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Pleiades...bright, and bringing out the microlens diffraction?

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#51 sharkmelley

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Posted 30 December 2016 - 03:44 AM

The new image I mentioned above makes it clear to me that there are (at least) two overlapping diffraction patterns.

 

The primary pattern involves a reflection off the inside surface of the sensor cover glass located a fraction of a millimetre above the sensor surface.  The second pattern involves a longer light path and is probably caused by

either:

A double refection between the sensor and the inside surface of the cover glass

or more likely:

A reflection off the outer surface of the cover glass i.e. light that is not reflected back by inner surface enters the glass and is subject to an internal reflection within the cover glass - back towards the sensor.

 

This would account for why we observe large discs overlapping smaller discs in the diffraction pattern.

 

Mark



#52 roofkid

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Posted 30 December 2016 - 05:56 AM

Stupid question: If it is indeed the cover glass. Could it be simply changed to a different one with better coatings?



#53 sharkmelley

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Posted 31 January 2017 - 06:42 PM

Stupid question: If it is indeed the cover glass. Could it be simply changed to a different one with better coatings?

Yes it's something the sensor manufacturer could do. It's not something you could reasonably do aftermarket because it's bonded tightly to the sensor and you risk destroying the sensor.

 

Another excellent example of the effect here:

http://www.cloudynig...right-star-halo

 

It's also noticeable in this image from Luis Campos using the QHY163M which uses the same sensor:

http://www.cloudynig...ight-m42-in-ha/

In that thread Luis also posts a video which demonstrates how reflective sensor cover glass can be.

 

Mark


Edited by sharkmelley, 31 January 2017 - 06:52 PM.



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