New Focuser for the Telescope
One of the great(?) things about amateur astronomy is the fact that there is almost no end to the amount of accessorizing you can do! Forget shoes and jewelry, gimme focusers, auto-guiders and computer pointing control!
As the years go by, it seems like less and less of my scope hangs in there through each upgrade. The latest victim: the focuser.
There were two issues with my old focuser, one was that the speed it moved was too fast making it hard to achieve good focus without running right by it; it was stiff and the tiniest movement of the knob moved the eyepiece a LOT. The other issue is that there was this one rough spot in the travel that always seemed to be where you wanted to be.
So a quick visit to the online sites revealed that if I wanted to, I could spend over $500 on a new focuser! Well my rule is that I don’t spend more on a single accessory than the cost of the entire scope so I looked for something a little more reasonable finally settling on a Crayford design focuser from Orion for $80. It didn’t have the two knobs for two rates of travel but those were two and a half times the price.
In no time at all there was a box in front of my door (with a couple other things in it as well) and it was time to assess how to get it on to the scope. I didn’t have any illusions that the screw holes for the old focuser would match the new ones but what I wasn’t prepared for was that the size of the actual hole in the side of the tube was too small! So that left me with the dilemma of how to cut a circular hole on a tube where you can’t mark the center because there’s a hole there already. My solution: do something else! The tube is made of plastic so I thought that if I could draw a reasonable circle around the too small but perfectly cut circle that was there I could use a really rough file to widen the hole to its new width. Precision wasn’t terribly important since the base of the focuser itself would cover any little gaps between the focuser barrel and the tube. So one rat-tail file and 1/2 hour of elbow grease later I had something that worked.
A "Crayford" design focuser to replace the old rack and pinion one
I knew this was going to be messy business so I had to take my scope apart–ALL the way. I’ve never had it this far apart before but fortunately Newtonian reflectors are pretty easy to maintain and adjust with nothing more than a standard screwdriver and a couple of hex wrenches. So off came front assembly that supported the secondary mirror and the main mirror cell in the back (great opportunity for mirror cleaning) leaving me with nothing but the bare scope tube.
After a couple test fits I had the hole just wide enough to accommodate the focuser then it was time to get it on there straight, mark some hole drilling spots, drill and screw it on there.
First Light
Anxious to check it out I set up the scope behind my car in the parking lot of my condo. The only real target in the sky that night was a nearly full moon so that’s what I looked at. This new focuser is a lower profile model which is generally good for carrying the scope around and such but created an unknown in the area of what combination of extension tubes and 2” to 1.25” adaptors and such I would need to reach focus with all my nine various eyepieces.
The big task was to go through every eyepiece both with and without a magnification boosting barlow lens and see where they achieved focus best and whether there was a kind of “new standard setup” would emerge that would allow me to change eyepieces and refocus quickly at the stargaze events I run; nobody wants to stand around and watch me fiddle with the equipment for more than a few seconds.
New focuser looks great and is smoooooth!
During all this I saw a bunch of really great views of the moon, from 19x to 508x power. Honestly the extreme high power views were not that great and the eyepiece lens size you have to look through is so tiny that it’s almost useless if you wear glasses like I do.
There’s a guideline regarding scope magnification amounts that’s good to keep in mind: for every inch of scope width (diameter) you have, under perfect circumstances, you can only really achieve 50x magnification before your image turns to smeary mush. However, things are never that perfect, especially all at the same time. The term “perfect circumstances” refers to the combination of equipment quality plus seeing conditions so that means, perfect mirrors in your scope, $500 eyepieces and remote mountaintop observing conditions with a perfectly still atmosphere all the way to space. Obviously that never happens, especially all at once so the real magnification amount is usually about 25x per inch of aperture.
This is about right since my 8-inch scope’s image starts looking pretty ratty once you get up past 200x. The good thing is that you don’t need powers that high for most objects; only planets, close double stars and small planetary nebulae. I honestly do 85% of my viewing at 125x or less.
Add-Ons
Also in the box was a finder “scope” known as a ‘reflex sight’. The reason I put the word scope in quotes is because these things don’t actually do any magnification but instead superimpose a red dot on the sky when you look through it. When I saw these things come on the market I initially questioned their value since they don’t magnify at all but they’re a part of the standard setup for the scopes we have at Marriott’s SurfWatch and The Barony and I have to say I find them quite useful during the alignment run at the beginning of the night.
Because of the nature of my scope/mount setup, when looking at certain areas of the sky the eyepiece can end up in some awkward viewing positions requiring getting up on the 2nd step of the stepstool or having to crouch down when looking near the horizon.
To make it easier for people to get to the eyepiece (since not everyone does Yoga) I bought a little thing called a “star diagonal” which gives the light a 90° bend for a better viewing angle. These are commonly sold with refractor and Schmidt/Cassegrain style telescopes as a necessary standard accessory.
Hole Thing
Over the years I have taken off, put on, and taken off again a number of things which has left more than a couple holes in the tube. Every now and then some stray light will get in through these holes and ‘pollute’ a view I’m trying to get which is especially annoying if that something is a dim galaxy or whatever. So the last thing was to plug these holes and since I couldn’t find a variety of WD-40 that was dark enough, I went with duct tape!