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Nikon IF SP WP (Prostars) 7x50 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 (nothing changes!) and they mostly all said that I should start off with binoculars – 7x50 binoculars, to be precise.

 

So I believed them and spent weeks poring over the Tasco catalogue before finally choosing the “International Bright View” model. Now 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 that format 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. So 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?

Design and Build

The first thing I said when I opened the big, gold Nikon box was, “wow!”

 

The Prostars are an impressive binocular on many levels. They exude quality and they are simply huge for a 7x50. They look immensely rugged and rather military.

Body and Ergonomics

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 “Tropic” model) that the 15x70s 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, for the Prostars 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 (Nikon, I believe, make their own optical glasses).

 

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 superior to these (Japanese made) Nikon Marine 7x50s

Optics - Eyepieces

The eyepieces give a narrow apparent field of less than 50 degrees (7.3 degrees 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 ever saw 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 and Zeiss SFs.

So the field is both flat and commendably lacking in other off-axis aberrations such as coma and astigmatism.

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 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, sadly, is that I am middle aged: older pupils don’t open as far and mine measure about 5-6mm in low light. Suffice to say that 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 a very tiny area. So that flat field and careful optical fabrication yields tiny, pin-point stars with superb brightness, almost all the way to the edge.

 

Point 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.

 

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. Clustered can be enjoyed right out towards 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.

So 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 degree 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 glas in the lenses and false colour is much better controlled.

·         The Victory FLs have more eye relief and so are more comfortable for specs wearers.

·         The Victory FLs seem almost as bright to my older eyes.

·         The Victory FLs weigh almost exactly half as much.

·         Brightness is similar, perhaps even better in the Victorys which use special prisms that transmit as much light as the Prostarsporros.

·         The Prostars are much less comfortable on cold nights because the Victory’s are made of low-conductivity plastic.

·         The Prostars look and feel better made, as if they’d last several lifetimes.

·         The Prostars generate more perfectly pinpoint stars.

·         At the time of writing they cost about the same in the real world (i.e. with the VIctorys quite heavily discounted).

Summary

The Nikon Prostars are an unusual binocular in today’s market. They are a classical 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.

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