HOW TO MAKE A BARLOWED LASER TARGET

 

Gene Baraff has a good document on how to make a target that will work for most any telescope.  There is also a copy on the Skyquest group.

Another suggestion that just popped up on the Skyquest group was a spray paint can lid.  You could use any plastic cap that fit the draw tube of your focuser.  A white one would be ideal.  They usually have a dimple conveniently located right in the middle of the cap.  Drill an 1/8" or so hole right there, put some black magic marker on the inside to prevent any leakage and you're all set.

I made an extremely simple peep hole thingy for the barlowed laser out of index cards.  I taped 2 index cards end to end with scotch tape and rolled them around the outside of the bottom of the draw tube (I took the draw tube out of the focuser for convenience).

A little scotch tape once I had it wrapped firmly, and I have a nifty tube that is quite sturdy and the perfect size.  Now I just put the focuser draw tube bottom on a stack of 5 index cards and cut out 3 perfectly sized and matched little index card circles:

This worked great because the circles were the exact size and shape to match the inside of the paper tube I had made earlier.

Now you have to blacken both sides of 2 of the index card circles to keep the barlowed laser from leaking through outside the center hole. I did this with the kid's crayons. 

Next, I slid the index card tube over the bottom of the draw tube until it butted up against the bottom of the rack. I left the index card tube about 1.5" long for strength, but that's certainly not required. I then slid the index card circle that had no black on it inside the paper tube until it was flush with the bottom of the draw tube. Now, where to put that darned little hole and how big to make it? I just put the Orion laser in (not barlowed), turned it on and used that spot size and position as a guide. I checked this later with the cheshire ep and it matched perfectly. I'm not sure how critical the exact placement of this hole is, but it seems critical, so I was careful to get it right in the center. You could also do the fold the circle twice trick and the intersection is the middle.

I cut a hole through all three circles at once with a sharp exacto knife. Glued the circles together with the kid's glue stick. Now I put the circles in the paper tube with the black ones up and the white one on the bottom. Scotch taped them in, and voila, a most excellent barlowed laser spot placement thingy. Works like a champ.

The best part was wiggling the focuser and laser all over the place and the shadow of the center spot never moved on the most excellent barlowed laser spot placement thingy. That is truly spectacular.

Anyway, this looks like the way to go for primary alignment. I'm tickled pink.

Well, my MEBLSPT did not survive the heavy dewing last night. For those that might remember, it was made of index cards and scotch tape. Worked great for the winter and spring, but, alas, summer dew has caused its untimely demise.

So I replaced it with the NIDPMEBLSPT (New and Improved Dew Proof Most Excellent Barlowed Laser Spot Placement Thingy). It's the same concept but this time I made it out of one of those flexible cutting boards Gene recommended for an aperture mask. Here's a pic:

I used electrical tape to secure the center piece of plastic. I put electrical tape on the inside (facing the laser) to block stray laser light from getting around the hole. I put a piece of carpet tape across the middle outside for the return donut. This may get replaced with white electrical tape if I can find it in the work bench.

Much sturdier and dew proof. So, if you have built or were considering constructing a MEBLSPT, I highly recommend going with the NIDPMEBLSPT if you are expecting dew.