Saturday, September 4, 2010

Daisy red dot finder modifications

The Daisy red dot sight (the best price I've seen was about $8 at Walmart, but last I checked, my local stores didn't have it) makes a decent non-magnifying finder for telescopes. I have them on two of my reflectors, and the third reflector has the Galileo version.  Mounting requires a dovetail.  One option is to take a piece of wood of the right thickness, and then file a roughly shaped dovetail.  Another option is to take a piece of wood, and screw on washers of the right size for the dovetail to fit around.  It's a good idea to mount it offset from the scope for comfort.

A few modifications make the Daisy finders nicer to use.

1. Resistor.  The stock sight is designed for shooting in daylight, so the red dot is too bright for night use.  You can solder in a resistor (I think probably 2K-5K ohm, depending on taste), or you can fold a resistor in half, put a piece of paper between the leads, and put this resistor sandwich between the battery and a contact.  Even better, you can buy a 5K or 10K ohm trimmer pot (e.g., at Radio Shack), drill holes for the leads, and solder wires in place.  Then you can adjust brightness.  The photo shows the version with the pot.

2. Altitude/azimuth adjustment.  The stock sight needs a screwdriver for adjustment.  Since the sight needs to be adjusted from time to time (or even every time, as on my 13" split-tube scope), and using a screwdriver in the dark is no fun, it would be nice to have tool-free alignment.

On the Daisy that's on my 13", the azimuth adjustment screw has a hex nut (attached with some thread locker, I assume) that can be easily turned by hand.  Only the altitude is an issue.  What I did for the altitude adjustment is I removed the screw and turned it upside down so the hex nut is on top.  That nut wasn't big enough to turn with comfort, so I used Super Glue (or some other cyanoacrylate glue) to glue a larger hex nut on top of it.  Works just fine by hand.

The Daisy on my 8" is an older model with round (!) nuts.  The adjustment screws are #6-40, a bit less than an inch in length.  Amazon's Industrial and Scientific store had a really cheap pack of 100 black nylon socket cap screws (about 50 cents), so I got that.  I was a bit worried if nylon screws would work well.  But they did.  The azimuth adjustment was straightforward: I just replaced the stock screw with the nylon socket cap screw, and the knurled head of the screw nicely turns by hand.  The altitude adjustment was moving poorly with the first screw I put in.  I removed it, and put in another, and it was fine.  Maybe there was something wrong with the thread in the sight, or maybe the screw wasn't good.  But, hey, I had 98 others at that point.  Looks good, too.

Finally, I trimmed the screws right outside the nuts by cutting them with kitchen scissors.  That also spread out the ends of the plastic screws, which should keep the nuts from coming off them.  But for good measure, I took a soldering iron and squashed the part sticking out of the nut, so the nut wouldn't spin off.  (If I need to exchange screws, I can always trim with box cutters.)  I went for nylon screws in the first place because they were so cheap, but in this application, they're also easier to work with (no need for any thread locker or hacksaw), and they won't rust.

The only issue is that (as of Sept. 4, 2010) the price on the screws has gone up to about $6.  Fortunately, they still have a pack of 50 of white versions of these screws for 82 cents.  If you have Amazon prime, or are doing a $25 order, the shipping will be free.  (If you can't get free shipping, you can paypal me the price of a stamp and if I still have enough, and there aren't too many requests, I can send you two of the black ones.  And maybe even a resistor if you want.)

3. Removing coating.  The stock sight comes with a lens that's coated with a dark reflective coating.  The sight is still usable, but you can't see dimmer stars through the lens.  That's not a big problem as you can keep both eyes open and see the stars with the other eye, but stripping out the coating is a nice idea.  This was hard work--about an hour for each sight I did this to.  And one of my sights now points differently from before--I don't know why.  To get it aligned with the scope, I had to angle the dovetail mount on the scope quite a bit.  The image also isn't as neat a dot (and some have seen ghost images).  All in all, I still think it's an improvement, though just barely worth it given the work.

The first step was to remove the lens--I can't remember if there was more than one.  There is a plastic retaining ring holding the lens in place.  Remove that first.  I did it by use of a jeweler's screwdriver, wedging it in behind it.  Once when I did it the ring got creased--it's not so strong--but it was still fine.  Be careful that the lens not fall out, as you will need to note the direction the lens is pointing.  Then remove the lens assembly.  Make careful note of the direction in which the lens is pointing--one side is coated, and the curvature is only on one side.  If there is more than one lens, do it for all of them.

Now, it's time for the hard work of polishing off the coating.  I don't have a satisfactory method.  I used two different polishing compounds: toothpaste plus water, and baking soda plus water.  Generally, I first did the toothpaste, and then moved on to the baking soda.  I applied them with denim.  I did this by hand, which was slow and inefficient.  The other thing I tried was to wrap the cloth with polishing compound around the handle of a screwdriver, duct tape it into place, load the screwdriver blade into a drill, and run the drill.  Eventually, you notice that the coating in the middle is disappearing.  It's really frustrating to get every spot off near the edge.  Some you may just want to live with.  Once done, wash, dry and put back in.

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