How to make a Focal Reducer

[Dragon Man]

I have been asked how did I make my Focal Reducer by some people during my broadcasts on NSN .

I keep saying I will do a tutorial but keep forgetting.

Today I made one and took pics as I did it so I can know show others how to do it.

The parts you will need:

- Cheap 35mm-40mm Binoculars (old busted ones are perfect)

- 2" to 1.25" Eyepiece Adaptor (almost everyone has at least 1)

- Super Glue

- Lens Cleaner

-Toothpick

STEP 1: 

Obtain cheap new, old, or broken 35mm - 40mm binoculars and remove 1 Primary lens (if an old binocular, pick the best lens)

[Dragon Man]

STEP 2:

Thoroughly Clean the lens on both sides

[Dragon Man]

STEP 3:

clean the surfaces of the 2" to 1.25" EP Adaptor

[Dragon Man]

Use a good lens cleaner. I like using Isopropyl Alcohol.

You will also need Super Glue.

[Dragon Man]

STEP 4:

Very sparingly put tiny droplets of Super Glue around the edge of the hole on the EP Adaptor.

Be very careful because if you put too much it will run under the glass and out onto the lens.

Less is best.

Then carefully spread it around the hole with something like a toothpick to get a fairly even spread and to stop blobs.

Don't go too slow or the toothpick will stick 

[Dragon Man]

STEP 5:

Very carefully place the lens, flat side down, onto the glue, making sure it is centred.

And that's it. You are done 

Even though it won't fall of within about 30 seconds, allow it to dry properly for about 30 minutes to be sure. 

[Dragon Man]

STEP 6:

Go use it and enjoy. 

[Dragon Man]

Before anyone asks, those 32mm binoculars in my 1st photo, yes the lens is actually 35mm. The clear aperture of the opening in the front of the binocular is only 32mm. The other 3mm is behind the rubber seal.

But if you have a 32mm lens it will still work if you are happy to glue only 1mm all the way round the edge. 

The lens has to be wider than the 1.25" opening (obviously   )

[hoops86]

Hahaha very nice DIY reducer job!

How the hell did you even work out that this can be done lol?

Also how do you know what amount of reduction it will give?

And would using the funky coloured coated lenses that most bins have still work or would it need to be clear like in your pics?

[johnno]

Nice one Ken, while your at it, can you turn my mak 127 into a C11 on the cheap.

[Dragon Man]

Hahaha very nice DIY reducer job!

How the hell did you even work out that this can be done lol?

Also how do you know what amount of reduction it will give?

And would using the funky coloured coated lenses that most bins have still work or would it need to be clear like in your pics?

Good questions Chris.

- I didn't work out how to do it. An Astrophotographer friend of mine (Bert van Donkelaar) is a world-leading Optics expert and he taught me how (he made my 1st one for me). Apparently it used to be common practice before FR's were easily available.

- Mathematics (which I am no good at). Bert told me this one is 0.7x Google may help here 

- The one I just used in the photo does have coatings. Not those strange bright yellow, blue or orange etc that they use on terrestrial Binocs, but proper Astronomy Coatings as found on good scopes and Astronomy Binocs (usually a UHTC coating).

The one in my photos is my favourite FR. I dropped it a few weeks back and the lens popped off, so I thought I would do a tutorial as I put it back together today.

[Dragon Man]

Nice one Ken, while your at it, can you turn my mak 127 into a C11 on the cheap.

Nothing a hacksaw, angle grinder and a welder won't fix 

[johnno]

[Joves]

Nice work, MacGyver!!

[jturner9]

Yes I do remember watching a Snake Valley show where the guy dropped the FR while we were watching.

Here is a small screen capture of him after he had done it.    

I think the show was titled BUTTER FINGERS.  

[Dragon Man]

Yes I do remember watching a Snake Valley show where the guy dropped the FR while we were watching.

Here is a small screen capture of him after he had done it.    

I think the show was titled BUTTER FINGERS.  

Yes Jim, I remember you were one of my viewers, laughing at me 

[Dragon Man]

Due to damage to my Focal Reducer (the one above) I made a new one, and this time I made a Video Tutorial of the whole process as I went along, so any one wanting to make one can see how it's done.

Here: http://www.youtube.com/watch?v=9l66Sch9PWY

[ronin]

Depending on where the prime focus from the scope sits in relation to the prime focal plane of the lens usd it could be a reducer, barlow or even an eyepiece.

[Dragon Man]

Depending on where the prime focus from the scope sits in relation to the prime focal plane of the lens usd it could be a reducer, barlow or even an eyepiece.

No, a Focal reducer cannot be used as a Barlow no matter where it is place in the optical path.

A Barlow is a Concave 'Negative' lens which increases the distance to the Focal point, therefore increasing Focal length.

A Focal reducer is a 'Positive' lens which consists of a Convex and a Flat lens and reduces the distance to the focal point, therefore reducing focal length.