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Philippe's Telescope / Detector
Calculator |
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Red Light: |
630 |
nm |
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Input Parameters: |
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Green Light: |
550 |
nm |
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Derived Parameters: |
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Blue Light: |
480 |
nm |
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| 1. TELESCOPE |
Type: |
18"
Galaxy Optics (MPT-46) |
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| Aperture
(Diameter) |
D = |
457,00 |
millimeters |
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| Focal Length |
F = |
2.057,00 |
millimeters |
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| Aperture D = |
17,99 |
" |
inches |
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| Focal Ratio N = |
4,50 |
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| Maximum magnification = |
914,00 |
X |
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| Eye-piece for max.
magnification: |
2,25 |
mm |
millimeters |
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| Light Power: |
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| Calculations
based on a 7 mm pupil size and 6th magnitude for the naked eye |
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| Gain = |
4.262,24 |
X |
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| Faintest Star (visually) = |
15,07 |
m |
magnitude |
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| Faintest Star
(photographically) = |
17,07 |
m |
magnitude |
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| Barlows: |
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Effective F (mm) |
Focal Ratio N |
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| Barlow 1 = |
2,00 |
X |
4.114 |
9,0 |
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| Barlow 2 = |
4,00 |
X |
8.228 |
18,0 |
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| Eye-pieces: |
Magnification |
Exit |
Magnification |
Magnification |
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| Eye-piece focal lengths in
millimeters: |
without barlow: |
Pupil: |
with Barlow 1: |
with Barlow 2: |
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| 4,8 |
429 |
1,07 |
857 |
1714 |
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| 7 |
294 |
1,56 |
588 |
1175 |
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| 9 |
229 |
2,00 |
457 |
914 |
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| 13 |
158 |
2,89 |
316 |
633 |
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| 17 |
121 |
3,78 |
242 |
484 |
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| 20 |
103 |
4,44 |
206 |
411 |
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| 25 |
82 |
5,55 |
165 |
329 |
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| 27 |
76 |
6,00 |
152 |
305 |
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| 58 |
35 |
12,89 |
71 |
142 |
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| Size of the Airy Disk: |
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| Linear
diameter of the disk out to the first dark diffraction ring |
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| Red Light: |
0,69 |
" |
arc seconds |
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| Green Light: |
0,61 |
" |
arc seconds |
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| Blue Light: |
0,53 |
" |
arc seconds |
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| Full-Width
at Half-Maximum (FWHM) of the Airy Disk: |
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Size of the Airy |
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| 50
% of all incoming light is concentrated in this central core |
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Disk at focal plane |
Resolution |
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| is
a realistic measure for the smallest detail in an astronomical image |
|
in µm |
in lpm |
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| Red Light: |
0,29 |
" |
arc seconds |
2,89 |
346 |
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| Green Light: |
0,25 |
" |
arc seconds |
2,53 |
396 |
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| Blue Light: |
0,22 |
" |
arc seconds |
2,20 |
454 |
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| Rayleigh's resolution limit |
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Resolution |
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| resolution:
the center of one Airy Disk is just one radius away of the other one |
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comparisons: |
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| Green Light: |
0,30 |
" |
arc seconds |
Cassini Division |
0,50 |
" |
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| Dawes's resolution limit |
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Encke Division |
0.0n |
" |
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| resolution:
empirical method based on the separation of binary stars |
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Rille in Alpine Valley |
0,27 |
" |
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| Green Light: |
0,25 |
" |
arc seconds |
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| Optimistic Sparrow's
resolution limit |
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| resolution:
2 PSFs (Point Spread Function) are separated by 1/2 radius of the airy disk |
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| Green Light: |
0,15 |
" |
arc seconds |
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| 2. DETECTOR |
Type: |
SBIG
ST-10XME |
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| Width: |
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14,85 |
millimeters |
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2.184,00 |
pixels |
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| Height: |
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10,01 |
millimeters |
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1.472,00 |
pixels |
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| Number of Pixels: |
3.214.848 |
pixels |
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| Diagonal: |
17,91 |
mm |
millimeters |
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| Magnification factor: |
2,40 |
X |
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| Pixel Heigth: |
6,80 |
µm |
micrometers |
Comparison Objects |
Size |
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Width |
Height |
| Pixel Width: |
6,80 |
µm |
micrometers |
Moon/Sun |
31 |
' |
124,9 |
185,3 |
| Field
of View (FOV) of the detector on this telescope: |
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Jupiter |
40 |
" |
2,7 |
4,0 |
| Width: |
24,82 |
' |
minutes of arc |
Mars |
25 |
" |
1,7 |
2,5 |
| Height: |
16,73 |
' |
minutes of arc |
Saturnus |
20 |
" |
1,3 |
2,0 |
| Resolution: |
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M51 |
11 |
' |
44,3 |
65,8 |
| Resolution in height: |
147,06 |
lpm |
lines per mm |
M13 |
17 |
' |
68,5 |
101,6 |
| Resolution in width: |
147,06 |
lpm |
lines per mm |
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in % |
in % |
| Angular Size of a Pixel: |
Zonder Barlow |
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Barlow 1 |
Barlow 2 |
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| Width: |
0,68 |
" per pixel |
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0,34 |
0,17 |
"
per pixel |
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| Height: |
0,68 |
" per pixel |
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0,34 |
0,17 |
"
per pixel |
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| Rescalings: |
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Scale: |
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| 1456 |
1,02 |
" per pixel |
66,67% |
0,51 |
0,26 |
"
per pixel |
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| 1092 |
1,36 |
" per pixel |
50,00% |
0,68 |
0,34 |
"
per pixel |
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| 728 |
2,05 |
" per pixel |
33,33% |
1,02 |
0,51 |
"
per pixel |
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| Maximum
focal ratio to obtain diffraction limited images: |
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| When the seeing is perfect ! |
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| Red Light: |
21,16 |
Barlow: |
4,70 |
X |
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| Green Light: |
24,24 |
Barlow: |
5,39 |
X |
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| Blue Light: |
27,78 |
Barlow: |
6,17 |
X |
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Average: |
5,42 |
X |
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| Depth of focus (DOF): |
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| this
tells you how accurately you must be able to focus the detector to have a
sharp field |
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| Geometrical DOF: |
0,045 |
mm |
millimeters |
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| Diffraction DOF: |
0,045 |
mm |
millimeters |
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| DOF: |
0,045 |
mm |
millimeters |
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| Diffraction limited images
(DLI) |
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P = chance to obtain a
diffraction limited image |
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FWHM = long exposure
image width |
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| Example |
r0 in mm |
P (in %) |
1 DLI per |
Resolution |
FWHM |
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W |
H |
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… images |
in " |
in " |
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pixels |
pixels |
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20,00 |
0,00000 |
################ |
6,90 |
5,56 |
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8,2 |
8,2 |
| Typical Seeing |
25,00 |
0,00000 |
################ |
5,52 |
4,45 |
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6,5 |
6,5 |
| Typical Seeing |
30,00 |
0,00000 |
877.510.820.510.725 |
4,60 |
3,71 |
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5,4 |
5,4 |
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40,00 |
0,00000 |
119.742.207 |
3,45 |
2,78 |
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4,1 |
4,1 |
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50,00 |
0,00126 |
79.567 |
2,76 |
2,22 |
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3,3 |
3,3 |
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60,00 |
0,06688 |
1.495 |
2,30 |
1,85 |
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2,7 |
2,7 |
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70,00 |
0,73466 |
136 |
1,97 |
1,59 |
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2,3 |
2,3 |
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80,00 |
3,48000 |
29 |
1,73 |
1,39 |
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2,0 |
2,0 |
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90,00 |
10,10868 |
10 |
1,53 |
1,24 |
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1,8 |
1,8 |
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100,00 |
21,67496 |
5 |
1,38 |
1,11 |
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1,6 |
1,6 |
| WHT 4.2m (La Palma) |
150,00 |
131,98677 |
1 |
0,92 |
0,74 |
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1,1 |
1,1 |
| ESO 3.6m EFOSC2 |
200,00 |
248,38800 |
1 |
0,69 |
0,56 |
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0,8 |
0,8 |
| ESO (Paranal Site) |
300,00 |
390,18774 |
1 |
0,46 |
0,37 |
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0,5 |
0,5 |
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400,00 |
457,00786 |
1 |
0,35 |
0,28 |
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0,4 |
0,4 |
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| Eyepiece Projection
Photography |
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| A |
The amplification factor
also called magnification factor. |
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| S |
The distance from the
eyepiece to the film plane or CCD chip. |
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| F2 |
The focal length of the
eyepiece, i.e. 20 mm |
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| F total |
Effective focal length
for the whole system including primary of the telescope. |
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| F1 |
The focal length of telescope
itself. |
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| f |
The
effective focal ratio of the whole system, i.e. f/20 |
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| D |
The
diameter of the primary objective or mirror of the telescope, i.e. 200 mm or
8 inch |
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| Distance eyepiece - detector
S: |
100 |
100 |
100 |
100 |
mm |
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| Focal length of the eyepiece
F2: |
5 |
7 |
9 |
13 |
mm |
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| Magnification A = |
19,83 |
13,29 |
10,11 |
6,69 |
X |
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| Effective focal length F total
= |
40.797 |
27.329 |
20.799 |
13.766 |
mm |
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| Effective focal ratio f = |
89 |
60 |
46 |
30 |
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| Source: |
http://www.licha.de/AstroWeb/articles_fullsize.php3?iHowTo=2 |
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