From an e-mail to Baader back in January about their filters:
And as promised, the more detailed response from Baader:
“- and we are very silent - to say the least...
The "V" marks the "preferred orientation". That is:
"Normally" - always the more reflective side of any filter should point away
from the imaging plane (chip). This works better for about 95% of all filter
installations.
It is logical - to try and send reflections from the more reflective metal
side (= dielectric coating stack) of the filter back right into the sky -
and to not have the stronger reflective side of the filter point towards the
chip surface, eventually causing more of retro-reflections between chip
surface - and camera window - and filter surface - than necessary.
Alas - this cannot be declared the general rule.
Sometimes the customer uses an optical system that would put a lens or a
series of lenses so close in front of the filter that it again can cause
reflections focusing at or near the chip surface - and this will affect any
filter make, regardless of the manufacturer.
So - only if there is a focal reducer or field flattener (or barlow lens)
added into the optical train - that is - if an otherwise reflection free
optics suddenly produces halos - it certainly can happen that the user must
try to reverse the filter orientation and reposition filters within the
optical train and check if the situation will improve.
So for this reason we hesitate to imperatively declare a preferred filter
orientation or to claim a sole solution. Every optical system will require
to find the best compromise. Some systems though are already designed with
the given position of a filter implemented into the design of the auxillary
lenses - such as Planewave CDK´s for instance.
Best regards,
Service Team
BAADER PLANETARIUM GMBH
BAADER PLANETARIUM GMBH * Zur Sternwarte * D-82291 Mammendorf
Tel.: +49(0)8145-8089-0 * Fax: +49(0)8145-8089-105 *
