I began using my new Player One Apollo-M Mini Sunday and was getting some great solar images with it. But I noticed a bunch of spots on the images from junk somewhere in my image train, so I thought I would try to take some flats. I was using the latest SharpCap Beta and I noticed a flat capture option. I tried that but I kept getting an error about too much dark area being in the image. I was taking a full disk image and of course there would be a lot of dark area as the Sun's disk does not cover the entire image. If I bumped the exposure way up, I get an overexposure message about that as well. I tried zooming in, but that did not help either. So in this type of full disk image where the Sun does not fill the entire frame, how do you take flats?
JohnD
P.S. I love the new ability to darken the surface which highlights the prominences. You just have to be careful not to expose the proms too much as those can be darkened as well.
Creating Solar Flats
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Re: Creating Solar Flats
Hi John,
how were you getting the flat field illumination? I use a piece of translucent plastic over the end of the telescope to spread the light out, then turn up the exposure. If you can still see the shape of the solar disk in the image when capturing the flat then you need to use something that spreads the light out even more - maybe a sheet of A4 paper? Alternatively you can use some sort of light source like an electroluminiscent panel etc.
Once you get good even illumination, the warning should go away unless the image is very badly vignetted by the optics of your telescope (in which case you have to just ignore it).
cheers,
Robin
how were you getting the flat field illumination? I use a piece of translucent plastic over the end of the telescope to spread the light out, then turn up the exposure. If you can still see the shape of the solar disk in the image when capturing the flat then you need to use something that spreads the light out even more - maybe a sheet of A4 paper? Alternatively you can use some sort of light source like an electroluminiscent panel etc.
Once you get good even illumination, the warning should go away unless the image is very badly vignetted by the optics of your telescope (in which case you have to just ignore it).
cheers,
Robin
Re: Creating Solar Flats
Hi Robin,
An illumination panel will not work as it cannot get light through the H-a filter and blocking filter. I will look around for a translucent plastic sheet or try a sheet of paper or a plastic bag to see if that will work. There is an expert solar imager that goes by the moniker MalVeauX who uses a cereal bag. The key he says is to find something that will diffuse the light but still let enough H-a light through. I will see what I can do.
JohnD
An illumination panel will not work as it cannot get light through the H-a filter and blocking filter. I will look around for a translucent plastic sheet or try a sheet of paper or a plastic bag to see if that will work. There is an expert solar imager that goes by the moniker MalVeauX who uses a cereal bag. The key he says is to find something that will diffuse the light but still let enough H-a light through. I will see what I can do.
JohnD
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admin
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Re: Creating Solar Flats
Hi John,
yes, I use the cereal bag trick - I cut out a disc of that slightly translucent plastic and mounted it in a 3D printed frame so it can be easily placed over the telescope... Here's what it looks like on the scope
However, with a single layer, you need to get the sun image to fill the frame before capturing a flat, otherwise even with the film in place you can see the difference between dark and light areas. Maybe multiple layers would help? I haven't tried yet...
cheers,
Robin
yes, I use the cereal bag trick - I cut out a disc of that slightly translucent plastic and mounted it in a 3D printed frame so it can be easily placed over the telescope... Here's what it looks like on the scope
- PXL_20230208_110028400 (Medium).jpg (243.72 KiB) Viewed 7253 times
cheers,
Robin
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Jean-Francois
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Re: Creating Solar Flats
Hello,
If you use 2 layers, it is best to have a larger distance between the foils.
So, not 2 foils one over the other, but to add a spacer in between (I guess that 10 mm could be sufficient).
Jean-Francois
If you use 2 layers, it is best to have a larger distance between the foils.
So, not 2 foils one over the other, but to add a spacer in between (I guess that 10 mm could be sufficient).
Jean-Francois
Re: Creating Solar Flats
Well I decided to do a "Spring Cleaning" of the image train and I have eliminated the nasties. I ordered a Daystar Solar Flat Cap to fit my scope for future use.
JohnD
JohnD