A Leica Noctivid 8x42 with Schott HD glass, so it has no CA.
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Which ones are your dream binoculars? (1 Viewer)
- Thread starter Swedpat
- Start date
hopster
Well-known member
Both SPs and AKs can be designed with offset. It's just that AKs take up a lot of space in the longitudinal axis, so they are usually used in binoculars with large objectives and correspondingly long focal length, and it's there that offset is required.
I just measured my 56 mm SLCs, which have an IPD range of 56-75 mm and an objective spacing of 68-87 mm. That's 12 mm difference or 6 mm offset per barrel.
A 70 mm roof prism binocular requiring 12 mm offset per barrel would probably need very large and heavy prisms.
So what's wrong with Porros in this size? No prism edge in the light path, no need for phase coatings and cheaper too.
John
Absolutely, I love the natural view that seems easier to achieve with porros because of the simplicity of the prisms, light path and manufacturing tolerances, but I'm not so keen on the apparent mutually exclusive choice between (genuine, long-term) waterproofing and an easy & fast focuser.
M
hopster
Well-known member
Doesn't the Noctivid already have Schott HD glass?
David,
Unless your Canon 18x50 is a heap of rubbish, which I doubt, you are going to need a lot more magnification than 18x to see its resolution limitations.
The Dawes' limit for a 50 mm objective would be 2,32" and even if it only reached half that (4,64"), it would need to be boosted on a tripod.
The general concensus is that, even with excellent eyesight, you need about as much magnification as the objective diameter in mm.
Some years ago I measured the resolution of my 65 mm and 88 mm scopes with a 3,5 mm eyepiece at 130x and 140x, rather high but that was all I had available.
Regards,
John
Dennis,
You can't eliminate CA , only reduce it and it's senseless to speculate what glass sorts are used by Leica. We just don't know.
Nothing magical about Schott, who have several ED glass sorts on offer, but Ohara's FPL-53 and FPL-55 would surpass all of them for low dispersion.
However, I know of no binocular using them and they would not be necessary to reduce longitudinal CA at low binocular magnifications.
Or did you mean lateral CA, which is caused by the eyepieces?
John
Swedpat,
I have the Bushnell 5x25 but it is actually about 4.4x It is quite good.
I use the Dowling and Rowe/Libra 4x22 a lot. The measured field is 16.3 or 16.5 degrees. It is cheap and quite good.
Avoid the fixed focus one. The independent eyepiece focus one is better, and one rarely needs to refocus once set.
I also use the Bushnell Xtrawide 4x21. It is actually 3.5x, but has a measured field of 18.5 degrees.
It is fixed focus with a curved field, but I use it as near the edges it is in focus for me.
It shows the Pleiades and Hyades in the same field easily.
The transmission is rather low, but still a very useful binocular.
The Beechers Mirage binoculars are available in several low magnifications.
Regards,
B.
P.S.
The Libra Superview 4x22 is also available as Kasai Superview 4x22.
Also available as Libra 6x30.
They are roof prism binoculars.
Reports vary a lot, but some say they are very good, some say not.
My Dowling and Rowe example is good.
I have the Bushnell 5x25 but it is actually about 4.4x It is quite good.
I use the Dowling and Rowe/Libra 4x22 a lot. The measured field is 16.3 or 16.5 degrees. It is cheap and quite good.
Avoid the fixed focus one. The independent eyepiece focus one is better, and one rarely needs to refocus once set.
I also use the Bushnell Xtrawide 4x21. It is actually 3.5x, but has a measured field of 18.5 degrees.
It is fixed focus with a curved field, but I use it as near the edges it is in focus for me.
It shows the Pleiades and Hyades in the same field easily.
The transmission is rather low, but still a very useful binocular.
The Beechers Mirage binoculars are available in several low magnifications.
Regards,
B.
P.S.
The Libra Superview 4x22 is also available as Kasai Superview 4x22.
Also available as Libra 6x30.
They are roof prism binoculars.
Reports vary a lot, but some say they are very good, some say not.
My Dowling and Rowe example is good.
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I would like to try the Bushnell X-wide 4x21 but it's discontinued. And that Libra 4x22 is very interesting! But I don't find it anywhere.
Imagine a high grade model of this kind of binocular...
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William Lewis
Wishing birdwatching paid the bills.
I'd go for a waterproof e2 7x35 with the same fov as the current 8x as a few have suggested above. I could sell 3 of my bino's that are all doing elements of what one modern, quality, waterproof, 7x35 porro would do too.
Holger mentioned Nikon were thinking of bolting on a field flattener to the E2 a couple of months back In his correspondences with them so you never know, the E3 may not be quite such a (2) pipe dream after all...
Holger mentioned Nikon were thinking of bolting on a field flattener to the E2 a couple of months back In his correspondences with them so you never know, the E3 may not be quite such a (2) pipe dream after all...
tenex
reality-based
Do you really mean "caused" or just exacerbated, and could you elaborate? Discussion always seems to concentrate on the objective.
Longitudinal CA is observed on axis when the objective has significantly different focal lengths for red, green and blue light.
Lateral CA, or better lateral colour, is colour fringing outside the optical axis and is present in all eyepieces.
Imagine a point source 10° removed from the optical axis in the focal plane of the eyepiece.
Dispersion is going to occur at the surface of the field lens and there will be a lateral shift of the red, green and blue light bundles emerging from the eyelens.
Regards,
John
I believe one reason Leicas and the Noctivid have more CA than Kowas and Zeiss is because Leicas only use one ED element per objective and Kowa and Zeiss use two. It obviously makes a big difference because Kowas and Zeiss have no CA in the center and Leicas do. A lot of the Kowas and Zeiss and some of the Swarovski are nearly apochromatic, so CA can be eliminated with the right design and glass types.
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tenex
reality-based
So is this dispersion actually a greater problem than that of the objective in the first place, and if so why doesn't ED glass reduce it there too?
(I do understand the difference between longitudinal and lateral CA and am talking about the latter.)
With objectives we are dealing with angles of incidence around 4° and with eyepieces of up to 30°. so dispersion is going to occur at the surface of the eyepiece field lens or its inner surface at the latest.
The best we can hope for is that if the point source were towards the edge of the focal plane of the eyepiece, then the red, green and blue light bundles would all emerge parallel from the eye lens, but with some lateral shift.
If one or more of these were not parallel, that might be spherochromatism, but I'm not sure. You'd have to ask Henry.
John
MiddleRiver
Well-known member
I continue to be drawn towards compact, relatively lightweight binoculars. While I love the Noctivid 8x42, the weight (and to a lesser degree size) are a turn-off. In contrast, I'm finding 8x32FL about as heavy as I want to go, and a nice compromise between 8x30SFL/8x30MHG and the 8x40SFL. The 8x32SF has great optical specs, but size is similar to 8x40SFL, so I'm sticking to the SFL's (so far at least).
If Leica could make an 8x32 Noctivid, and keep size/weight down with the larger more grippy/knurled focus knob (I find the UVHD too slick) and keep ER at least at 17-18mm, I'd buy one immediately.
If Leica could make an 8x32 Noctivid, and keep size/weight down with the larger more grippy/knurled focus knob (I find the UVHD too slick) and keep ER at least at 17-18mm, I'd buy one immediately.
I understand that wide FOV is attractive. But I still wish the manufacturers would not sacrifice eye relief in order to compete with FOV.
The most 8x30/32 and 10x42 have too short ER for eyeglasses.
And I wonder why have almost all 8x32s wider FOV than 8x42s? And 10x42 wider than 10x50s? It does not need to be so.
Why is that a trend followed by almost all manufacturers? It's like there is a common agreement that: 8x32 and 10x42: not for eyeglasses. 8x42 and 10x50: for eyeglasses.
Not only that the same power with shorter focallength results in shorter ER with same eyepiece design. Wide angle design results in even shorter ER.
So: a 8x32 and 10x42 with non wide angle would get longer ER.
And: a 8x42 and 10x50 with same AFOV as 8x32/10x42 models would get longer ER than they have.
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