Telescope Reviews: Small Binocular Reports: Part II

Hi Mardi,

good question, one that has been discussed before. Let me adress what I think is the easy part first.

I think handheld resolution is a combination of normal resolution and the comfortable abitlity to hold a binocular without it moving. I notice some fit well and some dampen well. Some just don't seem to be easy to handhold.

We've had numerous discussions about the differences between normal resolution and boosted resolution. There are differing opinons about which holds more weight. I'm of the opinion that in a binocular, since in normal use it will never be used at boosted power, that normal resolution holds far more weight.

The other school of thought is that boosted resolution is showing potential aberrations in the system, such as spherical aberration or astigmatism, aberrations that could show up in the on-axis image. These might not be seen in the normal power test. The thought is, test for maximum potential resolution in the system, even if it can't be seen at normal power, for even if you think you can't see it, it may add to or detract from the image. Frankly, I put a lot more weight in what I really see in the image at normal power.

It is very possible that some of these binoculars that have really poor boosted resolution do indeed have some aberrations in the system that show up at higher magnification. But if they are not seen at normal power, then IMO, there is no reason to make much issue out of it. So, while I perform the boosted resolution test, and I do see anomolies in some binoculars, I give little weight to boosted resolution. However, I do not lose sight of the fact that aberrations in the system may be potential contrast reducers, so I do give some count to boosted resolution.

Most important, in my opinion, is the normal resolution value multiplied by the actual magnification to a get a reading of apparent resolution. In this way all binoculars can be compared to each other. Straight readings unadjusted cannot be compared across a range of binoculars of varying magnification. Apparent resolution values can be compared.

The other school of thought suggests that normal resolution is controlled by the eye, so the eye is the limiting factor. That is a strong reason to suggest using boosted resolution, to get it beyond having the eye be the limiting factor. However, if you look closely at ALL the data for all 34 binoculars ( you won't get to see that trend in the smaller reports), you can see that normal power resolution varies considerably across a range, from a best of 76 arcseconds apparent (a 7x binocular could see 10.8 arcseconds) to a worst of 97 arcseconds (more than one 10x binocular could see only 9.7 arcseconds), a variation of about 25% from top to bottom of the range. Therefore, IMO, at least across this broad selection of 34 binoculars, the eye is not the limiting factor. Typical very good normal resolution falls in a range of about 82 to 90 arcseconds. Four or five out of 34 bested that 82 mark; this leads me to believe that the eye is NOT the limiting factor in normal resolution reading, at least in this case not for about 30 out of 34 of my binoculars. Seven or eight were worse than that range, in the low to high 90s.

One more factor to consider re normal vs boosted resolution. Depending on the outdoor daylight pupil of the eye, since binocular pupils range from about 4mm to about 7mm, the tester, with perhaps a 3mm to 4mm eye pupil, in some cases is not using the entire aperture in the normal resolution test. In the boosted test all the aperture is always used, since pupils are on the order of 1mm to 0.8mm. Normal power tests that are not using the entire aperture may give a better result than might be indicated by the boosted resolution test. FWIW, I sorted my data several different ways and found almost always the largest percentage of best normal/ best boosted and worst normal/worst boosted corellated, regardless of how much exit pupil was used in the normal test.

edz

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