Re: MEMO to Meade: How to write an honest news release

From: CLT (not_at_thisaddress)
Date: 02/02/05 

Date: Wed, 2 Feb 2005 00:46:55 -0800

> I agree words have meaning and what Meade did was probably an act of
> marketing. I also agree that the RCX is not a true Ritchey Chretien.
> But if it is a Ritchey with a Schmidt corrector then it could be called
> a Schmidt Ritchey Chretien the same way a Richey with a Baker corrector
> is a Baker Richey Chretien. Can Takahashi call their BRC250 a Richey?

It isn't a Ritchey with a Schmidt corrector. It is an SCT. The SCT
definition includes using a spherical primary and hyperboloid secondary.
Look at how they claim they are mounting that primary, without any provision
for collimation. And, if it were a hyperboloid primary, it wouldn't need the
Schmidt corrector. And, there wouldn't be this nonsense about the corrector
and primary working together to act like a hyperboloid.

> If, on the other hand, Meade did not use two hyperbolic mirrors then I
> totally agree with you: calling the RCX a ritchey is fraudulent and the
> name should be changed.

Then we have no disagreement on this.

> You, on the other hand, decided to attack my products in a way that has
> nothing to do with the issue and I do not appreciate it. I especially
> do not appreciate your spreading false information about my products
> you were entirely out of line and now I need to correct the remarks you
> made.

You know Ian, you really should have left well enough alone. I had no desire
to attack your scopes. And to be honest, at first glance I didn't even
realize how bad the numbers are on your scopes. And even after I realized, I
wasn't going to point them out. But since you want to push it, and accuse me
of spreading "false information," I'll point it out after your brief
interlude on what is a Mak Cass. I don't like that accusation, so I'll lay
it out clearly. Anyone that wants to can follow the math and see which
information is false.

> For "P" to be identical to "Q" they must share all properties.
> If they do not share all properties then they are not the same thing.
> So which is it, do words only mean one thing or don't they. You said
> a mak cass can have a spherical mirror or it can have an aspherical
> mirror. You gave two things the same name. If the conical constant of
> the primary mirror is irrelevant then there is no reason why Takahashi
> cannot call their mewlons Ritcheys. You just blurred the term mak cass.

No, the definition of Mak Cass includes that range of surfaces. Mak Cass has
never been restricted to spherical surfaces. A basic intro to telescope
optics will reveal that. If you do not know this, you might profit from
reading any of a number of good books on the subject. May I recommend
Telescope Optics by Rutten & van Venrooij?

But on to your scopes:

<my inital comment> "I suppose as long as people realize the limited size of
the fully
> illuminated FOV, it is fine."

<your response> The fully illuminated field is considerably larger in my
telescope than
> a newtonian of equal obstruction. I designed the field to be equal to a
> typical Newtonian.
>
> I wont dignify the rest of the paragraph with a response. Read the site
> again.

I did read your site again. And this time I did the math and found it is far
worse than I thought. Then I ran it on ATMOS. For the 6" scope you state a
CO of 12 mm. Let's we add the back focus necessary for a diagonal (Because
unless you are mounting it on a huge pier and only allowing midgets to view
through it, you will need a diagonal. The eyepiece is placed the same as for
a refractor. Anybody who has used a refractor without a diagonal has a tall
pier or a good chiropractor). With this extra light path, the cone of light,
converging at an f/8 ratio means by the time you get to your eyepiece you
have a fully illuminated FOV that is going to be far smaller than the 12mm.
In fact, it gets so small it ceases to exist. The math for a rough
approximation is easy if we remember what the focal ratio means. Roughly
speaking, for every eight mm of travel, the cone is going to converge one
mm. For a star at the center of the FOV, the light cone starts out with a
diameter of 150mm. For every 8mm of travel, it gets 1mm smaller. So it takes
8 times the 150 to reach a point of zero size (ignoring diffraction and the
airy disk size). We'll get more precise in a bit and allow for something
that isn't in the exact center, but for now, that is a rough approximation.

Your site describes the focuser as 2" with 1.25" height racked in and a
1.25" adapter. I just measured a Televue 2" diagonal (you need a diagonal
unless you are going to observe lying down) and found 140 mm of optical path
length. I'm assuming your scope will reach focus with this diagonal. In that
case, if we transfer the adapter to the end of the diagonal and go with an
eyepiece that needs to be farther out as opposed to the greater travel in
required for some of the the Pans and Nags (that is, a simpler design which
is what you will probably be using for the high power planetary views you
designed this scope for), then we have a total back focal length of 195mm.
That is the path length for the focuser, diagonal and 1.25" adapter. Of
course, this is from the back of the plywood backplate which is another 20mm
plus the distance to the back of the cell, plus the thickness of the cell,
plus the thickness of the mirror to the front, where the hole is that can be
no larger than 12 mm. Of course, it is at a slight angle, which makes the CO
actually a little bigger than the physical size of the hole, but we'll give
you that one.

Let's see, if we figure a thin mirror, we still have 20mm plus another 25
for a thin cell and from your pictures, easily another 25 mm for adjustment
space between the back of the cell and the front of the plywood. So we have
the 195mm from above + 20mm for the plywood + 20mm for the mirror + 25mm for
the cell + 25mm for spacing since the mirror is at an angle and needs to
have room for collimation (your photos look like there may be more there,
but I'm going with the minimum figures it probably needs to work so as to
give you every advantage I can) 195+20+20+25+25=285mm

If divide that by 8 and we have 285/8=35.625. Oh my, something didn't work.
We didn't have 35.624 to work with. We only had 12mm according to what you
quoted for CO. And the CO certainly can't be smaller than the hole in the
middle of the mirror. To have a fully illuminated field one millimeter in
diameter would require the hole to be a little over 35mm in diameter.

I guess it doesn't reach focus with a 2" diagonal, even though it has a 2"
focuser. Well, if we have a 1.25" diagonal, we can run the figures and
reduce the light path through the diagonal. Of course, it still doesn't work
out to give you a fully illuminated FOV of any size. My son has my scope
right now with the 1.25" diagonal, but it is still more than 100mm in path
length. If we allow your flat to be perfectly parallel to the plywood the
diagonal is on (it wouldn't work since they need to be at an angle to each
other --- but I'll give you those extra 25mm completely), you still end up
with 220mm of optical path before you reach focus. Now, even if we give you
that every eyepiece will reach focus with the focuser racked in the entire
way (I don't know anyplace this happens, but it would be nice so I'll give
you that inch of travel completely and well let it slide that eyepieces need
to reach focus), you still have 195mm of path. And that gives you a fully
illuminated circle of zero size. You need a hole in your mirror at that
point of a little over 25mm in size, roughly twice the 12mm you claim.

You could of course keep the scope level so you don't need a diagonal. But
then you'd need a *much* larger flat. And, the hole would have to be quite a
bit larger so it didn't vignette the view as the flat tilted.

(At this point I dug out ATMOS, a ray tracing program. Newt is free and can
reach the same conclusions --- just treat it as a standard newtonian --- use
the hole size as the size of the diagonal and the optical path distance as
the distance from the diagonal to the focal plane)

Even if you just stick the diagonal into the hole in the mirror (you
can't -- the hole is supposed to only be 12mm or smaller) and had only a
100mm path way to the focal plane (the length of the path in the
diagonal --- without any room for mirror cell, tilting the flat or even a
focuser), you would still have a non-vignetted field diameter of only one
millimeter, ane even then, only if you increase the hole another millimeter
and a smidge. ;-)

BTW, you can't get around it by claiming the CO is in comparison to the flat
because the flat is, well, it is flat. The light at that point is parallel.
It doesn't converge until it hits that 150 mm mirror at the other end.

This is the 150mm version. As I originally said, you will start to make up
some of the ground as you get to the 16" version. I won't run the numbers
here unless you want me to.

> "I did have some questions though. You wrote, "You can understand my
> reluctance to simply quote a specific number. The optics in my
> telescopes
> are hand made by Barry Arnold to be atmosphere limited. This means the
> optics will not be the weak link of your equipment.""
> When you quote me quote all of what I say. I wont give a number because
> there are an infinite number of ways to rate a telescope.
>
> " "Atmosphere limited" I like that. But what exactly does
> "atmosphere limited"
> mean? If nomenclature is trivial, what is the surface accuracy in
> nontrivial
> terms? Saying, "the optics will not be the weak link" really doesn't
> say
> anything."

<your reply>> Interesting, I thought that did mean something. I already told
you why
> I refuse to give a number. "atmosphere limited" means the optical
> system is limited only by the quality of atmospheric seeing. "the
> optics will not be the weak link" means the quality of my optics will
> not be the limiting factor in what you can see.

No, you linked to some people who talk about how to use numbers honestly.
Then you state you don't want to use numbers. Of course, most of your
readers won't check those links. "atmosphere limited"? I could make a
telescope out of a shaving mirror and make those same claims. And, before
you get too upset, advertisers that makes up phrases like "atmosphere
limited" are usually selling spheroid mirrors as paraboloids or something
similar. You don't really think the average reader here is dumb enough to
fall for that do you? Even "diffraction limited" has more meaning than
"atmosphere limited"

BTW, last April Fool's Day I did a satire on optics ads. You can read it at
http://tinyurl.com/6jqr7 The part that gets me is that when I wanted to
satirize it to the point everybody would see how ridiculous it gets, I said
it would be "seeing-limited." I wrote it that way because it was the most
ridiculous way I could think of for an optics ad/news release. I almost put
atmosphere-limited and then thought it sounded too corny and stuck with
seeing-limited. There are other jabs in there, like that ED means that the
color is extra (more) dispersed and more (if you look, you can find a lot of
things deliberately backwards) But now you come out with an web announcement
that has an almost identical phrase to my worst parody of an ad. ;-)

> "What is "qualitatively perfect"?"
> When the telescope is in focus you will not notice an improvement from
> higher optical quality. For those who have not read my site yet I
> should mention I said this about ALL hand made telescopes.
> Qualitatively means "in someone's opinion." In this context it
> means "in your opinion". In other words the statement I made on my
> website could also be phrased as "when you look through any hand made
> telescope you will not be able to discern the in focus image from that
> of a perfect telescope."

That is hilarious! In "someone's" opinion, "any" handmade scope has perfect
images? I really hope that isn't what you meant to say. Please correct me
and tell me your words have some objective meaning about the wavefront error
we will see if we look through your scope.

I noticed you stayed away from comparing intra and extra focal images. Any
reason? <g>

> "With that tiny illuminated FOV, it is not going to keep up with
> other scopes
> at "low power [wide field] deep sky viewing." That is fine if people
> understand that."
> I suppose you think that about all Newtonians and cassegrains. My
> telescopes have the same field drop off.

See above math.

I didn't really set out to attack your scopes in my first post. The
observation about a small FOV was a small aside that I wasn't really going
to develop. I hadn't even done any math, or even any real thinking about it
other than just noticing it didn't add up. My main point was simply that
without the words retaining their meaning, your own ads have no meaning.
Your comments about "aspherical" Mak Cass designs shows you don't understand
what words like Mak Cass mean. But that is fine. I wouldn't have embarrassed
you over that. I would have simply pointed out that "Mak Cass" includes both
spherical and aspherical designs.

But since you wanted to push the issue and accuse me of "false information,"
I have pointed out that your figures don't add up. You can't have a 12mm CO
on that 150mm scope and reach focus with a nonvignetted field of any size.

Now, may I make a suggestion? Instead of flaming me, get out a roll of
butcher paper and draw out the scope in full scale. When you lay it out,
don't worry about drawing the diagonal and the 90 degree bend in the path,
just add the extra light path distance in straight. Either your CO is bigger
than you think, or you are really vignetting that objective. Then correct
your design or webpage and let us know. Besides, I just did you a favor.
There are people here who will think this conversation is interesting enough
to go to your site, and read what you wrote so they can see it for
themselves. Now if you trace it out and make the corrections, someone here
may see you fixed it and buy one from you.

Clear Skies

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/

Are you interested in understanding optics?
Try http://groups.yahoo.com/group/ATM_Optics_Software/

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