Data of All My Telescopes and Eyepieces

Data that Is Independent of a Specific Eyepiece | Visual Power (Magnification), True Field of View, and Exit Pupil for Different Focal Lengths of Eyepieces | My Current Eyepieces | Use of Magnifications | Exit Pupil | References | Links | Appendix: Simplified Tables

On this page, I present data for my all telescopes and eyepieces (including the sold ones). In addition, I list data for three variants of 6" telescopes. The actual data is presented on a seperate page for space reasons.

I also list a number of useful links.

Note: The appendix presents simplified tables that contain only the telescopes and eyepieces that I currently use (plus a telescope tube that I sold in the meantime and a few eyepieced that I had borrowed)..

Note: For definitions in a small glossary, see page Quick & Dirty Astronomy Glossary. For more information on the topic "exit pupil as a criterion for eyepiece selection" see page Eyepiece Selection (Focal Length).

 

Data that Is Independent of a Specific Eyepiece

Telescope

Focal
Length
(mm)

Aperture
(mm)
Focal
Ratio
Light
Gathering
Power
Maximum+
Minimum*
Maximum*
Minimum+
Usable Magnification
Usable Focal Length
of Eyepiece (mm)
Factor/Exit Pupil (mm) >
Manuf.
1.5
2
6.5
7
6.5
7
1.5
2
PS 72
432
72
6
106
144
108
144
11.08
10.29
39.0
42.0
4.0
3.0
TLAPO1027
714
102
7
212.3
 
153
204
15.69
14.57
45.5
49.0
4.7
3.5
Heritage 76
300
76
3.95
118
114
152
11.68
10.85
25.7
27.7
2.6
2.0
Heritage 100P
400
100
4
204
150
200
15.38
14.29
26.0
28.0
2.7
2.0
Heritage 114P
500
114
4.4
265
171
228
17.52
16.27
28.5
30.7
2.9
2.2
Heritage P130
650
130
5
345
220
195
260
20.00
18.57
32.5
35.0
3.3
2.5
Explorer PDS150/Dobson 6"
750
150
5
459
225
300
23.08
21.43
32.5
35.0
3.3
2.5
Dobson 6"
900
150
6
459
225
300
23.08
21.43
39.0
42.0
4.0
3.0
Dobson 6"
1200
150
8
459
225
300
23.08
21.43
52.0
56.0
5.3
4.0
Dobson 8"
1200
200
6
816
300
400
30.77
28.57
39.0
42.0
4.0
3.0
Dobson 10"
1270
254
5
1317
600
381
500
39.08
36.29
32.5
35.0
3.3
2.5
ETX 90/EC (Maksutov-Cassegrain)
1250
90
13.89
165
325
135
180
13.84
12.85
90.4
97.3
9.3
6.9
Skymax-102 (Maksutov-Cassegrain)
1300
102
12.75
212
153
204
15.69
14.57
82.9
89.3
8.5
6.4
Skymax-127 (Maksutov-Cassegrain)
1500
127
11.81
329
191
254
19.54
18.14
76.8
82.7
7.9
5.9
Celestron C8 (Schmidt-Cassegrain)
2032
203
10
841
305
406
31.26
29.03
65.0
70.0
6.7
5.0
Celestron C8R (Schmidt-Cassegrain)
1280
203
6.3
841
305
406
31.26
29.03
41.0
44.1
4.2
3.2

*) Calculated for an exit pupil of 6.5 mm and 7 mm
+) Factor 1.5 or 2 for Dobsonian telescopes; in general, the lower value of 1.5 is used for Newtonian telescopes; if the manufacturer specified a different magnification, it is also listed (some manufacturer provide considerably higher numbers...).

 

Visual Power (Magnification), True Field of View, and Exit Pupil for Different Focal Lengths of Eyepieces

The following table comprises data for all the eyepieces that I ever owned. I link to it because of its size. It appears in a new window/tab.

The preview is not in the current state...

 

My Current Eypieces

As of end of January 2020, I own the following eyepieces:

    

Photos: Top row (from left to right): 24 mm TeleVue wide angle eyepiece, 26 mm Sky-Watcher Panaview eyepiece, 35 mm TS UFL ED eyepiece, 40 mm Lacerta ED eyepiece, and 32 mm DigiScope Plössl eyepiece; bottom row (from left to right): 4 mm, 7 mm, and 16 mm TS UWA eyepieces, and 10 mm TeleVue Delos eyepiece.

My 12.5 mm Plössl and 23 mm crosshair eyepieces are also not shown.

 

Use of Magnifications

I found (and added to... source regrettably unknown...) the following recommendations for the use of magnifications:

Note that similar recommendations are given in the literature as well as on the Internet based on the size of the exit pupil. For more information on the topic "exit pupil as a criterion for eyepiece selection" see page Eyepiece Selection (Focal Length Selection).

 

Exit Pupil

The definition of the exit pupil can be found in the glossary.

General rules:

Calculation of the exit pupil:

*) Telescopes of the same aperture but of different focal lengths have the same exit pupil at the same magnification (even though the focal lengths of the eyepieces are different...).
**) This is how I calculate the exit pupil for a given telescope the fastest.

For more information about the topic "exit pupil as a criterion for eyepiece selection" see page Eyepiece Selection (Focal Length).

 

References

 

Appendix: Simplified Tables

The following simplified tables apply to the telescopes and eyepieces that I currently use (exceptions: the sold Explorer 150PDS, some borrowed eyepieces). This way, they are easier to use for me.

Data that Is Independent of a Specific Eyepiece

Blue: eyepieces that I borrowed for evaluation

Telescope

Focal
Length
(mm)

Aperture
(mm)
Focal
Ratio
Light
Gathering
Power
Maximum+
Minimum*
Maximum*
Minimum+
Usable Magnification
Usable Focal Length
of Eyepiece (mm)
Factor/Exit Pupil (mm) >
1.5
2
6.5
7
6.5
7
1.5
2
Photography Scope 72/432
432
72
6
106
---
144
11.08
10.29
39.0
42.0
4.0
3.0
TS-Optics Photoline 102 mm f/7
714
102
7
212,3
---
204
15.69
14.57
45.5
49.0
4.7
3.5
Explorer PDS150 (Newton)
750
150
5
459
225
300
23.08
21.43
32.5
35.0
3.3
2.5
Skymax-127 (Maksutov-Cassegrain)
1500
127
11.81
329
---
254
19.54
18.14
76.8
82.7
---
5.9
Celestron C8 (Schmidt-Cassegrain)
2032
203
10
841
---
406
31.26
29.03
65.0
70.0
6.7
5.0

*) Calculated for an exit pupil of 6.5 mm and 7 mm
+) Factor 1.5 or 2 for Dobsonian telescopes; in general, the lower value of 1.5 is used for Newtonian telescopes; if the manufacturer specified a different magnification, it is also listed (some manufacturer provide considerably higher numbers...).

Visual Power (Magnification), True Field of View, and Exit Pupil for Different Focal Lengths of Eyepieces

Blue: Equipment borrowed for comparison purposes; gray: sold equipment; italic: 2" eyepieces

Telescope
Further Data
Focal Length of Eyepiece (mm)
Magnification
 
Focal Length of
Telescope (mm)
4
7
10
16
18
24
26
28
32
32
35
38
40
56
PS 72/432
432
108.00
61.71
43.20
27.00
24.00
18.00
16.62
15.43
13.50
13.50
12.34
11.37
10.80
7.71
ST120
600
150.00
85.71
60.00
37.50
33.33
25.00
23.08
21.43
18.75
18.75
17.14
15.79
15.00
10.71
TLAPO1027
714
178.50
102.00
71.40
44.63
39.67
29.75
27.46
25.50
22.31
22.31
20.40
18.79
17.85
12.75
150PDS
750
187.50
107.14
75.00
46.88
41.67
31.25
28.85
26.79
23.44
23.44
21.43
19.74
18.75
13.39
Skymax-127
1500
375.00
214.29
150.00
93.75
---
62.50
---
---
46.88
---
---
---
---
---
C8
2032
508.00
290.29
203.20
127.00
112.89
84.67
78.15
72.57
63.50
63.50
58.06
53.47
50.80
36.29
C8 (Red.)
1280
320.00
182.86
128.00
80.00
---
53.33
---
---
40.00
---
---
---
---
---
 
True Field of View (°)
Apparent Field of View (°) >
82
82
72
82
82
65
70
56
52
70
69
70
68
52
 
Focal Length of
Telescope (mm)
4
7
10
16
18
24
26
28
32
32
35
38
40
56
PS 72/432
432
0.76
1.33
1.67
3.04
3.42
3.61
4.21
3.63
3.85
5.19
5.59
6.16
6.30
6.74
ST120
600
0.55
0.96
1.20
2.19
2.46
2.60
3.03
2.61
2.77
3.73
4.03
4.43
4.53
4.85
TLAPO1027
714
0.46
0.80
0.91
1.84
2.07
2.18
2.55
2.20
2.33
3.14
3.38
3.73
3.92
4.08
150PDS
750
0.44
0.77
0.96
1.75
1.97
2.08
2.43
2.09
2.22
2.99
3.22
3.55
3.63
3.88
Skymax-127
1500
0.22
0.38
0.48
0.87
---
1.04
---
---
1.11
---
---
---
---
---
C8
2032
0.16
0.28
0.35
0.65
0.73
0.77
0.90
0.77
0.82
1.10
1.19
1.31
1.34
1.43
C8 (Red.)
1280
0.26
0.45
0.63
1.03
---
1.22
---
---
1.30
---
---
---
---
---
 
Exit Pupil (mm)
 
Focal Ratio
4
7
10
16
18
24
26
28
32
32
35
38
40
56
PS 72/432
6
0.67
1.17
1.67
2.67
3.00
4.00
4.33
4.67
5.33
5.33
5.83
6.33
6.67
9.33
ST120
5
0.80
1.40
2.00
3.20
3.60
4.80
5.20
5.60
6.40
6.40
7.00
7.60
8.00
11.20
TLAPO1027
7
0.57
1.00
1.43
2.29
2.57
3.43
3.71
4.00
4.57
4.57
5.00
5.43
5.71
8.00
150PDS
5
0.80
1.40
2.00
3.20
3.60
4.80
5.20
5.60
6.40
6.40
7.00
7.60
8.00
11.20
Skymax-127
11.81
0.34
0.59
0.85
1.35
---
2.03
---
---
2.71
---
---
---
---
---
C8
10
0.40
0.70
1.00
1.60
1.80
2.40
2.60
2.80
3.20
3.20
3.50
3.80
4.00
5.60
C8 (Red.)
6.3
0.63
1.11
1.59
2.54
---
3.81
---
---
5.08
---
---
---
---
---

Magnification: Yellow: low (30-50 x); magenta: medium (80-100 x); violet: high (150-200 x - and more); red: beyond maximum usable magnification.
For use of magnifications, see above.

Field of View: Allows to predict whether an extended object can be fully captured or whether adjacent objects can be observed together.

Exit pupil: Values in magenta cells are either too small (< 1 mm) or too large (> 6.4/7 mm); yellow background: best for galaxies (about 2-3 mm).
For more information on the exit pupil, see above.

 

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gerd (at) waloszek (dot) de

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15.07.2020