RE: [APML] Borg 100ED (Jon Kolb, Thu Jan 2 22:09:38 2003)
[snip ]
> ...can you give us your opinion on the hardware quality of the Borg
> compared to the TMB? From what I can see in your images the
> optics compare nicely.
I had a long note to Shekhar on this subject written back in May, but
the server at work timed it out of my "sent" folder, so here's an
abbreviated version from memory.
The optics are not really on the same level. The TMB is really an APO
triplet and is color-free even on the brightest objects like Venus and
Vega, at least from what I can see. The Borg ED doublet is not a true
APO, and will put a blue halo on the brightest stars, but I don't find
it objectionable. The Borg is really more like a Petzval design, since
it's used either with a two-element field flattener or a two-element
"super reducer," either of which mount inside the focuser The TMB has a
field flattener, too, and it is essential to use it for phtography.
Mechanically, both scopes are well put together, but the TMB is
remarkably heavy for its aperture. This is not due only to the triplet
lens (which is indeed heavy by itself), but also to the tank-like
construction of the tube, rings, and most of all the 4" focuser. The
TMB focuser and extension must easily weigh 10 lbs by itself, but I
haven't taken it off and weighed it. The Borg on the other hand is
light but solid, with very fine threads on everything since the whole
Borg system is modular.
Both scopes are machined very well, but I must admit to prefer rotating
the camera mount only on the Borg, rather than rotating the entire
focuser, finder, flattener, and camera on the TMB. Rotating the whole
focuser puts the finder scope in an awkward position most of the time
(thus I never use it), and the rotation can be a bit stiff at 10F. Both
focusers are excellent, but the Borg helical unit, with graduation marks
cut into the circumference, makes KEF focusing a true pleasure. Both
focusers lock up tightly with no discernable movement.
Borg positives:
1) Excellent value for the money for medium format work at two
hard-to-find focal lengths.
2) Immediate, or nearly immediate availability.
3) Light weight and modular design is good for storage and travel to
dark sites.
4) Helical focuser is outstanding for astrophotography, especially with
a KEF.
5) Lots of well-conceived accessories for Borg scopes.
TMB positives:
1) Outstanding optics.
2) Excellent rotating 4" focuser, very solid.
3) Excellent fit and finish, well-machined to tight tolerances,
essentially bulletproof (but not UPS-proof, as I found out the hard
way).
4) Comes with mounting rings, themselves well-made, so you don't have to
hassle with finding something that fits.
5) One of only a few APO scopes at this focal length capable of medium
format photography, and costs somewhat less than the others (Tak BRC,
Tak FS152, for example).
Borg negatives:
1) Optics not as good as APOs. Some blue halos on brightest stars.
2) Too many things to mess up in the field (fingerprints, dust, etc.) if
you want to switch focal lengths in the dark and cold. I wound up
buying a second focuser and camera mount so that I would only have to
move the objective between the long and short tubes when I wanted to
switch.
3) Poorly designed dewshield dustcap. The threads are too fine and
plastic, and it's nearly impossible to get it back on the 6x9 dewshield
(required for use at f/4 instead of the supplied dewshield). I don't
use it any more and instead use a $0.99 shower cap from the local
drugstore.
TMB negatives:
1) Heavy. Well over 50 lbs. with FC60 guidescope, rings, STV,
flattener, camera mount, and camera. I had to get an MI250 mount to use
it for photography. Works fine on a G-11 for visual use, though.
2) More available than AP, by a long ways, but still can be up to a year
or more to get one unless you catch one right when a production run is
done. I'm not aware of a long waiting list for this model.
3) Rotating focuser can be stiff in cold weather.
4) Finder mostly unusable with camera mounted, due to rotation of
focuser required for composition, and placement of finder on focuser
instead of up the tube farther (all manufacturers seem to do this except
for the Tak "accessory ring" optional mounting).
Since the two scopes are of such different size and focal length, it's
not much of a comparison - they're both good at what they're good at.
At similar focal lengths, say Borg vs. TMB 105 f/6.2, the choice would
come down to either wanting the f/4 option and a 4" focuser bad enough,
or wanting the best optics you can get your hands on.
Hope this helps.
Sincerely,
Jon Kolb
Adventures in Astrophotography
http://home.datawest.net/jkolb/
jkolb@datawest.net
