This time, we will take a break from Little Grebe and introduce how to take a picture of the planet with a telephoto lens for the camera.
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Mars approaches the earth on July 31, 2018.
It was the closest approach since 2003.
So, in order not to miss this chance, the manager also tried to shoot Mars.
This time, as I mentioned in my blog before, I attached a telephoto lens for photography and an eyepiece for a telescope behind 300mm.
The camera used was DMW-GH4 manufactured by Micro Four Thirds and Panasonic.
Mars, which has been very close since 2003, is about 58 million kilometers away, around 1:00 on August 1st.
The reason why I shoot with a telephoto lens without using a telescope is that I just don't have it.
I'm doing my best to shoot with the equipment I have.
It's fun to try something with something.
The 300mm f2.8 lens can be said to be a telescope with a diameter of 107mm.
The purpose is different, but the mechanism is the same for both telescopes and telephoto lenses.
To find the aperture of a telephoto lens, you can easily calculate it by dividing the focal length by the F value.
The caliber of the sunnipper
300 (mm) ÷ 2.8 (f) = 107 (mm) 107 mm.
It can be said that it is a telescope with a diameter of 107 mm and a focal length of 300 mm.
Not all camera lenses can be used as telescopes.
Many modern lenses cannot even focus unless power is supplied from the camera body. This is fatal. Also, lenses designed for mirrorless cameras have too short a flange back, which makes them out of focus as a telescope.
To summarize the conditions under which a telephoto lens can be used as a telescope
1. Focus can be adjusted mechanically with a single lens
2. Those with sufficient flange back, (mirrorless lenses are almost impossible)
3. Aperture values can be set freely (although it does not have to be, you can select the aperture value that gives the sharpest image).
Looking at it like this, it's a little disappointing to see that many of the recent lenses can hardly be played with a telescope.
Some recent lenses have an atmosphere where everything is prohibited, such as "Don't do this!" And "You must use it as prescribed!".
The lens itself seems to be rebelling against the user, saying, "I haven't heard that it will be used in this way!" Come on.
On the other hand, old lenses have less restrictions, are a little cursed, but have a very tolerant personality, do not rebel against the user, and are versatile, so there are many things to play with.
Among them, the autofocus lens with Nikon's aperture ring, which was a long time ago, is a versatile player who can do anything, play and work.
The 300mm f2.8 used this time is almost 20 years old, and is the first model of Nikon with a built-in ultrasonic motor in autofocus.
The focus ring is mechanical and can be focused without power supply, and the aperture ring is attached, so you can freely set the aperture.
In addition, the built-in ultrasonic motor realizes quick autofocus, which can be used for shooting wild birds. There is no image stabilization, but conversely, all the lenses are firmly fixed on the optical axis, so there is very little worry that the axis will be out of order or broken due to the vibration of the car, and the reliability is very high. high.
AF-S Nikkor 300mm 1: 2.8 D
The 300mm f2.8 used this time, although the accuracy of autofocus is slightly inferior to the latest one, it is a must-have.
So, I used this 300mm f2.8 telephoto lens as a telescope this time.
Now, when it comes to shooting distant planets, the focal length of the lens alone is 300mm, which is too short to shoot a planet.
It is known that it has a double teleconverter.
Then, even Jupiter, which looks the largest, can only be seen as dots.
Is the Galileo satellite somehow tiny?
That's where the telescope eyepiece comes in. This eyepiece is sandwiched between the lens and the camera.
A strong expansion method called the so-called collimating method.
It's the same as when I often attach a digital camera to the back of binoculars.
This time, I used a 6mm Vixen eyepiece (Vixen NPL 6mm).
Attach the eyepiece in this and connect the camera and lens
Since the eyepiece cannot be attached directly to the camera lens, an adapter is used to attach the eyepiece between the lens and the camera.
In order to attach the adapter to the camera mount, a hole with a diameter of 36.4 mm is hollowed out in the center of the rear cap of the lens and the adapter is attached.
If you hollow out the hole exactly, you can attach it by screwing in as it is, which is convenient.
This adapter was once purchased by the caretaker when he was a high school student. It's a long time ago, more than 30 years ago.
When you disassemble the adapter, it looks like this
The parts on the left side of the photo will be attached in order from the lens.
The left end is an adapter with the lens rear cap hollowed out by piercing work.
In the photo above, the eyepiece is 20mm, but for high magnification, I used a 6mm eyepiece for this shoot.
Since the camera is Panasonic's GH4, I also use Nikon and Micro Four Thirds adapters.
It has a lot of parts, and it's fun to make something like a united robot.
By building this system, it will be possible to take pictures with a strong magnification based on the telephoto lens.
The composite focal length that can be taken with this system can be calculated by the following formula.
Composite focal length = Lens focal length x (Distance from eyepiece to camera sensor ÷ Eyepiece focal length-1)
When I calculate the composite focal length of this system,
The distance from the eyepiece to the sensor surface of the camera is about 120 mm, so
300 x (120 ÷ 6-1) = 5,700 (mm)
The total focal length is 5,700 mm, which is a super-telephoto lens.
By the way, when I try using the 20mm eyepiece in the photo above,
300 x (120 ÷ 20-1) = 1,500 (mm)
Therefore, it is not enough for planetary photography.
Since this focal length is 35 mm full size, the actual output field of view is still much narrower.
The camera used this time is Panasonic GH4 and Micro Four Thirds.
In the range of Micro Four Thirds, the focal length ratio is twice that of the 35 mm version, so
This is equivalent to 5,700 x 2 = 11,400 mm.
It also crops 4K (3820 x 2160) images into SD (640 x 480) images.
The field of view of the final output image is
11,400 x 3,820 / 640 ≒ 68,000 (mm)
When converted to the full size of 35 mm, this system is 68,000 mm, which is a ridiculous super super telephoto.
The photo below is the super-super-telephoto, shooting system for planetary photography used by the manager this time.
The connection is just a free platform.
It is extremely difficult to put a planet in the field of view of 11,400 mm in a free platform that cannot make fine movements, and it is a very difficult task even in a crouched posture.
Although I was finally able to put the appearance of the planet in the edge of the field of view, I often greedily tried to put it in the middle of the field of view and returned to the beginning again.
The viewfinder attached to the top of the camera is indispensable for super-telephoto shooting like this one.
Furthermore, if you do not use the equatorial mount, the strongly expanded planet that you finally got into the field of view will go out of the field of view in a blink of an eye, so the equatorial mount is a necessity.
This time, I used Sky Memo T made by Kenko Kinner as an equatorial mount.
It was a system that completely ignored the weighting, but Sky Memo tracked it firmly.
Planet photography system used by the caretaker, Kenko Sky Memo T is used for the equatorial mount
As I introduced before, the mainstream of recent planetary photography is to shoot a video, and combine only a number of images with stable images to make a photo, and the manager also shot in the same way.
For image editing after shooting, I used Registax 6 free software to compose.
Most of the processing is done automatically, so you can save a lot of trouble.
The picture of Mars on the top is a 90-second shot of a 4k video of GH4, cropped to SD (640x480) and combined. The aperture of the lens is f4, which looks the sharpest.
Furthermore, the three photographs synthesized by the above method are composited again to make the pattern as easy to understand as possible.
The composite photo has been heavily emphasized, so you can clearly see the polar cap and pattern of Mars, but the pattern does not look so dark to the naked eye.
I developed the photo of the above shooting system and noticed that the camera is bent down quite a bit.
It will also cause aberrations, so next time I'll try to take a picture so that it doesn't bend.
This time, seeing and atmospheric conditions were not so good, and the images of the planets were swaying.
As long as I actually saw the finish, the details came out more than I expected, so I was surprised.
Under good conditions, the surface of the planet should be visible in more detail.
I will try shooting again.
This time of year, it is a very gorgeous night with many planets including the moon in the sky as well as Mars.
Furthermore, if you go back to just after sunset, you can see Mercury and Venus in the west sky.
Pluto, which has been downgraded from the planetary constellation to a dwarf planet, is also between Saturn and Mars, but it is so small and dark that it cannot be seen, of course.
Luxurious planets lined up in the night sky around 21:00 on July 23
The next approach to Mars will be in October 2020, two years and two months later.
Even with this approach, it can be seen quite large, about 90% of the diameter this time.
Then the next big approach will be in 2035, at which time it will look a little bigger than this time.
Mars will gradually move away from the Earth for a while, but its speed will be slow.
The Earth, which has a faster revolution speed than Mars, overtakes Mars and looks behind Mars.
Therefore, you can enjoy the appearance of Mars shining red for a while.
By the way, how much would you like to compare the size of Mars to a 500-yen coin this time? So, if you compare it with familiar things, Mars with a diameter of about 6,800 km is at a distance of 58 million km.
Converting this ratio to a 500-yen coin with a diameter of 22.6 mm, the distance is about 190 meters away.
It is important that it is exactly the center line of the 10-car train, the 10-car train, and from the perspective of the conductor at the rear, it is around the side light in the middle of the leading car. (10-car train of 20 meters per car, the position of the side light of the leading car is exactly 190 meters when viewed from the end of the last car with the conductor)
The side light is a red light to confirm that the door is completely closed and that it is safe.
Each vehicle lights up while the door is open and turns off when the door is completely closed. The conductor confirms that all the lights have been turned off and sends a departure signal to the driver.
It's just red and the size is about the same as a 500-yen coin.
If you go to the conductor and look at the side lights of the leading car, you can see that the red side lights are shining in a size that is almost equal to the size when Mars approaches.
Speaking of the earth seen from Mars, it feels like the conductor has a blue billiard ball.
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When it comes to shooting planets, it is not easy to shoot because the magnification must be increased evenly, but why not try it?
Recently, cameras with lenses that can be magnified strongly have come out, and it seems that you can easily take pictures of planets in combination with image stabilization, and there are also seamos sensors specialized for taking pictures of planets, so compare with before. It is becoming very easy to take pictures of the planet.
It's also quite a good idea to take a picture of the planetary companions who have traveled around the sun with the earth for billions of years.
Related article
Planet shooting with Sannippa! Part 1, the planet is in full bloom this summer (2018)
Planet shooting with Sannippa! Part 2, Saturn, Mars
Planet photography with Goyon (500mm f4 telephoto lens), rendezvous of Jupiter and Saturn
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