What are the photographic guidelines for eclipse photography?

Firstly, the ISO (value) of film sensitivity is selected by photosensitive technology. Then select the aperture number; Last exposure time. For example, if ISO 100 and aperture number 1 1 are selected, then the exposure time of celestial prominence should be 1/500 seconds. Or calculated by the formula, t = N2/(i× 2q) =112/(100× 29) ≈1/423 seconds.

Some examples of exposure time of solar eclipse shooting are summarized. It can be said that the selection of exposure time is very important, and there are certain selection rules, but it is not too strict, as long as it is controlled within a reasonable range. Because the actual situation involves many factors such as the high angle of the sun, the transparency of the earth's atmosphere, and the bright corona at that time, the exposure time can be appropriately reduced.

The brightness of the colored ball is only a few thousandths of that of the light ball, so it takes shorter exposure time to shoot colored balls, prominences, etc. But Bailey beads are often too exposed to light to be seen by the naked eye. The brightness of the corona is only a few millionths of the photosphere, which is roughly equivalent to the brightness of the upper or lower chord of the moon, so the conditions for shooting the corona are similar to those for shooting the moon. The outer corona is hundreds or even thousands of times darker than the inner corona, so it is impossible to take care of both the inner corona and the outer corona at the same time. It is necessary to combine the negatives with different exposure times to understand the whole picture of the corona. It is particularly important to minimize stray light in the instrument when shooting the corona. As long as 1% chromosphere light stray to the outer and middle corona, it will exceed the brightness of the corona there, thus seriously damaging the image quality of the corona. The way to reduce stray light is to add a shading tube in front of the objective lens (but its diameter should be large enough not to block the effective field of view) and a light bar in the telescope tube (but not to reduce the effective field of view). Many telescopes are painted with matte paint, but there is still stray light. One of our simple inspection methods is to aim the telescope at a bright star or a distant light source in the dark, take off the eyepiece and scan all parts directly with glasses. The bright part is the source of stray light. Sticking a piece of black velvet there can eliminate stray light. As mentioned earlier, photographic film is not sensitive enough to capture very bright and dark image features. Although the tolerance of CCD digital camera is very high, the developed photos are still not tolerant enough. The human eye is highly sensitive, adaptable, or tolerant; The faint features of the corona seen by the eyes through a telescope are often not photographed in a limited time. Therefore, the printed good photos are not as wonderful as they are seen. Therefore, interested people go to the total solar eclipse area-hot and dry desert, cold polar region or bumpy ocean to observe the total solar eclipse.

The brightness of the inner corona is very different from that of the outer corona. Generally, features such as long corona cannot be displayed at the same time in photos. In order to display at the same time, we can add or subtract the light film in front of the bright part of the corona on the negative, or combine the two images inside and outside the display into one by developing and printing technology.

Now with computer image processing technology, the program can better weaken the super-strong part of CCD image and enhance the dark part, thus showing corona and other characteristics. Pseudocolor images can also be made. Therefore, it is really interesting to screen and highlight the information obtained by photography. Just after eating, the colored ball flashed into a thin bright arc, and the photographed spectrum was called "flash spectrum", showing some emission lines, which was not only interesting to look at, but also of certain research significance. I talked about the important discovery of this early observation before. Now, astronomers use large spectrometers to take more detailed chromosphere spectra. Generally, eclipse observers do not have such conditions, but they can still make some attempts with simpler equipment and achieve certain results.

Prism camera is actually formed by adding a prism (or transmission grating) with a small vertex angle (for example, about 7 degrees) in front of the objective lens of a small telescope. When it is aimed at the chromosphere, the spherical spectrum can be displayed on the focal plane of the objective lens. The range of this spectral expansion is proportional to the focal length of the objective lens, which requires a long focal length of the objective lens (for example, greater than 1 m) to achieve a considerable expansion (about several millimeters). You can also use the combination of the above objective lens and digital camera to increase the focal length, but you still need to consider that you have enough effective optical power (D/Fe) to capture the spectrum in a short time. Obviously, you can capture beautiful chromatograms with high sensitivity color negative. It should be pointed out that the beam deviates due to prism dispersion, and the optical axis of the telescope should point at a certain angle away from the sun. You can change the angle between the star-seeking telescope and the prism camera, so that when the star-seeking telescope is aimed at the sun, you can just shoot the spectrum.

If you want to shoot better chromosphere or prominence spectra, you need to use a spectrograph with an incident slit. Remove the eyepiece of the telescope and install a small spectrograph at the terminal so that the incident slit is on the focal plane of the telescope objective. Let the color ball or the image of the selected part of the telescope prominence form on the incident slit, and the spectrum is photographed by the spectrograph. In order to make full use of the prominence light collected by the telescope, the focal ratio of the collimator lens after the spectrometer enters the slit should be equal to that of the telescope objective.