Homemade Solar Flat Caps

Over the past week, in between bouts of lousy health, I have been working on making two homemade solar flat caps.  

A flat cap comes in handy when imaging the sun.  The flat cap will diffuse the view for images that are called "flat frames".  These flat caps are placed over the front end of the telescope, temporarily, to shoot these flat frames.  The flat frames are then divided into the stack of normal image frames.  

A good flat frame will allow me to create even light across the frame (solar filters create mildly uneven light across the frame).  It will also help to eliminate any dust specks on the image files.   Of course, keeping the camera's sensor clean also eliminates specks and blobs of dust but using a flat frame is another process to effectively smooth out many of these types of defects in the solar image stacks. 

This little project called for scrounging up various household materials and some hobby tools.  I always have some thin styrene on hand and that definitely came in handy for this project.  I also used an old tomato puree can for one of the filters.  This can, with some felt applied inside the can, fits perfectly over the end of my smaller Skywatcher refractor that I use for viewing and imaging the full disk of the sun.    

I made two flat caps because I needed to use two different strengths of gel diffusers.  When shooting full disk solar images, I've heard that you need to use a stronger diffuser gel so the sun gets diffused more.  When shooting closeup images of the sun, I've heard that I need to use less diffusion for the flat frames.  My smallest telescope is used for full disk solar astronomy so the smaller flat cap with the stronger diffusion was made for that telescope.  My larger telescopes are used for closeup images so the larger adjustable flat cap with a milder diffusion will be used for those telescopes. 

I made this wood filter frame, below, a couple of years ago to hold solar film to be used as a homemade white light solar filter.  I hated the solar film for a few very valid reasons such as I found the film to be far too fragile and thus dangerous.  The film used for that filter quickly deteriorated (within a year or two) rendering it extremely dangerous and useless so I am now repurposing this nice filter frame as a much-needed flat cap.  I also hated the bluish, cold color balance that the solar film created.  When the film deteriorated, I removed the film from my homemade frame and the frame has been sitting around awaiting a new purpose.  This homemade filter frame really is a nice filter frame so I didn't want to toss the whole filter and frame in the trash when the solar film deteriorated.  I'm glad I kept the frame because it has now been repurposed as a flat cap.  

In this photo, below, you can also see the medium-level diffusion of the filter gel material used for this flat cap.  

Below is the smaller flat cap to be used for full disk solar imaging.  This gel filter material produces a more aggressive diffusion which is needed for full disk imaging.  I will need to test this level of diffusion though.  This amount of diffusion might actually be a bit too much diffusion.  If so, I'll need to swap out the gel filter with a less aggressive gel filter.

Here, photos above and below, you can see the difference in the amount of diffusion created by each flat cap.  The above photo shows the flat cap with more diffusion for full disks...  the below photo shows the larger flat cap with less diffusion for closeup images.

We'll see how well these work when I finally have a day with clear skies.  We've had torrential rains here for the past week and a half and the next few days should also be overcast, damp and wet.  So now I wait for the skies to clear.   

Of course, my health will also need to cooperate with the weather because if my health is lousy when we finally get clear skies then nothing will get accomplished regardless of the weather.  

I'm looking forward to testing these flat caps though.  At the very least, if the smaller flat cap is too diffused, I might be able to get by with the larger, less diffused flat cap for both purposes.  

Time will tell...