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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Daytime benefit of large objectives? (1 Viewer)

Tried handholding a pair of 25x100 once, not an easy hold. My binocular purchases seem to be shrinking with time... I’ll be down to near unity opera glasses if I don’t stop soon!

Peter

My normal binocular used to be a 20x80.
I think it weighed about 80 oz., but I had no trouble hand holding it for 20 minutes at a time.

Some of my friends couldn't hand hold it at all.
Nor can I nowadays.

I have no trouble with the Canon 18x50 IS, about 40 oz.
 
my 8x52 and 8x56 only get used around the yard/ or off the breakwater pier/ lake bluffs at the lake front [lake Michigan].........the 30/32 or 40/44 are for purposeful hiking/glassing....the 8/10x25 or monocular are for walking the dog....but the best picture seems to come through the larger objective, from a decent quality bin...
 
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I also have a 25x100, but it is difficult to hand hold, and nowadays I wouldn't try it.

Try hand holding a Ross 10x80. I took 6 boxed examples up the stairs to Kays for refurbishment. Wish I hadn't.

The 20x80 was the best of three Japanese Celestrons bought about 1974?

There are at least two birdwatchers who regularly use the Zeiss 20x60S binocular, and I think they take them on hikes.
These to me are held with one hand and the other used to hold the button down.

There seem to be many birdwatchers who use the Canon 10x42L, which is about 40 oz.

I suppose a month's gym membership should be included with any binocular of 40 oz. or more.

My 14 1/4 inch f/5 Newtonian was completely open tubed, just a one arm large pipe holding the secondary with clever shielding.
Jim Hysom reworked the mirror and made a new flat. It was a fine performer.
Everything Jim Hysom made was as far as I know top grade.
The base was a truck or large car wheel.
I used to roll the scope around on the wheel base to get it into position.
It was a bit noisy in the early hours.
I got an early sighting of Comet Halley with it.

The 20.5 inch was mounted on castors.
1/20th wave mirror.
 
my 8x52 and 8x56 only get used around the yard/ or off the breakwater pier/ lake bluffs at the lake front [lake Michigan].........the 30/32 or 40/44 are for purposeful hiking/glassing....the 8/10x25 or monocular are for walking the dog....but the best picture seems to come through the larger objective, from a decent quality bin...

Hey Gunut I grew up playing on the lakefront. It's good to know my big pond is still there. I loved the big dunes around Ludington. I used to spend whole summers living in a tent up there.
 
my 8x52 and 8x56 only get used around the yard/ or off the breakwater pier/ lake bluffs at the lake front [lake Michigan].........the 30/32 or 40/44 are for purposeful hiking/glassing....the 8/10x25 or monocular are for walking the dog....but the best picture seems to come through the larger objective, from a decent quality bin...
An 8x56 is fine if your not hiking with it. Sitting on a pier or a tree stand they are no problem. I would use one in that situation.
 
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Binastro.The 20.5 inch must have been awesome. I had a 10 inch Orion IntelliScope and it gave me great views of the lunar surface. With a Nagler eyepiece it was almost like you were orbiting it. Pretty good scope.
 
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Assuming its Ludington Michigan...as Ludington Wisconsin is centrally located about 150 miles from the lake....

Yeah Michigan. Ludington State Park has one of the most beautiful trail systems running between Hamlin lake and Lake Mich you'd ever want to hike on. My heart is still there on those trails and along the beautiful bird and wildlife infested lake shallows and dunes. I'm about to tear up just remembering. I wouldn't mind laying down my mortal coil among those dunes along those lakes.
 
I also have a 25x100, but it is difficult to hand hold, and nowadays I wouldn't try it.

Try hand holding a Ross 10x80. I took 6 boxed examples up the stairs to Kays for refurbishment. Wish I hadn't.

The 20x80 was the best of three Japanese Celestrons bought about 1974?

There are at least two birdwatchers who regularly use the Zeiss 20x60S binocular, and I think they take them on hikes.
These to me are held with one hand and the other used to hold the button down.

There seem to be many birdwatchers who use the Canon 10x42L, which is about 40 oz.

I suppose a month's gym membership should be included with any binocular of 40 oz. or more.

My 14 1/4 inch f/5 Newtonian was completely open tubed, just a one arm large pipe holding the secondary with clever shielding.
Jim Hysom reworked the mirror and made a new flat. It was a fine performer.
Everything Jim Hysom made was as far as I know top grade.
The base was a truck or large car wheel.
I used to roll the scope around on the wheel base to get it into position.
It was a bit noisy in the early hours.
I got an early sighting of Comet Halley with it.

The 20.5 inch was mounted on castors.
1/20th wave mirror.

Binastro I have a pair of Oberwerk 25x100 binos that give pretty outstanding views off my upper deck. I had no idea how great they would be when I bought them for Astronomy. I ended up using them much more on the elk and hikers passing around joints on Grizzly Peak several miles away. They do have just a touch of CA occasionally however. :t: Really not that much though.
 
Just remembered this post from last summer:

https://www.birdforum.net/showpost.php?p=3424981&postcount=17

The images are the closest I've come to photographing the visual difference between a small binocular (Swarovski 8x30) and the Zeiss 8x56 FL stopped down to the same 30mm aperture.

Hi Henry,

The way I've thought about it, the added resolution (and fewer aberrations) of the Zeiss 8x56 is primarily due to its objective lens having a longer focal length and smaller f-ratio (at any effective aperture) than an 8x30. So, other factors held equal, e.g., magnification, FOV, etc., the instrument with a longer focal length objective will necessarily have better image quality.

Using this rationale, 42mm instruments should also have better image quality than 32/30mm instruments, — and to my eyes (and many others) this seems to be born out.

Your thoughts?

Ed
 
So to recap, the claims of the BVD article about larger objectives in daytime are indeed false:
Higher resolution - if present at all, due to reduction in aberrations from slower effective f/ratio, not diffraction limits of objective size (the real limit being observer's pupil size).
Better penetration of shadow in mixed bright light - if present, due to different choice of coatings etc, not objective size.
Better color detail - ditto.​

On the other hand, people do sometimes seem impressed by something about the daytime view in a larger glass, however far they're willing to carry one. This wasn't a principal reason for finally getting a 10x56 (I'd been looking for a while) but I was curious how it would do. It's growing on me. Compared to my 32mm, it has a bit of extra brightness, clarity, sparkle... I'm trying not to use technical terms like resolution, because this is a subjective impression. Of course there's also a few percent difference in transmission due to AK prisms; can one actually notice that? And it controls lateral color better; I'm not one of the most sensitive to that, but could this contribute to a slightly crisper image?
 
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So, other factors held equal, e.g., magnification, FOV, etc., the instrument with a longer focal length objective will necessarily have better image quality.
Using this rationale, 42mm instruments should also have better image quality than 32/30mm instruments, — and to my eyes (and many others) this seems to be born out.

And yet manufacturers try to keep even (especially?) 42mm glasses compact and lightweight, so their objectives don't really have that much longer a focal length? (Except the SF...)
 
Hi Tenex,

I did say: "So, other factors held equal, e.g., magnification, FOV, etc., the instrument with a longer focal length objective will necessarily have better image quality."

Of course, if other factors are not held equal for whatever reason, e.g., prism construction, coatings, etc., the advantage could be masked. But I'm referring to an optically ideal case, which isn't too unrealistic considering the quality of the instruments.

Ed
 
So to recap, the claims of the BVD article about larger objectives in daytime are indeed false:
Higher resolution - if present at all, due to reduction in aberrations from slower effective f/ratio, not diffraction limits of objective size (the real limit being observer's pupil size).
Better penetration of shadow in mixed bright light - if present, due to different choice of coatings etc, not objective size.
Better color detail - ditto.​

On the other hand, people do sometimes seem impressed by something about the daytime view in a larger glass, however far they're willing to carry one. This wasn't a principal reason for finally getting a 10x56 (I'd been looking for a while) but I was curious how it would do. It's growing on me. Compared to my 32mm, it has a bit of extra brightness, clarity, sparkle... I'm trying not to use technical terms like resolution, because this is a subjective impression. Of course there's also a few percent difference in transmission due to AK prisms; can one actually notice that? And it controls lateral color better; I'm not one of the most sensitive to that, but could this contribute to a slightly crisper image?

In principle, I wouldn't be surprised.

Ed
 
Hi Henry,

The way I've thought about it, the added resolution (and fewer aberrations) of the Zeiss 8x56 is primarily due to its objective lens having a longer focal length and smaller f-ratio (at any effective aperture) than an 8x30. So, other factors held equal, e.g., magnification, FOV, etc., the instrument with a longer focal length objective will necessarily have better image quality.

Using this rationale, 42mm instruments should also have better image quality than 32/30mm instruments, — and to my eyes (and many others) this seems to be born out.

Your thoughts?

Ed

Hey Ed,

Yes, I agree that (all things being equal) 42mm binoculars have lower aberrations in daylight than 30/32 binoculars. That's pretty obvious to me when comparing the 8x42 FL to the 8x32 FL. In addition, your 42mm SLC has unusually low aberrations among 42mm binos.

8x56mm (once again, all things being equal) takes the difference up another notch or two in daylight. I know you already know this, but for others who may not, I should add that the 8x56mm FL and (judging from star test photos I've seen) the 8x56mm SLC have very high aberrations at full aperture, worse than a typical 42mm or 32mm binocular because the designers know they can get by with using unusually short focal length objectives in large aperture/large exit pupil binoculars to reduce weight and size. The low focal ratios don't do much if any damage to the perceived image quality in low light where eyesight is extremely poor. In daylight, where the eye reaches its best acuity, the effective focal ratio becomes high enough to produce nicely corrected aberrations compared to small binoculars. For that reason 10x56 and 10x50 binoculars don't enjoy quite the same freedom from aberrations in daylight that 8x56s and 7/8x50s do, and 12x50s and 15x56s have no aberration advantage at all (more likely a disadvantage) compared to small binoculars with the same exit pupil size (once again, all things being equal).

Henry
 
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And yet manufacturers try to keep even (especially?) 42mm glasses compact and lightweight, so their objectives don't really have that much longer a focal length? (Except the SF...)

tenex,

Keep in mind that the SF uses a different simpler objective design compared to most of its 42mm peers, so its effective focal length and aberration corrections can't be predicted from its longer physical length. It's a good example of all things not being equal.

Henry
 
Another reason why physically large diameter tubes are better is because stray light is better dealt with or lost.

One of the problems that I have with my early Monarch 8x42 HG is that the barrels are too small and the black paint is shiny, not matt black.

Newtonian telescopes in large square box tubes are often better than those in close fitting round tubes. With these, tube currents are also less, which isn't a problem in binoculars but may be in spotting scopes.

I haven't seen anything on Birdforum about how different spotting scopes cope with thermal problems. I doubt binoculars will vary much unless perhaps high powered ones.

The material the tubes are made with also matters.
Some large lenses have terrible thermal problems, also due to their optical design.

Short focal length refractors handle temperature effects less well than long focus refractors.
 
I suppose I must have checked over a couple of hundred different models and something over a 1000 separate samples in recent years. I've seen what I would regard good and bad binoculars in most objective sizes, but we all seem to differ in what we rank as important. When I first walked into a specialist optics shop shortly after joining the forum and tried twenty or so binoculars, I was surprised to find the most striking difference was on-axis sharpness. I've since learned that CA and stray light control are part of that, but on-axis effective resolution seems the critical determinant for me. I certainly haven't found that to be the exclusive domain of large aperture models.

As was mentioned earlier in the thread it was Henry that first checked out the Zeiss HT 8x54 and found high levels of aberration. Others including myself didn't find if sharp either, and I passed on these observations to someone at Zeiss and invited him to have a look at the stopped down resolution. At a subsequent meeting he produced MTFs for 54mm and 20mm apertures, but refused to let me scrutinise them. I'm no expert in reading upside down down semi-log plots in apparent cycles per degree, but I made a note of my best guess at the x-axis values. For 54mm I made it 2.5 arcseconds (135/D) and for 20mm, 9.5 arcseconds (190/D). I would like to think I would be within 0.5 arcseconds of the actual value but I cant't be sure. Those values, or anything reasonably close, would definitely explain user complaints though.

The Zeiss guy did say they would ne revising their QC, but I haven't checked out whether the HT 8x54 has improved.

One model doesn't prove any point, but I think it does illustrate that objective diameter, longer focal length, good CA, stray light control and good instrument resolution doesn't ensure great optical performance. I've certainly seen a few budget x32s, and at least one small x30 that undoubtedly were considerably better than that one.

David
 
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