Barlow lens for Nikon Fieldscope ED82A (also applies to ED82, ED78 etc.) (1 Viewer)

[Beyond Swarovski]

I am the happy owner (mixed use - birds, astronomy, distant scenery) of the following spotting scope and accessories -

Nikon Fieldscope 82A (approx. FL = 520mm, f6.3)

Nikon Eyepieces (apparent angular field of view; approx. FL)
Standard:
25x (55°; 21mm)
Wide-field:
30x (64°; 17mm)
38x (64°; 14mm)
50x (64°; 10mm)
75x (64°; 7mm)

I have one use in bright illumination where a higher (say a further 2x, so 150x) magnification would be very useful and a narrow real angular field of view unproblematic.

I believe the only way to accomplish this is with a Barlow lens.

What could I use with the above setup that would fit?

Thanks.

 

[jring]

Hi,

first of all, welcome to birdforum!

Unfortunately I am not aware of a barlow lens or 3.5mm EP fitting the Nikon fieldscope classic series and due to the narrow EP mount, adaptions are not easy.

You could help by measuring the EP mount thread and protruding barrel diameter and length - this might help finding sth that fits...

Joachim

 

[Beyond Swarovski]

Thanks.

By classic Nikon fieldscopes, I believe you mean the immediate predecessors to the bayonet-fit ED85 - i.e., the ED82 series (mine) and the ED78, ED60 and ED50.

As you know, the EP mount diameter is 1.25" (31.8mm)

Measuring from the front of the fieldscope EP mount inwards, 10-11mm in there is a baffle. The diameter of the baffle's circular aperture is 23mm. There is no way to remove it; it is integral to the moulding of the instrument.

The rears of all except the 25x Nikon EP are narrow and poke through this hole in the baffle.

I think the complication to do with fitting is entirely to do with this baffle. Are these the measurements you wanted?

 

[Binastro]

A 4mm orthoscopic eyepiece in 24.5mm or 0.965 inch barrel might work if the barrel is removed.

But some of these use thorium glass in the rear element.
A small glass filter will stop any alpha particles or glasses, but the eye relief is minimal so the field will be small.

There are 24.5mm Barlows. Maybe a new 23mm barrel can be made by any workshop with a lathe.

The microscope standard diameter is 23.2mm.

I am not sure if microscope eyepieces are available in short focal lengths.

The Clave 3mm might work if the 1.25 inch barrel is removed. A Plossl eyepiece.

Regards,
B.

 

[Binastro]

I looked for my 24.5mm Barlow but couldn't find it.

I notice, though, that 23.2mm microscope 2x Barlows cost £1.33 to a maximum of £15.
Most around £5 to £7 some noted all aluminium barrels.

The magnification of a Barlow depends on position, so I think one could get 3x out of a 2x Barlow.

I think that 10mm microscope eyepieces are available, but I don't know the shortest ones made in 23.2mm fit.

Some are quite high quality.

Regards,
B.

 

[Binastro]

Some of the cheap Barlows in different fittings have only one lens element.

I think that one needs to look for an achromatic Barlow with two lens elements.

There are also three element Barlows.

In 1.25 inch fit they go up to 5x.

There are variable 2x to 3x Barlows with an extra tube where needed.

There is a British firm, SRB Griturn, Dunstable, that makes such items to order.

They would make a sub 23mm unit to order, or could reduce a 23.2mm item slightly.

B.

P.S.
Also SRB Photographic.

 

[Tringa45]

Hi,

I'm doubtful that a magnification of 150x would offer any benefits in an 82 mm scope, certainly not terrestrially, where a 0,5 mm exit pupil would severely diminish brightness and degrade the performance of your observing eye.
Additionally, the scope may not achieve infinity focus with a barlow: Birding Scope plus Barlow..
Small monoculars all have very narrow AFoVs but would work as a booster and provide some flexibility with your selection of eyepieces.
I once had an excellent view of Jupiter at 90x in my 65 mm Swaro using a 3x12 Zeiss mono.
The Zeiss now costs €490 but you might find something suitable from Specwell.

John

 

[Beyond Swarovski]

Thank you. Time for me now to research and contact.

 

[Binastro]

SRB Griturn seems to have become a much bigger operation, but I am sure they still do small jobs,

I have bought many adapters from them, mainly to use lenses from one make on another makers body.

The most interesting was an old Canon FD adapter on Minolta or Sony bodies.

I got a new or as new Sigma 300mm f/2.8 lens for £100 and a Canon 500mm f/8 FD mirror for £50 as well as a canon FD 2x teleconverter for about £10.
These are all about 10% of new cost.
The Sigma lens has a manual iris etc. and is very good.
The shops thought these FD lenses are useless.
Also a Canon 50mm f/1.2 lens for £6.

If I bought any of the Nikon, Kowa or Swarovski scopes around 78mm to 88mm aperture, I would be most peeved if I couldn't use them at 120x and hopefully 150x.
Either here terrestrially or for astronomy.

Just because some don't like 0.5mm exit pupils this does not apply to all observers.

I think that in the case of the original question one should aim for 120x, which should be fine in bright daylight with the Sun behind or to the side.
A really good scope should be O.K. at 150x.

An astro scope of this size should be good at 180x, if one has a very sturdy mount.

Whether the Nikon scopes allow the use of thin Barlows, I don't know.

Regards,
B.

 

[Alexis Powell]

Depending on what you are needing to do, an easier alternative might be to use a 2x or 3x magnifier (e.g. Swarovski 2x doubler, Eagle Optics 2.5x Universal Eyepiece Extender, Zeiss 3x12 monocular for binocular) as a "booster" with your 50x or 75x.

--AP

 

[Hermann]

Depending on what you are needing to do, an easier alternative might be to use a 2x or 3x magnifier (e.g. Swarovski 2x doubler, Eagle Optics 2.5x Universal Eyepiece Extender, Zeiss 3x12 monocular for binocular) as a "booster" with your 50x or 75x.

I personally like the Zeiss 3x12 Mono a lot. Works really well for a quick view at high magnification. A good combination is the Zeiss Mono with the 16x/24x/30x MC eyepiece, one of the Zeiss adaptors fits nicely into the eyecup.

Hermann

 

[GrumpyBuzzard]

Missed out on a 3 x 12 Zeiss a while ago and regretted it.

How did this experiment end up?

 

[Hermann]

Missed out on a 3 x 12 Zeiss a while ago and regretted it.

How did this experiment end up?

What experiment? I've been using the Zeiss 3x12 for years and years now as a booster.

Hermann

 

[GrumpyBuzzard]

OP was talking about a Barlow option for his Nikon spotter.