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This is a weird eyepiece.


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Just stumbled upon this weird eyepiece.






A Vixen 100mm eyepiece. You don't get many eyepieces in this focal length.


In my scope:


Magnification will be X 8.4

Exit pupil will be 15mm

TFOV will be 6.8°

Field stop will be 96mm in diameter



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Very weird! Not seen that one before.


4500 yen is about £30.00


You're right about the 8.4x magnification Mick, but the field stop can't be more than about 28mm as is says it is in a 31.7mm barrel. This would give it an apparent FOV of only about 16 degrees and a True FOV of just under 2 degrees! Why would they choose a 1.25" barrel? It really would be like looking through a straw. :)

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I got those figures from a eyepiece calculator website Pete. It is a strange one, I cannot really imagine why they would make it, but for £30 might be worth a punt.

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That ep calculator obviously didn't want to work with those weird numbers. You can't put a 96mm field stop inside a 31.7mm barrel. :)


I can't see what use it would be in 1.25" format. All the other ~100 mm plus eps I've seen are in much bigger barrels. Siebert do some long focal lengths in up to 4.7" barrels!

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Just got google to translate the Japanese text...


It's easy even for beginners! You can quickly find the objects you want to see!
No need to adjust the viewfinder to replace the eyepiece. It can be used immediately without troublesome optical axis alignment.

Features of the Vixen Astronomical Telescope Finder Eyepiece 100
Eyepiece type finder
It is a simple eyepiece with a focal length of 100 mm. It is equipped with a crosshair and can be used as a viewfinder by replacing it with an observation eyepiece. Since the focal length is long, low magnification can be obtained and a wide range that can be used as a viewfinder can be seen.
When used for a telescope with a focal length of 600 mm
Magnification = focal length of telescope 600 ÷ focal length of finder eyepiece 100 = 6 times

No adjustment required
Since it is replaced with an eyepiece lens, it is difficult for beginners to use the optical axis of the viewfinder without difficulty, and can be used immediately. After putting the target on the crosshair, replace it with the observation eyepiece and adjust the focus and observe.

Compare products
Viewfinder Eyepiece 100

Focal length 100 mm
Mounting eyepiece diameter 31.7 mm
Size Φ 50 × length 186 mm
Weight 180g
* Please contact directly to each dealer or mail-order site for arrival / stock check of the products that you wish to purchase.
※ Specifications and appearance may be changed without prior notice for improvement.

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The £30 price for a 'Vixen' product says it all......

Edited by Bino-viewer
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