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drksky
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Reged: 09/01/09

Loc: Bloomington, IL
Possible to eliminate Newton Rings? new
      #5716195 - 03/06/13 11:17 AM

I've got an e2v Flea 3 that shows some pretty obvious Newton Rings when shooting with a 2.5X powermate. Are there any adjustments that I can make which might lessen or eliminate them? This is with an LS80DSII.

Oddly enough, I don't see any sort of artifacts when not using the powermate.


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ourobouros2k2
sage


Reged: 11/10/11

Loc: okc area, oklahoma
Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5716228 - 03/06/13 11:42 AM

Might try twisting the camera and see if it eliminates the rings. If not, google "newton rings tilt adapter" to find examples of DIY solutions that will let you tilt the imager off axis slightly to eliminate the rings.

In certain cases with imagers that use certain Micron or Aptina sensors, the rings are produced within the sensor itself (as I understand it). I have this problem when attempting to use the orion SSAG for imaging h-alpha. Unfortunately no amount of axial tilt can fix that.

good luck


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frolinmod
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Reged: 08/06/10

Loc: Southern California
Re: Possible to eliminate Newton Rings? new [Re: ourobouros2k2]
      #5716279 - 03/06/13 12:13 PM

Perhaps one of these T2 tilt adjusters may be of use:

http://www.optcorp.com/product.aspx?pid=1289-17692


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neotesla
Pooh-Bah
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Reged: 11/18/10

Loc: Canada
Re: Possible to eliminate Newton Rings? new [Re: frolinmod]
      #5716512 - 03/06/13 02:15 PM

There was another thread obout problems with the 2.5X Powermate...

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5671143/page...

another Barlow might be the solution to the problem.

Edited by neotesla (03/06/13 02:16 PM)


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ourobouros2k2
sage


Reged: 11/10/11

Loc: okc area, oklahoma
Re: Possible to eliminate Newton Rings? new [Re: neotesla]
      #5716608 - 03/06/13 03:01 PM

Also if you wish to go with the teleskop adjuster, be advised they go out of stock quickly. I have seen solar imagers report success with that unit

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drksky
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Re: Possible to eliminate Newton Rings? new [Re: ourobouros2k2]
      #5716630 - 03/06/13 03:13 PM

I would think if it were the sensor, that I would see them when using native focal lengths, no? As far as the issue with the 2.5X powermate, that was in internal reflection and I'm not seeing that issue with mine. I've tried a normal 2X barlow and still got the rings.

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drksky
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Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5716639 - 03/06/13 03:19 PM

There's a good amount of play in the blocking filter tube that might allow my to tilt it enough to eliminate the rings. or would it literally have to the camera itself that needs tilted?

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molniyabeer
Confused and Asleep
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Reged: 01/08/05

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Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5716974 - 03/06/13 06:06 PM

You can also try a "pseudo flat field." With the barlow or powermate in place, defocus on the center of the solar disk until you get a smooth grey wash with the rings visible in it. Use that video to make a "flat field" in Registax and then use that flat to process your normal videos. Seems to work pretty well, although it helps if you don't have a lot of drift in your tracking. I've found that the drift on its own will help to damp down the appearance of the rings but when you use the flat it seems to add them back in!

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ourobouros2k2
sage


Reged: 11/10/11

Loc: okc area, oklahoma
Re: Possible to eliminate Newton Rings? [Re: drksky]
      #5717366 - 03/06/13 09:59 PM

Quote:

I would think if it were the sensor, that I would see them when using native focal lengths, no? As far as the issue with the 2.5X powermate, that was in internal reflection and I'm not seeing that issue with mine. I've tried a normal 2X barlow and still got the rings.




Correct, my rings are present with or without barlow. They are certainly annoying.


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drksky
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Re: Possible to eliminate Newton Rings? new [Re: ourobouros2k2]
      #5717788 - 03/07/13 06:44 AM

Thanks for the tip Steve. I'll give that a try if I can't get rid of them otherwise.

I worry about using the Teleskop tilt adapter. It seems like with all the adapters that are needed to make it work might take up too much focal range to allow focus when using the powermate. That'd kind of defeat the purpose.


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marktownley
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Reged: 08/19/08

Loc: West Midlands, UK
Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5718568 - 03/07/13 02:32 PM

Any pictures? At various focal lengths... That will help us diagnose you the best course of action...

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Spectral Joe
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Reged: 02/28/11

Loc: Livermore CA
Re: Possible to eliminate Newton Rings? new [Re: marktownley]
      #5719575 - 03/07/13 10:49 PM

Try a lens cap, works every time. But seriously, the problem may be in the camera, I'm sorry to say. This sort of fringing occurs in CCDs and is more pronounced with longer (red and IR) wavelengths. Some chip designs are worse than others and even with the same design there is variation from one chip to the next. If that's the case then tilting the camera is your best option.

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Spectral Joe
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Reged: 02/28/11

Loc: Livermore CA
Re: Possible to eliminate Newton Rings? new [Re: Spectral Joe]
      #5719578 - 03/07/13 10:52 PM

Also, the problem is worse with larger F numbers, this may be why it's worse with the Powermate.

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drksky
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Re: Possible to eliminate Newton Rings? new [Re: marktownley]
      #5721029 - 03/08/13 06:56 PM

Quote:

Any pictures? At various focal lengths... That will help us diagnose you the best course of action...




Finally got out today for a bit, although the seeing was lousy.
Here is a detail that was taken with the Powermate:


And, here is a two panel full disk mosaic:


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drksky
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Re: Possible to eliminate Newton Rings? new [Re: Spectral Joe]
      #5721037 - 03/08/13 06:58 PM

Quote:

Try a lens cap, works every time. But seriously, the problem may be in the camera, I'm sorry to say. This sort of fringing occurs in CCDs and is more pronounced with longer (red and IR) wavelengths. Some chip designs are worse than others and even with the same design there is variation from one chip to the next. If that's the case then tilting the camera is your best option.




I know that CMOS sensors tend to be worse for issues like this. The e2v sensor in the Flea was supposed to be not as susceptible. I guess that's not quite right. I may start looking for a different cam with a CCD, at least for solar. The Flea should still be good for lunar and planetary.


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molniyabeer
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Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5722053 - 03/09/13 11:06 AM

Another possibility is to try dithering your video by slewing the image around while you capture it. When you stack the frames, you'll somewhat average out the rings. The drawback, of course, is you lose some of the margins of the frame.

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marktownley
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Reged: 08/19/08

Loc: West Midlands, UK
Re: Possible to eliminate Newton Rings? new [Re: molniyabeer]
      #5723373 - 03/10/13 04:53 AM

I think dithering is the best way to try first...

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drksky
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Re: Possible to eliminate Newton Rings? new [Re: marktownley]
      #5723506 - 03/10/13 08:40 AM

Do you need to do anything special in Registax to account for the movement, or will it automatically just adjust as it stacks?

How fast should the movement be? I have a CGEM, so are we talking Rate 1 speed?


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marktownley
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Reged: 08/19/08

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Re: Possible to eliminate Newton Rings? new [Re: drksky]
      #5723539 - 03/10/13 09:12 AM

No, registax should automatically compensate for it. Often the best way to get the drift you need is just to do a poor polar alignment, it will naturally drift for you then...

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drksky
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Reged: 09/01/09

Loc: Bloomington, IL
Re: Possible to eliminate Newton Rings? new [Re: marktownley]
      #5723760 - 03/10/13 12:01 PM

Quote:

No, registax should automatically compensate for it. Often the best way to get the drift you need is just to do a poor polar alignment, it will naturally drift for you then...




Being as I'm just plopping the thing on the patio and letting it rip, that shouldn't be difficult.


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