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Messages - Marvin Neboet

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General Astronomy & Observing / Re: Better than GoTo:
« on: February 08, 2018, 11:03:20 PM »

Vocal GOTO was done in the late 90s by Astro Physics. Often wondered what happened to it.

Wow, I never knew that. So, AP had a Mount you could ask to slew to "object X" and it obliged?
I heard it got rebranded as something called The Clapper

Thanks Jeff. That sounds like a fun lineup.
I ended up going with the Denk 32 neutral plossls without the undercut (and screw in ring that sharpens the field stop) for widefield (and h-alpha) views and added a TV 15 plossl to complete my pair for planetary views.I do have a pair of 20mm silver top plossls one of which OPT threw in with my Denk purchase.
I think I'm all set. Just waiting for the darn skies to clear. Been miserable even down here in Southern California.

Hah! so do I. 30+ year old eyepieces but still excellent.



Reflectors Telescopes Forum / Re: Why are most 10" dob bases 22"?
« on: February 03, 2018, 03:57:29 AM »

To answer the "why" of the OP in another way, the answer hit me while sketching a dob mount for an old 6" f/8 that has been mounted on a GEM. It is meant for a beginner/loaner scope and will be getting a dob base. The mass-produced dobs with the circular bases have to have circles wide enough to encircle three panels of significant width. For example, a 12" GSO scope has a tube of 14" diameter and its front and side panels are all around 16-3/8" wide. By the time you've separated the two rockerboards by 16-3/8" (required for the altitude bearing design), the corners of the three uprights are all about 12" away from the center pivot bolt. You've got to have at least a 24" diameter base board.

I wonder why they make them circular though. The bottom of the rocker could be a square, and the ground board a triangle, oversized if you want to keep the original estability of the base. That base would be lighter and easier to pass throught doorways and fit into trunks.
Dob bases look simple, but I believe that designing a base that maximizes the utility of a small Dob might be a much more difficult engineering exercise than it appears to be at first.[/quote]
I agree, but I know by first hand you can end up with a completely functional, smaller, stronger and lighter base if you make the work right.[/quote]
That's true "if you make the work right," but how does a person know what's "right" before building the base?

General Astronomy & Observing / Re: Question about galaxies coming together
« on: February 03, 2018, 02:24:50 AM »
... Why, an n-body solution of the dynamically evolving encounter shouldn't be too much to ask for, right?

Oh... Ignoring the gas clouds and stars that form during the collision, this means we need a statisical study covering a couple of hundred billion particles, each with at least twelve** degrees of freedom... what can possibly go wrong?

** (x, y, z), (p<sub>x</sub>, p<sub>y</sub>, p<sub>z)</sub>, (L<sub>x</sub>, L<sub>y</sub>, L<sub>z)</sub>, mass, temperature (a proxy for radius), age

Let's see... I have 12 cores and 96 Gb ram in my machine. This lets me address about 7 million degrees of freedom. So it would need around four million cores and 30 terabytes of ram... wow. and. wow.

<p class="citation">QuoteBut just because two items look the same doesn't mean they're identical.

And just because they look different does mean they're not identical. I have told this story before but I was rather surprised to discover that the Antares 8.7 mm "made in Canada" W-70 was nothing more than a generic "made in China" 9 mm Expanse with an aluminium barrel glued over the stock barrel..

That pic/story always seems to infuriate me. What a shyster.

The problem we have here is not with the EP.[/quote]
Exactly. Jim pointed out the gist of it although I was still disappointed in Antares.

Mounts Questions & Expirience / Re: ioptron vs. celestron mounts
« on: February 02, 2018, 10:18:31 PM »
I have three Celestron Mounts (CGEM and 2xAVXs) and three iOptron Mounts (SmartEQ Pro, ZEQ/CEM25, and CEM60)

Of those three, the CEM60 is by far the best mount I own for doing AP. It's quiet, it tracks very well -- I can get round stars with 10 minute UNGUIDED exposures (this is NOT a CEM60-EC) using a focal length of 880mm and about 28 pounds of equipment (i.e. 50% load). My only complaint is its goto accuracy which is sometimes spot-on and sometimes terrible and I have never been able to understand what makes the difference. It's not things like polar alignment or the accuracy of star alignment. There is NOTHING for AP in its price class ($3000 with pier), nothing even close IMHO.

The AVXs are solid performers and much more "robust" than the ZEQ/CEM25 with with they compete. They're also built better and have had much better quality control (again than the ZEQ/CEM25). The ZEQ/CEM25 has much more "promise" -- innovative design, etc. but fails to consistently deliver. The AVXs deliver mediocre AP performance (compared to the CEM60) but they deliver it consistently and predictably. And their goto performance and the utility/quality of the hand control is light years ahead of the ZEQ/CEM25.

The AVXs are impossible to balance due to the massive amount of "stiction" between the ring gears and the clutch mechanism. This is in both axises and in both of my AVXs. The iOptrons (all of them) are trivial to balance and swing like buttered silk when the clutches/worms are released.

The ZEQ/CEM25 is the much more portable of them all and when it's on, it's a great performer. I actually had it running very well until I cratered another RA motor and then went for the CEM25 upgrade, which is not so far going well.

The CGEM is just a beast. It has the same great goto performance and hand controller as the AVX but it weighs about five thousand tons, it drips diesel fuel and leaks steam and will give you tetanus if you so much as look sideways at it. It also sounds and shakes like the Titanic in full reverse seconds after the iceberg was sighted.

Beginners Forum / Re: So I may be stupid, wouldn't be the first time!
« on: February 02, 2018, 09:01:08 PM »
Sounds about time for the sacrificial emptying of the bank account.



Maybe a dumb question, and I know professional astronomers don't "look" through eyepieces anymore but we've all seen the old pictures of those 20-40 inch Clark refractors, and even the huge 100-200 inch reflectors and there would be the astronomer on some kind of raised platform with his eye up to a ridiculously huge eyepiece. Has anyone here done this with such a telescope? If so, what was it like? What do planets and galaxies or the moon look like when the aperture area can be expressed in terms of square feet or meters!? I imagine you would need a serious lunar filter to avoid being blinded. Doing a search for images from the Yerkes, Hale and Hooker scopes basically look like what guys post on astrobin from a 3" frac in their back yards. But in both cases, I know they're long exposure photos so I imagine what took a few seconds on plate film with the big old scopes can be replicated with a fat stack of multi-minute exposures on a CCD. But visually, what is the difference between the view through a good backyard scope and a titanic monster?
Thanks in advance for any replies.

Personally, I put the limit on telescope usefulness at about a 3000mm focal length.
Beyond that, pffft.
It comes down to

1-what do you want to see
2-how much are you willing to pay
3-how much are you willing to transport/maintain

But even assuming #2 and #3 are infinite, and #1 is the brightest 200,000 objects in the sky, &gt;3000mm focal length just has too small a true field.
I did say that was for me, personally.
Once the telescope itself starts ruling out thousands of visible objects because of size, it becomes a "specialist's tool", which is fine for an area of professional astronomy,
but less desirable as an amateur's instrument.
Of course, I've met so many amateurs that spend nearly 100% of their time looking at planets or double stars that I wouldn't rule out the suitability of some long focal length
instruments for special uses.

Beginners Forum / Re: Dark Sky Meter?
« on: January 31, 2018, 11:05:22 AM »
I'd also love to have a meter to measure sky transparency, since a completely cloudy sky in a dark place will yield a darker reading with an SQM than will a clear sky.
Call it an "extinction meter", but I'd love to have an objective read of clarity of the air.
In general, high altitude is better than low altitude, but I'd rather observe at a low altitude 21.9 sky than a high altitude 21.0 sky, so sky brightness is still very important.

at risk of beating the topic, you do have a *useful* measure of the transparency of the air -- it's the NELM.

of course, the NELM confounds water vapor all types of particulates, along with light pollution and the seeing disk expanding effects of turbulence, which all reduce limit magnitude.

the subtext is -- why? why is transparency separate from other factors of specific interest? you can't possibly confuse a midnight seaside fog with alpine nocturnal lights if you're using NELM.

i don't mean to be contrarian for work or fun. but think how far, in contemporary infrastructure, your experience is mediated by devices. you look at video displays instead of landscapes. you look at power point presentations rather than presenters. you look at cosmetically enhanced faces rather than bare skin. you interact with a card reader rather than the grocery store clerk. you listen to music under headphones instead of in a club or concert hall. you have facebook friends instead of dinner companions.

all that may be functional, fine, modern, productive, efficient, convenient. and it may be similarly fine and productive in astronomy. i'm proposing that devices always be secondary to experience -- lived experience and cumulative experience or skill.

Mounts Questions & Expirience / Re: First start with the mount, help?
« on: January 31, 2018, 12:31:08 AM »
Here is/are the 2 screen shot by camera:

Mounts Questions & Expirience / Re: Anyone running a TSA-120 on an EM-11?
« on: January 30, 2018, 07:19:23 AM »

Does anyone have experience using a Takahashi TSA-120 on an EM-11 mount for visual? If so, how does it work? A loaded TSA-120 with diagonal, finder, rings and eyepiece seems to be a bit over the ~18 lbs. limit of the EM-11.

And would anyone know if the same telescope would be steadier or less steady on a Losmandy GM-11?

I have gotten some opinions in the refractor forum from a related question, but thought I'd post here and ask whether there were anyone with actual experience with the TSA-120 and EM-11 mount, or alternatively, the same scope on the Losmandy. Both would be ideal. Thanks for sharing any personal experience.


What tripod would you be using with the EM-11? I don't have an TSA-120 on an EM-11 but I've been happy overloading my similarly sized EM-2s with a 5" triplet (780mm f/6) that I'm guessing weighs about 24 pounds with finder rings and plate. I'm using the non adjustable wooden tripod for an EM-200 however. Using the adjustable height Tak tripod that came with the EM-2s isn't sturdy enough.

The EM-2s is rated at 7kg. The OPT site says that the EM-11 is good for up to 25 pounds. Maybe that's for visual only? The same webpage states that the optimum load is 6kg and that max is 9kg.

Thanks, John. Yeah, all the different rating numbers are confusing. That is why I was hoping for some voices of experience. I would probably put the EM-11 on a Berlebach Uni, or maybe even Planet tripod.[/quote]
I have no experience with either of those mounts but I'm a firm believer that any mount is only as steady as the tripod it is on. If you plan on getting a heavier mount in the future, the Planet would probably be the best investment up front.

Do do you already have the TSA-120, Brent?

John, I do not have the TSA-120. I am thinking of acquiring it. I have a GM-8, but am also considering switching to the Takahashi mounting system.

ATM, Optics and DIY Forum / Re: Gyro-Scope!
« on: January 30, 2018, 12:45:31 AM »
Here's my take on it.
Once again, my drawing sucks.
Sort of a U on top of an inverted U.
The bottom circle is a lazy susan in order to give the yaw direction.

Attached Thumbnails

Beginners Forum / Re: OK to keep dob in metal shop with no heat/ac?
« on: January 25, 2018, 09:12:13 PM »
I have had my 12 in dob in a garage for about a yr now and np..I keep a blanket wrapped around it..and it never gets any further than the edge of the door due to me not being able to carry the

But I do have a ? for you guys..What about an unheated "shed" that would hold a pier mounted Advanced VX mount with a refractor on it......BUT if the whole setup can not tolerate the temps then why build it....Temp range from the extreme of maybe 10 below to 115 degrees...{average would be like 15-100 degrees...} It did hit 117 on 8-8-11..that was a week from ****
Thanks for any info.

From what I read very very few observatories are heated or cooled/Air conditioned.  You want the place to be the same temperature as the ambient air.

Again, from what I read, going through the normal highs and lows of typical areas are not an issue.

Now, if you want to store it in a sealed black shed in Death Valley in the summer, the optics might not care but any rubber or plastic parts might degrade over time.

I store my XT8i and ETX 80, fully assembled in my attached garage which is well ventilated. No moisture build up, no heat and no AC.  The ETX 80 is on a tripod. The Dob sits on a cart which is how I move it in and out to the observation location.  All my eyepieces and other astronomy live out there too.  That is where I use them.

No cool down or warm up and no condensation from coming from a cool house to the warm humid air of evening.

Others with more experience will correct me if needed.  Just be sure it is dry, no rain or snow inside, no leaks.  And well ventilated so there is no moisture build up from the ground.

Years ago I was on the AP list for a mach 1, I decided to buy a used mount till my name came up ! I narrowed my choice down to an EM-200 and a G-11 after reading the Tak and Losmandy user groups I quickly decided on the EM-200 !
My name came up on the Mach 1 list shortly after the great recession so I passed! Still happy with the EM-200!

Beginners Forum / Re: Orion Apex 127 on Altazimuth mount?
« on: January 25, 2018, 08:17:50 PM »
Forget buying a beginners scope, you will want to replace it within the year.
Buy as much mirror as you can afford; buy from the big three Celestron, Meade, Orion.

Yes... "aperture rules"... But...

I'm not sure what if a 127mm mak qualifies as a "beginner scope."

My first telescope was a B&amp;L 4000 astro: a 4" SCT on an A/C-powered fork drive.  Yes, after a few years I "upgraded" to an 8" SCT, but I continued to use the B&amp;L. It went on vacations. It went on business trips.  I still have it-- almost 30 years later. It's small, compact, quick to set up, and I can carry it on its wedge and tripod, plus a bag with eyepieces, battery and a drive controller out the door in one trip.

There is a heck of a lot you can see with a 127mm mak. And it is an excellent complement to a larger scope. It's physically a lot bigger than my little 4" SCT, but still relatively light-weight and compact. For someone viewing from suburban skies, and mainly interested in planetary and lunar observing, a 127mm mak can put up a final image, and its portability is excellent. The best telescope is one you use...

Now a 6SE or 5SE might be worth considering as alternatives. A C5 actually has more effective aperture, while being lighter, shorter, and needing less time to adjust to temperature changes.  A C6 is only a bit wider, about the same length, and still weighs less, even though it represents a significant increase in aperture. Maks seem to need les fiddling with collimation, though, and have charms of their own.

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