A Work Commenced August 26 2022

Preamble 1

Preamble 2

Preamble 3

Preamble 4

 

There’s been many highs and lows on my 4-year journey through the wonderful and sometimes weird world of binoculars. Arguably the greatest high for me was my re-discovery of the many charms of Porro prism binoculars. Yet, it’s certainly the case that these instruments have been unfairly demurred for reasons that continue to baffle me. The simple truth is that a well-made Porro prism binocular can produce outstanding images using relatively simple technology compared with roof prism models that never seem to stand still. Almost every other week a new model hits the market promising out-of-this-world performance at out-of-this world price tags. I spent more than three years testing all manner of roof prism instruments without ever giving a thought to the humble Porro prism binocular- apart from the quirky reverse-Porro design of the Pentax Papilio II. Why? I supposed I swallowed hook, line and sinker the urban myth that the latter were simply inferior just because they were cheaper. After all, you get what you pay for, right? I mean, how could a full-featured Porro prism binocular costing a couple of hundred pounds realistically compete with a sexy, streamlined roof prism model costing a cool grand or more? Fortunately, I’ve spent the last six months buying in and testing some really nice Porro prism binoculars, and these collective experiences have consolidated my preference for these over their roof prism counterparts.

And I appear to be in good company.

UK-based Opticron is to be lauded for keeping high quality Porro prism binoculars alive and well in the 21^st century. As one of my main birding binoculars, I enjoy the excellent quality views of the now discontinued SR.GA 8 x 32 which delivers very similar though not quite as stellar views to my favourite instrument; the superlative Nikon E II 8 x 30, which I tend to baby just a little owing to its lack of rubber armouring.

But that got me thinking about what higher power instrument to use for the dull days of Winter and/or for longer range work, but most especially as a general purpose astronomical instrument to be used during our long, dark(and often cold) winters  here at 56 degrees north latitude. I had enjoyed a high quality 10 x 32 for a while but it lacked the light gathering power of bigger 10 x 42 models, which I also seriously considered. I had contemplated using the Opticron Adventurer T WP 10 x 42, a larger format Porro, but instead I decided to buy in and test two intriguing 50mm instruments from the same company – the 7 x 50 and 10 x 50 Imagic TGA WP models – to field test and learn as much as I could about them. I’ve been testing both of these instruments in various conditions, by day and by night, both at home here in Scotland, and while on vacation in south Wales, and have been so impressed with them that I decided to hold onto one model – the 10 x 50 – as I now firmly believe that it will do everything a 10 x 42 model can do, only better! To see why, read on!

A Closer Look at the Ergonomics of the Instruments

As outlined in Preamble 1 above, I had previously acquainted myself with the many delightful features of the Opticron Imagic TGA WP in the smaller 8 x 32 format, which is now in the capable hands of a keen lady birder on Jersey, in the Channel Islands. I was delighted to see these larger instruments had precisely the same features. Porro prism binoculars are not generally known to be waterproof, and this is one reason cited by some for rejecting them for serious field use. These instruments are o ring sealed and purged with dry nitrogen gas, so that traditional excuse is no longer valid.

“I don’t like the old-fashioned rubber eye cups on those classic Porros,” I hear you say.

These Imagic TGA models have fully modernised twist-up eyecups that click solidly into place and hold their positions firmly.

What about eye relief? That’s quite poor in classic Porros isn’t it? Not on these models; the 10 x 50 has 19.5mm of eye relief and the 7 x 50 has a full 21.5mm. That’s ample for any eyeglass wearers. And yes, I’ve tested them both using my own eyeglasses and both present the full field in complete comfort.

“What about the dioptre mechanism? Isn’t that the usual ring under the right ocular?”

No, these models possess an ingenious click-stop mechanism. The ring has an unusually high degree of tension and clicks its way round to your preferred setting. Once there, it clicks into place and doesn’t budge: just as effective as any locking dioptre setting featured on much more expensive roof prism models. What an excellent piece of applied engineering! Incidentally, fellow author, Stephen Tonkin, a highly experienced astronomy binocular enthusiast(see Preamble 2 above), whose opinions I trust, referred to the dioptre as being ‘very stiff.’ That’s true, but he likely under-appreciated this feature for daytime uses, when dioptre settings are more likely to wander.

“Oh but Porro prism binoculars are big and clunky right?”

Ah, no, both of these instruments tip the scales at just over 800g. The 7 x 50 weighs 823g, while the 10 x 50 weighs just one gram more. That’s lighter than some of the heavier 42mm roof prism models I’ve tested, and for a 50mm specification, these are reassuringly lightweight.

“Yer but they’re awkward to handle!”

Nope, these instruments are exceptionally easy to handle. The weight is brilliantly balanced in my medium sized hands. Indeed, both instruments rate very highly in terms of pure form factor. They feel great in the hand.

“What about the armouring? I’ve heard this can be a bit skimpy on classic Porro models.”

Maybe on older models, but not on these. Both are endowed with a good, thick, protective rubber armouring, with upraised ridges for exceptional grip, even in wet weather.

“OK, OK, but they just don’t look as cool as roof models.”

Oh please; don’t be so shallow!

Ocular & Objective Lenses

Both instruments are fully multicoated and treated with the company’s proprietary differential  F coat to minimise glare and internal reflections. The objectives are nicely recessed to protect the instrument from rain, dust and stray light. Check it out below:

The ocular lenses are large and easy to engage with.

There is only one significant physical difference between the two instruments, and it pertains to the size of the eyepiece lenses. The 10 x 50 has a 21mm diameter, while the 7 x 50 lens measures only 18mm.

The focuser on both instruments is exceptionally smooth and backlash free in either direction: very similar if not identical with my smaller SR.GA. 8 x 32. Tension is perfect for my taste – excellent in fact! It takes just three quarters of one revolution anticlockwise to go from near focus to infinity, and beyond.

Tripod/monopod compatible?

Yep, just unscrew the cap at the head of the bridge, mate it to a good quality tripod/monopod adapter and you’re off to the races!

Both binoculars have a decent IPD range: 57 to 73mm, so even smaller faces can engage with them easily.

What about accessories?

Well, you get a basic but perfectly functional rain guard that can be attached to the strap if you like it that way. I don’t like any appendage hanging from my optics so I usually carry it in my jacket or trouser pocket if its raining or threatening to do so. The objective caps are basic plastic covers but they fit tightly.

The carry case accompanying both instruments is well made from faux leather. It is lined internally and has enough space to carry the binocular with its strap attached

 

Optical Assessment: 

I measured the effective aperture of both instruments simply by shining a bright light through the ocular lenses and measuring the size of the circle of light projected on a flat surface. Both showed no evidence of stopped down optics with effective apertures of  about 49mm for both the 7x and 10x instruments.

Next I examined the exit pupils of both instruments. Both delivered satisfactory results. Shown below is the results for the 10x instrument.

Both pupils are perfectly round, so no truncation here. There is some light outside the exit pupil but this had very little effect in practice, as my subsequent tests showed.

Placing an intensely bright light at a distance of about 5 metres and examining the focused images through both instruments produced pretty much identical outcomes. Both showed very good results, with only a few minor (read very low intensity) internal reflections, no diffraction spikes(as expected with Porro models) and no diffused light around the beam, all indicative of high quality, homogeneous glass. Testing on a bright sodium street lamp after dark showed excellent results too – again clean with no annoying internal reflections. So far, so very good!

In agreement with all of the reviewers cited in Preamble 2, 3 and 4  above, the daytime images delivered by these binoculars are very impressive. Both deliver very bright, high-contrast images, with very large sweet spots. Even the edges near the field stop are satisfyingly sharp. Colours are very faithfully represented and appear neutral to my eye. Chromatic aberration is very well controlled. It’s pretty much non existent for the most part but a trace can be seen when viewing roosting corbies perched high on treetops against a grey sky background. A small but very tolerable amount of lateral (off axis) colour can also be witnessed when viewing branches near sunset against an overcast sky. Incidentally, the light transmission of these instruments was measured by allbinos to be in the region of 88 per cent, so these are very efficient light cups which will prove especially useful for my primary use for them – astronomical viewing.

Glare suppression is excellent too. Indeed, when comparing the images in both my Japanese-made SR.GA 8 x 32 and the Imagic TGA 7 x 50, I judged the latter superior in this regard. On dull afternoons, for example, glare usually manifests itself in most binoculars when glassing in the open air, in the direction of the Sun. Under these conditions, the 7 x 50 produced a slightly more contrasted view when imaging a hill top. Veiling glare was also slightly better controlled in the 7 x 50 Imagic TGA too. You can readily test for this by imaging the topmost boughs of a tree against a bright overcast sky with the Sun nearby. Indeed, consulting my notes on the smaller 8 x 32 Imagic TGA model,  I had already noticed this when I briefly compared it to my newly-acquired SR.GA.

This may come as a surprise to some readers, as the SR.GA  is arguably one of the best modern compact Porros available until recently(they replaced Opticron’s excellent HR series you’ll remember). I understand the Imagic TGA models are also Japanese-designed but are actually manufactured in China. So what’s going on here? I think it’s the coatings applied to the lenses and prisms on the Imagic TGAs. These were introduced later than the SR.GAs and so may have benefitted from slightly better coating technologies. Just a hunch, but I’ve yet to come up with a better explanation!

I took some images with my Iphone 7 hooked up to the 10 x 50 Imagic TGA, using my Nikon EII 8 x 30 as a control and comparison. Both are 10-burst images taken with a 3-second delay to reduce vibrations. They were taken just a few minutes apart on the afternoon of August 27 2022. The results are shown below:

• The reader will note that the field of view of the 10 x 50 is 5.3 angular degrees (confirmed later by measurement). The Nikon E II 8 x 30 is a world-class compact Porro with a stupendously wide field of 8.8 angular degrees.

You can make up your own mind about these images.

Notes from the Field

Both these large aperture binoculars are extremely comfortable to look through, with no blackouts experienced while panning across a landscape. Close focus on the 7 x 50 was measured to be 5.6 yards while the 10 x 50 was slightly longer at 5.9 yards. Both instruments present nice, well defined field stops, as well as instantly recognisable stereopsis. This is especially noticeable when viewing  objects in close proximity to each other, such as in a forest, with the 10x glass being a little bit more pronounced in this regard. This is yet another feature I find particularly charming about Porro prism binoculars in that they readily deliver views with more spatial information owing to the larger separation of the objectives than in their roof prism counterparts. I had a particularly vivid experience of this stereoptic effect in the very early morning of August 7, when I sat, completely enchanted, observing a magnificent dragonfly hovering over my brother’s garden pond in South Wales. The mist was still dissipating from the water’s surface in the cool of the morning, as I watched in sheer amazement as its iridescent wings, bulging compound eyes and body glistening in the feeble, hazy sunshine some 10 metres in the distance. I became totally captivated by the dexterity with which it manipulated its two sets of wings, changing both their orientation and power stroke from moment to moment before accelerating at breakneck speed off into the distance. I later found out that these giants of the flying insect world have been clocked moving at more than 18 miles per hour!

“How wondrously designed these creatures are,” I thought to myself. Small wonder they’ve served as the inspiration behind drone technology and a whole raft of artificial visual systems that enrich human life.

The 7 x 50 gives an ultra-stable viewing experience owing to its lower power, allowing the user to view for significantly longer periods of time. That said, I found viewing through the 10x glass to be the more immersive of the two, despite its smaller field of view(5.3 degrees as opposed to 6.0 degrees for the 7x 50). Depth of field is noticeably deeper in the 7x instrument though. Indeed, having both instruments readily at hand, I conducted some measurements of this with the help of my son’s golf rangefinder. Carefully targeting well defined objects in the centre of the field to minimise the effects of field curvature, the 7 x 50 unit delivered a close focus at infinity of 50.9 yards, while the 10 x 50 produced a value of 70.5 yards.

In previous work, I fleshed out some of the details of the factors that influence depth of field, showing that the most important parameter was magnification and which scales inversely with power. I thus expected a (10/7)^2 or two fold greater field depth in the 7x 50. Plugging the figures in yielded (70.5/50.9)^2 = 1.92, in close agreement with theory.

Neat!

Large aperture instruments such as these naturally come into their own in low light situations, such as late evening viewing. Observing at sunset, and about half an hour into the dusky twilight, I was readily able to discern that the 7 x 50 yielded brighter images of targets set in the shade, such as leaf litter under bushes. But here’s the thing; I was very impressed by how well the 10 x 50 was keeping up! Magnification is, of course, at play here, providing a more enlarged view of targets which partially compensates for the grater brightness of the lower power glass. I mean, what good is a brighter image if it doesn’t show detail? You can find more on this interesting topic here.

Ad Astra

Although I could more or less instantly tell both instruments were well collimated in daylight tests, I was easily able to verify this under the stars. Centring the bright star Altair in both the 7 x 50 and 10 x 50, I turned the dioptre setting to the end of its travel, defocusing the star from a tight pinpoint to a defocused anulus of light. Both instruments showed the focused star well inside the anulus, indicating that both instruments had their barrels well aligned.

Turning to the Big Dipper, I took the opportunity to test the size of the field of view in the 10x glass by noting that the pointer stars(which show the way to the North Star, Polaris), Dubhe and Merak are precisely 5 degrees 21′ apart, or 5.3 angular degrees. I was delighted to see that both stars could just fit inside the field of view, so no discrepancy here with the stated field size. Impressive!

While I was in this part of the sky, I took the opportunity to hunt down the two Messier galaxies in The Great bear – M81 and M82  – easily swept up by drawing an imaginary line from Phecda through Dubhe and extending that line as far again until I could see both galaxies close to each other in the same field of view. Comparing the views in the 7 x 50 and 10 x 50, it was immediately obvious that the 10x glass showed these faint fuzzies considerably better than the 7x glass. This is all textbook behaviour for these binoculars. The 10x glass delivers ~ 0.5 magnitude boost over the 7x glass. The main reason is the larger magnification of the 10 x 50, which darkens the sky approximately (10/7)^2 or 2x greater than the 7 x 50, making these faint objects stand out better in the former. This is a very convenient way to see the immediate benefits of a 10 x 50 over a 7x 50 under dark skies.

But it was also obvious when I turned the binoculars over to the Alpha Persei Association in Perseus, where the 10 x 50 swept up more stars than the 7 x 50. The same was also clear from looking at the Double Cluster, located roughly midway between Cassiopeia and Perseus. Fainter stars could be seen in the 10x glass than the 7x glass.

Bringing both the 7x 50 and the 10 x 50 to a very dark site in rural South Wales during warm and settled summer weather afforded ample opportunities to do some quality stargazing. For the steadiest, deepest views, a monopod is recommended with either of these instruments, but on this occasion, I enjoyed simply hand-holding them while lying back on a zero gravity chair. Views of the Milky Way through Cygnus were breath-taking in both binoculars, particularly in the region around Sadr. What I really like about these binoculars is their very well corrected fields. As I’ve stated before, optical defects are much easier to see under the stars than during the daytime, when the eye tends to be overwhelmed by the amount of detail seen in and around the centre of the image, but star images are less forgiving. Under some super dark skies and the Moon setting early in the first week of August, I could see that the central 80 per cent or so of the field of these binoculars produced sensibly perfect star images, but in the outer 20 per cent, the effects of field curvature began to manifest themselves. Thankfully, these aberrations were very mild(as you can see from the photos taken above), with the images nearly all the way up to the field stops still being acceptably small and sharp to my eyes. Indeed, the views very much reminded me of those served up by my largest binocular – the Pentax PCF 20 x 60 WP, with its aspherical eyepieces – only with a much wider field( 5.3 compared with just 2.2 degrees).

Images of the Moon in both binoculars displayed excellent contrast and sharpness, and I could detect very little in the way of chromatic aberration in the centre of the field, with lunar craters peppering the southern highlands with impressive clarity. Off axis, a small amount of lateral colour (mostly yellows and a splash of purple) began to creep in but that’s all par for the course in most any 10 x 50 you’ll look through.

The formidable light gathering power of these high-quality Porro prism binoculars from Opticron proved very beneficial for enjoying the colours of bright stars. I enjoyed some magnificent views of the Pleiades in the wee small hours of late August, as well as M34 in Perseus, and the ghostly light from the Great Spiral Galaxy in Andromeda(M31). The Dumbbell Nebula(M27) in Vulpecula looked terrific too in the 10 x 50 but less impactful in the lower power of the 7x glass. The same was true when I turned the instruments on the Coathanger asterism(Brocchi’s Cluster) nearby. And moving back across the sky into Cassiopeia, I compared and contrasted the view of the ET Cluster in both instruments, with the victory, once again, going to the 10 x 50.

The excellent sharpness and contrast of these binoculars proved ideal for observing colourful single, double and multiple stars, with the 10 x 50 coming out on top once again. Mu Cephei – Herschel’s Garnet Star – was compelling in deep red, as were the beautiful colour contrast binocular doubles O^1 Cygni and Delta 1 & 2 Lyrae sailing high in the late Summer sky. Colourful stellar associations, such as brilliant white Altair contrasted against the  orange giant star, Tarazed, in the same field, were admired in all their preternatural beauty.

I’m of the opinion that star images are more aesthetically pleasing through good Porro prism binoculars, owing to their complete lack of diffraction spikes. I came to notice this in comparing a few bigger roof prism binoculars with the 10 x 50, and in particular, a Vortex Diamondback HD 10 x 50. During daylight tests, for example, the Opticron Imagic TGA WP  10 x 50 produced crisper images with noticeably better contrast and less glare than the big Vortex roof. But that really didn’t surprise me as you’d probably have to fork out at least two or even three times more money to get a roof prism model that can compete favourably with these very well appointed Porro glasses. Under the stars though, the Diamondback HD did quite well, but didn’t quite deliver the same off-axis performance to the 10 x 50 Imagic TGA WP I compared it to. Eye relief is noticeably shorter on the big Diamondback HD too(16mm). It was also a little bit heavier(~850g) than the Opticron, which counts in extended hand-held use.

Are there better Porros out there? Yes, the Nikon SE 12 x 50 comes to mind, or a Fujinon FMT 10 x 50, or even a classic Swarovski 10 x 50,  but these cost several times more than either of these binoculars – if you can even get them. But if, like me, you can live with the smaller field of view offered by these instruments, you’re in for a real treat when you test them out in daylight or better still, under dark, starry skies where they’re in their element. Couple all this to their modest cost – both under £200 – and Opticron’s excellent 30-year warranty, and you may begin to see why it’s really hard not to like them!

Highly recommended!

 

 

Neil English has been observing the night sky for over 40 years. His latest book on binoculars will hit the shelves at the end of 2023.

 

 

 

 

De Fideli.