Nanchang astronomy enthusiast

Tips for shooting stars with digital camera

Celestial photography has always given people an unattainable feeling-almost all traditional celestial photography is taken by professional astronomers through professional telescopes, and the recording methods used are either extremely rare drying boxes or extremely expensive professional CCD. Now this situation is quietly changing. Just because we have a new weapon-digital camera.

Have you ever seen such a shocking picture of the moon? You might think it was shot by a professional astronomer with a giant telescope. But you are wrong. I can tell you clearly that this is my work with a small telescope and a Nikon995 digital camera.

Astrophotography with digital camera has its unique advantages, as follows:

1, instant shooting. For celestial photography, which is difficult to accurately grasp the exposure, the digital camera can check it immediately after shooting, and if it is not ideal, the chance of success is greatly improved.

2. It is very convenient to connect and focus with a telescope. Digital camera lens is small and convenient for eyepiece; Light weight, it is not easy to change the center of gravity of the system after connecting with the telescope; Whether autofocus focuses accurately can be seen through the LCD screen, which solves a big problem that it is difficult for traditional cameras to focus through the viewfinder.

3. Low cost. Will not waste film.

4, black and white, choose at will.

In this way, due to the emergence of digital cameras, the threshold of astrophotography has been greatly lowered. In the past, you needed a combination of a large telescope and a traditional camera to take pictures. Now you can easily surpass them with a digital camera and a small telescope. If you read this article carefully and have the right equipment, I believe you can also take such photos, maybe even better than me.

The Primary Stage of Digital Color Stars-Constellation Photography

Shooting constellations is the simplest, and you don't need any auxiliary equipment except a tripod. Generally, the lens focal length of a digital camera is short, which is equivalent to 35 ~ 38 mm of a 135 camera, and it is most suitable for shooting constellations. Choose a night without moonlight, in a place with less light damage, firmly fix DC on the tripod, point to the constellation you want to shoot, set it to manual mode, set ISO to the maximum, open the aperture to the maximum, and set the shutter to the longest exposure time (take my Nikon995 as an example, set ISO800, and the exposure time is 8 seconds, F2.6). Remember to turn it on if there is noise reduction function. At this point, you may not see anything on the LCD screen. It doesn't matter, just press the shutter to expose, and you can see the result later (Figure 02, Figure 03).

If the photos taken are underexposed, you can consider exposing them for more time (for example, 30 seconds) with B-door. If your feet are not strong or your hands are shaking, it is recommended to use cable release to reduce the "starry sky" caused by vibration.

If you like the traditional film shooting style-bright stars look big and dark stars look small. Then you can also borrow its method: add a soft light filter in front of the camera.

Auxiliary equipment:

1, tripod

2. It is better to release the cable.

Shooting point:

1, must be fixed on a tripod.

2. Manual setting must be used. Never use automatic exposure.

3. If yes, try to turn on the noise reduction function. If there is no noise reduction function, try to shoot in cold weather.

4. Choose a place with weak light influence.

Medium-scale digital color stars-photography of the moon, sun and planets

Lunar photography

The targets of lunar photography are craters (Figure 04) and the Moon Sea. The viewing plane of the moon is small, and the moon photographed by the lens of a digital camera is also small, even 8X/ 12X. So how long is the lens to make the moon fill the picture? About 2500 ~ 3000 mm, depending on the telescope.

What kind of telescope can be used for lunar photography? An ordinary astronomical telescope will do. Even binoculars with a diameter of 50mm can be tried.

The easiest way to match a digital camera with a telescope is to aim the telescope at the moon and then aim the digital camera at the eyepiece of the telescope to shoot. However, the effect of the photos taken in this way is not ideal, and the instability of hands can easily lead to inaccurate focusing, and the camera shake will blur the image.

The solution is to rigidly connect DC and telescope. There are two practical methods:

1. The lens of a digital camera is directly connected to the eyepiece. There are generally internal threads in front of DC lenses, which are used to install filters or auxiliary lenses. Using it, the eyepiece of the telescope can be screwed into the DC lens by screwing external threads of the same size on it.

Taiwan Province Province has produced an eyepiece specially connected with DC. One end of the eyepiece is American standard 1.25 inch interface, and the other end has 28mm external thread, which means it can be well connected to Nikon950/990/995/4500. When in use, just screw the eyepiece into the lens, then insert the eyepiece into the interface of the original telescope and tighten the fixing screw. This is before and after the connection (see Figure 05). This kind of eyepiece has excellent technology and large objective lens. After connecting with DC, the imaging black circle is very slight and the effect is excellent, which can be applied to most astronomical telescopes. There are other types of eyepieces to choose from, suitable for different DC lens diameters. Unfortunately, the price is expensive, and the price is around 1000 yuan.

The eyepiece with 28mm external thread is also produced by domestic manufacturers, and the imaging is quite satisfactory, but the price is cheap. In addition to the serious black circle, the price/performance ratio is good. The price is less than 100 yuan.

Secondly, the digital camera and the eyepiece are connected by a specially designed connecting device. This connection device is generally designed as a sleeve, one end of which is externally threaded and screwed into the thread of the filter of DC lens, and the other end is a cylinder, which is sleeved on the eyepiece and fastened around with 1 ~ 3 screws. This device can eat most eyepieces and can be made by simple machining.

After combining the telescope with DC, we can calculate the combined focal length of this combination:

Synthetic focal length = DC focal length × telescope magnification

For example, my combination: Nikon995 and Jingde Megrez80 telescope (Figure 06), the maximum synthetic focal length is:

152mm× 20 times = 3040mm

The moon shot by this combined focal length is a little bigger, and the picture can't accommodate the whole surface of the moon. The focal length of Nikon995 can be shortened from 152mm (Figure 07). When shooting the lunar surface, it is suggested to choose an eyepiece with a long focal length (15 ~ 30 mm), so that the magnification is small and the picture is bright, and it is easy to get good quality photos. Let's get started:

1. Fix the telescope barrel on the tripod.

2.DC is closely connected with the telescope.

3. Minimize the DC focal length (so that the field of view is larger and it is easier to aim at the moon).

4. Adjust the telescope to the moon, and an image of the moon appears on the LCD screen.

5. Set the shooting mode to black and white (color mode will make the moon yellow and highlight the chromatic aberration of the telescope, while black and white mode will not have such a problem and the picture quality will be more delicate).

6. Set the manual mode, open the aperture to the maximum, and set the appropriate shutter (1/30 seconds can be used initially. Then increase or decrease the exposure according to the shooting effect. If you encounter a new moon or a waning moon, the exposure time may be longer, and the wind may affect the stability of the system. If you encounter a similar situation, you can appropriately increase the ISO value to 200 and shorten the exposure time.

7. Adjust the DC zoom to make the size of the moon meet the requirements of the picture.

8. Set to self-timer mode and press the shutter to expose. (Self-timer mode is used to keep the system stable and prevent the hand from shaking when pressing the shutter).

Shooting the surface of the moon does not require much skill and the cost is relatively low. It is a "sword test stone" to enter the field of astrophotography. The moon is sunny and round, and there are different customs every day. If you are careful enough, you can shoot some wonderful scenery. Figure 08: Does the moon have ears? )。

Necessary auxiliary equipment:

1, the telescope is in good contact with DC.

2. A tripod for fixing the telescope.

Shooting point:

1, shooting in black and white mode.

2. Use self-timer mode or cable release to prevent jitter.

Sunshine photography

The visual size of the sun is similar to that of the moon, and the shooting method is basically the same, mainly shooting sunspots on the surface. What needs special attention is that the sun is very bright. After focusing through the telescope, the heat concentration is enough to burn the CCD of the digital camera. At the same time, the lens of the digital camera and the eyepiece of the telescope are likely to explode, which will burn the eyes by visual inspection. Therefore, a special solar filter or filter must be added in front of the objective lens of the telescope. This silver metal film can block most of the sunlight in front of the telescope and only transmit a little sunlight (see Figure 09).

Be sure to install a special filter or filter before shooting. For other steps, please refer to "Moon Photography".

Necessary auxiliary equipment:

1, shoot a special filter or filter for the sun.

2. Telescope and good communication with DC.

3. A tripod for fixing the telescope.

Shooting point:

1. Make sure to put the filter or film in front of the telescope objective to avoid burning the camera and eyepiece.

2. Use self-timer mode or cable release to prevent jitter.

3. You can shoot in color mode.

4. Automatic exposure mode can be used.

Planetary photography

Saturn, Venus, Jupiter and Mars are all suitable for shooting, and the shooting target is the details of the planet surface. They look much smaller than the sun and the moon. To make it bigger, you must rely on a telescope with a long focal length. The combined focal length should be greater than 10000 ~ 15000 mm to get an ideal image (see figure 10).

So telescopes with long focal lengths perform better. Suppose your telescope has a focal length of 800mm and you choose an eyepiece with a focal length of 8mm, then the magnification is 100 times. The maximum combined focal length of Nikon995 is:152mm×100 =15200mm, which is just right.

Because the combined focal length is so long, the stability of the system is naturally required to be higher. The declination instrument with fine adjustment is a better choice than the ordinary tripod, and of course it is better to have electric tracking.

Digital cameras are much better than traditional cameras, but some cameras with higher sensitivity seem to be better at shooting planets. Because the camera can get many images in a short time. In this way, multiple images can be selected under the condition of relatively stable atmosphere, and the best image quality can be obtained through special superimposition software (see figure 1 1).

Necessary auxiliary equipment:

1, telescope and DC are in good contact.

2, a stable tripod, choose the equatorial type is better than the usual tripod.

Shooting point:

1, due to the larger magnification, the time with better atmospheric tranquility should be selected.

2. Use self-timer mode or cable release to prevent jitter.

3. The exposure should not be shorter than 1/4 seconds, so as not to blur the photos caused by planetary motion. When the exposure is insufficient, improve ISO to make up for it.

4. Take as many shots as possible, and then overlay multiple images with special image overlay software.

Photography of high-order digital color stars-nebulae, clusters and galaxies

The constellations, moons, suns and planets photographed by digital cameras are nothing more than bright celestial bodies, which can't be photographed even if they are effective. The real challenge is those dim celestial bodies-including nebulae, clusters and galaxies. The weakness of DC is that it can't be exposed for a long time (even the longest exposure time of Nikon D 100 is only 5 minutes, which is far from the exposure time of traditional film from tens of minutes to one hour), which is the big taboo for shooting dim celestial bodies.

Is DC really powerless in such a field? Of course not. If you use a digital SLR, it is promising to use the so-called "direct focus photography" in astronomy. The specific method is to remove the eyepiece of the digital SLR and connect it directly with the telescope. In other words, the objective lens of the telescope is directly used as the lens. In this way, fewer optical lenses pass through, and the optical power is strong, so that the exposure time can be appropriately shortened when shooting. Do you have the courage to take off your DC lens if you don't have a digital SLR?

On the other hand, due to thermal noise, DC cannot be exposed for a long time. In order to solve this problem, someone introduced a freezing method-DIY a freezing module behind the CCD of DC to keep its temperature below "freezing point" (generally-10 to -20 degrees). This solves the problem of too much noise.

Look at the following two nebula pictures, and you will understand that it is worthwhile to remove the lens and add freezing (see figure 12 and figure 13)! This has completely achieved the effect of traditional film, even comparable to professional astronomical CCD.

Necessary auxiliary equipment:

1. Digital SLR (or DC body with lens removed)

2. High-power telescope

3. Automatic tracking of equatorial plane

4. Try to add cooling system to DC.

Shooting point:

1. Be sure to choose a place with little light damage.

2. Cable release must be used to prevent jitter.

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Small knowledge

Types of telescopes: According to their uses, there are observation telescopes and astronomical telescopes.

Types of astronomical telescopes: refraction telescope, reflecting telescope, folding reflecting telescope, etc. According to the optical structure.

Structure of astronomical telescope: Astronomical telescope is mostly composed of objective lens and eyepiece. The light emitted or reflected by distant objects first hits the objective lens, then passes through the objective lens, and finally exits from the eyepiece and enters the observer's eyes. The eyepiece adopts a unified American standard interface (currently, 1 inch, 1.25 inch, 2 inch, etc.). ), the most common is 1.25 inch (3 1.7mm), and the low-grade universal telescope mostly adopts 1 inch (25.4mm) interface.

Aperture of telescope: The resolution of telescope depends on aperture. The larger the aperture, the stronger the resolution.

Magnification of telescope: Magnification = objective focal length/eyepiece focal length. It can be seen from the formula that the longer the focal length of the telescope objective, the shorter the focal length of the eyepiece and the greater the magnification. For an astronomical telescope, it is often possible to change different eyepieces to obtain different magnifications. The larger the magnification, the darker the image. The magnification of the telescope is limited. After this magnification, the telescope can't see anything more clearly, but it will reduce the resolution. The empirical value of the ultimate magnification is: the number of millimeters of the telescope ×2. For example, a mirror with a diameter of 80mm has an ultimate magnification of about 80×2= 160 times. This is to process better quality telescopes. Poor quality mirrors often can't reach such magnification.