Nikkor 360/f8 T ED chromatic abberation

I recently began printing some 4 X 5's I'd shot recently. One of

these was a highly detailed image shot using the Nikkor 360/f8 T ED

tele at f16 or f22 (I don't remember for sure). The orginal chrome

was drum-scanned on a Tango drum scanner.

 

I noted red fringes at high contrast edges over much of the image,

particularly towards the edges. These fringes were somewhere between

1-2 pixels wide (in a 300MB 8 bit scan). Additionally, sharpness

seemed to fall off substantially towards the edges as well. I

attributed the red fringing and sharpness fall-off to chromatic

aberration.

 

As I tend not to print any smaller than 20 X 24 (32 X 40 being my

preferred size), any sharpness loss due to chromatic abberation is a

big concern.

 

So I have a few questions:

1. Are these effects likely the result of chromatic aberration?

2. Has anyone had any experience with competing designs such as the

Schneider 400mm APO Tele Xenar?

 

As a side note, this lens is back from Nikon's optical bench to

correct a misalignment and bad shutter, so I have reason to believe

it is performing fully according to spec.

 

Thanks.

Lloyd:

 

Chromatic aberation, if I recall my physics, is characterised by two colour fringes: red on one side of a light source and blue on the other. These represent the opposite ends of the spectrum that is inaccurately refracted by the optic.

 

If the lens is a APO unit, this kind of birefringant aberation should be very small, if present at all. If it is not an APO lens, then it may indeed be that, but there should be the opposite colours on opposite sides of the subject.

 

A point source, such as Venus viewed thru a non-APO telescope will have a distict blue fringe on one side and a distinct pink fringe 180 degs opposite. The scope I used at a university observatory

had chromatic aberation so bad that the fringes were bigger than the crescent of Venus herself.

 

The optics or alignment of the scanner and its light source may well play a large part in any distortion present. This is one of the relatively few situations where the subtle differences in optics DO show up.

 

Are you printing onto paper thru an enlarger or via an inkjet printer? If it is an inkjet printer, it may be an artifact of the printer or the software, as the print heads may not be perfectly aligned. Also, if you're using an inkjet unit, then a quick examination of the original chrome with a 10x loupe should give you the answer, as the aberation will be on the chrome itself. Make sure the loupe does not introduce such aberrations by checking it with a small point source first. A clear north sky viewed through a pinhole in black paper or plastic should do.

 

Good luck.

I use the 400mm Osaka Tele. and have not noticed anything like you describe.

 

Is the misalignment that you had corrected the kind where the front and rear lens groups are not co-axial? This can happen quite easily to big lens groups that are held together with small shutters.

 

If you have access to a lab or machine shop, you can do a rough test for parallelism by placing the lens on a surface plate and running an indicator over the top edge.....shouldn't be off by more than .002".

 

Good luck.

I will second the opinion of Richard.

 

You should check the fringes by enlarging the film with an apochromatic enlarger lens, with a smaller focal then 150mm used for 4x5 film, in order to have the big magnification ratio as the scanning, and the problematic (assumed)edge of the chrome placed in the negative holder near the optical axis of the enlarger lens.

 

In addition to this, my point of view is that, the CCD in the scanner should create these artifacts in red, and may be the chrome is not correctly wrapped around the drum for scanning, causing the sharpness fall off near the edges.

 

Mehmet Kismet

Thanks for the feedback everyone. Nikon does not claim this lens is APO, just

that it uses ED glass. The effect I observed is on the computer screen, so the

printer is not in the loop.

 

The Tango drum scanner certainly does *not* introduce effects of this kind.

However, I checked the original chrome and observed the red fringing on one

side and blue on the other, so it is in the orginal chrome and therefore a

function of the lens. It does require a 20X loupe to see this, so perhaps I'm

being too picky, but then again why shoot 4 X 5 if not to get all the potential

resolution of the film! I need that resolution for the large prints, and I'm

certainly paying for it in the time and labor to take the orginal, and the money

to have it scanned at 300MB.

I once tested a Fujinon T600 and an Apo-Ronar 360. Both had a fair amount of color fringing (the Apo-Ronar being APO only at repro ratios). The best long lenses that I tested were the Fujinon C series. They are virtually free from chromatic aberration. I don't own the Nikon T but have made some shots with them. Although better than the Fujinon T, the scans I have just checked have some slight fringes, just as you described, one reddish pixel line on one side, one greenish pixel line on the other side, but on my opinion, nothing to be really worried about. That's the price you have to pay for the tele design: lower micro contrast and some aberration. I have no idea of how the Apo Tele-Xenar perform though.

It's not a complete fix for chromatic aberration, but since you're scanning anyway it should be fairly easy to take the worst of the aberration out in Photoshop: <a href="http://www.luminous-landscape.com/reviews/chromatic.shtml">http://www.luminous-landscape.com/reviews/chromatic.shtml</a>.

Thanks everyone, this has been very helpful. I found my local dealer has an APO Tele Arton in stock and I'm going to take a look, hopefully some test shots. If not, sounds like the Fujinon C series is a good bet.

I must correct something that I said earlier here. I said that the Apo-Ronars have some chromatic aberration when used for distant subjects. I just checked some scans and must admit I was completely wrong ! In the selection of scans that I just checked, there was no fringing at all. My mistake !