(Getting into the
ballpark of the Pig eyepieces without the weight! )
while maintaining simular
performance, eye relief, edge focus, a desent field of view and best of
all no added counterweights.
Having made a very light secondary
cage for the 40 Pounder was one thing now complementing it with a light
wide angle eyepiece was another. The scopes 1 to 6 balance ratio meant
not to exceed about 8 oz. when it came to eyepieces otherwise an extra
counterweight would be needed, for example a 2 pound eyepiece represents
an extra 12 pounds of counter balancing, not good!. My favorite eyepiece
is the 14mm shown in the image above, great FOV and eye relief but a pig
when it comes to weight, nothing can through off the balance of scope faster
then popping in this baby. Not wanting to give up on field and to spend
a lot of "money" I set out to come up with my own solution. It
was simple many years ago I played around with the idea of moving barlow
lenses towards and away from an eyepiece to attain different effective
focal lengths and it worked great so when the need to lighten the load
for the 40 Pounder came up I already had the plan in the bag. At this point
you might say why not just go out and buy a 65 degree, 6 element eyepiece
in these focal lengths the answer is simple to much money and second after
doing a lot of testing using an 80mm f4 lens I concluded my 7 element concoction
using an old 20mm fl., wide angle 5 element erfle and my new ( 1.5x ) barlow
rendered me a way better edge correction and eye relief (20mm) then the
newer commercial 13.8mm unit I was testing plus a flatter field then my
favorite 14mm. Most important it weighs only 6 oz.. Also I can put any
eyepiece I want in the new ( 1.5x ) configuration!! adding to my array
of different magnifications and it stays parfocal thanks to the ring you
see in the image above. If you want the original amplification of the barlow
( 2.5x ) you just unscrew it and put it back on it's original tube. (see
above right)
Above is my 80mm f4 test scope with the appropriate extension
tubes so as to allow me to focus on an interior wall. Using an f4 lens
really shows up coma therefore asking a lot from the eyepieces used in
it. I taped different test pieces on the wall ranging from straight lines
to high quality text each time checking for focus at center to extreme
edge and for overall curvature of field.
