2018-11-06: COLLIMATE THIS

I got my new Celestron EdgeHD 1100, named Max, on the 5th and took it for a spin that evening. It was a learning experience. Like how many pounds of counterweights can one scope require?? All I wanted to do was set it up, do a little star testing, pack up and go home. I just wanted to see if it worked on this outing.

One of the first things I had to do was collimate the scope to get the secondary mirror reflecting the light straight down the tube and out the back of the scope. It was off a fair bit. That can happen during shipping. I guess. Some people's scopes rarely require collimation no matter how much they drag them around. For this kind of scope the secondary mirror is tilted using three screws on the front of the scope. Sounds simple. The problem with this multi-thousand dollar scope was that it was made a little too simple. Above are all of the parts that were involved. That's not enough parts for me.

The three smaller screws were the ones that made the mirror tilt. They were M3x.5 Phillips head screws. Two were 12mm long, and one was 10mm long. No clue why, unless they just ran out of 12mm screws that day. Celestron used Phillips head screws in the 1970's. I thought they learned their lesson about using small Phillips head screws when they changed to hex head (Allen wrench) screws like on my 1979 C8. The slots in the head get messed up pretty easily if the scope requires frequent collimation. The gist of the whole collimation operation is 'turn the screws'. For unexplained reasons the screws on this, and I assume all of the other EdgeHD's, were glued in place with something like Loctite. Why? I had a heck of a time adjusting all of them. If the screw driver slips the corrector plate is about an inch away. That's another hint as to why they are not a good idea.

What are those screws even made of?

I took everything apart and made a trip to the hardware store. I managed to find hex head screws matching the Phillips screws in respectable stainless steel, as well as some additional parts to bring this mechanism into this century or at least into the last century. All three were going to be 12mm long.

In the middle of the black plate is the bump that the mirror rests and tilts on. Keeping the screws tight keeps the mirror resting on the bump. You should always make very small adjustments when collimating. Don't try to take out all of the error at once. Adjust, recenter, adjust, recenter... Pretty simple.

I don't like it when moving parts rub against parts that aren't supposed to move, like how the screw heads were grinding directly on the mounting plate. I'm not sure how much washers cost Celestron, but three of them to put between the screws and the plate set me back a whole $0.33. Why didn't they do this? Probably the $0.33. The washers fit just right in the recessed area around each hole.

I only have two hands. To keep everything where I wanted it I used scotch tape. I had to get all three screws threaded into the aluminum base plate at the same time. With the scotch tape I was able to poke the Allen wrench through it and turn the screws while it held them in place.

In lieu of Loctite I decided to go with small compression springs clipped from a larger spring to help keep the screws stay put after being adjusted. They keep pressure on the screws to keep them from turning without human intervention. I've seen this method used since the 60's because I've been around that long. Celestron must have new engineers. I'm not sure how you classify springs, but these ones were not too stiff and were short enough to fit in the space between the base plate and the mounting plate with the mirror fully settled on the bump.

Before I took everything apart I, of course, marked the mirror and its base plate so they could be correctly lined back up with the mounting plate. The set screw on the mounting plate goes into a slot in the portion of the secondary mirror mount that is attached to the glass corrector plate so as to get everything aligned with the primary mirror. That black surface is a mirror. I should have held a cat or something above it to make it not look like a black hole.

The secondary mirror is attached to the base plate disk of aluminum with what looks like double-sided sticky foam tape. Not wild about that, but it seems secure enough for now. It's not a full disk of whatever is between the glass and the aluminum, but looks like random strips. I don't know if that will cause uneven heating of the secondary mirror.

I managed to get just a sliver of a finger print on the edge of the secondary mirror during all of this. What removed it? Scotch tape! I just pressed a clean piece on the print, pulled it off, and the finger print was gone. Never heard of that one before. I couldn't even see where the print had been when I breathed on the mirror. Huh.


Much better! Now I'll be able to sleep at night AND adjust the mirror easily. I now also have a clear idea of how the secondary mirror adjustments work and know what will happen if I loosen an adjustment screw too much. It's nothing. The screw and wavy washer in the middle is for attaching the "propeller". It is a M4x.7 8mm long screw. I may change it to 10mm long later just to give it a bit more grip. The hole it screws into is pretty deep.

So the first evening with the scope (which is what led me to redoing the collimation screws) kicked off with a big bang. This propeller is on the front of the scope and it rotates about an 1/6th of a turn to expose the collimation screws. When it is turned so they are hidden it also acts as a handle for removing the secondary mirror. Well, it wouldn't rotate. One thing led to another and it broke off. The little black ring of plastic should be attached to the back of the plastic propeller. But never fear...a replacement is on order. I think the screw holding it on was too tight, or some of the thread glue on that screw got into where it shouldn't have been, or something like that. That prevented it from turning until I ripped it from its foundation, but I digress...

Overall I'm not too impressed with the workmanship of this new scope. I don't really blame the word "Celestron" since the company sold out to a big Chinese corporation a long time ago. I guess these scopes make a buck for the company and keep people employed, so it can't be all bad, right? Most(?) people get scopes that are perfectly fine, but this shoddy mechanical construction is in every one of them. Hey, it's only the secondary mirror and if the cheapest possible solution works most of the time why change it? Just my opinion.

Maybe some year I'll get to take apart the back of the scope and see if something can be done about the little shift in the position of the main mirror when you change the direction of the focus knob. It's a small problem that has been around for over 40 years, because I've had one of these scopes for that long.

NEXT NIGHT: MUCH BETTER! I should patent this thing.