Finderscope turned Guidescope

Last weekend I went out to do some imaging and was having problems with my guidescope.

I used a super long 60mm Tasco with a webcam mounted to it. It worked okay, but it wasn’t working so great with the clouds, and it did not help that I was imaging near the zenith. That meant that the webcam was near the ground. I spent so much time laying in the dirt that night that I had to come up better solution.

With a little online research on forums (www.cloudynights.com) I started reading about people using their finderscope as a guidescope with good results. This appealed to me because of its small size, wider field, and its easy mounting. Since I had all the necessary parts already, I decided to give it a try.

I had an 8X50 right angle Zhummel finderscope so I decided to give it a try. I was able to unscrew the mirror portion off of the finder, and also the piece that attaches that to the tube.

I had to figure out how to mount the webcam to the finderscope. I attached a .965 eyepiece barrell onto the webcam (from a Tasco-originally to use in a Tasco 60mm). It simply screwed on the existing webcam lens assembly. I added some epoxy to hold things down nice and tight.

I was able to unscrew the right angle mirror and viewfinder. Luckily the crosshairs are attached to this part.

I was trying to go as low budget as possible so I went to Home Depot and picked up two PVC parts. One piece fits snug inside the finderscope tube. The other piece fits snug inside of that and has an opening that a .965 eyepiece barrel fits into perfectly. I first did dry runs of everything.

Camera to adapter

Camera and adapter to sleeve

Now that I knew how I was going to mount everything I now could figure out where the webcam focused and position the webcam accordingly. Since I am able to adjust the objective lens by screwing it in and out, I will have some working room for focus. I wanted to position the webcam in the middle of where the objective lens would focus.

I had to sand down some edges to get the parts to fit perfectly. I like to take off as little material as possible. You can’t add material once you’ve gone too far. I sanded and tested, sanded and tested. It did not take too long since PVC sands easily.

Before I glued everything, I made sure I was able to focus. I also took a took a few shoots with the webcam to make sure the focus was right on.

After the glue dried I painted everything flat black with spray paint.

I took the oportunity here to make sure everything was clean before I did an instal. And since my tolarances were so tight, I had to do a little sanding after the paint dried. I was able to press fit the PVC adapter into the finderscope tube without having to add screws to hold it into place. No slop here!

Here’s the unit all together. A 1.25″ eyepiece cap fit the finderscope adapter perfectly.

Here is the completed product. I threaded three screws to really hold down the webcam. I also removed the plastic screws in the finder mount and changed them with metal ones. I also added a third screw next to the spring push to tighten everything down once a guide star is found.

Remember to get everything nice and tight, you want to rule out any slop (flexure) that can a ruin your guide setup.

On my first attempt a couple of weeks ago, I could not get it working. The calibration failed. I later realized that the telecope would have to move more when guiding because of the short focal ratio of the guidescope. A simple tweek in PHD from 750 to 1000 for the calibration step size was all that was needed to get this working.

Now I have a small light weight easy to setup guidescope! And it all fits in my Fat Max toolbox. No more laying on the ground trying to get a guide star.

This weekend I tested it again and I was always able to find a guidestar within the adjustments of the finder.