Sunday, February 14, 2016

Celestron Astromaster 130EQ

Red dot finderscope update

This is the red dot finderscope that comes with the Celestron Astromaster 130EQ. Is not a secret that it is a nightmare for beginners and hated by experienced amateur astronomers to the point that many of them refer to it as junk or useless. 

For me it was not a total failure. I just need to always choose the same right spot behind the scope to align both the red spot with the star or planet in the sky and the telescope. The problem comes when the star can’t be seen through the finderscope. In very light polluted skies stars below 2nd magnitude are difficult to see with the naked eye and because the red dot can’t dim the light, those stars are difficult to spot with the finderscope. Then the option to star hop is severely reduced when one starts with just a few stars in the sky. A better option is to have an optical finderscope so stars invisible to the naked eye will appear in the FOV. 

Many stargazers can live with the red dot finderscopes and a wide field eyepiece to do star hopping, but if you want to update your finderscope I will provide a quick tutorial to set a dovetail base bracket (also known as shoe bracket) that allows you to set an optical finderscope such a 6x30, 8x50 et al. I myself ended setting a 6x30 which I think is a good size that allows seeing enough for star hopping but an 8x50 will be much better. Personally, I also wanted to avoid putting more weight to the EQ mount because it is not a secret that it is already a bit overloaded with the original setup. 

I will also recommend getting a RACI (Right Angle Correct Image) finderscope instead of another one. When looking at objects near the zenith it is more comfortable, so you won’t have to twist your neck and hurt your back. 

Let’s start with the process…

1. Equipment. Set of Allen keys phillips,
screwdriver, tape, tape measure or ruler,
pencil and drill with metal drill bits
2. Disassembling the scope. Drilling the tube is the easiest way to end up scratching or breaking the mirror. I found the best way to protect them was to remove them before starting to work on the tube (OTA).

The focuser uses 3 Allen screws to stay attached. They all had a nut inside the tube so a suitable position to take off those screws is with the front of the OTA looking at the floor.

There is considerable space in the windows of the secondary mirror holder (spider) so as long as the hand fits it is better to hold those nuts while loosening (or tightening) the screws. 

Internal edge that keeps the
primary mirror and base from
falling inside the OTA
To take apart the primary mirror, unscrew the black Phillips head screws that are in middle of the double set of galvanized “screws”. To not lose collimation, do not touch the double set of screws and using tape set a mark on the OTA and the mirror so that you can place the mirror in the same position when you put it back. 

This step can be done with the OTA looking at the floor. There is an internal edge that will keep the mirror from falling into the OTA after removing the screws.

I did not want to remove the secondary mirror. I found that a big problem and potential a collimation nightmare, so to protect it I just taped a piece of paper inside the tube, behind the secondary mirror and it was more than enough to protect it. 

3. Drilling holes. For myself, I found the best spot to place the shoe bracket was right behind the old red dot finder using the edge of that plastic piece as a guide. I also kept the red dot in place, but you can get rid of it by unscrewing it and use a knife or a little saw to cut off the cylinders where the screws go. 

After choosing the spot, make sure it will be right and parallel to the OTA. Most finderscope mounts allow some millimeters of correction, but you don’t want a big mistake that could not be corrected. Once the shoe is in the position you want to use a pencil to mark the spot. Then use the smallest drill just to make a mark. Many metal drilling videos would advise to make a little hole with a puncture tool, but I think the risk of making a dent in the OTA is too great. 

Then using the correct size drill bit drill the holes. My drill bits were not the ideal ones, but they made the hole through the metal. I had to push the drill and in doing so ended up with dents around the holes. The paint around the holes also chipped off so I had to use some epoxy filler to avoid future rust. 

4. Putting on the dovetail base. Screw on the shoe bracket with the Philips screws and washers. And finally the dovetail base will be on the OTA. I bought this one in the Orion store in Cupertino, CA and it fit well the finderscope and the OTA. Just make sure it fits well on the OTA. It had a notch that fits the dovetail ring so make sure that notch is free so anytime the finderscope can be taken off the OTA for transportation. 

Now assemble the scope together and you will have the telescope updated with an optical finderscope to surf the sky!!! 

Good luck on your future OTA’s updates and keep posting opinions and advices here.


Edited by: Jennifer Steinberg (editor in chief).


  1. Excelente !! ... yo tengo ese mismo telescopio y también me decidí en realizar el reemplazo. En mi caso use el mismo soporte del "Red dot finderscope" y le acople un laser verde de 200 mw.

  2. Que bien Fabián. Me gustaría ver como te ha quedado. Podrías enviarme una foto a mi correo

    Gracias por seguir mi blog y por aquí bienvenido todo el tiempo.