Daytime benefit of large objectives? (1 Viewer)

henry link · Mar 14, 2018

typo said:
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.

David

Hi David,

Here's a link to my review of the 8x54 HT:

https://www.birdforum.net/showthread.php?t=285414

In post #16 my measurement of the full aperture resolution was 189/D and my estimate of the the resolution when stopped down to 22mm was 135-140/D. Those are in such good agreement with the Zeiss MTF, if its numbers are reversed, that I can't help but wonder whether it was mislabeled or misread. Can you think of a likely scenario in which the center 14% of the surface area of an objective lens would have higher wavefront error than the full lens?

Henry

denco@comcast.n · Mar 14, 2018

I have a new Swarovski SLC HD 8x56 coming tomorrow. I will let you know if I think large objective binoculars are more aberration free.

typo · Mar 14, 2018

henry link said:
Hi David,

Here's a link to my review of the 8x54 HT:

https://www.birdforum.net/showthread.php?t=285414

In post #16 my measurement of the full aperture resolution was 189/D and my estimate of the the resolution when stopped down to 22mm was 135-140/D. Those are in such good agreement with the Zeiss MTF, if its numbers are reversed, that I can't help but wonder whether it was mislabeled or misread. Can you think of a likely scenario in which the center 14% of the surface area of an objective lens would have higher wavefront error than the full lens?

Henry

Henry,

If I had reversed the numbers they would have been 513/D for full aperture and 50/D stopped down. I think that rules out that error.

I note you guessed the 135-140/D stopped down from the diffraction patern, and add that "the HT had poorer resolving power in bright light than the FL at 8x." I know very well what 135-140/D looks like from the binoculars I own and the sample I tried on the Zeiss stand wasn't anywhere near as good as that. Later you say your unboosted chart result was worse than your native acuity giving about 100". That would suggest an effective resolution around 250/D so there would seem to be some contradiction in your observations that I can't explain.

It was when I told the Zeiss guy that my visual estimate on the sample on the stand was 8.5-9.5" or about 170-190/D, he then produced the MTFs from his briefcase. Given that we were almost certainly looking at different samples I thought it was reassuringly close to the 190/D value I estimated form the MTF.

I'll leave the interpretation of diffusion ring patters to you. I've said before, I've not as yet been unable to relate the patterns I've seen to any observable performance difference. As I mentioned before, it may not be the most common trend, but I've seen a few other examples of binoculars where there has been a relative decrease in resolution performance as their objective is stopped down. Probably one for the ray tracers.

Cheers,

David

henry link · Mar 14, 2018

I agreed, even when I wrote the review, that the 8x54 HT presents some odd anomalies when comparing high and low magnification. My best effort at an explanation then and now is that high lateral color close to the field center, as seen in post #4 of the review, is the big spoiler at normal magnification. At 8x it's visible at only 1º of apparent field from the center, but that very same lateral color would appear 8º from the center in a 64x star test or resolution measurement. It wouldn't affect a well centered star or group of line pairs at 64x, but could be close enough to the field center to degrade the center field image for the eye at 8x. I don't think this is a case of the classical axial aberrations failing to predict axial performance, but of the unusual appearance of what is normally an off-axis aberration so close the field center at low magnification.

Henry

typo · Mar 14, 2018

Henry,

I'm not sure what to make of the image in #4. From the CA on the central cross it looks like the target might have been significantly misalligned vertically, and the edge curvature of the adjacent stripes seems quite odd too. Could there have been an axial misalignment?

David

henry link · Mar 14, 2018

David,

I made quite a few photos trying to get both good vertical and horizontal alignment, which wasn't very easy looking through a camera viewfinder. I considered precise horizontal centering to be more important than vertical, so I probably posted that one because it has good horizontal alignment and what I considered close enough vertical alignment not to affect the appearance of color along the horizontal axis too much. You can see that the FL image is not quite as well centered horizontally as the HT image, so it shows a little more lateral color to the left side than the right. These backyard methods do have their limitations.

When I look directly through binoculars at this target I find the center cross bobs around in a little circle, even with tripod mounting, so the lateral color constantly flares slightly in one direction or another.

Henry

typo · Mar 14, 2018

I've had little success persuading cameras to cooperate on similar tasks myself, so you are a step ahead of me. Unfortunately It sometimes seem to add another layer of complexity to an already pretty complicated story.

David

tenex · Mar 17, 2018

About the SLC 10x56...

My early impression is that it's just excellent, a real pleasure to use in the daytime as well. I'm not in a position to compare apples here, but relative to my Leica 10x32 it seems to have a more neutral rather than red cast (not cool though), and similar (excellent) sharpness. I don't claim to see any advantage in resolution from the larger objective, for whatever reason. I'm easily bothered by pronounced field curvature or aberrations near the edges, but no such problems here. The really obvious difference is greater brightness (AK prisms?), which I wouldn't have thought mattered in daylight, but in fact it gives the view a nice extra sparkle and crispness. Some of that may also be due to better control of CA. (I'm not sure whether it actually has a bit less contrast as I first thought, or that's just an impression created by greater brightness.) So this isn't a dedicated low-light glass but a real all-rounder, apart from the weight. And in darker conditions of course, it's pretty amazing.

etc · Mar 27, 2018

tenex said:
About the SLC 10x56...

My early impression is that it's just excellent, a real pleasure to use in the daytime as well. I'm not in a position to compare apples here, but relative to my Leica 10x32 it seems to have a more neutral rather than red cast (not cool though), and similar (excellent) sharpness. I don't claim to see any advantage in resolution from the larger objective, for whatever reason. I'm easily bothered by pronounced field curvature or aberrations near the edges, but no such problems here. The really obvious difference is greater brightness (AK prisms?), which I wouldn't have thought mattered in daylight, but in fact it gives the view a nice extra sparkle and crispness. Some of that may also be due to better control of CA. (I'm not sure whether it actually has a bit less contrast as I first thought, or that's just an impression created by greater brightness.) So this isn't a dedicated low-light glass but a real all-rounder, apart from the weight. And in darker conditions of course, it's pretty amazing.

I have a 8.5x42 EL and am thinking about adding 10x56 to the collection.

A larger objective gathers more light and will always be brighter.

It seems to me 10x is a great match for either 50 or 56mm objective. If I am limited to 42mm, I would rather have 8x.

8 works with 42 and with a smaller 30mm objective, 6x or 7x works best.

looksharp65 · Mar 27, 2018

etc said:
A larger objective gathers more light and will always be brighter.

This is not correct. Your own pupil will limit the width of the beam pencil entering your eye.
A larger objective binocular with the same magnification will be brighter than a smaller one, as long as your pupils can dilate to wider than the small binocular's exit pupil, and you're in circumstances when they actually do.

//L

denco@comcast.n · Mar 28, 2018

About the 8x56 SLC...

The big advantages of the 8x56 SLC are no veiling glare even when you get close to the sun because of the big 7mm exit pupil, almost no CA, the clearest, most transparent aberration free on-axis view I have ever seen and unbelievable low light performance. I never realized a 56mm would you give a you all these advantages over smaller aperture binoculars avoiding them in the past because of their size and weight. I really feel that aperture makes more difference in a binoculars performance than coatings and glass although they all play a part after using a 56mm. If you are not hiking too far or you have no problem with a harness I highly recommend a 56mm.

Hermann · Mar 28, 2018

[email protected] said:
I never realized a 56mm would you give a you all these advantages over smaller aperture binoculars avoiding them in the past because of their size and weight. I really feel that aperture makes more difference in a binoculars performance than coatings and glass although they all play a part after using a 56mm. If you are not hiking too far or you have no problem with a harness I highly recommend a 56mm.

The size and the weight will be the killer for many here. Probably for most. And it's not just hiking that's a problem, it's also keeping the bins still when watching a bird for more than a few minutes. Unless you spend long hours in the gym to get really fit ... :king:

Getting the weight down in such binoculars is difficult to impossible, there's just too much glass inside. A neat compromise would be an 8x50 roof, ideally also with AK (or Perger) prisms. That should keep the weight down somewhat while still keeping the advantage of (largish) objective lenses. The Leica Ultravid doesn't quite cut it compared to the Swarovski IMO, it is lighter but has a smallish field of view and uses SP prisms.

Hermann

etc · Mar 28, 2018

looksharp65 said:
This is not correct. Your own pupil will limit the width of the beam pencil entering your eye.
A larger objective binocular with the same magnification will be brighter than a smaller one, as long as your pupils can dilate to wider than the small binocular's exit pupil, and you're in circumstances when they actually do.

//L

A larger objective will always be brighter but I understand it's not a certainty you can use it - but it's brighter, period.

If you cannot use the entire light, the larger exit pupil size will mean the device will have larger eye relief and just be easier to use all around.

10x50 is brighter and easier to use than say 10x42 and especially 10x30.

etc · Mar 28, 2018

[email protected] said:
About the 8x56 SLC...

The big advantages of the 8x56 SLC are no veiling glare even when you get close to the sun because of the big 7mm exit pupil, almost no CA, the clearest, most transparent aberration free on-axis view I have ever seen and unbelievable low light performance. I never realized a 56mm would you give a you all these advantages over smaller aperture binoculars avoiding them in the past because of their size and weight. I really feel that aperture makes more difference in a binoculars performance than coatings and glass although they all play a part after using a 56mm. If you are not hiking too far or you have no problem with a harness I highly recommend a 56mm.

that is a great advice. I am undecided about 8x56 or 10x56.

Binastro · Mar 28, 2018

etc.
It is not brighter period.
It could be, depending on transmission, vignetting, light levels, pupil size etc.
But it may not be.

The eye relief may be more, but not necessarily so.

etc · Mar 28, 2018

We are not talking about different coatings or pupil size. Two equivalent devices - one with 42mm and the other with 50mm - the latter will gather more light. It's just optics / science 101.

Leica 7x50 will be brighter than same model in 7x42.

I've compared 42mm optics with 30mm optics - the former are noticeably brighter. You cannot get any 30mm optic to show up as bright as a 42mm, nor can you get a 42mm to show up as bright as a 56mm. Same brand, same configuration.

if you have issues seeing it, then that is another problem. It is a user problem at that point.
The larger the pupil exit size, the brighter it appears and the easier to use.

Brightness is determined by exit pupil size and more is better. You get bigger exit pupil size by keeping the same power and going to a larger objective. Or something like a 6x42 device - not sure if anyone even makes that.

In a 7x50 configuration, if your eyes cannot make full use of the 7mm exit pupil, then it's a user issue. But 7x50 is scientifically brighter than say 10x42. If this applies to you, 8x42 might be just as effective as 10x56.

here is a post articulating this well:

https://www.birdforum.net/showpost.php?p=1563082&postcount=3

Optically, the Swarovski 8x56 SLCNew is one of the very finest large-aperture binoculars available, an excellent choice for birding at dawn and dusk due to their outstanding light-gathering ability. This binocular would also be a SUPERB candidate for viewing the upcoming Perseid Meteor showers! The overall quality of construction of this binocular is first-rate.

In my opinion, you will indeed notice a substantial increase in the quality of the image during dim or overcast viewing conditions in direct comparison to any 8x42 binocular. This configuration does suffer from VERY poor close focus in comparison to birding binoculars equipped with seven to eight-power magnification and the more popular 32, 42 and 50mm objective lens diameters. Close focusing distances for these models often hover somewhere between twelve to seven feet. Swarovski’s technical literature lists a close-focusing figure of 26.5 feet, making them of somewhat limited use for everyday birding. This is quite typical for a binocular manufactured primarily for hunters and astronomers. A noteworthy exception to this caveat may be North American or Mexican hawk watching, where observation often consists of canvassing roiling clouds of migrating raptors against a gray sky a half-mile or more above assembled observers.

Binastro · Mar 28, 2018

etc.
Brightness is determined by your pupil size.

If your pupil size is 4mm then a 7x42 is just as bright as a 7x50, the binoculars being equal.

The longer focal length of the 7x50 objectives will slightly benefit the 7x50.
However, the thicker glass elements will slightly reduce the 7x50 transmission.

The eye relief is determined by the eyepiece.
For the same type eyepiece then indeed the longer focal length eyepiece of the 7x50 will give longer eye relief, but the 7x42 may have a different eyepiece type.

As in the movie.'My cousin Vinny', the star witness, his girlfriend, says 'You are wrong'.

denco@comcast.n · Mar 28, 2018

Hermann said:
The size and the weight will be the killer for many here. Probably for most. And it's not just hiking that's a problem, it's also keeping the bins still when watching a bird for more than a few minutes. Unless you spend long hours in the gym to get really fit ... :king:

Getting the weight down in such binoculars is difficult to impossible, there's just too much glass inside. A neat compromise would be an 8x50 roof, ideally also with AK (or Perger) prisms. That should keep the weight down somewhat while still keeping the advantage of (largish) objective lenses. The Leica Ultravid doesn't quite cut it compared to the Swarovski IMO, it is lighter but has a smallish field of view and uses SP prisms.

Hermann

I have no problem holding the the SLC 8x56 up and keeping it still. In fact it seems easier to hold steady because of the weight. The balance is exceptional and the ergonomics are very good. You almost forget it is a 56mm. An 8x50 would be a nice size for birding but the 8x56 would still outperform an 8x50 and it is not really that much bigger. I would like to see an 8x50 SV or SF.

denco@comcast.n · Mar 28, 2018

etc said:
that is a great advice. I am undecided about 8x56 or 10x56.

The 8x56 will have more of the advantages Henry describes with the bigger 7mm exit pupils. It will be more aberration free on-axis and show less veiling glare than the 10x56. Really the 8x56 and 10x56 are two different animals.

" 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)."

etc · Mar 28, 2018

[email protected] said:
I have no problem holding the the SLC 8x56 up and keeping it still. In fact it seems easier to hold steady because of the weight. The balance is exceptional and the ergonomics are very good. You almost forget it is a 56mm. An 8x50 would be a nice size for birding but the 8x56 would still leave it in the dust as far as performance and it is not really that much bigger.

For me, 8x56 SLC is automatically ruled out due to diopters at infinity being only -5D. Not enough. I do not like to use eyeglasses in conjunction with binos. The 10x56 model has -8D. So it's either that or 12x50 EL (-7D) or a Zeiss. Or 10x42 EL which is also great but I think I want a 50mm objective with 10x, not 42mm.

https://www.swarovskioptik.com/hunting/slc-56-c20010302/slc-15x56-p5068619

Daytime benefit of large objectives? (1 Viewer)

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