Home made RDF or Telrad

[mjonesy1]

Hi All,

I have an Astromaster 114 EQ and, like so many others, I can't get along with the RDF at all, the parallax of the two dots and concentric circles is too much for me!

I have been looking at 'proper' RDFs where the dot is shown on a lens and always remains on the distant object no matter where the eye is and these look like the sort of thing I am after.

The Telrad and Rigel also look impressive but I don't think they solve the parallax issue but lots of people love them - maybe they do but I can't see how and I've not seen enough information on the web to properly see if there is anything else other than an LED, mirror and display glass.

There are a few videos out there on how to make RDF 'scopes' (the rifle guys make loads!) and some of them look great to experiment with although the quality of their lenses leave quite a bit to be desired of nighttime working!
 

I did search the forums but found nothing, has anyone made successful parallax free RDFs?

Also - has anyone attempted to make a Telrad type finder?

I have plenty of red LEDs, batteries, switches etc. so to spend 40 GBP+ would upset me if I open the finder up and just find 5 GBP of plastic lenses!!

Thanks

Jonesy

[AstroTux]

I don't think you'll ever completely remove parallax errors from a Rigel or Telrad style finder, although the best way I've found to reduce such errors is to look through the device from further away. Essentially they are designed to get you "in the right area" and some find them easier to use than a finder 'scope. I use the Rigel to get me close as I just need to look at the sky with it, and then use the finder 'scope to close in on the object I wish to view.

The basics of Telrads/Rigels are very simple. I found this diagram on the web  that you may find useful:

.

As can be seen it is simply a case of an LED, a graticule, a mirror ( and adjusters ) and a viewing window.

hope this helps,

Alan

[bambuko]

Have a look at this lot:

Greg's right angle Telrad

Reflex sight

One power aiming device

35mm finder

Split pupil finder

I don't think any of these address your exact question, but they all are about DIY reflex finders, so maybe will inspire you?

I for one will follow your progress with interest.

ps and another one, but only if you know Polish or are willing to use Google translator (although most of the pictures are self-explanatory):

DIY Telrad

click "nastepny" for next

click "poprzedni" for previous

and "powrot" for return

[mjonesy1]

Great feedback - thanks - no matter how much you Google something someone else will always find something extra - I had thought I'd exhausted Google's resources but I only got one of those links previously!

I can see quite a few evenings tinkering when it's cloudy now.

Many thanks

Jonesy

[mjonesy1]

All,

I had a few experiments and success but producing a decent graticule had me stumped and frustrated.

I succumbed to pay day spending and purchased a Rigel Quick Finder, partly so I could see how a proper system worked and partly so I had a new toy!

I must admit it is a cracking piece of kit! I've removed the Astromaster's 'finder' (see later) and put the Quick Finder in its place - 2 minute job. Simple alignment and it is spot on every time and so easy to use. It will save me hours and hours!

It wasn't a great night last night but Orion gave some good targets to test the system out and every time I aimed through the Quick Finder the required star was centered in the scope - perfect.

I will still make my own finder, I have something to model it on now, but I really do think I made a wise investment with the Rigel. 

The Astromaster 'finder': Is no such thing and would consign my scope to the attic if I hadn't pursued a replacement - many will not and will leave the hobby I am sure.

Apart from a decent telescope/EPs/mount I think there are 3 other essentials:

A good finder scope

A good star map

I have the EQ114; Revelation Astro EP kit; GE mount; Rigel Quickfinder and Sky and Telescope's pocket atlas. I now feel I am ready to make a decent start at last. If only there were some more clear skies

[Adir]

"Old topic, BUT....my ideea is....!   (can still be useful for some people)

Using either glass or plexiglass, and glowing paint (phosphorescent) to draw circles.

The need of batteries will be eliminated.
The finderscope will be lightweight.

If it doesn't work at least you'll have fun:)

Cheers!