ksbird/foxranch
Well-known member
A group of us were birding in the back pastures of the ranch on Friday evening, July 14. The temps had been brutally hot and were actually rising during the evening. The humidity is astounding back there because of the small marshy area where formally hibernating mini-frogs come out now, and then go back underground in a few short months, until the rains and heat wake them up again next year. It is a great fast food stop for larger birds like heron, egrets, gulls etc. We waited for the fireflies to come out at about 9pm although their numbers are greatly reduced from a month ago, all the more because I mowed some of the hay in that back pasture and the fireflies didn't have as many high perches to hold onto while they signaled their mating light show.
A 14 year old asked me what the "big bright star" in the sky was, slightly to the south and about 70 degrees up. Of course it was Jupiter. I said rather off-handedly that everyone should be able to see Jupiter as a clear disk with a number of very tiny pinpoints lined up straight on either side of it, and that those were Jupiter's moons. I was using well-sealed Tasco International 410 10x50 binoculars and there were 4 nice moons on display, with unusually subtle banding on Jupiter that night. There were a few oohs and aahs from 2 or 3 others in the group of 9 visiting tourists, but generally there was just allot of fussing with binoculars.
After a few family groups traded their binoculars around (the 14 yo was using a rented pair of our 8x30 Hensoldt DFs while her dad had rented Tasco 334BWs waterproof 7x50s, and mom had the family's Quest 9x32 roofers [Sorry but I don't know anything about these Quest binoculars]). Dad and daughter clearly saw Jupiter as a disk and the moons were more or less visible, although the 7x50s picked up an extra moon the 8x30s didn't. Mom saw Jupiter as a disc with a small spike coming out of it, and only one moon.
Eventually every other family passed me their binoculars to look through. Only one other family had binoculars that were able to see Jupiter as a distinct disk with banding and pinpoint moons strung out in a line. In this family dad had Zeiss 7x50 Marine BG*T porros and mom had Steiner 8x30 porros. Their son had Leica 10x40 roofers and the Leica had spikes coming off Jupiter that made it impossible to find the best focus, and those spikes obliterated the moons. A pair of Zeiss Dialyt roofers both had flares coming off of Jupiter that made the planet look more like a blob than a disk and the nearby moons weren't able to be distinguished. Other bins included the Canon 8x25 and 10x30 IS bins, a few pairs of Swift Audubons sold by the local bider suplly store and a few pairs of Bausch & Lomb 10x40s and Bushnell 8x42 Elites. All of these had spikes or flares that made it impossible to see Jupiter as a disk with moons, or Jupiter was so oval at best focus that no details could be seen and often the two ovals didn't orient the same way so they wouldn't line up to focus.
Everyone who brought their own bins had nice equipment. The rental stuff was all of reasonable quality and well collimated but not extraordinary. This test can't be considered extremely difficult but if your lens/prism/eyepiece alignment is off even slightly your binocular will have trouble. Jupiter is a bright little beacon with definite but subtle banding, and its moons are delicate little pinpoints. To see them both isn't really a challenge as much as it tests the binocular's condition and flare resistance. Some of the binoculars I looked through from Swift had 7 or 8 Jupiter ghosts floating around in the field of view due to internal reflections.
Jupiter will be up in the evening sky for some months now as the first "star" visible each evening and the brightest. Even a 7x binocular should resolve Jupiter's disk clearly and some 6x bins do it well also. ANY properly aligned binocular should show the 2 largest moons of Jupiter as long as they are not in front of or behind the planet. Even small exit pupil binoculars like 10x30s should have no problem with resolving Jupiter because it is so bright. The moons are more of a test for small exit pupils because they are not nearly as bright as Jupiter but if your bin is able to focus well for a super-sharp view, then I've viewed Jupiter's moons with 8x21s that are properly set up. The banding on Jupiter takes perfect color correction and enough brightness to show light colors.
More than half the people I "spring" this test on are disappointed no matter how expensive their binoculars are. Jupiter and its moons test many things. If your sharpness resolution is not good then Jupiters edges will be "soft" or wavy and the moons won't be visible because the tiny pinpoints of light won't resolve and their light will be diffuced over an area that is too large. If your color correction is poor then since Jupiter is so bright, it will have yellow or purple fringes that interfere with resolving it sharply and some of this "corona" may slop over onto the moons, also the bands on th planet won't show unless your color correction is true. If your coatings aren't good then Jupiter will have lots of glare and ghost images so it won't be a crisp disk. Poor internal baffling will produce allot of ghost Jupiter images in your view and unless they are movable by changing your position they can obscure Jupiter's moons. If your lens/prism/eyepiece alignment is not straight and true then you will get allot of spikes that will extend off Jupiter or Jupiter will look oval and the two images for left and right may not even have the same direction of "ovalness", so seeing anything with 2 eyes might be difficult. Since "glass" alignment is crucial for this test, zoom binoculars seem to fail more than other designs and in general roofers fail it much more often than porros.
If everything is "right" with your bins, then Jupiter is a sight to see. If you are in the countryside like we are, Jupiter is a sharp disk (slightly flattened on the top and bottom by its gravity, rotation and gaseous make-up, and the flatter top/bottom are usually visible with 15x+ bins.). The planet is usually banded and may even show its 2 spots. It's up against the black reaches of space, usually with a few dim stars floating behind it.
Birders knock their bins around quite a bit. Over time they don't notice how poorly aligned their equipment becomes. Even though most birders carefully clean the objective and eye lenses of their bins, they don't seem to send them out for internal cleaning and realignment of the glass parts often enough. I find the same is true of most spotting scopes we encounter here too, although a large percentage of Nikon Fieldscopes and Bushnell Spacemasters work well even after years of abuse. But straight line roof prism spotters seem to have a particularly hard time doing well on the "Jupiter Test" at low power. Higher magnifications seem to help with this test if you have 20x or more available, but it's no guarantee.
Try it yourself and see how well your bins do, and when the earth's moon returns it makes a fine test object as well (the full moon is especially good for testing color correction [CA]). It might help you understand why you have trouble resolving details on a bird 100 meters away, in brilliant sunshine, against a dark background, or even the reverse, with a bird in the shadows of a leafy tree with bright outer leaves all around it. Either of those birding cases tests the same characteristics of your bins that Jupiter tests.
A 14 year old asked me what the "big bright star" in the sky was, slightly to the south and about 70 degrees up. Of course it was Jupiter. I said rather off-handedly that everyone should be able to see Jupiter as a clear disk with a number of very tiny pinpoints lined up straight on either side of it, and that those were Jupiter's moons. I was using well-sealed Tasco International 410 10x50 binoculars and there were 4 nice moons on display, with unusually subtle banding on Jupiter that night. There were a few oohs and aahs from 2 or 3 others in the group of 9 visiting tourists, but generally there was just allot of fussing with binoculars.
After a few family groups traded their binoculars around (the 14 yo was using a rented pair of our 8x30 Hensoldt DFs while her dad had rented Tasco 334BWs waterproof 7x50s, and mom had the family's Quest 9x32 roofers [Sorry but I don't know anything about these Quest binoculars]). Dad and daughter clearly saw Jupiter as a disk and the moons were more or less visible, although the 7x50s picked up an extra moon the 8x30s didn't. Mom saw Jupiter as a disc with a small spike coming out of it, and only one moon.
Eventually every other family passed me their binoculars to look through. Only one other family had binoculars that were able to see Jupiter as a distinct disk with banding and pinpoint moons strung out in a line. In this family dad had Zeiss 7x50 Marine BG*T porros and mom had Steiner 8x30 porros. Their son had Leica 10x40 roofers and the Leica had spikes coming off Jupiter that made it impossible to find the best focus, and those spikes obliterated the moons. A pair of Zeiss Dialyt roofers both had flares coming off of Jupiter that made the planet look more like a blob than a disk and the nearby moons weren't able to be distinguished. Other bins included the Canon 8x25 and 10x30 IS bins, a few pairs of Swift Audubons sold by the local bider suplly store and a few pairs of Bausch & Lomb 10x40s and Bushnell 8x42 Elites. All of these had spikes or flares that made it impossible to see Jupiter as a disk with moons, or Jupiter was so oval at best focus that no details could be seen and often the two ovals didn't orient the same way so they wouldn't line up to focus.
Everyone who brought their own bins had nice equipment. The rental stuff was all of reasonable quality and well collimated but not extraordinary. This test can't be considered extremely difficult but if your lens/prism/eyepiece alignment is off even slightly your binocular will have trouble. Jupiter is a bright little beacon with definite but subtle banding, and its moons are delicate little pinpoints. To see them both isn't really a challenge as much as it tests the binocular's condition and flare resistance. Some of the binoculars I looked through from Swift had 7 or 8 Jupiter ghosts floating around in the field of view due to internal reflections.
Jupiter will be up in the evening sky for some months now as the first "star" visible each evening and the brightest. Even a 7x binocular should resolve Jupiter's disk clearly and some 6x bins do it well also. ANY properly aligned binocular should show the 2 largest moons of Jupiter as long as they are not in front of or behind the planet. Even small exit pupil binoculars like 10x30s should have no problem with resolving Jupiter because it is so bright. The moons are more of a test for small exit pupils because they are not nearly as bright as Jupiter but if your bin is able to focus well for a super-sharp view, then I've viewed Jupiter's moons with 8x21s that are properly set up. The banding on Jupiter takes perfect color correction and enough brightness to show light colors.
More than half the people I "spring" this test on are disappointed no matter how expensive their binoculars are. Jupiter and its moons test many things. If your sharpness resolution is not good then Jupiters edges will be "soft" or wavy and the moons won't be visible because the tiny pinpoints of light won't resolve and their light will be diffuced over an area that is too large. If your color correction is poor then since Jupiter is so bright, it will have yellow or purple fringes that interfere with resolving it sharply and some of this "corona" may slop over onto the moons, also the bands on th planet won't show unless your color correction is true. If your coatings aren't good then Jupiter will have lots of glare and ghost images so it won't be a crisp disk. Poor internal baffling will produce allot of ghost Jupiter images in your view and unless they are movable by changing your position they can obscure Jupiter's moons. If your lens/prism/eyepiece alignment is not straight and true then you will get allot of spikes that will extend off Jupiter or Jupiter will look oval and the two images for left and right may not even have the same direction of "ovalness", so seeing anything with 2 eyes might be difficult. Since "glass" alignment is crucial for this test, zoom binoculars seem to fail more than other designs and in general roofers fail it much more often than porros.
If everything is "right" with your bins, then Jupiter is a sight to see. If you are in the countryside like we are, Jupiter is a sharp disk (slightly flattened on the top and bottom by its gravity, rotation and gaseous make-up, and the flatter top/bottom are usually visible with 15x+ bins.). The planet is usually banded and may even show its 2 spots. It's up against the black reaches of space, usually with a few dim stars floating behind it.
Birders knock their bins around quite a bit. Over time they don't notice how poorly aligned their equipment becomes. Even though most birders carefully clean the objective and eye lenses of their bins, they don't seem to send them out for internal cleaning and realignment of the glass parts often enough. I find the same is true of most spotting scopes we encounter here too, although a large percentage of Nikon Fieldscopes and Bushnell Spacemasters work well even after years of abuse. But straight line roof prism spotters seem to have a particularly hard time doing well on the "Jupiter Test" at low power. Higher magnifications seem to help with this test if you have 20x or more available, but it's no guarantee.
Try it yourself and see how well your bins do, and when the earth's moon returns it makes a fine test object as well (the full moon is especially good for testing color correction [CA]). It might help you understand why you have trouble resolving details on a bird 100 meters away, in brilliant sunshine, against a dark background, or even the reverse, with a bird in the shadows of a leafy tree with bright outer leaves all around it. Either of those birding cases tests the same characteristics of your bins that Jupiter tests.
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