Re: Broken Pentax Beam Splitter

[P3D John Ohrt <johrt@xxxxxxx>]

P3D, Eric, J, Fleischer@xxxxxxxxxxxxxxx, MD wrote:
> 
> A few days ago, I had a most unfortunate accident. I dropped my camera
> bag, with my camera and Pentax beam splitter in it. It must have
> landed exactly wrong, because one of the front-surface mirrors
> shattered. The case of the splitter isn't bent or dented in the least.
> 
> The broken mirror is 1.5" x 1.75" x 3/32".=20
> 
> Does anyone know where I can get a replacement for this mirror, and
> how to get the mirror mounted in the splitter?  It is not apparent how
> to open the case, and I don't want to damage it trying.
> 
> Edmund Scientific has some front surface mirrors, but they are not
> quite the right size. They are too big, and I suspect it would be
> difficult to cut a mirror down without damaging it.

If the broken mirror didn't have the edges protected by flat black
paint, then the odds are that the precise size is a little flexible
because a baffle is likely protecting the edges from stray light.

Making an optically flat mirror is no big deal,  amateur telescope
makers consider it about the eaasiest of their tasks.  Question Edmund
about their surface flatness. From what I have heard of Nikon, their
spec is likely 1/40 lambda (lambda = wavelength).  You don't much care,
but it will likely be quoted about lambda = 635 nm.

Mounting and adjusting the mirror is more tricky and I would suspect you
need access to an optical bench to do it quickly, but trial and error
will do it.

I would ask Nikon for a repair quote.  If they say forget it and buy a
new one, well you could do that or you could play around given your
time, patience and aptitude.

If you can wait a bit, I will ask an acquaintance, a professional
telescope and astrograph maker what he thinks.  He also has some pretty
pricey cameras :-).

I will post the answer.


By the way, a beamsplitter splits an image into to different directions,
at some prearranged ratio of intensity.  Beamsplitters do work in
reverse but unless your imaging device is polarized or filtered to
distinguish the two fields of view, which are coaxial (ie overlayed on
top of each other), I don't see how a beamslitter would work.


As I understand it, what we are talking about in P3D are field combiners
which combine two different fields such that the optical axis lies on
the boundaries where the fields meet so that an imaging device can
record both views simultaneously.  There are many limitations on field
combining if you place the combiner before the lens.  If you place the
combiner after two lens, then life is simpler but not cheaper :-).

The faster the system, the more important the lens match is.  At f/1, it
is critical and expensive to achieve.  Lietz will be pleased to do it
for you :-)  

Regards,
John

--
John Ohrt,  Regina, SK, Canada
johrt@xxxxxxx


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