Kowa TSN-14WD eyepiece on the TSN-773? (1 Viewer)

[Peregrine Took]

I know it's designed for the Kowa TSN-663, but can anyone tell me what magnification you get from this eyepiece on a Kowa TSN-773, with the appropriate adapter?

And if you've actually tried it, is it a worthy, or otherwise, addition to the 20-60 zoom for the 773?

Thanks.

 

[jring]

Hi,

the 770 and 880 series have a focal length of 500mm or so, the TSN-14WD has 14mm (hence the name). So you should expect 36x and it will be a lot wider at that magnification than the 20-60x zoom.

Joachim

 

[Peregrine Took]

Thank you Joachim. I'm not entirely sure it's worth buying for the 773, because I really don't find anything lacking in the 25-60x zoom. But I tried the 14WD today on the 663 and it is a great eyepiece for that scope (as it was designed to be), with a much wider FOV compared to the standard 20-60 zoom.
..

 

[jring]

Hi,

if you have the 25-60x wide zoom, the difference is not big. I thought you had the old 20-60x narrow zoom (now discontinued) that the 880 series was started with back in the days... which is similar to the 20-60x zoom for the small body scopes.

Joachim

 

[BoldenEagle]

I have the TSN-14WD eyepiece, wich I use with an adapter to fit 883 scope. I have never looked through 773.

Compared to the TE-11WZ (25-60x) it has more lateral CA at the edges, maybe a bit more distortion, but significantly longer eye relief (25-60x is a bit tight [for me at least] but just ok). TSN-14WD is maybe a little wider than the TE-11WZ @~36x, no big difference though. In general it offers very relaxed and easy view even with eye glasses.

So if you don't use eye glasses and 25-60x offers enough eye relief, I think there is little or nothing to gain from the TSN-14WD, as the zoom is about as wide, has less CA and of course is more versatile.

Regards,

Juhani

 

[Peregrine Took]

Can I ask you guys, if you could recommend a specific fixed eyepiece for the Kowa 773 to give me a wider FOV than the Kowa 25-60 at 25x, with magnification of about 15-18x. I'd just like to consider a fixed eyepiece to give a wider FOV for viewing the bird feeder; 25x is a big leap from my previous scope that started at 15x and I'd like to see a bit more of what's going on around the feeder, as birds move in.

I read a lot about astro eyepieces for field scopes, but I'm never too sure if people are discussing them for astro or field work.

Thanks.
.

 

[jring]

Hi,

there is no optical difference between astro and spotting scope EPs. The spotter EPs are often weather sealed themselves and also seal the bayonet
and you can immerse the whole setup in water without ill effects... or so the manufacturers say... we have seen different results...

For the 883 there are multiple threads on CN about which astro EPs work and which are good - chances are good that they will also work on the 773. There are two parameters to look out for - and the obvious one, 2" astro EPs will not work...

- focal plane - spotters have very limited focus travel as compared to most astro refractors. Often EPs don't reach infinity focus due to the focal plane being too far out. Baader offers two different adapters, one with knurled screws and one with grub screws. The latter offers more infocus and thus will often mean that an EP which doesn't quite reach infinity in the other will work....

- field stop diameter - 1.25" astro EPs can have a field stop diameter of around 27mm - which limits the true field of view. This is what the usual suspects for widest field in a 1.25" EPs, the Televue Panoptic 24mm or its cheaper clone from Explore Scientific, the 24mm 68 deg or some 30-32mm Ploessls, have...
The problem is that the Kowa prisms allow for a maximum field stop of 23.45mm before the prims will vignette the exit pupil. If you can live with some part of the exit pupil cut off, then those will be your best bet - otherwise look for sth. with a 23mm field stop diameter...

Joachim

 

[Peregrine Took]

Wow, Joachim, thank you so much for that! I've learned a lot.

It seems I'm asking too much of the scope itself, to expect a wide field of view, without vignetting, at the sort of low magnification that would achieve what I'm after. This is probably why Kowa designed the 25-60x EP... as the optimum eyepiece for the scope.

I'm more than happy to accept that it's not possible to have 15-60x, given that the question was really a speculative one - and that in all practical respects I find the scope perfect and a joy to use.

It was wet all day here, but I have an upstairs window that is sheltered from wind and rain and gives a great vantage point for my main bird feeder. The view through the Kowa is so immersive, it was a joy to observe even everyday birds in such detail and clarity... as a step up from a 60mm scope, the Kowa is like a window into another world, it really does feel like that.

Thanks again for the time you've taken to explain these things.
.

 

[jring]

Hi,

I have looked up the true field of the 25-60x zoom and it is 2.4 - 1.32 deg on the 880 and 770 series. This converts to a field stop diameter of 20.9mm (tfov in deg = field stop diameter in mm / 57.2958).
So you could get up to almost 2.7 deg with an eyepiece with the maximum 23.45mm field stop diameter (if that value as found by some cloudynights reader is correct).

You could try with a cheap 30 or 32mm Ploessl (which will result in 16 or 17x and most probably vignetting) and then stop it down from 27mm to 23.45 or whatever is necessary to stop vignetting.

Joachim

 

[Peregrine Took]

Thanks Joachim. A cheap Plossl and the Kowa adapter would be an inexpensive way to scratch the itch.