Improving Performance With A Barlow Lens
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By taking photographs with and without the Barlow
lens in place, I discovered that it magnified the 40mm
Plossl 1.33x. It expanded the useful unvignetted zoom
range of the Coolpix 5400 from just one setting at
24mm with the Plossl eyepiece alone, to a range of
18.8mm to 24mm, with the camera to eyepiece
adapter configured so the the external zoom lens
of the Coolpix 5400 can be zoomed all the way out
without hitting the eyepiece. I checked the eye relief
measurements of the 40mm Plossl alone in the
Swarovski AT80HD and it measures at 34mm, while
it is rated by Televue as being 28mm. When I
measured the eye relief with the 1.33x Barlow in
place, it measured an almost unbelieveable 57mm.
The extension tube that came as part of the Barlow
lens assembly makes a nice extension tube for the
Plossl eyepiece alone when you want to reduce the
minimum focus distance of the scope for small nature
subjects.
The photograph to the right and
the two photographs on the next
page I have included as examples,
one each to show color, detail,
and distance using the 1.33x
Barlow, 40mm Televue Plossl,
Swarovski AT80HD, and the
Coolpix 5400.
The 35mm equivelant focal length
in each example is about 1400mm.
All three are uncropped and
downsized with minimal post
processing.
