Agronomy

[xilman]

(Moved from the happy me thread).

Just set up and looked through my telescope for the first time in several years. It's a Meade 25cm Schmidt-Newtonian and so it is just about portable. As it is close to local noon here, all I saw was the decrescent moon and the tops of a few trees. There was not much to see on the moon because of the low contrast and appalling seeing but at least Grimaldi was obvious.

Here's hoping the sky will remain clear tonight, even though it never gets dark at this time of the year up here in the sub-arctic.

Longer term aim is to hook up a web cam and take some images.

[xilman]

Originally Posted by xilman

Here's hoping the sky will remain clear tonight, even though it never gets dark at this time of the year up here in the sub-arctic.

Longer term aim is to hook up a web cam and take some images.

Eight-eighths here now, so no chance of observing and the scope has been put back indoors.

An old plastic pot with OD of 49mm is close enough to the 2" ID of the focusing assembly to serve as a mount for a cheap webcam. The pot now has a hole in the base and the entire interior surface painted mat black. The webcam has been suitably dismantled (primarily its lens and a protuberance on its front surface also taken off) ready to be glued onto the ad hoc adapter tomorrow when the paint will be dry.

With luck I'll be able to post some images next week when the moon is in a more favourable phase.

[Xyzzy]

http://www.space.com/16154-asteroid-...rth-flyby.html

[xilman]

Originally Posted by xilman

An old plastic pot with OD of 49mm is close enough to the 2" ID of the focusing assembly to serve as a mount for a cheap webcam. The pot now has a hole in the base and the entire interior surface painted mat black. The webcam has been suitably dismantled (primarily its lens and a protuberance on its front surface also taken off) ready to be glued onto the ad hoc adapter tomorrow when the paint will be dry.

With luck I'll be able to post some images next week when the moon is in a more favourable phase.

I'm amazed. Given my usual standards at DIY(*) I never expected the camera to work first time. The moon couldn't be seen --- too close to the sun and so too low contrast --- so the most distant object on which to practice was a tree about 100m away. Attached is a snapshot taken with the lash-up. With a 1016mm F/4 telephoto lens a remarkable amount of detail can be seen even at that range and with only 640x480 resolution and no post-processing at all.

Paul

(*) A commonly used abbreviation for "Damage It Yourself"

[Xyzzy]

When we were little, Questar used to have ads in National Geographic magazine, and we always wanted to have one of their telescopes.

Of course, for what they want for one, you could buy a real awesome telescope, but even still we think the Questar is pretty cool.

We also think this is real cool!

[cheesehead]

Originally Posted by Xyzzy

When we were little, Questar used to have ads in National Geographic magazine,

... not to mention Sky & Telescope every month ...

and we always wanted to have one of their telescopes.

Ah ... yes ...

When I was in high school, I found out that our school system had a Questar that students could check out and take home for a weekend. So, I did. Wonderful.

Of course, for what they want for one, you could buy a real awesome telescope,

(as true in the '60s, at $995, as it is now)

but even still we think the Questar is pretty cool.

Dreamy ...

[only_human]

Originally Posted by cheesehead

... not to mention Sky & Telescope every month ...

Ah ... yes ...

When I was in high school, I found out that our school system had a Questar that students could check out and take home for a weekend. So, I did. Wonderful.

(as true in the '60s, at $995, as it is now)

Dreamy ...

The El Camino College science club took a tour into Questar's Torrance facility that I attended. They were using red lasers to test collimation. I think they were using interferometry because they said something about half wave or quarter wave. They said something about them having a competitive advantage at the time because they found a way to get reliable precision more cheaply than competitors.

[cheesehead]

Originally Posted by only_human

They were using red lasers to test collimation. I think they were using interferometry

Collimation would use the straightness, rather than any interferometric property, of the laser beams.

because they said something about half wave or quarter wave.

Traditional mirror tests sometimes involve interference bands and can measure whether a mirror surface is within a quarter-wavelength of the desired shape, but do not need laser beams to do so.

One test of mirror shape, the knife-edge test, doesn't use interference.

Another mirror shape test, the fringe test (http://bhs.broo.k12.wv.us/homepage/a...getesting.html or http://bobmay.astronomy.net/johnpierce/part8.htm) does involve inspection of interference bands, but isn't really what is usually meant by "interferometry".

The fringe test is used for measurements of properties of an optical system, not measurements of the properties of distant objects.

Interferometry uses measurements by an optical system to deduce properties of a distant (outside the optical system, at least) object.

Interferometry can be (and is, nowadays, for expensive optics) used to test/measure optical systems, in ways differing from the classical fringe test. I don't know whether Questar was using it back then -- nothing in your description necessarily implies that it did.

They said something about them having a competitive advantage at the time because they found a way to get reliable precision more cheaply than competitors.

... which could have been through use of interferometry, or not.

[only_human]

They were looking for interference bands in laser light. There was splitting and recombining the laser light and observing things through an eyepiece that was part of the test rig. That is what my hazy and flawed memory thinks I was shown. I've never known what test was applied or term is appropriate for what I saw. I should have paid much closer attention. I would have liked to have seen some mirror grinding too but don't remember seeing any.

[Uncwilly]

I have been inside the dome of a 4.1 m scope and been inside the largest solar scope. Also have been to a company that produced an ~1 m Dobsonian back in the day. Have looked through the telescope that holds the record as the most viewed through (more people have looked through it than any other).

[LaurV]

Originally Posted by Uncwilly

I have been inside the dome of a 4.1 m scope and been inside the largest solar scope. Also have been to a company that produced an ~1 m Dobsonian back in the day. Have looked through the telescope that holds the record as the most viewed through (more people have looked through it than any other).

I went about 6-8 times to a tall mountain which holds the biggest Thai astronomical observatory. The mountain is really nice, with many waterfalls, beautiful landscapes, and paved way to the very top (you can drive with a normal car there, is exhausting for the car, hehe, but really convenient for lazy guys like me), and the fucking observatory was closed for public visits EVERY time. The guards told us that it will be open "next month". Every time.