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ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia

Low Magnifications and Large Exit Pupils on Birding Scopes (1 Viewer)

Tringa45

Well-known member
Europe
The following should be considered a diversion rather than a recommendation. The whole purpose of scopes is to provide magnification so trying to achieve the minimum magnification would seem to be a pointless exercise, at least for terrestrial use.

I recall that several years ago a birdforum member wanted to observe animals at dusk at the end of his garden and a scope permanently trained on a garden feeder might be another application. However, low magnifications can be visually appealing, just as they are in binoculars, e.g. 7x42.

I don't own an astronomical scope and neither do I know my way around the night sky very well, but have nevertheless acquired a few astro eyepieces for use with my Swaro ATM 65HD and Kowa 883 for occasional looks at the moon, planets and the Mercury transit in 2016.

One often sees comments on birdforum from members wishing to improve on the performance of their scopes with astro eyepieces, but I think that in general that is a vain hope. I see field curvature and pincussion distortion through all my astro eyepieces and in this respect, none of them can compete with the 30x wide on the Swaro or the 25-50x TE11WZ on the Kowa. The eyepieces are tailored to the scopes and probably use a Smyth lens to correct for field curvature.

All waterproof birding scopes have a plain glass window in the body to retain the nitrogen filling. On the Swaro this has a diameter of 26 mm and on the Kowa 24 mm, so it would not make sense using astro eyepieces with larger field stops such as a 32 mm Plössl or 24 mm Panoptic (both 27 mm), which have the maximum available field stops with a 1 1/4" barrel.

Enthusiastic reports on "Cloudy Nights" encouraged me to buy a 28 mm Edmund Optics RKE, which has a 23 mm field stop and should not vignette significantly. It's a simple triplet with single coatings (espoused by some, including Brandon to offer some advantages) and a mere 45° AFOV. The eye lens is 25 mm in diameter so with 21 mm of eye relief the slim eyepiece mount seems to disappear and the image just floats in space. On the Swaro it gives 16,5x magnification with a 4 mm exit pupil and on the Kowa, 18x with a 5 mm exit pupil. Particularly on the latter, the brightness and contrast are absolutely outstanding.

I expect anyone with an astro adapter for his scope and a long FL eyepiece has already tried this. Otherwise forget it. Eyepiece collecting is a really pointless addiction!

John
 

Boogieshrew

Well-known member
I am a big fan of 7x binoculars and I have never liked zoom EPs on scopes. I much prefer fixed EPs on all the scopes I have owned. My eyes are totally comfortable up to around 24x. They happy up to 30x but 24x is the best balance of msg and eye comfort.
My latest scope is a Nikon EDG 65 and I have been using the 16x ep on it most of the time. It is not just comfortable, it is a joy to use. No effort to use for long periods and sooooo wide a fov. And i can ID everything I see with it, even in wide open marshes. If anything distant intrigued me I can quickly swap to 24x or 16-48 zoom.
There is a lot to be said for low mag EPs.
If there was a wide zoom at 15-30x that might divert me from fixed EPs but I haven't seen one yet.
 

Ian Byrnes

Well-known member
Agree and disagree about improving performance .... I have an Opticron 665 with 24 & 38 Fixed EP's which is Very acceptable but limiting. I also have a Zeiss Diascope 85 T*FL with a 20-75 zoom. The image and comfort through the zoom is excellent..... But what actually makes it much more comfortable is attaching your IPhone (phonescoping) and not just photographing but using the phone as your image screen.... Once you eliminate the vignetting you can stand back, scan the horizon and take it all in at great or lesser magnification without having to glue your eye to the eyepiece. It gives you the opportunity to keep checking for birds with your binoculars and then pan your scope to your next capture. Admittedly this zoom needs very little focusing once set up. Not quite what you were getting at but it works for me.
 

Alexis Powell

Natural history enthusiast
United States
...you can stand back, scan the horizon and take it all in at great or lesser magnification without having to glue your eye to the eyepiece...

I feel the same way about using straight scopes. Keeping both eyes open, I can shift my attention to the scope view or the whole view, inserting the scope as desired but keeping my vision directed at the big wide world. Angled scope users spend a lot of time looking at the ground inadvertently.

--AP
 

Ian Byrnes

Well-known member
I feel the same way about using straight scopes. Keeping both eyes open, I can shift my attention to the scope view or the whole view, inserting the scope as desired but keeping my vision directed at the big wide world. Angled scope users spend a lot of time looking at the ground inadvertently.

--AP
My Diascope is a straight but I can't master the 2 eye vision, I get distracted that's why having the phone screen is good sometimes ......it's like watching a live film, although glare does get in the way on bright days.
 

CMB

Well-known member
If you use a spotting scope that is built to work natively with astronomy eyepieces (no adapters required) you can get very high optical quality. Unfortunately there are not many options out there.

We use Pentax angled scopes (80mm and 65mm with different focal lengths) with fixed Televue astronomy eyepieces (Delos and Delite lines) in order to get the 20mm eye relief needed for a family member. The eyepieces selected for each scope yields 36x. The optical quality is very high. The image is bright, flat, crisp edge to edge, and I see no vingetting. I don't see distortion or field curvature when panning the scopes. I am very sensitive to CA, and this combination is essentially CA free. (I say essentially because I have yet to find a bin or scope where I cannot induce some level of CA).

If you can learn to use a scope with both eyes open you get better image quality and it is a much more relaxing experience. Very seldom do I look through a scope with one eye closed.

We have Televue's phonescoping attachment that mounts directly to their eyepieces. I find that viewing through the phone doesn't work as well as viewing directly through the scope. My experience has been that viewing through the phone attached to the scope degrades the image quality and makes the image smaller. The image sensors on smartphones and digital cameras don't work as well as our eyes.

Chris
 
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PCreed

Member
Astronomical eyepieces can deliver amazingly-sharp images in spotting scopes, but there's a bit of mismatch in applications between the main hardware and the user interface.

Spotting scopes typically work best at 60X or less for most things, namely to keep the exit pupil decently-sized and the effect of tripod stability on vibrations. Bumping things up to 150X can be problematic on many easily-portable tripods, and those that ARE sturdy enough tend to be bulkier.

For lunar and planetary observing, high powers work better, typically 100X or more. The aperture of spotting scopes (small in the world of astronomy) will limit resolution to roughly 50X/inch or 2X/mm (Dawes Limit). While things like Saturn's rings only need ~50X or separate from the planet, fine details on Mars often require 200X or more.

--Phil
 
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
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