[gazonk]

What I wanted to show is that it is possible to reduce the effect so much that it isn't noticeable anymore. The example is extreme, of course. But, lens design can take this into account. Pentax does not seem to be interested in these color fringes. All DA lenses I owned have shown this effect strongly.

I may be wrong, but I have the impression that the effect is stronger on my DA70 @ 2.4 than on my M-50/1.7 @1.7. Anyway, most of the time it's really not an issue.

[falconeye]

the Voigtlander APO lenses do not show this. At least I never really noticed it. The 90/3.5 is using ED glass.

I specifically chose the 125mm Apo-Lanthar

Thanks for reminding us of the Voigtlander Lanthar lenses which use ED glass indeed.

That seems to be a rather cost-effective approach to produce images with less Bokeh fringing.

the effect is stronger on my DA70 @ 2.4 than on my M-50/1.7 @1.7.

70/2.4 = 50/1.7. Use your pocket calculator to confirm

[gawan]

Thanks for reminding us of the Voigtlander Lanthar lenses which use ED glass indeed.

That seems to be a rather cost-effective approach to produce images with less Bokeh fringing.

Out of curiosity (and maybe OT too), does Pentax use ED glass or similar in any of it's lenses, I don't remember having seen it in any Pentax lens specs?

[Asahiflex]

Out of curiosity (and maybe OT too), does Pentax use ED glass or similar in any of it's lenses, I don't remember having seen it in any Pentax lens specs?

Yes, some lenses do have ED glass. It's actually part of the (official) name. For instance the DA* 16-50/2.8 AL ED [IF] SDM.

[Blue]

This is Bokeh Fringing. Not (longitudinal or transversal) CA. Every lens has it due to the finite dispersion of any glass.

The effect is proportional to the aperture used and you normally won't shot macro at wide apertures.

It is possible to reduce the effect somewhat by using extra low dispersion glass (ED). But prime lenses w/o ED should all be similiar in this regard and the effect is unavoidable anyway. E.g., the Zeiss 100mm f/2 Macro (9/8 elements) and the Pentax DFA 100mm f/2.8 Macro (9/8 elements too) should be very similiar in the regard, i.e. they both don't use ED elements. The Zeiss has floating elements and may have better performance at portrait distances and/or wide open. It may have tighter production tolerances too. The Pentax is more lightweight, with WR and AF. The Zeiss is 2.8x as expensive as the Pentax.

FYI, the Pentax D FA 100 and WR have the Fixed Rear Element Extension (FREE). This design allows low field curvature and limits spherical aberrations when focused close to infinity as well as at very short distances. When used as a short tele the FREE system leads to small physical extensions which allows this lens to be physically smaller and lighter. However, during macro usage, FREE this lens exhibits non-proportionately long extensions which aid precise manual focusing. The A/2.8, F/2.8, FA/2.8, D FA/2.8 and D FA/2.8 WR all have the F.R.E.E.

[rparmar]

FYI, the Pentax D FA 100 and WR have the Fixed Rear Element Extension (FREE).

As do the A*85 and its successor the FA77, apparently.

[Blue]

As do the A*85 and its successor the FA77, apparently.

The DA 17-70 and DA* 16-50 do as well.

I see both sides of the argument here, but after having 50/1.4 for about 4 months, I am certainly hooked on Zeiss lens. It makes me want to acquire the entire line up. Tight specs, or lack there of, means absolutely nothing to me. Also, I have been around long enough to accept the fact that you don't always get what you pay for, and that is ok. Not the end of the world as we know it. There will always be a bargain somewhere to make up for it.

[falconeye]

FYI, the Pentax D FA 100 and WR have the Fixed Rear Element Extension (FREE)

Blue, thanks for the info. I looked it up a bit now and would say that it is a special case of the more general floating lens element design.

As always, execution of the idea is what matters. Otherwise, adding a teleconverter to a lens makes it having the FREE design

[Zav]

About Zeiss offer updates: a 35 f1,4 will be announced for Nikon and Canon (where is the ZK mount? )

[deejjjaaaa]

This is Bokeh Fringing. Not (longitudinal or transversal) CA.

if so - why objects behind focus have greenish fringing and in front of focus plane have reddish fringing like LoCA ?

for example

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/222-nikkor-af-105mm-f...report?start=1

Typical for many ultra-large aperture lenses the DC-Nikkor suffers a bit from Longitudinal Chromatic Aberrations (LoCA) resulting in greenish and reddish out-of-focus edge transitions.

[ewalk]

About Zeiss offer updates: a 35 f1,4 will be announced for Nikon and Canon (where is the ZK mount? )

I'm pretty sure a ZK mount will be offered as well.

[gawan]

Yes, some lenses do have ED glass. It's actually part of the (official) name. For instance the DA* 16-50/2.8 AL ED [IF] SDM.

Ah, of course! I have two of those kinds..

[blende8]

if so - why objects behind focus have greenish fringing and in front of focus plane have reddish fringing like LoCA ?

Focus is optimized for green.

[falconeye]

if so - why objects behind focus have greenish fringing and in front of focus plane have reddish fringing like LoCA ?

Make a drawing with RGB rays.

With LoCA, not all rays meet ln the focus plane, RB hits the plane slightly behind (or in front of) G. (The first order dispersion corrections make RB behave similiarly and different from B.)

With Bokeh Fringing, all rays meet in the focus plane (LoCA is zero). But outside the focusplane, the RB rays are distinct from G rays.

Of course, LoCA can add to Bokeh Fringing if not zero.


More formally, LoCA prevents the image of the exit pupil to ever have zero diameter, even in the focus plane. Bokeh Fringing makes the image of the exit pupil outside the focus plane (which has a disk like shape) have a colored border. But it's diameter (with or without a colored border) still shrinks to zero in the focus plane (if there isn't LoCA too).