Posts Made By: Roland Christen

My M13 taken with 10" Mak-Cass at F11, 300 sec exposure, 1/2 size image.

Roland Christen

>>1) The most strange happens when I try to keep a star inside the rectangle of an illuminated reticle. When I press on button (RA or DEC) the mount moves to the opposite side for a while and then to the correct side. I have checked the motors and they seems to move to the right side according to the buttom command. Then I have tried using the knobs and noticed the same problem.>>

This first problem is quite common on all inexpensive mounts. It means that the worm is moving sideways in the worm block or in the worm bearings. It may also mean that the RA and Dec axes have too much play in the main bearings (tolerance too loose). It is impossible to fix loose fitting shafts inside bearings without resorting to some sort of plating and then careful hand honing until the part fits without any play. (By the way, this is one of the ways that a high end mount differs from a mass market version).

One way that inexpensive mounts sometimes can mask the problem for a while is to use a heavy sticky glue/grease between the rotating parts. This works ok in warm weather but becomes too stiff in colder conditions.

>>2) Another problem is that the RA motor seems to move a litle bit slow so that I can observe a slow drift of the star. Any idea? >>

This may be a simple case of polar alignment. The mount will seem to track slow or fast depending on whether the altitude axis is above the pole or below the pole. I suggest that you do a drift alignment, and the problem will probably be resolved.

Roland Christen

Closeup of the three

Roland Christen

M65 full size

Roland Christen

M66 full size

Roland Christen

NGC3628 Full size

Roland Christen

I have one of the first Starlight Xpress cameras. It is indeed a nice camera to use with excellent resolution. Although you don't need dark frames, you will need to do flats in order to eliminate the dark background splotches. If you have the time, do some darks also and you will see an improvement in noise and overall resolution.

Roland Christen

>>Why cant computer controlled CNC type machines and/or tuned lasers be used to cut, ablate and figure very high quality optics>>

Lasers can't remove glass while still maintaining a polished surface. The whole idea of an optic is to be able to look through it, therefore the surface must be highly polished.

CNC machines, and even manual machines exist that can quickly polish a ground surface so you can look through it. In fact, the Criterion/B&L Schmidt-Cass corrector plates were polished at such high speeds that it took only 17 seconds to polish out a full 8" corrector. The plates came off the polishing machine smoking hot and would burn your finger. Accuracy was not the goal here, cost and production rate were the primary goal. One of our employees has one of these beauties. Talk about a rippled surface!

The act of polishing a piece of optical glass generates localized heat, only part of which is carried away by the recirculating slurry. The faster you polish, the more heat builds up. The underlying glass surface distorts with this heat, and when it cools, it springs back to a new surface figure, one that you may or may not want. A 6" lens that is polished quickly in 5 minutes or less from a fine ground surface may change as much as 10 - 30 waves. Even one that is polished in 1 - 2 hours at a slower pace will change at least 2 waves once off the polisher. Since a precision lens surface needs to be on the order of 1/10 wave, it follows that a super slow polishing process is needed at some point to achieve the final lens surface figure. Slow = time = money

The alternative to this is to polish a surface quickly, then measure it interferometrically, then use a magnetorheological finishing process (very expensive CNC machine) to place the final surface figure onto the lens. Measuring a surface requires at least 15-20 minutes of waiting time after handling a lens, and careful measurement by a qualified technician. Again, Slow + trained Tech = time = more money. On top of that, a magnetorheological finishing process is quite a long process also, and does require several intermediate measuring steps to achieve the best result. The end result is probably a 6" surface which costs on the order of $1000 of shop time production rate. Since at least 4 surfaces are required for a doublet, and 6 for a triplet, the cost can rise very quickly, even with the fanciest CNC equipment.

Right now there are no mechanical technologies that can achieve the highest accuracies that astronomical optics require at reasonable cost. Low cost is achieved by limiting something in the design or performance of the final optic.

Roland Christen

I doubt it. I know where all these scopes are, and he is not one of our customers.

Roland Christen

As far as I know, there are no 10" AP Maks in Italy. Perhaps it is an Aries version made in Ukraine.

Roland Christen