The Swift Audubon 8.5x44 model
804
Mark Vints
When I bought my Swift 10x50 SP over
15 years ago, the Swift sales brochure clearly described the Audubon 8.5x44
(model 804) as a superior product that very much appealed to me. At twice the
cost it was unfortunately out of my reach at the time. However I was lucky
enough to find one in a close-out sale now almost 10 years ago, and didn't have
to think twice about buying it.
By that time I had become aware of
the good reputation these binoculars had. In my first forays on the internet
this name kept coming up in discussions on optics for birding (which at the
time was just about the only context binoculars were discussed in on the
internet - or at least the part of it I managed to find). Even today you can go
to betterviewdesired.com or to birdforum.net and read about the 8.5x44 porro
model. Also here on the CN binoculars forum and the Cloudy Days forum, the
Swift Audubon has a loyal following, and I would count myself as one of those.
So what is so special about the
Swift 8.5x44 porro- In two words: specifications and performance. For details,
read on.
Even on paper its specifications
stand out. The 8.5x magnification is not common to say the least (though
increasing in popularity in recent years). The 8.2 degree true field of view
(TFOV) give it a 70 degree apparent field of view (AFOV) which is truly wide. A
view this wide is something that has to be experienced - it changes your
perspective of the night sky. This is 90% more area of sky than what a 6 degree
TFOV would show you. Sweeping along the Milky Way is a superb experience - it
is so too in my 20x80s, but it's a different type of viewing: overview versus
depth. And the wide AFOV gives as close a spacewalk experience as I've come
across in binoculars.
For me the 8.5 times magnification
is the sweet spot for hand-held use. Not surprisingly this is where these
binoculars see probably 95% of their use. I can and do hand-hold 10x50s, even
larger binoculars, but shaking affects the viewing experience. On the other
hand the image scale of a 7x binocular is noticeably smaller. When I bought
these Swift Audubons I felt they were giving me the view of a 10x50 with the steadiness
of a 7x50. To a large extent that's still how I feel about them today.
Other relevant specifications are as
follows:
- BAK-4 prisms and multi-coated
optics (not fully multicoated)
- IPD labelled 60-70 mm, measured
56-70.5
- eye relief 15 mm (not verified) -
people wearing glasses could find this too short
- weight 815 grams without caps and
straps
I consider these binoculars light-weight,
compact and small. This is one area where a typical birder's description of
this binocular will fundamentally differ. The handling is excellent, although
for my liking the hinge connecting the two barrels moves a bit too lightly. For
this reason I normally set them at widest IPD even though that's just a touch
above what my eyes have. I have found that with IPD set in this way, and
eyecups placed where they best seem to fit my eyes, there is some spiking and
flaring on brighter stars. For hand-held use I normally can live with that
though.
Sometimes I do put these on a tripod,
and take care to set the correct IPD and place my eyes in just the right
position against the eyecups. On those occasions it is as if they become
another set of optics altogether. With careful focussing they are TACK SHARP.
Stars focus to true pinpoints, and only the very brightest stars show some
minor spiking. These are the one pair of binoculars where I could contemplate
looking for double stars so tight that they just show as elongated.
To quantify this sharpness somewhat,
I decided to look at a few double stars. I started out with the nice double in
the heart of open cluster NGC 1502. The two mag 6.9 components are 17.8 arc
seconds apart. In 8.5 power glass this gives 151 arc seconds of apparent separation
- if resolved... I was expecting this double to be at the limit of my resolving
abilities. I thought I remembered reading that 150 arc seconds is a typical
value for good visual acuity at night. Well anyway this double is nowhere near
the limit of resolution for me: the two components are cleanly split with
plenty of black space between them.
I then went for 59 Andromedae. Its
mag 6.1 / 6.7 components are separated by 16.5 arc seconds to give 140 arc
seconds of apparent separation. The result was basically identical: a clean
split with ample space between the two components. Of course I did notice these
were a bit closer. Quite a bit closer at 96 arc seconds apparent separation,
STF401 in Taurus would best be described as Òalmost splitÓ: two small dots of
light just barely touching. I think I have to give some credit to my eyes, but
either way these are sharp optics. I've not seen equal in other binoculars yet
(but I keep looking...).
So with the Swift Audubon 8.5x44 we
have a pair of binoculars that is well built, is perfect for hand-held use, has
sufficient performance on the night sky to be interesting for astronomy, has a
picture-window 70 degree apparent field of view, and when put on a tripod is
tack sharp. And yet these binoculars also have a serious if not FATAL FLAW and
that is ... their edge sharpness.
When looking through these
binoculars it is immediately apparent that the outer edge of the field of view
has some serious problems. Even to the extent that I was thinking my particular
sample of these binoculars is a lemon - until others reported seeing the same. It
is nothing new to me that bright stars at the edge of view can look something like
seagulls. And as such this should not be so much of a problem since the edge of
a 70 degree AFOV is normally not looked at directly. But here the edge
fuzziness is such that it creates a ring of diffuse light all around the
perimeter of the FOV. This really attracts the attention and destroys the aesthetics
of the superbly crisp view in the center of the FOV. I notice this much less
with the binoculars tripod-mounted, maybe because of more precise eye placement.
This is however no solution for a binocular mostly used hand-held...
And so it is that this flaw in the
outer area of the FOV is downgrading my overall impression and enjoyment of an
otherwise quite excellent piece of optics. I really have to wonder why Swift
(or rather whoever was producing this for them) couldn't have put a field stop
in just the right place and made this a 60 degree AFOV binocular that is
excellent without any reservations.
I have also tried to quantify the
edge sharpness by observations of suitable double stars. For this purpose they are
put near the field edge and their position is noted when no longer resolved.
The nice double star 74 Pisci (also
labelled Psi 1) was my first target. Its components are mag 5.3 and 5.45, and
they are separated by 30 arc seconds. This provides a measure for determining
where in the FOV the apparent resolution drops below 255 arc seconds. I found
this limit to be at 1 degree from the edge. At this point there is some field
curvature noticeable, as refocusing pushes the limit of resolution a bit
further towards the edge.
Next I took the two brightest stars
at the core of NGC 869 - the right cluster in the Perseus Double Cluster. These
mag 6.6 and 6.7 stars are 144 arc seconds apart. Their apparent separation
therefore is 20 arc minutes, but still I cannot resolve them within less than 30
to 45 arc minutes of the field edge.
I've found a much easier alternative
testing method which gives a simple yes/no answer to the question if the view
is acceptably sharp or not at any distance to the field edge. Just look at the
Full Moon and place it as close to the edge as you can without making part of
it go Òout of focusÓ. Then compare the distance to the field edge with the
Moon's known half-degree diameter, and that's it! With my Swift Audubons the
Moon needs to be at least two diameters away from the edge, i.e. the outer 1
degree is unsharp.
Some minor points to add:
- the soft padded case these come
in are a definite step below the hard cases that came with my other Swift
binoculars;
- the single large cap covering
both eyepieces is OK but means you have to reset IPD at the start of every
session. The two objective caps are definitely too loose - I can never get
these binoculars out of their soft case without at least one cap remaining
inside;
- the eyecups are a rather stiff
rubber that you need to fold down for use with glasses. On the right eyepiece
doing so without changing the dioptre setting is next to impossible;
- when looking at the Moon there is
some glare and internal reflections - not bad, just there. The most obvious
reflection is actually between the outer eyepiece lens and the eye;
- something inside protrudes a tiny
bit into the light path and results in a very small clipping of the otherwise
round exit pupil;
- on the positive side, build
quality is excellent and I've really had not one issue with them in the 10
years that I use them.
As an overall comment on their use
for astronomy, I'd have to first come back to their outstanding center
sharpness. This binocular manages to resolve things not otherwise expected
in this size instrument. For example, during the March 2007 total lunar eclipse
I
happened to wander over to nearby Saturn. After carefully adjusting IPD and
eye position, I had the cleanest sharpest view of the ringed planet imaginable
at
this magnification: a beautiful well-defined little oval. Likewise when viewing
open clusters this instrument is capable of resolving stars from the background
glow where you'd normally expect to need more magnification. They've also given
me my best ever view of the crescent of Venus during bright twilight.
The edge sharpness problems of the
Swift 8.5x44 are not normally limiting its potential on most celestial targets.
One notable exception would be M36 + M37 + M38 together in the same FOV. The
two outer clusters M37 and M38 are really affected by the edge fuzz. My TS
7x50 MX with their smaller 7.5 degree TFOV give a superior view of this threesome
simply because of very much improved edge sharpness.
I've never been much of a nebulosity
observer (mainly due to my local viewing conditions) but under the best skies
this instrument is showing excellent views of difficult targets such as the
Veil or Rosette nebulae, or the (to me) difficult galaxies like M101. Back
home under my mag 5.5 backyard skies I can pick out M81 and M82 easily enough,
but
normally for such targets I'd choose my 20x80s.
The strength of any pair of
hand-held binoculars for astronomy is not in giving the best view of individual
targets. It is in the overview on the celestial scenery it provides and in
the way it naturally extends my vision and connects me to the sky. For this
activity which I would call stargazing rather than astronomical observation,
my
Swift Audubon 8.5x44 has given me many moments of joy and I expect it will
continue to do so for years to come.
Mark Vints, March 2007.
