What is the photographic observation of the total solar eclipse?

The development and progress of society is really amazing. Just ten years ago or earlier, watching photography was still a very strange thing. After black-and-white film photography and color photography, digital photography and computer image processing are now popular, leaving countless wonderful objective real-time memorials, which makes me relaxed and happy, and my artistic conception rises. Nowadays, people's interest has shifted from natural scenery to astronomical wonders. It is not exciting to see that many enthusiasts and even beginners have successfully taken wonderful photos of the solar eclipse. Some of them can not only be watched for a long time, but also have certain research significance. Of course, there will be more people who want to know more about and master some photography skills of solar eclipse, so as to effectively seize the rare opportunity of total solar eclipse and take many good photos of solar eclipse wonders. There are too many contents and materials in this respect, so I won't mention them. I can only talk about some main points here in the form of an outline. Generally speaking, getting started is not difficult, as long as you practice thinking more. You can quickly master skills and reach a higher level.

First of all, the principle and skills of eclipse photography are similar to those of general photography, but there are some special features in eclipse photography. These characteristics were also mentioned in the previous visual inspection. During the total solar eclipse, the sun gear during the partial solar eclipse is extremely bright, so it is not safe to shoot directly with a camera, which will burn out the negative film or charge coupled device (CCD) of a digital camera. The light should be dimmed before shooting, and the exposure time should be determined according to the size of the partial solar eclipse. In the stage of total solar eclipse, the chromosphere, especially the corona, is extremely dim, which requires the camera's "optical power (objective aperture/focal length)" to be large, the sensitivity of the negative film or CCD to be high enough, and the exposure time to be long (which involves tracking the apparent motion of the sun).

Second, choose the shooting plan according to the wishes and conditions. For an eclipse observation team, it can be divided into several observations.

(1) Shoot the panorama and process of the solar eclipse with negative film. During the August 1 solar eclipse in 2008, the horizon of sun gear was relatively small, so the general camera could capture the partial solar eclipse and the ground scenery in sun gear at the same time. Using a tripod to fix the camera, the altitude angle and azimuth range of sun gear and the ground scenery are estimated according to the whole process of the total solar eclipse, and the camera is fixed in the direction of sun gear during the total solar eclipse. Add and subtract light sheets in front of the objective lens (the transmission "density" is greater than 4, that is, the transmittance is less than110000), and expose them at regular intervals (such as10 minutes) from the beginning of the partial solar eclipse. From the beginning (eclipse) to the end (light) of the total solar eclipse, take off the dimmer and shoot the color ball and corona. When the light is generated, a dimming film is added to shoot the partial eclipse at intervals until the eclipse is over, and a similar effect is obtained.

It should be pointed out that the diameter of the sun gear image on the negative is about 0.0093 times of the focal length of the objective lens. For example, when the focal length of the objective lens is 60 mm, the diameter of the sun gear image is only about 0.56 mm, and the resolution of the image is acceptable, because the particle size of the negative is about 20 microns. If the focal length of the objective lens is too short, it is difficult to see the shape of sun gear during the partial solar eclipse. However, if the focal length is too large, the wheel image of the partial eclipse will be large, but the field of view may not be enough.

For the total solar eclipse on July 22, 2009, it is difficult for even a wide-angle camera to capture the ground scenery and the partial solar eclipse at the same time, so we have to give up the ground scenery to ensure a similar total solar eclipse process.

This kind of filming the whole process of solar eclipse with negative film is a wonderful scientific and artistic appreciation, especially in color. However, it also has some shortcomings: ① The sun image is very small, and the "resolution" is poor, so it is difficult to distinguish the detailed features (such as sunspots on the sun gear). ② Only one photo is taken of the corona (the images of the corona will overlap if exposed multiple times during the total solar eclipse). The specific photographic exposure time should be estimated according to the size and sensitivity of the negative. For example, use one of the eight "120" negatives with a general sensitivity of 21din (= ISO100/2/ASA100) and add1/. Use the aperture (number) of 16 (that is, the ratio of effective aperture of objective lens to focal length 116) from shooting to solar eclipse 1/2, solar eclipse 1/500 seconds, and solar eclipse 1/2 to/. During the total solar eclipse, remove the dimmer and shoot the corona 1/30 or115 seconds or longer. Under other conditions, the exposure time can be converted by the following rules: the exposure time is inversely proportional to the transmittance of the dimmer, inversely proportional to the square of the aperture (number), and inversely proportional to the film sensitivity (ISO).

It should be pointed out that the cable release button should be used when shooting light, and directly using the button on the camera is easy to cause jitter!

(2) Take a larger image at a time. Because the diameter d of sun gear image is proportional to the focal length f of the objective lens (d=0.0093F), it is necessary to use a telephoto objective lens to obtain a wide range of coronal images. For example, in a telephoto camera with a focal length of 250 mm, the diameter of the sun gear image taken on the negative film is only 2.325 mm, which is much smaller than the short side (24 mm) of the "135" negative film, and the negative film is enough to shoot a super-long corona or mass ejection with a radius of sun gear 10 times. It is not appropriate to fix the orientation with a camera (the partial eclipse cannot enter the field of vision), so it is necessary to adjust the orientation in time during the filming of the eclipse. The photographic exposure time of partial solar eclipse and total solar eclipse can be converted according to the above rules. Because the sun is in apparent motion, the exposure time should be as short as possible, so use film with high sensitivity. You can make full use of the duration of the total solar eclipse and take more coronal photos with different exposure times. After observation, multiple images (the main part of which is cut) can be combined in sequence by darkroom copying technology, and the effect will be better with the clever technology of computer scanning and image processing.

Because the brightness difference between sun gear and corona is too big, you can use two cameras. A camera is equipped with a negative with low sensitivity, adding and subtracting lenses in front of the objective lens, and shooting sun gear with a partial solar eclipse. The other camera is equipped with a high-sensitivity negative film, which does not add or subtract light films, but only photographs the chromosphere and corona during the total solar eclipse.

(3) Take a high-resolution solar eclipse image with a telescope. Because the angular diameter of sun gear is only more than half a degree, even the images formed by telephoto cameras are not large, and it is impossible to distinguish the detailed features such as sunspots, prominences and coronal rays. For example, "135" (35 mm long side) film is used to shoot corona features within the range of 5 times the diameter of sun gear, and the diameter of sun gear image is 6 mm, so the objective lens with f = 6/0.0093 mm =645 mm ≈0.6 m is selected accordingly, which is beyond the reach of the objective lens of general telephoto cameras. Moreover, because the sun is in apparent motion, especially when it is exposed for a long time (more than110 seconds), it is necessary to follow the sun to obtain high-definition images. Therefore, a telescope with tracking drive should be used as a camera. A simple method is to shoot the negative directly on the focal plane of the telescope objective. You can take off the objective lens of the camera and use its black box, shutter and viewfinder. Make shooting procedures according to the above rules, and shoot one by one. However, the focal length of the telescope objective is fixed. If it is too long, even the image of sun gear will exceed the negative range, but it is good to shoot the polar rays near the prominence and corona arc or the edge of sun gear. If you want to take a full view and a partial view of the corona, you can use the method of secondary imaging of the camera to combine the objective lens of the telescope and the camera into an equivalent "zoom" objective lens. Take off the eyepiece of the telescope, and install the camera (the front focus of the objective lens) at the distance d behind the focal plane of the telescope objective lens, then the equivalent focal length of the combination of the telescope objective lens (focal length Fe) and the camera objective lens (focal length Fe) is Fe-FF/D, and the image of the focal plane of the telescope objective lens is imaged by the camera objective lens twice on the negative film, and the distance between the negative film and the camera objective lens is l = f (1+d)/d, and the image. It can be seen that if F/D > 1, the image is enlarged, and Fe/F > 1- is equivalent to focusing the telescope; If f/d < 1, the image will be reduced, and Fe/f < 1- is equivalent to defocusing the telescope. Because Fe and f are fixed, changing the distance d is equivalent to zooming. The required Fe can be estimated according to the shooting purpose, and then D can be estimated, and D can be fine-tuned and finally selected in actual operation. Using the aperture, equivalent focal length and negative of the telescope objective to draw up an observation plan, you can shoot the moon to practice your skills. Because the camera may be too heavy and too long at the eyepiece end of the telescope, the balance of the telescope should be considered. Obviously, it is appropriate to use a light short-focus camera.