Why The Plague of Longitudnal CA

[willie_901]

This is really a question about retro-focus lenses and DSLRs, so it may be inappropriate for this forum. If so, just let me know and I'll delete the thread.

Recently all the reviews of new fast lenses DSLR I've read report high levels of longitudinal CA artifacts. The most recent is a review of the Zeiss 35/1.4 F mount lens (Lenstip Review). The recent release of expensive, fast Nikkor G F mount lenses (24, 25, 50 and 85 mm) also show high levels of longitudinal CA. Nikons older AF primes behave similarly. I don't follow other lens vendors, so perhaps the problem is unique to Nikon.

I have read a retro-focus design is works well with digital sensors as the light rays are more perpendicular to the sensor. Could it be that the combination of interchangeable sensors and DSLR digital sensors are the root cause of longitudinal CA? Does Nikon and Zeiss (and perhaps other vendors) feel very few photographers care about longitudinal CA artifacts?

I read that Nikon's proprietary RAW processing software (NX2) corrects for longitudinal CA. DxO's software claims purple fringing is longitudinal CA (but they says nothing about the green color artifacts) and DxO Pro corrects purple fringing. Maybe lens designers have given up on longitudinal CA control because consumers can purchase post-processing solutions.

Any insights or comments?

 

[kbb]

My take:
I've seen the recent "test reports", and pixel-peeping forum folks who run their own tests, showing "pronounced" longitudinal color. I'm particularly fascinated by the shots of the ruler they all do. I also possess some of these new fangled lenses from Nikon and Zeiss, as well as a few 30+ year old ones. My conclusion, for now, is that the lenses ALWAYS did this---especially fast wide angle lenses-- but film made it look cool, so no one complained back in the day. Also, no one had a way to instantly blow up a frame(in color) to 30X at home. I sure as hell don't find it interfering with my attempts to exploit these lenses to make pictures. I would find it interesting to see one of these "testing" outfits throw a $12,000 cinema prime from Zeiss, Panavision, Cooke, or even the new Leica-C and see if by paying way more money, the Lo-CA can be eliminated. But none of us is going to shoot with those lenses on our still cameras anyway...maybe it'd be better not to know!

 

[ampguy]

yes it's there, with the lens in high contrast lights, when zoomed way up on-screen, but even in JPGs, I think starting with the D60, they correct for it, and with later bodies, also correct for the barrel distortion which is prevalent in the kit lens.

Today, I was at a Costco, and shot parallel beams on the ceiling, that you could see distorted through the dSLR VF, but then on screen, with the distortion correction on, they were straight. No need to go raw to get these corrections.