How to turn a binoculars objective into a tele macro lens

[Gerald]

When a photographer needs a 200 to 300mm telephoto lens, he/she can imagine three types of solution: the good, the bad... and the funny!

The good
The best solution is simply to buy a lens that was designed since the beginning to be used with the photographer's camera. The second best solution is using a commercial adapter so a lens designed for a different camera than the photographer's could be used.

The bad
A bad solution is when one tries to adapt a lens designed for an application that is much different than usual photography. For example, adapting lenses for process or aerial photography is not in general a good idea. Most of these lenses are heavy, and have no mount or focusing mechanism. Even if possible, adapting in these cases can be a nightmare, and the result is usually cumbersome and impractical.

The funny
Funny are the solutions that can be implemented with little effort and, at the same time, are practical and inexpensive! This post aims to show one such solution. You'll see that if you have all the parts at hand, how a tele macro lens can be set up in minutes.

Implementation
As the title of this post suggests, the idea is to use the front lens (objective) of a Zeiss-type prismatic binocular as a photographic tele macro lens:



A binocular objective is an achromatic doublet corrected for infinity. The focal length is typically around 200mm and the diameter is 50mm for binoculars with magnification of 7x to 20x. In this case, the relative aperture is the objective is given by:

F-number = 200/50 = F4

The objective lens I used in this experiment was purchased on eBay for only 8 GBP. However if you already have an older binocular that can be cannibalized, you have two objectives for free!

First the objective has to be removed from the binocular and then mounted on a step-up or step-down filter ring. The simplest way to fix the lens is to glue it to the rings. The assembled lens will be like the photo below. I used two rings because I wanted threads on both sides. My original goal was to use the lens as close-up lens for macro photography.



The next step is to mount the lens on a bellows, perhaps with some extension rings if the bellows is short. A rack-and-pinion bellows is ideal but with a bit of skill it is possible to focus using a primitive bellows as the Pentacon.

The weight of the set bellows + extension rings + adapter rings + lens is quite modest:

set with Pentacon small bellows: 607 grams
set with Pentax auto bellows: 843 grams

Pentacon small bellows:


Pentax auto bellows:


If the bellows is long enough, it is possible to focus to surprisingly small distances. With the Pentax auto bellows and extensions rings I could do close-ups with magnification of 1:2.5 approximately.

If desired the aperture can be reduced with a disk of plastic or cardboard with a hole in the center. The relative aperture of the tele macro will then be given by:

F-number = 200/D, where D is the hole diameter in mm.

Results
The photo below shows a pot plant at a distance of approximately 3 meters. The depth of field is extremely small. Note how the bokeh is excellent.
The bellows allowed closer focusing than the usual telephoto lenses. The 100% crops show that sharpness is pretty good.

Pot plant about 3 meters away at F4 (wide open) - full picture:


Pot plant about 3 meters away at F4 (wide open) - 100% crop:


Close-up of pot plant at F4 (wide open) - full picture:


Close-up of pot plant at F4 (wide open) - 100% crop:


Distant landscape
The photos below show buildings approximately 2 km away. The atmospheric conditions were not ideal for long-distance shooting, as shown by the wavy lines of the buildings.

For a more accurate assessment, I also took some photos with telephoto lenses with similar focal length. The CZJ 180mm F2.8 is a well known and recognized high-quality lens. The aperture used for the CZJ 180mm was F5.6, which is the aperture for which this lens works at its peak performance. The Fujinon 54-270mm F4.5 is a lens that was designed for professional use. It was the Fuji's response to the Nikon 50-300mm F4.5, which was one of the most desired lenses by professionals in the late 70's. The performance of the Fujinon 54-270mm is not exceptional by modern standards, but it is quite reasonable for a zoom lens, especially when aperture is closed to F8 and focal length is less than 200mm.

full view:


Distant landscape - tele macro lens (binocular lens) at F8 - center 100% crop:


Distant landscape - Fujinon 54-270mm at 200mm and F4.5 - center 100% crop:


Distant landscape - Fujinon 54-270mm at 200mm and F8 - center 100% crop:


Distant landscape - CZJ Sonnar 180mm at F5.6 - center 100% crop:




Distant landscape - tele macro lens (binocular lens) at F8 - off-center 100% crop:


Distant landscape - Fujinon 54- 270mm at 200mm and F4.5 off-center 100% crop:


Distant landscape - Fujinon 54- 270mm at 200mm and F8 - off-center 100% crop:


Distant landscape CZJ Sonnar 180mm at F5.6 - off-center 100% crop:






ANALYSIS OF THE RESULTS

Center
Performance of the tele macro lens at F8 was as good as the CZJ 180mm at F5.6, and better than the Fujinon 54-270mm wide open (F4.5). The Fujinon at F8 was as good as the CZJ Sonnar at F5.6.

Off-center
The performance of tele macro lens was worse than the Fujinon F8, but better than the Fujinon at F4.5. As expected, the CJZ 180mm at F5.6 had the best performance of all.

[philslizzy]

A great idea, so which should I cannibalise? My 1947 Nippon Kogaku 7x50 Naval binos, My 60's Baush and Lomb 10x50's or my 70's Boots 8x30's All superb instruments I may add. Or perhaps a charity shop pair that are out of collimation?

[luisalegria]

Very nice results actually.
I have a couple of these extemporized lenses. Both based on some sort of military optics (I didn't do the adapting).
Both seem to be achromatic doublets like this.

[scsambrook]

[philslizzy]

[scsambrook]

That's a nice old Nikon binocular - some of these old ones are not only excellent performers but are worth more money than one might expect (Phil - I sent you a PM ) and I'd urge anyone fancying following Gerald's interesting example to check before they start.

[Gerald]

Of course I do not recommend sacrificing a good binoculars for an experimente like this. However, there are millions of cheap Japanese, Russian, etc., unused binoculars in drawers, closets and bookshelves. Most likely these binoculars have fungus, hazy prisms and lenses, which would have to be dismantled anyway for cleaning and maintenance. These binoculars are good candidates to "borrow" the front lens. The removal of the objective is a reversible operation and the lens can return to binoculars after the experiment. It is interesting to put a mark on the lens with a felt pen, allowing it goes back in exactly the same original angular orientation. With this precaution, the risk of losing collimation is practically zero.

An alternative to a binoculars objective is an achromatic close-up lens with power from +3 to +5 diopters. The focal length in millimeters of the tele macro lens will be given by:

FL = 1000 / D

For example, if D = +4 diopters, then FL = 250mm

Orientation of the lens is important, and is the reverse of that used in macro photography. The surface of the close-up lens that faces the subject in macro photography should be facing the camera sensor when the lens works as a telephoto.