Prism modified RDF for ergonomic aiming angled spotting scopes (2 Viewers)

[billb9430]

About 5 years ago there was some information and discussion on this forum regarding the use of Red Dot Finders (RDF's) to aid in precision aiming higher powered spotting scopes. A couple of members from Germany had particularly good ideas about this. Recently, I've developed a prism angled modification for the common multi-reticle RDF for use with refractors having a 90˚ diagonal. This gives easy aiming for my 5"f/5 "owl watching" refractor, but my reason for posting here is that some members may want to use this simple idea of adding a low cost "Bed Glasses"Littrow prism to the back of an RDF to allow "finding" that is comfortable and ergonomic when used with their angled spotting scope.

I use and like the compact "cable tie" sighting scheme described on this forum on my little angled Nikon ED50, but other angled scopes using higher magnifications would benefit from the greater precision of "Red Dot" aiming. Rather than posting a long "how-to" thread, I'll just post a couple of photos of a finished Littrow-RDF below and a link to a detailed "how-to" post I recently made on Cloudy Nights ATM astronomy forum.
The link is here: Better RDF sighting ergonomics with a "Bed Glasses" prism - ATM, Optics and DIY Forum - Cloudy Nights

Hopefully some forum members will be able to use this DIY idea to make their angled spotting scopes easier to aim.

 

[wllmspd]

Great idea, I was just thinking about wanting to use that exact model for helping aim a scope at high power… will be trying this out! Do you have magnification on your “5” owl scope”, I keep wanting more power, but stuff gets dim fast with a 60mm scope!

Peter

 

[billb9430]

That refractor is one I made with a 127mm 629 mm FL Jaegers objective. A 30 mm FL eyepiece gives 21x with a bright 6 mm exit pupil. I rarely use more than 60x, which is about what a 10mm eyepiece gives. That's down to a 2 mm exit pupil, though, so is for daytime only. I've been lucky the past two years to have a Great Horned owl nest with two owlets each year just 55 yards from my family room window. Great views and photos. Since the nest is in a fixed position,, I just leave the scope pointed on it. I use the Littrow-RDF finder more for pointing to critters and birds at varying distances and locations during the summer when in Montana.- Bill

 

[Binastro]

I have a 123mm Jaegers objective telescope.

That is the clear aperture in its cell.

Focal length 630mm.

3 inch draw tube.

I used it extensively at night.
I did a whole sky survey with this lasting several years.

16x 4.7 degree field.
20x 3.2 degrees.
35x 2 degrees.
80x
100x
145x.

210x with a Clave eyepiece is too high and reveals a small amount of miscollimation at this high power.

My most used scope.

Nice views of comet Halley.

On a Broadhurst Clarkson garden tripod, single wood legs.
Light weight.
Very simple altaz brass head with 10 inch spacing holes.
This fits most of my scopes.
I wore out the wood with so much use, but Broadhurst Clarkson repaired if free after about 25 years of use from 1957.
They fitted brass inserts.

No finder.
But simple carrying handle of aluminium as on most of my scopes, with holes for sighting.
But I just sight along the tube usually.

Regards,
B.

 

[billb9430]

Just to be clear, the refractor partially shown in the first post is not my Jaegers 5" f/5, but another ATM 4" f/6 with a conventional rack and pinion focuser. The Jaegers 5" f/5 I use for "owl watching" has a different type of home-made focuser (LSDF) with built-in Amici prism, pictured below. In this one, the Littrow-RDF is mounted very close to the eyepiece to allow easy "glance up 30˚" finder use. - Bill

 

[wllmspd]

Having just picked up a secondhand 127mm mak and needing a good way of pointing it I decided to make another version of the previous design that I could mount the Pinty onto a standard Synta mount.

I got some “lazy glasses” (much to family amusement) and extracted the silvered prisms, I had hoped to take it out in its plastic housing as noted before but things didn’t go quite to plan with the pliers and I ended with the bare prism. The long face is silvered and it is held into the plastic housing with a blob of glue that I had to very carefully trim off with a razor, trying to avoid scratching the prism coating. I very slightly chipped the very pointy end of the prism, but it’s not noticeable in use.
Being a 3D printer user I decided to print up a fixture, rather than go metal bashing.
I went to Thingiverse to see what I could find that would address the synta/picatinny parts, easier to mod rather than design, found one that connected the Pinty to a synta foot.
Measuring the prism and where I needed it with respect to the Pinty I added in the right parts to give an overall model. The prism rests in a recess the same size as it, I cleaned it and then used some strong mounting tape to hold it in place. Should hold well as it cannot get knocked in use.
Printed fine and everything fitted first time just nicely. I’ve rounded the tips of the prism holder so they’re less of a potential eye poking hazard.

Looking down into it you get a nice wide field with the marker in the middle, don’t need to get your eye right up into the prism to get a nice view. If I slide the Pinty forwards a little I can then still adjust the reticle control.

Many thanks for providing the idea for the mod and finding the source of prisms to make it a reality.

Peter