Rigt angle finder

[scopemankit]

I became fed up with my Canon 350D not having "live" focusing. It is impossible to focus a star using the peephole (apart from the fact that it is on the optical axis and requirs some neck bending to see through it).
I started experimenting with a prism, a couple of binocular eyepieces and a small negative achromat. Setting them up as in the plan, together with a clip on bracket, I managed to get acceptable 2.5X images (easily accessible too). This in an improvement on the bare camera but I wanted more magnification. Rummaging through my old focussers and finder scopes, I came across a Celestron 8X20 finder. To make it work, a 15mm extension (in white) had to be made to be able to focus on the central fosusing spot on the Canon's viewfinder screen. The gizmo fits and works very well and cost me R100 (about US$17), which is a massive saving on the local price for a 2.5X Canon right angle finder. What's more I get 8X magnification!

[scopemankit]

This morning I tested the finder out with a 700mm, F7 telscope and the focus achieved was great. Here is an illustration of the final result showing the camera's 18mm & 55mm lens results and then the 700mmlens. Sorry about the orientation!

[bojan]

Hi Chris,
This looks very good.
Only perhaps you could do something to stabilise the whole thing - have a look at what I have done with mine (at the very bottom of the thread).
http://www.iceinspace.com.au/forum/showthread.php?t=23756

I used cork pads at the end of those rails.



What you really need here is positive achromat - the whole finder should actually be the small scope, focussed at infinity. Then, you can have the same viewer focus setting, both for your eye and finder.

[scopemankit]

HI Bojan,
Sorry, I have only been a member for a couple of years and had not seen your posting on the same subject. Your right angle finder looks great. What power does it give?

My device is very rigid, The prism is glued into the bracket with a steel putty. The Celestron finder is glued into 10mm Perspex which i secured to the bracket with three screws. The bracket has a profile which slides into the camera's rubber eye guard groove and it is held in place with a strong rubber band made out of old car tyre inner tube ;see pic.

Re the negative achromat, that was to serve as a mini Barlow between the two bino eyepieces (one serving as an objective lens and the other as an eyepiece). That concept was shelved when I went for higher power and used the Celestron 8X20 finder.

I have taken a pic of a till strip though the 350Dand added another pic of the till strip through the finder. In setting the finder up, I found that I had to focus my finder on the camera focus screen That's why I had to put in the white extension for close up focus (on one of the squares with the dot in the middle). Focussing on infinity did'nt work. I'm off to my observatory on the week end and will try the finder/focusser and will report back on how it works.

By the way, old car tubes make fantastic heavy duty bands which can be used for hundreds of attaching and clamping jobs in the workshop.

I hope your weather situation improves, I feel so sorry for the people who have lost so much. I wish them strength.

Clear skies

[bojan]

Hi Chris, it is ~15x.
I am surprised the infinity focus didn't work for you, it should have. My RA finder works as a scope as well :-)
Basically, those finders with magnification are actually small scopes.
When you are looking through SLR viewfinder, your eye should be focussed to infinity (that is how the viewfinder works).
The same applies to telescopes - you are looking at distant objects (and virtual image inside camera viewfinder is in infinity), and your eye should again be adjusted to infinity.
Anyway.. Good job :-)

[scopemankit]

Thanks Bojan