Cheap and easy tuneups for your 10” SkyLine/Apertura/StellaLyra Dobsonian

[Jim L]

So you just bought your wife a very nice new 10” Dob, the weather’s gone to the dogs, and the gods look with contempt upon your pleas and sacrifices for clear stars. Oh yeah, you’re also broke. What now? Cheap and easy tuneups, that’s what!

Some of the following tips are specific to 10” GSO made Dobs, but many are universal, so let’s get started.

1) Rotate your focuser. There are two grub screws that when loosened will allow you to rotate the focuser to whatever position you desire. The location of one of the screws is shown with the blue pen below, the other screw is directly opposite:

Here is the focuser repositioned:

 

2) Red dot finder shoe: Finding objects with your Dob will likely be easier if you attach a lightweight red dot finder. I found a mounting shoe in my spares and picked up a super light but effective red dot finder for around $15. I didn’t want to drill any new holes so I used a couple of thin strips of 3M double stick tape to attach the shoe:

Here the red dot finder is installed between the focuser and the shoe for the 8x50 RACI finder. That 3M tape is strong, and the finder isn’t going anywhere:

 

3) RACI Finder cross hair delete. I was using the 8x50 finder to search for M13, which in my skies is very dim, and I found the cross hairs in the finder field to be too thick, too dark, and more often than not a distraction. They were particularly annoying when they completely blocked the desired target from view. The solution was to unscrew the eyepiece and to pluck out the cross hair wires with a pair of tweezers. With the cross hairs deleted I can more easily find the objects I’m looking for, it’s just as easy to center the target in the field, and using the finder is far more pleasant! Sorry, no photos.

4) Eliminate the need for the 2” 35mm extension. Some of my 2” eyepieces wouldn’t come to focus without the included 35mm extension, but swapping eyepieces, adapters, and extension was inconvenient in the dark. The solution was to install parfocal rings on the 2” eyepieces, and to adjust the rings to make the 2” eyepieces parfocal with the first 1.25” eyepiece I usually go to when switching from 2” to 1.25” eyepieces.

First, install the 1.25” eyepiece you want the others to be parfocal to. Focus the telescope at a distant object and then lock the focuser in position by tightening the screw shown below:

 

Next, remove the 1.25” eyepiece and adapter and install the 2” eyepiece with a parfocal ring loosely installed and the eyepiece holder set screw loosened. Focus the eyepiece by sliding the eyepiece barrel in and out of the focuser until the image is sharp. Do NOT turn the focuser knobs. Tighten the eyepiece holder set screw to secure the eyepiece in the focused position:

Finally, slide the parfocal ring down the eyepiece barrel until it rests atop the eyepiece holder, and tighten the parfocal ring grub screws. This eyepiece will now be parfocal with your 1.25” eyepiece.

I got my 2” parfocal rings from Astromania via Amazon, but FLO also stocks them:

https://www.firstlightoptics.com/adapters/astro-essentials-parfocal-rings.html

5) Battery counterweight. You’re most likely going to need to add some weight to your optical tube to balance your heavier eyepieces, so why not use something you’ll also likely need as that weight, like your fan battery pack.

I placed a self adhesive strip of extra strong Velcro along the bottom tube seam and the mating strip along the back of my battery pack:

I affix my battery on the underside of the tube because it better offsets the eccentric load created by the focuser and finders:

That’s it for now, I hope some of it is helpful, and I’ll have more to follow.

 

 

Edited June 12, 2023 by Jim L
Extraneous photo snuck in…

[Jim L]

Most of our scopes have several set screws to assist in collimation or to hold diagonals, eyepieces, or other gear in place. One of my favorite and most effective fixes improves the function and reduces the damage from set screws, and costs virtually nothing but a little spare time.

The problem with most set screws, grub screws, set bolts, etc., is that the unfinished end of the screw usually takes the shape of whatever results from the screw being cut from its origin material. That surface is often sharp and it deforms, or worse yet cuts, the surface it is tightened against. The more the screw deforms the opposing surface the less effective the screw is in securing it. The solution, fortunately, is relatively easy and entails shaping the screw end into a nearly flat but very slightly convex surface using nothing more than fine abrasive paper or a knife sharpening stone.

On larger bolts, like the primary mirror cell lock screws, I begin with a fine abrasive paper placed upon a flat surface. Holding the screws in my fingers, I move the end of the screw over the paper or stone in small circles, occasionally rotating the screw to avoid creating an angled surface. Rub in circles, rotate, repeat; a drop of cutting oil helps. Before long the sharp edges of the screw ends are eliminated and a very effective and non-damaging contact surface is generated.

The photo below shows the three primary mirror cell screws in varying stages of modification. The left most screw is as it comes from the factory, the right most screw has been partially shaped, and the center screw shaping has been completed:

Here’s a closer, albeit poorly focused, view of the same three screws:

Smaller screws respond equally well to reshaping and here are the secondary mirror collimation screws in various stages of reshaping:

In the case of very small grub screws, rather than hold them in my fingers I insert an Allen wrench or hex driver in the hex end of the screw and use it to hold the screw against the stone. Remember: circles and rotate. Here’s one of the finished parfocal grub screws within its ring:

The very slightly convex contact surface created by rubbing the screw against the abrasive surface in circles, and by rotating it, holds the ring without damage to the eyepiece barrel and requires less tightening in the bargain.

I reshape every set screw on all of my telescope gear. It only takes a few minutes and the improvement in the function of the screws is surprisingly large.

[Guest]

At some point better springs under the primary are a must as well as thumbscrews to adjust the secondary mirror.  

[bosun21]

You are better to have a moveable counterweight IMO as the different weights you introduce to the front ie: different eyepiece weights and dew shield etc can easily be accounted for by simply repositioning the counterweight.

[Mr Spock]

2" industrial Velcro. You can put the counterweight wherever it's needed to balance heavy eyepieces or camera.

[Jim L]

4 hours ago, Mr Spock said:

2" industrial Velcro. You can put the counterweight wherever it's needed to balance heavy eyepieces or camera.

Essentially that’s what I did, but instead of a chunk of iron that serves no other purpose I substituted the fan battery.  The Velcro strip is long enough to allow the battery/counterweight to be moved up or down as required to achieve balance.

[iapa]

On 13/06/2023 at 00:16, Jim L said:

Smaller screws respond equally well to reshaping and here are the secondary mirror collimation screws in various stages of reshaping:

 

While you have the secondary mirror of, install a steel washer between the spider and the mirror.

It will stop the screws catching on any indents on the mirror caused earlier, and makes mirror rotation smoother especially.

[Ratlet]

6 hours ago, iapa said:

While you have the secondary mirror of, install a steel washer between the spider and the mirror.

It will stop the screws catching on any indents on the mirror caused earlier, and makes mirror rotation smoother especially.

I did this and cut a similar sized washer out a milk jug carton and put it between the washer and the mirror for a bit less friction.  Buttery smooth collimation.

[Mr Spock]

I put a plastic disk in between. The screws on a StellaLyra fit into indentations which make collimating the secondary impossible as it just wobbles about. The disk cures this and makes collimation easy.

[Jim L]

Thanks gentlemen, a hardened steel washer and HDPE disk will be included.

I purchased stainless steel 4x30 mm thumbscrews shipped for less than $10 from a well known PRC market place, and I reworked the screw ends. A CatsEye combination sight tube, autocollimator, and Cheshire eyepiece are scheduled to arrive tomorrow. I’ll complete the mods to the secondary holder that evening and begin work on the primary cell afterwards.

The primary cell will have its collimation screws replaced with studs and through thumb nuts, the fan will be shimmed so it sits a few more millimeters from the mirror, and the back of the cell will get a fitted cover to better direct airflow. Next will be some minor tweaks to the mount.

 

[iapa]

You also mark and drill indentations in the steel washer to match the screw positions, that helps prevent the washer moving in relation to the secondary mount. 

I used a couple of layers of HDPE between washer and secondary.

[PeterStudz]

I did the milk bottle mod to my secondary of my SkyWatcher 200p Dob. Cut milk bottle washer and intended to use a steel washer too.

Worked really well in the end. But I found that the gap in the secondary was so tight that in order to get the secondary under the focuser I couldn’t use the steel washer. Image shows the secondary roughly collimated when I was trying to work out what was going on. 

[Mr Spock]

There's a lot of adjustment space in the StellaLyra.

[Jim L]

The secondary mirror holder and mirror mods are completed. For reasons unknown, here in the states it’s nearly impossible to purchase 1-3/4”x 1/4” washers unless you want a 1,000 or so. After fruitless searches for the proper size in more reasonable quantities I picked up a 2”x1/2” washer. A few minutes with a the grinder, lathe and flat file later:

The aluminum bushing keeps the washer centered; it’s an interference fit in the washer so it’s unlikely to come out of its own accord.  The other side of the bushing is wider, and provides a platform for the mirror holder spring, like so:

The spring will further ensure that the bushing never comes out of the washer. Here’s how it stacks in the mirror holder:

I chose to not include a HDPE washer as the polished thumb screw ends will not cut into the washer, the setup as shown is very precise and is as solid and immovable as Gibraltar, and the extra washer is superfluous.

Last on the list was darkening the side of the mirror. As delivered the mirror side facing the focuser looks like the core of a globular cluster with thousands of sparkling points of light. That can’t be good for contrast so I picked up a chisel point Sharpie and gave it a good blackening. I chose the non-waterproof version since I know it can be removed easily with isopropyl alcohol if desired.

You definitely want the chisel tip otherwise it will take forever to coat, and the chisel tip lays down nice, thick, ink.

All together, collimated, and ready to observe:

Total cost, including the stainless steel thumbscrews, was around $12.

I went back and blackened the edge of the washer after I took the photograph above, though it would have been easier had I done it before the holder was mounted.

One final thought: the screws throughout the scope aren’t the self destructing Phillips head type, they’re JIS (Japanese Industry Standard). If you use a proper JIS screw driver you’ll be far less likely to round the heads and everything will come apart and go back together much easier and with less drama.