Howdy hoo....

[rochler]

Just lookin' for some advice, since I'm very new to this. I'm trying to get the best out of my very cheap 6" newt on a GEM which I picked up new at a local auction house. It's a rough piece of work, but the optics appear to be o.k. when it's collimated. Before I started fiddling with it I've had some great views through it already...

The tricky bit is keeping it accurately collimated though - hard to do with a crappy plastic R&P focuser and cheap mounts for the mirrors. So anyhow, first thing was to replace the focuser with something decent - so I got a moonlite CR2. Seems insane I know, a bit like putting a V8 in a mini, but I figure that I'll never lose in the long run since I will always transfer it to my next scope (as finances allow me to upgrade). However, I also need to improve the mountings for the mirrors i.e. replace the screws with bigger ones that make adjusting easier, and put springs behind them so that there is some tension to keep the mirrors in place. At the moment the whole arrangement is a bit dodgy.

However, I digress, the bit I need help with is regarding the focuser - the previous one was a 1.25" and the CR2 is a 2". Since I've replaced the focuser, I need to make sure that the new focuser is square to the tube, but I don't know if I also need to make the hole bigger? Probably a dumb question, but does the slightly smaller 1.25" hole have an effect if you're going to a 2" focuser? Depends on the size of the cone coming off the secondary mebbe? Can I assume that if I can see the entire secondary I'm o.k. or will I run into problems later if I start using 2" eyepieces? (at the mo. I've only got a couple of 1.25" ones....)

I want to sort this out before I go to the trouble of aligning the focuser, realigning the secondary & finally collimating everything.

Any advice greatly appreciated!

[Starkler (Geoff)]

Ummm is the hole big enough to allow the 2 inch focuser draw tube to enter the scope when racked in ?

[h0ughy (David)]

Hi there rochler, I know not of the mechanical bits and fitting to the scope, but there is nothing wrong woth putting a V8 in a mini. Makes for more fun!!

[rochler]

Yep, it really flys now hehe... Anyhow, in a way it's good to start with something that requires you to really get involved in how it all actually works. I'm sure that the fiddling around will really help me learn about newts. When I get it all working nicely, I can go out & get a dob. Then mebbe an SCT.... Argghh....

[h0ughy (David)]

well then sounds like your well on your way. Don't forget other types of scope to look at either. I have a refractor, a Muscatov cassegrain and a SCT. they are all great. Mind you though, I haven't owned a newt yet!

[rochler]

No it's not big enough to actually enter the tube - but good question. Is it supposed to? I remember that the old 1.25 drawtube did actually enter the tube (but almost an inch) but didn't come to focus unless it was racked out by around an inch...

When fully racked in, the bottom of the new 2" standard drawtube is almost exactly connecting with the outer surface of the tube. I just checked and the top of the drawtube connects with the focuser very slightly before the bottom of the drawtube hits the tube - there wouldn't be more than a mm difference!

However, being a newb I don't know what this is supposed to mean. I just know that I have to get it right. I have already used the focuser with a 1.25" eyepiece and had no problem getting it into focus on Mars.

Luckily, I've got several adapter plates of different sizes to go with the focuser, so I can make it lower profile (or higher if need be). I also have an extension tube, so that I can still rack it out further if I need to make it lower profile. I just need to find out which way to go....

Sorry for being so verbose, but I'm trying to give you a clear picture....

Thanks for your pondering!

[ballaratdragons (Ken)]

Rochler,

Pics help us understand what you are trying to explain. Any chance of posting some pics so we can see if you are on the right track.

If it focuses on mars it sounds right.

[rochler]

O.k. will climb inside scope and get some pics.... stay tuned! I'm only a wee laddie hehe.

[rochler]

as suggested.

First some further clarification. The newt is a short tube f5 (750mm). The original focuser had a 3" drawtube. The CR2 is only a 2" drawtube, so even though I've put spacers on the crayford to build it up to the same height as the old one, the drawtube isn't as long (but I can use an extension if I need more height). So the 'missing inch' between the old & new drawtube, is the bit that used to protrude into the tube.

If I need to rack out more I've got no problems, since I have an extension tube, however, if I need to rack in the extra inch into the tube (like the old focuser) then I've got problems - since the internal hole is still 1.25". Hope this makes sense. The other issue is - what effect will it have with 2" eyepieces i.e. am I going to vignette because of the smaller hole?

The pics should help to explain. The side view is just the CR2 mounted - to give you some perspective. The front view looks down the drawtube, you will see the edge of the OTA hole at the end. The inside OTA shots show the hole from the other side - in the close-up you can see the slight shadow inside the drawtube.

Hope this helps!

Cheers 4 now....

[rochler]

Or am I just worrying about nothing....

[RAJAH235]

I think you'll get vignetting having a 1 1/4" hole & a 2" focuser. As you say, focusing should not be a prob.
Try >http://home.att.net/~dale.keller/atm...t/newtsoft.htm
HTH. L.

[rochler]

I'll try this program out... Looks like it might be just what I need. I'm starting to think that irrespective of current eyepieces, making the hole match the drawtube diameter is the safest way to go in the long run.

Thx. again for your help RAJAH235.....

[Starkler (Geoff)]

If you can achieve focus without the drawtube entering the scope tube thats all good.
Obviously you want to align the focuser as well as possible to the existing hole.
As for two inch eyepieces, whether they'll vignette you may be able to calculate for yourself given the dimensions of how it all fits together.

[rochler]

now thx. Geoff. I'll try out the Newt 2.5 prog. to see what it reveals. I'm fairly sure that I'll end up enlarging the hole since this seems to be the safest course of action. At least I don't have any focussing probs. - that's all fine so I'm happy! Got my replacement cap screws for the mirror mounts today & was able to get things aligned so much easier.

All I need now is some clear skies to test it out, but that seems to be harder at the mo. than working on the scope <groan>. It's currently full clouds in Adelaide with no relief in sight. Mebbe it will clear in the early hours? Ever hopeful hehehe...

Appreciate the help folks!