solar filter

[darren west]

i have a celestron 8se but i want to make a solar filter 

i have also got the film and a  8 inch spare lens cover 

so my question is does the filter have to be as big as the whole cap or can i leave 20mm of the cap around the edge to enable me to secure the filter film to please

 

thanks

 

[Davey-T]

It doesn't need to be full aperture so that would be fine, you can even just make a small hole offset between the central obstruction and the edge.

Dave

[Geoff Lister]

I don't know if this is the case with the 8se, but the objective-end covers on some 'scopes come with a built-in, offset (reflector) or central (refractor), removable cover, with a hole of a couple of inches diameter. I believe this is provided so that you only need a small solar filter, and, if you are lucky, the same filter can be used with several, different sized, OTAs.

Geoff

[Luna-tic]

One thing to consider when using the offset, reduced aperture filter on an SCT, is that it drastically increases the focal ratio. Focal length doesn't change, so changing your 8" aperture to 2" makes your telescope into an f/38. Sun is bright enough, even with a filter that blocks 99% of the light energy, to still allow photography with reasonable exposure times.

I made a full aperture solar filter for my C6, using the Thousand Oaks film. I used 3/16" foam core poster board for the rings, and heavy poster paper for the collar, then wrapped the collar with black masking tape to further strengthen it. Works great; I'm working on one right now for my Edge 8". I cut a piece of cardboard just larger than the filter to cover the outside and protect the film, with a thinner piece of cardboard cut just smaller than the inside to protect the inner surface. The filter is a slide fit over the corrector frame, snug enough to not fall off. The notch on the collar fits around the dovetail on the telescope. I cut two rings, the inside diameter is the same as the outer diameter of the corrector, so no decrease in aperture. If you make a reduced aperture that is centered, the central obstruction becomes very apparent, which is why the reduced aperture hoods are offset, and can be no larger diameter than the distance from the central obstruction to the edge of the corrector.  I could make a 2.5" offset aperture for mine, my Edge would become f/31. You central obstruction is slightly smaller, you could have a 2.75" offset aperture, you'd have f/28.

On the C6, I made eclipse pictures through the full aperture filter, at prime, with exposures of 1/160 @ ISO 400 to 1/800 @ ISO 800. I'd expect with a reduced aperture, your ISO could stay at 800 or 1600 and adjust shutter speeds accordingly, but why not just go full aperture if you're going to make one. I have about $30 in the one for the C6 (pic below) and maybe $45 in the one for the Edge 8. Took me a couple of hours to make one.  The eclipse picture below was made at 1/125 sec, ISO 400, with a Nikon D3400 at prime focus on my C6, with a .63 reducer in place.

[MarsG76]

It definitely does NOT have to be full aperture.... The Solar caps from celestron have about a 20mm ring around the edge...

[JOC]

Take a look at this thread in which there are pictures of my home-made filter and those of many others - as you can see mine leaves a deliberate edge around the filter

 

[LukeSkywatcher]

On 11/11/2017 at 15:36, Geoff Lister said:

I don't know if this is the case with the 8se, but the objective-end covers on some 'scopes come with a built-in, offset (reflector) or central (refractor), removable cover, with a hole of a couple of inches diameter. I believe this is provided so that you only need a small solar filter, and, if you are lucky, the same filter can be used with several, different sized, OTAs.

Geoff

The 8se comes fitted with only a full 8" dust cap. 

[skywatcher58gb]

Made this for my 8" Meade LX90 out of a cake tin bought from local supermarket. The cut out is about 6" dia using Baader Film.

The click in tin fits perfectly onto my scope, it looks like a bought for purpose filter.

[JOC]

I really like the cake tin approach.  I wish I'd have done that - brilliant idea.

[LukeSkywatcher]

11 minutes ago, skywatcher58gb said:

Made this for my 8" Meade LX90 out of a cake tin bought from local supermarket. The cut out is about 6" dia using Baader Film.

The click in tin fits perfectly onto my scope, it looks like a bought for purpose filter.

I love that. Before i read about it i thought that looks like a proper expensive Solar filter. You just know with those clips that the filter is not going to move anywhere. 

Nicely done. Inspiring.