This morning I have had the chance to talk with the old Masteroptician in Eastgermany who producing the BW optik Binoviewers and my questions he answered as follow
1, Question: what is better Bak4 or BK 7?
Answere: Bak 4 is used to compensate some spherical aberrations, but prism made without real spherical aberration better using BK 7, because that BK 7 glas is way better in homogeneity than Bak4 and can be much better polished
2, Question. what kind of coating is used in BW optic Binoviewers
answere: Braodband spectral coating with 99.5 5 transmission per surface over the visual spectral range
3, Questions: why one side is in most dimmers than on other side and why some are more similar on each side ?
answere: standart nonobstructed systems with best coatings show and must show a bit diffrenc ein brightness due diffrent long optical path. Binoviewers showing equal brightness on both sides using a design with 30~50% obstruction at one side . Some technics excist to make a binoviewer looking equal bright on each side, but it requires very special ultraexpensive coatings and such binoviewers going for not less than $ 2,000 worldwide on the market
I hope this info helps a bit
best wishes
Markus
1, Question: what is better Bak4 or BK 7?
Answere: Bak 4 is used to compensate some spherical aberrations, but prism made without real spherical aberration better using BK 7, because that BK 7 glas is way better in homogeneity than Bak4 and can be much better polished
2, Question. what kind of coating is used in BW optic Binoviewers
answere: Braodband spectral coating with 99.5 5 transmission per surface over the visual spectral range
3, Questions: why one side is in most dimmers than on other side and why some are more similar on each side ?
answere: standart nonobstructed systems with best coatings show and must show a bit diffrenc ein brightness due diffrent long optical path. Binoviewers showing equal brightness on both sides using a design with 30~50% obstruction at one side . Some technics excist to make a binoviewer looking equal bright on each side, but it requires very special ultraexpensive coatings and such binoviewers going for not less than $ 2,000 worldwide on the market
I hope this info helps a bit
best wishes
Markus
clear skies
Markus Ludes
APM-Telescopes/Germany