'High-end' objective lenses (1 Viewer)

Can I just double-check a few things as regards the objective lenses in high-end scopes?:

Swarovski scopes have a doublet either of standard or 'special' (HD) glass.
Zeiss scopes only have a doublet of 'special' (FL) glass.
Leica scopes have either a doublet of standard (?) glass or a triplet of 'special' (flourite) glass.

Does this mean that Leica make the only apochromats, the others making 'super-achromats'?
Do any other scopes (e.g. Kowa) use an apochromatic lense system?
Does the Leica non-APO still use an ED-type glass in its doublet?

Thanks

Edit: It's said that an ED/HD/FL lens has about 94% colour correction, whereas an APO has 99%. Is that difference even noticeable in the Leica compared to others?

Mike Johnston said:

Does this mean that Leica make the only apochromats, the others making 'super-achromats'?
Do any other scopes (e.g. Kowa) use an apochromatic lense system?
Does the Leica non-APO still use an ED-type glass in its doublet?

Click to expand...

Mike,

There is quite a lot of inconsistency in colour-correction terminology - especially in marketing materials. It seems also that astronomers favour functional definitions whereas eg. microscopists & birdwatchers seem to like structural definitions. For me (being a non-astronomer) it is easiest to understand achromats, EDs, APOs and superachromats by their structural definition (http://www.pinnipedia.org/optics/chromatic.html).
- achromat: two "standard" lenses bring blue and red to common focus.
- ED-doublet: "much, much better achromat" (Swaro, Kowa...)
- APO: one standard lens, one fluorite (ED) lens and one "anomalous" lens bring three wavelengths to common focus. (Leica)
- superachromat: four lenses (one ED/FL) bring four wavelengths to common focus. (Zeiss, the 85FL has a 5-lens objective)

In my experience the Leica and Zeiss have had the best colour correction, but they are also more complex and may be subject to more sample variation than the ED doublets. Also, the EDs may actually be sharper at wider range of the spectrum - and have better contrast.

Best regards,

Ilkka

iporali said:

Mike,

There is quite a lot of inconsistency in colour-correction terminology - especially in marketing materials. It seems also that astronomers favour functional definitions whereas eg. microscopists & birdwatchers seem to like structural definitions. For me (being a non-astronomer) it is easiest to understand achromats, EDs, APOs and superachromats by their structural definition (http://www.pinnipedia.org/optics/chromatic.html).
- achromat: two "standard" lenses bring blue and red to common focus.
- ED-doublet: "much, much better achromat" (Swaro, Kowa...)
- APO: one standard lens, one fluorite (ED) lens and one "anomalous" lens bring three wavelengths to common focus. (Leica)
- superachromat: four lenses (one ED/FL) bring four wavelengths to common focus. (Zeiss, the 85FL has a 5-lens objective)

In my experience the Leica and Zeiss have had the best colour correction, but they are also more complex and may be subject to more sample variation than the ED doublets. Also, the EDs may actually be sharper at wider range of the spectrum - and have better contrast.

Best regards,

Ilkka

Click to expand...

Thanks Ilkka. I didn't realise the Zeiss has 4/5 lenses.

I'll add to Ilkka's list:

Kowa 823/4 have a fluorite crystal element, not an ED element in their doublet objective. The smaller Kowas use ED. Nikon Fieldscope ED's have an ED triplet objective.

The Zeiss Diascopes as well as the Nikon Fieldscopes have triplet objective cells and a doublet focusing achromat. Without knowing more about the designs, I cannot say whether one or both elements in the focusing achromat are designed to contribute positively to CA correction, but In my current understanding the Zeiss objective should be considered a triplet.

Kimmo

kabsetz said:

Kowa 823/4 have a fluorite crystal element, not an ED element in their doublet objective.

Click to expand...

Well, I think some (at least I) classify fluorite as the ultimate Extra-low Dispersion (=ED) element.

The Zeiss Diascopes as well as the Nikon Fieldscopes have triplet objective cells and a doublet focusing achromat. Without knowing more about the designs, I cannot say whether one or both elements in the focusing achromat are designed to contribute positively to CA correction, but In my current understanding the Zeiss objective should be considered a triplet.

Click to expand...

My (mis)understanding came from a Zeiss brochure which had a somewhat "inexact" cutout picture of the Zeiss 65FL. I thought there were more than three lenses, but as I said earlier, you shouldn't trust marketing materials too much :t:.

Ilkka

Ilkka,

You are right that fluorite is, of course an extra-low dispersion material. However, it is usually differentiated from ED and HD glass since it is not a glass but a crystal.

Interesting your picture from the Zeiss brochure. I have the exact same looking picture in a Diascope brochure which dates from sometime during the first year or two after the introduction of the scopes, and the text pointing to the objective reads: "All Zeiss Diascope models feature 3-element objective lenses with fluoride glass." I guess that later they realized that they could consider every element ahead of the prism as belonging to "the objective" and that for marketing purposes, 4 or 5 sounds more impressive than 3.

Go figure.

Kimmo

There is a lot of confusion with terminology. A lens that brings all the visual wavelengths to essentially the same focus - that is, close enough that you won't see on-axis out of focus halos around bright objects - is an Apochromat. (Although there is a very stingent definition by optician Baker that no one meets.)

The common term for the abnormal dispersion material that allows such fine lense is ED - Extra-low Dispersion. (Oddly, a couple of optics experts have translated this as Extra-Dense, adding to the confusion.) Crystal fluorite is an ED material. There are also ED glasses, such as Ohara's FPL51, 52, and 53. FPL53 provides essentially the same color correction as true fluorite. There are materials that just barely qualify as ED glasses, and they provide marginal improvement, although allowing the maker to brag about using ED.

The various manufacturers seem to need a way to distinquish themselves from the competition, so other terms have sprung up. Swarovski calls their finest lenses HD or "High Definition." Canon uses UD, probably for Ultra-low Dispersion. I've also seen SD - perhaps for Special Dispersion.

The bottom line is that they are all using the same basic approach.

Attached is a small section of a glass diagram showing how close CAF2 (fluorite) and FPL53 are to each other.

I am starting a new thread called "What is ED glass?"

Clear skies, Alan

AlanFrench said:

The various manufacturers seem to need a way to distinquish themselves from the competition, so other terms have sprung up. Swarovski calls their finest lenses HD or "High Definition." Canon uses UD, probably for Ultra-low Dispersion. I've also seen SD - perhaps for Special Dispersion.

Click to expand...

And Nikon has its own ED-material, which it has branded... "ED"

Ilkka

Where does Opticron ED stand? ..... for us "Poor" people.