Interferometer testing and design of Rumak Mak Cass optics.

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?. I have a situation where I
ordered Maksutov (Rumak)optics from a source that certified them to be
1/8.4 p/v wavefront, yet didn't even know what the f# of the primary
was. I measured it myself with the corrector in place and with the
corrector removed and found in both cases, that it was f3 and not f2.7
as was claimed. I am now wondering about the optical evaluation test
itself and whether it was actually performed and how accurate it was.
I will be happy to take emails or see postings on this subject if
anyone can enlighten me.At this f# it appears that the secondary
mirror is a bit too small to catch all the light from the primary and
still achieve proper backfocus, is this normal with this design or do
I have a problem? The f# of the secondary is claimed to be f4.5 and is
at a nominal distance of 19.8".The primary is 9.5" Diam. the secondary
is 2.5" diam.
Thanks Brian.

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?

No, one does not test the individual items on the interferometer, only the
final optical system.

As far as the secondary being too small, how do you know that? In order to know
the path of the various light rays, you would have to know the curvatures of
the various optical elements, and then lay it out with a design program (I can
recommend ATMOS design program see:
http://astro-physics.com/index.htm?p...re/atmos/atmos ).
This will tell you whether or not all rays are being used, or if some are being
vignetted.

Roland Christen

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?

No, one does not test the individual items on the interferometer, only the
final optical system.

As far as the secondary being too small, how do you know that? In order to know
the path of the various light rays, you would have to know the curvatures of
the various optical elements, and then lay it out with a design program (I can
recommend ATMOS design program see:
http://astro-physics.com/index.htm?p...re/atmos/atmos ).
This will tell you whether or not all rays are being used, or if some are being
vignetted.

Roland Christen

brian morse wrote:

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?.

No. As Chris says you test the whole system, as a working whole, for
assessing
final wavefront error. But, it does seem curious the focal length of the
primary
would not be specified? Did the set include a full set of specs
(including component
positions)? What's the focal length of the system?
jerry



I have a situation where I
ordered Maksutov (Rumak)optics from a source that certified them to be
1/8.4 p/v wavefront, yet didn't even know what the f# of the primary
was. I measured it myself with the corrector in place and with the
corrector removed and found in both cases, that it was f3 and not f2.7
as was claimed. I am now wondering about the optical evaluation test
itself and whether it was actually performed and how accurate it was.
I will be happy to take emails or see postings on this subject if
anyone can enlighten me.At this f# it appears that the secondary
mirror is a bit too small to catch all the light from the primary and
still achieve proper backfocus, is this normal with this design or do
I have a problem? The f# of the secondary is claimed to be f4.5 and is
at a nominal distance of 19.8".The primary is 9.5" Diam. the secondary
is 2.5" diam.
Thanks Brian.

brian morse wrote:

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?.

No. As Chris says you test the whole system, as a working whole, for
assessing
final wavefront error. But, it does seem curious the focal length of the
primary
would not be specified? Did the set include a full set of specs
(including component
positions)? What's the focal length of the system?
jerry



I have a situation where I
ordered Maksutov (Rumak)optics from a source that certified them to be
1/8.4 p/v wavefront, yet didn't even know what the f# of the primary
was. I measured it myself with the corrector in place and with the
corrector removed and found in both cases, that it was f3 and not f2.7
as was claimed. I am now wondering about the optical evaluation test
itself and whether it was actually performed and how accurate it was.
I will be happy to take emails or see postings on this subject if
anyone can enlighten me.At this f# it appears that the secondary
mirror is a bit too small to catch all the light from the primary and
still achieve proper backfocus, is this normal with this design or do
I have a problem? The f# of the secondary is claimed to be f4.5 and is
at a nominal distance of 19.8".The primary is 9.5" Diam. the secondary
is 2.5" diam.
Thanks Brian.

Thanks to Jerry and Roland for responding to my questions.To reply to
yours, I constructed a simple on-axis ray diagram of a 9.5 " f3.0
mirror and placed a 2.5" obstruction at the nominal distance of 19.8 "
it appears that some of the light rays miss the secondary which seems
to indicate to me that the rays from the outer half inch of the
primary are not reaching the secondary. This means that the effective
size of the primary is now 8.5" instead of 9.5" As I am not an optical
expert, could you tell me if my reasoning is correct or not?. I took a
look at the program that you recommended to me Roland but feel that it
is a bit beyond my capabilities at this time without a whole pile of
study. I would be prepared to pay for costs to have someone look at
the design and give me an opinion of whether the baffling and layout
is correct. I have redesigned the primary baffle and there is no
secondary baffle supplied with the scope. In addition there were no
baffles installed on the inside of the main tube which I have
corrected since and am getting better images now, but still believe
that I have a way to go.
Cheers Brian Morse.jerry warner wrote in message ...
brian morse wrote:

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?.

No. As Chris says you test the whole system, as a working whole, for
assessing
final wavefront error. But, it does seem curious the focal length of the
primary
would not be specified? Did the set include a full set of specs
(including component
positions)? What's the focal length of the system?
jerry



I have a situation where I
ordered Maksutov (Rumak)optics from a source that certified them to be
1/8.4 p/v wavefront, yet didn't even know what the f# of the primary
was. I measured it myself with the corrector in place and with the
corrector removed and found in both cases, that it was f3 and not f2.7
as was claimed. I am now wondering about the optical evaluation test
itself and whether it was actually performed and how accurate it was.
I will be happy to take emails or see postings on this subject if
anyone can enlighten me.At this f# it appears that the secondary
mirror is a bit too small to catch all the light from the primary and
still achieve proper backfocus, is this normal with this design or do
I have a problem? The f# of the secondary is claimed to be f4.5 and is
at a nominal distance of 19.8".The primary is 9.5" Diam. the secondary
is 2.5" diam.
Thanks Brian.

Thanks to Jerry and Roland for responding to my questions.To reply to
yours, I constructed a simple on-axis ray diagram of a 9.5 " f3.0
mirror and placed a 2.5" obstruction at the nominal distance of 19.8 "
it appears that some of the light rays miss the secondary which seems
to indicate to me that the rays from the outer half inch of the
primary are not reaching the secondary. This means that the effective
size of the primary is now 8.5" instead of 9.5" As I am not an optical
expert, could you tell me if my reasoning is correct or not?. I took a
look at the program that you recommended to me Roland but feel that it
is a bit beyond my capabilities at this time without a whole pile of
study. I would be prepared to pay for costs to have someone look at
the design and give me an opinion of whether the baffling and layout
is correct. I have redesigned the primary baffle and there is no
secondary baffle supplied with the scope. In addition there were no
baffles installed on the inside of the main tube which I have
corrected since and am getting better images now, but still believe
that I have a way to go.
Cheers Brian Morse.jerry warner wrote in message ...
brian morse wrote:

Can anyone who has used an interferometer tell me, is it necessary to
determine the focal ratio of the primary mirror when assessing the
optical quality of the entire system?.

No. As Chris says you test the whole system, as a working whole, for
assessing
final wavefront error. But, it does seem curious the focal length of the
primary
would not be specified? Did the set include a full set of specs
(including component
positions)? What's the focal length of the system?
jerry



I have a situation where I
ordered Maksutov (Rumak)optics from a source that certified them to be
1/8.4 p/v wavefront, yet didn't even know what the f# of the primary
was. I measured it myself with the corrector in place and with the
corrector removed and found in both cases, that it was f3 and not f2.7
as was claimed. I am now wondering about the optical evaluation test
itself and whether it was actually performed and how accurate it was.
I will be happy to take emails or see postings on this subject if
anyone can enlighten me.At this f# it appears that the secondary
mirror is a bit too small to catch all the light from the primary and
still achieve proper backfocus, is this normal with this design or do
I have a problem? The f# of the secondary is claimed to be f4.5 and is
at a nominal distance of 19.8".The primary is 9.5" Diam. the secondary
is 2.5" diam.
Thanks Brian.

Thanks to Jerry and Roland for responding to my questions.To reply to
yours, I constructed a simple on-axis ray diagram of a 9.5 " f3.0
mirror and placed a 2.5" obstruction at the nominal distance of 19.8 "
it appears that some of the light rays miss the secondary which seems
to indicate to me that the rays from the outer half inch of the
primary are not reaching the secondary. This means that the effective
size of the primary is now 8.5" instead of 9.5" As I am not an optical
expert, could you tell me if my reasoning is correct or not?

At first glance, it sounds reasonable.

One thing I could not understand is why your images would look better when you
installed tube baffles. A baffle has no effect on rays of light that form the
image. They certainly cannot make an image look better.

Roland Christen

Thanks to Jerry and Roland for responding to my questions.To reply to
yours, I constructed a simple on-axis ray diagram of a 9.5 " f3.0
mirror and placed a 2.5" obstruction at the nominal distance of 19.8 "
it appears that some of the light rays miss the secondary which seems
to indicate to me that the rays from the outer half inch of the
primary are not reaching the secondary. This means that the effective
size of the primary is now 8.5" instead of 9.5" As I am not an optical
expert, could you tell me if my reasoning is correct or not?

At first glance, it sounds reasonable.

One thing I could not understand is why your images would look better when you
installed tube baffles. A baffle has no effect on rays of light that form the
image. They certainly cannot make an image look better.

Roland Christen

(Chris1011) wrote in message ...
Hi Roland, what I am saying is that the baffles greatly improved the
image by cutting down on the stray light and increasing contrast. The
planets and stars lost that foggy halo around them and the overall sky
looked a lot darker after I had flocked the interior of the Main tube
with black treated felt and three baffles.I also treated the interior
of the primary in the same fashion which made a big difference. I also
tapered inwards the primary baffle tube to stop light rays from the
primary being obstructed on their way to the secondary, while not
choking off the rays from the secondary to the eyepiece.This also
allowed me to keep the masking (all but 3mm ) on the primary miror
surrounding the primary baffle tube down to a minimum. This seems to
be a balancing act between the various needs and compromises between
perfect baffling and light loss. As I am not obviously an optical
expert, this is why I am keen to have someone who realy understands
these things to have a look at my design to see if I'm on the right
track or not. It's been a steep learning curve for me that's for
shore.
Thanks again Brian Morse.
Thanks to Jerry and Roland for responding to my questions.To reply to
yours, I constructed a simple on-axis ray diagram of a 9.5 " f3.0
mirror and placed a 2.5" obstruction at the nominal distance of 19.8 "
it appears that some of the light rays miss the secondary which seems
to indicate to me that the rays from the outer half inch of the
primary are not reaching the secondary. This means that the effective
size of the primary is now 8.5" instead of 9.5" As I am not an optical
expert, could you tell me if my reasoning is correct or not?

At first glance, it sounds reasonable.

One thing I could not understand is why your images would look better when you
installed tube baffles. A baffle has no effect on rays of light that form the
image. They certainly cannot make an image look better.

Roland Christen