PST Stripes

[eliot]

I am trying to make animation of sunspot development. When capturing the image I see stripes across the image. I have been using flats, captured by finding a blank area of the sun and gentle tapping the PST whilst taking 200 frames, but they have had limited effect.

The example below is a bit extreme (using 5x Powermate), but does illustrate my problem is.

2 frame animation

PST, 5x Powermate, QHV5v

200/1000 frames, stacked AS2, Wavelets Regitax 6

The strobing effect is caused by the original AVI's not been exactly aligned at capture, therefore the stripes are in different places on each frame of the animation.

I understand that pushing the optics to f/50 will give me trouble (manly a soft image), but does it also effect the etalon as well? This also happens to a less extent when I use an Orion 2x Shorty Barlow. Any thoughts?

Cheers,

Eliot

[Merlin66]

I think what you are seeing is Newton's rings caused by the mixture of your optics and the CCD chip.

Not easy to remove.

Nothing to do with the etalon.

[DrRobin]

Hi,

If you camera (QHY5v) is a colour camera it will be the Bayer matrix on the camera that is causing the stripes. I have tried several colour cameras and all of them do something similar in my PST. A change to a mono got rid of them?

If it is a mono then it must be something else in the optics that is giving rise to the stripes. Are they still there if you change Barlow?

[GlassWalker]

Any modification you do to the system focal ratio is after the PST so wont affect its operation.

I found flats did work for me, but my bands were much broader. If you suspect it is due to them being in different positions, then I'd suggest you set your mount to allow the image to slowly drift through the capture region, thus you sample at different parts of the banding and hopefully it'll average out in stacking.

[eliot]

Thanks for all the quick responses.

The camera is the mono version. The main difference between the 2 barlows is the widths of the stripes. The in the 2x they are narrower and less prominent probably because in the 5x I'm magnifying the aberration. I've attached the first frames of the AVI's I used to make flats for the 2x and 5x barlows.

I'm going to have to read up on Newton's Rings. Having a quick glance at Wikipedia and could the underlying issue be the reflective coating causing the diffraction pattern?

I'll have to try letting the region drift across. Given how badly I polar align my Astrotrac in the day time it should be quite easy! All I'll have to do orientate the camera the right way.

Eliot

[DrRobin]

Hi,

I think yourt last post proves it is not the barlow, just what you would expect if it was diffraction pattern, the size would change with different orientation. As you are using a mono camera it can't be a Bayer matrix, but might still be a coating on the image sensor.

Does your camera have an IR filter? You could try with this removed as the PST blocks IR. It might be that?

I have tried a DMK21 (no diffraction rings), a DKF31 (colour and very pronounced diffraction), an Xbox camera (some diffraction rings) and a MS Lifecam, (probably less diffraction rings than any other of the colour cameras). Unfortunately I haven't got any other mono cameras to try, I have a DMK41 on order but no one has reported this as a problem.

If you can't get rid of them let the image drift a bit and then hope to get rid of them with stacking and flat frames.

By the way, I take a flat frame by putting a piece of drafting film over the front of the PST whilst pointed at the sun and with the same Etalon/focus settings. I need 1 second exposure, but get a great flat file. A piece of tracing paper would also work and some people use a thin supermarket plastic bag to diffue the incoming light.

[GreatAttractor]

Hi Eliot,

Attempting a sunspot animation is very commendable and I hope to see some goodies from you soon! But you may find that with a 40 mm PST you're not getting that much detail. For sunspots I'd suggest at least 80-100 mm aperture (simple achromat is fine), and white light will suffice, with just a Baader solar film on the objective. But prominence/filament time-lapses - now that's what I'd use a PST for

[riklaunim]

Micron sensors (QHY5* have them) give Newton rings quite easily and there is no way to avoid them if the given camera has them. And they usually are very strong:

[eliot]

Well I think that that settle's it then. Other than I don't seam to get them without the barlow, which is quite puzzling... Thanks for the tips on creating flats. It's something that I'm very bad at (I never do it for night time astrophotography). I'll try drifting the scope a little perpendicular to the stripes when I next see some sun.

To be honest I am due to give a talk on white light observing/imaging next spring. This summer is has been so bad that there have been very few weekends where I could get some data. I'm starting to come to the conclusion that solar astronomy in the UK is a retired man's game (as they have the time off to do it when it is clear). I'm only trying to hone my technique with the PST whilst I'm on away on holiday in France. I thought of bring the 250PDS and EQ6 down, but that would mean I would have to have left my daughter behind! The idea is if I could create an animated sequence like the image I took a couple of months ago (attached). Hopefully it will show the spot changing over the course of a few hours. If I can't get the data I have a fall back plan using data from the SDO.

[thenews24]

I'm getting lines all over my images now, and they were never there before. Using the same camera I always use (dmk41) with the same powermate. Any thoughts on why the lines decided to show up all of a sudden.

They show up even more during post processing.

[Merlin66]

I find the Newton's rings with my double stacked SM60/ED80/BF15/TV x2.5 Powermate/DMK21 can vary day to day...I put it down to slight changes in the optical alignment/axis and temperature variations affecting the interference gap.....

[Peter Drew]

My solar imaging is limited to video only but I did notice that Newton rings were obvious when using a Powermate. This is a telecentric Barlow, different from regular Barlows, could this be part of the problem?.

[riklaunim]

Try tilting or rotating the camera (and in the end the diagonal). If that doesn't make any effect then the rings are not-removable (this happens for the Micron sensors). With PGR Chameleon (Sony CCD) I got weak Newton rings sometimes and playing with camera position/tilt solved the problem.

[Merlin66]

Peter,

No, I don't think so. I get them with other barlows as well. My good Klee x2.8 sometimes shows them....I think it very much depends on the camera.