December 26, 2014 – Upgrading the Mak, part 4A – mounting the ST-80, Barlow

Tonight it was clear.  Or at least it was “clear.”  There was a high, thin, persistent haze that never went away all night.  Damned Weather Channel, screwed me again!

At least I got a chance to test out the Ultrascopic Barlow on the Mak.  And it worked perfectly.  As I noted in yesterday’s post, I didn’t have enough inward travel on the ST-80 to get it to come to a focus.  Not actually a big deal, because there’s no advantage to using the ST-80 at that high of a magnification; that’s what the Mak is for.

Fortunately, the Mak did have enough focus travel.  And the Barlow gave me lovely views of the moon and Jupiter.  Having the extra eye relief by using lower-powered eyepieces was actually pretty nice.  I Barlowed the 32mm, and got a wonderfully sharp 96x.  The 15mm Barlowed nicely to give me 206x.  And even the 8mm TeleVue, my prize jewel eyepiece, was great at 385x.  Because of that extra eye relief, the detail on the moon was more easily seen in the 8mm than in my 4mm, and the 8mm was easier to focus on Jupiter as well.

One little problem about the Barlow is that the focus is wildly different than the EP being Barlowed.  In other words, going from the 32mm to the 32mm Barlowed requires a LOT of refocusing.  However, leaving the Barlow in, and just switching EPs requires the same small amount of refocusing as using the different EPs without the Barlow does.   So that’s what I did.

Another little problem is that the Barlow gave me a much narrower field of view than expected.  Oh, sure, I expected the field of view to be cut in half, but it was cut more than that.  The TFOV of the 32mm normally is just over a degree, so the TFOV with the Barlow should be just over half a degree – still large enough to see the entire moon.  However, it seemed like I could only see about two-thirds/three-quarters at any one time.  Not a big deal, just something a little surprising.

Unfortunately, because of the haze, I couldn’t do the second part of my diagonal test – detail.  I wanted to see if I could see better/more on Jupiter by switching the stock diagonal with the dielectric, but that will have to wait until it is actually clear, and not merely “clear.”  The forecast is for clear skies tomorrow, and an appearance by the GRS, but as usual, we’ll see.

I had a lot of fun observing with the ultra-wide-field ST-80 last night, as discussed in yesterday’s post.  But I had it mounted directly onto the Vixen dovetail mount in place of the Mak.  Now comes the interesting part – mounting the ST-80 onto the Mak somehow so I can use both of them at the same time.

I set forth a few ideas in my last post yesterday, one of which involved mounting rings from ScopeStuff.  As I mentioned, I had some concerns about the clearance between the outside of the tube at 88mm across and the inside of the mounting rings at 91mm, and more importantly, the ability to adjust the ST-80 so it could be aligned with the Mak.  I gave ScopeStuff a call to ask about this, and spoke with Jim there.  I told him what I wanted to do, and he spent a nice amount of time on the phone with me, carefully explaining all my options.  In particular, he first explained that in relation to the rings I wanted to use, putting aside that potential problem of alignment for the moment, there were much bigger fish to fry with this particular mounting selection.

For example, there was the problem of adding 4 pounds of telescope, diagonal, eyepiece, and mounting rings to that little Vixen finder dovetail.  It just wasn’t designed to hold that much weight, so that the attachment – and therefore the alignment – wouldn’t be very stable.  Beyond that little problem, there was the bigger problem of balance.  All 4 pounds would be attached to both the back and to the side of the scope.  This would affect the balance two ways:  one, that it would be difficult to balance the Mak + ST-80 front to back by moving the Mak forward far enough along the main dovetail, because those 4 extra pounds would all be concentrated right on the back of the scope; and two, that having that weight hanging off of the side of the Mak like that, as opposed to being closer to the middle of the Mak, would wreak havoc with the mount’s motors, as it would put too much stress on the main dovetail in seeking to rip both scopes out of the mount, so that the weight on top of the scope would have to be balanced by a weight on the bottom of the scope.  And more weight is even worse for the motors.

We went through a few different options.  First was this dual dovetail mount that has a long dovetail bar that fits into the main dovetail mount, and then has two dovetail slots, one for each of the scopes, perpendicular to the long axis of the bar.  The bottom picture at that link is almost exactly my configuration – an ST-80 refractor mounted onto the same mount as a 127 Mak.  Pretty neat.  But the difference between that picture and my potential setup is that the dovetail bar in the picture is parallel with the ground, so both scopes are mounted horizontally and the weight is going right into the main dovetail mount.  Because it was infinitely adjustable, it should eliminate the balance problems.

On the other hand, to use this bar on my scope, the long dovetail bar would have to be perpendicular to the ground. The two scopes would be mounted almost directly on top of each other.  In that orientation, the ST-80 extends farther backwards from its dovetail connection than the Mak does.  This means that the diagonal/EP of the ST-80 might interfere with my using the diagonal/EP of the Mak.  Also, because the long dovetail bar and dual dovetails are constructed of 1.9 pounds of heavy-duty aluminum, this would put a total of almost 6 pounds more weight on the mount and motors, not just 4 pounds.  And to make it manageable, it looks like I would have to lower the Mak down lower by extending the connection point on the long bar below where the Mak now attaches to the mount.  Since this would put the Mak closer to the top of the mount, it would bump into the mount when I tried to look at something high in the sky.  Hmmm.

The next option Jim showed me was a set of rings similar to the ones I had been looking at, except these rings had a thumbscrew in front to take some of the weight off of the dovetail bar in back, potentially making that mount more stable than the original set of rings I was looking at.  However, this still wouldn’t solve all the balance problems or the resulting motor problems I was likely to encounter.  Also, the weight would shift from the front to the back the higher the tube pointed up in the sky.

Finally, Jim offered me a fourth option, which wasn’t even listed on his main ScopeStuff page, but at his eBay store:  the Lyra Double-Double mounting system.  This would also eliminate the balance problems because it was pretty infinitely adjustable – place the ST-80 wherever you want on top of the Mak, forward, back, left, right, and then just strap it down tightly with the included bungee cords.  While not quite as elegant looking as the other options, this should mean that I’d be able to put the ST-80 on just about anywhere along the Mak so that there wouldn’t be any undue problems with the motors or the two EPs getting in the way of each other. It also had the advantage of being very lightweight, and having adjustable set screws so that once the ST-80 is strapped on, I could still align it with the Mak.  The attachment points, both where it touches the Mak and where it touches the ST-80, are all nylon-coated metal, so it wouldn’t mar the finish of either.  And, as an extra added bonus, it’s cheaper than all the other options.  Kinda nice when you’re unemployed and looking to save a few bucks.

Before buying, I needed to test this out by “attaching” the ST-80 to the Mak, and seeing what balance problems – if any –  that would cause, and to make sure the motors could handle the extra weight without struggling or getting burned out.  Before doing that, I carefully calculated the extra weight of the entire rig, including the Double-Double, and it came to just less than 4 extra pounds.  That shouldn’t be too bad.  I took some stretchy telephone cord and some rope and tied the ST-80 on, putting it as far to the right as possible, right above the mount and above the center of gravity.  I put diagonals and heavy EPs into both scopes.  The two EPs did not interfere with each other, so this was at least theoretically workable.  Then I started the scope up.  The motors sounded loud and laboring, but no more loud and laboring then they did when I then took the ST-80 off and listened.  Success!  This could work!

I ordered the Double-Double, and it should be here in about a week or so.  Thanks, ScopeStuff!

Next time – cleaning your optics, even when it isn’t necessary.


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