Telrad on SW Dob 10"

[reeaal (Mark)]

Hi,
I've bought a Telrad for my SW 10" Collapsible Dob and am having a bit of trouble finding the best spot for placement. I wanted to have it between focuser tube and finder scope but it doesn't quite fit. Other positions on the top of the scope seem inconvenient for using the Telrad.
Am I better off removing the finder scope and replacing it with the Telrad?
If anyone has a pic of how they've managed to keep both finderscope and Telrad I'd be grateful to see it.
Thanks,
Mark

[astro744]

Is other side of the finder too much of a stretch?

Is the finder secured to the tube with two bolts? If so move it over and re-use one of the holes and drill a new one further out and perhaps you can fit the Telrad in between.

Or remove the finder altogether and attach the Telrad base with double sided tape and try and observe without the finder. You may find you actually dont need a finder at all since the Telrad is a joy to use when combined with a very low power wide field eyepiece in the main 'scope.

Not sure what eyepieces you have but a 30mm/80deg eyepiece will give you 2 deg TFOV which is the middle circle in the Telrad. The outer being 4 deg and the inner 0.5 deg.

Of course an inexpensive 30/80 eyepiece will have strong field curvature and other edge abberationes whereas a 31/82 Nagler will be considerably sharper at the edge but both will show coma with you f4.7 short primary. (A Paracorr will help greatly but reduce your field by 1.15x).

[taminga16 (Greg)]

Mark,
Trial and error might be the best way to go, after all we are all very different.

Regards,
Greg.

P.S. Try all of the options using Blue Tac and insulation tape until the Telrad is right for you.

[chrisp9au (Chris)]

Just a thought, based on experience!
I found that when I put mine on, when I looked through my 50mm finder I would breath on my Telrad, dewing it up immediately!
So I put the Telrad where I wanted it and moved the finder back down the tube a bit.
It's a case of finding out what works for you.

Cheers
Chris

[Sarge (Rod)]

Mark, I have a 12" SW Collapsible Dob and was looking at fitting a Telrad. The secondary mirror housing on my scope is 19 cm in length (between the white bans) while the base of the Telrad is 21 cm, which means -it don't fit. How is yours fitted?

Looked up the Telrad web site and they give dimensions as:
Length 21.3 cm
Width 4.7 cm
Height 12.7 cm (mounted on base)
Weight 30 gm.

Rod

[reeaal (Mark)]

Is the finder secured to the tube with two bolts? If so move it over and re-use one of the holes and drill a new one further out and perhaps you can fit the Telrad in between.

I like this idea as I'd like to keep both finders on if possible. Just a bit cautious about drilling holes into my pride and joy.
Thanks

[astro744]

Originally Posted by reeaal

Is the finder secured to the tube with two bolts? If so move it over and re-use one of the holes and drill a new one further out and perhaps you can fit the Telrad in between.

I like this idea as I'd like to keep both finders on if possible. Just a bit cautious about drilling holes into my pride and joy.
Thanks

OK, just had a closer look at the picture of your 'scope on the Skywatcher web site. Yes it's too nice to be drilling holes (not for a few years anyway).

Not much room there so back to the two suggestions I had earlier and that is to mount the Telrad on the other side of the finder (use double side foam tape if you dont want to drill or PVC electrical tape around the tube and over the Telrad bracket), or remove the finder altogether. You could also try mounting the Telrad on the lower tube section if it's not too awkward to use.

There is another option that may work that will require a custom made mounting bracket for the Telrad base. It looks to me from the photo that the Telrad may fit between the finder and the focuser if mounted higher (at finder level, maybe slightly lower) and forward so the front of the Telrad is say 5-10cm past the white tube ring. You probably dont want to put any holes on the white tube edge (or the dust cap wont fit) so you will need to mount a 'C' section piece of aluminium (edges parallel with tube, say 50mm long piece or whatever fits. Then a second 'Z' folded piece of say 3mm aluminium would bolt to the flat side of the 'C' piece. The upper part of the 'Z' piece would hold the Telrad base. Minor vibration shouldn't be a problem since it is 1x power and aligning would be done with the three bolts at the rear of the Telrad.

Have the Telrad a little forward would mean you wouldn't be breathing on the unit when reaching over for the finder.

Before drilling holes for the 'C' piece, use PVC electrical tape (Black would look nice) and wrap around the entire upper tube and over the 'C' bracket. This way if it doesn't work out you haven't marred the upper tube with unnecessary holes.

You should be able to get aluminium off-cuts from an alumminium supplier or maybe a hardware store or even Revolve or what ever they call themselves now.

One last suggestion is to use a smaller red dot finder and save the Telrad for another 'scope. It's not ideal but call this the last resort.

[stephenb (Stephen)]

Just a thought out of left field...What about ditching the finder altogether and putting the Telrad in its place?

[dalemadison]

I ordered a mount for my telrad and replace my finderscope. the mount fits right into the finderscope mount. Found it on the net at a place called Scope Stuff. They provided great service.

http://www.scopestuff.com/ss_telr1.htm

[reeaal (Mark)]

Thanks astro744; your idea would work but it looks like a fair bit of fiddling around.
I think I'll go with a purpose-made riser like the ones on dale's link. I didn't know these kinds of things were available and it would let me keep both finders in a easily accessible position.
glenluceskies, I'm Just not ready to replace the current finder with the Telrad yet as I'm still finding my way around this hobby, but I think this will happen at some stage.
Thanks for all replies and help.
Mark