collimation, a question

astrum (tony) · #1 26-06-2008, 12:33 PM

when i used to hunt little furry animals with a rifle many years ago we had to collimate a new scope first,then adjust it(fine tune) on a fixed target........

question is: it sounds like just about every new scope on here needs the mirrors collminated, am i right? isnt this a bit ,um bodgy? shouldnt a new scope come completely and accurately focused? (fleabay stuff aside lol) or am i missing something like usual lol.

mark3d · #2 26-06-2008, 01:06 PM

mine came fairly well collimated i think i initially made it worst like a lot of people.

even taking it outside affects collimation.. a long ride in the car on a dirt road especially..

its fairly sensitive

erick (Eric) · #3 26-06-2008, 01:47 PM

Tony, I suspect they could be a lot better, if the mechanics were super robust and precision pieces of work. For the price we can pay, they are not - they are pretty rough bits of work at this low end of the market, certainly not "precision german engineering". Regardless of the flash paint jobs and fancy stickers! So screws wobble, springs are pretty weak, tubes and bases can flex etc.

We'd rather pay the money for good optical surfaces and put up with the face that we have to play with the mechanics to get the best out of them. Collimating a basic newtonian reflector to acceptable, even good performance, is straightforward, even without the mods we make.

But even the best scientific equipment (I worked on million dollar mass spectrometers for years) needs calibration and adjustment.

Eric

renormalised (Carl) · #4 26-06-2008, 03:22 PM

It would be nice, though, if just for a change, the makers of some of these scope would take the time to make them robust enough to take a bit of whack. Or designed robust enough mirror cells so that when they collimated them in shop, they stayed reasonably well collimated when it was delivered to you. It might mean paying a bit more for the scope, but so what.

erick (Eric) · #5 26-06-2008, 03:38 PM

My experience is that my 8" and 12" GSOs, once collimated, survive long trips to the country - the 12" in a trailer - without going far out of collimation. I have the secondary holder held firmly in place with the three collimation screws tightened "against" the centre screw, and the three "lock screws" tightened on the primary mirror cell during transport. They sit variously on carpet, blanket, styrofoam for transport. So I'm satisfied, given I'm able to tweak as necessary, once setup.

It's a good question as to how much more one would pay to get superb mechanicals and engineering. Based on the cost of Takahashis and Obsessions etc, I have a sense that 10 times more would be likely. However, based on the fixes people sometimes employ to great effect (eg. stiffer springs), you would imagine that an extra 20% spent on them might make a significant difference?

renormalised (Carl) · #6 26-06-2008, 04:29 PM

That was the sort of price difference I was thinking about...20-50%. It's probably not feasible to look to getting absolutely superb mechanics and engineering, unless you were prepared to pay the premium that you'd expect for such quality. However, it would be good to see the manufacturers up their ante a bit and make something a bit more usable out of the box, so to speak. Most people wouldn't expect to have to tweak the mirrors, modify or fix the rocker box, or replace parts that weren't quite good enough...straight out of the box. That's why a lot of people become disappointed in the equipment they've bought, especially those only new to the hobby.

astrum (tony) · #7 26-06-2008, 11:12 PM

oohhh! sounds like more than a few people agree with me.lol having worked in a toolroom for a number of years im well versed in the need to calibrate things,was just wondering why it seems nearly all new scopes seem out of whack so to speak lol.
as long as collminating isnt to hard or/time consuming i dont think ill have an issue with it.was just wondering........

erick (Eric) · #8 27-06-2008, 10:11 AM

Quote:

Originally Posted by astrum

as long as collminating isnt to hard or/time consuming i dont think ill have an issue with it.was just wondering........

Tony, with a basic reflector, and presuming nothing has gone terribly wrong, collimation to achieve good visual use takes minutes.

astro_nutt · #9 27-06-2008, 07:29 PM

Hi Tony!
I guess the practical side of design for the mass produced Newtonian Reflector is to make it easy to use and to transport. Otherwise they would be too heavy unless permanetly set-up in an Observatory. Yes, some bits do move and require adjustment..imagine if the factory made an error in colimation and you had to send it back to have it adjusted by them!!
Better to do it yourself...whenever you like..then enjoy the views!!!
Cheers!

astrum (tony) · #10 29-06-2008, 01:02 PM

hmmm thanx eric and nut,starting to make more sense now. is a laser collminator better or just eye it up?

erick (Eric) · #11 29-06-2008, 10:02 PM

Tony, if the secondary mirror is correctly positioned under the focusser (using a long sight tube is best), then using a laser is a convenient way to complete good collimation. I prefer the style with the viewing window on the side and the 45 deg angled surface to see the returning beam. Then it's a two step job to adjust the secondary then the primary, being able to see the results of your adjustments in each case.

Laser itself need to be collimated (check it bu projecting from a "V block" to a wall say 4-5 metres away, then rotate and see if the bean stays in a tight circle. Secondly, laser needs to be a snug fit in the focuser/adapter. I have a layer of "contact" around the barrel to make it a tight fit.

Many prefer a cheshire collimator to a laser. Many use a technique called a barlowed laser which improves accuracy. I have both and often use both to check final collimation. It's always good enough for what I want, after simple laser collimation.

astrum (tony) · #12 02-07-2008, 12:46 PM

hhmmm thanx eric, seems the more i ask,the more i uncover....

this is one of,if not the most,friendly forums im a member of.a credit to you all!.

still looking for propertys to buy,so i wont be getting a new scope for a while,at least till i move into my house.id love to set up a perm or semi-perm viewing area but i suppose it depends on the amount of light pollution were we end up.

bird (Anthony Wesley) · #13 02-07-2008, 01:21 PM

Tony, the main differences between the rifle scope you remember and a modern telescope is mainly in the size of the optics (diameter) and the amount of magnification.

Modern scopes with large diameter mirrors have to be collimated much more precisely than small scopes, as the allowed error for light coming from the edge of the mirror is much less than light near the centre, and the larger the diameter the smaller the allowable error.

It's likely that an 8" reflector is about 50x more critical in it's tolerances than the small scopes like those used on rifles. If you don't get the collimation spot on with the large mirrors then you see a blurry mess.

Typically the reflected image from the primary has to end up within a few mm of the exact centre of your focusser, and this is hard to do with low cost scopes and have it stay there as you point to different parts of the sky. Many people recollimate as a matter of course when they move the scope a large amount since that's just the easiest solution.

cheers, Bird

psyche101 · #14 10-07-2008, 10:34 AM

Getting game, thinking I better learn more about this scary sounding stuff.....

I have been perusing sites looking for a kit, as looking through the threads here, that seems the way to go. However, no site seems to come up with anything when I search for "Collimate Kit" comes up with confusing results. Eyepieces, laser pointers, lots of jazz I am not sure if I need or not. Is there a "Kit" form of tools one can purchase, or is it a personal collection sort of thing one defines over time?

erick (Eric) · #15 10-07-2008, 11:55 AM

I recommend that you start with a Cheshire Collimator and follow its instructions. Most people seem to like the Orion Collimating eyepiece (around $69). Maybe you'll try different approaches and tools as you see other people using them?

psyche101 · #16 11-07-2008, 10:40 AM

Quote:

Originally Posted by erick

I recommend that you start with a Cheshire Collimator and follow its instructions. Most people seem to like the Orion Collimating eyepiece (around $69). Maybe you'll try different approaches and tools as you see other people using them?

Thanks (again) Eric. I was not sure where to start as I read about laser pointers and colliimation tools, but it seems all I need is a collimation tool. Not that I think the scope needs it right now, but no doubt in time, and when I least expect it... I am struggling to get to star parties, I work fairly long hours and have a young family, but I hope to get to the big one (IISAC) in Lowstock where I hope to get some first hand knowledge from the more experienced gazers - already doing ground work with the wife on that one

. However, upgrading recently to the 10" Dob seems to have brought the heavens a little closer, and given me a deep appreciation for deep sky viewing. I am amazed at how well my Celestron 4" GT performs next to it though. Darn good scope that one. I found a SSWOLL tool for $70.00 on the web in a shop fairly close to me, I will pick that one up, and take the bit between the teeth

Thanks for all your help, I have taken to "just swinging" my scope around the sky as you suggested and have discovered a treasue trove I didn't know existed. The Butterfly cluster was my first Dob deep sky, and I rarely miss swinging across to see it on a viewing night. I feel a little silly now, but at the time I was so excited at it's beauty I ran in and dragged the whole family out to see this wonder. Each one expressed awe. I have found many objects scince, proud I managed to spot M13 (I am pretty sure), and the Orion nebula. Now that was really something. Now my next big goal is to spot myself a galaxy. Great stuff, not so keen on the cold at the moment.....but may have to brave it to see Mars and Saturn tonight. Getting there at my snails pace, but enjoying smelling the roses along the way

erick (Eric) · #17 11-07-2008, 11:07 AM

Quote:

Originally Posted by psyche101

Now my next big goal is to spot myself a galaxy.

Can you get up early!!

Around 5am - M31 (Andromeda Galaxy) almost directly north, up at about 22 deg elevation from your location. If it is dark enough, you may catch a glimpse of it naked eye - otherwise a pair of binoculars should locate it for you. (in fact, you will probably have 2 or maybe three galaxies in the FOV - research M32 and M110)

Roger Davis · #18 11-07-2008, 11:17 AM

The best collimation systems do not use springs because they add an element of flexure.
There is a name for the mirror which is supported in a system that can hold a piece of glass whilst remaining totally inflexible, it's called "glass shards".
The reason for the movement is to absorb any shock that may be imparted to the optical system. So for a portable scope some movement is needed.

Remember collimation: Square focuser to optical and mechanical centres, then adjust your secondary and then finish with the primary.

I'd love a dollar for every cheap rifle scope that has come to me with imparted shock damage.

psyche101 · #19 11-07-2008, 11:28 AM

Quote:

Originally Posted by erick

Can you get up early!!

Around 5am - M31 (Andromeda Galaxy) almost directly north, up at about 22 deg elevation from your location. If it is dark enough, you may catch a glimpse of it naked eye - otherwise a pair of binoculars should locate it for you. (in fact, you will probably have 2 or maybe three galaxies in the FOV - research M32 and M110)

Thanks for the heads up!! I get up for work about quarter to 5 most days and try to sleep in a little on week ends. (when the kids let me

)

Not tomorrow

Think I'll get the Dob next to the door tonight for an easy setup nice and early.

psyche101 · #20 11-07-2008, 11:30 AM

Quote:

Originally Posted by Roger Davis

The best collimation systems do not use springs because they add an element of flexure.
There is a name for the mirror which is supported in a system that can hold a piece of glass whilst remaining totally inflexible, it's called "glass shards".
The reason for the movement is to absorb any shock that may be imparted to the optical system. So for a portable scope some movement is needed.

Remember collimation: Square focuser to optical and mechanical centres, then adjust your secondary and then finish with the primary.

I'd love a dollar for every cheap rifle scope that has come to me with imparted shock damage.

I was thinking of ducking out later today to pick this item up.

http://www.yorkoptical.com.au/Produc...%2cProductName

Look OK?