ZWO120MM camera FOV

The initial focal ratio of each sub aperture was 50 inches (the focal length of an f/10 5" scope) divided by the sub aperture cutout diameter of 1.5 inches. (f/ = 50/1.5 = 33.3). By adding a converging lens just prior to the camera, the focal ratio was reduced to f/19.4, or an effective focal length of 0.74 meters or about 29 inches.

My initial detector was a ZWO120MM monochrome CMOS camera. Here are the specs:

The chip height was 3.6 x 4.8 mm, which gave an FOV of (0.0036/0.74)*57.29 = 0.28 x 0.37 degrees. With a solar diameter of about 0.5 degrees, I wasn't going to be able to see the entire solar disk all at once. I had already decided to measure the altitude of the upper and lower limbs of the Sun separately, because the difference would give me a measure of the solar diameter without any image processing.

Here is a photo of an early solar observation taken in my computer room:

In this photo you can see, on the Mac screen at left, the remote desktop of the scope computer showing the scope control window and the camera window. In the camera window, you can see the upper limb of the Sun placed tangent to the camera horizontal center line via a software reticle. On the right monitor are displayed my two observatory webcams; one showing the sky conditions near the Sun, and the other showing the scope itself, pointed at a high altitude angle. On the wall are some of my favorite SpaceX posters.

I was already seeing the limitations of this small FOV because of my az encoder problems. When I measured separations, the problem was worsened because both the direct and the pitch FOVs were the same small size, which meant that getting both stars simultaneously onto the camera chip was going to be difficult. All this was nudging me to rethink my camera selection.

Table of Contents Previous Page Next Page