Kaizen 200mm F/7 Binocular Telescope

by The Bolton Group

UPDATE 2019: After extensive testing a new pair of binoculars will shortly be available outfitted with digital shaft encoders for easy object location. They incorporate a wifi interface to a phone or tablet running Sky Safari. Any object in the latter's database can be selected and the software will guide the binoculars straight to it using simple push-to directions. Full details to follow soon.

UPDATE 2016: A second pair of binoculars has been completed and is now available.

The latest model was tested out at this year's (2016) Kelling Heath Star Party and proved to be probably the best pair ever made. Images were apo refractor like. New to this pair is the addition of polypropylene inner lining tubes covered in black velour flock. The eyepiece tubes have also been enclosed. They are now much more suitable for less than absolute dark locations. At Kelling the number of "oh my God" comments by first time users probably broke all records! Users were blown away by the experience of using two eyes. My favourite was the Veil Nebula and even the usually boring M31 was spectacular.

Binocular Telescope Pair 007

Note a Tablet holder for using planetarium software (Skeye) to guide the binos to their target has been added to the design. It makes it easy to push-to.Gerald and Brian have done it again - another fabulous pair of large binoculars. Tube assemblies/optical tubes are by Gerald and the 6 mirrors by Brian.

Below is the sixth pair and they incorporate all their experience and know-how gained along the way. The Japanese have a word for it - Kaizen - continuous improvement. They are 200mm aperture again but have gone back to the full skeleton tubes and adopted a slightly longer f/7 focal ratio.

To go with these new binos, Brian has produced another superb set of matched mirrors. Under autocollimation (double light pass doubling any errors) they exhibit virtually straight Ronchigrams as is his norm.

Tablet Guiding

Below are the binoculars on display at the Kelling Heath Star Party, September 2014. We had two good clear nights and the binoculars performed magnificently - probably the best ever!

bino 2014
The finished binoculars (Pair 006) ready for Kelling Heath 2014.

All design goals have been met, ie:-

1. Ultra stable
2. Hold collimation
3. One touch inter-ocular adjustment
4. Easy one-man assembly and move
5. 60 lbs total weight
6. Eyepiece height at sensible level

Note although the side-bearings look like simple Dobsonian bearings they have real bearings - no teflon here. The bottom bearing (azimuth) is a giant ball race.

The inter-ocular adjuster is a single thumbscrew just below the eyepiece plate

They dis-assemble into 3 components for easy transport and storage. What assembly there is, is by thumb-screws - no allen keys required.


bottom cage
Mount with bottom cage lowered on

Top cage ready to go on


Gerald and the assembled binos - note new "secret" joins to tubes.
The f/7 focal ratio has been chosen to provide a very practical eyepiece height.

All the parts (about 500) before assembly.


All the optics were made by Brian ie the 2 matching parabolic mirrors, 2 elliptical secondary flat mirrors and 2 elliptical flat tertiary mirrors. The main mirrors are 200 f/7 (1400mm focal length) and are perfectly matched. They were tested using autocollimation with a high quality test flat. In this test the light strikes the mirror under test twice. This is therefore a severe test as any errors present are doubled. They are certainly better than 1/10 wavelength accuracy probably nearer 1/20 wave.

Ronchigram of one of the mirrors - no turned down edge here!.

The f/7 focal ratio, as well as giving a sensible eyepice height, provides other benefits too. It has a bigger coma free field and it requires smaller secondary mirrors - an important factor given the longer light path through to the eyepieces.

Return to Telescope Making menu