Which Is Best? - TV-102 Or FS-102

"ValeryD" wrote in message
om...
[...]
My own 7" F/7.8 fluorite doublets shows no any violet false colors
on ANY object in focus. Only unfocused images shows some minor violet
around outer ring. But scopes purposed to be used in the "in focus"
mode.

Valery,

Is your 7" F/7.8 an all-spherical doublet ?

clear Skies,
Magnus

[...]


V.D.

"Magnus Nyborg" wrote in message ...
"ValeryD" wrote in message
om...
[...]
My own 7" F/7.8 fluorite doublets shows no any violet false colors
on ANY object in focus. Only unfocused images shows some minor violet
around outer ring. But scopes purposed to be used in the "in focus"
mode.

Valery,

Is your 7" F/7.8 an all-spherical doublet ?

clear Skies,
Magnus

Yes, it is all spherical doublet. Fluorite lens inside and fully
multicoated. The cell is with thermalcompensation.

I prefer this objective vs same 7" F/8 Fluorite triplet.

Of course, triplet has no color regardless in or out of focus.
But the doublet has one lens less (less scattering, less reflection,
less light loss) and significantly shorter cooldown time.

For visual scopes this design is better than triplet for F/7.5 and
slower (in 6"-8") range.


V.D.

On 20 Jul 2003 03:23:40 -0700, ValeryD wrote:


Yes, it is all spherical doublet. Fluorite lens inside and fully
multicoated. The cell is with thermalcompensation.

I prefer this objective vs same 7" F/8 Fluorite triplet.

Of course, triplet has no color regardless in or out of focus.
But the doublet has one lens less (less scattering, less reflection,
less light loss) and significantly shorter cooldown time.

For visual scopes this design is better than triplet for F/7.5 and
slower (in 6"-8") range.


V.D.


Valery,

Where can we see these on the web? Do you offer only the Fluorite doublets
in a cell, or complete optical tubes?

Lawrence Sayre

--
My philosophy, in essence, is the concept of man as
a moral being, with his own happiness as the moral
purpose of his life, with productive achievement as
his noblest activity, and reason as his only absolute.

Ayn Rand (in the appendix to 'Atlas Shrugged')

Hi,

I got the Tak. I found that the diffraction pattern in focus was not
perfect. Sent it back twice to the Texas guys. Came back twice with the same
problem. I gave up, now waiting for my turn on the AP list.

Gert

"Jim" wrote in message
...
I am considering a 4" APO.

The Takahashi - FS-102 is on sale for around $1900 while the TV-102 is
around $2200.

It would seem to me the Tak is a better buy unless I am missing something.
Opinions?

Gert,
Did you actually try to use the Tak? I've got an FS-102 and its perfect,
both in terms of visual and CCD imaging. Your micro-pickups would probably
have zero effect on what ever task you decide to put a scope to. You might
want to read Shawn Grants thread on Elitism in Astronomy!

--
Regards
Rob Pollard

My Astro CCD page is:
http://www.robpol.demon.co.uk

"Gert Gottschalk" wrote in message
...
Hi,

I got the Tak. I found that the diffraction pattern in focus was not
perfect. Sent it back twice to the Texas guys. Came back twice with the
same
problem. I gave up, now waiting for my turn on the AP list.

Gert

"Jim" wrote in message
...
I am considering a 4" APO.

The Takahashi - FS-102 is on sale for around $1900 while the TV-102 is
around $2200.

It would seem to me the Tak is a better buy unless I am missing
something.
Opinions?

On Fri, 25 Jul 2003 13:41:12 -0700, "Gert Gottschalk"
wrote:

Hi,

I got the Tak. I found that the diffraction pattern in focus was not
perfect. Sent it back twice to the Texas guys. Came back twice with the same
problem. I gave up, now waiting for my turn on the AP list.

Gert

Giving up a few years of observing waiting for an AP isn't much of a
solution, IMO. There are other alternatives out there.
-Rich

Daniel Drabek wrote:
What diffraction pattern in focus? In focus there should be an airy disk
and one faint diffraction ring. Maybe two. Any atmospheric turbulance
will certainly make it less than perfect.

I think it is certainly true that it is much harder to divine errors
in focus (where they are all mixed in inextricably) than out of focus.
Technically, all of the necessary information is there; in practice,
as you say, it's much harder to make it out.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Yes, my good trusty 13" and 16" newts which are just fine. Thought I would start
venturing into lenses a bit. I guess I'll keep refractors for some quicky looks
on moon and sun (spots + h-alpha) and do my fuzzis with reflectors.

Clear Skies,

Gert

wrote:

On Fri, 25 Jul 2003 13:41:12 -0700, "Gert Gottschalk"
wrote:

Hi,

I got the Tak. I found that the diffraction pattern in focus was not
perfect. Sent it back twice to the Texas guys. Came back twice with the same
problem. I gave up, now waiting for my turn on the AP list.

Gert

Giving up a few years of observing waiting for an AP isn't much of a
solution, IMO. There are other alternatives out there.
-Rich

--
---

Gert G. Gottschalk, Ph.D.
Tel 510)-354-6118
Email

Hi DD,

I did the usual tests. Intra and extra focal disks are OK with the color tinges as
expected in this type. In focus (at about 300x) Airy disk is round and well
defined. Two concentric diffraction rings are there. However they are not equally
bright around the circumference. One side perhaps 20% brighter than the other. Not
always discernible in usual seeing conditions. The usual precautions were applied.
Few hrs cool down, no diagonal, try with multiple eyepieces (Naglers + LVs).
Turn my head - diffraction ring asymmetry does not rotate,
Turn eyepiece - diffraction ring asymmetry does not rotate,
Turn tube - diffraction ring asymmetry does rotate. - Thus it's in the lens!
Suiters book says the issue is consistent with either tube current or
miscollimation (probably decentering?) As I haven't seen tube currents that
repeatedly rotate with the tube I guess the lens simply has a problem.
The Texas guys said it was out of collimation the two times when I shipped it
there. When ever I got it back the flaw was still/again there. They said the scope
left their place in 'perfect condition' and it would be the shipping to blame.
When pressed they said they would replace the lens but at the time I had already
ordered accessories that match f-length and also who would know what I would end
up with after an exchange.

One guy on another list probably said it right when he asked: 'what do you want to
observe, stars or diffraction patterns?'

Clear Skies,

Gert

Daniel Drabek wrote:

What diffraction pattern in focus? In focus there should be an airy disk
and one faint diffraction ring. Maybe two. Any atmospheric turbulance
will certainly make it less than perfect.
DD
Hi,

I got the Tak. I found that the diffraction pattern in focus was not
perfect. Sent it back twice to the Texas guys. Came back twice with the same
problem. I gave up, now waiting for my turn on the AP list.

Gert

--
---

Gert G. Gottschalk, Ph.D.
Tel 510)-354-6118
Email

(TMBack) wrote in message ...
Opti wrote:

Unfortunately. There is one disadvantage of the TMB
Triplet. If you drop it, the lens can get decentered. And
mine got decentered. If I can sell it. I'd be back to
square one, whether to get Tak or TV.The ultimate test
would be as someone here suggested, dropping and
letting both Tak & TV roll down the stairs and see which
one has the best figure after that. This means I can just
use a big bag to carry it with my things when mountain
tripping and not using any hard case and not worried
the lens may get decentered (But for those who won't
use it rough, the TMB has great optical quality, the
diffraction pattern on both sides is almost perfect
(roughly 1/14 wave corrected (this means you can push
it above 300X with no image breakdown compared to
1/4 wave where you can use it up to 130X only)).

I'll take that paragraph as a compliment to my apo
refractors. Telescopes are not made to be dropped,
and I don't care who's telescope you buy, sooner or
later, if you keep manhandling it, you will have more
than collimation problems. Yes, any refractor can
become de-centered, if damaged. Worse, you can
chip the very expensive glass.

Thomas Back
TMB Optical


Absolutely correct. But... all depends also how easy an objective can be
re-centered and re-adjusted if something happens.

Markus can confirm, that 125mm F/8 Borg objective was damaged during
air-line trip. It was not only decentered, but also has a chip at the
ED lens (15x10mm).
The lens then was easily painted black at the chip and I was able to
re-center lenses within 15min. It will take only 5 min if only there
will be 3 centering screws instead of unusual four! :-)


V.D.