TS Optics Photoline 102/715 Information (4" Refractor)

Motivation | Look | Visited Sky Objects | First Experiences | Issues and Solutions | Photo Attempts | First Conclusions | Links | Appendix: Data

On this page I provide some information about my TS-Optics PHOTOLINE 102mm f/7 FPL53 Triplet APO Refractor - 2.5" RPA Focuser (received on July 8, 2020); the focal length is 714 mm. For simplicity, I will mostly call it (TS-Optics) TLAPO1027. I use this telescope for quick-and-dirty observations and also for EAA sessions (with photos).

See the appendix for the data.

Note: All in all, I have unfortunately used my TLAPO1027 refractor far too little, so I sold it to a star friend in the beginning of October 2024. I therefore can no longer report any further experiences with this scope here.

 

Motivation

Refractors are praised again and again for their sharp and constrasty image, but also criticized because of their color aberrations. Only refractors with very expensive glass seem to be free of color aberrations. And not always seems too be "ED" inside where there is "ED" written on the tube... Although I had no experiences with refractors initially, the praises that I have read have enticed me again and again to purchase one. Every time I found a cheaper refractor on the Internet, I called my astronomy dealer and asked him for his opinion on the respective device. And he advised against it again and again because of the strong color fringing, so that I never actually purchased a refractor.

But then I bought one at the AME2018 astronomy fair in Villingen-Schwenningen in September 2018. Again, it had an "ED" on it and in its name, but as the salesman told us and as I later found out, it exhibits quite a lot of color fringing, although I do not find this disturbing.

In autumn 2019, I even borrowed a SkyWatcher StarTravel 120 refractor, which is really called a "paint bucket" or "paint thrower" (Fraunhofer type), and rightly so. I was tempted by its large aperture of 120 mm, and with a focal length of 600 mm, it is a good rich-field telescope, especially because the color fringes are hardly noticeable when observing DSO; this is definitely different at the moon and the planets or when observing during the day. In the end, I did not the ST120, because everyone around me said that I did not need such a device, because it is too similar to my other telescopes, especially to my 6" Newton. This is true from the data, but while I do not consider the Newton to be suitable for travel, the ST120 is...

Even after a certain change in my telescope equipment (C8 exchanged for 6" Newton), I still longed for a refractor with pure colors, and I was also willing to spend a little more money for it (about 2000 EUR). When I wanted to reward myself for some "personal reason", the time had come for me to buy a refractor. I chose some models and asked my astronomy dealer for his opinion on them. This time I, was "absolutely right" with a refractor from TS-Optics! I had however a more expensive, similar model in mind and wanted to buy this with a lighter focuser. First of all, according to my dealer, both tubes were identical, even if some Websites state slight differences, and secondly, a conversion to a lighter focuser did not seem possible, although TS-Optics advertises with it on its Website. There were also inconsistencies in the tube weights...

In the end, I decided for the device suggested by my dealer, the TLAPO1027 from TS-Optics. But all of a sudden, this device was no longer available from my dealer, and he did not receive a delivery of already promised devices either. After some back and forth, we postponed to "later" (in several months, how many, was unknown...). When I then went back to my dealer for another similar refractor, he advised me not to buy it, but he wrote that I should buy the TLAPO1027 if I would find it at another dealer, because "it is worth it". In fact, I bought it from another dealer who stated on his Website that he was able to deliver it within 1-4 days. But the dealer was probably not aware of the seriousness of the delivery situation. Astonishingly, after some back and forth he was able to deliver it (drop shipment from TS-Optics), because in some corner at TS-Optics a last sample could be found. That actually arrived at my home! However, someone must have taken the "drop shipment" too literally, because the "very stable aluminium case" was unfortunately damaged. In fact, it is a cardboard case with aluminum fittings, and the cardboard has a brittle plastic layer on top. Actually, it is a brazen advertising lie to call such a case an aluminium case. By the way, I had a similar problem with the Omegon PS 72/432 travel case... For details, see below.

 

Look

Unpacking

Outer box

Ditto, opened

Ditto

Outer box opened and inner box

Inner box taken out

Inner box opened - transport case visible

Ditto

Transport case taken out of the box

Transport case

Telescope Tube

Transport case opened, telescope visble

Telescope taken out of the box

Plastic bag removed

Telescope, front lid srcewed off

Ditto

Ditto, side view

Ditto, focuser lid removed

Ditto, turned

Ditto, dew cap at full length

Details

Focuser, cap for focus knob in place, self-centering adapter for accessories and eyepieces in place

 

Focuser, self-centering adapter for accessories and eyepieces removed

Ditto

Self-centering adapter for accessories and eyepieces, lid removed

Focuser, self-centering adapter for accessories and eyepieces, lid

Ditto, other view

 

Focuser, self-centering adapter for accessories and eyepieces in place, focuser cap removed

 

Refractor on AZ4 Mount

Horizontal, dew cap extended

Vertical, dew cap extended

Oblique, dew cap extended

Ditto, dew cap retracted

Refractor on Star Discovery Mount

 

Visited Sky Objects

So far, I have visited the following sky objects with the TS-Optics TLAPO1027:

 

First Experiences

As a Spotting Scope...

On the first day, I already performed a daylight comparison with my Omegon PS 72/432. As a two-lens ED refractor, it should be inferior to a three-lens APO. That is how the Omegon salesman had presented it on a fair - and that is how it was! The TLAPO1027 showed almost no color fringes, whereas the PS 72/432 showed partly quite a lot of them. Visually, the difference was almost astounding. In addition, the image in the APO was much more uniformly sharp and therefore much more pleasant to look at.

I took a lot of photos with the Sony RX100 M4 held to the eyepiece, but it is difficult to get really comparable photos to prove the differences. I present some of these photos below.

As a Telescope (First Night)...

And in the first night I also made a very first comparison test with the PS 72/432 on the globular star cluster M 3. Both telescopes were operated at a magnification of about 100 x (4 mm eyepiece on PS72 and 7 mm eyepiece on TLAPO1027). In this test, the TLAPO was again clearly superior, showed a brighter image and more details, that is, a better resolution into stars.

A subsequent short test on Jupiter and Saturn also showed an advantage for the TLAPO1027, but not as clearly as with M 3.

As a Telescope (Second Night)...

Three weeks later I did a second comparison test with the PS 72/432 at night. I observed the moon, Saturn and Jupiter, as well as the three DSO M 13 (Hercules Cluster), Cr 399 (Coat Hanger), and M 11 (Wild Duck Cluster), three "classics".

It was a day after half moon, which I observed at 27 x (16 mm/26 mm) and a about 40 x (10 mm/16 mm). In general, the APO was better and its image had more contrast; after I adjusted the sharpness a bit, the PS72 became more on par with the APO; but at 40 x, the image of the PS72 was already quite flat, and the APO was much better. Down in the south of the moon where there are many craters around Clavius, the PS72 showed yellow color fringes; at the edge of the moon, the APO had color fringes, as well, sometimes yellow and sometimes blue ones, depending on the eyepiece... Among other things, I observed: Rules Alpes, Rupes Recta, Rupes Altai, and many small mountains in the sea (e.g. Montes Spitzbergen). The small crater Ammonius (8 x 9 km) in the crater Ptolemy only appeared in the APO (all white), later also in the PS72...

I observed Saturn at a magnification of up to 100 x (4/7mm), Jupiter up to 100 x, in the APO also up to nearly 180 x (4 mm). Then clouds appeared... At the planets, the differences between the refractors were not as obvious as at the moon.

Finally I searched for M 13, Cr 399 and M 11, and with a lot of luck I found them without a viewfinder!

Especially at the moon and at the globular star cluster M 13, the TLAPO1027 showed its superiority over the PS 72/432!

As a Telescope (Third Night)...

At the beginning of October 2020, I did a third comparison test with the PS 72/432 during the night. During this test I observed Saturn and Jupiter, as well as the two globular star clusters M 13 (Hercules cluster) and M 92, again "classics".

Once more, the APO performed better and the image was more contrasty, whereas the image in the small refractor turned faint more early than in the large one. This is not surprising, if you look at the exit pupils at the same magnification. In addition, the larger refractor collects twice as much light as the smaller one. All in all, I made enough comparisons to be sure that I do not regret the purchase of the TLAPO1027, even if it is much bigger than the PS72/432, and therefore requires a sturdier mount.

Perhaps, I should conduct another comparison with the Skymax-127, which has a slightly larger aperture, but also a lot of obstruction...

A Quick Comparison at the Orion Nebula (End of December 2020)

On December 28, 2020, I did a quick comparison with four of my telescopes using the Orion Nebula M 42/43, which the TLAPO1027 clearly won (nearly full moon, moon close to Orion). The order was: PS 72/432 < C5 < Skymax-127 < TLAPO1027.

 

Issues and Solutions

Travel Case, Travel Bag

Unfortunately the transport case arrived slightly damaged at my home:

Damage left

Ditto

Damage from above

Damage from above

Damage from above/front

Damage, front view

I therefore sent e-mails with photos to the dealer APM and the supplier/manufacturer TS Optics. The same evening, TS Optics regretted me, but, although being the sender, declared to be not responsible. APM took a week to react and then offered me 50 EUR "compensation". I accepted this suggestion, especially since I do not use the case, but bought a Geoptics bag for storage and travel use, instead:

A warning!

First test

Tube in the bag

I put a cardboard at the bottom

Test with styropor parts...

... and plastic bag

 

Ready for travelling!

  

Vixen Rail

The TLAPO1027 is supplied without a rail for attaching the tube to a mount. I therefore ordered one from my astronomy dealer. This was a 13.7 cm Vixen rail:

Vixen rail (13,7 cm)

Ditto, detail

Ditto

This rail fit, but firstly it seemed a bit short to me (because the tube is so long), and secondly the tube with the rail attached did not fit well into the polystyrene recesses of the transport case. I therefore replaced this rail with one that is 20 cm long (not shown) and fits well into the recesses:

Vixen rail (20 cm) mounted, everything fits

Ditto, clamp turned

Ditto, detail

Focuser

There are a number of wheels and screws at the focuser, the function of which was in part unknown to me:

    

In the meantime, I was able to clarify the meaning of the screws with the help of my astronomy dealer Mr. Kloß, especially that the Allen screws are indeed intended for a finder shoe (see below).

The "Finder-Problem", Rigel Finder

Like many other refractors, such as my Omegon PS 72/432, the TLAPO1027 is delivered without a finder shoe. Why this is so, is a mystery to me, because without a finder, I can find only a few sky objects. My astronomy dealer therefore recommended that I attach a finder shoe to the clamps, but that did not seem so easy to me, even less so if it has to be a Rigel finder. More about this below!

In order to make first experiences with the Rigel finder, I "designed" a rubber band construction for the finder shoe, which is put on the dew cap, like I did with the PS 72/432. This is the easiest way to start, and that is where the finder shoe fits best. But probably, the finder is too distant and has to be moved backwards. Since I do not have enough double-sided adhesive tape left, I decided not to use it. But this means that the finder moves at the slightest touch and has to be realigned.

Rigel viewfinder attached with rubber bands, seen from behind

Ditto, oblique front view

Ditto, more distant view

For quite some time, I had not used the TLAOP1027, because for various reasons my eVscope had priority. In October 2020 (Oct 10, 2020) I dealt with the "viewfinder problem" once again. On the one hand, I screwed a red-dot finder to the rear clamp to see whether it could be used that way. It was, however shifted by 90° to the eyepiece; 45° or less would have been better. On the other hand, I moved the Rigel viewfinder shoe to the back, because it was difficult to look through the viewfinder when it was sitting in the front of the dew cap. I wanted to try out the red-dot finder at night and I was able to do so. All in all I, was able to work with it even in this unfavorable position. I did not try out the Rigel finder. On the one hand, the foot, which was held by rubber bands, was sitting very "wobbly", on the other hand, I needed the Rigel finder for my second refractor. Here are a few photos of my attempts:

Red-dot finder mounted to the rear clamp, rear view

Red-dot finder mounted to the rear clamp, rear view

Rigel finder fixed with rubber bands, rear view

Rigel finder fixed with rubber bands, front view

Rigel finder fixed with rubber bands, rear view

Ditto

Solution to the Finder Problem

After it did not work out with the Rigel finder, I inquired and found out that there are two "empty Allen screws" on the eyepiece extension, which are meant to hold a finder shoe. However, they sit behind each other and not next to each other. So I ordered a matching TS-Optics finder shoe with elongated holes and a red-dot finder from my astronomy dealer and installed them without much effort. But I put some plastic between the eyepiece extension and the finder shoe to avoid scratching the extension too much...

Eyepiece extension with two Allen screws meant to hold a finder shoe

Screws removed to install a finder shoe

TS-Optics finder shoe with 4 elongated holes

Ditto, oblique view

Ditto, seen from above

Losely fixed finder shoe

Finder shoe with plastic to save the eyepiece extension from scratches

Telescope with red-dot finder in the finder shoe

Ditto, closer view

 

Photo Attempts

Used as a Spotting Scope

As mentioned above, I did a daylight comparison with my Omegon PS 72/432 already on the first day. I took a large number of photos with the Sony RX100 M4 held to the eyepiece, but was is difficult to get really comparable photos and thus, prove differences. The following photos are nevertheless an attempt to do so. The originals were brightened up in order to make details more visible; this led to stray light effects, especially on the PS72. To make color fringes clearer sections were sometimes taken more from the periphery, where the sharpness is no longer present, especially on the PS72. For a more detailed analysis, I recommend downloading the brightened up originals.

PS 72/432

TLAPO1027

original (made brighter) original (made brighter)

original (made brighter) original (made brighter)

original (made brighter) original (made brighter)

original (made brighter) original (made brighter)

original (made brighter) original (made brighter)

original (made brighter) original (made brighter)

Dry Run with Atik Infinity

In several dry runs (December 2020), I checked whether the Atik Infinity camera can be operated at the TLAPO1027.

Results

Italic: Works; italic and bold: recommended

Selected Photos

TLAPO1027 with T2 extension sleeves, overview

TLAPO1027 with T2 extension sleeves

Result

TLAP1027 with 2" zenith mirror

Result for photo left

Atik Infinity with T2 extension sleeves

Two Night Tests with the Atik Infinity Camera

March 23, 2021

Note: These night tests appear in more detail on page Atik Infinity - Further Experiences (Nightly Tests). More results will be presented elsewhere on this Website.

On March 23, 2021, I made a first "night test" with the Atik Infinity camera at the TS-Optics TLAPO1027 refractor. I used the following configuration: TS-Optics TLAPO1027 refractor on the Star Discovery mount, which I operated with the SynScan app on the iPhone. I performed a 1-star alignment. The camera was adapted to the telecsope using T2 extension sleeves.

I observed M 42/43 (Orion Nebula) and M 78. Here are some of the photos (processed) that I took during this session:

   

M 42/43 - March 23, 2021, processed

 

M 42/43 - March 23, 2021, processed

 

M 42/43 - March 23, 2021, processed

         

M 78 - Mar 23, 2021, processed

  

M 78 - Mar 23, 2021, processed

  

M 78 - Mar 23, 2021, processed

Focusing worked better than with the PS72, the FWHM values were very low, but did not give any final certainty... The alignment was only so so... I only found M 42/43 and M 78 (thanks to its "eyes"). M 42/43 was very nice, but M 78 rather poor. The photos showed strange dark spots in the background, especially with M 78.

March 24, 2021

On the next day, March 24, 2021, I did a second "night test" with the Atik Infinity camera at the TS-Optics TLAPO1027 refractor, using the same configuration as during the first test. I tried a few things out, everything worked right away, but the results were rather disappointing, except for those for M 42/43. Then also clouds appeared. I observed M 42/43 (Orion Nebula), NGC 1977 (Running Man Nebula), NGC 2024 (Flame Nebula), M 35 and M 78. Here are some of the photos that I took during this session (only processed versions):

      

M 42/43 - March 24, 2021, processed

 

M 42/43 - March 24, 2021, processed

 

M 42/43 - March 24, 2021, processed

      

M 78 - Mar 24, 2021, processed

  

M 78 - Mar 24, 2021, processed

  

NGC 1977 - March 24, 2021, processed

      

M 35 - Mar 24, 2021, processed

  

M 35 - Mar 24, 2021, processed

  

NGC 2024 - Mar 24, 2021, processed

Night Test with the ZWO ASI224 (September 4, 2021)

Note: This night test is presented in more detail on page ZWO ASI224 Color Camera - Further Experiences.

TLAPO1207 on Star Discovery with SynScan WLAN Module; SQM about 20; the observations started at about 9:10 p.m. and ended at about 0:30 a.m.; SynScan app on iPhone, ASILive (hotpixel removal activated, no darkframes); Observation order: M 13, M 92, M 51, M 16, M 17, M 20, M 11, M 27, M 57.

Photos

          

M 11, 60frames, 5sec, gain300, processed

 

M 13, 60frames, 5sec, gain300, processed

  

M 16, 48frames, 5sec, gain300, processed
   

M 17, 84frames, 5sec, gain300, processed

  

M 20, 72frames, 5sec, gain300, processed

  

M 27, 96frames, 5sec, gain300, processed
   

M 51, 96frames, 5sec, gain300, processed

  

M 57, 73frames, 5sec, gain300, processed

  

M 92, 60frames, 5sec, gain300, processed

Photo Comparison with ZWO ASI224 against the PS 72/432 (September 2021)

PS 72/432

 

TLAPO1027
    

M 11, 60frames, 5sec, gain300

  

M 11, 60frames, 5sec, gain300, processed
 

M 13, 61frames, 5sec, gain300, processed

  

M 13, 60frames, 5sec, gain300, processed
 

M 27, 85frames, 5sec, gain300, processed

  

M 27, 96frames, 5sec, gain300, processed
 

M 51, stacked from single frames

 

M 51, 96frames, 5sec, gain300, processed
 

M 57, 72frames, 5sec, gain300, processed

  

M 57, 73frames, 5sec, gain300, processed
 

M 92, stacked from single frames, processed

  

M 92, 60frames, 5sec, gain300, processed

On the one hand, the difference in the field of view is noticeable, and on the other hand, the TLAPO1027 shows "whiter" stars than the PS 72/432, where the stars are quite colourful. Unless I need the large field of view, I prefer the TLAPO1027.

Note: For details see page ZWO ASI224 Color Camera - Further Experiences.

 

First Conclusions

First tests during daytime show a clear superiority over my double-lens ED refractor PS 72/432. Up to now, I have not had many opportunities to try out the TLAPO1027 at night, but so far, it looked superior. With a camera attached, the results also look better. Particularly, the stars are less bloated than with the PS 72/432* and whiter (less chromatic aberration). I think that further comparisons are not necessary!

*) With a Baader UV/IR cut filter I can reduce the bloating of the stars for the PS 72/432. For the TLAPO 1027, such a filter does not seem to be needed.

Note: All in all, I have unfortunately used my TLAPO1027 refractor far too little, so I soldit to a star friend in the beginning of October 2024. I therefore can no longer report any further experiences with this scope here.

 

Links

 

Appendix: Data for TS-Optics TLAPO1027 Refractor

Technical Data

Telescope: Omegon TLAPO1027
Optical Design Refractor (Triplet)
Primary Mirror Diameter 102 mm
Focal Length, Focal Ratio 714/715 mm, f/7
Resolving Power (arc secs) 1.15" **
Limiting Visual Stellar Magnitude about 12 mag **
Light Gathering Power 212.3 **
Maximum Practical Visual Power 204 x
Optical Tube Dimensions (diam. x length) 10.5/12.6 cm x 61.5 cm (transport size)
Net Weight Basis n.a.
Net Weight Optical Tube 5.6 kg
Net Weight Complete n.a.

Dark Blue: Telescopes that I still own; italic and dark red: telescopes that I owned; black: for comparison; *) own measurement; **) values taken from similar telescopes

See also the table of data for all of my telescopes (and a few more...)

Observation-Relevant Data (in Comparison with PS72, ST120, and PDS150 Newton Tube)

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
PS72
432
72
6
106
144
108
144
11.08
10.29
39.0
42.0
4.0
3.0
ST120
600
120
5
290
180
240
18.46
17.14
32.5
35.0
3.3
2.5
TLAPO1027
714
102
7
212.3
153
204
15.69
14.57
45.5
49.0
4.7
3.5
Explorer PDS150/Dobson 6"
750
150
5
459
225
300
23.08
21.43
32.5
35.0
3.3
2.5

*) Calculated for an exit pupil of 6.5 mm and 7 mm
+) Factor 1.5 or 2 for Dobsonian/Newtonian 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) and Other Data for Different Focal Lengths of Eyepieces (Mostly My Current Eyepieces)

Note: These tables include the StarTravel 120 refractor, a TSWA32 eyepiece (2", 32 mm focal length, 70° viewing angle) that I borrowed together with the StarTravel 120, a 18 mm eyepiece (2", 82° viewing angle), a 38 mm eyepiece (2", 70° viewing angle), and a 56 mm eyepiece (2", 52° viewing angle).

Magnification
Focal Length of Eyepiece (mm)
  
Telescope
Focal Length
of Telescope
(mm)
4
7
10
16
18
24
26
32
32
35
38
40
56
    
PS 72/432
432
108.00
61.71
43.20
27.00
24.00
18.00
16.62
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
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
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
23.44
23.44
21.43
19.74
18.75
13.39
    
SM127
1500
375.00
214.29
150.00
93.75
---
62.50
---
46.88
---
---
---
---
---
    
SM102
1300
325.00
185.71
130.00
81.25
---
54.17
---
40.63
---
---
---
---
---
    
C5
1250
312.50
178.57
125.00
78.13
---
52.08
---
39.06
39.06
35.71
32.89
31.25
22.32
    
C5 (Red.)
787.5
196.88
112.50
78.75
49.22
---
32.81
---
24.61
---
---
---
---
---
    
C8
2032
508.00
290.29
203.20
127.00
112.89
84.67
78.15
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 (°)
Focal Length of Eyepiece (mm)
Camera
Apparent FOV (°) >
82
82
72
82
82
65
70
52
70
69
70
68
52
ZWO
Atik
Telescope
Focal Length
of Telescope
(mm)
4
7
10
16
18
24
26
32
32
35
38
40
56
ASI294
Infinity
PS 72/432
432
0.76
1.33
1.67
3.04
3.42
3.61
4.21
3.85
5.19
5.59
6.16
6.30
6.74
 2.54° x 1.73° 1.19° x 0.89°
ST120
600
0.55
0.96
1.20
2.19
2.46
2.60
3.03
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
2.33
3.14
3.38
3.73
3.92
4.08
 1.54° x 1.05° 0.72° x 0.54°
150PDS
750
0.44
0.77
0.96
1.75
1.97
2.08
2.43
2.22
2.99
3.22
3.55
3.63
3.88
    
SM127
1500
0.22
0.38
0.48
0.87
---
1.04
---
1.11
---
---
---
---
---
    
SM102
1300
0.25
0.44
0.55
1.01
---
1.20
---
1.28
---
---
---
---
---
    
C5
1250
0.26
0.46
0.58
1.05
---
1.25
---
1.33
1.79
1.93
2.13
2.18
2.33
 0.88° x 0.60° 0.41° x 0.31°
C5 (Red.)
787.5
0.42
0.73
0.91
1.67
---
1.98
---
2.11
---
---
---
---
---
 1.40° x 0.95° 0.65° x 0.49°
C8
2032
0.16
0.28
0.35
0.65
0.73
0.77
0.90
0.82
1.10
1.19
1.31
1.34
1.43
 0.54° x 0.37° 0.25° x 0.19°
C8 (Red.)
1280
0.26
0.45
0.63
1.03
---
1.22
---
1.30
---
---
---
---
---
 0.86° x 0.58° 0.4° x 0.3°
 
Exit Pupil (mm)
Focal Length of Eyepiece (mm)
  
Telescope
Focal Ratio
4
7
10
16
18
24
26
32
32
35
38
40
56
    
PS 72/432
6
0.67
1.17
1.67
2.67
3.00
4.00
4.33
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
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
4.57
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
6.40
6.40
7.00
7.60
8.00
11.20
    
SM127
11.81
0.34
0.59
0.85
1.35
---
2.03
---
2.71
---
---
---
---
---
SM102
12.75
0.31
0.55
0.78
1.26
---
1.88
---
2.51
---
---
---
---
---
    
C5
10
0.40
0.70
1.00
1.60
---
2.40
---
3.20
3.20
3.50
3.80
4.00
5.60
    
C5 (Red.)
6.3
0.63
1.11
1.59
2.54
---
3.81
---
5.08
---
---
---
---
---
    
C8
10
0.40
0.70
1.00
1.60
1.80
2.40
2.60
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
---
---
---
---
---
    

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

Magnification: Yellow: low (30-50 x); magenta: medium (80-100 x); violet: high (150-200 x - and more); red: beyond maximum usable magnification.
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).

Recommendations for the Focal Lengths of Eyepieces for TLAPO1027 (Following My Recommendations and Those of Others)

Criteria Exit
Pupil
Focal Length of Eyepiece
Category Application Area
from...to
Calculated
On the Market
Examples
Existing
Maximum FOV Search
7
10
49-70
40-56*
40, 56*
40
Minimum Magnification / Large FOV Overview, large-area nebulae
4.5
6.5
31-36
32-35*
28, 30, 32, 35*
35
Normal Magnification Large-area, faint nebulae; nebulae, open star clusters
3.5
4
24.5-28
24-28*
24, 25, 26, 28
24, 26
Best for many objects, e.g. for most galaxies, and mid-size DSO
2
3
14-21
15-20*
15, 16, 18, 20
16
Maximum Magnification / Maximum Resolution "Normal" upper magnification limit; globular star clusters
1
1.5
7-10.5
7-10.5
7, 9, 10, 10.5
7, 10
Maximum perceptibility of small, low-contrast details; planetary nebulae, small galaxies;
maximum magnification for moon and planets
0.6
0.8
4.2-5.6
4-6
4, 5, 6
4
Separation of narrow double stars, small planetary nebulae;
perception of faintest details
0.4
0.5
2.8-3.5
2.5-3.5
2.5, 3, 3.5
*, 4

*) Partly available as 2" eyepiece; **) typically no suitable 1,25" eyepieces available; problems with viewing at 40 mm; italic: not possible; red: magnification too high; blue: commercial focal lengths

 

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18.11.2024