Posts Made By: Erik Hammarlund

As I'm ordering my new truss Dob (12.5" f5) I'm trying to decide how many degrees to rotate the focuser.

By "rotate" I mean this: a zero rotation would put the focuser in line with the altitude rotation axis, would allow the focuser to remain horizontal at all elevations, and would mean that at low elevations you would have to crouch way down to view the image.

Obviously there's a plus for low elevation viewing if you rotate it. It's easier to look down than to crouch. But then again the rotation means that you look down (at least a little) all the time, which isn't as comfortable as looking straight ahead. I can see why normand fullum uses rotating tubes :S

Anyway, my old Dob was much shorter, which made rotation mandatory. I'm having trouble deciding what to get for a dob size I've never used. Any input from other owners on what they like (or don't like) and why? 45 degrees? 30 degrees? Nothing?

So there I was, reading Markus' ad for a 12" APO and--I swear--thinking "well that actually sounds pretty cheap for a scope and mount like that; this is a lot more money and a fair bit smaller"
http://www.buytelescopes.com/product.asp?t=&pid=1727&m=35
Then I thought "and Herb's 100k unit is pretty $$$ as well."

And THEN I thought "Wow, Markus's scope is really cheap".

Then I stopped. I realized that i had honestly considered a 120,000 dollar scope to be cheap. Oy.

Now I do that all the time (don't we all?) but recently I seem to be doing a lot of that for telescope stuff.

$80 for a TV 32mm plossl? Cheap! (never mind that you can get a functional plossl for half that)

$2400 for a new scope? Cheap! (the mirror and mechanics should be much better than an Orion 12.5", but are they $1500 better? A focuser only costs $300...)

On the other hand,

$24 for a haircut? Madness! (never mind that they take a full 30 minutes, do a great job, and that I'll only save $10 by driving 20 minutes and waiting in line at a no-appointment place which gives middling cuts).

And so on. Am I alone in my illogical cognitively dissonant world? Or do I have company? 8)

I'm trying to decide which things to put on my new scope. It's hard to do (surprise, surprise) and I can't afford them all--that would be too easy. It's time to poll the audience. I'm putting in prices because they're extremely relevant.


For a 12.5" dob, how would YOU rank these? And why?

THE LIST (in no special order)

-Paracorr, $275
-2-speed Moonlite (instead of 1-speed), $100
-Wide angle EPs--probably Panoptics--instead of Plossls, $150 per 'trade'
-Sky Commander, $500 or so installed
-Moonlite tri-knob upgrade for 2-speed, $40
-Filter slide to encourage actually using the damn things, $150 including new 2" moon and planetary filter
-Tracking platform, $500
-'Observing' chair instead of cheap 'regular' chair, $150
-Low-end 46mm field stop 'finder EP', $50
-Right angle 9x50 finder to supplement Rigel, $75

All opinions encouraged. Thanks!

1) Good to have HH back.

2) Astromart's credit card scheme is good.

3) For the "only verified emails make me happy" people: HH's "verified ISP" won't give you his address, or phone number, without a warrant. Hell, there's nothing to prevent him from giving his school a fake address and number. Should someone using an alumni address 'go rogue', they're almost as untraceable as if they used their real name and a Yahoo address. And they're much LESS traceable than with a credit card.

the press doesn't distinguish between private folks and government. That's important. REALLY important.

But when you do bring up government, some folks (Christians, mostly) start spouting the whole "government expression of religion is OK" stuff. Now, some people simply disagree with the general premise of separation and feel that any majority should rule. But my experience suggests that most of those who oppose limitations on government expression of religion are often secure in their majority role.

Let's find out.

An exercise which is useful to those with open minds is this: Choose a religion which conflicts strongly with your own beliefs, perhaps even one that you find extremely distasteful. Many Christians might choose Satanism; perhaps the worship of Anubis or Odin might be popular. Or imagine all three.

Have you done that? Good. Now:

Imagine that overnight, a vast grassroots movement has converted a supermajority of elected officials and 90% of the public to this religion. Unfortunately, they have decided to adhere to a conservative view. Which is to say, for this exercise they'll have the commonly held view that government and its officials should feel free to express themselves, minorities be danmed. And hell, why not--they all love to express it in private, too.

In the main town square, there's an inverted cross, a sacrificed goat on the altar, and the smoldering entrails of a calf accompanied by priests auguring the new year. Depending on your personal opinion of other faiths, it might be towering over a much smaller "had to let them in" creche, menorah, and star.

Government officials smilingly wish you a happy "Slaughter of the False Messiah Day" on Easter. National and school vacations have been moved to accomodate the ancient Egyptian calandar, and your child is occasionally penalized (or ostracized) for taking Christmas, and other Christian holidays off.

Your public school play now takes place at the fall equinox, and focuses on the antics of Anubis, or perhaps Odin. Your child is torn between playing a part which disagrees with her beliefs and staying home away from friends. Though even you must admit it: the music to "And Those Who Do Not Worship Idols Shall Be Disemboweled" is quite pretty.

When you go into the town hall, town square, and perhaps even the courthouse, trapping of other religions are everywhere visible, year 'round. Your public officials make no attempt to hide their religious faith, and you are concerned that they may marginalize your views based solely on your beliefs--even if your opinions are objectively valid. When your building permit application is turned down, although the rejection seems legitimate, you wonder whether your status as the only local non-worhipper of Cthulthu had anything to do with it. Or perhaps the fact that you choose conservative dress instead of the striped pink robes preferred by His adherents.

Ain't life fun?

You may protest this is unrealistic (and if you're Christian, it's unsurprising you would say that). But try the exercise nonetheless. And welcome to the world of a religious minority in America. Do you understand yet why the private/public argument is important?

You know, I was just thinking as I read the various posts passing off the civilian deaths as "collateral damage". Plenty of people here seem to subscribe to the notion that it's OK to kill civilians, so long as your UNDERLYING objective is to kill the enemy. Hey, it happens all the time, must not be so bad, right?

So, that got me thinking about numbers. Collateral damage fans, this is for you. You don't even have to explain your numbers, if you don't want to. Now, this is an odd hypothetical. But DON'T FIGHT THE HYPO, as my professors used to say, or the point is lost...

You have a room. In the room is a bomb, which will kill everyone in it when the button is pressed.
How many innocent Iraqi or Afghan civilians would you be willing to send into the room to get the following persons(s) in there as well?
Remember, it's an 'all die or none die' hypo here. Only a few numbers; DO try to answer them all...
Edited: Just as in real life, the civilians don't volunteer. Random selection from the population; men, women, and children.

1) Osama Bin Laden
2) The top 5 Al Quaeda leaders other than Osama
3) A random, unidentified "member" of Al Quaeda (could be Osama, could be an accountant)
4) The top 5 members of the Iraqui resistance movement
5) The entire membership of AL Quaeda
6) The entire Iraqi resistance. Yup, all of them. We can go home.

Great, you answered them all! Now, let's add to the hypo a little:
Everyone you want to kill is in the U.S. It'll be U.S. civilians who go in the room. Do your numbers change?

I think it's an issue of physics rather than optics. Tubes, by design, are equally resistant to bending forces in all directions. Angle isn't exactly so, but is strong enough so it doesn't matter.

Although I haven't tried aluminum bar stock for trusses, my experience with it elsewhere (mostly on boats) suggests that it simply isn't a good choice: too bendy, or (if you make it strong enough) too heavy. Take that same mass and put it into a tube and the strength goes up an enormous amount (just ask the makers of Cannondale bikes).

Obviously it'll be strong as heck in the long axis... but unless you have extremely good mounting you'd be subject to torsion (in which it won't be taht strong) or bends in the short axis.

Of course, if you design it right it technically wouldn't matter since everything's theoretically in direct tension or compression--the wonders of triangles. Still, "in theory, theory and practice are the same. in practice, taht is rarely the case". Given the wide range of tubes and angles available, I'd wonder why you'd bother.

Not incidentally, you could acheive a similar look by using an aluminum I beam cut lengthwise down the "I". You'd get two "T" strips per I beam. If you grind the T flange down a lot, it's still MUCH stronger than a flat strip but you can put the flange on the inside where it won't show. Grinding the T off entirely at the top and bottom make it possible to moung but don't affect the overall strength taht much. It'll look like flat strips from the outside but work like angle stock.

You have $25k, or about $2k per team.
First:
Get each team
-an orion 8" f6 dob with autostar (take it away to teach star finding, give it back for quick lectures on DSOs). Or just get 6 autostars.
-An Orion ed80 on an alt/az mount
-A couple of functional but cheap UO Plossl eyepieces and a decent barlow for the short tube.
Total cost $1000 or so/team

Second: get each THREE teams a 5" f12 or f15 D&G refractor on an Atlas mount. You can end up with four of these. maybe only three if you add some more extras like eyepieces. Definitely four if you sell the AP focuser and replace with lower end but still nice version (don't need that much precision at f15 anyway). If you sell the AP focusers and stick with 3 scopes you can get more barlows, more eyepieces, nice finders, etc.

You ended up with
12 dobs. Handy, indestructible, low maintenance. Good light gathering. Functional DSOs. Kids can learn about mirrors.
12 apochromatic ST80s. portable, good for field trips, good for moon, wide scanning, learning sky.
3 long refractors. Great views, wonderful for planets. Look cool.

Also: Can anyone easily describe how to check a binoc for collimation? I have trouble merging images at times, and I'm not sure whether it's me or it.

Ya, 6" dob. Get the Prion, so you can add the hand controller now/later if it becomes an issue. if you have extra cash, just get a nicer eyepiece set. It's so light, and so simple, that it'll be used all the time.