Posts Made By: Roland Christen

>>One is the loud noise it makes when slewing--I presume this is because the motors are more exposed than they were on my AP600.>>

The reason for the louder noise on the Mach1 is twofold. First, the servomotors are 3 times as powerful as on the older 600 mount. Secondly, the 600 was geared using a commercial gearbox mated directly to the motor. The reason we chose not to do that is due to the nature of all commercial gearboxes - basically the tiny spur gears on all gearboxes are very small and have only a few teeth. This makes them very quiet even at full slew speed which is close to 10,000 rpm for the servo motor itself. The downside to these small spur gears is that they impart a cyclical oscillation to the output speed when tracking. This means there is a short period variation superimposed on top of the longer period PE. These short period speed variations, even if they are only 2 - 5 arc sec in height, means that the guider must work much harder during guiding, plus you cannot get good long period unguided tracking, even with periodic error correction implemented. In order to eliminate these short term variations we decided to make our own gearbox (same as with the 900/1200 mounts) and use high quality, large size, precision spur reduction gears with lots of teeth. This results in ultra-smooth tracking, which is the name of the game for getting high quality images.

Of course, running a servo motor at 10,000 rpm into a set of gears with 75 and 100 teeth on the high speed gears results in a number of audible whining noises that resembles a miniature jet turbine. We didn't have a heck of a lot of room left for sound deadening material inside the gearbox (it is already crammed with gears and motor) so it was not possible to do much about the sound. You can reduce the noise level substantially by running the GoTo at 900 or 600x, if noise is a major concern. You will get there pretty quickly either way.

Rolando

Once you use Maxim DL you won't go back to any other.

Rolando

I have seen similar designs before. How sensitive is this one to alignment of all the elements? Looks like a good possibility for a large apo, but for smaller apos there is too much work involved.

Rolando

I used ATMOS to develop this design in about 15 minutes using the built-in Optimization Routine, starting from flat surfaces. The basic design goes back about 25 years to a fellow that came to Stellafane and tried to interest people in an airspaced apo using only standard glasses (can't remember his name). At the time we did not have powerful programs like ATMOS available to us poor amateurs. Today it is quite possible to design stuff like this in an evening when the rain is coming down and you can't use your scope 8) .

This design is not optimized and can be further developed using less number of elements and corrected over a larger wavelength range. This particular design puts all wavelengths from 656nm to 460nm into the Airy Disc and has very little sphero-chromatism.

Rolando

Yopu can't compare an 80 with a 125. Color error is highly dependent on aperture.

Rolando

The design of this scope may have 4 color crossings, but that is not important to the performance. One of the crossings is in the very far infrared, which may be of interest to IR researchers, but does nothing for you visual folks. To get this correction in the IR, the design does allow a bit of violet error, something that may or may not be of concern to imagers who are using modern blue-enhanced CCD cameras.

A super apo can be defined for any wavelength range, visual, photographic, infrared or what have you. In any case, at F12 a 5 inch lens should work exceptionally well no matter where the correction is placed. You will find that for planetary work, the longer lenses have a small advantage over a shorter lens because aberrations such as sphero-chromatism can be better controlled and you can use longer focal length eyepieces with their inherent better optical characteristics.

Finally, I know that the lenses were made to a high standard, they were smooth and well corrected, which in the end is really all you need to know - so forget about any of the other details such as 4 color crossings, FPL52, etc. The important thing is that this lens will perform at the peak of what a 5" can do visually.

Rolando

Polar alignment is only one thing. Next comes periodic error which will make your stars oval in the RA direction. You will need to guide to eliminate that.

Rolando

This second image adds H-alpha detail taken by me with an AP 160 refractor, STL11k and Baader narrow band filter, added to an image taken by Gilles Cohen in France with an AP155 refractor and ST8 camera(most of the HA data is Gilles'). This is a multi-national effort.

This image shows how H-alpha seems to cut through the mist of the bubble, rendering the insides in more detail, but making it look somewhat more flat, no?

In the future I will add closeup data of the inside of the Bubble taken with my AP 10" Mak-Cass. It shows some tiny protostar bubbles within the bright twisty thingamajig - but more on that later after I've had a chance to process several hours worth of H-a data.

Rolando

Very nice shot, Jim.

Roland

>>poor collimation, decentering of lens elements, etc.)? >>

Astigmatism and perhaps some coma is always present in any lens as you go away from the center of the field. Eyepieces also add astigmatism as you go off-axis. It is not a collimation or decentering probem of the objective. If the astigmatism is not uniform around the edge of the field, you may have a tilted focuser.

A miscollimated objective lens will cause the "sweet spot" of zero astigmatism to shift from the center of the field toward the edge. It is a simple matter of tilting the lens cell back to square to bring this sweet spot back to the middle of the field. Gross misalignment of the lens or lens cell causes the sweet spot to go completely off the field of view (or focal plane). Decentered lens elements always will cause severe coma on axis as well as off-axis.

Rolando