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Posts Made By: Joplin Motisher-Chittenden

July 29, 2002 11:44 AM Forum: Equipment Talk

2" Focuser for Newt With compression holder.

Posted By Joplin Motisher-Chittenden

The Feathertouch focuser made by Starlight Instruments is one of the best and I believe that it has a brass compression ring holder. Here is a link to the manufacturer's info:

http://www.astrofieds.com/docs/feathertouch.htm

A search on google will turn up lots of information as well.

Joplin

July 29, 2002 12:16 PM Forum: CCD Imaging and Processing/Solar System

Digital camera with long exposure capability

Posted By Joplin Motisher-Chittenden

The Nikon Coolpix 995 (3.34 mp) is a popular one. It allows exposures up to 1 minute. It also has a large support base of aftermarket adapters, accessories, etc. The lens does not extend out of the camera so it is easier to securely attach it to a telescope than a camera with a zoom lens that extends outside the camera. It is also is in the process of being replaced with newer models so if you look around, you can get a good deal on one.

Joplin

July 31, 2002 12:55 AM Forum: Telescope Making

unknown F-ratio

Posted By Joplin Motisher-Chittenden

Sounds like it is an F6. The easiest way to confirm it would be to aim it at a very distant object and project the image onto a piece of paper. If it is an F6 it should come to focus about 4 inches from the outside of the tube. From what you have described I would be very surprized if the true F ratio is outside the F5.5 to 6.5 range.
You can also use an eyepiece with a known field stop diameter (Televue publishes theirs, others will have to be measured very carefully with a caliper, taking care not to nick the field stop) to measure it at night using a star on the celestial equator. Time the star's travel time across the field of view of the eyepiece you measured. It must travel directly across the center of the field of view. If the scope is an 6" F6, the star will take exactly 15 seconds for every millimeter of field stop. So say, for example that you had a Televue 32mm Plossl (which has a 27mm field stop diameter), the star would take 6 minutes and 45 seconds to drift across. If there is any variation from this, the difference is directly proportional to the focal length of the scope.

Joplin

August 2, 2002 06:33 AM Forum: Equipment Talk

anyone looked out of or own the 10" dob from OPT

Posted By Joplin Motisher-Chittenden

Check out the reviews of the the Orion XT10 (Sky & Telescope has reviewed it and so has cloudynights: http://cloudynights.com/reviews/xt10.htm
as well as scopereviews.com.
It is basically the same telescope made in the same chinese factory.

Joplin

August 3, 2002 07:06 AM Forum: Equipment Talk

Anyone know anything about Obsidian Optics?

Posted By Joplin Motisher-Chittenden

The main thing that concerns me is the thickness ratio of the mirrors they have, 1:13.3 It appears they are limited by their choice of surplus porthole glass that is only 3/4" thick. A more conservative size for that thickness is a 6" mirror, and 8" at the most. One would need a superb mirror cell to addequately support a 10" with only 3/4" thickness.

Joplin

August 3, 2002 02:54 PM Forum: Equipment Talk

Camcorder & mount

Posted By Joplin Motisher-Chittenden

There are numerous adapters made by Scopetronix, Televue and others to fit the threading on a camcorder or digital camera (usually the threading on sony handycams is 37mm). Orion also makes a "SteadyPix" universal camera mount that will clamp around the eyepiece to secure the camera. I would combine both devices to secure a camcoder since they are a bit heavier than the smaller digital cameras. The main question with this setup is how sturdy is your focuser? If it isn't very sturdy, a support that clamps onto the main telescope tube will be required so that there is no risk of failiure.

Joplin

August 6, 2002 05:29 AM Forum: Equipment Talk

solar filter & dovetail for Orion ST 80

Posted By Joplin Motisher-Chittenden

I have both the Orion Glass Solar filter and a home brewed one made with Baader solar film for my 80mm refractor. The Baader film has much better performance as it is sharper and shows far more granulation on the surface of the sun as well as more detail on sunspots. It is also cheaper, I got a piece that was more than large enough to make my filter for $11 unused on Astromart. Even if you are considering the an H - alpha system (which costs close to 5 times as much as an ST80 you will want the Badder film in the meantime and for sunspots later on. The bandwidth issue you mention applies mainly to the H - alpha systems, the closer they are to the H - alpha emission line and the more they reject on either side of it is what determines how much detail is seen.
In regards to your other question here are links to the items you will need (Ken's rings is probably the cheaper option):

http://users.kricket.net/ken/rings.htm

http://www.losmandy.com/secondary.html#DM

Joplin

August 10, 2002 02:31 PM Forum: Equipment Talk

Which eyepiece to binoview moon?

Posted By Joplin Motisher-Chittenden

I'd go with the 13mm nagler T6 since it will give the largest image of the moon and will still fit neatly within the fov. It will produce a moon image that is a bit over 60 degrees across within the 82 degree fov. There is some geometric distortion with all of the superwide eyepieces but if you limit the size of the moon to 65 degrees or less and keep it fairly well centered, it shouldn't be a problem. No experience with that paticular eyepiece but I've heard that it is one of the better Naglers for binoviewing.

Joplin

August 13, 2002 03:48 PM Forum: Equipment Talk

TV 85 vs. Tak FS78

Posted By Joplin Motisher-Chittenden

I would keep the one that you find the easiest to use (focuser, etc.). If airline portability is a concern, the TV85 will be easier to fit in a regulation size bag. I use a Vixen FL80S for portable use. All of the premium refractors at this size are quite versatile and great to have when you don't want to drag out a big dob.

Joplin

August 14, 2002 06:35 PM Forum: Equipment Talk

Mounting a refractor to a tripod

Posted By Joplin Motisher-Chittenden

I have a 5lb refractor (about 6 or 7 with diagonal, eyepiece) that I have mounted on a pan head on occaision, but it is not an ideal combination. There are plenty of midsize tripods that will handle the 10+ lb. weight of the 120ST with accessories weight but very few heads of reasonable size that will. I would recommend a balanced alt - azimuth head for ease of use and stability, they can even be made fairly easily if you are handy with shop tools. I would give a conservative estimate that the ST90 is the largest scope I would mount on a reasonably sized tripod head. Anything larger and you might as well go will a real alt-azimuth (balanced) mount. Keep in mind that I am picky about vibration, etc.
That 80mm plossl is a way longer focal length than you would need unless you plan to use it with an F 12 or longer scope. At F5 I would stay at or below 35mm and at F6 42mm or below. Also, if there is much light pollution in your area, I would go for 32 to 25mm for an F5, 37 to 30mm for an F6 scope. My advice - send the 80mm back to Surplus Shed for a 31.9mm (same price and much more pleasing apparent field of view).

Joplin