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Topics - Santosh Wolf

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I had a project where I needed to know the focal length of a Televue 2X Powermate. I couldn’t find this information on a web search so I decided to measure it myself. This is how I measured the focal length of a Barlow.

The Powemate is a diverging lens assembly and has a negative focal length.
e.g. Catch sunlight with one and there is no convergence of light into an intense focal spot as with a magnifying glass (convex lens). Instead the light diverges with no apparent focal spot. Thus measuring the focal length of such a ‘concave’ lens is a challenge.

There may be several ways to do this but this is how I measured the focal length of a 2X Powermate.

Here’s my Televue 2X Powemate.Unscrew the extension barrel (black) from the lens assembly (chrome).Here’s a close up of the lens assembly. In use, light enters the bottom and exits at the top (black ring).I needed a laser to perform the measurements and used a Kendrick laser collimator.
Note: Any laser with do; I was going to use my $2 dollar-store laser but couldn’t find it.I mounted the lens assembly in a vice – very gently.I mounted the laser in a cross-slide vice and aligned the components.
Note: The back reflection form the first lens element shows on the front of the laser so I would adjust positions to get the laser reflection onto the center of the laser.I fixed a sheet of graph paper behind the lens assembly so that I could mark where the laser dot hit. I began with the laser striking the center of the front lens element and marked where the laser dot hit the paper.TO BE CONTINUED…

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We truly live in interesting times...

https://en.wikipedia.org/wiki/GW170817

GW170817 is a gravitational wave signal observed by the LIGO/Virgo collaboration on 17 August 2017, and is the first such event simultaneously observed in telescopes with an electromagnetic counterpart.[1] The signal, which had a duration of about 100 seconds, is the first gravitational wave detection of the merger of two neutron stars, and was associated with a soft short gamma-ray burst GRB 170817A,[2][3] found in NGC 4993.[4] No neutrino candidates consistent with the source were found in follow-up searches

This pretty much confirms that short gamma ray bursts are from merging binary neutron stars. This also shows where much of the elements heavier than Iron come from:

The gravitational wave signal indicated that the gravitational wave event was associated with the collision of two neutron stars[6][7][12][9] with masses between 0.86 and 2.26 times the mass of the Sun (solar mass). If a low spin is assumed, consistent with those observed in binary neutron stars that will merge within a Hubble time, this mass range reduces to 1.17 to 1.60 solar masses.[1] The total mass of the binary system was between 2.73 and 3.29 solar masses.[1]
The neutron star merger event is thought to be a kilonova. Kilonovae are candidates for the production of half the chemical elements heavier than iron in the Universe.[4] A total of 16,000 times the mass of the Earth in heavy elements is expected to have formed, including about 10 Earth masses of gold and platinum.[13]
It is not known what object was produced by the merger. Candidates are a neutron star heavier than any known neutron star today, or a black hole lighter than any known black hole.[11]

That is a LOT of precious metals...

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Mounts Questions & Expirience / What determines mount weight limitations?
« on: December 31, 2017, 02:18:03 AM »
I'm assuming a mount like the computerized Orion sirius which is rated for 30lbs. Is that weight limit determined by the motors in the mount, the tripod stability or balancing? Sorry if this is a silly question, and thank you for your help.

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General Astronomy & Observing / How do you plan for your viewing session?
« on: December 29, 2017, 02:29:47 PM »
How do you guys and gals here prepare for a viewing session? Is it a simple process or something more complex? I don't even have a telescope and view through binos right now. I usually consult deep sky objects browser, stellarium, and tonight's sky for ideas then move to my pocket sky atlas and binocular highlights books to finish it off.. I would assume that most telescope users have a certain routine to get ready for that night's viewing, what is yours?

Mike

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Beginners Forum / Need to pull eyepiece out just a little to focus
« on: December 28, 2017, 03:57:01 AM »
Hello, Is it normal to have to pull en eyepiece out of the holder just a little bit (and then tighten it down slightly out of its normal position) in order for it to be able to focus? I have an 8" Dob and I was trying out a wide FOV 12mm eyepiece, and it wouldn't focus unless It was a few mm out from being fully seated. Thanks!

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ATM, Optics and DIY Forum / 1870's 13.5" mirror
« on: December 24, 2017, 04:22:39 PM »
A friend connected with the Twitchell Observatory in Western Maine said that the mirror and scope might need a little attention.  Some discussion was concerning the glass substrate, and coat.

Here's a quote from the observatory's site: http://www.twitchell....org/home/about

"The telescope main mirror is 13.5 inches in diameter with a focal length of about 5 feet.  The mirror has had an interesting and varied history.  The mirror was originally crafted by H. C. Maine in the mid-1870's in Rochester, New York."

Anyone have experience with such mirrors?  I expect going to the website and want opinions on how to approach such a historical thing concerning determining if anything greater than recoat is warranted.

I am knowledgeable about basic star testing will begin with that, and will discuss the mechanical performance afterward.

C

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Beginners Forum / How to read seeing conditions
« on: December 24, 2017, 02:03:03 PM »
Hi, I had been wondering how to speed transparency and seeing requirements?  Just what are the things you look for?

I recently downloaded Sky Safari 5Plus and I would love to be a bit more accurate in my viewing logs rather than simply taking a wild guess.

In my mind, if I can resolve individual stars inmag 8 clusters and bring in colors of planetary nebula then seeing is 10/10, but I know that is much fromreality.

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Beginners Forum / An update to Burnham's? Whaddaya say?
« on: December 24, 2017, 02:00:37 PM »
Only got the first volume of Burnham's Celestial Handbook this day, and all I can say is WOW!  What an undertaking!  What a plethora of information!  What good descriptive commentary and background!  I'm currently hooked.

It is a really terrific read.  Very intriguing stuff.

BUT - ow!  My eyes!  A typewriter?  Really?  Come on!

I notice that I happen to have bought the 1978 "Revised and Enlarged Edition"; and there was a previous 1966 variant listed in the copyright info.  Evidently, this means there were buyers of this first variant to justify another version.  Isn't it time to get a third variant?

Is there no strategy, no movement, nothing in the works to upgrade this fine reference again for the 21st century?  There have to be 10 times as many amateur astronomers today as there were nearly 40 decades ago.  There would still be a market for a volume (well, three actually) such as this.

And they can do so much more with it to make it considerably more attractive - the least of which are a better typeface, but also colour photos of these objects, better charts, and updated info about the things which have shifted from the past nearly 40 decadesago  Keep all his prose but make the rest of it better.  I would imagine that all of the info that he provided on the double/variable stars might easily be pulled from computer databases and plugged to the book today.  New charts are a computer click away.

The Whole collection seems to be available at Google Books, here:

http://books.google....epage&q&f=false

So that I can't imagine there are that much trouble with copyright issues.

What do folks think about it?

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General Astronomy & Observing / Where can I find ...
« on: December 24, 2017, 05:18:19 AM »
... a precise place (website) for deepsky objects "distance".

There are various places to see the "deepsky distances", however there's a really major gap in certain value ...

I know it's hard to measure the appropriate distance, but like 22 Mly vs 50 Mly is a hugh gap for the same object at some software applications!

Regards and thanks!

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Beginners Forum / Altitude Adustment and
« on: December 24, 2017, 04:14:23 AM »
Except for the absolute noob questions, however I have not even had my first viewing session yet, and am studying hard to receive my mind around my brand new Sky Watcher EQ6 Pro.
My question is: I've just spent some substantial elbow grease wrenching the T-bolts to bring the altitude on the EQ6 in line with my latitude (47.03).  Am I supposed to leave the mount at this angle once I use my GoTo SynScan?  Or am I supposed to place the mount altitude back to 0 for SynScan, and only use the T-bolts for manual viewing?
Thanks,
Eno

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