Friday, May 22, 2015

New Hinode Solar Guider

Sun on the Dashed Line

Nearly perfect conditions prevailed before noon on May 4th: clear sky,  temperature in the upper 60's to low 70's, periods of good seeing, and almost no breeze.

Large sunspot group 2335 was positioned left of center above a horizontal dashed filament line stretching across the Sun's southern hemisphere. The following 19-image mosaic, made with a 2X Barlow lens, shows features above the dashed line. (Click on the image for a larger view.)
Sunspot group 2335 included several small umbras amid complex structure with a nice curving filament to its right.
Today I used my new Hinode Solar Guider for the first time. The guider is the white rectangular device mounted near the top of the telescope tube in the image below. It is designed to correct the telescope mount if the mount is not tracking the Sun accurately.
In the next image below you see two small circular apertures in front of the guider facing toward the Sun. Each circle contains a narrow slit. The two slits are mutually perpendicular. Sunlight enters through these mutually perpendicular slits and the device thereby detects the position of the solar disc. The guider repeatedly detects the position of the disc, notes any changes in position, and sends signals to the telescope mount to keep the Sun centered. The small glowing yellow circle at the rear of the guider shows the solar finder in action. When the bright yellow image of the Sun is approximately centered within the darker yellow target area, the guider is correctly pointing at the Sun.
How well does the guider work? I've used it twice so far. Each time the calibration procedure was not immediately successful. In the first session I had to run the calibration procedure twice before the device would guide correctly. In the second session I had to calibrate four times before success. This wasn't a major difficulty, just a puzzling inconvenience. In the first session it didn't calibrate with a 17-second test run, but did calibrate with a 25-second test run. In the second session it didn't calibrate with a 25-second test run, but did calibrate with a 17-second test run. Maybe I'll get more efficient with more practice.

Once the guider was properly calibrated I found the most aggressive correction setting to be unsatisfactory. At this setting the image jerked around more rapidly than it would due to bad seeing. The medium aggression setting seemed to be most effective. I monitored a live laptop image from a DMK41 camera with a 2X Barlow lens in order to observe the guiding. On the medium aggressive guide setting guiding was smooth and helpful, though not absolutely perfect. During my first session the guider kept image drift within a 40 by 40 pixel box (equivalent to a 20 by 20 arc second box) for 15 minutes. During my second session the guider did better, keeping image drift within a 16 by 16 pixel box (equivalent to a 7.8 by 7.8 arc second box) for 17 minutes. So the image was not absolutely rock steady, but the guider did eliminate accumulating unidirectional drift. It successfully kept a full disc prime focus image of the Sun centered in the field of view of my new ZWO ASI174 camera for many minutes. The guider, of course, cannot eliminate the random swirling dance caused by ordinary atmospheric turbulence.

I intend to use the guider when I make time lapse movies. It probably doesn't make sense to use it for normal solar imaging since my cameras take only a few seconds to capture enough video for individual still images. 

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People say I'm crazy doing what I'm doing
Well they give me all kinds of warnings to save me from ruin
When I say that I'm o.k. well they look at me kind of strange
Surely you're not happy now you no longer play the game

People say I'm lazy dreaming my life away
Well they give me all kinds of advice designed to enlighten me
When I tell them that I'm doing fine watching shadows on the wall
Don't you miss the big time boy you're no longer on the ball

I'm just sitting here watching the wheels go round and round
I really love to watch them roll
No longer riding on the merry-go-round
I just had to let it go

John Lennon