Re: Megrez vs. ZenithStar Family
- Hi Michel,
There have already been some wonderful comments in this thread - if
you read back, they will probably go a long way towards answering
some if not all of your questions, but I'll throw in my .02 cents
here as well.
ED and SD are generally considered to be two different names for the
same family of glasses. I think it was Nikon coined the term ED -
prompting Canon to counter with SD. Both were marketing terms that
described glasses with extra, special or supra dispersion properties
as measured by their abbe number. ED is more typically used today,
but there's nothing inherently incorrect about SD.
ED/SD glasses can cover a wide range, but for today's astronomical
applications usually consist of glasses with similar properties to
those found in Ohara's catalog under the designations s-fpl51, s-
fpl52 and s-fpl53 (more often referred to as FPL51, 52 and 53). For
the record, from it's abbe number there is minimal diffference
between fluorite and fpl53. I've been given to understand that pure
fluorite does have a small advantage in that it has a slightly
higher transmission and lower scatter in certain wavelengths than
fpl-53, but the advantages are mainly photographic, and not all that
great. Equally important to the choice of the ED/SD glass is the
choice of a good mate.
Everyone talks about color correction, but the sheer fact of the
matter is there really are other things that are just if not more
important depending on the application you have in mind. I suspect
everyone picks on color correction because it's easy to see.
In any case, the design of the lens and the glasses used are
paramount in determining correction, however, many other factors
come into play as well. Typically the best doublets are not as well
corrected as the best corrected triplets - however, doublets are
lighter, cool down faster, and have a few other advantages as well
(largely to the visual observer). Triplets, OTOH, are generally
preferred for photographic applications.
As I see it, the major difference between the ZenithStar and Megrez
family have more to do with the OTA than the lenses. Outside of the
FLT-100 (which is a different beast entirely) the Megrez scopes are
white with a painted or powercoated finish, and use a foam baffle
system. They have a more traditional look to them. The Zenithstars
tend to be anodized and use a cone baffle system. The anodizing
looks extremely sharp, but has a single drawback - it picks up
fingerprints like crazy.
I've seen samples of both lines, and both do their job well. Which
you prefer is entirely up to you.
As per the 66 doublet / triplet / petzval discussion - well, as a
visual observer, I tend to prefer doublets. In general, a good
ED/SD doublet is smaller, lighter (and thus easier to mount), and
still offers acceptable color correction. I haven't seen the 66 SD
doublet yet, but I'm lucky enough to have the fluorite version (a
very limited production). Assuming the SD version performs like the
fluorite version, I'd recommend the SD doublet for the visual
observer. The triplet generally offers better color correction for
those who are really picky about that or who are photographers.
Petzvals are an excellent choice for someone who is on a slightly
more restriced budget. The petzval gives about 30-35% less false
color than a similar size achro simply due to it's design. While I
wouldn't recommend it for typical photography due to it's color
correction, it would do very well for narrow band applications.
Hope something here helps.
--- In William-Optics@yahoogroups.com, "michelderomme"
> What are we talking about ?
> SD APO, ED APO, fluorite APO, fluorite doublet ...
> CA F2, FPL53 or others ?
> are red and blue waves focused at the same point ?
> TMB use ED, TAk use fluorite, AP uses ED, Skywatcher use ED(FPL53
> indeed), WO use DE, ED, fluorite, are some better than others ?
> Membre SAPL 87
> PROTEGEONS NOTRE ENVIRONNEMENT NOCTURNE !!!
> ADHEREZ A L'ANPCN
> Commandez les nouveaux autocollants ANPCN !
> --- In William-Optics@yahoogroups.com, "Timm Bottoni"
> <t.bottoni@c...> wrote:
> > Oops - another typo
> > Should be
> > $399 ZenithStar 66 SD Doublet APO
> > And nice job of explaining the optics choices Chris! I am fine
> > the specs, but as to why one is better, I will leave that to you
> > folks who are more experienced.
> > Timm
> > --- In William-Optics@yahoogroups.com, "Timm Bottoni"
> > <t.bottoni@c...> wrote:
> > >
> > > Hi Daniel,
> > >
> > > Looks like you were replying while I was - good evening here,
> > > morning for you :)
> > >
> > > Here is a simple listing...
> > >
> > > I would suggest you decide first - do you want AP0 or not?
> > > Second - how much do you have to spend?
> > > Third - how much aperture do you want
> > > Fourth - doublet, triplet, base your decision on feedback from
> > users
> > > who have tried both (Like Tom Trusak)
> > >
> > > APO scopes
> > > Price Model
> > > $3295 Fluoristar 110
> > > $1998 ZenithStar 105 package
> > > $1698 ZenithStar 105 OTA
> > > $798(sale) ZenithStar 80 Fluorite Doublet (Anniv special
> > > $399 ZenithStar 80 SD Doublet APO
> > > $548 ZenithStar 66 ED Triplet APO 2-speed OTA
> > > $498 ZenithStar 66 ED Triplet APO OTA
> > > $1595 Megrez 80 Triplet Fluorite APO
> > > $928 Megrez 80 Triplet ED APO
> > > $848 Megrez 80 Doublet Fluorite
> > >
> > > NOT APO scopes
> > > $399(sale) ZenithStar 80 2-speed OTA plus new year gift
> > > $499.95 ZenithStar 80 Package
> > > $399.95 ZenithStar 80 Short OTA
> > > $499 ZenithStar 80 Short Package (astro or terra)
> > > $699(sale) ZenithStar 80 Short BinoViewer package
> > > $498 ZenithStar 66 Petzval 2-speed astro package
> > > $414 ZenithStar 66 Petzval 2-speed terra package
> > > $348 ZenithStar 66 Petzval 2-speed OTA
> > >
> > > I know this is a quick breakdown, but this is how my overly
> > > analytical mind can assemble it shortly so that its reasonably
> > > straight forward.
> > >
> > > Hope it helps!
> > >
> > > Timm
> > >
> > >
- Just so there's no confusion, I should make it clear that my comments
about the petzval design were in reference to the 66 currently
offered. Other petzvals (even perhaps those on tap at WO) can have
better color correction than nearly any other style of telescope.
(The NP101 is an excellent example of best of a breed apochromatic
petzval.) Like any other design however, they have their own benefits
- Hi Tom,
You mentioned it briefly as 'a whole different story' but can you
comment on the FLT 110 as the best choice for wide field
astrophotography? I was able to play around with an 102mm f/5 achro
and found the wide field of view to be very exciting. The relatively
poor color correction resulted in poor color results but the images
shot through a green filter were great. I have decided to get a better
scope largely for CCD work, and it seems that the Petval design
produces nice wide views. However, I mainly want to make sure that I
get good color correction and good resolution - small stars with
no 'bloat' are important to me. The FLT 110, the Tak FSQ and and the
TV NP101 are all candidates at present and somehow I have to get my
choice down to the best one...
--- In William-Optics@yahoogroups.com, "Tom Trusock" <tomt@c...> wrote:
> Just so there's no confusion, I should make it clear that my comments
> about the petzval design were in reference to the 66 currently
> offered. Other petzvals (even perhaps those on tap at WO) can have
> better color correction than nearly any other style of telescope.
> (The NP101 is an excellent example of best of a breed apochromatic
> petzval.) Like any other design however, they have their own benefits
> and limitations.
- --- In William-Optics@yahoogroups.com, "fccolosimo" <fcc0@h...>
> Hi Tom,
> You mentioned it briefly as 'a whole different story' but can you
> comment on the FLT 110 as the best choice for wide field
> astrophotography? I was able to play around with an 102mm f/5
> and found the wide field of view to be very exciting. Therelatively
> poor color correction resulted in poor color results but theimages
> shot through a green filter were great. I have decided to get abetter
> scope largely for CCD work, and it seems that the Petval designthat I
> produces nice wide views. However, I mainly want to make sure
> get good color correction and good resolution - small stars withthe
> no 'bloat' are important to me. The FLT 110, the Tak FSQ and and
> TV NP101 are all candidates at present and somehow I have to getmy
> choice down to the best one...Hi Frank, I really can't comment a whole lot on the astrophotography
side. About all I can say is that take a look at images of all
three with your camera of choice, and then talk to the
photographers. An astrophotographically inclined friend purchased
the FLT I had for review - about all I can tell you is that that
last I knew, he was very happy with it.