Photographic problems of direct focus photography

A few problems that will make your hard work for a night go to waste are: the balance of equatorial plane, the calibration of polar axis, the target can't be found (or the wrong choice), vibration, lighting, and the wrong choice of film.

The influence of balance and polar axis has been mentioned before, so I won't talk about it any more. I can't find the celestial body to shoot, which is a common problem for beginners. Because most celestial bodies are very dark, if the aperture of the telescope is too small, we can't see the celestial bodies to be photographed in the camera window at all, so we should use coordinates to help us determine the position. Each equatorial telescope has a coordinate ring. First, find a star with known coordinates in the field of view of the telescope, then align the coordinate ring with the coordinates of this star (this action is called zeroing), and then you can use this correct coordinate ring and the coordinates on the catalog to find out the celestial body to be photographed. Of course, we can also use the viewfinder to look at the starry sky in the viewfinder, and then compare the star map, so that we can also find the celestial body to be photographed correctly. But it is suggested that the diameter of the star finder should be above 5 cm to avoid any danger.

Vibration and lighting are small details, but they will still affect the shooting effect. Be careful. Choosing the wrong negative is a problem that won't make you completely annihilated, but it will make you shoot it again. The celestial body is very dark, so we should choose a negative with high sensitivity, but the negative with high sensitivity has coarse particles and poor resolution, so we should consider the focal length of the telescope, the stability of the atmosphere and the photographed celestial body to choose the negative. The film usually used is 400 ~ 800 degrees. As for what kind of film to use, the author can't explain it in detail because of the space limitation, so he can ask the elder of astrophotography directly.