Binoculars review

Delta Optical Extreme 15x70 ED

Delta Optical Extreme 15x70 ED
16 September 2014
In 2005 the William Optics company presented two huge pairs of Porro prism binoculars with the following parameters: 7x50 and 10x50. They were deceptively similar to the Fujinons FMTR-SX, renowned for their excellent image quality. It soon became clear that the WO instruments were produced by the Chinese United Optics factory. As the binoculars have fared very well in all tests there were a lot of imitators; soon the market was inundated by various WO clones under different brand names.

Already in 2006 the Oberwerk company launched models of the same series with 70 mm objective lenses. That time they weren’t just faithful copies of the Fujinon devices. Their parameters were different for one thing: when the Fujinons came as 10x70 and 16x70 binoculars the Oberwerks, produced by United Optics, were 10.5x70 and 15x70. At the end of 2012 the Polish Delta Optical company decided to get a move in that class of equipment as well, announcing a launch of four models: 7x50, 10x50, 10.5x70 and 15x70.

As we already mentioned above the parameters and appearance of the Extreme ED series binoculars are very similar to the Fujinons from the FMTR-SX series. They are fully waterproof, equipped with individual focusing and nitrogen-filled so often recommended as perfect devices to use near or/and on water. They are also great as astronomical instruments – their big objective lenses are able to gather a lot of light, huge prisms don’t cause any vignetting and the efficient Porro construction is supposed to guarantee a high transmission level.

Delta Optical is a company well-known for improving the constructions offered by their rivals by introducing small but handy changes – that’s why we were very curious how the DO Extreme would compare to the William Optics or Fujinon binoculars we’ve already tested.

Buyers get cups, a strap, a hard case, a tripod adapter and a cleaning cloth in the box. The product comes with a five-year guarantee period.

  • Lornetka Delta Optical Extreme 15x70 ED
  • Lornetka Delta Optical Extreme 15x70 ED
  • Lornetka Delta Optical Extreme 15x70 ED
  • Lornetka Delta Optical Extreme 15x70 ED
Manufacturer data


Delta Optical
web site

Distribution / Sales:

Delta Optical
web site

Magnification Lens diameter Angular field of view Prisms Eye relief Weight Price
15 70 77/1000(4.4o) BaK-4/Porro 18 mm 2550 g 1499 PLN
Results of the review
Real front lens diameter Left:   70.05+/- 0.05 mm
Right:  70+/- 0.05 mm
8 / 8.0 pkt
Real magnification 15.03+/- 0.05x 3/3.0
Transmission 85.2+/- 1.5% 13/25.0
Chromatic aberration Almost invisible in the centre, slight on the edge. 8.5/10.0
Astigmatism Corrected in the proper way. 7.3/10.0
Distortion The distance of the first curved line from the field centre compared to the field of view radius: 39% +\- 4%. 4/10.0
Coma Appears near 75-80% of the field of vision and is low on the very edge. 8.7/10.0
Blurring at the edge of the FOV The blur occurs in a distance of 80% +\- 3% from the field of view centre 5.5/10.0
Darkening at the edge the FOV Slight. 4.2/5.0
Whiteness of the image Very good. The difference in transmission between red, yellow-green and blue light amounts to about 5%. 4.4/5.0
Collimation Perfect. 5/5.0
Internal reflections
Left: Right:
Delta Optical Extreme 15x70 ED - Internal reflections - Left Delta Optical Extreme 15x70 ED - Internal reflections - Right
Housing Huge, heavy and solid. Comfortable to hold in big hands. Rubberized eyecups which can be folded – a bit shorter than those in the 10.5x70 model so they are more comfortable around the eyes. The black rubber armour padding the rear parts of the prisms (with inscriptions ‘Delta Optical’ and ‘Extreme 15x70 ED’) doesn’t stick well to the body – it can be torn away by one slight pull. Additionally the rubber padding also sticks out a bit; it ends near the objectives where the parts are made of metal covered by black paint. The paint is easy to scratch if you put the binoculars on any harder surface. 5/8.0
Focusing Individual focusing on huge eyepieces works evenly in a range from -5 to +5 dioptre and seems to be very solid. 5/5.0
Tripod There is a comfortable tripod exit. 3/3.0
Interpupilary distance from 56.9 to 74mm 5/6.0
Closest focusing distance 19 meters 0/2.0
Eyepieces FOV Apparent field of view of 65.1 deg (according to simple formula) and 59.2 deg (according to tangent formula). 14/20.0
Field of view Measured by us amounted to 4.33 +\- 0.04 degrees and it was narrower than stated in the specifications. A very wide field of view for this class of equipment. 7.5/8.0
Quality of the interior of the barrels Tubes and bottoms black and almost matt – the tubes are additionally covered by fine ribs. The glue near the prisms is white but the screws are already nicely blackened. Deeper, behind the cell with prisms, some grey elements which aren’t blackened and are a bit scratched too. Quite clean – some fine specks of dust. 3.3/5.0
Left: Right:
Delta Optical Extreme 15x70 ED - Vignetting - Left Delta Optical Extreme 15x70 ED - Vignetting - Right
OL: 0.75%, OR: 1.80%
Prisms quality Good quality BaK-4. 8/8.0
Antireflection coatings Greenish everywhere. Average intensity; strong reflections of light only near the prisms. 4/5.0
Warranty [years] 5 years 3.5/6.0
Final result
140.6 / 190 pkt
Econo result 0pkt.


  • huge and solid casing,
  • good transmission,
  • wide field of view,
  • excellent correction of chromatic aberration,
  • proper correction of astigmatism,
  • negligible coma,
  • low brightness loss on the edge of the field of view,
  • very good whiteness rendering,
  • dark areas near exit pupils,
  • huge prisms made of BaK-4 glass,
  • good price/quality ratio.

  • some annoying bungles in the casing construction,
  • very high value of the minimum focusing distance.

Taking into account the price of those binoculars we can boldly say you deal here with an optical pearl. Only the distortion is corrected a tad below average, the rest of optical aberrations the Delta Optical Extreme 15x70 ED manages to correct very well or exceedingly well.

If you want to be a purist you can also notice that the exit pupils are slightly truncated. You should also expect a higher transmission level from a well done Porro construction. Still for less than 400 Euro, because such a sum you have to pay for the Extreme 15x70, it would be difficult to demand the usage of the best coatings; that’s why the transmission is hardly outstanding. On the other hand you can certainly call it good. The result of 92% for the red light and about 85-87% for the middle of the visible spectrum is certainly nothing to be ashamed of.

It would be also difficult to complain about the 19 metres minimum focusing distance in a piece of equipment which is so obviously not designed for observation of birds or butterflies. It is a huge pair of binoculars which might be used in astronomy or on water; you won’t need to focus on objects which are situated just several meters away.

The biggest difference between the Delta and the device it’s been modelled on, the Fujinon FMT-SX 16x70, is the quality of the casing. The rubber armour of the Delta doesn’t cover the area near the objectives which is made of painted black, matt metal. The result? As soon as you put the binoculars down on any harder surface with the objectives downwards the edges of the casing become scratched.

The second thing, characteristic for the Extreme ED series, is the sparse glue usage. There is not enough of it not only near the black rubber covering the prisms, which can be pulled out without the need of excessive force; also near the rubber covering the tubes the glue coverage is simply lacking so, in several places, the rubber is visibly ballooned. It can be annoying especially that such a flaw should have been easy to catch and fix in the factory.

Would it be actually better if the binoculars were a bit more expensive but also better polished up mechanically? Maybe it’s more convenient to pay those 400 Euro and then buy a tube of good glue to fix the shortcomings left by the factory workers on your own; after all it’s a simple task that wouldn’t take more than half an hour.

No matter what the answer is, it doesn’t change the most important fact: slight shortcomings don’t make these binoculars optically worse in any way. If you can’t accept the price of the Fujinon and you feel tolerant for small mechanical flaws, the Delta won’t disappoint you for sure.