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Moonlite CR Focuser Travel?

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#1 hotdogx

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Posted 17 January 2013 - 09:12 PM

I'd like to hear from folks who are using a Moonlite CR focuser on a newtonian. I am building a newtonian using a ZOC 8" F/5.9 mirror. Secondary will be 1.52". I will be using a Moonlite CR focuser. I am trying to decide how much travel I will need. I'm thinking 1.5" or 2". I have 6, 10, and 14mm TV Radians, 26 and 40mm TV Plossl, Meade 20mm Erfle, and TV 2X Barlow eyepieces. I don't want to have the drawtube getting into the light path when racked in. I will be using a 10" O.D. tube on the scope.

#2 David Pavlich

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Posted 17 January 2013 - 10:38 PM

I would think that you should emulate the stock focuser when it comes to viewing. If you plan to image at any time, you'll probably need a low profile focuser.

David

#3 Mirzam

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Posted 18 January 2013 - 10:37 AM

He's building a scope so there is no stock focuser.

Generally, you need about 1" of travel to accomodate most eyepieces. There are a few oddballs that may need more travel. I design for Televues, and the Radians are a good middle of the road (wrt focuser travel) choice. Give yourself at least 3/4" of in-focus as this is the thing that is difficult to fix after the fact. In other words place the focal plane 3/4" above the fully racked in focuser. If you use the 1.5" focuser tube you should clear the light path.

Out-focus range can be increased easily by using an extender so there is no need for a longer drawtube.

If you want to design the scope to enable direct photography of the focal plane you will need to place the focal plane at a greater height above the focuser. The actual amount will depend on the camera. Note that you can still do afocal photography (using an eyepiece to project an image into a camera which has its own lens) without changing the focal plane position from the usual visual position.

If you want to use a binoviewer you should also allow more in-focus, similar to using a camera. The amount will depend on the light path length of the BV so you will need to do some research. Many BV's come with a lens attachment that helps to achieve focus with only a relatively small in-focus requirement compared to ordinary visual use.

JimC

#4 cliff mygatt

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Posted 18 January 2013 - 02:52 PM

I changed out my stock Orion focuser for a moonlite with longer travel primarily to allow my Ethos to come to focus in 2 inch mode and have not looked back. Good Luck!

#5 hotdogx

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Posted 18 January 2013 - 08:05 PM

JimC,

What you have said aligns with what I've been thinking. Currently I am using the eyepieces I mentioned on a 100mm refractor I built. I guess I need to go out one of theses next clear nights and verify the total focus range for all my EPs, and determine which one requires the most inward focus position. I don't plan on using a binoviewer but will be doing prime focus photography. I do prime focus with my refractor and my DSLR and it works out nicely. Guess I can make/buy an extension tube for use with my camera. Thanks!

#6 Mirzam

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Posted 18 January 2013 - 09:01 PM

Your welcome!

One thing that comes to mind is that a crayford focuser tube will actually be quite a bit longer than its travel. To get 1.5" of travel will require a focuser tube length of around 3". It would be a good idea to check with Moonlite to be sure that your focuser tube will not stick out more than an inch below the base when the tube is racked in all the way. The Moonlites are low profile focusers--about 1.75-2.00" tall with the mounting kit (for adapting to a curved OTA). A 2.5-3.0" long focuser tube will be just about right to avoid intrusion into the light path.

JimC






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