Fixed or Zoom Eyepiece (2 Viewers)

[btooze]

I have an Opticron IS 60 ED WP field scope with a HR2 16-48x zoom eyepiece.

In use, the eyepiece is normally used at the lower magnification ranges as the image darkens at higher magnifications.

I would like to know if a fixed magnification eyepiece (e.g. 25x) will give a better quality image than a zoom eyepiece set to the equivalent magnification (i.e. 25x).

How may birders prefer a fixed over a zoom eyepiece and what is considered to be a good magnification for birding?

Regards,
Brian

 

[AlanTh]

Thank you for posting the question. This is something that I am interested in learning. Looking forward to replies.

 

[Keith Dickinson]

Because a fixed eyepiece has fewer components (normally) than a zoom eyepiece there will always be a difference between them optically when compared at the same magnification. There will also be a difference in fixed eyepieces if you increase the magnification, higher mag = darker image.
I used to use a Kowa scope with 2 fixed eyepieces, 32x and 50x, there was a noticeable difference between them in terms of image brightness and quality.
I now use an Opticron ES80 with the SDLv1 zoom eyepiece and still notice a drop off in brightness as you get up towards 60x magnification but as I never use that mag for normal viewing it matters little to me.

 

[AlanTh]

Thanks for the reply Keith.

So for us that have a zoom eyepiece, there is no advantage in getting a "mid range" fixed eyepiece?

 

[Keith Dickinson]

If you are using a mag of about 30x then stick with it, you'll probably not be happy with a zoom.

If you are a digiscoper then maybe a zoom is the way to go, then you can crank down the mag for digiscoping and crank up for watching.

 

[btooze]

Thank you Keith for your assistance.
I think that I will have to compare my current zoom eyepiece with either a 20xWA or a 25xWA to see what suits my needs the best.
Does anyone have any suggestions what would be the best match for my scope (20x or 25x). Also what does the WA stand for, is it Wide Angle?

 

[normjackson]

I suspect in early zoom eyepieces their performance at high magnification could compromise definition in a good scope (I'm thinking of the excellent Kowa TSN-3/4 scopes being able to perform better at 60x magnification than the early 20-60 zoom eyepieces allowed.). But zooms have improved in all areas and the main shortcoming folks find with good quality zoom eyepieces these days is a narrower field of view, particularly at the low power end.

Anyone who uses 20x or 30x power a lot will probably enjoy using a fixed wide angle eyepiece more. Those who make use of higher power regularly (viewing on estuaries being a typical example) would tend to get more use from a zoom (scanning or finding targets on low power and then zooming in). The other point already made is that viewing at high power demands more light to maintain brightness and contrast in the image; that is why those who regularly need the higher magnification in different light levels are prepared to put up with a bigger, heavier scope with a larger objective lens.

 

[njlarsen]

When I bought my IS60, I actually did have the dealer put on a fixed eyepiece on the scope (not certain, but one of the 20 or 24 mm eyepieces mentioned earlier in the thread). I was surprised how little difference it really gave relative to the zoom that was intended as the default eyepiece, so I went with the zoom and have been happy with it. You need a different scope to really get a lot better output of light.

Niels