Question....

[Guest Gneiss]

I'm currently building a dedicated solar telescope....

It is a standard Newtonian design with a very good four inch primary mirror of around 1000mm focal length, both the primary and secondary mirrors are unsilvered.

Nothing exactly revolutionary about this idea, the final reduction in intensity will employ either a neutral density filter or an unsilvered star diagonal to act as a variable poloriser. As I say, all tried and trusted...

The question...

I want to use this scope with the Baader K-line filter. If I use it with the scope i.e just the primary/secondary combination how much further reduction will I need?

a) For visual use; I already know some detail may be difficult/impossible to see but it does produce good contrast in sunspot detail.

For imaging use; which will be the main purpose.

[FLO]

Astroman is the man for this type of thing, having built a gaggle of them.

Here's his website: http://tinyurl.com/yjgapp

[Astroman]

Hi Gneiss, sorry I didn't answer right away-been busy and had an observing run this weekend. Pretty typical for dark-of-the-Moon weekends.

The welder's glass I use is to eliminate IR and UV wavelengths, which are still reflected in this design, for protection. With a narrow band Calcium K-line filter, the light reduction can be accomplished by a variable polarizing filter. For visual, it's just a matter of taste. For photography, I'd suggest as much light as you can get, just be careful not to burn your sensor or camera shutter. (You're a film guy, right? If you tend to lock up your mirror before exposure, it may lead to embarrasing smoke and severe damage if too much light is let through. Of course, you probably already know that.) With more light for photography avavilable, you can increase your shutter speed, freezing the seeing and giving better focussed images.

That said, there's a wealth of detail visible at Ca-K. Super cells of convection, some coronal "flaring" or CME's are possible, and tons of detail around sunspots. The more you look, the more you'll see.

[Astroman]

Sounds fine, except for the NP/polarizing filter part. Neither one will protect against IR or UV exposure. When I built my first scope of this type, I was chastised severely for trying one of the plastic, golden colored welder's glass filters for fear they had insufficient IR coverage. I mean, one of my friends literally drove 250 miles to my house and wagged his finger in my face because of it. Another friend publicly beat me up on another astro forum for it, too.

I can not state strongly enough, EVEN IF IT'S FOR PHOTOGRAPHY ONLY, PROTECT AGAINST UV AND IR RADIATION FROM THE SUN.

[Astroman]

Ok, so I won't be catching a flight over to wag my finger in your face. I'm not entirely satisfied with the IR curve, but it should be ok if you're not looking at it for long, like aiming.

BTW, how narrow is that Ca-K filter? And how much does it cost? I may look into one for my scopes.