150811 A Prom with a problem

[Photosbykev]

I took this today at lunchtime using a PST with DMK41 and 2.5x Powermate and I've noticed some slightly off vertical banding all across the image, the bands appear to have a gentle curve in them.

The system is run completely from a 12v leisure battery and the laptop from the internal battery so I'm guessing it isn't from noise but I can't figure out what it would be. Looking at the 20 second video the banding is present but less visible so it isn't from post processing, although the processing has made the bands more visible.

[smerral]

Great picture of the proms. I'm wondering whether the banding is newtons rings .i.e diffraction from the optical surfaces - this is one I took with the Tal x3 and extension. I defocused it so I could use it in future as a flat, but since then I've used the Tal x3 on its own and haven't noticed any problems.

[Photosbykev]

it does have the appearance of interference ringing, but why? lol

[smerral]

it does have the appearance of interference ringing, but why? lol

I'm by no means an expert Kev - I heard it mentioned on another forum and can't remember which one. Maybe try a different barlow?

[smerral]

If you scroll down this thread there is a short discussion on the problem:

Telescope Reviews: Newton's Rings ... Solutions? ... First Post

[Photosbykev]

If you scroll down this thread there is a short discussion on the problem:

Telescope Reviews: Newton's Rings ... Solutions? ... First Post

Useful link Smerral. There are options I can try there next time I get some sun.

[markt]

Hi Kev, the banding is indeed Newtons rings. It will be caused by something, probably the 2.5x powermate not sitting entirely squarely in the optical train. You can get rid of them in one of 2 ways:

1) Take a flat frame as already suggested - this is my preferred method.

2) When taking your avi let the sun drift slowly across the field of view, when the frames are stacked they will average the banding away.

You're getting some nice images with your new DMK lately Kev

[Photosbykev]

Hi Kev, the banding is indeed Newtons rings. It will be caused by something, probably the 2.5x powermate not sitting entirely squarely in the optical train. You can get rid of them in one of 2 ways:

1) Take a flat frame as already suggested - this is my preferred method.

2) When taking your avi let the sun drift slowly across the field of view, when the frames are stacked they will average the banding away.

You're getting some nice images with your new DMK lately Kev

I'll work on squaring up the optical path as I'm using software that corrects any tracking errors by applying a mount correction to maintain the position of a feature which I target. Letting the sun drift across the view would defeat the purpose of the software.

[markt]

I'll work on squaring up the optical path as I'm using software that corrects any tracking errors by applying a mount correction to maintain the position of a feature which I target. Letting the sun drift across the view would defeat the purpose of the software.

My money would be that it is the interface between the PST and the 2.5x Powermate.

[Photosbykev]

My money would be that it is the interface between the PST and the 2.5x Powermate.

There is a bit of float between the diameters of the PST eye piece holder and the Powermate, the nylon EP retaining screw doesn't inspire me with confidence either. Does anyone know what the thread form is for that screw? I could replace it with a proper screw and fit a skinny compression sleeve inside the eye piece tube to self centre it all.