What's the difference between black and white, color and digital photography observation?

It is a traditional method to shoot solar eclipse with black and white dry film, which is economical and convenient, and the effect is quite good. There is a set of professional processing and analysis methods for eclipse images of black and white negatives, especially large astronomical negatives. Even amateurs can easily build a simple darkroom, where they can develop, reprint and enlarge photos at will, but the general process of photo studio can not meet the special needs of developing solar eclipse negatives. As mentioned above, the brightness of the corona varies greatly with the distance from the edge of sun gear, and the image developed by the general development method even looks like an uninteresting little white spot. If you use granular developer and dilute it, and extend the rest time, you can get interesting images with wide range and clear details, or copy the negative with low hardness (contrast) in a dark room (even two or three times) and "develop" it with low contrast developer, so you can fully display the corona information of hard photos. If you are interested, you can also use scanners and computer skills to process them into eye-catching pseudo-color images.

The solar eclipse images taken by color negative are convenient for scientific and artistic appreciation. However, besides studying morphology, it is difficult to measure and analyze brightness. Because I don't have color developing equipment, I can only send them to the photo studio to develop negatives and photos according to ordinary procedures, and I often lose a lot of hard-won details and information.

Many years ago, charge coupled devices (CCD) were rare and expensive. In recent years, CCD digital cameras and video cameras have developed rapidly, and even high-performance ones have begun to be widely used. It is displayed on the screen immediately after shooting, and it is also convenient to print photos. Now there are many digital cameras with 4 million and 8 million pixels. It is the general trend that CCD replaces negative film. The serious disadvantage of photographic film is that its photosensitive range-"tolerance" is small, and it can only be shot in the brightness range of 100 times. The bright part is overexposed and the dark part is underexposed, so it can't be shown on the film. Moreover, the sensitivity effect ("blackness" response) is not proportional to the brightness of the image, or it is "nonlinear", so "photometric scale" is needed as "feature". However, CCD does not have these shortcomings, and it is also "linear" in the brightness range of 10000 times, so the data can be recorded on the memory card immediately, without the troublesome blackness measurement and characteristic curve restoration like negative film. The sensitivity of CCD is also very high (ISO200, ISO400, ISO800).

The above eclipse sensitivity estimation method is also suitable for digital camera shooting, so there is no need to repeat it. The following is a guide to eclipse photography. The formula for calculating the exposure time is t (second) = N2/(i× 2q), where n is the aperture number (i.e. the focal length ratio of the camera objective, N= focal length/aperture), i is the film sensitivity (ISO number) and q is the brightness index.