Comparison of two budget 2" low power eyepieces

On Sat, 19 Jul 2003 13:07:13 -0400, "Stephen Paul"
wrote:


snip

Getting all of this corrected is possible, but expensive. Let me ammend
that, to exclude floaters. Floaters are the worst of all aberations, since
some form of high risk eye surgery is the only means to be rid of them.

sip

Stephen, if you have a problem with floaters at high mags, I highly
recommend you give binoviewing a try. Using both eyes helps this
*quite* a bit.

And the subjective experience can be quite profound. M17 at 185x with
twin 13mm nagler t6's is quite sublime, M13 is mesmerising, and the
moon and planets are simply outstanding.

Clear Skies

Tom T.

On Sat, 19 Jul 2003 17:38:39 GMT, Tom T.
wrote:

Again, I don't see *crap* exactly as an objective term, and I have
done a side by side with the pano 35 (not without the paracorr tho).
I've owned a 40 pentax XL, and had opportunities to compare these to
the nagler 31. I've done this at multiple focal lengths, and would
ahve to agree that slower scopes are easier on eyepeices, but this
particular eyepiece performs acceptably *for me* at this focal length.

Let me clarify that a bit...

Side by sides without paracorr:

10" f7.5 (reflector), 70mm f6.8 (refractor), 102mm f8.6 (Apo)

15" F5 I've only used it with the paracorr.

Tom T.

"Tom T." wrote in message
s.com...

Stephen, if you have a problem with floaters at high mags, I highly
recommend you give binoviewing a try. Using both eyes helps this
*quite* a bit.

Indeed, this is a strong desire of mine, and the primary reason I hang onto
my current set of Ultima eyepieces. I just can't justify spending more on
Naglers, or Pans for binoviewing. I figure the 18mm and 12.5mm Ultimas will
be perfectly fine for general binoviewing and the 7.5mm for planet
observing. Binoviewing would be primarily practiced in my Ultima 8 SCT. Do
you know if a binoviewer can be used with a F6.3 R/C?

Unfortunately, I am also in the midst of a complete moratorium on astro
purchses as we are building a new home, and there were a couple of
unexpected, and costly expenses. Unfortunately these will also push out my
observatory project for another year, which really sucks since one of the
primary motivations for building on the site was to get one up and running.

Ain't life grand?

Best regards,
Stephen

Just an added note. Last night I went up to the mountains with my 12.5 =
inch
F4.1 DOB. Wasn't super dark but it was pretty nice. Used the BW-Optik =
30mm 80
degree FOV eyepiece for a number of objects.=20

Hi Jon,

I was up in the Joshua Tree desert last night and tried the eyepiece =
under farily dark skies with my 10" F5. One thing i really noticed last =
night that i didn't from home was extreme field curvature. Sort of felt =
like i was looking through a big droplet of water. At home i'd only =
looked at a few comparatively sparse starfields and didn't notice. Last =
night i was panning through Cygnus and the Veil and the curvature was =
obvious and quite bothersome. Not so bad that i'm going to return the =
eyepiece, but it was quite annoying. (I'll probably sell it someday when =
i'm ready to invest in a proper 2" eyepiece.) Actually, i'm not sure i'm =
using the correct term. Do curvature and pincushion refer to the same =
type of image imperfection? What i saw in the Cygnus starclouds last =
night looked like a domed pincushion.

-Florian

"Shneor Sherman" wrote in message
om...

I have used a 30mm Widescan II, lately with blackened idges, for
several years in an 18" f/4.5. The effects of coma are visible toward
the edge of the field when looking at stars in the field. But it's not
the distortion that's the worst effect of coma (which is minimized by
accurate collimation). It's the loss of light, up to 2 magnitudes
toward the edge of the field. This is also quite apparent with a 31mm
Nagler in an f/4.5.

How can the effects of coma be mitigated? By use of a coma corrector,
such as a Paracorr (in my case, a Vosual Paracorr). I've used one for
several years with my Widescan II 30mm, and the views rival those
obtained with a 31mm Nagler with the same Visual Paracorr.

Well, all I know is that the 35mm Panoptic was _much_ better behaved in my
10" F5. My first comparison was between a 30mm 1rpd, a 30mm WSII, and a
35mm Pan without the Paracorr advantage. The Panoptic had a much larger
field of sharp focus, that the WS and clone simply couldn't touch. Same
scope, same session, drop in one, drop in the other, compare, repeat.

Later I ordered and tried the WideScan III, giving it every advantage by
purchasing a Paracorr, and also collimating the scope well. I just couldn't
get it to perform as well as the Panoptic had without Paracorr, so back it
went and few days later I had the Panoptic and Paracorr in my eyepiece case.

The 35Pan with the Paracorr is absolutely beautiful all the way across the
field, and only the extreme edge shows any aberation at all, and that is
astigmatism right at the field stop. Star images flare one way and then 90
degrees the other way as you try to focus the stars at the edge. The
remainder of the field is completely clear of flaring of any kind, if you
come to focus while looking directly at a point half way across the radius.
This was simply not possible in the WideScans. Focusing at the half point
would leave stars looking like crap at the edge and out of focus at the
center.

I explained this as curvature, whose effects are subjective. But even so,
the WideScan's astigmatism out toward the edge prevented focus from being
achieved near the edge, even with will and intent to allow the center to be
defocused because of the curvature.

Honestly, I just can't handle curvature, and the astigmatism, whether
brought on by coma in the primary mirror or no, is simply there at the edge
without remedy. While it is true that everyone needs to try an eyepiece
before they can know how it works for them, my red flag goes up when people
make things sound rosey, when the design issues are well understood to be
problematic for certain human conditions.

For me, the very idea that the 30mm WideScan is good enough to replace a
35mm Pan, is preposterous. Others will no doubt have an experience like
mine. I'm just not that extraordinary a case.

For them, the expectation should be that this eyepiece will have edges that
look like crap in a fast scope. Because they will, because they do. And if
your accomodation is bad enough that you can't handle high levels of field
curvature across an 80+ degree apparent field of view, you are going to get
the double whammy of inability to focus more than a fraction of that field,
combined with the impossibility of a sharp edge.

When all is said and done, if you are anything like me, you are going to
understand why I said the eyepiece was crap in a fast scope. But again, on
the other hand, the eyepiece is simply wonderful at F11.

If someone tells me that an eyepiece is crap, then I expect it to be crap.
If they tell me it works good enough to forego an expensive piece, then I
expect it to perform at least somewhat in the range of the expensive piece.

At F10, the $95 30mm WideScan performs like a $365 eyepiece, but do not
expect as much at F5. If at F5 it works well for you, then more power to
you. I prefer having low expecations, followed by pleasant surprises.
Anything else has to be a result of hype, which we may be subject to in our
desire to save a buck.

I gave an honest evaluation, albeit with a poor choice of words to some
minds. I still stand by my assesment that it is crap at F5. I actually
prefer the 2 degree views in my ST80 with a 18mm Ultrascopic/Ultima. At
least the entire field is somewhat sharp. In fact, my 20mm MA has better
edge of field stars in the ST80 than the widescan has in the 10" F5!!

I'm going to shut up now.
-Stephen Paul

Curvature results in a focus difference across the field.

Then curvature is what i saw. Bad curvature at that. I'm still keeping
the eyepiece for now. ;-)

-Florian

"Florian" wrote in message
...
I'm still keeping the eyepiece for now. ;-)

Whatever floats your boat. g

Stephen Paul wrote:
Whatever floats your boat. g

Ahem. Boats do not float; they sail, or are rowed, or are driven, or
something along those lines. *Buoys* float.

Oh, wrong thread. So sorry.

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

In article , Brian Tung wrote:

Stephen Paul wrote:
Whatever floats your boat. g

Ahem. Boats do not float;

Not all boats are like the Titanic.... :-)

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On 25 Jul 2003 09:09:25 -0700, (Bogdan Tudose)
wrote:

By the way, is anybody successfully using ( focus-wise) a 2" barlow with
the Orion 100f6 refractor?

I can barely use a 1.25" barlow with a 2" diag with that scope by
completely removing the small ring that is provided on the focusing
tube and screwing the provided 2" adapter all the way in to get enough
'in travel'.

I don't know anything you could do with a 2" barlow short of
replacing/modifying the focusing tube. Perhaps you can find another,
shorter 2" adaptor to screw into the tube?

---
Michael McCulloch