Image of the day

From the
ATWB Customer Gallery

Great Horned Owl

My Account

New to Astromart?

Register an account...

Need Help?

Laser Collimator Dot Shape

Started by SocalDarkSkies, 01/26/2007 01:11PM
Posted 01/26/2007 01:11PM Opening Post
Hello everyone!

I need some other opinions and couldn't think of a better place to post this.

I just sent an Orion Deluxe LaserMate to another Astromarter and he's concerned about the shape of the emitted dot. Below is his letter and under that is my response. Anyone else have a take on this?

*******************
Hi Jery,

Okay, I got the laser yesterday. It looks to be in great condition. But when I shine it at the wall from 5-6 ft away, I see 3-4 points of light making a tight circle instead of one point. I don't think that's good. I tried doing it at the approximate distance of my secondary from the holder (7") and it then appears as a short line instead of a point. I think something may be out of whack. I'll try to talk to Orion today and get back to you.

Paul

*******************
Hey Paul,

All of the consumer lasers I've had access to show a less than perfect dot (laser pointers, both of my collimators, laser sites for handguns). The important factor is: does the dot fit back into it's originating hole when you collimate your Newtonian (my EZ collimator shows a little fuzzy corona when it goes back inside its hole... almost like a total solar eclipse). That and: is the dot centered within the axis of its housing (I'm very confident that the unit I sent you is tack on).

All that being said, if you are not happy, then let me know. Go ahead and send it back to me and I will re-PayPal ya.

Call if you feel it would be easier (949) 858-xxxx. Another thing you might do is to post this question on the Astromart forums and let everyone else chime in. As a matter of fact, I think I will post this in the Equipment Forum now. Take a look when you can.

Thank you!

Jerry

*******************
Posted 01/26/2007 11:50PM #1
I had noticed the same thing with both an Orion laser and one from Agena. They both produced a short line instead of a round dot. Also the Orion also had what looked to be a cresent shaped moon under the line. I took them apart to see if there was something that could be done. First thing I noticed was that they both looked like the same thing the gas stations and corner party stores were selling. The man at the corner party store let me go thru his supply of lasers untill I found two that produced a nice round dot on the wall at about ten feet away. I paid $2.50 each for them, built a V-block to collimate, and now have standered and deluxe units that form nice, clean round dots when I use them.

Roger
Posted 01/31/2007 09:04PM #2
Hello All,

Well, my LaserMate came back today and I took a look to see what was wrong. Right after sending off a refund I popped the thing into my 8" f6 Newtonian and took a few shots.

Attached are some quick images. What's the consensus? Is this a working tool? I kinda feel it is. I certainly do not see "3-4 points of light making a tight circle" when the laser is pointed at a wall 5' away.

Thanks for all your input so far.

Jerry

Attached Image:

SocalDarkSkies's attachment for post 111254
Posted 02/01/2007 07:12AM #3
Just a short bit. What you all are refering to is TEM or transverse electromagnetic wave of the laser. Inexpensive diode lasers haven't the best TEM figure. A good laser has a TEM figure of TEM 00. The 00 is usually shown as a subscript but I can't type that here. TEM 00 is a nice round spot, with TEM 11 not so great.

The other item you're referring to is called a spatial filter, the hole thingy. It's used to stop down the straying beams. A spatial filter's aperature is about 0.010 inches in diameter for your size lasers. It's critical to position the aperature to the beam. Usually four adjustment screws, up down, left right are used. This way you can project the beam to a target and then adjust the spatial filter such that you get a nice round spot.

You can make a spatial filter with a piece of tin foil. Take about ten small cut pieces of tin foil and stack them. Poke a hole in the center of the stack with a pin, but just barely with the pin point. Use the piece of tin foil in the middle of the stack. It's an old trick used in the lab.

How you position this spatial filter in front of your beam is up to you. Not sure how you'd do it.