This comparison is to test a group of lenses I have for longitudinal chromatic aberrations or LOCAs, also called Bokeh CAs, at 1X. The reason that I spend the time to run a test like this is simply to find out how my lenses perform and to share my LoCA results since testing for this is just about unheard of online. There is only one site that I know of, www.Photozone.de, and they don't run their tests at close up distances.
What are LoCAs?
Longitudinal chromatic aberrations or LoCAs are ugly purple and green fringing seen in the out of focus areas in front of and behind the focus point of an image. LoCAs are common, especially with fast lenses, so chances almost all of your lenses have at least a trace, you just never noticed. The problem is that LoCAs are extremely difficult to correct with complex designs using special glass to fully correct the aberration, the Scanner-Nikkor for example has 14 elements, 6 of those being ultra low dispersion.
Test Setup
D810 camera was mounted on a Newport PRC-3 rail carrier and Arca Swiss style quick release clamp and moved back and forth to accommodate the different focal length lenses set at 1X. The Newport PRL dovetail rail system was bolted to a Thorlabs aluminum breadboard with a printed target set at 30 degrees on a tilt head. A single Nikon SB-R200 flash and the tilt head remained in place during the test.
Lenses Tested
Sigma 50mm F2.8 EX DG Macro
Sigma 70mm F2.8 EX DG Macro
Rodenstock 75mm f/4 APO-Rodagon D
Schneider Macro Varon 85mm f/4.5
Nikon Scanner Nikkor ED 100mm
Sigma 105mm f/2.8 EX OS Macro
Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED
Voigtlander 125mm f/2.5 APO-Lanthar
Sigma 150mm f/2.8 EX OS APO Macro
Sigma 180mm f/2.8 APO EX OS Macro
Sigma 180mm f/3.5 APO EX Macro
Nikon AF Micro-NIKKOR 200mm f/4D IF-ED Lens
Notes: All of the lenses above are my property except for the 105 VR and the 200 f/4 ED that are on loan from Nikon and the APO-Lanthar that is on a long term test loan from a friend. Later this year I hope to add the Sony FE 90mm f/2.8 Macro G OSS, the Zeiss 100mm macro, and a few of my own Canon lenses to this comparison. Since I am only testing my own sample lenses, your results may vary.
Laser printed test target at 1X with crop area outlined in blue
Sigma 50 and Sigma 70
Both of these lenses show LoCAs wide open but clean up by f/5.6 with the Sigma 70mm macro slightly cleaner than the 50. Clicking on the image below will open a larger 2400 pixel version in a new window.
Nikon Micro-NIKKOR 105mm VR f/2.8G IF-ED vs. Sigma 105mm f/2.8 EX OS Macro
This is interesting comparison since both lenses are similarly priced new at $900. There isn't much of a comparison in terms of LoCA correction though. The Sigma is very clean by f/4 but the Nikon 105 VR shows moderate LoCAs, even stopped down to f/8. The level of LoCAs is disappointing to see with the Nikon even though the design of the lens supposedly incorporates some type of ED or extra low dispersion glass to correct for it. Clicking on the image below will open a larger 2400 pixel version in a new window.
Sigma 150mm f/2.8 EX OS APO Macro vs. Voigtlander 125mm f/2.5 APO-Lanthar
The APO-Lanthar exhibited more LoCAs than I expected but it does clean up by f/5.6. This lens has an unsurpassed optical legend online, but in the real world I didn't see it.. This lens is not a true APO. To be fair the lens is more than 15 years, so with that in mind the performance is very good. Also you need to consider that the Voigtlander only has 2 low dispersion elements, where the Sigma has 3. Even with 3 UD elements, the Sigma is not completely free of CAs either, it does show some traces of LoCAs wide open and at f/4 if you look closely, but anyway, it does seem to have some of the cleanest images in this test, so well done Sigma!
For CA correction the APO-Lanthar is not the best value, considering it costs 3X the price of a Sigma 150 on the used market.
Clicking on the image below will open a larger 2400 pixel version in a new window.
Sigma 180mm f/2.8 APO EX OS Macro vs Sigma 180mm f/3.5 APO EX Macro vs Nikon AF Micro-NIKKOR 200mm f/4D IF-ED
Wide open, all three lenses below show LoCAs. Closing down a stop, the problem goes away for the Sigma but the the Nikon 200mm ED lens shows pretty bad LoCAs, even at f/8! The Nikon performed the worst here even with the slowest maximum aperture and a design that uses ED glass. Clicking on the image below will open a larger 2400 pixel version in a new window.
Rodenstock 75mm f/4 APO-Rodagon D, Schneider Macro Varon 85mm f/4.5 CAS, Nikon Scanner Nikkor ED 100mm
These are the most specialized lenses in this comparison and personal favorites of mine. They are all optimized to work at specific magnification ratios. The Rodenstock is used for duplication and is optimized to perform its very best at 1X and at f/4. I was surprised to see level of longitudinal CAs honestly, I guess I have just never noticed it before working with this lens over the years, the image quality is fantastic otherwise. The Schneider Macro Varon CAS is really special lens so the lack of LoCAs is no surprise, the image quality of this lens is just amazing. One of the selling points of the MV is a special chromatic aberration suppression system, and believe it or not, it looks like it works! The Scanner-Nikkor is completely free of any trace of LoCAs and shows excellent all around image quality thanks to a superb design using 14 elements, 6 of these being low dispersion glass!
Clicking on the image below will open a larger 2400 pixel version in a new window.
Eliminating LoCAs
Longitudinal chromatic aberrations cannot be corrected in camera or in RAW conversion like lateral chromatic aberrations.
LoCAs can be reduced in the focus stacking process with software like Zerene, see: https://zerenesystems.com/cms/stacker, since the LoCAs shows more strongly in the slightly OOF regions that are mostly ignored so they do not appear in the in-focus stack. Color casts can sometimes still remain though, either through information leakage or since some of the out of focus remain in the completed stack.
The Results
All of the lenses in this comparison did pretty well in terms of longitudinal CA control but the 105 and 200 Nikons stood out as having, by far, the worst results, even with the aperture closed down! The cleanest images in this comparison have to be from the Macro Varon and the Scanner Nikkor, both shot wide open! It's interesting that Nikon lenses are at the very top and the very bottom of the results!
If you are looking for a well corrected lens for not a whole lot of money, the Sigma 70mm and 105mm macro are hard to beat, sharp, decent working distance, decent CA correction and a overall great values. I have seen these for sale on Ebay for $250 in like new condition. If you are looking for absolute best value out there in terms of sharpness and the most optical correction per dollar, the Sigma 50mm can'e be touched. Its a super performer, LoCA and CA free at f/5.6 and smaller, very sharp, and can be picked up used for $100, sometimes even less!