18 replies to this topic

[Mikeiss]

Hello Cloudy Nights peeps, my question is referring to these vertical black bands that appear in my image when I use my ASI174 with my 2.5x Powermate attached to my Lunt 50mm H/a scope. I've tried this before and the bands are very apparent and very annoying. I tried an experiment where I removed the nose-piece from the diagonal and replaced it with a male to male  coupler. I did this hoping it would get rid of this anomaly, and it did help a little, maybe. I'm actually not sure as it's been quite a while since I've tried it.There was at least one benefit from doing that as now I can at least use my Powermate visually which I couldn't do before as there wasn't enough inward focus travel so that's cool at least. Anyways if anyone knows what these are and are willing to shed some light on it for me, I would be very appreciative. Thanks for looking and clear skies.

 

-Mike

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Edited by Mikeiss, 09 December 2024 - 09:18 PM.

[Jim Waters]

Are you referring to the vertical bands?

[gstrumol]

No. Newton's rings are a series of nested circular rings across the disk. For example, during my early days of Ha imaging (10 years ago) I took this:

 

 

see the rings?

[Mikeiss]

Are you referring to the vertical bands?

Hi Jim, yes I was referring to the bands.

[Mikeiss]

No. Newton's rings are a series of nested circular rings across the disk. For example, during my early days of Ha imaging (10 years ago) I took this:

 

rings.jpg

 

see the rings?

Hi Gary, thanks for the info, now I just need to figure out what the heck that is, and what's causing it. I don't have that problem when I image with just the 174, or my ASI120 with a Powermate. My guess is that the weight of the imaging train is just a little too much for the stock helical focuser, even with the focus knob locked.

Edited by Mikeiss, 09 December 2024 - 09:43 PM.

[Mikeiss]

The real kicker in all this is for the second time I saw a plane fly across the Sun and of course I wasn't capturing when it happened. Just plain poop on a stick.

[hopskipson]

Hi Mike
I’m not 100 percent sure but they might be Newton Rings. Sometimes they can be very broad and not very arched. Try introducing some tilt into your imaging train to eliminate them

[LarryAlvarez]

I used one of these to add tilt when I'm shooting close ups:  Daystar Interference eliminator   I got it in the classifieds a long time ago.  Its pricey but it works.  Player one makes one too: Link.  I only ever see them on close ups when I use barlows but in all cases the tilt fixes the issue.  Good luck

[Tapio]

Hi Mike
I’m not 100 percent sure but they might be Newton Rings. Sometimes they can be very broad and not very arched. Try introducing some tilt into your imaging train to eliminate them

Agree. They can be thin or thick.

[Mikeiss]

I sent the image to one of my friends and he also thinks that they look like Newton's rings. I will try to introduce some tilt into the imaging train and see what happens.

[Mikeiss]

Well I tried leaving the the screws on the nose piece loose when I put inserted the imaging train, and I also tried alternating just tightening one screw on the nose piece and neither seemed to have any effect. One thing my friend also said was that if the Powermate was made really well, then this may an unavoidable thing. Being that it's a Powermate, I do suspect that Televue made that thing very well. I guess I'm stuck using the 120 if I want to do some close ups.

[hopskipson]

To lessen the effect of the “rings “ try using a flat frame or the flat tool in fire capture

[hopskipson]

To lessen the effect of the “rings “ try using a flat frame or the flat tool in fire capture

[DAVIDG]

 Yes they are interference fringes. They are caused by the fact that the light entering the camera is monochrome, the top of the sensor is optically flat and the bottom of the cover glass over the sensor is very close. They form for the same reason they do when testing the flatness of optical surfaces when they are placed very close to each other so there is very small air gap.  This is what your observing in your images. There is constructive and deconstructive interference of the light from the light reflecting off the surfaces  The smaller the air gap the fewer the bands and wider and thicker they are. 

   Here is  a picture of  diagonal I'm testing against an optical flat that shows the interference band. Since the two surface are optically flat and the air gap is very small,  the band are straight, thick  and only a few  are visible. If I increased the air gap the number of band would increase and if the surfaces were not optically flat the bands would not be straight but curved and can turn into rings. 

  By tilting the camera to incoming light, the light path between the sensor and the cover glass increases. This increases the number of bands and makes them thinner and  less noticeable.  If the gap is large enough they will disappear. 

 

              - Dave 

 

[DAVIDG]

 The reason why you are seeing the bands with the Powermate is that it is a telecentric system. It causes less angle of the light coming from it. With the straighter light entering the camera, then path length between the top of the sensor and the back of the window over it is smaller. The smaller the path length between the surfaces the fewer the band and the wider the bands. With your other camera the distance between the sensor and the cover glass is larger enough so bands don't form by itself. 

 

 

 

          - Dave 

[lorenzo italy]

Interesting topic.
Why does it seem that CCDs are less affected by Newton's rings?
It is said because of how they are built, but what is the difference with CMOS?
In addition to the way they "read" the sensor's pixels, is there a construction factor of the CCD sensor that prevents the formation of rings?

 

Lorenzo

[ch-viladrich]

Most "sensors" being covered by micro-lenses, it is most probable that interferences build within the cover "glass" of the sensor.

 

Here are some schematics of the cross-section of a sensor :

https://www.ephotozi...n5YdgthHHsvEVxR

 

https://www.neg.co.j...er-glass_03.png

 

And an actual photomicrography images showing the micro-lenses at the "surface" of the sensor :

https://www.semantic...db5c2f/figure/4

 

Source :

https://www.semantic...968ca641cdb5c2f

 

It could be that AR-coating of cover "glass" ismore of less effective depending on the sensor. For some reasons, some sensors (e.g. IMX 432) show stronger interference fringes. Thickness and flatness of the cover "glass" may play a role. It would be interesting to gather more data on this.

 

Some companies offer the possibility to remove the cover "glass" of the sensor of a camera. For example :

https://www.eureca.d...ing-Covers.html

 

But it is quite expensive. Using a tilt mount/flat is way more cost effective for solar imaging.

Edited by ch-viladrich, 15 December 2024 - 06:40 AM.

[ch-viladrich]

Here is a very nice in-deep analysis (by spectroscopy and interferometry) of the role of sensor cover glass in the formation of fringes :

 

http://www.astrosurf...tter/ripple.htm

[lorenzo italy]

Thanks Christian for the interesting links you posted 

 

Lorenzo