Do you believe in such a statement?

"Dan McShane" wrote in message
...
"ValeryD" wrote in message
om...
About BO's new 127mm F/8 achromatic refractor quality:

"I called BO on Monday 12:00 noon EST. Tammy answered and took a
message for Bill about my situation. Bill called me back 2 minutes
later and gave me a brief education on how the BO 1278 is made. I
enjoyed my call tremendously! Bill told me about my objective as he
had inspected and tested it himself. He told me that these objectives
are polished to 1/20th wave after the 3rd polish. That's how fine the
grit is that is used. Also that a good number of these objectives are
testing null, as well as approaching null! That explains the Star
test results with my Ronchi EP. Anyway in Bill's usual engaging
conversation he told me he had one other call that day about what
were thought to be scratches on the objectives. I can't say what the
out come of that call was. But mine I can and will."

1/20 wave? Yes? Did I understood you correctly?

Anybody else believe in such a statement?

V.D.

Greetings Valery,

I wonder if those values are determined with an interferometer or other
test
method(s)?

In general, I think the properly conducted interferometer test results
would
show lower values, but a bit more realistic values.

Dan McShane
Also, (critical one), whether these are peak, or RMS values. I have a scope
here, where the entire optical system, tested on a Zygo interferometer to
0.026 RMS (nudging towards 1/40th wave). However the peak error was nearer
1/7th wave.

Best Wishes

"Roger Hamlett" wrote in message
...

"Dan McShane" wrote in message
...
"ValeryD" wrote in message
om...
About BO's new 127mm F/8 achromatic refractor quality:

"I called BO on Monday 12:00 noon EST. Tammy answered and took a
message for Bill about my situation. Bill called me back 2 minutes
later and gave me a brief education on how the BO 1278 is made. I
enjoyed my call tremendously! Bill told me about my objective as he
had inspected and tested it himself. He told me that these objectives
are polished to 1/20th wave after the 3rd polish. That's how fine the
grit is that is used. Also that a good number of these objectives are
testing null, as well as approaching null! That explains the Star
test results with my Ronchi EP. Anyway in Bill's usual engaging
conversation he told me he had one other call that day about what
were thought to be scratches on the objectives. I can't say what the
out come of that call was. But mine I can and will."

1/20 wave? Yes? Did I understood you correctly?

Anybody else believe in such a statement?

V.D.

Greetings Valery,

I wonder if those values are determined with an interferometer or other
test
method(s)?

In general, I think the properly conducted interferometer test results
would
show lower values, but a bit more realistic values.

Dan McShane

Also, (critical one), whether these are peak, or RMS values. I have a
scope
here, where the entire optical system, tested on a Zygo interferometer to
0.026 RMS (nudging towards 1/40th wave). However the peak error was nearer
1/7th wave.

Best Wishes

Roger,

Agreed, PTV by itself is somewhat useless. We`ve had off-axis parabola`s
measure near 1/10 PTV, 1/50 RMS and but very small local errors (maybe
something like 1/8 wave) have had a more profound effect on the image than
optics with noticably less overall values but a smoother surface.

If Dr Ruth was into optics she might say; "It takes smoothness, smoothness,
smoothness"

:-)
Dan McShane


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