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Messages - coachroninil

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General Astronomy & Observing / Re: Solar Eclipse 2017
« on: February 09, 2018, 10:56:01 AM »
I just hope that the original poster got their question answered.

Hi John,
 Yes I spoke with the OP offline.

Beginners Forum / Re: Yet another beginner looking for a telescope
« on: February 08, 2018, 11:28:56 PM »
A Dobsonian is not ageneralpurpose scope,it's mainly alight collector for deep space objects. You do get a lot of aperture for your money, but everything else is barebones. That means 90% of the experience with Dobsonians is abouttryingto land the scope manually on things you can't even see throughthe finder.

If you like thehunt, if you thinkit's fun to star-hop and translate left-is-up and down-is-left while flippingcharts upside-down in the dark, theyou'll like the Dob.

On the other hand, if you're willingto give up some aperture, there are any numberof systems that will steer themselves to any catalogued object and then track it, allowingyouto sample dozensof objects per hour, and to share them with your viewing partnerswithout fighting the earth's rotation all night long.

If youwantto look *for* things, get a Dob. If you want to look *at* them, get a goto mount with the most aperture you can afford. I have seen so much more stuff sinceI gota scope that already knows where everything is. I would not trade that for six more inches of aperture.

I also like the security Astromart provides to buyers and sellers. I choose to contribute $100/yr to Astromart as I have saved much more than that by buying used equipment from reputable sellers. I have also bought from a few sellers on CloudyNights, but only if I could verify who they really were.The forums on CloudyNights are far and away a better source of shared knowledge and current events. Astromart's forums have waned in many respects in recent years.

So each serves a purpose...I am glad to have them both as resources to feed my addiction, er...uh...hobby!

Thanks, caveman!

Here's the best part of the whole idea:

<p class="citation">Quote
The satellite will orbit Earth for "several weeks" before falling through the atmosphere and burning up, according to the project website. The sculpture will therefore be a "temporary space gesture" and "will leave no trace."
Unfortunately if this is successful then it will just pave the way for more of the same to come, with each successive one trying to outdo the last.

Last thing we need is advertising in orbit. Gold names making the night sky polluted and tacky.

It's simple, really. Have a nice meal, go up and observe for awhile then come back down and have a few brews.

Parks made a convertible focal length newt/cassegrain.
By switching secondary and focuser placement I believe.
Perhaps someone can share how that worked.

A Newtonian secondary is flat, a cassegrain secondary is convex and provides magnification. The primary mirror is F/4 in both cases but the cassegrain secondary acts like a Barlow so the effective focal length is greatly increased.


ATM, Optics and DIY Forum / Re: Share photos of your DIY focusers
« on: February 02, 2018, 08:49:23 PM »
I think I saw something like this in All About Telescopes by Sam Brown. Is it correct that the secondary moves up and down? Do you size the secondary differently?


How about a homemade all plywood Horizontal Leadscrew focuser with a 2 inch (I.D.) PVC eyepiece holder?

A horizontal focusercan be made to havea lower profile over a traditional rack and pinion focuser thatis commonly used on most Newtonians...especially Dobsonians.A well designed horizontal focuser provides a very stable platform for a very smooth and linear motion as it travels during focusing...and without any accompanying pitch or tilt as is sometimes seen in some traditional rack and pinion focusers.These are just a couple of advantages described about a horizontal focuser...there are others too.A Horizontal Focuser (leadscrew or otherwise)along with the horizontal focuser's secondary holder and it's support arm is relatively easy to design and make...especially if you're interested in a different type of focusing mechanism for your Newtonian....(see attached photos)

Simplicity is everything when it comes to making a mechanical focusing system.


Hello Brucesdad13.....

The secondary travels 'centered' along the optical axis....The secondary maintains the same size as would be found in a typical Newtonian. There are several advantages using a horizontal focuser verses a typical focuser.....It's easier making a horizontal focuser out of wood than for me to fabricate one out of aluminum or brass....However...if I did....I would probably go with the aluminum.



ATM, Optics and DIY Forum / Re: Polishing a 6" f8
« on: February 02, 2018, 06:26:59 PM »
I started this 6" f8 project in 1970 with an Edmund kit. I had to put it aside to finish college. I had polished it, but don't remember how long. A laser test showed it wasn't polished out.

Thanks to IvarB I'm trying a different technique for lap making. I bought some 1/5" square plastic mesh used for needle work. IvarB uses 1/7" inch mesh which gives 49 facets per sq inch, while my mesh has only 25 facets psi. The mesh is about 1/16" thick.

 This is the mesh sitting on a container lid.

The lap I'm using is thin, less than 1/4", maybe 1/8". It's hard to measure due to the large bevel on the plate glass tool.

Lap after some use.   Closeup In use

The technique is to the pour the lap against the mirror curve. The surface of the lap is heated with a heat gun and then I press in the wetted mesh. This creates bumps almost the thickness of the mesh. The mesh is lifted almost immediately and then I warm press until the facets are a nice size.

It's very convenient because, when the facets close up, all you have to do is heat the lap, repress with the mesh and trim the edges of the lap. I use one of those infrared thermometers to check the surface temperature (70C is about right for Gugolz #64).

Using KFrederick's suggestion,I press with a piece of thin grocery plastic bag wetted with water. This works great. The mirror never sticks so I can leave the mirror on the lap overnight to have perfect contact when I start polishing.

 Lap ready for pressingI'm still polishing out, but as soon as I finish and make a Foucault tester I'll see what sort of surface it produces.

Anyone else try this method?


General Astronomy & Observing / Re: Ring Nebula
« on: February 02, 2018, 02:32:15 PM »
Good point made by BrooksObs! I had actually realized that some time ago, when I wanted to understand why I couldn't see it although I could see nearby stars that were at least as dim. Thanks for making a note of it.
By the way, the 15.6 (or 15.7, I don't recall for sure) star outside the ring I could barely detect, and that was only on one occasion. Typically I could detect reliably the 15.3 star that is also in that neighborhood as well as the pair of 15.6 or so stars seen as a single star.

The optical quality of my 13.1 Coulter was poor. So was the mechanical quality. I sold the telescope and decided to spend more to get better quality.

Beginners Forum / Re: If you could own just 2 telescopes...
« on: January 31, 2018, 11:58:27 AM »
Just two? I'd have to go with my 8" LX90 and my Lightbridge 16. The LX90 is a nice size and gives me the option of altaz or equatorial, GoTo or star-hopping. The Lightbridge combines light grasp, simplicity, and portability.

Eyepieces Questions & Recommendations / Re: Spacewalk eyepiece
« on: January 31, 2018, 07:33:08 AM »
There is no spec per say. Some EP manufacturers will state minimum reccomendation but that's uncommon unless they are touting performance on very fast scopes. All will "work" with a fast scope. What happens on some EPs is that the stars at the edge of field will get a bit soft (fuzzy) on fast scopes. Usually the best indicator is price unfortunately. The more you spend, in general, the better...

I don't have any experience with fast scopes so hopefully others will advise on what to avoid. But at f/5.92 your scope isn't extremely fast so you should be good with any of the 82 degree EPS out there. Especially since you actually need to try and find the edge of field at that AFOV so it's not something you should be overly concerned with.

As with most things, you pay a lot to get from very good to perfect...


How about this one?
The Celestron Luminos is something I can afford.

23mm will frame everything deep-space related? Or 31mm?

But I also might want to use my nebula filter on it which is 1.25 (so it wont work).
I do have a 2in light pollution filter though. So I could use that.

Light Pollution Topics / Re: The City Dark will air on PBS July 5
« on: January 31, 2018, 02:59:17 AM »
I wish the stream would work for me.  Is this US only?

Here is carbon star U Lyrae and NGC 6791, ~10 second single image. Third image NGC 4565.

Teeter 18" f/3.5
Canon EOS M3
Earthwin power /filter slideAttached Thumbnails

CalPoly made their own direct drive mount (wound the large motor themselves, actually). I don't see why the number of poles is actually relevant to an end-customer.. of course more poles is better (within reason).

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