Right-angled red dot finder?

[michaelmorris]

Strange request number 1,433,128 - Has anyone tried adding a 45 deg mirror to a red dot finder?  (yes I've seen the Televue starbeam but it's too heavy and way too expensive).

Let me explain what I'm after.  Last night was spent imaging the area to the west of the W of Cassiopeia with my DSLR mounted on an Astrotrac.  I have found using a DIY red dot finder mount on top of the DSLR a great way of centring the target.  However, Cassiopeia is near the zenith at the moment and trying to look through the red dot finder was a complete pain in the neck (in every sense of the expression).  What I ideally do with is a red dot finder with a extra wide 45 degree mirror on the back so that I can see the red dot and a wide area of surrounding sky.

My though is to take the mirror out of an old diagonal I have and mount it on some sort of light weight rig on the back of the red dot finder.  Has anyone tried this before?  Any better ideas?

Thanks

[John]

Hi Michael,

I had a Telrad once that was fitted with a combined dew shield and mirror so you could, with some careful adjustment, see the view through the Telrad in the mirror. It was a little "clunky" but it did work. I guess a similar principle could be used on any RDF but I think it would have to be a DIY job as I've not seen any suitable add on kits for sale for other finder types. This is the Telrad one:

http://www.firstlightoptics.com/finders/dew-shield-for-telrad-finder.html

And here are some pics of it installed:

http://stargazerslounge.com/topic/176856-telrad-dew-shield/?p=1820907

Maybe the Telrad job could be adapted for other finders ? - it's not that expensive from FLO.

[Sporadic Dobstronomer]

A thought: I don't think there is any reason why the mirror for this application needs to be first surface or especially flat.  My thinking is that since both the sky and the dot are at infinity, you will have no problems due to multiple reflections.

If I am right, you can confirm that by trying it out using any mirror you have lying about.  If it works, you can get a piece of thin, and therefore light, mirror from your nearest glass merchant.

[Stu]

I've tried the Starbeam, which despite the angled mirror I always used straight through. Never totally got on with it.

I also have a TelRad with the dew shield and again generally find it easier to use straight through.

I was wondering for your problem, would a prism from a broken pair of binos be any good? Compact and easy to mount? Astroboot would have them.....

Sent from my iPhone using Tapatalk

[michaelmorris]

I've tried the Starbeam, which despite the angled mirror I always used straight through. Never totally got on with it.

I also have a TelRad with the dew shield and again generally find it easier to use straight through.

I was wondering for your problem, would a prism from a broken pair of binos be any good? Compact and easy to mount? Astroboot would have them.....

Sent from my iPhone using Tapatalk

Whilst a prism will probably work, will it give the extra wide field of view I would need to use with a red dot finder (i.e red dot finder and wide field around it)?