Question Please

I am not sure what to buy. I am moving for to a high floor apartment and I want to look out over long distances. I live right on lake Erie, but also I am an avid star gazer. At one time I build a 9.25C with a Losmandy Mount a few years back. So I love both types of viewing, terrestrial and astronomy. Money it tight but I have it narrowed down to two units. The Zhumell Tachyon 25x100 or Barska 30x80 x-trail. I read on cloudy nights a pretty decent review on the Barska. I giving up the 5x mag worth the +20mm gain in appature and light gain? I want to also look out at night out on the streets below and I wand I don't want to be nagged to much by a dim FOV, but I love the 30x.

Anything help here would be soo much appreciated. I need to decide here. Thank you SOO much)

Hi John- In my experience more than 20x starts to be bothered b y seeing conditions when looking at objects at ground level over long distances in daytime.
Regards
Keith Parizek

Hi John,

You have stated that you don't want to be nagged too much by a dim FOV, but you love the 30x.

If much of your viewing will be in the daytime, the image brightness will be determined by your eye pupil, not by the aperature of the binoculars. The useful daytime aperature can be determined by the magnification times your eye pupil which is probably about 2mm. At 30 power you can only use about 30 X 2mm = 60mm of objective in the daytime. At 25 power, this is somewhat smaller at 25 X 2mm = 50mm. This applies anytime there is enough light in the view to restrict your eyepupil and that includes any daytime use, any nightime use when you have lots of light around, or any time you are looking at a bright target such as the moon or a lighted billboard.

Large binoculars are really great for sweeping dark skies when your eyes are dark adapted and your eye pupil is opened up to 4-5mm. If you can't get these conditions, the large aperature never comes into use as I have stated above. So, if your viewing is not in dark conditions, the difference in aperature of the two binoculars you are looking at, should not be an issue.

Have you considered the value of a smaller scope such as an 80 - 100mm? One of these would allow you to change the eyepiece to obtain much higher powers as you want but still allow some pretty nice low power views if you should get dark conditions.

I have a 100mm F6 refractor that I use with a 32mm Erfle eyepiece that provides about 18X. I can just get all of Orion's belt in the field of view. Open clusters and star fields are excellent at this power. I use a 19mm eyepiece for 32X, and a 9mm for 66X. It is not a binocular but I decided for my purposes, the ability to change viewing power was more important than the binocular view.

Good luck,
dan

I have not tried either unit, but I think it comes down to
importance of day vs. night. If night is important, I would
get the 25x100. The 5x difference (25x vs 30x) is not very important
in terms of what detail you can see.