Getting back into imaging after a long break

[wimvb]

4 minutes ago, Gina said:

I'm not sure the Flats setup I'm using is working well for the widefield rig ie. 4 layers of white T shirt stretched over the dew shield.

Add another T-shirt? 😉

Glad it worked out in the end.

Edited July 7, 2019 by wimvb

[Gina]

Tried without the dew shield - straight on top of the lens.  It's different!

[wimvb]

I think I can see the fabric. Maybe use a white paper first?

[Gina]

Image file in PI.

[wimvb]

Try with stf applied. The pattern is very weak. The image in fits viewer in kstars is usually shown with a stretch, similar to Pixinsight stf.

[Gina]

OK.

I guess the way to see which is better is to try both processing in PI.  OTOH I'm wondering if an LCD screen would be better.  Though don't know if the wavelengths produced would work with the NB 3nm filters.  Guess a filament lamp lamp with wide spectrum would be a better source as an alternative to daylight.

[Gina]

[Gina]

CurvesTransformation.

[wimvb]

25 minutes ago, Gina said:

OK.

I guess the way to see which is better is to try both processing in PI.  OTOH I'm wondering if an LCD screen would be better.  Though don't know if the wavelengths produced would work with the NB 3nm filters.  Guess a filament lamp lamp with wide spectrum would be a better source as an alternative to daylight.

I agree that an old fashioned light bulb will work better for taking flats. Lcd screens are back illuminated by leds, so you'd essentially be seeing the led colours. RGB leds have three more or less, distinct wavelengths, which may or may not coincide with your nb filters. White light leds are essentialla uv leds with a phosphorus coating. But filament lamps have the whole black body spectrum. Seems much safer to me.

[Gina]

Disc of paper placed on top of lens the 4 layers of T shirt on top.  Exposure increased to 2.5s.  Light source is cloudy sky.

Edited July 7, 2019 by Gina

[Gina]

I think fewer layers of fabric may be better.

[Gina]

It's stopped saving again!

[Gina]

Closed up for the night.  Looks more likely to rain than clear.

[DaveS]

Hi Gina, have you tried taking "Twilight Flats"? They're something I've been exploring, to avoid any chance of T-shirt weave appearing.

As a BTW, I've been sort-of following your battles with Kstars etc with interest. Fortunately (Or unfortunately depending on your point of view) ASA mounts have their own, Windows-only, software requiring Maxim and Pinpoint, so I'm pretty well locked in. The whole lot does integrate quite well.

[Xplode]

I've tried several methods for taking flats and i found none really worked perfect and consistent all the time except using a real flat panel.

Artesky makes flat panels that aren't too expensive and they have both manual and USB controlled version. (they can also be bought through FLO, but don't seem to be stocked)
Here's the 550mm version in use (full brightness here, it's also bright enough to double as a worklight)

[Gina]

3 hours ago, DaveS said:

Hi Gina, have you tried taking "Twilight Flats"? They're something I've been exploring, to avoid any chance of T-shirt weave appearing.

As a BTW, I've been sort-of following your battles with Kstars etc with interest. Fortunately (Or unfortunately depending on your point of view) ASA mounts have their own, Windows-only, software requiring Maxim and Pinpoint, so I'm pretty well locked in. The whole lot does integrate quite well.

I've used twilight Flats in the past as well as other times of day and didn't see T-shirt weave appearing but I guess the previous Windows software didn't apply as much stretch to the images.  Using paper as well as the T-shirt solved the weave problem but cut the light transmittance right down and I was finding it needing 30s exposure by early evening with Gain at 0.

Fortunately I don't have an ASA mount - mine is SW EQ8 (and also an NEQ6) and when I make my own mount later I shall make it compatible.  This means that I can use a standard INDI driver but if I find any problem making my own mount compatible I could probably edit the INDI driver to suit.  One advantage of open-source software.

Talking of battles with KStars, this is nothing compared with all the trouble I had getting Windows software all working together a few years ago.  And then I was younger, with a younger brain.  KStars seems much better.

Edited July 8, 2019 by Gina

[Gina]

4 hours ago, Xplode said:

I've tried several methods for taking flats and i found none really worked perfect and consistent all the time except using a real flat panel.

Artesky makes flat panels that aren't too expensive and they have both manual and USB controlled version. (they can also be bought through FLO, but don't seem to be stocked)
Here's the 550mm version in use (full brightness here, it's also bright enough to double as a worklight)

I had a "real flat panel" several years ago but stopped using it.  I forget why now.  I may make up a light-box using filament bulb(s) and an opal sheet (or two).  KStars has provision for remote controlled use of a light-box or flat panel.

FLO don't seem to have any Artesy flat panels and they're very expensive direct from Artesky. 

Edited July 8, 2019 by Gina

[Gina]

I've ordered this 5mm Perspex Opal for LED Light Box Gloss Acrylic Sheet with the idea of making a light box.  Due to arrive tomorrow.  Seems to me that it would be better than relying on the sky.

[Gina]

Thought I'd try just the paper diffuser with the rig pointing at a clear blue sky with a shield to keep direct sunshine off.  The field doesn't look even - I would expect to see a circular pattern, brightest in the middle and dropping off to the edges.  This screenshot shows a strange shape (as well as a typo in the filename).  The sky is not a flat field.  The amount of Ha reaching the sensor is small - the exposure went to over a second!  The more I experiment the more a light box seems that answer.

[Gina]

Results of Flats experiments so far :-

1. 4 layers of T-shirt over dew shield, cloudy sky - dreadful, very uneven
2. 4 layers of T-shirt over bare lens, cloudy sky - better but showing fabric weave
3. 4 layers of T-shirt over lens with white paper disc, cloudy sky - much better but too much light loss
4. White paper disc over lens, blue sky - uneven illumination

Conclusion :- sky is too variable and unreliable.

[sloz1664]

1 hour ago, Gina said:

I've ordered this 5mm Perspex Opal for LED Light Box Gloss Acrylic Sheet with the idea of making a light box.  Due to arrive tomorrow.  Seems to me that it would be better than relying on the sky.

This is the Light Panel I have built and set-up in my Observatory. Brilliantly simple, and with auto dimmer control:-

https://www.cloudynights.com/topic/536533-diy-alnitak-flat-panel/

Steve

 

[Xplode]

3 minutes ago, sloz1664 said:

This is the Light Panel I have built and set-up in my Observatory. Brilliantly simple, and with auto dimmer control:-

https://www.cloudynights.com/topic/536533-diy-alnitak-flat-panel/

Steve

 

Good idea!
I have both a small and a large panel like that and they are pretty good, the A4 panel was perfect, but the A3 panel wasn't totally even (might not matter for everyone, depends on the usage, for example mosaics require pretty much perfect flats)
I think converting one of those panels would be right up Gina's alley and give consistent results

[Gina]

The problem with LED light sources is that the wavelengths produced do not match narrowband filters - ie. 3nm Ha, OIII and SII.  Hence my idea of using an incandescent lamp with a continuous spectrum.  I have tried LCD screens in the past.

[Xplode]

LED works great, they work perfectly for NB too.

[sloz1664]

6 minutes ago, Gina said:

The problem with LED light sources is that the wavelengths produced do not match narrowband filters - ie. 3nm Ha, OIII and SII.  Hence my idea of using an incandescent lamp with a continuous spectrum.  I have tried LCD screens in the past.

Not had any issues with mine. I have had to put 6 layers of drafting film over the LED panel to cope with the range of exposures from Lum to 6nm Ha. Longer exposures certainly help.

Steve