Helios Fieldmaster A90R 25 to 75 x 90mm spotting scope

 This review was first published on January 2020 and I have edited it in italics.

Helios Fieldmaster A90R 25 to 75 x 90mm spotting scope

I really like Helios optical products. I used one of their Japanese made telephoto lenses with my 35 mm SLR film camera way back when. I also have two pairs of their binoculars which I use for astronomy. Their Fieldmaster 7x50 Porro binoculars are nothing short of amazing value for money at £50. They compare favourably with the much more expensive German made ( but possibly not - Japan ?) ED roof prism binoculars that I use mainly for birdwatching.

My existing spotting scope was given to me and was beginning to show its age. So, I decided to replace it. I am not an avid birdwatcher, but I like to visit local lakes every now and then for a couple of hours of long-distance observations. I do bird surveys for the local nature reserve, which does not include a lake, and of course spotting scopes are useless for this type of location – I use binoculars.

The Helios scope serves my needs perfectly. The forums that I visit recommend that you should buy the most expensive optics that you can afford. Well said, but I am not prepared to shell out £2,000 for a Leica scope that I would only use for two hours a week under favourable weather conditions and when the light is good.

As far as I could see no-one had written an independent review of this Helios scope so I was buying it on the trust that I would be getting a reasonably good scope for a fair price. I paid Harrisons Telescopes £149.00. I was not disappointed; the scope was better than I expected it to be. Here is my opinion and independent review.

The refractor scope features:

A 25 to 75 mm zoom eyepiece,

A 90 mm triplet objective lens,

Black rubber protected polycarbonate body,

BAK 4 fully multi-coated prisms,

Other optics are fully multi-coated,

Single speed focusing wheel,

Nitrogen filled waterproof body,

Standard tripod bush,

Sunshield,

Body length of about 450mm and a weight of 1800 gm,

Looks the business and made in China.

It has all the features of a reasonably good spotting scope apart from ED high definition lenses.

One thing that attracted me to this scope was its triplet objective lens. Triplet lenses help to reduce the distortions and optical aberrations which can plague all sorts of optical equipment.

I tested the scope, out of the box, by observing a chimney about 125 metres away. A starling was perched on the brick work. I could see its colourful body and the sharpness of its beak both clearly and naturally. A magpie showed no chromatic aberration or colour fringing even though its black and white body was contrasted against a bright blue sky. My wife was impressed by the improvement over my old scope. The image was bright and clear with very little distortion or aberrations almost to the edge of the field of view.

   

I thought that I would wait for dark to observe the night sky. The scope performed better after sunset than I expected. I was lucky to have a break in the weather and to have clear skies.

I tested the scope alongside my reflector astronomical telescope at about the same magnification at 35x. The quality of view of the moon was about the same in both scopes; the craters, mountain ranges and rills were equally well defined. There was, however, some chromatic aberration on the limb of the waxing gibbous moon but none on the terminator. When I moved my eye this colour fringing disappeared as my vision found the sweet spot on the optical axis - bizarre. My reflector astronomical telescope does not suffer for chromatic aberration, so my new Helios spotter was performing almost as well. The stars were pin sharp through the Helios and I could not observe any optical aberrations over 85% of the field of view. I was able to pick out the stars of the Trapezium embedded within the Orion nebula. Its performance on the astronomical front was very good but I won’t be using it for astronomy because of the difficulty in finding the stars to look at.

The next day, I returned to my chimney to watch out for chromatic aberration and I found it; there was some purple and yellow fringing just as I found on the view of the moon. This fringing disappeared when I found the optical sweet spot. This is a bit of a drawback.  A Leica spotting scope would not show any appreciable fringing anywhere, but I would have to pay £2,000 for the privilege.

I went to a lake to observe a couple of times. I could see the details on the head of a Heron clearly from 250 meters. The scope handled the reflections from the water adequately. I could clearly see fishermen and their rods at 500 meters. Basically, my observations were distortion and aberration free. The colour fringing problem was not apparent because I was not observing high contrast subjects. Across one of the lakes, at about 200 meters, my wife and I observed a couple of barn owls in their nest box in quite low light just before sunset. We could clearly see their faces and their beautiful feathers. The zoom lens performed well up to about 40x and then the quality fell off, so the results were just about passable at 75x.   A Zeiss zoom lens would perform much better but then again you will have to pay £2,000 or more.

The scope has a few drawbacks, the intermittent colour fringing is the primary one, but I won’t be seeing this most of the time. The scope might be a bit too long and heavy for some people, but it does not bother me. A double speed focus wheel would improve focussing speed and accuracy.

For me, the spotting scope fits my purpose of occasional observing from a fixed location at a lake. If I was a professional hunter, target shooter or naturalist I would buy a Leica or a Swarovsky and I would gladly fork out £2,000 plus for a top of the range model to be proud of. I paid £149 for a Helios spotting scope which is only marginally worse than a Zeiss and I am pleased with it. It is a bargain and exceptionally good value for money. I recommend it, if like me you are only an amateur and occasional observer.

Recently, I bought an Orion Apex 102 mm Maksutov-Caissegrain telescope for astronomical use but it also makes a good spotting scope it is reviewed later.

I compared the Helios Fieldmaster with the Apex. The Fieldmaster could resolve the shafts of a fence at a distance of 1.25 kilometers in a playing field. The shafts measure 1.5 centimetres in diameter. The Fieldmaster could, also, just about resolve some bolts on a park bench. The Fieldmaster did this through a window and with less than perfect seeing conditions. I estimate that  it was resolving down to 1.6 arc seconds where its theoretical limit is 1.289 arc seconds. At 40 x magnification the Helios shows appreciable chromatic aberration when viewing very high contrast subjects: the Apex shows none. 

 In comparison to the Apex scope which is designed to show completely minimal chromatic and spherical aberrations, the Helios holds up well. I was going to replace it with a much more expensive model. I have changed my mind I am keeping it - 21 April 2021.