Archive for the ‘Article’ Category

This is kind of an adjunct to part 4 of my “Server Upgrade Chronicles”.

ZFS root pools have some requirements and best-practices at variance to other ZFS pools. One of the most annoying is that you can’t use a whole disk, and you can’t use an EFI-labeled disk. This is annoying because for most ZFS uses using a whole disk is the best practice, and when you do that ZFS puts an EFI label on that disk.

So, when you try to use in a root pool a disk you’d previously used somewhere else in ZFS, you often see this:

bash-3.2$ pfexec zpool attach rpool c4t0d0s0 c9t0d0s0
cannot attach c9t0d0s0 to c4t0d0s0: EFI labeled devices are not supported
on root pools.

What do you do then? Well, you google, of course. And you find many sites explaining how to overwrite an EFI label on a disk. And every single one of them omits several things that seem to me to be key points (and which I had to play around with a lot to get any understanding of). The fact that ZFS is what drew me back into Solaris, and that I wasn’t ever really comfortable with their disk labeling scheme to begin with, is no doubt a contributing factor.

This is going to get long, so I’m putting in a cut here. (more…)

This got sufficient praise when I posted it as a comment to a question on LiveJournal that I’m reprinting it as an article here, where I can find it when needed.  The question was initially about Sigma vs. Nikon lenses.  I currently consider Sigma, Tokina, and Tamron to be the third-party lensmakers who sometimes make first-rate mainstream lenses (no offense intended to specialists and weird people like Zeiss, Cosina/Voigtlander, or Coastal Optics (now a division of Jenoptik Optical Systems, it looks like)).

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Who’s ahead in which parts of their lens lineup changes over time—so one thing that influences the advice you get is the age of the adviser. I’m 55 myself .

For a while, zoom lenses were only made by third-party companies (absolute statements probably aren’t absolutely true, but this is how I perceived it in the 1970s). Then the camera companies made overly-conservative zooms, and the third-party companies made better zooms. This covered parts of the 80s. Then the camera companies started making first-rate zooms.

Also, the camera-companies started making second- and third-rate zooms, and even some primes. And the third-party companies didn’t always do their best anyway.

So, TODAY, IMAO, the situation is confused to the point where there’s no simple general advice. You have to specifically consider each type of lens and decide which ones are good and which aren’t. Nikon isn’t ALWAYS better or worse than Canon—or than Sigma, either. (Sigma was a third-tier company even 10 years ago, but they aren’t today.)

One thing to keep in mind is that, if you’re buying Nikon’s consumer-grade lenses like the 18-200 or the 70-300, there’s a lot less to lose going to Sigma, Tamron, or Tokina. Those aren’t Nikon’s top work. Similarly, the Sigma 120-400/4.5-5.6 may actually be better than the Nikon 80-400/4.5-5.6 (though Nikon just did or is about to update that lens, so who knows?). It’s the Nikon 200-400/4, the $5000 professional lens, that Sigma probably doesn’t have a real competitor for.

Also remember that wide-range zooms always carry compromises. You simply can’t make an 18-200 and sell it for a 3-figure price that’s first-rate throughout. However, the convenience can be important, and the quality might be good enough for you. Don’t pretend you always need “the best”—at least not while talking about a D40x . Be realistic, it’ll stand you in good stead; probably save you thousands of dollars. Junk is never worth it, but the very best is probably completely out of your reach, too. You HAVE TO compromise—and even the “very best” has flaws which the people who use its full capabilities all know about and have to work around. The best photographers I know don’t own a single piece of “perfect” equipment; instead they own lots of very good equipment that they fully understand. They avoid using it for the things it’s bad at.

You’re probably better off with Sigma’s pro-grade lenses than with Nikon’s consumer-grade lenses. Although every now and then, a consumer-grade lens happens to be really outstanding anyway. (As a rough guideline, fixed-aperture zooms, especially if the aperture is fast for the focal lengths, are nearly always considered pro-grade lenses. Slow, variable-aperture zooms are nearly always consumer lenses. Primes are nearly always pro-grade lenses. I believe Sigma uses the “EX” designation for what THEY think are the pro-grade lenses. But even this is, in the end, a matter of opinion.)

And if you want the very best autofocus 50mm/1.4—that’s almost certainly the Sigma; but it costs a lot more than the Nikon. (The Zeiss manual focus 50/1.4 may be better, partly depending on what you care about.)

When reading customer reviews, consider the number sold. Something sold by the tens of thousands is nearly certain to have more bad reviews than something sold by the tens.

Here’s a trick I used. I still think it’s clever. Go someplace like photo.net where you can search by the lens, and look at the pictures taken with each lens you’re considering. Some kinds of problems won’t show up at web resolution, others will. But in addition to what you can see yourself, there’s a second source of information: If a number of photographers who take really gorgeous pictures all use a particular lens, you’re pretty safe in concluding that lens is pretty good. This path led me to the Tokina 12-24/4, which indeed was a fine lens (and quite cheap), and which served me well when I was on a DX sensor.

Note: This started life as a post on a mailing list, but it was suggested that I should archive it here for future reference, and it does seem to be fairly extensive and maybe worth keeping around.

Obviously what one “likes” is significantly a matter of taste, and people will simply disagree to some extent. There are usually tendencies and trends in taste among large enough groups of people which can still be useful guides to design—if you want this group, don’t do that, if you want the other group over there, do some of this, and so forth.

What there isn’t is a large enough group of GOOD designers. I’d rate myself in the upper half of fannish web designers (I’m talking design, not implementation mechanics), perhaps optimistically; but that doesn’t put me on the scale at all in comparison to real professional designers. I worked for 4 years doing web work with some GOOD designers, and I can tell the difference. My attempts at elegant simplicity (which admittedly is hard) never quite come together, and I end up with things like this site and dragaera.info. My tastes and skills don’t lend themselves to the busier kind of designs at all.

With a GOOD designer, a site can be graphically rich and complex without creating a problem finding things on it, and it can still load decently for people with broadband (real graphic richness doesn’t work so well with dial-in; just too much data). Multiple media can be used to draw in people who like that, without hiding information from people who just want to read it.

This requires some extra work, some duplication of information, and suitable design. And it requires committing to some things and carrying them through in the course of the year. But it’s not terribly expensive, if you have the design talent available (hiring it commercially is expensive, by local con standards).

To add the media, maybe find people into that and appoint them your “web media team”, and tell them to go around and interview a department head each month or something.

Some potential members will feel more of a connection to the con having “face-to-face” informal time with the staff that way. Others will ignore it.

Got some good writers? Maybe they should blog about planning the convention and getting it ready. Again, it will make some people feel a connection they wouldn’t have otherwise. It’s also a great way to get across some of the important things about the convention—like that it’s all-volunteer. For the kind of convention I like, writing is better than streaming media to convey what it’s like, because showing people sitting around having a fascinating conversation makes for boring film (but don’t overlook the personal essay delivered as streaming video by somebody with some presence). Get new members and long-time members to write about their experience of the convention, either some specific year, or in general. Search other web sites and mailing lists for such articles, and ask permission to republish them (and you can generally link them in place even if they won’t let you republish).

In addition to making the content on the web site deeper and richer, you need to drive traffic to it. Obvious things include using your URL consistently in con materials. You need to do outreach. A minimum suggestion is to put stuff (flyers, bookmarks, business cards, postcards, as appropriate) at libraries, bookstores (especially specialty stores and those with a good SF selection!), teachers and schools, SF clubs, other conventions. Try for news coverage on public radio. Can you do something with public access television?

Remember that the site has to convince people who don’t know about SF conventions to give your event a try. You’ve been marketing for years to the ones who know about cons, and they’re already coming or have decided your con isn’t for them.  The growth potential is in people who haven’t found classic SF fandom yet.

And you need a multi-year commitment to this stuff; it takes time for the effects to build up, and you really only get to sample the results once a year (when you hold your convention).

(This is based on the assumption that your convention is basically fine, and that there are a significant number of people who would be interested but don’t know about it in your area. As you get in new members you may start to find ways you should extend your convention itself some as well, perhaps.)

For a well-established convention that feels it’s not getting its share of new members lately, I don’t think anything much smaller than this effort is likely to make much difference. A new convention is different, but a long-established one already has about all the word of mouth it’s going to get, and probably has some mis-perceptions floating around out in the population by now.

Very very roughly, what I’ve outlined above is a few hundred person-hours of EXTRA pre-con work in the first year, and perhaps half that (not nearly so much brainstorming and figuring things out, the web site structure will be in place and the design set) in the second and later years. Which no doubt explains why so few conventions have ever taken such an aggressive promotional stance. The monetary cost is low, though; mostly printing the new flyers, bookmarks, business cards, and such (I’m assuming you already have a web site, so no new cost for that). Unfortunately, those people points are probably your scarcest resource.

It’s possible (despite what I say above) that this is subject to the 80:20 rule (since the rest of the universe appears to be). I would venture to guess that the key components are regular new content on the web site, a more personal and less monolithic view into the convention, and considerable outside action to point new people to the web site.

What do photographers mean by “soft” light?  And how do you produce it?

This is one of the most important things in photography, important everywhere from the sunlit outdoors to the studio.  So pay attention.

Light: Science and Magic (Hunter & Fuqua), a textbook on lighting that I highly recommend, talks about this as early as chapter 2, using the term “contrast” (but talking about “soft” shadows produced by “low contrast” light). “For single light sources, the size of that source is the primary factor influencing its contrast.” (Amazon appears to have the third edition of the book, with a third author; mine appears to be the first edition; it was a present from Oleg Volk years ago when I asked if he’d run into any good textbooks on lighting.

There’s also the question “why should you care?”  I’m mostly skipping that; sometimes you want soft light, sometimes hard, and it’s useful to know how to recognize and produce each.  Deciding which you want is an artistic rather than technical decision, and I don’t write articles on artistic issues.

The softness of light is controlled by the apparent size of the light source as seen from the subject, and the distance from the subject to the background (where the shadow is cast).

Soft light—Critical Rays

The blue lines show the rays from  both extremes and the center of the light source as they pass the top of the subject, and where they hit the backdrop. The red lines show the same for the bottom of the subject. The area completely behind the subject has the darkest shadow, with the shadow gradually brightening from there to the edge (both top and bottom).

A couple of useful things come out of this immediately.  You can make light softer simply by moving the light closer to the subject, or by moving the subject farther away from the background.

Closer and Softer—Critical Rays

Moving the light in has made the central, darkest, shadow smaller, and the zone in which the shadow gradually transitions from dark to light larger—a much softer shadow. (Moving the light closer also has other consequences—it makes the illumination on the subject brighter, and the difference between near and far parts of the subject stronger.)

Similarly, although I’m not going to draw it, moving the background farther away would make the shadows softer.

Wide-Angle Setting

Now, let’s illustrate this with actual light. Here’s an actual fairly soft shadow, being cast by a small flash unit quite close to the subject, with the background nearly equally far away. As you can see, precisely defining the “edges” of this soft shadow is fairly hard.

So I have marked the shadow edges, partly by eye but largely by measured image brightness.

Wide-Angle Setting, Shadow Edges Marked

So, here’s a full-resolution crop of the part showing the shadow and the ruler. I’m going to say the gradient goes from from 19mm to 23mm, or 4mm.

Now, I’m wondering something. Does the flash head really produce light coming off in all directions (except backwards)? Or is the beam more focused? If the beam is enough more focused, rays from the top edge won’t stray far enough down to contribute as much to the wide shadow—essentially, an efficient reflector will make the flash head behave (in terms of softness) as smaller than it physically is.

Parallel beams leaving an efficient reflector

If the range of directions the beams leave the reflector is small enough, the light will be much harder than the physical size of the head suggests.

So, do my flashes behave this way?  (The flash pictured is a Vivitar 285.)

"Wide" setting, diffusion material

Only one way to find out. Putting a couple of layers of “diffusion” material (like tissue paper) directly over the front of the flash will pretty much guarantee that the beams can leave in any forward direction. Let’s see if doing that makes the light any softer.

It’s obvious that there’s a lot more light emitted towards the sides now—the two vertical pieces of foamcore are much more brightly lit than in the first test, for example. And, visually, the shadow is clearly softer.

Here’s the marked version.

"Wide" setting, diffusion material, shadow edges marked

And, finally, here’s the close-up of the shadow over the ruler.

"Wide" setting, diffusion material, full resolution shadow on ruler

I make that 20mm to 25mm, or 5mm of gradient. Since it’s clearly visually softer than the un-diffused version, it’s nice that the measurement is in line with that.

Since the flash head is focused so well, does the zoom setting make a difference?

Flash at "tele" setting, no diffusion material.

Well, visually it seems to.

Flash at "tele" setting, no diffusion material, shadows marked

Flash at "tele" setting, no diffusion material, full-res shadow on ruler

I read that as 19.5mm to 23mm, for 3.5mm, the narrowest shadow we’ve measured.

So, what have we learned here? We’ve confirmed some basic things about what makes light soft. We’ve shown that even a source as small as your flash can produce fairly soft light at close distances.

And we’ve shown that the physical size of the light source isn’t always the whole story. A light source can behave as smaller than its physical size for purposes of softness, and units based on small light sources plus reflectors are probably significantly more likely to exhibit this behavior (electronic flashes, in particular). This is why putting diffusion material over a light can make it softer, even though it isn’t making the light physically larger. It can’t, however, make the unit behave as if it were larger that its actual size.

I always wondered about putting diffusion material directly over a light source (across the front of the reflector for a studio light is the common example). It “obviously” couldn’t work, to my mind. Enough real photographers used it so I figured I must be wrong for some reason, but I think now I understand how it works.  So that’s good.

Suppose you’ve been taking pictures with your digital camera for a while, and you’re wondering why some of your pictures look so much better than others.  Or suppose you’ve noticed that somebody else’s pictures look a lot better than yours, and you’ve decided it’s time for you to do something about it.  What should you learn?  Well, if you’re a beginner, it’s very likely that you need to learn to understand exposure better.

This article is my attempt to teach somebody who is in the habit of  letting the camera set the exposure how to take control of  it themselves.  I hope this will get you started with the basics. There is immensely more to be learned, but I’m not qualified to teach it all, and you don’t want to try to learn it all at once anyway, it’d just bury you in details.  If this gets you started, I’ve done my job, and you’ll be able to understand more advanced articles on exposure when you’re ready for them.

These instructions are for digital cameras. The meaning of setting an ISO differs between digital cameras and film cameras; the other two are the same.

Despite common usage, you should remember that exposure is a matter of opinion.  There is no objective “right” or “wrong”; there is only “what you want” and “not what you want”. The purpose of taking control of your exposures is to be able to get “what you want” more often.

There are three controls on your camera that affect exposure: shutter speed, aperture, and ISO. Each of these things affects both the exposure and one other aspect of the picture. Often getting the picture you want is a matter of balancing different effects to get a compromise you can live with.

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