Author Topic: Zeiss 10x25BT  (Read 534 times)

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Offline Buckfever

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Zeiss 10x25BT
« on: February 25, 2005, 05:23:08 PM »
Guys these are very good lightweight binoculars, however they are not very good at twilight!  How big do I have to go in size and weight to have good dawn and dusk performance?  I am going to keep the one's I have because they are just great for everything else.  Like keeping track of nephews and nieces in the canoe on the other side of a small lake.  I don't know mush about binoculars however I am looking to get acceptable performance without carrying around a heavyweight pair.  Thanks for the Help!  Buckfever

Offline Naphtali

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Zeiss 10x25BT
« Reply #1 on: February 27, 2005, 07:47:21 AM »
Buckfever:

This is an excellent question. Let's assume that you have spent more than about $300 for your binocular. Your optics should probably be as good as any. My experience is that investing large numbers of dollars for best-quality binocular insures durability -- barrels' alignment, water resistance, warranty, scratch resistant lenses, roof prisms -- rather than lens quality.

You have two contrary factors (NOT contradictory) to consider: twilight factor; and exit pupil diameter. Without investing pages of text, twilight factor weights magnification -- the higher the magnification, the better you can view something regardless of how much available light there is. Exit pupil diameter weights the ratio of ocular lens to objective lens -- the higher the [ratio] number the more available light reaches your eye.

You have butted against one of the kickers. If the exit pupil diameter is too small, you cannot see your target well in low light. And it won't matter how good your optics are.

The other kicker is that the human eye's pupil has a maximum dilation of about 5 mm. As you age, this number drops to about 3.75 mm after you're 40-some-odd.

And when you use a binocular having large (40+ mm) objective lens with 7 or 8 powers of magnification, the binocular tends to be BIG and usually HEAVY. Investing more money to buy roof prism binocular tends to reduce the bulk and weight. It also reduces the stereoptic effect of the binocular barrels. Your depth of view is less.
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Having wasted thousands upon thousands of dollars buying best-quality binoculars that fuctioned perfectly but were unsatisfactory on hunting trips, I have the perfect solution to YOUR PROBLEM from my point of view.

I use Zeiss 8x30 B/GA IF Olive binocular with F2 range finder in right barrel; objective and ocular lens covers; and Zeiss snow filters. Total weight is less than 25 ounces. Notice the exit pupil is 3.75 mm.

This is not the smallest or lightest or the easiest to use binocular. They were first manufactured in 1964 for NATO service, then became commercially available. They have individually focusing eye pieces -- more durable than center focusing but slower. This is not a problem if you think about what distances you intend using your binocular.

Other binoculars I have used that were nearly as effective include: Leitz Trinovid 6x24s, in the Midwest; Leitz Trinovid 7x35s.

The reason I always buy a best-quality binocular is that when you're out in the field, having a back-up binocular in camp is useless. You invest nearly all your time (Rocky Mountain and Cascades Mountains west) looking through your binocular. All this time your binocular is the most important tool you have. If it fails, you're through.

My experience is that binoculars using Schott optical glass are more scratch resistant than others. Schott is a German company. Zeiss, Leica, and some other European manufacturers use Schott glass.

Japanese manufacturers do not use Schott glass. The quality of the glass and grind appears to be excellent in best-quality binoculars -- comparable to best-quality European binoculars.
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I would never consider anything made in Red China. Not only will it be made for a budget, I refuse to buy from a place that uses slave labor, where no technician in this country would want to work. I'll back my prejudice with the few extra dollars difference.
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Differences I think I detect become noticeable after several years of use. And please note that I cannot confirm this difference via rigorous testing. This is anecdotal -- my experience plus perhaps three dozen others over the past 15 years.

Were I on a budget, I would look at porro prism binoculars before roof prisms. I would also look at recent military surplus binoculars. 8x30s made, say, after 1985 might be an excellent solution.

One final thing, Zeiss discontinued distribution my binocular in 2001, I believe. They are available only in Europe now.

Hope this helps.
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Offline Cement Man

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Zeiss 10x25BT
« Reply #2 on: February 27, 2005, 08:38:50 AM »
That was a great reply from Naphtali.  I learned from it and appreciate the knowledge that can be gleaned here.  Optics can be very challenging and a lot of performance and quality issues are relative.  There is a website called "better view desired", written primarily for bird watchers; however, lots of very good information on binocs.  Goood shootin'  :-)
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Offline Buckfever

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« Reply #3 on: February 28, 2005, 05:06:42 AM »
Thank You for one of the best reply's I seen on this board!   Buckfever

Offline Naphtali

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« Reply #4 on: March 01, 2005, 04:01:09 AM »
While the information is essentially correct, The calculations are "twilight factor" and "relative brightness." Relative brightness must include factoring binocular's magnification also.

Where was my head????

My 8x30 B/GA IF Olive (ClassiC), while available only in Europe now, can be specially ordered via Zeiss-USA Customer Service.
In a time of universal deceit, telling the truth is a revolutionary act. George Orwell

Offline ranburr

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Zeiss 10x25BT
« Reply #5 on: March 06, 2005, 05:53:09 PM »
I have to disagree with the previous post that there is not a difference in the quality of the glass at prices above $300.00.  Nothing could be further from the truth.  There are different kinds and grades of glass available from companies like Schott.  (Incidentally, Schott is an Austrian company that is owned by Zeiss.  They do have locations in Germany, but they have factories all over the world including the U.S.).  The quality of the glass is directly reflected in the price and quality of the binos.  Hi-grade Flourite and ED glass will cost substantially more than lower-end glass.  The view will also be substantially better also.  And, just because a bino has a German sounding name, does not mean that the Glass is from europe.  Japanes glass from places like Ohare can be just as good.  Don't get wrapped up in where the glass come from.  I think good binos start at about $500.00 and price is usually a direct indicator of quality.  I don't like pocket binos.  If you must use them do not get a magnification higher tha 8X.  I would look at roof prisms at around the 8x32/33 level.  This will allow you to keep things relatively small, which porros are not.  The roofs are much tougher, smaller, lighter and waterproof.  The offerings from Minox, Kahles, and Pentax SPs are a very good balance between cost and quality.  You really have to step up to the big three and their big prices to see a significant improvement in quality.

ranburr