NEW FMC Knight OWL labeled Wide-Angles

Hi,

Just saw these they are new and improved 66° model offered in 20mm,
15mm, 9mm and 6mm from (seller owl1) on eBay. Example link:

http://cgi.ebay.com/ws/eBayISAPI.dll...9954 890&rd=1

Also assumingly available directly from Knight Owl, too. Tom Roginski
emailed me some extra details. Forwarding them by permission for you
folks (see below). I have no affiliation with this seller.

I bet Jon Isaac will be particularly excited he likes this well
reputed series in short FL. I liked the MC version of the 15mm myself
it was great. Now they are FMC coated and slightly improved (?) too!

I'm told these are not a GSO product, there are some of those yet to
be introduced in approx. 10mm and 5mm FL Wide-Angle late this year or
early next.

----------------------------------
From Tom R. on the new OWL WA's:

"These are supposed to be and appear to be fully multi-coated. I also
am told that this is a slightly modified version of the previous
series sold by others.

This is a product that we have never carried before, and it has the
Knight OWL brand on it - our first branded eyepiece. This series have
members from 20 mm to 6 mm. The previous shortest super-wide eyepiece
that we carried was 8 mm and that had only a 60 degree field - these
are 66 degree. The shorter focal lengths of these have been especially
interesting to a number of people. These have the negative element as
the bottom lens in the system. This is essentially a dedicated barlow
designed just for this optical system.

These are new product - not used and we supply a good bolt-type case
with them.

TOM (OWL1)"
----------------------------------

Clear skies,

Pete

I bet Jon Isaac will be particularly excited he likes this well
reputed series in short FL.

I like the 9mm but the 6mm has ghosts that seem to come from the sleeve between
the elements in the front section. I wonder if this has been taken care.
According to the website these eyepieces have blackened edges.

Here's one for you Pete and anyone else interested.

I bought a 42mm GSO SuperView with a supposed 66 degree AFOV.

When I took the barrel off and measured the clear aperture of the field lens it
is only 41mm. This is the diameter of the field lens retaining ring which is
probably 2-3mm thick. Using the basic geometry that TV uses, this would result
in AFOV of 56 degrees.

Using my tape measure against the fence with my Pronto (2 inch Everbright
diagonal), I get a TFOV of 4.9 degrees which again corresponds to an AFOV of 56
degrees.

So then while using the eyepiece in my 1250mm Focal length 10 inch Newtonian I
noticed that I could not quite see both Nu Lyrae and Gamma Lyrae (Sulafat) in
the same field of view. I tried this several times and positioned my eye for
the maximum view in each direction. These stars are separated by 1 degree 55
minutes. Doing the basic math, this means that AFOV of the eyepiece would have
to be less than 57 degrees which corresponds nicely with my other measurements.

When I look at other eyepieces like a TV 32mm Widefield, they have a field stop
but the clear aperture behind the field stop is larger than the field stop.

Is the AFOV of this eyepiece such that it really does give TFOVs that are
associated with a 41mm field stop such as it seems or is there something else
going on here...

jon

Pete Rasmussen wrote in message . ..
Hi,

Just saw these they are new and improved 66° model offered in 20mm,
15mm, 9mm and 6mm from (seller owl1) on eBay. Example link:


Hey Pete - thanks for the heads up on those. They claim to have
improved coatings over the Synta widescan and Orion expanse, eh?

Did ja order any? Enquiring minds want to know....

T

Jon Isaacs wrote:
Is the AFOV of this eyepiece such that it really does give TFOVs that are
associated with a 41mm field stop such as it seems or is there something
else going on here...

I noticed that in all cases, you are measuring the true FOV directly, and
then making a conversion of some sort to the AFOV. All of these conversions
neglect the possibility of distortion, although I must confess it would take
an extraordinary amount of pincushion distortion to expand an apparent field
that would be 56 degrees if orthoscopic by a whopping 10 degrees.

More likely, some combination of distortion plus exaggeration is responsible.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

I noticed that in all cases, you are measuring the true FOV directly, and
then making a conversion of some sort to the AFOV. All of these conversions
neglect the possibility of distortion, although I must confess it would take
an extraordinary amount of pincushion distortion to expand an apparent field
that would be 56 degrees if orthoscopic by a whopping 10 degrees.

More likely, some combination of distortion plus exaggeration is responsible.

So exactly how does one interpret the idea of having 65 degree FOV due to
distortion?
Does this mean that the magnification is not constant across the field of view?

jon

(Jon Isaacs) wrote in message ...
I noticed that in all cases, you are measuring the true FOV directly, and
then making a conversion of some sort to the AFOV. All of these conversions
neglect the possibility of distortion, although I must confess it would take
an extraordinary amount of pincushion distortion to expand an apparent field
that would be 56 degrees if orthoscopic by a whopping 10 degrees.

More likely, some combination of distortion plus exaggeration is responsible.

So exactly how does one interpret the idea of having 65 degree FOV due to
distortion?
Does this mean that the magnification is not constant across the field of view?

jon

I think you could call it exaggeration, wishful thinking, a typo or
false advertising - take your pick. The field stop is the determining
factor.
Clear skies,
Shneor Sherman

I think you could call it exaggeration, wishful thinking, a typo or
false advertising - take your pick. The field stop is the determining
factor.
Clear skies,
Shneor Sherman

That was my "simple minded" thinking but still looking for magic....

jon

On 1 Nov 2004 10:47:28 -0800, (Tom T.) wrote:


Hey Pete - thanks for the heads up on those. They claim to have
improved coatings over the Synta widescan and Orion expanse, eh?

Did ja order any? Enquiring minds want to know....


Hi Tom,

Sorry, I was away hence this late reply. Yes they seem like are to be
FMC vs the older combo coatings. No indication on exact other
improvements if any exist.

I'm not needing any of these myself but would not hesitate getting the
new style 15mm.

I've looked through the (now older style) 20mm Orion the other day at
a friends through an f/6.7 Newtonian and "indirectly speaking" would
suggest the 15mm is the better toward the edges in original SWA
clone-athon series' with starfields. The shorter FL's like 9mm and
6mm would of course be quite a bit better yet across the viewing field
and benefit even further from coating improvements.

Pete