Saturday, May 30, 2015

New ZWO ASI174MM Camera

Testing New Equipment

It was warm, even borderline hot on May 5th, but I withstood the heat because I was anxious to try my new ZWO ASI174MM monochrome camera. The camera is the small red cylindrical device attached at prime focus on the back of my telescope in the images below.
The new camera is theoretically superior to my old DMK41 camera in three ways. First, the chip size is significantly larger. The new ZWO camera's chip has 5.86 micron square pixels in a 1936 by 1216 array compared to the DMK's 4.65 micron square pixels in a 1280 by 960 array. This means the ZWO chip is 11.34 mm by 7.13 mm compared to the 5.95 mm by 4.46 mm DMK chip. The ZWO chip has three times the imaging area of the DMK chip. 

Second, the new camera has the ability to record a greater brightness range. The DMK camera is an 8 bit device capable of 256 brightness levels. The ZWO camera can function as an 8 bit, 10 bit, or 12 bit device. In 10 bit mode it records 1024 brightness levels. In 12 bit mode it records 4096 brightness levels. 

Third, the new camera has faster download speed. The ZWO camera uses USB 3.0 communication while the DMK uses USB 2.0. This speed increase might be the most useful improvement for my personal observing requirements. For reasons I've never been able to figure out the DMK camera usually freezes temporarily during capture downloads. For example, the capture of a 400-frame video takes 27 seconds when the DMK is behaving properly. But proper behavior seems to come and go at random. More times than not the DMK takes 54 seconds or more to download a 400-frame video. In 8 bit mode the ZWO took only 6.67 seconds to download a 400-frame video, and in 12 bit mode it took only 12.76 seconds! This is a very pleasant change from the DMK! Unfortunately, I still experience temporary download freezes with the new camera. The freezing isn't constant. It comes and goes as if the laptop is handling competing tasks. I just don't know what these competing tasks could be. It would be wonderful to discover some computer setting that would eliminate this problem.

The new camera's large chip size means a full disc solar image can be captured at prime focus with my Lunt 100 mm telescope. The picture below has not been cropped. It shows exactly how the full disc fits on the imaging surface. The field of view is 51.7 arc minutes wide by 32.5 arc minutes high. Resolution here is not pleasing, but the full disc image could be obtained from one video without making a mosaic. Unfortunately, illumination is slightly uneven from left to right, perhaps because the disc was not precisely centered horizontally on the chip.
I usually use a 2X Barlow lens with the DMK camera because it gives a more pleasing resolution than prime focus. So I used a 2X Barlow with the new ZWO camera to see how images would look. The following 3-image mosaic, made with the 2X Barlow, shows large sunspot group 2335 below center, 2338 near center, and newly visible sunspot 2339 near the limb in the upper left. (Click on the image for a larger view.) There is a slight uneven illumination, particularly in the bottom right corner. The resolution here is much better than the prime focus image, but still not quite as nice as what I get with the DMK plus 2X Barlow.
The next picture, a 2-image mosaic, shows filaments stretching across the southern hemisphere. It was processed to show disc features, so prominences are not visible.
The next image is the same mosaic as the previous one, but disc features are overexposed in order to reveal the filament to prominence transition on the right limb. (Click on the image to see the transition in more detail.)
The best picture obtained with the new camera so far is the following single image showing prominences, sunspot group 2335, and nearby filaments.
Resolution is not quite as good as I'd like. Click on the image to view it full size, then compare the area around sunspot 2335 with the resolution of the next image. You will probably agree that the DMK41 image below is a little nicer.
I may need to use a 3X Barlow with the ZWO camera in order to achieve the resolution I'm looking for. It will take a while to try different exposure times, Barlow lenses, and settings in the FireCapture software that runs the camera. But I'm encouraged by these initial results and I'm looking forward to using the new camera again soon.

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. 

Thursday, May 14, 2015

Enormous Prominence

Prominences Galore!

On April 23rd a dramatic giant prominence rotated into view on the Sun's eastern limb. Although only two days had passed since my last observing session, I went out again to image the behemoth. It was another windy spring day with gaps between clouds.

The following 5-image mosaic, made with a 2X Barlow lens, shows a huge portion of solar limb occupied by the monumental prominence.
A magnified view shows the mighty prominence itself.
Prominences also graced the Sun's western limb as shown in the following 5-image mosaic. (Click on the images for a larger view.)
Disc features are overexposed in each of the previous images in order to reveal the dim prominences.

I spent a good deal of time this day trying out a new camera and wondering why it wasn't functioning as expected. It finally dawned on me that I inadvertently bought a color camera instead of a monochrome camera! I thought I had purchased a monochrome camera and expected monochrome camera behavior, so I was constantly puzzled by the results I was getting. It makes no sense to use a color camera for hydrogen-alpha solar imaging because solar filters pass only very, very monochromatic red light. I hope to have the correct monochrome camera soon. I'll write about the camera's performance in a future post.

Wednesday, May 6, 2015

Dodging Clouds

Windy Day

It tends to be windy at my observing site in spring. On April 21st it was 67 breezy degrees with fair weather clouds drifting by. I managed to image a few sunspots and one interesting prominence through gaps in the clouds.

I captured only ten videos this day because I explored possible solutions to communication problems between my camera, telescope mount, and laptop. Hoping to reduce USB traffic, I removed the USB receiver for my wireless trackball and controlled the laptop only through its touchpad. Next, I connected my DMK41 camera directly to its own dedicated USB port instead of feeding camera data through the same cable used by the telescope mount. With this setup the camera and the telescope mount each have their own dedicated USB ports. I was pleased to find the camera downloading captured video at full speed. There was also no communication break between the mount and computer. I wondered if this setup would work during longer observing sessions. (It didn't. Camera downloads were frequently slow in subsequent sessions.)

The following 3-image mosaic, made with a 2X Barlow lens, shows prominent features in the Sun's western hemisphere on April 21st. Double umbra sunspot 2325 is at lower left. Sunspot group 2324 is above 2325. Sunspot 2326 is on the right among filaments. A loop prominence is faintly seen lower to the right of 2326.
Nice prominences along the western limb can be seen in the next 2-image mosaic where disc features are overexposed in order to reveal the dimmer prominences, particularly the bottom one.
A magnified view of the lower prominence, associated with departing sunspot 2322, reveals a loop structure.
Sunspot 2327 sat in isolation near center on the solar disc with a small magnetic dipole to its right.
It would have been nice to make a time lapse movie of the loop prominence, but there were too many clouds drifting past the Sun, and it was too late in the afternoon.

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