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Updated Konica information on artaphot
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PostPosted: Mon Sep 18, 2023 4:00 pm    Post subject: Reply with quote
@ Jean Jaques: I lost your PM asking about the origins of the AR 2.8/35-100mm Varifocal and therefore wasn't able to respond - please contact me again via PM, or leave a message here! SORRY & thanks!

S


PostPosted: Mon Sep 18, 2023 9:30 pm    Post subject: Reply with quote
stevemark wrote:
alex_d wrote:

i have noticed on 16mb aps-c purple ca wide open on lot of 'one-of-the-best' legacy std vintage lenses, all off course multi layered with stuff and coating.
however, the 'worst' a lens it is in general ranking - the less purple ca occures.

so, in your opinion - what causes that purple ca on a type of a sensor to be stronger and on other (almost) not exising ?
i'm aware that all lenses have it but some are better corrected.


This are plain good old "chromatic aberrations" (CAs) - longitudinal chromatic aberrations to be precise.
First a short explanation / definition:
1) lateral CAs appear as colored lines towards the edge & corners. They occur since usually the green and blue image have the same size, but the red or purple image is slightly bigger than the blue/green image. Easy to correct in PP.
2) longitudinal CAs are caused by a different focal point for different colors, e. g. when blue/green is in focus, the red image is slighhtly unsharp, and vice versa. This results in a purple "overcast" in the entire image, especially wide open. Difficult to correct in PP.

It's the latter phenomenon that explains your observation:
alex_d wrote:

i have noticed on 16mb aps-c purple ca wide open on lot of 'one-of-the-best' legacy std vintage lenses, ... however, the 'worst' a lens it is in general ranking - the less purple ca occures.


Here again a simple general principle:
1) glass with a high refraction has also high dispersion (=lots of CAs)
2) glass with a low refraction has also a low dispersion (=few CAs)

As with all gereralizations it's not always true, but it's a good "rule of thumb".

If two lenses have a similar optical construction, and one is made from low refractive (=low dispersive) glass it will have less CAs than the other one made with high refractive (=high dispersive) glass.

However, high refractive (=high dipersive) glass is very useful for correcting the other monochromatic aberrations, especially with fast and wide lenses. Thus most manufacturers have been using high refractive glass when designing fast normal lenses as soon as they became available - but this often has led to more pronounced chromatic aberrations, too!

Glass with a high refraction (nD >1.8, v=25) is expensive, and glass with low dispersion (v=70, nD=1.5) or very low dispersion (v>80, nD=1.4) is expensive too. Using "normal" glass is much cheaper, and in the case of normal lenses results in lenses with higher monochromatic aberrations (spherical aberration, coma etc), but lower CAs.

Take for example the Minolta MD-III 1.2/50 vs the MD-III 2/50; The f1.2 has several lenses made from a expensiv glass with nD=1.8 and v=40, whereas the f2 lens is made from cheaper glass with nD=1.72 and v=52 thus resulting in (slightly) less CAs. Monochromatic aberrations are comparable though, since the f2 lens doesn't need the strogly curved lens radii of the f1.2 lens.

Konica seems to have used cheaper glass in several of their lenses, e. g. in the AR 4/200mm (v=64 instead of the more common v=70 found in the Canon nFD 4/200, or v=80 found in the Nikkor ED 2.8/180). Similarly the 1.8/85 has less CAs and more monochromatic aberrations than the MD 1.7/85 or the Canon and Nikon 1.8/85 lenses, indicating the use of glass with a lower refractive index nD (I don't know the exact numbers, though).

S


stevemark, thanx for this very very usable information & explanation.

I'll comment back (or ask..) when i find some piece & time.


PostPosted: Fri Jul 26, 2024 9:17 pm    Post subject: Reply with quote
I have updated (added) especially the German translations in the Konica AR lens section, adding some further information mainly about zoom lenses:

http://www.artaphot.ch/konica-ar/objektive

should be easier to read for native Swiss / Germans.

Additinal information about some zooms (AR 3.5/80-200mm, AR 3.5/45-100m, AR 4/65-135mm, AR 4/70-150mm, AR 4/80-200 UC, AR 4/80-200) willl follow in a few days, as well as images of the AR 3.5/45-100m, the AR 3.5/47-100mm "half format", the first version of the AR 2.8/100mm and a few more. In addition I have made a comparison of all versions of the AR 135mm lenses (2.5/135, early and late 3.2/135, early and late 3.5/135, Hexar 3.5/135, and AR 80-200 UC @ f=135mm).

S


PostPosted: Fri Jul 26, 2024 9:41 pm    Post subject: Reply with quote
stevemark wrote:
I have updated (added) especially the German translations in the Konica AR lens section, adding some further information mainly about zoom lenses:

http://www.artaphot.ch/konica-ar/objektive S


Error in this link.

-D.S.


PostPosted: Fri Jul 26, 2024 10:50 pm    Post subject: Reply with quote
Doc Sharptail wrote:
stevemark wrote:
I have updated (added) especially the German translations in the Konica AR lens section, adding some further information mainly about zoom lenses:

http://www.artaphot.ch/konica-ar/objektive

S


Error in this link.

-D.S.


Here on my computer it works ...


PostPosted: Sat Jul 27, 2024 12:13 am    Post subject: Reply with quote
Working here now too. First attempt resulted in a 404 error page- which is not all that surprising, given the current state of digital affairs.

-D.S.


PostPosted: Sun Jul 28, 2024 2:24 pm    Post subject: Reply with quote
Some information plus short test about the rare Hexanon AR 3.5/45-100mm UC added here:

http://www.artaphot.ch/konica-ar/objektive/599-konica-hexanon-45-100mm-f35-uc

As usual it's strongly recommended to download the test image and watch it on a proper program such as photoshop. "Intelligent" automatic improvemen (resizing/enlarging PLUS color corrections) of the image happens in most browsers these days, and often the result is pretty shitty.

S


PostPosted: Mon Jul 29, 2024 12:17 am    Post subject: Reply with quote
stevemark wrote:
"Intelligent" automatic improvemen (resizing/enlarging PLUS color corrections) of the image happens in most browsers these days, and often the result is pretty...

S


Seems to be a deepening problem after the latest round of M/S updates, at least in my case.
Good to see that I'm not the only one who noticed.
Color accuracy seems to be taking a major hit.

-D.S.
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