NEW SDM build

[jamespierce (James)]

I've just loaded and unloaded my scope twice in the last two days (holiday/family trip, observing next week) - gotta say I wouldn't mind if it was a touch smaller or lighter ! How about a compact 14.5 with one of Mark's mirrors - super portable, great optics etc. Aperture isn't everything...

[gb_astro]

Stacey, Phil Townsend, who lives on the Central Coast, has SDM #34,
an 18" F4.5 with Argo/SevoCat. He used to be a regular at the Pony Club
but has not been there for awhile.
If you wanted to see a standard 18" in the flesh he might be able to help.

gb.

[jamespierce (James)]

I think the problem with 18"s is that unless it's an F4 mirror you start getting into 'arkward to use' size ... at which point, why not a 20, or 22 etc ... You're very definitely getting into two person lift territory etc.

[sasup (Stacey)]

James I see your point but its still early days. I think I want the 18 and im almost sure of it. Peter seems to think it would weigh in at 90lb or 45 kgs roughly... This was off the top of his head and I can lift that. My issue is with the height. If I dont go the low rider then im at a focal length of 2080mm right?

[GrahamL]

I can't make my mind up on those lowrider designs around the net .

The lower focuser height does seem to come with a fair bit of baggage
always thought the angle could be a little tough on the neck and shoulders. I wasn't aware you also had to increase the secondary size/shape and baffle the focuser to ?

Looking at (sdm 10 ) .. and throwing a pair of decent stillettos on Peter the zenith height dosn't look to bad , trim a little more back in the build and you could probably live with it and a very small two step ladder.

But is that what you wan't ?... custom built scopes are a big investment .. there was a very nice 18 ' f4 at astrofest this year
and there are some very nice sub f4 scopes of larger apperture kicking around which seem to be ground based for visual observing .
If thats really important to you I'd try and have a chat with the owners of around the 18/20 " apperture and gauge there thoughts .

good luck.

[sasup (Stacey)]

Thanks nightstalker I to im thinking maybe Ill just live with the height but still the low-rider has me curious. The great thing is if it does not work, one only needs to replace the poles,secondary mirror and punch a hole in the uta. so either way i cant weight. merry Christmas.

[sasup (Stacey)]

OK heres the latest. 18" scope, semi compact, low rider and with diagonal.

[jamespierce (James)]

What do you mean and with diagonal ?

Low rider, but with a diagonal so you can change the viewing angle ? How extreme can you go with the lowrider ? Could you go as far as 45 degrees, then use a 45 degree prism ?

[sasup (Stacey)]

I think the thing to watch for here is the amount of times the light must be reflected. The secondary is at 30 degrees and then the focuser is at a slight angle ( to be determined). A diagonal will help, possibly with ease of use at low angles. I think it has some risk in going with an unproven application like the low rider but equally if there is a way to keep my feet on the ground and still play with large aperture, thats great. here is a photo of a 22" as I remember.It would be good not to be the Gennie pig but what the hell.

Would be great to catch up soon. Have you ordered your frame?

[gb_astro]

Stacy you are going to need about 9cm (3.5") of extra focus travel to accommodate the use of a 2" diagonal as an option.
Can't really see you getting it with a newtonian focuser. ??

gb.

[sasup (Stacey)]

Thanks for that ,Ya I am going to have some more talks with moon-lite. peter and I have thought of that and its one of the things Im working on.

Originally Posted by gb_astro

Stacy you are going to need about 9cm (3.5") of extra focus travel to accommodate the use of a 2" diagonal as an option.
Can't really see you getting it with a newtonian focuser. ??

gb.