Premium mirror not so good

About 2 1/2 years ago a good friend of mine spent a lot of money for
an 8 inch f/8 mirror. It cost more than most 8 inch dobs. After only 2
nights of using the new scope there was a major mishap and the mirror
took a very bad scratch. He dismantled the scope and moved on to other
projects.

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

I then decided to refigure the mirror under Dan's instruction. He has
over 1500 mirrors to his credit. After only 3 sessions the scratch is
gone and the figure is almost complete. It's already vastly superior
to what it was originally and hopefully in a few days will be done and
on it's way to Clausing. I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

After looking at the Foucault of that figure it's hard to imagine
anyone putting it out for over $100. It could be that it was a fluke
and I don't want to trash any reputations based on one data point but
people out there need to be familiarized with the star test so as to
be able to protect themselves from such circumstances. But soon the
mirror will have a KILLER figure and ready for the upcoming planetary
season.

Darren Drake wrote:
About 2 1/2 years ago a good friend of mine spent a lot of money for
an 8 inch f/8 mirror. It cost more than most 8 inch dobs. After only 2
nights of using the new scope there was a major mishap and the mirror
took a very bad scratch. He dismantled the scope and moved on to other
projects.

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

I then decided to refigure the mirror under Dan's instruction. He has
over 1500 mirrors to his credit. After only 3 sessions the scratch is
gone and the figure is almost complete. It's already vastly superior
to what it was originally and hopefully in a few days will be done and
on it's way to Clausing. I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

After looking at the Foucault of that figure it's hard to imagine
anyone putting it out for over $100. It could be that it was a fluke
and I don't want to trash any reputations based on one data point but
people out there need to be familiarized with the star test so as to
be able to protect themselves from such circumstances. But soon the
mirror will have a KILLER figure and ready for the upcoming planetary
season.


Should be a nice scope for the planetary season. Which coating are you
going to get?
I've heard the Beral coating is excellent and durable.

It IS important to be familiar with star testing (and collimation,
too!). It will save you a lot of heartache down the road.

I admire your willingness to take on the project. An 8" can be a
handful. Now you'll likely have a better mirror most people can buy.

Keep us posted and show us some images if you can.

Clear Skies,
Uncle Bob

__________________________________________________ _____________________________
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On 28 Nov 2004 21:16:48 -0800, (Darren Drake) wrote:

snip

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

snip

I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

Interesting story, but you've done the astro-community no good
whatsoever. If this really happened, have the moxie to identify the
culprit. Otherwise, this sounds like another "Look at my message"
troll.

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://users.adelphia.net/~w6wlr/

Uncle Bob wrote in message ...
Which coating are you
going to get?
I've heard the Beral coating is excellent and durable.


Ironic - I've had poor experiences with Beral.

YMMV

Tom T.

My point is not to trash a reputation but to emphasize the importance
of learning the star test.


WayneH wrote in message . ..
On 28 Nov 2004 21:16:48 -0800, (Darren Drake) wrote:

snip

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

snip

I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

Interesting story, but you've done the astro-community no good
whatsoever. If this really happened, have the moxie to identify the
culprit. Otherwise, this sounds like another "Look at my message"
troll.

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://users.adelphia.net/~w6wlr/

well these things are difficult when they happen. While I respect your
diplomacy you strike a general fear which maydo more harm than
simply naming the source of the mirror. Why should all suffer for
one "fluke". ? Let's see. Did the name start with a A B C D E F G H
I J KL M N O P Q R ST UV WXY or Z?

JR



Darren Drake wrote:

About 2 1/2 years ago a good friend of mine spent a lot of money for
an 8 inch f/8 mirror. It cost more than most 8 inch dobs. After only 2
nights of using the new scope there was a major mishap and the mirror
took a very bad scratch. He dismantled the scope and moved on to other
projects.

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

I then decided to refigure the mirror under Dan's instruction. He has
over 1500 mirrors to his credit. After only 3 sessions the scratch is
gone and the figure is almost complete. It's already vastly superior
to what it was originally and hopefully in a few days will be done and
on it's way to Clausing. I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

After looking at the Foucault of that figure it's hard to imagine
anyone putting it out for over $100. It could be that it was a fluke
and I don't want to trash any reputations based on one data point but
people out there need to be familiarized with the star test so as to
be able to protect themselves from such circumstances. But soon the
mirror will have a KILLER figure and ready for the upcoming planetary
season.

Before you send it off for a coating, try it in the scope with just the bare
glass.
You will be supprised at how much you will see that way. It is also a good
point at which to do the star test again to see how much improvement you
have done to the mirror. I've split the Double Double with a 6" mirror
before it got coated and you also should have no trouble with that test of a
mirror's quality.
Remember that bare glass reflects about 4% of the light and that is only
about 20x less light than a good coating.

--
Why isn't there an Ozone Hole at the NORTH Pole?

I'll give a clue as to the original maker: One only needs to change
one letter to correct who made it to who instructed me to make it....


Ray wrote in message ...
well these things are difficult when they happen. While I respect your
diplomacy you strike a general fear which maydo more harm than
simply naming the source of the mirror. Why should all suffer for
one "fluke". ? Let's see. Did the name start with a A B C D E F G H
I J KL M N O P Q R ST UV WXY or Z?

JR



Darren Drake wrote:

About 2 1/2 years ago a good friend of mine spent a lot of money for
an 8 inch f/8 mirror. It cost more than most 8 inch dobs. After only 2
nights of using the new scope there was a major mishap and the mirror
took a very bad scratch. He dismantled the scope and moved on to other
projects.

Recently he gave me the all the parts to that scope including the
mirror. I had my good friend Dan Joyce test it with his Foucault
tester. It had a badly turned edge and a significantly rough surface.
After assembling the scope I saw a poor star test and rough surface
with a null test at the focuser using a knife edge; confirming Dan's
test results.

I then decided to refigure the mirror under Dan's instruction. He has
over 1500 mirrors to his credit. After only 3 sessions the scratch is
gone and the figure is almost complete. It's already vastly superior
to what it was originally and hopefully in a few days will be done and
on it's way to Clausing. I won't mention who made the mirror (it
wasn't Zambuto or Swayze) but that person does have a decent
reputation and supposedly uses state of the art testing methods
including the use of an interferometer.

After looking at the Foucault of that figure it's hard to imagine
anyone putting it out for over $100. It could be that it was a fluke
and I don't want to trash any reputations based on one data point but
people out there need to be familiarized with the star test so as to
be able to protect themselves from such circumstances. But soon the
mirror will have a KILLER figure and ready for the upcoming planetary
season.

Subject: Premium mirror not so good
From: (Darren Drake)
Date: 11/30/2004 6:11 PM Eastern Standard Time
Message-id:



I'll give a clue as to the original maker: One only needs to change
one letter to correct who made it to who instructed me to make it....
*******************************
Royce???

Chas P.

"Darren Drake" wrote in message

I'll give a clue as to the original maker: One only needs to change
one letter to correct who made it to who instructed me to make it....

It takes a lifetime to develope a reputation as good as R. F. Royce has, a
mirror maker with few peers (I'd say 2). Any crank with a computer can
attempt to tear it down.

Luckily, of the people who read this thread, 80% will never buy a premium
dob, 19% will dismiss your post as one wildly incongruous data point and the
other 1% will buy a Zambuto or Spooner instead and not suffer any real
consequences.

Ed T.