A Leica Noctivid 8x42 with Schott HD glass, so it has no CA.
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
A Leica Noctivid 8x42 with Schott HD glass, so it has no CA.
David,When I try to read small print at a distance with the Canon 18x50 IS with 20/15 eyesight I can't read it.
When I take a photo or look at the camera screen at 40x optical zoom I can easily read it.
Dennis,A Leica Noctivid 8x42 with Schott HD glass, so it has no CA.
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.
Do you really mean "caused" or just exacerbated, and could you elaborate? Discussion always seems to concentrate on the objective.Or did you mean lateral CA, which is caused by the eyepieces?
Longitudinal CA is observed on axis when the objective has significantly different focal lengths for red, green and blue light.Do you really mean "caused" or just exacerbated, and could you elaborate? Discussion always seems to concentrate on the objective.
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.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
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?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.
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.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.)
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.