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Prof. Zarenski Writes the "Book" on Binos

Started by Milt, 02/27/2003 11:25AM
Posted 02/27/2003 11:25AM Opening Post
Hi Ed,

I have just finished reading your 'Comprehensive Comparison' report on CloudyNights and congratulate you on a job well done. The strength of your article extends far beyond the bino comparison, providing the best description of methodology I have seen. Before anyone buys another binocular of any size or type for astronomy, they should go to and read your report!

IMO, the most significant aspect is that you confirmed Mr. Adler's performance index with quantitative measurements. I don't know how many threads I have read on this subject, but the arguments were always qualitative "I feel this way" or "I believe that." You have hopefully laid the matter to rest with definitive star counts. But you didn't stop there; your (-)10%, 0, (+)10% corrections for coating and baffle quality is a worthwhile improvement that helps to integrate Nikons, Fujinons, Kowas and Takahashis into the mix. Bravo.

Your point is well taken that magnification is so low in binos that the limiting magnitude and maximum resolution abilities of the objective lens cannot be reached. Consider this: if you used the 50x per inch of aperture rule, you would end up with 0.5mm exit pupils. Not much chance of simultaneously aligning both eyes to those!

In your eye relief discussions, the eyecup function really caught my eye . The more I have used my Canon IS', the more aggravating the 48mm OD eyecups have become because they rub the bridge of my nose. I much prefer the smaller diameter eyecups of my telescope EP's.

There is one minor caveat that could be placed on your focal ratio calculation: I think it only works if you have a single objective system like a closely spaced doublet. An example of a binocular with a negative (diverging) lens buried back in the tube is the Vixen BT80. If you calculate based on the light path length, it should be an f/5.5, but is actually an f/11. My TV101 scope has a second positive (converging) doublet, has the tube length of an f/8.5, but is really an f/5.4. As far as I know, your calculation should work fine for all fixed-mag binos.

I liked your common sense approach to evaluating coatings. Also the clear explanation of the difference between field sharpness and flatness, a distinction that I had missed! The use of tight (for binos) doubles to check edge sharpness is great, and your TFOV chart with various star spacings will come in very handy.

We'll have to start calling you professor!

Clear skies, Milt
Posted 02/27/2003 07:00PM #1
Thank you Milt. Comments gratefully accepted.

I think the reason we visit sites like these is to engage in information sharing. You might have noticed that a few paragrahs in the articles had their beginnings here in the Forum.

I've found that I can share a wealth of information by writing articles and CloudyNights provides me the forum to share that level and breadth of detail. I hope your endorsement and others comments lead more to benefit from my efforts.

I hope you all find my efforts worthwhile.

Clear Skies, and if not, Cloudy Nights.