brian_caldwell

The 28/3.5 PC is optically mediocre IMO, so I mainly use it for architectural "snapshots". I have no experience with any of the other Nikon PC lenses, past or present. I do alot of stitched work, and for wide to ultra-wide rectilinear stuff I almost always use a 55/2.8 micro since it has essentially no optical problems at all. I normally shoot 10-50 images per mosaic. For full spherical panoramas I use a 16/3.5 fisheye or a 17-35 @17mm.

 

The 17-35 is much better at 28mm than the 28/3.5 PC IMO. Although its true that you can correct the pronounced color fringing from the 28/3.5, you can't do the actual stitching, so it represents a time-consuming step. Correcting distortion can be done at stitch time, so this isn't really an issue. For a short time I did panoramas by shifting the PC lens, but found this very limiting.

 

I've always avoided using my 15/3.5 for panoramas because it flares too easily, and this can make blending a real chore.

 

Brian

I just feel compelled to chime in with an irrelevant comment. You need to pivot the camera about the entrance pupil, not the nodal point. This really just boils down to improper use of optical terminology, since the methods that all good panographers use to find the "nodal" point will in fact find the entrance pupil instead.

Figuring out the relative light loss is an interesting problem. Using an extension ring along with maximum extension in the lens to get to 1:1 will lose you about 2 stops relative to infinity focus. Putting a 2x converter on the lens when it is focused to 1:2 will lose you slightly more than 3 stops relative to infinity, if my calculations are correct.

 

On the other hand, you get significantly more working distance when you use the converter, which might clinch the deal.

 

Optically, the converter will give color fringing, which can be corrected in post processing if you work digitally. The extension ring will give coma, but only if you work at fairly wide apertures.

 

Frankly, I would try both, since there may be advantages to each.

 

Brian

Christian Mozetic wrote:

"Is anyone here using this lens on a D70 already? It would be worth knowing what the chromatic aberation performance is. I use a 180mm f/2.8 ED AIS on my d70 and it does show quite a bit (at times a lot) of chromatic ab. From what I've tested, ACR does a pretty good job, it seems, of correcting this."

 

I use the 105/2.5 on a D1x extensively. I haven't noticed any significant longitudinal chromatic aberration, but then I rarely shoot wide open, either. There is a small amount of lateral chromatic aberration, which I sometimes choose to correct with Panorama Tools. The amount of lateral color is less than with the 180/2.8 AIS.

 

To be honest, I really only notice the lateral color in my 105/2.5 when examining images on-screen at greater than 100% pixel magnifications. For my purposes its insignificant, although big enlargements from a D2x might be another story.

 

On a potentially unrelated note, the 105/2.8 AIS Micro has no lateral color at all as far as I've been able to measure. I would use the micro more often for landscape work, but I worry about possible flare problems.

 

Brian

Akira:

Ghosts involving a sensor reflection tend to be located away from the optical axis. Its possible to have an on-axis ghost involving a sensor reflection, but you have to have a bright spot in the on-axis image in the first place. In this case the ghost image coincides with the actual image.

 

On the other hand, hot spots are most pronounced when the subject matter in the center of the field is dark, but surrounded by bright stuff. Ray tracing inevitably shows that this can't be caused by a sensor reflection, and that it is instead caused by a pair of lens surface reflections.

 

I've never had a problem with hot spots using the 55/2.8. The new version of the 50/1.8 AIS is quite poor in this regard, however.

A "hot spot" is actually a ghost image of the aperture stop. It is caused by a pair of reflections from lens surfaces on the image side of the iris diaphragm. Often, these reflections take place at the very last element in the lens. Hot spots tend to be prominent in the IR because the anti-reflective coatings on the lens elements are less efficient at these wavelengths.

 

You can't predict whether a hot spot will appear based solely on the diameter of the rear element. The exact lens radii and stop position are critical here. Its best to rely on personal experimentation or on reliable reports from people like Bjorn.

Lex (perpendicularity consultant) Jenkins wrote:

"Judging from everything I've read there is no Nikon brand TC designed to produce top quality results with any version of the 180/2.8 Nikkor, manual focus or autofocus. In every case there was some form of disclaimer.

I surmise from this that at best we can expect good results only at the center of the photo. That may be enough for some purposes. "

 

I've never been disappointed with the 180/2.8 ED + TC14a.

As far as I know, there aren't any lenses available that will fit your needs. The Zeiss 21/2.8 Distagon has the right lens design technology, but the EFL is too long and can't be used with a Nikon F-mount.

 

Two alternatives come to mind. First, you might try a 16/2.8 fisheye, or even better an older 16/3.5 fisheye, and then correct the distortion with Panorama Tools or equivalent. This isn't really a great solution because the distortion correction will reduce resolution in the outer parts of the image. Second, you might try stitching using a longer lens having zero or nearly zero lateral color. I find stitching to be faster and better than shooting large format film. Lenses having very low chromatic aberration over the DX format include the 17-35/2.8 in the 24-28mm EFL range, the older 25-50/4, the 50/1.8, and my personal favorite 55/2.8. You'll need to take lots of shots with the latter two lenses to cover an ultra-wide field, but the image quality you can achieve is truly remarkable.

 

P.S., my site was accidently deleted by Yahoo, but I'm working on a re-birth.

 

Brian

Vivek Iyer wrote:

"When the Sony digicam hits the market, it would be possible to compare the D2X (with the Sony sensor) with a Nikon zoom and its performance with a Zeiss Vario Sonnar."

 

I wonder if Zeiss had anything at all to do with this lens except for licensing its name?

It sounds like what you're seeing is a ghost image of the aperture stop. Its normally caused by a pair of reflections from lens surfaces located between the stop and the image plane. These ghosts tend to be much worse in the near-IR (and possibly near-UV), since the lens coatings don't work well in that region of the spectrum. You might try experimenting with IR and UV blocking filters to see if you can get a better result.

 

The part that confuses me is that you see the problem with every lens. I normally only get this problem with my new version of the 50/1.8. The older long-barrel version doesn't have the problem at all, as far as I can tell. What sort of lenses are you using?

Michael:

I know that the viewfinder always uses the lens at full aperture. However, the scattering qualities of the screen can have a profound effect on how much of the full aperture you can actually see. As an extreme case, consider a focusing screen that is just a plain un-ground piece of glass. Yes, you could still see the aerial image through the viewfinder, but in bright daylight your eye will effectively stop the lens down to about f/30. If you were to press the DOF button and turn the aperture ring you would see no change in viewfinder brightness, even if you went all the way from f/22 to f/2.

 

The only way to accurately see what is going on at f/1.2 is to make sure that light from the outer portions of the ray bundles are actually getting into your eye. This can only happen if the viewfinder screen scatters enough light.

 

When I press the DOF preview button and turn the aperture ring, here's what happens:

 

1) Opening up from f/16 to f/11 to f/8, etc, through f/2.8 the brightness of the viewfinder image increases substantially at every one-stop increase.

 

2) Opening up from f/2.8 to f/2, the brighness increases a little, but not nearly as much as I would expect.

 

3) Opening up from f/2 to f/1.4 or f/1.2 produces no visible change in brightness, even in relatively dim conditions when my pupil is dilated somewhat.

 

In other words, the standard D1x viewfinder shows you *nothing* about what the lens is doing beyond about f/2. This is why its so hard to focus at f/1.2: you get f/2 viewfinder accuracy but f/1.2 DOF.

Joe:

Thanks for all the info. I hadn't heard of the DK-17M eyepiece, but I will look into it. I know it must be possible to replace the focusing screen, since it actually fell out of my D1x once. I really should get more serious about customizing my cameras to meet my needs.

 

My 58/1.2 must stay home - sorry. However, I do have a spare 55/1.2 . . .

 

Brian

The 17-35/2.8 is better than any of my wide angle fixed focal length lenses. This is particularly true in the 24-28mm region. I have heard that the 12-24/4 is excellent from 18-24, but I've never used the lens. The common thought that zoom lenses are a compromise relative to prime lenses may have been correct a decade or two ago, but is now completely incorrect.

 

This link may be helpful: http://web.archive.org/web/20030405124103/www.caldwellphotographic.com/LensTesting1735vsPrimesAtf8.html

Ellis:

I've always had *alot* of trouble focusing fast lenses such as a 58/1.2 on my D1x, and I believe its entirely due to the focusing screen. What's going on is that the focusing screen is designed for maximum brightness, and so it doesn't work nearly as accurately for apertures below f/2.8. This is obvious by simply observing that the viewfinder image doesn't get significantly brighter as you open up a lens from f/2.8 to f/2 and then to f/1.4.

 

Is the D2x viewfinder better than the D1x viewfinder for manual focusing with fast lenses?

Tessars are vastly overrated, both in terms of sharpness and bokeh. At f/2.8 a competently designed double-Gauss will beat a Tessar in all respects.

 

The bright ring with a bright region at the center is very typical bokeh pattern for the spherical aberration correction that is common to all f/2.8 Tessar lenses. If you stop down to f/4 the bright ring vanishes and your left with a bright core that gradually fades away, which is good. However, you can achieve the same thing with an f/1.4 or f/1.8 double-Gauss by stopping down to f/2.8.

 

The main problem with the bokeh of the Nikkor 50's is that the iris doesn't stay round when you stop down to f/2.8 or f/4. If it did, then the sub-$100 50/1.8 would be a complete embarassment for the 45P.

The 55/1.2 definitely has a different look than the 50/1.2 or 58/1.2 Noct, and for certain images that look might be preferable. Wide-open the contrast is low, but corner resolution is higher than the Noct since it has a flatter field. This latter characteristic makes it a better general purpose lens than the Noct IMO, since it will give sharper images at f/8.

 

Just use the lens. If you like it, then keep it. I've never been tempted to sell mine.

Ilkka Nissila , jul 30, 2005; 08:41 p.m.

"MTF is the lens transfer function, in effect what the lens does to the light. I think everything about the image quality of a lens can be described using modulation transfer functions. (I must be missing something, I can feel the heat on me after saying this ....)"

 

You won't get any heat from me on this! MTF measurments and calculations are a very powerful tool for understanding lens performance. Things like field curvature, color fringing, closeup performance and even bokeh are most certainly revealed by a lens' MTF data so long as the data is sufficiently complete and properly interpreted. Any aspect of lens performance that is related to aberrations (or lack thereof) can be represented by the MTF, with the exception of geometrical distortion.

 

On the other hand, I would agree that things like flare due to imperfect coatings, and transmission losses as a function of wavelength are not addressed by MTF at all.

You might want to consider attaching your D70 directly to a telescope. Adding an eyepiece and photographic objective is possible, but isn't really necessary and will almost certainly degrade image quality. The digiscoping thing is really more appropriate for digicams without interchangeable lenses.

Bjorn:

Thanks for the sample image - its certainly thought provoking. The only explanation that comes to mind - and its probably not correct - is that the poor bokeh at f/16 may be due to some sort of atmospheric effect. I'll have to try various lenses to see if I can get a similar result.

Bjorn Rorslett , jul 25, 2005; 01:49 p.m.

"Brian: I can only report what I see in my photographs. I'm not an optics expert as such and hence don't know what the theory says should be there.

For me, "bad" bokeh is about an OOF rendition in which lines get doubled and highlights get sharp, harsh edges. It is not about increasing DOF as such. Some lenses impart a very smooth and creamy texture to the background which holds up well when the lens is stopped down, despite the obvious increase in DOF. Typical examples are 85/1.4 AF, 200/2VR, and 300/2.8 AFS VR. The older versions of these three lenses, viz., 85/1.4 MF, 200/2 MF, and 300/2.8 AFS, differ significantly in the way they behave when they are stopped down. Hopefully, a theory exists to explain this. For me, the images suffice on their own."

 

Hi Bjorn:

Thanks for your comments. I hope you'll forgive me for invoking aberration theory, but this is one aspect of optics where I would really like to have theory and experiment coincide. Its practical importance actually goes beyond pictorial aesthetic considerations. For example, several years ago I designed a zoom lens that had good sharpness but poor bokeh. At the time I didn't think that mattered because the application was an inexpensive digicam, and most of the pictures would have everything in-focus anyway. However, the bright ring effect caused by the bokeh badly confused the autofocus system which was based on image contrast. Fortunately, the firmware engineers were able to tune the autofocus algorithm to ignore the bright rings.

 

I agree with your definition of "bad bokeh". As an aside; if you think about it, bright-edged highlights and doubled lines are two aspects of the same phenomenon. After all, a line is just a sequence of highlights.

 

The part that confuses me here is when you consider a single defocused highlight with an intensity buildup at its outer edge. As you stop down the bright outer edge disappears. There's just no way I can think of that a new bright edge with smaller diameter can suddenly appear as you stop down. And without an intensity build-up in the outer part of the highlights you can't get the line doubling that is so characteristic of bad bokeh. What I would expect to happen, and what I see in my own photographs, is that the defocused highlights become more uniform in intensity as you stop down, and that their shape of course corresponds to the shape of the aperture.

David:

Its unclear to me that other manufacturers have an edge over Nikon in this department. Its certainly not the case with Zeiss, whose 50/1.4 appears to have as bad or worse bokeh than the corresponding Nikkor: http://www.bokeh.de/en/bokeh_images.php?t=d&a=&ff=50&ft=50

 

Also, many people claim that the 45/2.8 GN and newer P lenses have better bokeh than the other Nikkor 50's. With respect to bright ring and line doubling effects I have to disagree. If you stop down any of the Nikkor 50's to f/2.8 you will not find bright edges on defocused background highlights, but both of the 45's show this. IMO the only bokeh advantage of the 45/2.8 is a more circular pupil shape. If the 50/1.8 and 50/1.4 only had a better iris diaphragm they would absolutely trounce the 45P.

 

Bjorn:

On several occasions you allude to lenses whose bokeh gets harsher as you stop them down. This is contrary to aberration theory, because virtually all photographic lenses have slightly undercorrected spherical aberration (just what you want for good bokeh) when stopped down. Is the effect you're seeing just due to increased DOF or polygonal aperture shape, or is it something else. I'm extremely curious about this.

Bjorn Rorslett , jul 21, 2005; 06:57 p.m.

". . . the AF 2.8 . . . has much harsher background rendition when it is stopped far down. "

 

I'm extremely curious about this. When you stop a lens way down it should become diffraction-limited. The only possible causes I can think of to create bokeh differences would be diaphragm shape and lateral color. Is this what you are seeing?

P.S.

Even if a perfectly ghostless lens could be designed, putting a plane-parallel filter in front of if would give you plenty of ghosts, as your images demonstrate.

"Robert Lai , jul 17, 2005; 04:20 p.m.

Sure, this is old news, but I'm one of those that refuse to believe conventional wisdom until I've reinvented the wheel :-)

How does Pentax make lenses that don't ghost? They know something that Nikon doesn't?"

 

Besides improving the coatings, the only thing you can do to reduce ghosting is to design the lens in such a way that none of the multitude of combinations of double-reflections from internal surfaces result in a focus near the image plane. Its actually more complicated than than, since the numerical aperture of the ghost images also plays an important role in how visible the ghost images are.

 

Simply put, there's no way to avoid the ghost images. But what you can do is to make sure they are very defocused at the film plane. Achieving this in a design is extremely tedious since tiny changes in the lens parameters can have a big impact on the ghost images. This is something that current lens design software is not particularly good at, so lots of trial and error is required.

Sharply-focused ghost images that have mirror symmetry about the optical axis with respect to the main image are almost certainly a reflection off the film plane followed by a reflection from the filter. Tilting the filter will move the ghosts, and it might be possible to eliminate them from the image altogether depending on the scene. I realize that tilting a filter may not be very practical, but it might make for some interesting experimentation.

 

A very easy thing to try is to stop the lens down as far as possible. This will block a return path for ghosts located well away from the optical axis. Try f/16 or f/22 instead of f/4 and see what happens.

 

Still another way to get rid of this kind of ghost images is to use a filter with curved surfaces, which is actually done nowadays in the cover glass of recent super telephoto lenses. This will defocus the ghost images, thereby spreading them out and reducing their brightness.