Observation Notes: Friday, November 10, 2000

There's a lovely open hillside about 5 kilos away overlooking my  hometown. From the yard I can train my telescope on it. Among the objects I can focus on is a snow fence. As you may know, a snow fence has alternating gaps between wooden slats. At 180X the gaps are visible but nothing much can be seen through the openings. I planned to test what (if any) benefit I might have in seeing fine detail when bumping up the magnification using the snow fence as a target. The first problem I encountered was the lack of focuser travel in the Argonaut. This made it impossible to use the barlow in the normal 2x configuration. To achieve focus I was going to have to use it in the 3x configuration (before rather than after the star diagonal). In 2x I would have had the following magnifications at my disposal:

Instead I now I have something more like this:

Initially I was skeptical about ever pushing a 6" scope to 90X per inch aperture. However, to be thorough, I made a series of observations to get a sense of just how bad things could get. Conditions for my day light test (using the snow fence) were outstanding. Even at 180X it is obvious when conditions are poor -- the air "boils" around the fence making things quite indistinct in the background. This was not the condition I saw at this time. The air was still with only a hint of haze. Things were in place to determine just how much of a problem high magnification was in and of itself (as opposed to atmospheric conditions). I started out with the 25mm at 3x and compared this to previous views with the 10mm at 180. First the 25mm at 3x was indeed showing larger images than the 10mm straight. So the configuration I was using probably was a true 3X. (Barlows are tricky. You can't assume that 2x and 3x are precision multipliers -- much depends on the distance of the eyepiece from the barlow lensing system.) Next, it was obvious that I was able to leverage off the better eye relief of the 25mm eyepiece. (Eye relief on the 10mm is poor compared to the 25mm. The barlow in itself did not improve the native eye relief of the eyepiece.) I also noticed some field flattening. Also, I noted that image brightness was slightly poorer (due to both the increased magnification and the additional three elements added by the barlow itself to the six already in the eyepiece itself.) Finally it was clear to me that an additional 16% gain in image size did allow me to view objects more plainly through the snow fence gaps. I repeated the above tests using the 15mm and 10mm oculars. At no time did I see a magnification cliff. Things just kept getting larger and darker. The gap in the fence got larger, more detail was accessible to my eye. Wow! But would this hold up in the night sky? NOTE: The next day I repeated the above test sequence. The snow fence looked bad at every power. There was a lot of atmospheric boiling. More power simply meant things got darker and murkier -- there was even a loss of detail above 210X. So once again, I confirmed for myself that seeing is the fundamental factor effecting the performance of excellent optics... As the sky darkened, I took the opportunity to test night sky performance. I did this by turning the scope on Epsilon Lyrae. An easy split at 150, more gap at 210X, still more gap at 360X (with the beginnings of an "airy disk" quite apparent) and finally at 540X. Double wow, good optics plus good seeing rules!

NOTE: 

At 360X and 540X I was able to distinctly see two additional stars between the brighter four components of the double-double. Therefore, in addition to the 9.5 magnitude star forming a triangle with the two binary components, I was also seeing the 12.0 and 12.5 magnitude comes that turn this true double binary into a line of sight septet. At lower powers, I had only seen the 12.0 magnitude with hints of the 12.5 comes in the darkest portion of the night. Now here it was dusk and I was confirming all seven stars. In this way I confirmed that higher magnification does, in fact, reveal dimmer stars. Unfortunately, before it got too much darker, low clouds were moving in. With the moon rising in the east, I began high power tests using my filter kit and barlow combination. Atmospheric boiling was visible at all three higher powers. The out of focus effect of increased magnification showed itself obviously. However, details visible at 210X were also visible at 360 and 540 so other than the annoyance of seeing things less clearly there was no real problem with using the higher powers (as long as you have a good clock drive...). I then brought out a succession of filters at 540X for testing. These consisted of the following types: 

I started with the yellow. It did appear to allow additional foreground details to be made out -- but for some reason I did not particularly care for the aesthetic affect. The red seemed to make things appear "blurier" (aesthetics were even worse). The green allowed off-axis background features (such as lunar rilles) to get my attention. (I didn't even notice one particular rille until I dropped in the green filter although I could find it with all the other filters -- and without one -- once I knew what to look for.) The blue seemed to improve focus.

During the test I used the maria-filled crater Plato as a target. The only feature I could make out within it was what appeared to be a slight central dimple? crater? and even this not particularly well...  With my initial Luna tests completed, I used the finderscope to penetrate the hazy clouds to find Saturn. It was kind of neat to see it so huge (dim, and blurry) at 540X. Cassini's division was suggested to my eye at all magnifications. But I never got to see the planet and ring system it as anything other than a low contrast "glow" through the low clouds and made no real tests with the filters. Later that evening I stepped out and found Jupiter high in the sky. Once again, I enjoyed seeing a disk the size of a quarter and on occasion I thought I saw some detail in the SEB. But once again, I basically needed more light to better exploit the high magnifications employed.

Conclusions: 

Use all the magnification you can get away with (on the moon and planets) depending on seeing conditions. If you can't see anything at all at 180X you probably won't see anything more at 360 or 540. Filters are probably useful to enhance low contrast details. But I need to do more testing to determine which filters, under what conditions, and how much improvement is possible. So, stay tuned!

Jeff

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