camera

For astrophotography, DSLR and DSLM cameras can be used. DSLM cameras, also called mirrorless cameras, don’t have internal mirrors, which means that their viewfinder is always electronic (which makes them lighter and more portable). Regardless of the type of camera, they need to be manually adjustable. Some of these adjustments are

• White balance adjustment for daylight
• Switching off flash and autofocus
• Adjusting the diaphragm setting B (f stop)
• The higher the diaphragm number, the smaller the aperture, i.e. the less light passes through it.
• Be compatible with a remote shutter release or have a delay shutter setting
• Support files with the lowest possible compression, such as RAW
• If available, internal noise reduction
• ISO 400-800 sensitivity setting, and in specific cases ISO 1600
• For lower ISOs, more light should be emitted by the subject

To photograph the sun, you need to attenuate the light using a solar filter for lenses or a Herschel prism.

Personally, I use DSLM cameras, the Fujifilm XT1 and the Fujifilm XT50. After some preliminary adjustments, I decided to use the XT1 as a dedicated astrophotography camera. Along with the camera you need to use a T2 adapter. Mine is a William Optics T2 adapter (Adapter T for Fujifilm FX48mm). For some reason this adapter doesn’t fit so smoothly on the XT50, but it works perfectly on both cameras.

So I plug the adapter into the lens socket and, instead of a lens, I use one of the telescopes detailed below.

telescopes

There are various types of telescopes on the market, but I’ll briefly describe the telescopes I own (and in future I’ll detail my experience with each one).

Refractor telescopes

The most famous refractor is the one used by Galileo Galilei to make important astronomical discoveries, such as the moons of Jupiter. Its essential components are

• Objective, which is the lens at the front end of the telescope, absorbing light from distant objects
• Eyepiece, the lens closest to the observer’s eyes, used to magnify the image formed by the objective lens
• Optical tube, the tube that holds the lenses in the correct position and protects the telescope from unwanted light getting in
• Mount, the support, similar to a photographic tripod. It can be altazimuthal or equatorial and will be more detailed in the topic of mounting.

There are several types of refractor telescope. The one I own is an apochromatic refractor.

Apochromatic refractors are refractors whose lens design combines at least three colours in a common focal point. This way, the typical chromatic aberration that happens with other refractors doesn’t occur. Without this correction, bright objects such as the moon or planets would appear with bands of colours that distort and reduce the clarity of observation.

The model I use is the William Optics Redcat 51, an apochromatic refractor with an aperture of 51mm, a focal length of 250mm and f/4.9. It has a Petzval design. It’s very light and portable, allows for short exposure shots and its Bahtinov mask helps with focusing.

Reflector telescopes

This type of telescope, unlike refractors, uses mirrors to collect and focus the light from celestial objects. The primary mirror has a concave curved surface that collects the light and reflects it towards a second mirror, called the secondary mirror. This, in turn, reflects the light to a focal point where the image is formed. This focal point is where a piece called an eyepiece fits in, used to visualise the enlarged image.

To focus, the secondary mirror moves forwards or backwards along the tube, allowing the sharpness of the image to be adjusted. To increase magnification, eyepieces are used, with a larger eyepiece allowing for more detailed observations and a smaller one provides a wider field of view.

Newtonian telescopes are very popular. As the name suggests, they were developed by Sir Isaac Newton during the 17th century. This type of telescope has a number of advantages and disadvantages.

1. Advantages
Elimination of chromatic aberrations that form coloured halos around objects
Greater capture of light due to its size, which makes it possible to observe objects with weaker and more distant light
2. Disadvantages
They can be large and heavy, making transport and assembly difficult
They need to be collimated regularly to ensure that the mirrors are aligned. Collimation involves adjusting the optical components so that the reflected or refracted light rays focus on the same focal point.
Cleaning the mirrors requires prior knowledge and dexterity to avoid damage.

The model I use is the SkyWatcher 150 PL. A Newtonian telescope with a 150mm optical tube and f/8. It is particularly suitable for lunar and planetary observation. As it has a pure optical mirror, it produces images free of chromatic aberrations.

Catadioptric telescopes

Maksutov Cassegrain

These are mixed telescopes that combine refraction and reflection. These can also be called compound telescopes, as they combine lenses and mirrors to achieve a balance between image quality and portability. Reflection occurs through the primary mirror and refraction occurs when the light passes through the meniscus installed at the end of the lens.Reflection occurs through the primary mirror and refraction occurs when the light passes through the meniscus at the top end of the tube. It also has a secondary mirror, which is a small metallised area in the centre of the meniscus. This area acts as a convex secondary mirror that reflects light in the direction of the primary mirror. The focuser and eyepiece are installed at the bottom of the tube.

I use the Celestron Maksutov-Cassegrain 127/1500mm. It has a direct T2 mount, so there’s no need to use an adapter. It is very compact and can be used for observation and astrophotography of the moon, planets and deep sky.

bayonet adapters

Eyepiece projection is used for photographing planets. Therefore, a special adapter is used, which is inserted into the telescope’s eyepiece space. The magnified image from the eyepiece is then projected onto the camera. A T2 ring may be required and must be compatible with the specific model of camera used.

For a Newtonian telescope, Barlow lenses are needed to reach the focal point.
My eyepiece projection adapter is the SOLOMARK 1.25 and my Barlow lens is the Celestron 93436.

mount

A tracker is very useful for photos with longer exposure times, as the Earth’s rotation causes a celestial body to move 1/4 degree per minute to the west. The longer the focal length, the shorter the exposure time.

With a focal length of around 80MM it is already possible to take deep sky images. For this, the best strategy is to take several consecutive photographs with an exposure time of just a few minutes and use software to ‘stack’ these images, reducing noise and increasing sharpness. I’m still researching the best software to use with my environment (iPad Pro and iMac).

My tracker is the SkyWatcher Mount Star Adventurer GTI Wi-Fi GoTo. It has an integrated polarscope, USB interface and other connectors. It also has a socket for cameras, which can be programmed via an app. The maximum load is 5kg. It is equatorially mounted.

Mounting type

High-zimuth mount: A high-zimuth mount in which the main axis allows movement in the direction of the azimuth, which is the horizontal angle that starts from north in the direction of east, south, west and returns to north. This axis is mounted vertically, with its origin strictly at true north. Its secondary axis allows for height movements, between the horizon and the zenith (an imaginary point intercepted by a vertical axis (also imaginary) drawn from the observer’s head and extending to the celestial sphere.
Equatorial mount: An equatorial mount has its primary axis precisely parallel to the Earth’s axis. It thus points towards the celestial pole, also called the polar axis. The secondary axis allows movement in the direction of declination from 0° at the equator to +90° at the north pole and -90° at the south pole.

I hope to be able to return soon with detailed reports and illustrative images.