Explore Scientific Focal Extenders 2 x and 3 x

Introduction | Look (2 x Extender) | Look (3 x Extender) | Look (both Extenders) | Eyepiece Data without and with Focal Extenders | First Experiences | First Conclusions | References

On this page, I present my Explore Scientific Focal Extenders (Tele Extenders) 2 x and 3 x (1,25") - as well as first experiences that I have collected so far using them.

 

Introduction

Many inexpensive telescopescome equipped with a 2 x or 3 x Barlow lens, which makes it possible to virtually "double" the number of eyepieces. Using a 2 x Barlow lens, the Sky-Watcher kit eyepieces, for example, change lens into a 12.5 mm (25 mm) and a 5 mm (10 mm) eyepiece. Admittedly, I do not use the Barlow lenses that I own because the achievable quality is too poor - I do not even use the slightly better lens from my Revelation eyepiece bag. But, of course, I find the idea of ​​changing the focal length of telescopes interesting...

In May 2017, I "stumbled" by coincidence across a focal extender (TeleExtender) on the Explore Scientific Website and just ordered one, namely the 2x extender because I thought the lower the multiplication factor, the better the quality (which does not necessarily have to be true ...). This extender is also available in a 3 x and a 5 x version. In addition to multiplying the focal length of a telescope, Explore Scientific highlights a further advantage of the extenders, namely that you can benefit from the better eye relief of eyepieces with a long focal length when using the extenders.

In contrast to Barlow lenses, which use a so-called "telenegative" design, the Explore Scientific Focal Extender has a "telecentric" design with 4 lenses, one of which is a dispersing lens. A similar design was sold by Meade, and Explore Scientific probably took it over (both versions are supposedly manufactured by JOS), and another one is being sold by TeleVue (obviously at a much higher price ...).

When the 2 x focal extender arrived at my home, the cardboard box was unfortunately "crumpled" at one corner, but fortunately the extender was left undamaged:

         

Photos: The "crumpled" box of the focal extender

I notified Explore Scientific of this issue, but did not ask for an exchange. I got a voucher of 4.95 EUR, which I used when ordering a 3 x focal extender from them - so to speak without shipping cost thanks to the voucher.

 

Look (2 x Extender)

   

Explore Scientific Focal Extender 2 x with caps

 

Explore Scientific Focal Extender 2 x top view

 

Explore Scientific Focal Extender 2 x rear view

   

Explore Scientific Focal Extender 2 x alone

 

Ditto with TeleVue 24 mm eyepiece

 

Ditto with TS Optics 4mm UWA eyepiece

         

Explore Scientific Focal Extender 2 x (left) with Barlow lens from Revelation eyepiece bag and Sky-Watcher "kit" Barlow lens for comparison

     

Sky-Watcher Heritage 100P with ES Focal Extender and eyepiece

   

 

Look (3 x Extender)

         

Explore Scientific Focal Extender 3 x with caps

 

Explore Scientific Focal Extender 3 x top view

 

Explore Scientific Focal Extender 3 x rear view

   

Explore Scientific Focal Extender 3 x alone

 

Ditto with TeleVue 24 mm eyepiece

 

Ditto with TS Optics 4mm UWA eyepiece

 

Look (both Extenders)

         

Explore Scientific Focal Extender 2 x and 3 x with caps

 

Ditto with boxes (right: boxes opened)

 
   

Sky-Watcher "kit" Barlow lens, Explore Scientific Focal Extender 2 x, Explore Scientific Focal Extender 3 x, and Barlow lens from the Revelation eyepiece bag for comparison (from left to right)

 

Eyepiece Data without and with Focal Extenders

The following table shows for my current eyepieces, which magnifications and true visual angles can be achieved with my current telescopes without and with the two focal extenders:

Telescope Telescope
Focal
Length (mm)
Extender
Eyepiece Focal Length (mm)
Max. useable
Magification
(1.5/2)
4
7
10
16
24
32
Magnification
Heritage 100P
400
---
100.00
57.14
40.00
25.00
16.67
12.50
150/200
Explorer 150PDS
750
187.50
107.14
75.00
46.88
31.25
23.44
225/300
Skymax-102
1300
325.00
185.71
130.00
81.25
54.17
40.63
204
Heritage 100P
400
2 x
200.00
114.29
80.00
50.00
33.33
25.00
150/200
Explorer 150PDS
750
375.00
214.29
150.00
93.75
62.50
46.88
225/300
Skymax-102
1300
650.00
371.43
260.00
162.50
108.33
81.25
204
Heritage 100P
400
3 x
300.00
171.43
120.00
75.00
50.00
37.50
150/200
Explorer 150PDS
750
562.50
321.43
225.00
140.63
93.75
70.31
225/300
Skymax-102
1300
975.00
557.14
390.00
243.75
162.50
121.88
204
 
Telescope Telescope
Focal
Length (mm)
Extender
Apparent Angle of View
 
82
82
70
82
65
52
True Angle of View
Heritage 100P
400
---
0.82
1.44
1.75
3.28
3.90
4.16
 
Explorer 150PDS
750
0.44
0.77
0.93
1.75
2.08
2.22
 
Skymax-102
1300
0.25
0.44
0.54
1.01
1.20
1.28
 
Heritage 100P
400
2 x
0.41
0.72
0.88
1.64
1.95
2.08
 
Explorer 150PDS
750
0.22
0.38
0.47
0.87
1.04
1.11
 
Skymax-102
1300
0.13
0.22
0.27
0.50
0.60
0.64
 
Heritage 100P
400
3 x
0.27
0.48
0.58
1.09
1.30
1.39
 
Explorer 150PDS
750
0.15
0.26
0.31
0.58
0.69
0.74
 
Skymax-102
1300
0.08
0.15
0.18
0.34
0.40
0.43
 

Red: Above maximum usable magnification; magenta: above maximum usable magnification for Newtonians

 

First Experiences

In the following, I present sample pictures taken with the Explore Scientific Focal Extender 2 x, the Revelation Barlow lens 2 x, and the Sky-Watcher Barlow lens 2 x (under unfavorable conditions, camera Ricoh GR held to the eyepiece). These photos should not be taken too seriously, but they provide a certain impression of the different performances of the three focal extenders. The Sky-Watcher Barlow lens 2 x is especially sensitive to stray light and shows the strongest color fringing. With the Explore Scientific Fokal Extender 2 x, I could not find any color fringing. The Revelation Barlow lens is in the midfield, but I also found it not good enough for using it in the past ...

The Sky-Watcher Heritage 100P used in these tests was actually beyond the maximum usable magnification (200 x instead of 150 x) when used with the 4 mm UWA eyepiece. The following photos are unprocessed!

         
Explore Scientific Focal Extender 2 x, 4 mm UWA   Revelation Barlow lens 2 x, 4 mm UWA   Sky-Watcher Barlow lens 2 x, 4 mm UWA
         
Explore Scientific Focal Extender 2 x, 4 mm UWA   Revelation Barlow lens 2 x, 4 mm UWA   Sky-Watcher Barlow lens 2 x, 4 mm UWA
   
Explore Scientific Focal Extender 2 x, 16 mm UWA   Revelation Barlow lens 2 x, 16 mm UWA (leicht verwackelt)   Sky-Watcher Barlow lens 2 x, 16 mm UWA

Comparison of the Magnification without Extender, with 2x and with 3 x Extender

The following photos are ment to give an impression of the achievable magnification with the 2 x and 3 x externders (not of the achievable image quality). They were also taken with the Sky-Watcher Heritage 100P and the Ricoh GR:

         
24 mm WA eyepiece at Heritage 100P   Explore Scientific Focal Extender 2 x, 24 mm WA eyepiece   Explore Scientific Focal Extender 3 x, 24 mm WA eyepiece

Weight

The Explore Scientific Fokal Extender 2 x and 3 x version weigh 260 g (232 g and 254 g according to my kitchen scales) and are therefore a problem for light telescopes such as the Sky-Watcher Heritage 100P. Experience will show whether I can live with this...

 

First Conclusions

In progress

My first impression of the Explore Scientific Focal Extender 2 x is very good. Surely one cannot expect miracles, and "real" eyepieces with the corresponding magnifications will certainly give better results than the equivalent combinations with the extender. But as a "start," extenders are a good and not too expensive solution. Very first impressions of the 3 x extender seemed to indicate that it does not perform quite as well as the 2 x extender (which does not come as a surprise to me...), but when I checked both extenders at the moon (nearly half moon), the 2 x with an 16 mm UWA eyepiece, and the 3 x with a 24 mm WA eyepiece, I could not see any significant differences (the same accounts for the 7 mm UWA eyepiece without extender, however, this magnifies a little more in comparison to the two other configurations).

When I look at the technical data of my current eyepiece (see above), I have, however, to admit that my eyepiece set does not have clear gaps (see elsewhere) and that therefore the purchase of the focal extenders was not really necessary...

When traveling, the extenders do not seem to have any real advantages for me: Two extenders instead of two short-focussed eyepieces actually increase the weight without really offering "must have" options. And since I mostly use the small Sky-Watcher Heritage 100P telescope when traveling, heavy extender solutions are not really ideal (see above)...

The following table demonstrates possible "travel sets " from my current eyepieces and focal expanders for the Sky-Watcher Heritage 100P telescope (two consisting of 5 pieces, two of 4 pieces):

3 Eyepieces (24 mm, 16 mm, 10 mm) + 2 Extenders (2 x, 3 x) = 8 Options
Extender
2 x
2 x
3 x
3 x
2 x
3 x
Eyepiece
24 mm
16 mm
24 mm
10 mm
16 mm
24 mm
16 mm
10 mm
10 mm
Magnification
16.67
25.00
33.33
40.00
50.00
50.00
75.00
80.00
120.00
Weight: approx. 1060 g*
3 Eyepieces (24 mm, 16 mm, 10 mm) + 1 Extender (2 x) = 6 Options
Extender
2 x
2 x
2 x
Eyepiece
24 mm
16 mm
24 mm
10 mm
16 mm
10 mm
Magnification
16.67
25.00
33.33
40.00
50.00
80.00
Weight: approx. 810 g with extender, approx. 580 g eyepieces alone*
3 Eyepieces (24 mm, 16 mm, 10 mm) + 1 Extender (3 x) = 6 Options
Extender
3 x
3 x
3 x
Eyepiece
24 mm
16 mm
10 mm
24 mm
16 mm
10 mm
Magnification
16.67
25.00
40.00
50.00
75.00
120.00
Weight: 830 g with extender, approx. 580 g eyepieces alone*
3 Eyepieces (24 mm, 16 mm, 7 mm) + 1 Extender (2 x) = 6 Options
Extender
2 x
2 x
2x
Eyepiece
24 mm
16 mm
24 mm
16 mm
7 mm
7 mm
Magnification
16.67
25.00
33.33
50.00
57.14
114.29
Weight: approx. 925 g with extender, approx. 690 g eyepieces alone*
4 Eyepieces (24 mm, 16 mm, 10 mm, 7 mm) + 1 Extender (2 x) = 8 Options
Extender
2 x
2 x
2 x
2x
Eyepiece
24 mm
16 mm
24 mm
10 mm
16 mm
7 mm
10 mm
7 mm
Magnification
16.67
25.00
33.33
40.00
50.00
57.14
80.00
114.29
Weight: approx. 1020 g with extender, approx. 790 g eyepieces alone*
5 Eyepieces (24 mm, 16 mm, 10 mm, 7 mm, 4 mm) = 5 Options
Eyepiece
24 mm
16 mm
10 mm
7 mm
4 mm
Magnification
16.67
25.00
40.00
57.14
100.00
Weight: approx. 1000 g*; *) all weights taken with kitchen scales and including caps, some bags, ...

The "eyepieces only" solution (5 pieces) looks best to me, next come the configuration with 3 eyepieces plus 3 x focal extender (4 pieces) and 4 eyepieces plus 2 x extender (5 pieces). I decided to go for the last configuration for my June 2017 holiday in France.

 

References

 

An den Anfang   Homepage  

gerd (at) waloszek (dot) de

About me
made by walodesign on a mac!
03.06.2017