This simulator helps you choose your observation equipment: it allows you to quickly get an idea of what you can see through an instrument, according to its power.
This simulator uses photos by Gérard Bauza, Fabrice Talotti, Thierry Legault, NASA / Hubble Heritage Team.
Is this simulator realistic?
The rendering is more or less realistic according to the intended use: visualize the field and magnification obtained, or simulate the details accessible with an instrument.
Field and magnification obtained
The simulated true field is a representation of the field obtained in real observation, relative to the size of the observed star.
The size of the image is representative of the magnification and the apparent field in real life, provided that it is placed at a short distance from the screen. Depending on the characteristics of your screen (definition & resolution), this distance will be about the width of the screen, or even less in some cases (wide screens used at the maximum definition). For example, if you simulate an ultra-wide-field eyepiece of 100 ° of apparent field, the image should fill almost all of your field of vision when you close one eye.
Details available for planetary observation
The simulator takes into account, to some extent, the resolution of the instrument as a function of its diameter. Thus, the Moon or Saturn will appear more detailed with a telescope of 300 mm, for example, than with a telescope of 114 mm.
However, the following parameters can have an important influence and are not taken into account:
- the quality of the instrument: an instrument of mediocre quality or poorly regulated will not reach its theoretical resolution power
- Atmospheric turbulence: very often, this prevents the resolution of the instrument, especially for medium and large diameters (> 200 mm).
Details available for deep sky observation
For the observation of weakly luminous objects such as nebulae or galaxies ("deep sky"), it is the luminosity of the instrument that is decisive. The simulator takes this into account by simulating, to a certain extent, the luminosity of the instrument as a function of its diameter. Thus, the spiral arms of the hunting dog galaxy (M51) will appear much better with a telescope of 600 mm, for example, than with a telescope of 250 mm. The simulator thus has a pedagogical value and is appropriate to get a rough idea of what one can hope to see with a given instrument.
But be careful, the following parameters can have an important influence in real situation and are not taken into account:
- light pollution: parasitic lights prevent seeing objects that are not bright like nebulae and galaxies
- the eye of the observer: Experienced observers perceive more details than novice observers (notably by the control of the offset vision, which increases the sensitivity of the eye)
In addition, the screen setting and brightness of the room change the perception of the simulated image: avoid strong lighting, and use a monitor that is set to brightness and contrast.
Finally, the overall rendering can be quite distant from reality because it is very difficult to account for all the shades of light. Thus, the image obtained in a real situation will be more pleasant (except instrument of poor quality or polluted sky) because of richer nuances: the brightness of the stars and the texture of the nebulosities will be better rendered. A simulation will never replace direct observation, whether from the point of view of realism or from the point of view of the pleasure felt!
Which diameter for a telescope?The power of an astronomical telescope is mainly related to its diameter. Typical values are for example:
- between 60 and 115 mm for a beginner instrument
- between 150 and 250 mm for a medium power amateur astronomer instrument
- between 300 and 400 mm for a high power amateur astronomer instrument
- between 500 and 600 mm for particularly well-equipped enthusiasts
Please enter a diameter value between 60 and 600
Incorrect eyepiece focal length: please enter a value between 2.5 and 50 mm
Wrong focal length and F/D ratio. F/D must be between 3 and 20.
What is an optimized set of eyepieces?
It is a range of eyepieces well distributed in magnification.Each magnification corresponds to an eyepiece focal length, which the simulator calculates for you. The obtained focal length values are rounded to values corresponding to what is usually found on the market.
How does the Stelvision simulator work out the optimized range?
Depending on the number of eyepieces selected (between 2 and 7), the simulator offers eyepieces to achieve various magnifications, ranging from minimum magnification to Maximum magnification. The choices offered make it possible to gradually equip themselves up to an "ideal" range of 7 eyepieces well staged and covering all magnifications from one extreme to the other.
Note: the focal lengths are deliberately limited to a range of 2.5 to 40 mm, corresponding to those commonly available on the market.
What is minimal magnification?
It is generally considered that it is better to avoid magnifying below the magnification giving an "exit pupil" greater than 6 mm. This corresponds to a standard size of opening of the human eye.
This rule is not absolute: you can magnify less, but part of the light will be lost and, in the case of a telescope, a kind of black task may appear in the center of the image because of the obstruction of the secondary mirror.
The eyepiece focal length corresponding to the minimum magnification is given by:
f = D / 6
where D is the diameter of the instrument in mm.
What is the maximum magnification?
Too much magnification can lead to poor quality images, because the images obtained have an intrinsic resolution limited by:
- the diameter and the quality of the instrument,
- the presence of atmospheric turbulence
Depending on the case, it will be limited by the instrument, or by the atmosphere. Also, the notion of maximal magnification is often debatable.
The simulator calculates the maximum magnification in the following way:
Gmaxi = 2 * D
Where D is the diameter of the instrument in mm.
For large instruments (D> 200 mm), this magnification can be interesting only in extremely stable sky, that is to say very rarely. It will generally be limited to half the magnification, equal to the diameter of the instrument in mm.
How many eyepieces do you need?
Two eyepieces are enough to start, but the ideal is to have 4 or 5 or more.
Optionally, the use of a good barlow lens can make it possible to double the number of magnifications available and thus to usefully supplement a range with only a small number of eyepieces.