Buying Checks and Simple Binocular Adjustments.

[Polar Bear]

This is a short intro to buying checks and minor adjustments on older Swift Tecnar Binoculars but the methods may be useful with other brands and models.

Buying used and minor repairs can save you lots of money and you have the satisfaction of bringing an optical item back into use,

Don't attempt unless

• you are used to using small hand tools,
  
• reasonably mechanically minded,
  
• not bothered if it all goes wrong and you are left with a pile of bits !
  

When buying second-hand from flea markets / car boots never impulse buy.

• Always take your time and although it may sound obvious look through the binoculars plenty.
  
• Carry with you a good quality cleaning cloth and if possible a small torch to shine into the eyepieces and check for internal problems by viewing into the objective lenses.
  

I bought these with their original leather case on my local car boot market.

Initial torch checks showed no internal damage , no signs of fungus / haze.

Mechanical checks showed no external damage and everything to work as it should, nice and smoothly with no play or tightness in any mechanisms.

Optical checks showed the focus to be fine with both eyes but a slight misalignment with the right image slightly higher than the left.

With the binoculars held at arms length I then checked that the exit pupils were round and reasonably central

This ensures the optical path is parallel on both sides and that the prisms are more or less correct.

If the exit pupils are cats eye shaped or way off centre there could be several faults ranging from a twisted pivot to misaligned objective lenses and badly aligned prisms.

Unless you are competent in repairs I would advise not buying them.

If you are not 100% sure they are in good order or can be easily renovated just walk away,

Cleaning the internals of binoculars is much more involved than a reflector or refractor scope and can be very time consuming.

There are 1000's of good second-hand pairs out there with a few web-sites for sales of used binoculars.

QUICKTEST Secondhand Binoculars

The exit pupils looking in good shape

A few simple screwdrivers and one of my trusty Leatherman's

Turn the cental focussing thumb wheel anti-clockwise

and whilst doing this pull upwards until the eyepieces and bridge units pull out.

The guides for the eyepieces can be screwed out and the end covers removed by taking out their small retaining screws.

Like so

After removing both covers screw back in the eyepiece guides and refit the eyepieces by simply screwing

the pivot / focus screw back in.

Now comes the fun bit and is achieved best if the binoculars are mounted on a tripod.

You now need a target , I use a rather convenient extractor fan cover on a neighbours wall approx 30 metres away that has concentric circles on it.

A circle is best as it seems easiest to adjust against.

Once focussed you can start the adjustments.

First check that all the locking screws and prism securing screws are tight.

It is no use doing any adjustments if any part of the assembly is loose.

With this model of binoculars there are 3 recessed adjustment screws (red) and 3 locking screws (black)

As I only need a slight adjustment I only needed to adjust the right prism.

Why right ? not easy to explain but when looking through the bins it seemed to me that the right one was out of adjustment.

It is just something that comes with looking through and adjusting lots of bins.

Next part is difficult to explain and has a thousand variations.

I always back off all the locking screws a quarter turn and then only move 1 adjustment screw a quarter turn then tighten up the locking screws again.

Check the view and see whether the image has moved away / converged / gone left / gone right or not moved !

You will soon get a feel for which adjustment screw does what to the image.

But remember no more than a quarter turn on one adjustment screw at a time or you will get in a right pickle.

As my old boss used to say 'little and often lad , little and often'

To give you an idea of time , it has taken me twice as long to type this as it did to adjust the binoculars.

Once happy with the images on your target remove the eyepieces and guides , refit the covers and then the eyepieces.

Unless the prism faces are very dusty or smeared I always resist cleaning them as this can make the situation worse unless you use the right materials and cleaners.

Be careful not to get the grease from inside the eyepiece guides and cental focussing screw on your hands or on the bins.

If you have found this useful I will do some more as and when I buy more binoculars.

Paul

[NGC 1502]

Hi Paul, thanks for that info. I'm going to try this with some Zeiss 8 x 30s that

I inherited from my Dad. He must have dropped them at some time as they are

definitely out of collimation.

I knew that the popular 15 x 70 bins have external collimation screws ( under the

rubber skin ) but didn't know about internal screws on other bins. I've got

nothing to lose, they have been lurking in a cupboard for several years.

Thanks, Ed.