Posts Made By: Roland Christen

..that is the question (apologies to the Bard)

I had heard from various sources that 2x2 binning would result in higher signal to noise than 1x1 binning. And you could cut the exposure in half, at the cost of some loss of resolution. If the focal length is long so that you over sample, then binning should give you a leg up. Well here is the result, side by side images, for your examination.

17"F8 astrograph 0.54 arc sec/pixel @1x1 bin, 1.08 arc sec/pixel @2x2 bin

On the left is 2x2 binning 26x600sec (4.3hours total exposure)
On the right is 1x1 binned 10x1200 sec (3.3 hours total exposure)

Resolution is 22% better for the 1x1 binning. Note how much better the little galaxy shows up. Even though the 2x2 binned image has longer exposure, the sig/noise seems to be better in the 1x1 bin image.

Rolando

Added 10 x 600 sec RGB with 3x600 sec Ha and 3x600 sec OIII to make this color shot of the Little Dumbbell

Rolando

Hi all,

this image was taken by Ignacio Babillo from the Pampas of Argentina, using an AP 167mm refractor. The image is LRGB.

Rolando

Hello All,

Some have wondered what encoders do for a mount, especially what do the very expensive encoders on AP mounts do to make tracking more precise. Besides eliminating the periodic error of the mount, they also provide real time update of exactly where the axes are pointing, and they do this at a rate of more than 780 per second.

We test every mount in-house before they are sent out so that we know they will meet our PE specs. We do this with a special version of PEMPro that measures the mount axis rotation with a precision lab encoder. These tests take time, approximately 2 hours just for the test sequence. We typically do 5 worm cycles, create PE curves, load them into the CPX controllers and test again with compensation on. In the case of the encoder mounts we also measure encoder tracking performance.

The attached image shows three tracking tests of the same mount (a production unit which will be shipped to a customer). Top is with encoders off and the raw periodic error of the mount. Middle is Encoders off with PEM turned on. The third one is tracking with the encoders turned on.

Compare the values of tracking accuracy with each setup.

Rolando

Roland

Vignetting in Binoviewers is caused by the size of the entrance aperture and the focal ratio of the scope used. The faster the scope, the more vignetting there will be. A typical binoviewer has about a 5 inch (127mm) optical path length (some are longer, some are shorter). When used with an F8 scope, as an example, the beam will expand from the eyepiece focus point to about 16mm diameter (127/8 = 16mm). This means that a Binoviewer with a 16mm opening will just barely illuminate fully the very center of the eyepiece field. For every 1mm more of prism opening you will have 1mm more fully illuminated field. A 20mm Bino will have a 4mm field, 25mm will have a 9mm fully illuminated field, etc.

>>Posted by Don Holcombe on 3/21/2004 7:18:37 PM

I finally had the time and energy to set up both of my scopes tonight. The TOA130F on the AP600E GTO, AP pier and JMI Wheelie Bars and the AP130 f8.35 on the Giro. I've said it before and I'll say it again, the TOA130 is the better of the two telescopes, at least for these specific instruments, both purchased new last spring >>

You mean, like in this case?

Rolando

> Luckily, they haven't solved the Newt problem yet, otherwise I'd end up with a pair of those as well.>>

They have. A Newt version will be available shortly.

Roland Christen

>>Referencing the latest thread: Roland, if it will focus in Newt's AND is still "completely free of spherical aberration and astigmatism" (Alan Dyer's words in S&T) you will have hit a home run.

Milt>>

Well, Milt, you have pointed out several intersting things. One is that most people cannot see aberrations in their telescopes and other equipment, and will praise them to the rooftops, regardless. In fact, they will write all kinds of equipment reviews and not be aware of some fundamental problems, and thus influence not only the buying decisions of a whole generation of users, but worse yet, the future product decisions of manufacturers. It goes something like this: "We can save money on this optic if we relax the specs since people seem to be deliriously happy with the lower performane. They'll never know the difference". I cannot tell you how many times I have heard that last one.

In any case, if you want to use a binoviewer without some kind of compensation for the prism aberations (both color and spherical aberration), then do all magnifications ahead of the prism with a barlow. Never use a shorter eyepiece than about 12mm.

Meanwhile, Baader is addressing the Newtonian focus problem. I recommend that Newtonian builders abandon their teeny-weeny-secondary obstruction obsession and bring the focus out to a reasonable level. I have a 23% obstruction in my 10" Mak and have had it side by side with the best available 10" mirrors and I guarantee that you will not see the difference on the planets. I think the only reason the Dob guys use such tiny secondaries it to save MONEY on the larger diagonal mirror.

Roland Christen

Resolution is not a matter of how much chromatic aberration is or is not in the lens. Resolution will always be the same. In an achromat, only a tiny portion of the visible spectrum around the yellow-green is focused. From red thru orange and from blue-green thru violet, the light is unfocused into an ever expanding halo.

Filters remove the unfocused light from these parts of the spectrum. In doing so, they lower the light grasp of the instrument. Devices like the Chromacor refocus these parts of the spectrum so that the light is not lost. Without a filter or Chromacor device, the unfocused light from the ends of the spectrum causes extraneaous light to wash over the image, thus lowering the contrast of delicate features. They may be there, fully resolved, yet they cannot be as readily seen because they are veiled in a cloud of unfocused blue, red, violet light.

The choice then is to eliminate this veiling glow with suitable filters (thus lowering the brightness of the subject) or to bring all light to focus so it can be used to form the image.

Roland Christen

Simply loosen the setscrew on the bottom of the tube adapter and turn the focuser counterclockwise to unscrew it from the tube adapter. Do not remove the tube adapter from the back end of the telescope tube.

Roland Christen