Sunspot Departs

Welcome Company

On April 16th I observed the Sun with my young friend, Luisa, a bright, curious international student from Brazil. Luisa has a deep interest in physics and astronomy. I feel so fortunate to be able to share common interests with Luisa. April 16th was a nearly perfect day with few clouds, light wind, low humidity, and temperatures in the mid to upper 60's.

We began using my troublesome new ZWO ASI 1600MM camera. From the start flashing horizontal lines were present on the laptop preview screen. I had hoped they would disappear when using a powered USB hub, but the powered hub by itself made no difference.

With Luisa's help, we were able to prove there is a faulty USB connection between the camera and laptop. She gently moved the USB plug at the camera while I looked at the preview screen. Sure enough, horizontal lines increased or decreased depending on how the plug was moved. There is a faulty connection right at the camera's USB plug on the camera body. The plug itself seems to be loose.

With Luisa holding the plug so that no lines were visible I captured the first image below showing sunspot 2738 approaching the Sun's western limb.

The picture above shows the kind of image the 1600 camera could produce if it were functioning properly.

With Luisa continuing to hold the USB plug, I took another image of the sunspot using a smaller region of interest.

Six days ago the umbra was split into two dark parts separated by a brighter dividing line. On this day the lower umbra was lighter than the upper portion.

Since the 1600 camera was malfunctioning, I decided to pack it up and use my trusty old ZWO ASI 174 camera instead. It has a smaller field of view, but at least it works as it should. The sunspot looked just as good with the older camera, but the reduced field of view is apparent if you compare the next image with the first image above.

As clouds increased I took three more images to blend together into the following three-panel mosaic.

Images from the old camera blended beautifully into a mosaic. In previous attempts, however, images from the new camera seemed to challenge and defeat all my mosaic building software.

I'm in the process of trying to return the 1600 camera, but don't know if this will be possible.

Rare Sunspot

Camera Struggles Continue

After many months with no significant sunspots a good sized spot finally appeared on April 10th. Two large prominences were also visible through an eyepiece. A four-hour window of clear skies along with comfortable temperatures in the mid 60's to low 70's made this a good day continue working with my ZWO ASI 1600 camera.

The first picture below, made with a 3X Barlow, shows solitary sunspot 2738, on an otherwise featureless disc. Only one prominence is dimly seen along the limb because exposure time and camera gain were not sufficient to properly capture dim prominences.

The camera malfunctioned from the very beginning of this observing session. Intermittent, thin, bright and dark horizontal lines appeared throughout the laptop preview screen. (A few of these defects show up along the limb at the very top of the previous image, but only if it is increased to full size.) It seemed like the camera couldn't download the chip contents completely without gaps in random locations. I tried pushing the USB plug in more firmly as well as using a different USB wire. I tried adjusting the USB traffic setting. Nothing eliminated the horizontal lines. Merely moving the Sun within the field of view caused horizontal lines to temporarily increase before settling into a less pervasive, but still existing effect. This problem did not happen during the previous three times I'd used the camera. Next time I'll try using a powered USB hub to see if it will eliminate the problem, but I'm beginning to think the camera has a hardware defect.

The sunspot itself had a bisected umbra more clearly visible in the next somewhat fuzzy cropped image.

A dramatic array of prominences were present around the limb as you can see in the next flawed image. Once again, I failed to capture prominences without also capturing unwanted, uneven background light. In this 2-panel mosaic the disc is overexposed. Horizontal streaks were also visible before I tediously removed some of them manually with Photoshop. (Click on the image for a larger view.)

Notice the imperfect blending of constituent panels at the bottom of the image.

After working with the 3X Barlow I switched to a 5X Barlow and successfully removed circular interference fringes by slightly loosening one screw on the tilt adjuster. This was one success in an otherwise disappointing session. Unfortunately, I couldn't continue working with the 5X Barlow because clouds moved in.

At this point I'm losing patience with this balky camera. If I can't find solutions to problems soon, I may try to return it and hope for a refund.

Flaws

Camera Struggles Continue

Beautiful observing conditions were in place on April 3rd - clear skies, light breeze, and temperature in the mid 60's. I began solar imaging with my new ZWO ASI 1600 camera and a 5X Barlow lens. Annoying circular interference fringes appeared with the 5X Barlow and stubbornly resisted all attempts at removal this day. Perhaps you can notice interference fringe traces in the first picture below. It shows active area 2737, the only significant feature on the solar disc this day.

Two prominences were present. With a 3X Barlow both were visible on the laptop preview screen only if I lowered the gamma value drastically. This caused flaws in the background. In other words, increasing the visibility of dim features also increased the visibility of flaws in the camera's chip performance. The next image shows the problem.

Prominences should appear against a uniform darker background. Instead, the background is neither uniform nor particularly dark. (Click on the image to see the flaws in more detail.) Any attempt to darken the background also removed the prominences. Also, notice concentric curved defects in haze above spicules along the upper left rim.

To understand the nonuniform background problem I examined several dark frames. These are images made when no light is falling on the camera chip.  Ideally, a dark frame should be uniformly dark. It should record zero brightness levels in every pixel on the camera chip. In the non-ideal real world the camera records small varying pixel brightness levels caused by thermal effects. There shouldn't be drastic variations between different areas on the chip. Unfortunately, drastic variations did seem to be happening on my camera's chip. For example, look at the image below which was constructed by averaging 10 video frames while the lens cap blocked light from entering the camera.

As you can see above, the dark frame isn't uniformly dark across the chip. A pixel on the right side is about 1.9 times brighter than a pixel on the left. (I have enhanced the difference slightly so it will be visible here, but the factor of 1.9 comes from the original unenhanced image. This dark frame was made with exposure time 29.7 ms, gain 123, and gamma of 24.) Apparently, the nonuniform response is inherent in the chip itself. It is not coming from the Sun. In the future I need to correct for this flaw in order to get better images. 

I captured more than enough overlapping images to construct a disc mosaic, but Photoshop Elements would not create a flawless mosaic. Close examination reveals blurred portions of the following 4-panel mosaic as well as slight discontinuities along the rim in a couple places. The flaws are more visible if you click to produce a larger image.

Once again, the background is not uniformly dark. One of the prominences on the right side doesn't even show up.

Apparently, I need to experiment more with exposure time, gain setting, tilt adjuster angle, and camera temperature to see if I can improve results. Although drastic changes to gamma made prominences visible, they also significantly increased background levels. The camera's wide field of view is definitely wonderful, but I have to eliminate flaws to take full advantage of it. Results so far have been very discouraging. 

Trial and Error

Mostly Error

I'm continuing to explore solar imaging with a new ZWO ASI 1600 camera. The first picture below shows my Lunt 100mm solar telescope with the camera attached to a tilt adjuster and 3X Barlow lens.

Observing conditions on March 28th were fairly comfortable with diminishing thin clouds, little wind, and temperatures in the mid 50's. Since there were no significant features on the solar disc, I tried to capture relatively dim spicules and prominences along the limb. The first image below was made using a 30.7 ms video frame exposure time with gain and gamma set at 50.

I then decided to overexpose the featureless disc it in order to enhance the limb. The frame exposure time was changed to 29.7 ms, gain increased to 123, and gamma changed from 50 to 24. This camera setting combination made limb features show up clearly on the preview screen where they had been previously invisible. The next image is a 3-panel mosaic made with camera settings mentioned above. It shows a variety of features around the limb with the overexposed portion blacked out. (Click on the image for a larger view.)

Although I captured enough individual images to include the entire rim circumference, construction of a full circle mosaic was impossible. None of the software tools I use to patch individual images together into mosaics would handle overexposed, featureless disc areas. It was also impossible to darken the yellow glow surrounding the Sun without simultaneously darkening limb details I purposely set out to capture. 

Next, I tried cooling the camera to zero degrees C. I could see no significant reduction in background level. A yellow glow still accompanied limb features. I tried a frame exposure time of 27.2 ms, gain of 100, and kept gamma at 24. Once again, it was impossible to make a mosaic. The last image below shows the largest prominence and other nice limb details in the midst of the yellow haze. (Click on the image for a larger view.)

Lots of time was spent stumbling through new software menus and features. The latest version of Firecapture is required to operate the camera. I also installed the latest version of Photoshop Elements to process and enhance the images. Operation of my new camera has still not settled into an efficient, comfortable routine. 

New ZWO ASI 1600 Camera

First Light

The Sun continues sleeping through the current sunspot cycle minimum, but things will eventually change. When activity picks up I'll be ready to capture images with a new ZWO ASI 1600MM camera. This camera has a substantially larger chip than my ZWO ASI 174MM, so it will produce a wider field of view and require fewer panels for full disc mosaics. The 1600 chip has 3.8 micron pixels in a 4656 x 3520 array and measures 17.69 mm by13.38 mm. The 174 chip has 5.86 micron pixels in a 1936 x 1216 array that measures 11.34 mm by 7.13 mm. Here are front, side, and rear views of the new camera.

A cool, clear afternoon in the low 50's on March 17th was a good opportunity to try the new camera with my Lunt 100 mm solar telescope. I began with the camera at prime focus, and obtained the full frame image below.

The field of view above is 81.5 by 61.6 arc minutes, obviously more than enough to capture the whole Sun at once. I worried this large chip would have a slow video frame download rate, but the image above was created from a 400-frame video that took about 40 seconds to download. The camera's onboard 256MB DDR3 memory buffer probably helped speed downloads.

Next, I tried defining a region of interest including the whole Sun while eliminating empty surroundings. With this reduced region of interest the 400-frame video downloaded in only 20 seconds and produced the next image below.

Unfortunately, these prime focus images don't have the best resolution. They don't show the most pleasing amount of detail. Click on the image above and then compare the detail with better images below. Magnification is required for better quality images. So I next tried using a 2X Barlow lens. The magnified 2X image, seen below, was now too large to fit the entire Sun in one frame. The 2X Barlow field of view is 31.6 by 23.9 arc minutes. (On this day the solar diameter was 32.2 arc minutes.) If you look closely, you can see hints of a circular interference pattern below center. (The 2X Barlow image is also rotated compared to the prime focus images.)

Click on the image above to see it has much better detail than the prime focus image preceding it. From past experience I knew a 3X Barlow lens would yield even better results, but the first 3X Barlow view included intense, dark, circular interference rings. I installed a tilt adjuster between the Barlow and the camera, but it had little initial effect. When I rotated the camera plus tilt adjuster 90 degrees while leaving the Barlow fixed, the annoying interference rings completely disappeared! The field of view had now diminished to 26.5 by 20.1 arc minutes. I combined four separate 3X Barlow images to produce the following 4-panel mosaic.

Click on this image to see better detail, including small prominences along the limb. I don't know why I didn't take two more images to cover the whole disc. Now I wish I had done so! No truly impressive features are present on the disc, only one small dark filament and a small white active area below the filament. Three or four days later the small active area developed into flaring sunspot 2736.

The resolution of the 3X Barlow looks pretty good. I may always use this configuration in the future. It looks like it can produce nice, detailed, full-disc mosaics with only six component images! This is much better than the 40-panel mosaics I labored to construct in the past.

Finally, I tried the camera with a 5X Barlow lens. Circular interference rings were present again even with the tilt adjuster in place as you can see in the following grayscale image.

The field of view with the 5x Barlow is 16.5 by 12.4 arc minutes. Next is a cropped and enhanced portion of the previous image showing the two disc features.

Interference fringes are visible but the detail is respectable. I'll have to work on eliminating the interference effects and decide between the 3X and 5X Barlow for future imaging.

The new camera also includes a cooling system and fan for cooling the chip to reduce unwanted thermal signal. Thermal signal (dark current) probably doesn't have enough time to significantly develop during relatively short exposure times (roughly 27 milliseconds) used to capture individual solar video frames. Cooling will be more important if I ever try to use this camera at night to take long exposures of dim celestial objects. Nevertheless, in the future I will see if cooling has any noticeable effect on the quality of solar images.

Lunar Eclipse

Frozen Fingers

Williamsburg was perfectly located to observe the January 20th total lunar eclipse. The entire event was visible in clear skies high above the horizon, but frigid temperature and strong wind made observing very uncomfortable.

I struggled with a tripod-mounted Nikon D40 camera over the course of two hours attempting to get a decent image. Adjusting camera settings by pushing tiny buttons with frozen fingers was frustrating. I must have taken more than 50 pictures, but only one of these had reasonable quality. This one good image is shown next. It's a 4-second exposure with a zoom lens set to 200mm. A few  background stars are visible, especially if you click on the image to enlarge it.

The next image is also a 4-second exposure, but the lens was zoomed out to 55mm.

During totality the following picture, underexposed at one second, shows the Moon's orange color.

During partial phases it was hard to simultaneously capture detail in both the lit and shadowed portions of the Moon. The next two images show this. In the first picture there is reasonable detail in the shadowed orange portion, but the lit portion is overexposed. In the second image the overexposure is less, but the shadowed portion is too dark.

The cold weather was brutal. Small camera buttons could not be operated with gloves, and my bare fingers became uselessly numb after only ten minutes in the cold. Consequently, I could spend only a few minutes outside before retreating indoors to warm up. Rinse and repeat for about two hours. 

Wide Angle Sky Pictures

First Try

My ZWO ASI120mc color video camera has a small 150-degree all-sky lens which can be mounted directly in front of the camera. When this lens is in place the camera can be used without a telescope to take wide angle images of the sky. The next picture shows the camera with the 150-degree lens attached.

On the relatively mild, clear, moonless night of January 5th I decided to try wide angle sky imaging for the first time. It was a rare night in my back yard with fewer bright nearby house lights than usual.

The camera was attached to a fixed camera tripod and did not compensate for Earth's rotation. A ten-second exposure with camera tilted slightly southeast produced the following image.

Orion and Gemini are rising at the bottom. Taurus and Auriga are in the center. Just above Perseus at top center an airplane is passing with blinking lights. Turning the camera northeast moved the view a bit and revealed Cassiopeia at top left of center above Perseus.

A few houses away a neighbor decided to turn on an outdoor spotlight producing annoying glare. With 10-second exposures surrounding lights are overexposed.

Tilting the camera to look up at the zenith eliminated neighborhood lights around the horizon. The next picture is the best of all my trials.

The image above was produced by stacking four 10-second exposures. Although the background sky looks grey from light pollution, hints of the dim winter Milky Way can be seen slightly left of center running vertically upward through the constellations Cassiopeia, Perseus and Auriga. Pegasus, Andromeda and Ares are visible to the right of center. The bright object to the right of Pegasus' square is Mars. Even the small dim patch of the Andromeda Galaxy is barely visible. (Click on the image for a larger view.)

Unfortunately, I spent most of the time trying to take single frame "snapshots" instead of capturing several frames and then stacking the results. I should have used this video camera to take actual videos! That's what happens when I rush outside on the spur of the moment without planning the imaging session.

Long exposure times were not possible because Earth's rotation would eventually smear star images. Also, light pollution washes out background darkness as exposure time increases. The next sequence of "snapshot" images shows the effect of increasing exposure time. In order, from first to last, the images have exposure times of 10, 15, 20, and 30 seconds.

Notice the increasingly bright sky background in the above sequence as the winter Milky Way becomes more noticeable. Notice also the scattering of red pixels throughout the images, probably caused by thermal noise and "hot pixels" in the uncooled camera. (The red pixels are easier to see if you click to get an enlarged image.) In the future I'll need to use a dark frame to eliminate background thermal noise.