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.