Most things are 'obvious extensions'....to a tinkerer.
Since you are the first other to mention it, it's not really "Far from being a new idea"..
(in that there really aren't "many others" who horse around)...
Technical hobbies used to be more hands-on and less 'salon/purchase'...so
I'm just having fun being a throwback, like radio buffs who tweek their own
I haven't seen this design commercially. I need to tune out the edges a bit more
to have a throw-down against some popular middle commercial EPs.
It certainly has the Expanse beat for easy eye approach, for me, and the contrast is excellent.
The big difference, in my case, is the thicker doublets from the Japanese
binoc EPs. They will produce a plossl with a clean 60 degrees in a long barrel.
It's too bad the 'thick long barrel plossl' isn't available commercially. "Long" starts at
a mere F7 equivalent for many EPs. I suppose Abbe/Ortho users know the boon of
Anyway...these doublets are not your typical surplus stock.
This scheme is icing on that cake, and opens to 70deg...
I know you can't do that with standard doublets.
Then again.....your surplus doublets could have been thick at the time....
And..maybe you aren't ordinary or obvious yourself ;-)
Weaker doublet stacks can be surprisingly flexible.
4 with about the same value, touching, make a super-correct DiPlossl.
Only 50 degrees, but super with short or long barrels.
A 2,2,2 same-fl-stack can be even better with a short barrel.
There are the 3 in the Kaspereit, but in that case the middle doublet gets in the way
physically/optically when trying for afov, so the singlet of the Erfle is a better play.
I've been trying for a tapered stack, a 2,2,2,2, but tht idea is very sensitive to the parameters.
Having a strong top pair and a weak field lens seems more tolerant and flexible.
Edited by MartinPond, 29 November 2017 - 09:21 AM.