Saturday, 11 August 2012

Which Eyepiece for Leica apo-Televid 77?

I carry three eyepieces with me when using the apo-Televid 77. Why?

Over the years we have had the opportunity of testing all the eyepieces made for the 77/62 range side by side and under different lighting conditions. The eyepiece lenses (available only on the secondhand market) are:

20x WW (41009)
32x WW (41011)
40x (41003)
40x WW (41007)
30-60x Zoom (41005)

Let’s start by considering the zoom.

The 20-60x zoom eyepiece (41005) is one I do not use. It has an angle of view of 1.9-1.2˚ equating to a 34-20 metre field of view at 1000 metres. At 20x magnification, its exit pupil is 3.85 mm (making it brighter, on paper, than the 20x WW) decreasing to 1.28 at 60x. There are several reasons why I do not favour this eyepiece. It has a narrow field of view compared to the WW series. It is pretty useless at magnifications above 40x under normal lighting conditions and it lacks the clarity and brightness of the single magnification eyepieces, despite the relatively large exit pupil. Having a family with two apo-Televid 77s, an apo-Televid 82 and an apo-Televid 62, the general comment is that Leica did not get the zoom right until the 82.

The other eyepiece we do not use is the 40x (41003) — the early, non-wide variety. It has a relatively narrow angle of view (1.25°; 22 metres field at 1000 metres) and a small exit pupil of 1.25 mm. The WW version is far superior.

In terms of Field of View the WW lenses are far superior as the diagram below shows.

Now to the eyepieces I carry with me:

I usually have the 40x WW (41007) fitted. It has a 1.8° angle of view (32 metres field at 1000 metres) and an exit pupil of 1.8 mm. It is a superb lens. But if the light is relatively low or a wider field is needed, then I can quickly switch to the 32x WW (41011) (2.3° angle of view — 40 metres field at 1000 metres; 2.3 mm exit pupil). Another superb lens. If the light really starts to fade or if I want to scan and count then the 20x WW (41009) comes into its own. This gives a 3.45° angle of view (60 metre field at 1000 metres) with an exit pupil of 3.45 mm.

40x WW fitted on the Apo-Televid 77

The value of carrying three eyepieces was illustrated by an evening in the Eric Morecambe  Hide at the RSPB’s Leighton Moss reserve. A flock of Black-tailed Godwits looked superb with the 40x WW but as the light began to fade, the 32x WW was needed. As the colours began to become indistinct, a quick change to the 20x WW brought the scene back to life.

The three WW eyepieces I carry

A factor in choosing eyepieces is digiscoping. It is worth noting that the Leica Digital Adapter 2 (42303) nor the Digilux 1 Adapter (42302) will not fit either of the 40x eyepieces. The diameter of the various eyepieces for fitting digiscoping collars are: 54 mm (32x WW); 53 mm (20x WW and 20-60x); 50 mm (40x WW); 45 mm (40x). It is worth talking to SRB Griturn about digiscoping adapters for all these eyepieces.

SRB Griturn can be found at:

Leica Digital Adapter 2 (42303) fitted to 32x WW eyepiece

Finally, these eyepieces were also made for the Televid 62 but have lower magnifications (by a factor 0f 0.8). 40x becomes 32x, and 32x becomes 26x on the Televid 62.