Image of the day

Captured by
Craig Bobchin

Coathanger CR 399

About Astromart

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: John Holt

July 28, 2008 05:06 AM Forum: Solar System Observing

Observing pluto in 5.5" refractor

Posted By John Holt
Way cool!
It's the seeing. Not many photons to work with on such a target, so atmospheric conditions between he and thee will matter.

July 28, 2008 03:58 PM Forum: Equipment Talk

S & T Recent Equipment Reviews

Posted By John Holt
Something that irked me this morning when paging thru S&T was their stupid caldwell renaming of already designated objects. Very nice photo of NGC 4565, but they just gotta marketeer. The caldwell fiasco show go down in astro history as S&T lowest maneuver.

July 31, 2008 06:49 PM Forum: Equipment Talk

Telescope Pier

Posted By John Holt
gary shrum said:

For a 8" SCT would a telephone poll be better than a 6-8 pipe for a pier?


Phone pole is very coarse grain wood. If it is old type , then it may have been treated with creosote for weather resistance, and this can come off on you when using it.

Structurally wood, steel or concrete will all work. Wood could be solid, as in phone pole, or a hollow column box made of exterior grade ply. A portable pier is even better. : )

August 17, 2008 09:02 PM Forum: Equipment Talk

Only One Scope

Posted By John Holt
jeff yonker said:

If you were a visual astronomer with lets say a $1000-$2500 budget and could only have ONE scope,what would it be and why?Dob,Sct??????



My vote is 2.

One large and very portable. As large an aperture as is manageable. With active cooling.
One small portable.

Within budget. Because there are more options available now than ever before. Including trussing an existing bulky dobsonian into a smaller package.

Also consider the thread here on 'great optics'.
IMHO good+thermal equalized+affordable optics, that are out under the night sky as often as possible, wins.



August 23, 2008 09:18 PM Forum: Beginning Astronomy?

Eyepiece cleaning?

Posted By John Holt
Christopher Scibelli said:

The web is full of instructions on cleaning a mirror but how do I clean eyepieces without doing harm?

Chris

Longmeadow, MA.



http://www.televue.com/engine/page.asp?ID=143


August 23, 2008 10:19 PM Forum: Eyepieces

Lower vs Higher power EPs

Posted By John Holt
walt durling said:

I'm a relative novice and recently purchased an Orion 10" Dob. It shipped with a 10mm and 25mm plossl. In an effort to modestly boost my EP line with two higher quality EPs ( Pentax and Televues are too hefty for my wallet), I first purchased a quality barlow (Antares UB2S 2x), and a 7mm TO/TMB for planetary viewing.

I now want an EP for DSOs. And herein lies my ignorance. I've read in various forums that having a low power EP should be in everyone's arsenal. I have deduced that that means an EP from 24-30mm and higher, more or less. Now, if a wider AFOV is desired for DSO viewing, all else being equal, wouldn't it be "better" to have a moderate power EP rather than a higher power EP? For instance, I've been looking closely at the Baader Hyperion line, which boast a 68 degree AFOV across the line (I think the 21mm is somewhat less for whatever reason). But why wouldn't I want to purchase, say, the 17mm rather than the 24mm? I'd get the higher magnification but the same generous AFOV.

I'm not as interested in opinions about Baader or any other EP maker as I am concering the pros and cons of eyepeices for deep space viewing. Any thoughts from the experienced would be appreciated. walt



Intelliscope or regular?

A powered finder scope, like a 9x50 will make it worlds easier to find stuff, if you do not have electronic assistance. See our sponsor Anancortes.

Detailed charting, at the very least Sky Atlas 2000, plots enough field stars too make it possible to BE on target with the powered finder.

Next consider, eyeglasses on or off during viewing? This narrows the field on ep options somewhat. If you don't need 20mm eyerelief on your ep's, then you really don't have to pay for it.

Consider a used 15mm plossl. Very modest priced and reasonably well corrected ep for your focal ratio. It's not wide field, but the vast majority of deep sky targets are small.

Shy away from the really budget 3, 4 and 5 element WIDE FIELD ep's. In these, at your focal ratio, most of the outer field of view will be a mess due to astigmatism, or they will be poorly coated (glares and ghosts).... or both.




September 1, 2008 02:59 AM Forum: Reflectors

Celestron/Vixen C6 Focus problems

Posted By John Holt
Michael Greenham said:

Hello everyone. I have a Celestron/Vixen C6 f/5 with a sliding focuser. My problem is that the focuser does not have enough travel to bring some of my eyepieces into focus. The 9mm ortho, 12mm widefield, and 32mm plossl will not come into focus. My 26mm, 22mm, 20mm & 15mm plossls all focus fine. Can anyone help explain why this is so. wink



Different makes and models will literally have the component elements grouped in different places within an ep barrel.

Determine which ep requires the most infocus. Then if possible adjust the primary up the tube, a bit closer to the focuser so it will focus. Sometimes it's just a matter of moving the mirror up hill with the collimation bolts.

Outfocus can be worked with para-focalizing rings, on those ep's that need to be out the focuser a bit. Or with an extension tube, which sometimes can be made with the right size piece of 1-1/4 drain pipe.

September 1, 2008 07:39 AM Forum: Mounts

Unorthodox question

Posted By John Holt
Dale Partin said:

I'm close to purchasing a William Optics ZenithStar 80mm II ED refractor telescope (6 pounds). I would like to use it to look out the windows of my house at the stars (yes, I know that this is not the best way to do things). What kind of not too expensive mount could I get that I could adapt so that I could easily clamp it to a windowsill. I would want the mount to either have slow motion controls or have adjustable tension so that it could be smoothly moved to the direction I wanted it to go. The scope has a 1/4 inch bolt mounting hole. Anything would be better than what I now do, which is use a very beat up old 80 mm F/5 achromat with a badly chipped, dirty lens on a 6 inch high tripod, balanced on the windowsill with two tripod legs outside and one inside, with a sloppy tripod adjustment that freezes the scope in one direction. Even at low mag, Jupiter is streaked past all of its moons. Thanks!



Visit this website:
http://www.planetatm.com/

And scroll down to the Pipe Mounts. I had a 9 pound short tube newt mounted on a round disc base with upright pipe and 90 degree elbow on top, very similar to what is shown there, after seeing those picts.

Use a round unfinished table top for the base. Galv pipe and fittings. Match the threads for smooth fit at the hardware store. Add a wrap of teflon tape to the thread sections that are to move, and replace it every now and then as needed, for smooth movement. No other lubricating required.

Simple and worked good.

September 5, 2008 06:22 PM Forum: Reflectors

Primary Mirror Cell

Posted By John Holt
Joe Ramacciotti said:

Hello Everyone.

I have a Coulter 13.1” scope and want to change the primary and secondary mirror cells.

The first to be changed is the primary cell, so I’m looking for any suggestions for mirror cells. I’ve looked at the University Optics light weight aluminum cell that is made for the mirror specifically, but I’m concerned with having only 3 support arms and possible mirror sag, opposed to a 9 or 12 point cell.

Also, I would like to keep the mirror captive so I don’t have to remove the mirror during transport with the OTA laid on its side.

As for the secondary, a classic 4 vane spider is what I’m looking for.

Any suggestions are greatly appreciated.

Just so you know why I’m doing so, the current primary wood cell is pinching the mirror and diffraction rings are triangular shaped. The mirror is about ¾” thick and even after 4 hours of stabilization the diffraction patters got better, but still triangular in nature. Not sure if this can be resolved, but though I’d mention it.


Thanks for your help!


Joe


The 13.1" UO cell is plenty strong enough for transporting the mirror. But not a good match for thin mirrors, because the support points are in the wrong configuration. Diffraction patterns show it. It sags.

September 29, 2008 03:15 AM Forum: Reflectors

skywatcher collaspible dobs

Posted By John Holt
anthony maida said:

has anyone purchased any of the new skywatcher collaspsible
dob,s? I,am thinking of getting one anthony



I have not.

But of the newest truss tube newts being imported for various retailers.... the Sky Watcher looks like they have the least sturdy, most prone to flex, of all the optical tube assemblies. They simply appear to have less structural support. No tubes in a triangular truss configuration, nor extruded alum struts. Just what appears to be three rather small diameter tubes. It looks simple and clean. And like it would sag and vibrate.

Funding Member

Sponsors


View all sponsors

Search