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Messages - snowcadere

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Reflectors Telescopes Forum / Re: Laser collimation question
« on: February 08, 2018, 11:29:57 PM »
The 1/2 inch circle at 30 feet seems a bit wide to me, but with this style of collimator I'm not sure how difficult it is to get a good measure of it and adjust it well. Sounds like it would have to be done in some sort of focuser tube or stand in for one--e.g. piece of pipe/tubing held firmly in place with the collimator rotated inside of it.

Assuming that the laser is well enough aligned with its own axis, then what is described with it in the focuser suggests a problem with the collimator. The focuser shouldn't be moving one way or the other since it isn't extended or moved and the collimator is doing its own thing when rotated. All of the off-axisradial movement has to be from the collimator.

One of the things I like about the 1.25" Zhumell that came with the Z10is that it fits snug and flush with the adapter,the same one that is used with high power eyepieces. I want my collimation centering to match the center of the eyepiece when in the focuser.

thanks. Yeah, i guess I could tighten the current 1/2 inch circle. Adjustment is not too difficult, and yes, i agree, using a "stand in" focuser tube is the best way. I will just firmly fix the 2" adapter that it comes with, and rotate it in that.

I will also try collimating the laser in the telescope.

But I asked about this, only because I was worried that maybe some other factors were working here. Although my focuser seems to be tight, and not floppy.

ATM, Optics and DIY Forum / Re: Foucault tester - 3D printed
« on: February 03, 2018, 04:17:04 AM »
Looks like it works very well after some initial tests. As always we were looking for errors to be fixed and found a few, hardly worth mentioning.
Still one major error(I should rather say shortcoming) in this unit is it's weight. It merely weigh 1.5kg (about 3 lbs). To hold the it fixed on the workbench we'll have to add some weights to the FTer.

Beginners Forum / Re: Is a 12" aperture really that much better than 10"?
« on: February 02, 2018, 09:15:39 PM »
Also, for wheeling the scope about, I made myself asuper easy dolly by just taking a piece of 2'x2' plywood and screwing four wheels on it. Insanely simple - literally just a piece of wood with some wheels on the bottom - and works just fine. Looks something like this (http://vincechanblog...latform-000.jpg) . For a 130lb scope I'd suggest some beefier wheels.
For a fairly modest financial investment, a handcart has several advantages over that solution:
It comes already assembled.
It has big wheels that travel easily over rough terrain.
It is trivial to remove from the telescope. No matter how well you lock the wheels on your caster, it will never be quite as vibration-free as having the scope sit on the ground.

It can be used for moving other large, heavy objects.
Depends - I find the hand truck more difficult personally since the platform is smaller and you need to incline it to move it. Wheel-barrow handles placed directly on the dob is the ideal solution - but like the OP said - that's a bit more difficult to assemble.

In any event - they all will work and none of them is terrible difficult to acquire (or make) or terribly expensive.

Reflectors Telescopes Forum / Re: Star testing
« on: February 02, 2018, 08:04:38 PM »
Re "shadow breaking out", just forget it. It's generally very hard to determine the point of exact breakout. Even when it's unambiguous, you have to be measuring focuser travel -- in the scopes where you can actually measure it -- or it's no use. It's much simpler to defocus a known distance and compare patterns. This is what Suiter's does in his book.

Also, I've found it a lost cause to compare patterns generated by Aberrator or in pictures in Suiters book to ones generated by real scopes on a real star, even an artificial star, with any degree of certainty. Theonlymethod I've found reliable is to compare shadow sizes on either side of focus when defocused about 10 waves.


I think what I'll do next is try the calculation and see what a mask at 5.5" will bring it to, assuming the full aperture is 1/3λ. If anyone else wants to give it a try, please do. I'm not sure I understand the process.

If it amounts to 1/4λ or a little better, then I'll do some observing and testing with that set-up.

What is annoying is that the scope is built well and very solid. but what you get optically, (and what most people can't determine) is a spin of the wheel. Mass produced or not, inexpensive or not, anything over 1/4λ is just unacceptable.


Joe, mass-production and high precision are incompatible. I'm surprised that off-the-shelf optics are as good as they are nowadays. Back in the '70s and most of the '80s that would have been just a wishful thinking. In those days, the C8 wasn't anything it is today. That's why refractors like Unitron and hand-figured optics like the early Cave Astrola were much better choices and dominated the market, and if you wanted a high precision scope, for most the choice was to get a loan for a 3.5" Questar. High precision optics cost $$$. That's just a fact of life. That's why today the Ceravolo's aplanatic reference element (a tiny 1-inch diameter Zerodur lens!) finished to /10 wave on the surface will cost you $600 + S&H.

I think it is a bit unrealistic to expect bargain-basement and surplus optics to be anything better than 1/4 wave -- if that good! -- in reasoanbly larger size. From Bratislav's scale, posted earlier by Pinbout:

"6. In focus image visibly suffers ( ~1/4 wf): 'Acceptable' good mass produced scope, most good large/fast mirrors I've seen"

Worth repeating.

This is my C8 I bought in 2005, brand new, in DPAC (oil flat). Let's be brutally honest -- that'sbad.And this is more the rule than an exception.
If I were to push the test to show 2 bands or 1 band only you'd see all sorts of things you didn't want to see...butit >forms and Airy disc!so technically speaking it's "diffraction-limited" (which is a rather meaningless term if you think about it, because optics worse than 1/4 wave optics will alsoform an Airy disc!)
The only way you'll get better optics consistentlyis (a)pay through your nose, or (b) make them yourself.Otherwise it's a lottery.


Mounts Questions & Expirience / Re: CGEM DX teardown help
« on: January 31, 2018, 10:27:57 AM »
The good news, I was able to get those screws loose. I now have the Dec opened up, the motor seems to turn ok, there is a lot of thick black grease, which I am going to clean and replace with SuperLube.
I also ordered the Hypertune DVD and will likely get some bearings while I have it all open.

I am very frustrated with the mount and it's constant issues, but I am looking at this as a chance to learn how these mounts work and get better at troubleshooting and adjusting them. I have already learned quite a bit just taking the Dec apart.

I did notice some of the large hex screws that thread into the mount body/housing seem to be stripped. It's the body that seems to be stripped. I guess I can try to re-tap those holes.

ATM, Optics and DIY Forum / Re: What Are These Glass Blanks For?
« on: January 31, 2018, 07:29:59 AM »
Ed, were USPL Pyrex blanks shaped the same?
The Pyrex we bought was mostly test plate and mirror blanks which looked similar but now that I think about it didn't have the circular rings.

To measure the specific gravity you weight it in air then in water (on a string) then divide the weight in air by the difference.


Mounts Questions & Expirience / Re: CGX aligment issue
« on: January 31, 2018, 05:28:27 AM »
hello Rod,

Apologize for my terminology. The procedure in the manual (p10, lower r/h column English version) just referred to as 'alignment'. I went down the two star path, or tried to.

The CS rep asked me if the prompt appeared for 'RTC yes/no' after the switch finding routine. It's not in the manual... and I said 'no', am i supposed to be getting that?

I just performed the HC reset, which is thankfully simple. On power up

went through switch routine.
Entered my city, date, time
When prompted for alignment I chose 'Solar System', and in that Mars (very close to sun now so i figured an easy ballpark) - yes all optics are capped!

It did go to near where the sun is! not the opposite side of my meridian as it was doing last night. Maybe the reset took care of it? I'll know this evening when I try on celestial alignment. Though just now it occurs to me that I could just go through again and see what stars it says are on which side? Think I'll do that, as it would be a huge toggle. I've still not seen a prompt for anything to do with the real time clock (RTC) as the CS rep said.

First thoughI want to post a new thread about 'side by side' mounting...

General Astronomy & Observing / Re: Dark sites near Las Vegas
« on: January 31, 2018, 05:16:15 AM »

Due north about 200 miles is Ely, Nevada. Ely was my home town. I had Mag 6.5 skies out my back door. Ely is 6,400 feet above sea level. I enjoyed my 4 inch, F10 Dynascope more in Ely than I did years later with telescopes later 20, 18, 13.5, and 8 inches due to its dark skies. That taught me something very important--dark skies may be the most important factor in observational astronomy, not size of the objective. The problem with viewing in the Las Vegas area is how far you need to travel to shrink the light dome. Tonopah is also a good option. There are a lot of people who view from Tonopah due to its dark skies, and excellent atmospherics.

I went to a Star Party outside of Tonopah (Central Nevada Star Party) about ten years ago and as you report, the skies were wonderful there. I'd also imagine that the skies at Cedar Breaks National Monument at 10,000ft would be exceptional too but snow could inhibit using that area in the winter months.
It can inhibit using that area in summer!! When I worked at Lake Mead I left late one Friday afternoon to drive to Cedar Breaks. I got there in the dark so threw my BEST down sleeping bag in the bag of my truck and crawled into bed. I awoke towards morning freezing cold. At first, I thought "I need to get this down bag dry cleaned". Then the 10,000 foot thing slowly crawled into my brain.

Freidb....It was a black zone in the 70's. Terrible shame what happened to Arizona skies even with the light pollution ordinances. Green zone is really city observing. I am in the green zone in Benson.

General Astronomy & Observing / Re: Another Nearby Monster Black Hole
« on: January 31, 2018, 03:53:22 AM »
Get ready for the fire works....The Largest Black Hole Merger Of All-Time Is Coming Soon.



Beginners Forum / Re: Im hoping i made the right choice (Orion XT8i)
« on: January 31, 2018, 03:25:38 AM »
The date is only needed for locating planets. I only set the date to locate planets.

Standard hockey puck - 161 grams
Modified puck - 111 grams

It's not as much savings as I would have suspected. I might try some smaller holes between the large ones and the periphery to see if I can reach 2/3 of the original weight.

No doubt you can, if that's your target. You're already within four grams of that.

(It sounds like someone is determined to claim eliminating at least one puck worth of weight....)

A slightly larger counterbore for your bolt alone would do that!

Beginners Forum / Re: New to Astronomy and Telescopes
« on: January 31, 2018, 01:17:02 AM »
What If I wanted to dabble in AP, nothing serious, just like if I saw something neat or wanted to snap a pic of a nebula? I know its not the best but would it be better than a SCT, since the focal distance is shorter?

No. The Dobsonian mount is even more inadequate. Among other things it's altitude-azimuth, not equatorial. Even though it "tracks" the field of view rotates.


It's difficult to wrap you brain around just how precise tracking needs to be. At 1200mm focal length, a 1/1000 of an inch error over a 2 minute exposure will blur the best scope and camera. Your eyes will compensate, the camera won't.

Here's a picture of the Orion nebula with a Dobsonian.


Compare that to one with a camera tracker.

Click on both to enlarge. It takes a while to learn to do this. Think months, not weeks.

You could also image with the camera and a lens on a fixed tripod. You can do shots of constellations. The Milky Way. Some of the brighter nebulae, although they'll be small.


You could dabble with the Moon and planets with the Dob, since the exposures are hundreds of times shorter.

Beginners Forum / Re: Are Truss Dob's A Haasel To Collimate Every Set Up?
« on: January 31, 2018, 12:51:00 AM »
Well last night was something special, but I'll start a topic about that later.
I did decide that a right angle is needed, I think,,,,,,,,,,,,,

Beginners Forum / Re: Beginner planetary filters
« on: January 30, 2018, 06:22:47 AM »
Put me down in the 'no' column too. Don't use them. I will occasionally use a set of ND filters on the moon but that's about it. Never saw much use in the color filters.

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