A Work Commenced August 20 2022
Product: Olympus EXPS I 10 x 42
Country of Manufacture: China
Exit Pupil: 4.2mm
Field of View: 96m @1000m(5.5 angular degrees)
Eye relief: 18.4mm
Dioptre Compensation: +/- 3
Coatings: Fully Multicoated Optical System, UV Coating, High-index Bak-4 Porro Prisms
Eyepieces: Aspherical design
ED Glass: No
Close Focus: 5m advertised, 3.38m measured
Weight: 785g advertised, 790g measured
Dimensions: W/L – 13/18.7cm
IPD Range: 60-70mm
Accessories: Soft case, padded logoed neck strap, rain guard, objective lens caps, instruction sheet.
Warranty: 25 years(European)
Recently, an amateur astronomer I correspond with told me how much he liked the Japanese camera giant Olympus’ entry-level model; the DPS I 8 x 40. Intrigued, I decided to buy in one of their premium Porro prism models; the EXPS I 10 x 42. Unlike the DPS I models which only have fully coated optics and BK7 prisms, the EXPS I instruments featured BAK4 Porro prisms and a full multicoating in a sleek, ergonomically advanced chassis.
A Walk Around the Instrument
The instrument arrived in a very similar blue box to the DPS I models, with the instrument neatly stored away inside a soft black carry case. The binocular also came with plastic objective lens caps and rain guard, together with a nice logoed neck strap.
The instrument itself is very solidly made, with a thick rubber armouring. In the hand, the instrument felt quite hefty but its redesigned contouring made it very easy to hold in a comfortable position. I measured the weight of the instrument without its neck strap to be 790g.
The focuser is Excellent.! I mean really, really Good!
Thick rubber-clad with really good grip. It moves with silky smoothness with no free play or backlash. It’s very fast too; taking just three quarters of a revolution anticlockwise to go from closest focus to infinity, and a little beyond.
The dioptre compensation ring is located under the right ocular lens and has just enough tension when rotated to hold its position well. There is a scale that allows you to easily memorise your optimal setting.
The eyecups are fully modern and twist up before locking in place, giving generous eye relief. The specifications state 18.4mm. I didn’t measure this but I could very comfortably engage with the entire field with my eyeglasses on, so no worries there.
The objective lenses have very nicely applied anti-reflection coatings and are quite deeply recessed to protect against dust, rain and extraneous light.
The central hinge is quite rigid, but I did note the rather narrow IPD range from 60 to 70mm. That pretty much rules it out for those who have smaller faces or narrow set eyes.
All in all, I would rate its ergonomics very highly indeed. But what about the optics?
As usual, I began by shining an intensely bright light from my Iphone 7 torch situated several metres away and examined the image presented by the binocular. I noted a few minor internal reflections which were certainly a bit more prominent than I’ve witnessed in other similarly priced Porros from other manufacturers. Next, I examined the exit pupils of the instrument. As you can see below, there was no sign of any truncation as evidenced by the perfectly round shafts of light, but there is a considerable amount of extraneous light around and in close proximity to the exit pupils. When I pointed the instrument at a bright yellow sodium street lamp after dark, I could detect some weak internal reflections but nothing too distracting. Close focus was considerably better than advertised; 3.38 metres compared with the 5 metres quoted in the specifications sheet.
But it was only as I began to study the daytime images that something was quite amiss. The image was good and bright in agreement with the high transmission values measured in independent tests. The centre of the image was really sharp with good contrast but the left-hand-side of the image was badly distorted in the outer 30 per cent of the field. And anywhere near the left-hand field stop was totally blurred! The same was not true on the right-hand-side of the image though. I found this aberrational asymmetry quite disturbing, especially when the field of view is quite small to start with( 5.5 degrees).
I was able to assess the situation better when under the night sky, where aberrations are much easier to identify. Centring the bright star Vega, now nearly overhead, I was able to obtain a really good, sharp image of the star in the centre of the field. Collimation was spot on. But as I moved it toward the left-hand field stop, the star became grossly deformed with what looked like a mixture of field curvature, astigmatism and coma. Attempting to refocus the star, I was only able to clean it up partially. That astigmatism and coma just couldn’t be focused out! So much for the aspherical lens elements advertised by Olympus!
I took the liberty of capturing a photo of the image on a flat rooftop several tens of metres away. The below image is a 10-burst image taken through my Iphone 7. I think you can easily make out the very badly distorted image near the left-hand field stop.
What a disappointment!
A de-centred element in the optical train? Maybe.
In other daytime tests, I compared and contrasted the image to another, similarly priced Porro prism binocular – the Opticron Imagic TGA WP 10 x 50. Comparing the views on a variety of targets and in different lighting conditions showed the Olympus EXPS I 10x 42 to have substantially more glare and less contrast than the former. And compared with the excellent edge-to-edge sharpness of the Opticron, the Olympus EXPS I was downright shoddy. I was also disappointed with its ability to control veiling glare, easily tested for by looking at the branches of a conifer tree with the Sun immediately above it. The Opticron image was clean and well contrasted in contradistinction to the badly washed-out Olympus EXPS I image. Now this was not exactly an apples-to-apples comparison, but it was enough to deliver my verdict; this so-called ‘premium’ binocular from the famous camera giant Olympus was nothing of the sort! This is an instrument I cannot in good conscience recommend, especially when there are other models in the same price range that deliver much better optical performance.
I was intrigued by the report of the less expensive Olympus DPS I 8 x 20 provided me by my astronomer pen friend, but its specifications lend me to believe that it might even be worse than this EXPS I.
My tests are all the more disappointing in light of the great ergonomics of this Olympus binocular, but it counts for nothing if the optics are so disappointing! The reader will also note that my unit did not fare as well as the unit reviewed by allbinos.com linked to in the text above.
Post Scriptum: August 25 2022
A second unit of the Olympus EXPS I 10x 42 was ordered up for testing but proved to have the same optical issues as the first unit.
Dr Neil English has tested binoculars of all genres to build a sizeable portfolio of work for his up-and-coming book, Choosing & Using Binoculars: A Guide for Stargazers, Birders and Outdoor Enthusiasts, which hits the bookshelves in late 2023.