initial spherical aberration tests completed

For those following along in my other thread, today I tested the 12" SCT for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a telephone
pole insulator for the test with the scope under the patio and 2) the scope
has only been set up for about 45 minutes. I can see plenty of heat waves
disturbing the diffraction patterns. Solution: I'm going to wait a couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to cool
the mirrors faster?

Thanks,
Jon

--
To reply, remove the "z" if one appears in my address
"Seth" wrote in message
ink.net...
For those following along in my other thread, today I tested the 12" SCT
for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a
telephone
pole insulator for the test with the scope under the patio and 2) the
scope
has only been set up for about 45 minutes. I can see plenty of heat
waves
disturbing the diffraction patterns. Solution: I'm going to wait a
couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to
cool
the mirrors faster?

Thanks,
Jon


http://www.lymax.com/sct/photos.php

You could, alternatively, uncap both ends of your scope, and point the
front end down, letting the warmer air inside the tube escape through the
open rear cell...

But the cooler above will do the job much faster...

--
To reply, remove the "z" if one appears in my address
"Seth" wrote in message
ink.net...
For those following along in my other thread, today I tested the 12" SCT
for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a
telephone
pole insulator for the test with the scope under the patio and 2) the
scope
has only been set up for about 45 minutes. I can see plenty of heat
waves
disturbing the diffraction patterns. Solution: I'm going to wait a
couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to
cool
the mirrors faster?

Thanks,
Jon


http://www.lymax.com/sct/photos.php

You could, alternatively, uncap both ends of your scope, and point the
front end down, letting the warmer air inside the tube escape through the
open rear cell...

But the cooler above will do the job much faster...

"Roger Hamlett" wrote in message
...

"Seth" wrote in message
ink.net...
For those following along in my other thread, today I tested the 12" SCT
for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a
telephone
pole insulator for the test with the scope under the patio and 2) the
scope
has only been set up for about 45 minutes. I can see plenty of heat
waves
disturbing the diffraction patterns. Solution: I'm going to wait a
couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to
cool
the mirrors faster?

Thanks,
Jon
Beware though, that an SCT, _even if perfectly made_, will display SA, at
all but one mirror spacing. Even if you have your eyepiece configuration
to give exactly the length 'designed for' at the rear of the scope,
focussing on something closer than the stars, will make SA appear. Ideally
you'd need to try at different mirror spacings (by changing the length of
the units behind the scope), and find the point with least SA.

Best Wishes


Hi Roger,

I've had a large house fan blowing across the ota for a couple of hours now.
After the first hour, I rechecked and, to my surprise, the in and out of
focus tests were producing a closer pattern. In another hour, I'm going to
check again. BTW, I could see this SA either with or without my 3x barlow
and just with the 14 mm eyepiece alone. Now, the patterns I'm seeing with
and without the barlow are getting closer in shape. I'm going to really
laugh if all of this has been the result of improper cooling!

Seth

"Roger Hamlett" wrote in message
...

"Seth" wrote in message
ink.net...
For those following along in my other thread, today I tested the 12" SCT
for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a
telephone
pole insulator for the test with the scope under the patio and 2) the
scope
has only been set up for about 45 minutes. I can see plenty of heat
waves
disturbing the diffraction patterns. Solution: I'm going to wait a
couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to
cool
the mirrors faster?

Thanks,
Jon
Beware though, that an SCT, _even if perfectly made_, will display SA, at
all but one mirror spacing. Even if you have your eyepiece configuration
to give exactly the length 'designed for' at the rear of the scope,
focussing on something closer than the stars, will make SA appear. Ideally
you'd need to try at different mirror spacings (by changing the length of
the units behind the scope), and find the point with least SA.

Best Wishes


Hi Roger,

I've had a large house fan blowing across the ota for a couple of hours now.
After the first hour, I rechecked and, to my surprise, the in and out of
focus tests were producing a closer pattern. In another hour, I'm going to
check again. BTW, I could see this SA either with or without my 3x barlow
and just with the 14 mm eyepiece alone. Now, the patterns I'm seeing with
and without the barlow are getting closer in shape. I'm going to really
laugh if all of this has been the result of improper cooling!

Seth

Hi Roger,

I've had a large house fan blowing across the ota for a couple of hours
now.
After the first hour, I rechecked and, to my surprise, the in and out of
focus tests were producing a closer pattern. In another hour, I'm going
to
check again. BTW, I could see this SA either with or without my 3x
barlow
and just with the 14 mm eyepiece alone. Now, the patterns I'm seeing
with
and without the barlow are getting closer in shape. I'm going to really
laugh if all of this has been the result of improper cooling!

Seth

This is actually a fairly effective way to equilibrate a large SCT.

I live in the low desert of Arizona, and that's EXACTLY how I cool my 10".
I roll it outside on it's wheeley bar, level it and raise the scope off
it's wheels, and rough polar align it. Then bring the OTA parallel with
the ground, remove the dust cover from the corrector, and aim a large fan
at the rear cell, and let 'er rip for an hour or two, depending on how
much temperature differential there is between the house and the outside
temperature. Here, in the summer, it's often 30 to 40 degrees, HOTTER
outside than inside... But the thermal equilibration process is still the
same... Interesting to note that here, the overnight low, in the summer
months, is virtually always warmer than the inside temperature, even after
dropping perhaps 30 degrees, or more, overnight...

Hi Roger,

I've had a large house fan blowing across the ota for a couple of hours
now.
After the first hour, I rechecked and, to my surprise, the in and out of
focus tests were producing a closer pattern. In another hour, I'm going
to
check again. BTW, I could see this SA either with or without my 3x
barlow
and just with the 14 mm eyepiece alone. Now, the patterns I'm seeing
with
and without the barlow are getting closer in shape. I'm going to really
laugh if all of this has been the result of improper cooling!

Seth

This is actually a fairly effective way to equilibrate a large SCT.

I live in the low desert of Arizona, and that's EXACTLY how I cool my 10".
I roll it outside on it's wheeley bar, level it and raise the scope off
it's wheels, and rough polar align it. Then bring the OTA parallel with
the ground, remove the dust cover from the corrector, and aim a large fan
at the rear cell, and let 'er rip for an hour or two, depending on how
much temperature differential there is between the house and the outside
temperature. Here, in the summer, it's often 30 to 40 degrees, HOTTER
outside than inside... But the thermal equilibration process is still the
same... Interesting to note that here, the overnight low, in the summer
months, is virtually always warmer than the inside temperature, even after
dropping perhaps 30 degrees, or more, overnight...

I'm going to really
laugh if all of this has been the result of improper cooling!

Seth


Hi:

Who are we talking to? "Seth" or "Jon" or neither?

The star test, especially when done by someone not that familiar with it, is
probably not the best way to evaluate an SCT. Much better is to take a look at
Jupiter, assuming you know how it should look under your current seeing
conditions. This scope should have _at least_ several hours of cool down before
being evaluated.


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

I'm going to really
laugh if all of this has been the result of improper cooling!

Seth


Hi:

Who are we talking to? "Seth" or "Jon" or neither?

The star test, especially when done by someone not that familiar with it, is
probably not the best way to evaluate an SCT. Much better is to take a look at
Jupiter, assuming you know how it should look under your current seeing
conditions. This scope should have _at least_ several hours of cool down before
being evaluated.


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

"Seth" wrote in message
ink.net...
For those following along in my other thread, today I tested the 12" SCT
for
SA. I get a pattern just like figure 2 he

http://www.robertvincent.freeserve.co.uk/testing.html

There are two issues here that I should mention: 1) I'm using a
telephone
pole insulator for the test with the scope under the patio and 2) the
scope
has only been set up for about 45 minutes. I can see plenty of heat
waves
disturbing the diffraction patterns. Solution: I'm going to wait a
couple
of hours and try again, just in case this is all due to the mirrors not
cooling down. I lack an internal cooler: can anyone suggest a way to
cool
the mirrors faster?

Thanks,
Jon
Beware though, that an SCT, _even if perfectly made_, will display SA, at
all but one mirror spacing. Even if you have your eyepiece configuration
to give exactly the length 'designed for' at the rear of the scope,
focussing on something closer than the stars, will make SA appear. Ideally
you'd need to try at different mirror spacings (by changing the length of
the units behind the scope), and find the point with least SA.

Best Wishes