Using an Astrocom solar filter with a refractor

[kev100]

Hello, I recently bought an Astrocom solar filter from Astroboot, and planned to use it with my 70ED refractor.

However, in the docs that came with it it states: 'Type B is quite bright, and when used for visual observations must be used in combination with one or two polarisation or ND filters attached to the eyepiece!'

I wonder if anyone has any experience with this filter, recommendations for a suitable ND filter (I was thinking something like this, but I don't know which of the three types would be best): Filter

Given the seriousness of getting it wrong I'd appreciate any suggestions.

Cheers,

Kev.

 

[LukeSkywatcher]

Glad you came asking before using. I'll let others with more experience than myself answer but i probably wouldnt be buying an ND filter off of ebay for 9 quid.

[kev100]

Well, I checked with Astroboot, and it seems there were 2 types of Astrocom filters, A and B. Astroboot only every had the A type, and I'm assured it's safe to use. I've made up a holder for it out of a bit of pipe and some craft foam (pic attached), and tried it out this afternoon. It works really well! The holder fits firmly over the dew shield, and the view is fantastic. Slightly warm yellow hue to the sun itself, and detail is incredible, with the umbra and penumbra of today's sunspot very clearly visible. 

I went for the 9 quid ND filter in the end, and it seems to work well enough. It's a 25% one, and drops the brightness down a little (but not much). I'll probably keep it and try it now and again on particularly bright objects and the moon (and possibly Mars).

Cheers,

Kev.

[LukeSkywatcher]

Do you actually need the ND filter with the solar filter?. The solar filter as sold looks like many other white light filters and with those types you dont need an ND filter. All i can say is that if it works and you didnt blind yourself............keep using the system in the way you did.

I know that with Hershel wedges, you absolutely DO need an ND filter (ND3.0). Some come with them pre-installed and some come without them and you have to buy them and install them. My wedge came without an ND filter (craziness!!!!!!!). I also bought a variable polarising filter and a solar continuum filter. 

Anyway............not trying to talk you out of using the 9 quid ND filter. Keep using it but be weary. I'm sure other will put your mind at ease 100%.

You are now set up for the Mercury transit on 9th May. I also use a 70mm scope (Celestron Travel scope) for my solar observing and its great. 

[michael.h.f.wilkinson]

There are indeed two types: ND 5.0 visual types and ND 3.8 photographic. The latter let through a lot more light to allow shorter exposures. It should be safe when combined with an ND filter, double polarization filter, and/or Solar Continuum filter

[kev100]

Thanks all. I used the filter again today (without the ND filter), and all's well. I will keep latter, and try it on a few things to see how it goes.

Kev

[Moonshane]

Whilst not an  ideal way to test I'd think that the imaging version would be simply too bright to observe with on its own so sounds like you have the visual one.