Posts Made By: Ed Zarenski

Malcolm,

As magnification increases the difference between what can be seen handheld vs mounted increases.

8x42s and 10x50s handheld (HH) can see stars about 0.4 to 0.5 mag less than when mounted. 15x70s HH can only see about 0.7 less than when mounted. The larger they get, the greater the difference. Unless you are certain you will sometimes mount these binoculars, I would not recommend anything over 12x.

You will see more with 15x70s HH vs 12x50 HH or 10x50 HH, but you will tire much more quickly, ending your viewing session sooner.

Few oportunities present themselves to use binoculars with 7mm exit pupils. Don't let aperture and large exit pupil take advantage of you. Get someone to measure your eyes dark adapted. If your eye pupil only dialates to 5mm than stick with a 5mm exit pupil. Otherwise, you are wasting aperture, and buying extra weight. 10x60 and 12x80 might be a waste.

edz

SO posts for sale a modified binocular that was a 10x50. By replacing with quality eyepieces of 26mm the binocular spec is now quoted as 6x50, but with better eye relief, sharpness and field flatness.

Keep in mind with a modified exit pupil of 8.33mm (50/6=8.33), for most people, depending on their maximum dilated pupil size which may range between 5mm and 7mm, this binocular will have an effective aperture of 40mm or less. While it will be extremely easy to hold the exit pupil in view, anywhere from 15% to 40% of the light will not enter the eye. This may not be very noticable on bright stars and will not affect sharpness or field flatness at all, but it will be a significant reduction on faint extended objects and stars at Limiting Magnitude.

Just the simple fact that magnification is reduced from 10x to 6x will lead to a decrease in Limiting Magnitude obtainable with this binocular, but in this case that loss will be even greater due to the loss of light from the oversized exit pupil.

Yes, it will be interesting to read reports on these.

edz

A good example might be the Celestron Skymaster series. In the 25x100 that I had, it looks to me like the objective is multicoated, but the prisms and eye lens are single coated.

edz

I knew I had something somewhere on coatings. I found it here.

http://www.cloudynights.com/ubbthreads/showthreaded.php?Cat=1,2,3,4,5,8,9,10&Number=206802&page=0&view=collapsed&sb=5&o=all&fpart=&vc=1&PHPSESSID=

edz

Well, Dawes limit is the most common referred to formula that most people are aware of for the calculation of some type of resolution, but it is not the basis for the measurement of angular resolution in optics. That is another of the mis-informations. Rayleigh Limit is the correct formula to use, as I described in detail above.

Dawes Limit is an empirical measure of the double stars that can be "seen" with a telscope, not resolved. In Dawes, you will always have overlap. Of course there will be those that can say, well if I can see it I have resolved it. But that would not be accurate. Seeing overlapped double stars, seeing resolved double stars and seeing an object that has not been enlarged by your telescope Airy disk are very different things.

NO object, no matter how small, can form an image in the telescope smaller than the Airy disk. Resolution is the determination of what size object can be seen to a dimension in the telescope image that is larger than the diameter of the central bright spot of the Airy disk. Any object smaller than that will be bloated up to the size of the Airy disk by nature of the telscope optics.

Dawes Limit has nothing to do with determining the size of the Airy disk in telescope optics, even yet another of the mis-informations spread on the internet and in text books.

And once again I will repeat, Rayleigh Limit is the radius of the Airy disk. Because only a percentage of the light is put into the central bright spot, you can see faint stars cleanly split at approx one half the diameter of the Airy disk, convieniently that is RL for faint stars. However you must double RL and calculate the diameter of the central bright spot to determine the size of a bright object that will form an image larger than the Airy disk. I gave a little more specific information in the previous post. see that post

edz

In those spa conditions, no binocular is going to be fog proof.

Be very careful about waterproof. That is a loosely used term. In some cases it means only that you can wash off your binoculars under running water. Others will hold out water at a depth of 1m or 2m for a time of 5 to 10 minutes. I would not trust ANY of those criteria if a binocular were dropped in HOT spa water. You should be fine holding it above the water.

Generally 10x is the maximum power for handheld. It varies a lot with the individual. Some people can hold 12x. Some claim to hold 15x and 20x. Don't believe those claims. While I won't dispute some few may be able to hold 15x steady, most would be seeing fireflies.

If you want higher magnification than 10x or 12x handheld, an IS binocular is the only way to go.

You mention Nikon 10x50s. The Nikon Action Extreme 10x50 or 12x50 is a pretty decent WP binocular. The Pentax PCF-WP 10x50 is a better binocular. all sell for between $150 to $189. The Canon 12x36 IS II (the newest model) is being talked about very well and is reported to nearly equal the performance of 50mm binoculars.

edz

Unless you have exclusively very dark skies, mag 5.5 or darker, I would not recomend any binocular with a 7mm exit pupil. In skies of mag 4.5 to 5, a 10x70 will act more like a 10x50. In mag 6 skies you will get more benefit from the 7mm exit pupil.

Also, before you consider a 7mm exit pupil, you should know the size of your own maximum dilated exit pupil. If your eye only gets to 6mm, then a 10x70 would never perform at more than 10x60 for you. If your eye never gets larger than 5mm, don't purchase anything larger than a 5mm exit pupil (10x50 or 12x60).

Other factors you absolutely must consider are, handheld or mounted, long eye relief or no glasses, star sweeping or detailed observation. Binoculars are not one size fits all, you've got some choices to make.

Some good binoculars in the under $200 price range Orion Ultraview 10x50 good, Nikon Action Extreme 10x50 good, Pentax PCF WP 10x50 better, Oberwerk Mariner 10x60 better. Nikon Action Extreme 12x50 good. All range about $139 to $179.

edz

Sorry I cannot comment on the Stellervue, I have not used them. Several come to mind, including Oberwerk 15x70s. However, I cannot help but think to recommend the Fujinon 16x70. Superior to most any binocular in it's size, rugged, sharp, but heavy at 4#12oz.

edz

I find it interesting that a search in the CloudyNights Feedback Forum does not turn up any reference to this question. Wouldn't you think if an individual had a question about a practice he would take it to the source to get an answer, before he would go elsewhere looking for a response? But anyway, I think Walter hit the nail on the head.

edz

I've not used any of the IS binoculars. The Canons will certainly provide for a still image, but that won't reduce the weight of the binocular you've got to hold to get that image. So the advantage of IS may just quickly go away when your arms get so tired from holding a heavy binocular.

Binoculars are not the instrument of choice for looking at planets. At 15x you will barely be able to see the separation of the rings from the disk of Saturn. You would be able to see the two main equatoral bands on Jupiter and the 4 moons will be obvious. You would be able to see Venus as a partial phase disk. At 12x, other than the moons, all of those things would probably not be visible. You need a 20x80 or better yet 25x100 binocular to see M57, the Ring nebula and even at that it's so small you would only just notice it as something that is not starlike. But, M31 the Andromeda galaxy can be seen very well even in a 10x50. There are plenty of other objects that CAN be seen in a 10x50, but to see most of the faint extended objects like galaxies you'll need dark skies, at least mag 5.

For use in mag 4 skies, stick with binoculars that have exit pupils of 5mm or smaller. Larger exit pupils give a brighter image. But in the case of observing in brighter skies all that will do is wash out the images you might see. A 12x50 might be a good chioce with a 4.2mm exit pupil, or a 10x40 with a 4mm exit pupil.

There are other choices I would consider along with the Canon IS as good first choice. I would go for something like a 10x50 or 11x56 if you plan to handhold. Maximum power for handheld 12x. However if you think you might do most of your viewing from a mount, then a 15x70 for $150 could be ideal. You could put a $150 15x70 on a $125 tripod and it would work really well.

As a first binocular, I would not go with anything less than a 4° field of view and I think it would be better to stay with 5°-6°.

edz