Posts Made By: Roland Christen

Tests of various mounts(in French): http://www.astrosurf.com/demeautis/ep/pe.htm

Superb!

Roland Christen

Hi all,

I'm still at it, testing the PE of the mount. It looks like I'm getting about
2 pixels of PE at 1.8 arc sec/pixel in a 7 minute exposure (approximately 1
complete worm rotation). It looks quite smooth and something that PEMPro could
easily reduce. This is a raw worm wheel which has not been run in yet, so I e
xpect that it will improve either with use or if I lap it in. We normally do
that in production. In any case, I am quite delighted with the performance of
this new mounting.

Some prelim specs:

Size wise it is just a hair taller than the 600 mount. It has 5.85" diameter
- 225tooth worm wheels on both axes. Both axes have 60mm shafts held in place
with high quality machine tool bearings preloaded to approx. 300 lb.

There is a 2" diameter hole that goes all the way through the mount on both
axes. This allows the user to bring wires from the bottom of the RA up through
the top of the Dec axis. There is no restriction on rotation with these wires
in place. You can go 360 degrees and more in both axes without snagging
anything. The mount itself weighs around 24 lb without the piertop attached and
about 26 with the piertop (normally the piertop is left on the pier). This is
without any mounting plates or dovetail plates attached.

The mount has clutches, and they are designed without using any plastic
parts, so no more splaying of clutch plugs. The clutch can be tightened to the
point where it locks down fully.

The motors are the same as what we use for the 900/1200 mounts. The motor
gearbox is totally new, as is the worm itself. We went to a much bigger bearing
system on the worm so we can put a lot more preload to hold it tightly in place
without stressing the bearings or bending the worm itself. The internal
reduction gears were redesigned to provide much lower backlash time for quick
reversal of the Dec axis, and to reduce the moment to moment error of the
individual teeth. In the tests that I have run so far, I cannot detect any tooth ripple
on the periodic error. On lesser mounts this can be as much as 5 to 10 arc
seconds and is very problematic to guide out because it occurs rapidly over a
period of seconds. We designed this gearbox with high quality fine pitch gears
of fairly large diameters to get this well under 1 arc second. Because of the
size of these gears and the size of the worm and worm bearings, the gearboxes
look a bit oversized for this mount, but trust me, it is all for the good.

The altitude adjustment allows the mount to be used from zero to about 70
degrees latitude. There is a scale on the side for approximate adjustment in the
field and the mount will have a bubble level in the base. The azimuth
adjustment is approximately +- 15 degrees.

At this point I have no idea what the payload rating will be for this mount,
but realistically it can easily handle the 160F7.5 EDF refractor and certainly
a 9.25" Celestron SCT. I have not seen a 10" Meade tube assembly, so I cannot
say for certain.

The mount was designed to fit into an airline carry-on case. We are looking
at a couple of different ones, but the favorite for me thus far is the Pelican
roll-on case, #1510. We'll be making some foam inserts for this case, and
hopefully I will get to do some traveling with it.

We have also designed a new pier with adjustable height and level
adjustments, but this has not yet been machined. It will fold up into one piece for easy
transport.

More on this mount later tomorrow.

Roland Christen

Oil does not go opaque.

The reason I went to airspaced has to do with the availbility of glasses to achieve zero color. In a triplet oil spaced, you can do this with fluorite in the center because two mating glasses exist that will cancel the color error and the spherical. With ED glass, you cannot cancel both the color and the spherical at the same time. Therefore you either have to use an airspace or you have to use an aspheric surface if you want to do oil spacing, or you have to allow some color error in the blue-violet end of the spectrum. An airspaced ED lens will achieve the same or better color correction than an oil spaced fluorite lens.

Roland Christen

Closeup of the core (with only 780mm focal length).

RC

That is a very impressive view of the entire area. It looks like a view out the window of an airliner. Very smooth processing.

Roland Christen

Cool shot, Augie

Roland

It has been known for about 10 - 15 years. Unfortunately, liquids have exceedingly high expansion co-efficients, so would have real problems under changing temperature conditions. This is the major drawback.

Roland christen

I have seen an 8" airspaced lens that performed well, but it was not winter. Large oil spaced lenses are quicker to cool down, but still take 1 - 2 hours to reach perfection.

I made one 8" airpaced triplet ED lens that is at Co7 in Maryland (Marty Cohen's shop). I know that it performed very well when we had it set up down in the Florida Keys, even when the temperature plummeted soon after the sun set, and almost all large Dobs were having the cooldown blues with tube currents and wandering plumes of hot air out the wazzoo.

I made a 10" triplet refractor with airspaced lens that resides in an observatory in Germany, and by all accounts performs very well with no cooldown issues.

There is a trick to getting a large airspaced triplet to stabilize in falling temperatures. Since this is a competitive business with everyone stealing from each other, I am not at liberty to reveal it. However, consider this: it is a well known myth that large Mak correctors take forever to cool down because they are so thick. That is absolute bunk. It ain't the corrector that causes Maks to not cool down, it is the way they are constructed.

Rolando

>> My little scope can't even come close to this!>.

You would be surprised what your little scope could do with an H-alpha filter. The resolution shown in this 32" image is not all that great. Consider this image by Gleason taken with a scope just 1" larger than your 6": http://www.celestialimage.com/page213.html
If you look closely, the resolutions are similar. Just the color is missing, but you can always add that later to the H-a image.

Roland Christen