:Does this occur more with refractors/reflectors? With or without focal reducer?

I have a Stellarvue 102mm triplet with FPL-53 glass. These reflections seem worrisome and I have not made the ASI1600 purchase yet.
This is likely due to the sensor not being AR coated. The new ASI183MM Pro uses the ICX183 Sony sensor and is AR coated. The sensor is a little smaller than the Panasonic sensor, but has 2.4 Micron pixels, which with that SV102 would produce incredibly high resolution images. If you are worried about the AR issue, and dont mind the sensor being a tad smaller, I would look at the new camera ZWO just released. :)

I put my pre-order in last night. $949 with the Christmas coupon!

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Fri Dec 29, 2017 3:04 am
by je2000
rockstarbill wrote:
je2000 wrote:Does this occur more with refractors/reflectors? With or without focal reducer?

I have a Stellarvue 102mm triplet with FPL-53 glass. These reflections seem worrisome and I have not made the ASI1600 purchase yet.
This is likely due to the sensor not being AR coated. The new ASI183MM Pro uses the ICX183 Sony sensor and is AR coated. The sensor is a little smaller than the Panasonic sensor, but has 2.4 Micron pixels, which with that SV102 would produce incredibly high resolution images. If you are worried about the AR issue, and dont mind the sensor being a tad smaller, I would look at the new camera ZWO just released. :)

I put my pre-order in last night. $949 with the Christmas coupon!
Oh man don't tell me that! I just got the camera yesterday!

I figure with reporting any issues with the 1600, ZWO can continue to put out good products at good prices. The more data they have, the higher chance they can work around coating issues if a known optical setup will be better or worse. Looks like we're all still trying to nail it down.

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Fri Dec 29, 2017 6:59 am
by Sam
thanks for your feedback
we will try our best to make the camera better and better
we hope to solve all the issues too

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Mon Oct 21, 2019 10:17 pm
by Dudley Richards
In my experience, the ASI1600MM suffers from bright star reflections between the sensor cover glass and the color filter in use. My experiments reveal that the protect window glass is not involved in the reflection issues (although the 2 mm thickness of that glass does cause undesirable refraction at faster focal ratios, producing elongated stars around the image periphery). The reflections really can't be eliminated if one has bright stars in an image that also contains nebula to be captured. The only remedy that I've found is using a clone stamp tool when processing the images. This is tedious and generally undesirable, and cannot really be done well if the star reflections fall on nebulosity (The Pleiades is an example).

I wonder if the new ASI1600GT camera addresses these reflection issues?

-Richard Tabbutt

Re: dealing with reflections and diffraction with ASI1600MM

Posted: Tue Oct 22, 2019 8:01 am
by Support1@ZWO
ASI1600GT use the same sensor with ASI1600.