focuser and secondary upgrade conundrum

I'm awaiting the arrival of a new Orion XT10 (10" f4.7) which I bought instead of a high-zoot dob, thinking I could upgrade the components, learn something, and save at the same time. My enthusiasm has outrun my knowledge, unfortunately. Two of the upgrades I want to make (focuser and secondary mirror / heated mount) seem to affect each other, and I am at a bit of a loss what to do.
The stock focuser is a full 3" high, and I'd like to replace it with a 1.5" moonlite or feathertouch. This seems possible, although some ungainly spacers may be needed. The secondary is 2.48", which seems oversized according to the sec.exe program. It is also not a normal size - the protostars and antares I'd like are either 2.14" or 2.60". Has anyone done a secondary upgrade on this telescope and have an idea about which I should choose? Will the lower profile focuser affect the secondary size I can use? From reading past posts here, it seems like it may even help to install a lower profile focuser and smaller diagonal mirror at the same time. A possible fly in the ointment is the Denkmeier binoviewer/OCS I'll be using.
My eternal thanks and the standing offer of a cold frosty one in central NC to anyone who can help.

The size of the secondary is due the the f/l I would think. Newt likes all the dimensions, no vignetting shown.
Floyd

With a 10" f4.7, assuming the tube is 12", you should be fine with a 2.14" secondary. The one you have will be a bit of overkill, although there is no reason you couldn't keep using it. Protostar is known for high quality digonals, so they would be a good choice if you want to downsize it.

If the binoviewer requires extra travel (i.e. needs the focal plane to come out from the focuser) that would affect your choice. Download Newt 2.5 and play with the numbers - it is a free program, excellent for this sort of thing. Whether or not you would want to downsize the secondary with the binoviewer depends on the numbers - you will have to make some measurements and plug in the numbers to see. If the binoviewer uses a built-in barlow, remember that it will need a smaller fully illuminated field anyway.

When you change the focuser and/or secondary, you may have to move the primary further down as well to bring the focal plane closer to the tube (if the binoviewer doesn't need it further out). You can try to do this by backing down the collimation screws, but you will probably have to drill new holes for the primary cell mount an inch or so further down the tube. That's easier than redrilling the focuser and spider, though.

Hope this helps,

Jarad

ben here in statesville nc. i build my 8" fl/7.5 with a newt software download. it allows one to plug in many values on just such a question. measure twice drill once. i don't have the adress of the website, but someone will. good luck. ben

Keep in mind that the focal point will remain in the same position regardless of the secondary or the focuser. If you go from a 3" high focuser to a 1.5" high focuser, you may require an extension tube so your EPs are out (away from the secondary) far enough to get to the original focal point. This may be what you need in order to use the bino-viewer.

If you want to move the focal point in (closer to the secondary) you will either have to use the travel in your collimation adjustment, or move your primary mirror cell further from the secondary (as suggested earlier). I'm not sure there is enough room at the lower end of the tube to move the mirror mount very much.

Do download and play with Newt.
http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm
It is a good overall program with quite a bit of information and by playing with the different parameters, you will come to a better understanding of what's going on.

Gary Weber