Nikon 7x50
IF WP SP (Prostar) Review
Nikon’s Prostar 7x50s are one of the few hand-held binoculars made
specifically for astronomy. They’re beautifully constructed, heavy and
expensive; but how do they perform compared to a modern 7x birding binocular?
In this review I aim to find out.
When I was 12 my astronomy books were mostly by
Patrick Moore and they all said I should start off with binoculars – 7x50
binoculars, to be precise. I believed them and spent weeks poring over the Tasco catalogue
before finally choosing the “International Bright View” model.
My new Tascos seemed
quite good. Made in Japan, with coated objectives, high-ish eye
relief oculars and a magnesium body, I had high hopes for them.
Alas, I couldn’t get into binocular astronomy at
all: I couldn’t find anything; the binoculars were heavy and jiggly; stars
seemed dim in my light polluted suburban skies. So I
put the Tascos away and forgot about them.
Because of that poor start with 7x50s, I didn’t try
a pair again, thinking it an outmoded choice for astronomy. Then I happened
across a pair of cheap 1990s Nikon 7x50s and was amazed at how nice they were
under the fairly dark country skies where I live now. So
I decided try some better 7x50s.
According to reputation, 7x50s don’t come any
better than Nikon’s ‘Prostars’, one of the few
small binos designed for astronomy.
Although an old design, many on the forums described the Prostars in glowing terms. I bought a pair to see if
they live up to the legend.
At
A Glance
|
Magnification |
7x |
|
Objective Size |
50mm |
|
Eye Relief |
16.2mm claimed |
|
Actual Field of View |
7.3 degrees |
|
Apparent field of view |
48.1 degrees |
|
Close focus |
~12m |
|
Transmissivity |
Est. 90%+ |
|
Length |
217mm |
|
Weight |
1.5 kg |
Data from Nikon
Europe.
What’s
in the Box?
The first thing I said when I opened the big, thick,
gold Nikon box was, “wow!”
Design
and Build
The Prostars are
an impressive binocular on many levels. They exude quality and they are simply
huge for a 7x50. They look very tough and rather military.
They are part of a range of traditional rugged and
waterproof porro-prism binoculars which share a design common decades ago, with
massive prism housings and a big, leather-covered body. Nikon still (as of
early 2021) make five models in this style, comprising two 7x50s, two 10x70s
and a single 18x70 variant. All are still 100% manufactured in Japan
(accessories included, I believe).
However, it’s important to note that these similar
binoculars actually have significant differences. For example, the 18x70s are
the only ones fitted with wide field oculars. Meanwhile, only two models –
these Prostars and one of the 10x70 variants – feature
‘SP’ glass and so are specifically designed for astronomy.
But it’s the 7x50 ‘Tropical’ model that could prove
deceptive when shopping for a pair of Prostars. The
Tropical looks almost identical, apart from the Prostars’ red-ring objectives.
It’s about 40% cheaper, but might not be a bargain. Why not? Well, for a start
the Tropical lacks that ‘SP’ glass, but it omits the field flatteners too. The
Tropical does have anti-fog coatings, but one variant also has an in-field
scale.
Perhaps the most important difference is that the
Tropical model has only single coatings, according to the highly respected
Albinos website and various forum posts. This would be a real negative for
astronomy, reducing the transmittance by perhaps 10-20%. The lack of flatteners
would reduce performance for astronomy too, as would that scale. If you’re
shopping for the Prostars, check carefully before you
buy.
These 18x70s have a similar design to the Prostars.
Body
The Prostars’ prism
housings and barrels (cast as one piece) are oversized, probably to help with
stray light. The barrels are 70mm in diameter at the objective and are marked
with the hallmark red ring (without it they are the similar ‘Tropical’ model –
see above) that the 10x70 SPs (and confusingly the 18x70s) have too. That
oversized body is heavy, at about 1.5 kg
The Prostars’ aluminium
is covered in heavily textured leatherette for grip and the heavy-cast backs of
the prism housings are held on by five screws per side. They are claimed
waterproof to 5 metres for 5 minutes and are nitrogen filled. Next to the left eyepiece
is marked simply “Nikon 7x50 7.3°”, cast into the metal, not painted on. On the
front of the hinge is a classy red-rimmed badge that reads “Nikon Japan TP”.
A note about waterproofing: it may not be
absolutely necessary for astronomy, but is more useful than you might think
(quite apart from when you forgetfully leave them on the lawn). It is often
very cold on starry nights and moving between freezing conditions and a warm,
damp house can lead to fogging inside the binoculars – but not if they are
fully sealed like the Prostars.
The Prostars are beautifully made, the
old-fashioned way that few things are these days. Nothing like a modern “Alpha”
binocular, these look like the kind of the thing the Navy might give to a
submarine Commander.
Prostar
build quality is the very highest.
Prostars
are much bigger and heavier than these 7x50 Nikon Marines.
Focuser
These
use the individual ocular focusing often found on military binoculars. It works
by just twisting each eyepiece to focus for that eye; there’s no separate
dioptre adjustment. This takes some getting used to and isn’t ideal during the
day. But, given the huge depth of field, it’s not the problem you might
imagine. During the night, you stick to a single focus so it’s not an issue.
Prostars’
eyepieces focus individually.
Optics - Prisms
These
are a conventional Porro-prism design. Porro prisms may smack of your
Grandfather’s binoculars, but they are still about the best type for critical
viewing: they introduce fewer distortions than most roof prisms and don’t
require mirrors, so have higher-transmission levels than Schmidt-Pechan roofs.
Optics – Objectives
Nikon claim “Superior optical design for
aberration-free observation, built especially for astronomical use” and I have
also seen claims that they use a special grinding procedure to finish the
lenses. The lenses are simple cemented achromatic doublets, though - not the
kind of fancy multi-element, air-spaced tele-objectives you get on modern
premium models.
The “SP” in the Nikon model designation means
“Special Purpose glass”, but this doesn’t seem to be ED glass – it probably
just means they used a particularly fine quality glass of high homogeneity and with
low levels of bubbles and inclusions, all things that matter more when viewing
point sources like stars.
The objectives are recessed by almost 2 cm and are
held in by 3 threaded slip rings that are beautifully machined and painted flat
black: they almost look like a ’scope lens cell.
The lenses may be an old-fashioned design, but
coatings are bang up-to-date – they are very dark and non-reflective, some of
the best I’ve seen.
Internal build looks very solid, with heavy
strapping for the prisms and careful shielding from stray light. There are no
baffles, but everything is painted camera-lens matte black.
Prostar’s
objectives are deeply recessed to protect from stray light.
Prostar
coatings are notably superior to these (Japanese made) Nikon Marine 7x50s.
Optics - Eyepieces
The
eyepieces give a narrow apparent field of less than 50° (7.3° true), but decent
eye relief. They are a complex multi-element design that incorporate a field
flattener.
Eye relief is claimed as 16mm, which seems spot
on if measured from the flat part of the rubber eyecup (14mm from the lip of
the rim). The eye lenses, very steep meniscuses, are deeply recessed and very
well coated.
The
eyepieces do suffer a bit from kidney-bean blackouts as you move your eye
around, like many older Nikon eyepiece designs.
Accessories
The
case is a minor phenomenon: made in Japan, huge and solid, it has little feet
so you can stand it upright; it reminds me of the leather case for my
1960s Questar. This is the finest case I have ever seen for a pair
of binos.
The
Prostars come with a choice of eye-cups: either
conventional fold-down ones that you’ll use, or weird wing-shaped ones that
you’ll leave in the box.
Is
this the finest binocular case ever made?
In
Use – Daytime
Ergonomics and Handling
Heavy the Prostars may
be, but they feel very nicely balanced in the hand, so that weight isn’t a
problem, for me at least. This surprised me, as I generally dislike heavy
binoculars. If you are considering these, don’t be put off by the weight: try a
pair if you can.
Focusing with the individual oculars is quite easy
because the Prostars snap to focus and the
mechanism is smooth and precise, with just enough stiffness to prevent
accidental changes. Once focused, they have very good depth of field too, so
you don’t have to re-focus much, even in the daytime.
The 16mm eye relief should be enough to see the
whole field with glasses on, but the tall rim around the eyecups when folded
mean that the effective eye relief is 14mm and that’s not quite enough. Shame,
because that spoils the Prostars just a little
for specs wearers.
The View
The field may be narrow, but it is tack sharp,
bright and full of vivid detail and contrast. Subjectively, resolution seems
exceptional. The Prostars contain a field
flattener and so that sharpness continues right to the edge. Nonetheless, the
field seems somehow a bit small given
the size of the binoculars.
The 3D effect you get with porros is
very pronounced in the Prostars. You quickly
forget the narrow FOV, because it’s just a very pleasant, easy and refined
view.
All-in-all the Prostars give
a very nice daytime view: very sharp and flat, with excellent brightness and
very good resolution. But... for ordinary terrestrial use I would generally
prefer something like the Zeiss 7x42 FL, because it is so much
smaller and lighter and has a wider field.
Flat field?
As
we’ve said, these binoculars, designed decades back, have the field flatteners
that have recently become a must have feature in “Alpha” binos
such as Swarovski’s Swarovision ELs, Zeiss SFs and
Leica Noctivids.
So
the field is both flat and commendably lacking in other off-axis aberrations such
as coma and astigmatism. As Nikon clearly knew ages ago, this matters much more
for astronomy than it does during the day, because coma and astigmatism are
immediately obvious as distorted stars.
Chromatic Aberration
Chromatic aberration is present, but only off-axis:
it disappears if you move your eye to look at the point directly. Chromatic aberration
does increase towards the field stop, though. In that respect, these are
typical of the best pre-HD binoculars.
In
Use – Dusk
Low light performance (twilight) is good for me
with the Prostars, but only a little better than
my binocs with 4mm exit pupils (12x50 SEs, 10x42 SEs and
8x32 Zeiss FLs). Why is this, given that a 7x50 should be much
brighter?
The answer is that I am middle aged: older pupils
don’t open as far and mine measure about 5-6mm in low light. So
I am not a good judge of the Prostars in
this respect; my 12 year old daughter says they are much brighter than binos with a 4mm exit pupil.
In
Use – The Night Sky
The Prostars, let’s
remind ourselves, are that rare thing – a hand-held binocular specifically
designed for astronomy.
The first time I used the Prostars at
night, there was a gibbous Moon low in the south and so few stars were visible
to the naked eye. So I was surprised when I turned
the Prostars on Orion’s belt and saw a mass
of stars spread like jewel dust. The Prostars are
designed for star fields and nebulae and their contrast at night is outstanding,
probably because their excellent optical figure means they throw all the
available starlight into very tiny, brilliant points. So that flat field and
careful optical fabrication yields tiny, pin-point stars with superb
brightness, almost all the way to the edge.
Aim the Prostars near
the Moon and they have impressive performance in terms of stray light, with
just a little veiling flare. Only the very finest modern roofs,
like Leica’s HDs, perform better. There is no ghosting with the full
Moon in-field and the high optical quality of the Prostars mean
stray-light levels in general are amongst the lowest I have encountered. Again,
this is a feature designed for the astronomer.
One minus point
is that the Prostars are
painful to use in cold weather. That big lump of aluminium, thinly covered by
leatherette, just sucks heat away, even from gloved hands.
The Moon
The Moon appears sharp with little CA and nice
detailing, like a cold hard ball. The view of Luna is very different at 7x
(it’s amazing how much more detail you can see on the Moon going from 7x to
10x, let alone 12x), but enjoyable in a different way - somewhere between a
naked eye and a telescopic aesthetic.
Jupiter
Point the Prostars at
Jupiter and the Galilean moons are visible, but again a higher power would be
preferable. A very minor amount of flare is present on the Jovian disk, but
this could well be residual astigmatism in my eyes exacerbated by the low power
(every 7x bino I have tried shows a little flare on
Jupiter).
Deep Sky
On a dark night it becomes clear that the Prostars are designed for sweeping star-fields.
Stellar images are tight and colour transmission is very good: intense orange
on Betelgeuse, vivid blue white on Rigel. Clusters can be enjoyed right out to the field stop.
The Prostars go very deep and the Milky Way is an
extraordinary feast of stars in these. The great contrast really makes clusters
stand out and the view is so relaxed and steady you can just stop and stare,
using inverted vision to fill out the starry detail. I really enjoyed the mass
of clusters in Auriga through the Prostars.
The Prostars aren’t so
good for smaller DSOs – planetary nebulae, globular clusters – due to their
small image scale.
The Prostars excel on star field and open clusters, but unless
you have young eyes capable of using the full 7mm exit pupil, a pair of “Alpha”
7x42s will perform nearly as well, will be much lighter to hold and may not
cost much more.
Nikon
Prostar 7x50 vs Zeiss Victory 7x42 FL
The
Zeiss 7x42 FLs are an increasingly rare breed – a modern 7x binocular. It’s
interesting to summarise their differences from the Prostars
here.
·
The Victory FLs
have a much wider field of view – an extra ten degrees apparent, more than one
degree true
·
The Prostars have a much flatter field, even though it’s so
much narrower
·
The Victorys have high-fluoride glass in the lenses and so false
colour is better controlled
·
The Victory FLs
have more eye relief and so are more comfortable for specs wearers
·
The Victory FLs
seem to go almost as deep on the night sky, due to my older eyes
·
The Victory FLs
weigh almost exactly half as much
·
Daytime brightness
is similar, because the Victorys use special prisms
that transmit as much light as the Prostars’ porros
·
The Prostars are much less comfortable on cold nights because
the Victorys are made of low-conductivity plastic
·
The Prostars look and feel better made, as if they’d last
several lifetimes
·
The Prostars display more perfectly pinpoint stars
Summary
The Nikon Prostars are
an unusual binocular in today’s market. They are a classic 7x50 porro-prism
design, but made with the finest materials and workmanship. What’s more, their
very simplicity means there is little to go wrong and I’m sure that if they are
looked after, these will still be giving someone not yet born nice views a
century hence.
Apparently, many years ago, a reviewer in a famous
magazine called these “the connoisseurs’ astronomy binocular”; I’d have to
agree. However, the fact that they are a
near-perfect 7x50 doesn’t mean that they are the perfect binoculars for you.
A good 10x50 would be a better general purpose astronomy binocular, if your
interests include smaller DSOs (like planetary nebulae and globular clusters)
and casual looks at the Moon. This is especially true if you live under
light-polluted skies.
If you do want to enjoy low magnification viewing,
with a wide field and steady view, a modern 7x42 will perform identically,
unless you are under 40, and will be much less tiring to heft.
Having said all that, if you are young
enough to use the full 7mm exit pupil and you have access to really dark skies,
these are a superb tool for sweeping star fields and will go very deep in terms
of limiting magnitude. They will last forever and you can leave them to
your kids.
The
Nikon 7x50 Prostars are recommended for lovers of
star fields and high-quality optics.
