http://www.forbes.com/sites/oracle/2016/09/12/electronics-retailer-looks-to-new-servers-for-ecommerce-breathing-space/#2eb70247b7f0

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OUCH!!! Dispersion is about the behaviours of waves at particular wavelengths, as in fluids, light, prisms, lenses, and chromatic aberration -- not as in photographic lighting. One commenter (CaptainC, echoed by dandi)is correct in clearly saying that "Dispersed light is NOT diffused light."

Moving from dispersion to diffusion:
1) A large source softens, but a small source (flash) can serve as a large source if it is an apparent large source, like a softbox, cloud, or flash bounce from a wall or a ceiling. Diffusion is the principle taking you from a small to a large (soft) source. Clouds are an apparent large source, due to diffusion of a small source (the Sun)
2) Maybe we should agree that bounced flash is diffused (softened). After all, bounced light must come to the subject, say, via the ceiling, from many angles)
3) The hard or soft edge of the subject's shadow will show that bounced light softens -- makes an apparent large source -- compared to less-diffused direct light. This is what you get from diffusion, bounced or not

To summarize, we can discuss the whole question without invoking dispersion ;>)
-We aim light by pointing a source, say at a subject or at a background -- and by use of coatings
-We direct light (1) by reflecting it, say, from on-camera flash, toward a wall; (1) with gobos; and (3) with (coated) lens elements
-We diffuse light by bouncing it and by sending it through the likes of toilet paper
-But we disperse light with optical devices, not with lighting appliances

One point to add about quality of the out-of-focus area is that Nikon is pursuing depth realism as a metric for their latest primes.

IMO, this means the DC lenses have a quality issue (only under the new metric) due to rendering the o-o-f area in a discontinuous manner, after the photographer's intervention.

With the zany understanding of bokeh among photographers, I wonder how many of us really know what Nikkor means by its new quality metric of depth realism. Probably this is a new frontier of image aesthetics, outside of Nikkor. One attribute could be that the transition from the focal plane to the adjacent o-o-f plane is preferably not abrupt.

85mm or 105mm for portraits?
See section V at http://nikkor.com/story/0059/ for an original PoV.

Keep us posted on your experiences with the 105mm E, please.

Your question wrt portraits' sharpness and bokeh reminds me of some useful authoritative remarks that have been published in recent weeks.

A Nikon-lens uberguru -- apologies for conflating a German word and a Hindi word into a new English word -- who clearly has influenced the 105mm E, says portraits do not require ultimate sharpness, as a practical matter. He also invites tuning sharpness with aperture, distance, and post. See the latest tale about 105mm 1.8S. http://nikkor.com/story/0059/. Also notes bokeh can be largely independent of moderate sharpening under certain circumstances.

Note that the 105mm E inherits from the 1.8S (per the above reference) and, per http://nikkor.com/technology/01.html, from the current 58mm G, and ultimately from the Micro-NIKKOR Auto 55mm f/3.5.

Agreed. I'd add that it may be necessary to further soften the light beyond what the tent does.
Supposing, for simplicity, that you are using one light; position it so that the angle of incidence prevents a direct reflection into the lens. See Hunter et. al.

This is a big, difficult topic.
First, we notice we can't fight the light; then we discover how to get along with it.

I have an 85mm f/2 PC Nikkor -- my first 85mm, with a few extras like a hood and a CPL. For small-product shots.
Decided the PC-E improvements might be not worth the extra money, but today I would get the PC-E if I could have a do-over. That way, I would not have to wonder.

Now, I am having trouble finding a compelling reason to buy any other 85mm lenses.
One possible reason to get another 85mm lens might be to better understand micro contrast by using a Zeiss 85mm 1.4 Distagon.
Anyway, I've so far bought fewer 85mm lenses because the 85mm PC lens serves well in various non-PC situations.

It may be that post processing is better at substituting for shifts than for tilts.

..."every piece of glass you put on your lens whether cheap or VERY expensive will add to CA."
Yes, and by definition a filter will add to CA.

However, CPL, when needed, trumps CA. The worst possible case would be to put a CPL on the new 105mm f/1.4. When this lens was announced, there was no CPL accessory. I suggested to Nikon that they should put their CPL onto the accessories list, and they did. See the first Q&A for the product.

Nikon has always treated their products as components of a total system; these components are made to play together. Accordingly, I try to use Nikon CPLs. For one thing, Nikon filters are notably flat.

A commenter mentioned a bad experience with a CPL at a very wide focal length. Wides and CPLs don't mix well. Such mixing is a well-known less-than-best practice.

It is commonly stated that AF lenses on DSLRs need circular polarizing filters rather than linear. I am not so sure that is accurate if you are focusing manually with an AF lens and DSLR. I likewise suspect that linear polarizing filters can be used in some DSLR-AF situations. These two effects are on my list of things to try out.

You can't necessarily expect your .jpg histogram in the camera to match, say, a raw histogram from Lr.

Note the frayed wiring...

Good post. I'm starting to understand that Nikon has overachieved the competion repeatedly in wides. Recent Nikon patents for a wide PC lens (17mm?) and fluorite indicate more to come; see very recent nikonrumors.com, for starters.

Building the ideal room
There is a lot of value in the earlier posts and I am about to re-read them after commenting here. I did not see much about my theme, which is bringing on-demand changes to the studio – dynamism.

Russ Halford, “Bounce Lighting,” 1958 defines the ideal room, p. 19. A couple of his points: (a) prefer smooth white walls to reflect a lot of light; (b) 12’x15’ – not too big due to light-intensity falloff; (c) start with basic (default) and try deviations.

Building on Halford, here are my three low-cost home-studio recipes that do not permanently change the room itself. These recipes allow for a dynamic color scheme while avoiding paint. Color seems to be top-of-mind for numerous respondents.

Flooring that protects equipment:
I laid down black rubber-like squares (2 square feet each) that interlock. A ten-minute task.
This is in case I drop equipment. In principle, I would not choose black, but I can dynamically cover it with a 6’ roll of paper, as needed. Have used it happily for a couple of months. No issues with my heavily-laden tripod. Try Costco for the stuff I use.

Swappable walls that address color casts:
There are 4x8' foam-insulation panels (R-Tech Insulfoam) at Home Depot. Each panel weighs a few ounces. With these panels, you can erect walls and a ceiling. Though the (horizontal) ceiling panels hold the (vertical) wall panels in place, I suppress light leaks by pinning the panels together with straight pins pushed in at an angle or I push in small nails. This arrangement has left room has a separate workshop, for my wife and a four-foot high chamber (Thanks, R-Tech) on a table top for seated post processing under defined lighting.
Back to the shooting studio, you can cover each panel with white or gray or black or other-toned paper on wide rolls or just go with the silver. I have Savage (Chandler, AZ, via Samy’s) 57-1253 gray tint and 9-1253 Stone Gray).
Now, for an example of the critical need for swapping out the color scheme. I'm photographing 19-th C Boston coin silver today and I know that white-wall reflections are far more obtrusive than reflections from silver walls. You can have extra panels and swap colors, according to your subject. When I shoot diamond jewelry, I don’t want the stones to pick up blacks, so if I’ve painted my walls black, I’m hosed. So just swap out your walls and ceiling, a one-minute task.
There are 2x4’ panels, as well, suitable for use as reflectors with gold foil and other tones. Taking it a little further, you might lower the ceiling dynamically with a 2x4’ panel from 8’ to get a stronger bounce.

Working lights that support focusing:
So you have a safe, enclosed space for controlled lighting. However, there is need for ambient lighting between shots and while focusing. The modeling light on strobe lights helps construct shadows, mid-tones, and highlights when posing a subject and when dialing in an exposure. Modeling lights go off automatically just before the strobes light up. It may help focusing to have strong dedicated light over a subject if you are on a tripod. When ready to shoot, these work lights for focusing need to be turned off. I do this with a remote switch at the tripod. The simplest switch is the Defiant 3-Pack Indoor Wireless Remote Control. You did not ask about this but it is huge. I have a smart-phone Wi-Fi switch as well but simple trumps complex dependencies, big time, at far less cost.

I would add that the subject is a fifth variable, in addition to field of view, speed, lens sharpness, and VR, which feeds into the decision to use a tripod. In Nikkor.com's "Thousand and..." Sato, in his discussion of the 85mm 1.8S AI-S notes that portraits may not require the ultimate in sharpness.

I like this comment, esp. about poor-quality tripods working against you. Maybe I can build on that. Here is a studio case study, of sorts.

I started with the flimsiest, smallest tripod and discovered the need to upgrade, repeatedly, starting with ball-head slippage. Nothing is reproducible w/o a tripod. I used to tie myself in knots shooting macro shots of makers' marks on jewelry but made up my mind to learn to do it better from a tripod, no exceptions. Results? With a tripod-only workflow, I get more -- way more -- keepers. Or maybe tripods bring good luck.

My preferred tripod steadily holds a cross arm and has a head with gearing in six directions, two focus rails for fine gearing in four directions, plus a JustRite for rotating the camera body by 90 degrees. The whole shebang can shoot straight up, straight down, or in between, from scraping the floor to about 7' high, by tweaking the attitude of the center post.

I no longer wonder if my apparatus has drooped or slipped. I rarely need to move the tripod feet, unless changing lenses. I almost never adjust leg height as I have a gear that can lower/raise the head. As Steve has suggested, tripod use can be less annoying than one might at first suppose.

Next on the menu is to rent/test a remote-controlled, motorized focus rail, for a more-stable live view. In other words, during manual focus, shaking of the live view image on the camera monitor or on the external monitor may arise from manually adjusting the focus rail -- distance to subject. Similarly, image shake during manual focusing can arise from moving the lens's focus ring. Either way, this shaking works against fine tuning the focus, especially under live-view magnification. Moreover, I expect that 1/50 mm -- (;>) -- adjustments will add to reproducibility in manual focusing.

Product photography highlights tripod issues, but other disciplines like macro photography can be as demanding. In short, the tripod saves time, boosts confidence, allows more attention to major issues like lighting...and even sets you up for mastering new skills, like focus stacking, bracketing, tilt, and shift.