More Mizar Mystery Mini Mount Mods

So, last night I bought a socket set, including a 17mm socket allowing me to fully disassemble the RA shaft on the Mizar mini-mount. The shaft is straight, but the hole in the Dec unit that the RA shaft screws into is at a slight angle. After cleaning the head of the shaft, it was clear there was some old washer/shim that had deteriorated over time.

I tried some rubber and metal washers, but didn't have any luck. I then made a shim from aluminium foil. This worked well when I screwed the shaft in by hand. I cleaned and greased everything and reassembled the mount, but there was no improvement! After some swearing and then a bit of investigation, I realised tightening the shaft hard torn the foil shim and spread it out.

After a bit of thinking, I realised the opposite of shimming was to remove material. So, the opposite opposite (i.e. same) effect could be achieved by filing down the base of the shaft opposite to where I had placed the shim, and also angling the sides perpendicular to this. I did this gradually, frequently checking the angle after some filing by screwing the shaft in tightly. I could see an improvement and eventually got it pretty straight. I filed off about 0.5mm.

I then cleaned and greased the RA shaft, greased the worm wheel and put it all back together. The RA shaft is now quite square to the Dec unit. Previously the RA circles were being pinched by the Dec unit due to the misalignment and could get stuck in place instead of moving with the RA shaft. This is now fully fixed, and the action of the RA setting circle is good - smooth and loose enough to move easily, but with enough stiction not to slip. So, now I have more accurate "push-to". The new grease improved rotation about the RA shaft itself, and is now very smooth.

The RA shaft has a simple but effective little "bearing". It is just 4 washers, with grease between each, behind the bolt holding the shaft in place. Re-greasing these led to smoother rotation and the ability to tune the shaft tension more finely.

Looking at the Orion site, the EQ-2 mount seems to be similar to this mount. Mizar had a smaller mount that the EQ-2 looks very, very similar to. My little mount is a bit more sturdy at the same weight. If you are having problems with an EQ-2 mount, it may be worth pulling it apart to check if the RA shaft is misaligned rather than bent. Obviously this is at your own risk.

Unfortunately I forgot to take photos of the disassembled mount and tear-down/rebuild process. It's very simple. The mount is nicely engineered apart from this misalignment.

I cleaned the whole mount with WD-40 and all the chromed parts with Brasso. It's looking pretty good:

On the near side of the RA unit, you can see, from left to right, a chrome bolt, a lever and a gear. This is clearer in a photo from the auction:

It seems likely that the chrome bolt is there to mount an optional RA motor drive, with the lever for some mechanism to (dis)engage the smaller gear(s) that would connect to the large gear.

You can also see the Dec knob points down towards the rear. So, when the mount is moved around RA, the Dec knob collides with the gear. Removing the lever and gear helps, but the Dec handle still collides with the RA worm shaft. Unlike other mounts, the Dec handle does not rotate with the Dec shaft, so this collision happens regardless of Dec.

Also, on the other side, again in a photo from the auction, you can see the RA knob:

Again, the RA worm shaft does not rotate with the RA shaft, but remains in place. This protudes quite a way, and the Dec worm shaft collides with it when rotating the RA shaft in the opposite direction.

Removing the chrome gear revealed that the inside of the worm shaft was threaded for an M4 bolt. This makes it possible to use a different knob to turn the shaft. The Dec worm shaft didn't look to be threaded, but after screwing a bolt in with some WD-40, it was clear that it too is threaded for M4.

I upgraded my Takahashi TOA130F with the MEF-4 micro focuser, and my Sky-90 with the MEF-3 micro focuser, so I had two spare Takahashi focusser knobs. I got some M4 nuts and bolts from a local hardware store and attached the Tak knobs:

Now there is complete clearance to rotate the mount fully in both RA and Dec. The only limiting factor is the telescope itself, but now I can track past meridian, and the mount is easier to use.

The other major modification I can think of would be to add a motor. To do this, I need to re-attach the gear and mount the motor on the rhs. Fortunately the RA and Dec worm assemblies are asymmetric. If I swapped them, I would be able to have the Tak knobs on the other side, allowing me to have a motor on the rhs.

The mount has fairly simple bushings, which could be improved by teflon bushings, but it's already very smooth.

I was able to use the mount for a short while last night to find some doubles in the haze between the clouds with a Pentax 75-SDHF. It is very rigid, with damping times less than 0.5 seconds, without the use of any damping pads. I'm not very practiced with old-fashioned setting circles, but I was able to find targets far (greater than 10 degrees) from nearby bright stars that were not visible to the naked eye. Scanning RA in the finder and at low powers, and using binoculars to get context also helps. Each goto is more effort and a bit slower than with an automatic mount but the set up time is minimal, so I can spend more precious time before the clouds come in.

So, this old, cheap little mount is now back in good condition and very usable.

Crepuscular Rays at Sunset

Storm clouds rushed in over the north of Singapore just before sunset, causing some nice crepuscular rays, the heavier, taller clouds to the right had flashes of lightning between the clouds.

Push-to versus Push-to classic

The weather is quite changeable here in Singapore, making anything other than "quick peeks" frustrating. So, I decided to try to get the most out of my quick peeks. I wanted a small lightweight mount that I can easily travel with in a taxi, that I can use for 20 minutes on the balcony, and that minimises the time spent finding objects . I already have a Vixen Sphinx, which is nice for a weekend trip, but I find it a bit too much trouble for a quick peek or a taxi ride for a night's viewing.

I sold my much-used Vixen Porta after replacing it with a Takahashi TG-L, which can take larger scopes. This is a nice alt-az mount for quick-peeks, but star-hopping can be time-consuming. The sky is so bright that you have to start from a very bright star, often resulting in a very long chain of hops.

Recently, I tried out a few astronomy apps on the iPhone. These allow using the compass to find objects in the sky, so I put together a simple bracket to hold my iPhone on a scope. I wanted a flexible rubber iPhone case to easily get the iPhone in and out of. I got the loudest colour I could find to help finding the thing in the dark in case I dropped it. Some of the apps require shaking the iPhone or moving it in a figure of 8 to calibrate the compass. So, I wanted to be able to remove it form the mount easily - so velcro!

This failed miserably.

The software works well, and is useful and fun, for wide field views at arms length, but doesn't recognise small movements. It can also be very inaccurate. The error was more than 20 degrees in some cases. I wasn't expecting high accuracy, especially with the iPhone attached with velcro, but I was hoping to get the target in the finder FOV. I tried various apps, but they all showed the same inaccuracy and lack of sensitivity to small movements.

So much for the simple, inexpensive hack.

I had already been thinking about getting a small equatorial mount with setting circles. The Vixen GP is light, but slightly too large. The Tak P2-Z would be great for astrophotography, but is too heavy and is also expensive. My Kenko Skymemo-R is great for portable astrophotography with a small scope or lens, but isn't much fun to use visually. It lacks slow motion controls, setting circles and doesn't have much clearance.

An old mount came up on Yahoo auction in Japan at a low price. I ignored it for weeks, but eventually gave in and bought it. It looks very similar to the older Mizar mounts on their page, but I'm not 100% sure what this mount is or how old it is.

The mount came with a 2kg counterweight, but for smaller scopes, the 1.5kg weight for my Kenko Skymemo (pictured) is fine. I bought the Takahashi FC-S legs from Starbase in Tokyo. Yamamoto-san was very helpful and sent the little mount to me with the FC-S legs. The mount is usable from 0-90 degrees without the need for a half-pillar. I like the retro look.

This setup, including couterweight, feels lighter than the TG-L. For trips in a taxi, it should be fine to just carry the mount with the counterweight and shaft in a rucksack. The whole thing should also fit in a fairly small case for airline travel.

The mount was in very good condition, but needed some lubrication. I took the mount apart and mixed small amounts of WD-40 with the old grease. The previous owner seemed to have overtightened everything, so I also adjusted the worm gears and shaft tension. Now, everything is very smooth. Unfortunately, the RA shaft is not perfectly square with the mount. The mount doesn't seem to have been dropped and the shaft doesn't seem to be bent. It's possible it is a manufacturing problem, or that the shaft is not seated correctly. The washers holding the RA shaft on are considerably off-centre, so it should be possible to improve the alignment. I couldn't disassemble the RA shaft completely as I don't have the right size of socket. I'll probably get a socket and try to straighten out the shaft, but it is perfectly usable as is.

Of course, it is cloudy, so I've not had a chance to try out this new mount.

Other options would be something like the iOptron or Sky-Commander. These are expensive, limited to visual only use, require batteries and are useless if power runs out or the electronics develop a problem. So, I think I'll stick with my old-fashioned mount for now.

Now I can get on with going through my observing lists of double stars and tracking some variables stars.