11.28.2014

Sharp versus SHARP. Taking time to fine tune the AF performance on each camera.


I got lots and lots of great feedback on the last blog. The one about diffraction and sensor size. And one of the things that commenters drove home is that a lot of what we were discussing is theoretically interesting but that diffraction effects, as they impact sharpness, are just one part of an assemblage of "moving parts" in the practice of real world photography. Yes, you'll see an erosion of sharpness as you push past the diffraction limited f-stops of your cameras but for many, many users that degradation will be amply masked by many other factors, from lens performance to sloppy user habits. In effect, to worry about diffraction effects while hand holding a camera and shooting a landscape is a bit daft.

I've had a busy, busy year and when we get swamped we always tend to look for magic bullets and quick fixes rather than just taking a deep breath and remembering how to do stuff right. A couple of weeks ago I mulled over the acquisition of a D810 or a D750 in a non-essential search for low hanging, sharp fruit. But a glitch during my photography at the Zach Dress rehearsal of "A Christmas Carol" did wonders to snap my brain back into "optimization" mode.

So, what was the snafu? Well, I had tested the 18-140mm Nikon lens on both my D7100 and my new D7000 bodies and found it to be very sharp wide open. Being a bit lazy and optimistic I assumed that this meant both cameras were focusing correctly and, by extension, would focus all lenses hung off the front of them correctly. Right? My previous experiences with the D7100 using the 85mm and 50mm lenses wide open showed me that that camera was pretty nicely zero'd in. It turns out that not all was merry and bright with the newer/older D7000. I had used it with a 50mm before and found it to perform well wide open but this was not the case with the 85mm 1.8G.

At the start of the performance I had the 85mm on the D7000 and I didn't like what I saw when I spot checked the first few frames at the maximum magnification of the review screen on the back. It just wasn't rendering a sharp image! I exchanged lenses between the two cameras and instantly saw the sharpness I expected with the D7100+85mm combination. Grumble, grumble.

I spent all day Weds. post processing files from four different jobs and then, after dinner, I headed back into the studio to do billing and to read through comments here concerning my thoughts on diffraction. A couple comments about how many different factors effect sharpness really resonated with me and I decided that it was time to check the AF accuracy of all the lenses I have on the D7000.

There are probably many methods that could be superior to my autofocus check process but this is what I do. I printed out resolution charts and taped them to the wall. I worked at getting my camera parallel to the wall and my exposure just right. I tethered the camera to Nikon's capture software and I went into "test mode." I went into the camera menu and found the AF-fine tune controls. I used the conventional AF, watching through the finder to make sure the green confirmation lit came on during focus. I had the camera set for center focusing point, S-AF. Once the focus showed a lock I switched the lens and body to manual to lock in the focus and then hit the live view switch. Then I painstakingly set and checked the lens at ever point, from +20 to -20. I had my monitor set for 100%. At that magnification it was easy to see the differences.

Once I knew where the ballpark of sharp focus resided I spent a while refocusing with the AF and reconfirming the sharpest setting. Turns out that the worst culprit in the tool box is the 85mm f1.8 ON THAT BODY. It needs a -19 correction to focus correctly. I suspected some sort of camera issue but the 50mm f1.8 required only a minus 3 to be convincingly sharp.

That led me to suspect that something must be wrong with the lens itself. So I put the lens on the D7100 and tried the same tests and found that the 85mm is right on the money with no calibration on that camera. The mysteries of cameras and lenses.

Cutting to the chase I went ahead and did the same testing with all the AF Nikon lenses on both bodies and fine tuned the crap out of the whole system. While some lenses were pretty accurate at zero most needed + or - tweaks of five points (out of twenty possible on either side of zero) or less to be as sharp as they are ever going to be on either camera.

Doing this convinced me of three things. First, that I'd been too lazy about technical stuff recently and I could see, immediately, the effects of increased sharpness in the photographs I took during my post calibration test drives. Secondly, that if I'm going to worry about things like diffraction and sensor size it behooves me to zero out and optimize as many parts of the equation I have control over. And, third, that the cameras we have in hand are already great performers once we've taken the time to optimize them and use the best technique.

One bright or sad note (depending on your particular camera inventory) is that the majority of my lenses, in combination with the two bodies, could use a bit of tweaking to get my money's worth when it comes to sharpness.  I did spot check a few of my mirror less bodies and found no focusing issues that I could test for. I would jump in and enthusiastically say that there were "no" problems but the cameras don't give me the tools to actually check the point of highest sharpness as driven by the camera's AF systems so, in fact, we really don't know if the mirror less (mirror free!) camera actually are any better in this regard. Maybe a bit more research is needed.

Now, when I shoot my 85mm lens at it's highest non-diffraction limited f-stop I'm actually getting all of the benefits designed into the lens and camera system and I'm hopeful that I'll see globally improved results. A fixed up camera and lens system is a good defense against incipient camera lust and delivers the same benefit of washing and waxing your old car = it makes you happier with it all.

Just a thought if you've already put in a twelve hour day and you need something to do after dinner. A sharper system is a happier photographer?


11.26.2014

Here's hoping that every VSL citizen has a wonderful Thanksgiving Holiday and safe travels. Be sure to take a camera along...

marketing image for Esther's Follies, the long running, very Austin
comedy club on Sixth Street. 

A spoof on the Wendy Davis track shoe story...

Can you feel it? The world seems wound up and anxious to sell us stuff. I've been getting Sony, Nikon and Olympus e-mailed "newsletters" non-stop for a week. They've trotted out their new stuff, marked down their old stuff and today, especially, they are trying to get me to take some of their refurbished stuff off their hands. There's something about hunkering down for the winter that just makes researching and reading about photographic gear seem so... comfortable.

Sadly, there's very little left that I have a keen interest in right now and the things that I would like to play with (Leica Monochrome, Leica S2 medium format system, Cray Super Computer (for video processing the new h.265 codec files) and any Zeiss lenses I can cram on the front of an m4:3 or Nikon body) are so extravagant and expensive that I can't consider them and the paying of income taxes with the same brain. 

So, instead I'm inventing little exercises in which I actually use the gear I've got or can borrow. I am writing a short, short film about the extinction of sex due to cellphone addiction, and the ensuing collapse of the human species. I'll try to convince Frank to bring along his collection of amazing video gear and help me film it. I'd like to shoot a film that's not about anything but it is a collage of moving images revolving around various winter swim practices at my pool. Dark cold mornings, bright tropical January noon workout and everything in between woven into a piece that I can just stare at and enjoy without the need for words.

And then there's family and travel. I love my family. I love Belinda's family but even saints need a break from time to time and during the holidays I always remember some prescient advice one of the media buyers at my old agency told me over drinks as we both waited in the Austin airport to catch planes for two different coasts. He said, "When your family starts to wear on  your nerves you have to learn to emotionally disconnect. Pretend you are making a documentary film. Pretend you are shooting a story about the occasion. Step back and be an observer rather than an active participant and I guarantee you'll have a lot more fun."

The same can be said for travel. We're all going to hit the airports at one time or another between now and the end of the year and chances are that our flights will be delayed. If you are traveling solo it's a wonderful time to pull out the camera and spend some time getting exercise and shooting whatever you'd like to photograph in an airport. You could make up a story about your shoes. You can look for interesting faces. Stand at a window and make images of taxi-ing airplanes. If you are traveling with a beautiful model then you can spend the time concocting one of those wonderful and inane fashion stories and then fulfill your fashion photographer destiny. 

Traveling with kids? Invent a narrative that happens in an airport and spend your time shooting the story instead of filling up on airport food and crappy $5 coffee. Photography can happen anywhere. At any time. 

I'll be in San Antonio, Texas tomorrow. Studio Dog and I are paying a visit to my parent's house. We'll go out to lunch while Studio Dog secures the premises. I'm planning to take along the camera and lens combo that's been my rock in a swirling sea this year. The one camera I have never considered selling or trading. I may not shoot with it all the time but it's a bedrock sort of tool for those times when I'm in desperate need of a "safety blanket."  I'll be carrying the Panasonic GH4 and the 12-35mm. If the parents start telling stories about the great depression or relatives I've never met I'll pull out the camera and start filming.  

If  you are in an airport when you read this I hope your plane is on time, that you are traveling with a wonderful and engaging person who you can cuddle with when appropriate and that you have the camera you really want right there in that bag by your side. Just imagine. Things could be much worse. You could be shooting with a Nikon 43-86mm zoom lens bolted on to the front of an original Canon EOS-M mirror less (evf-less) camera. And you could be waiting for that plane outside....


Trying zany stuff during a photo shoot of "A Christmas Carol" for Zach Theatre.



Wouldn't it be cool, I thought, to have one camera and one lens with which to cover an entire musical dress rehearsal? So, I looked around the studio and cobbled together what I thought would be a workable system. The idea was to have the gear nailed down so that no decisions would need to be made other than timing and zooming. Of course I'd need to mind the exposure settings and check in on the color balance but no more grabbing camera X for the wide stage shots or grabbing for camera Y for those tight head shots. And, of course there's always camera K with the medium to telephoto zoom. It gets old juggling camera bodies.

Choosing from the inventory in the studio at the time I decided on the Nikon D7100 and the 18-140mm zoom lens. The lens is pretty sharp in the vast center section of the frame and since most of the corners and edges in a theater shoot are dark I thought that would be okay. The 18mm end of the lens is fine for full stage shots but even though the 140mm end is about the equivalent of a 210mm on a full frame camera I knew there would be some times when I would really like a bit tighter crop. I decided that this would be the perfect opportunity to try out Nikon's in camera crop mode.

The camera's sensor is an APS-C, 24 megapixel version. But there is a menu switch that allows for another layer of crop which is a 1.3 crop of the standard DX size (if that makes sense). As near as I can tell it turns my zoom lens's long end into a 280mm lens while, of course, maintaining the same aperture, f5.6 (sorry, no clue about the T-stop...).

The upshot? Well, I shot mostly wide open and I reviewed the stuff today and it was all good. Not pin sharp like we'd use for giant promo posters but we do those in the studio with electronic flash and ISO 100 well before the shows open. This material is destined for publicity and will mostly wind up on websites and in newsprint. Different parameters for different applications.

From time to time I wished for a bit more foreground and background separation but not as often as one would think. It's rare that two or more people are positioned in a straight line, perpendicular to the camera, and so generally we are looking for enough depth of field juice to cover the spread.

One thing I did chaff at last night was having to pretty much shoot from one position.  And by necessity a bit far from the stage. Since we've been doing dress rehearsals with full houses of "family and friends" it's not possible to move around and get close to the stage quickly like it was when we shot in the older theater. That space was much smaller, the house wasn't as expensive to use by the day and we could be relaxed enough not to start our promotions on dress rehearsal night. I was able to roam the edges of that stage and shoot with wider angle lenses, closer. Always closer.

So, when I was using the camera in DX mode I shot in 24 megapixel settings but when I wanted to go tight I switched to the tighter crop and the frame dropped to 16 megapixels. In effect the smaller crop turns the frame into a 3:2 version of an M4:3rds camera.

Even in the darkest scenes the camera was able to nail focus well. I'm old fashioned and tend to stick with center focusing points and S-AF. I'm also happy to report that the VR in the lens should make the Nikon engineers proud. It really does work well. Either than or I am totally resistant now to the effects of caffeine...

But cutting through all of the techno crap I have to say that the production last night blew me away. Even mores when the director, David Steakley, told me that he was still making slight script changes to the play as late as 6:30am that morning. His version of "A Christmas Carol" is not at all traditional. Not the version you see on Masterpeice Theater. The entire production is peppered with modern music and lots of cool dancing. Even the ending, with all the cast on stage and the audience up on their feet, is a powerful blend of theatre and music as one actor does a perfect rendition of Pharrell William's song, "Happy." It's wonderful when theater can reach into your heart and reset that switch that makes you want to be a (much) better person. Belinda and I were humming "Happy" all the way home.

I'll probably shoot the next production differently but it was sure fun to try the "Swiss Army Knife" approach at least this once. If you focus carefully and breathe just right it can work out just fine....

I love the way the lighting designer created depth with the light and dark areas. Nice.
Good photo lighting lesson for me.

"Super Crop Sample"

"Over there....that's where Kirk's Novel is... over there at Amazon....arrrrh."



From now until 2015 the novel (Kindle Version) is on SALE
for only $3.99.  The perfect holiday read for every
photographer on your list.

11.25.2014

I'd like to open the floor to a technical discussion that's of interest to me lately: Pixel size, diffraction and apparent sharpness (or acuity).


I think everyone who has upgraded from a camera that has a resolution was just a little higher than the resolution of their desktop monitor to one that is much higher has had a disappointment in finding that the resulting new images just didn't seem much sharper. Or any sharper. Or as sharp. It's interesting to me because I've experienced this situation and I continue to experience it. I wish I understood it better.

The issue seems not to be so much about the actual number of pixels on the sensor of a camera but in how small the pixels are and how densely they are packed in. The idea is that denser sensors are prone to a quicker onset of a sharpness robbing effect known as diffraction.  As I understand it diffraction, or bending of light around the edges of an opening of a lens (or a pixel array) is what actually causes primary sharpness issues but the overlapping of "Airy disks" is what lowers resolution on the sensor.

Here's an in-depth and well done article  that I found on diffraction and its various effects:  http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

When I look at the details of the "science" I can understand that diffraction makes images progressively less sharp after a certain point. There is a calculator (actually two) in the linked article that shows the effect of pixel density and sensor size on diffraction limits. It shows, theoretically, what the minimum aperture would be for a given sensor size and pixel density before diffraction rears its mathematical ugly head and starts causing problems vis-a-vis sharpness.

I used the calculator for several different camera sensor sizes and density. What I found was that on an APS-C sized sensor a system becomes "diffraction limited" (where sharpness starts to gradually decline---it's not on or off in a binary sense) based on the density of the pixel packing. A 24 megapixel sensor (like the one in my D7100) hits the wall at f5.9. If I use a D7000 with 16 megapixels instead the diffraction limit sets in at f7.3 and if I use a 12 megapixel camera the diffraction limit steps into the equation at f8.4.

If I use my micro four thirds cameras at 16 megapixels we become diffraction limited at f5.9 (the same as the APS-C at 24 megapixels....) and if we were able to wedge 24 megapixels into the next gen of m4:3rd sensor we'd see diffraction rear it's ever softening head at f4.8.  Best case in the current market in respect to delayed onset of diffraction would be the Sony a7s at 12 megapixels. The calculation shows that lenses on that camera don't become limited until hitting f12.7.

The mind reels but essentially there's a fixed pattern that tells us you can have some stuff but not other stuff. If you are shooting with micro four thirds cameras of 16 megapixels it really behooves you to buy fast lenses that are well corrected wide open and at wider apertures. By the time you hit f5.6 you've almost got a foot in the optical quicksand. Stopping down to improve lens aberrations probably cancels out overall improvements with the advancing onset of diffraction.

So, the mind boggles even more. If I am shooting outside and want max depth of field the numbers tell me that I might be better off shooting with a less densely packed sensor camera. If I needed f11 to get sharp focus on a big bridge for example, I might be better off shooting on a 12 megapixel camera than a 24 megapixel camera. While the depth of field remains the same if the sensors are the same overall geometry the more densely packed sensor will succumb to unsharpness at lower f-stops. Now, theoretically if I resized the 24 megapixel image to the same size as the 12 megapixel file I'd get the same level of sharpness. At least that's what I gather. But there are so many other variables.

The optical detail transferred by our lenses is limited by the lenses ability to deliver sharply defined points. The lenses output quality has to do with something called, Airy Disks, that limit their ability to deliver more resolution beyond a certain point as well. The Airy disk is a 2D mathematical representation of a point of light as delivered by an optical system to film or to a sensor. As the pixels get smaller more of them are covered by the same single Airy disk delivered by the optical system. Additionally, when Airy disks overlap they loose their resolving abilities by a certain amount. Also their are different sub calculations for the different wavelengths of the different color spectra.

If the information represented by each Airy disk is spread over more and more smaller and smaller pixel there can be a reduction of sensor artifacts but it will be offset by the resolution limits of the actual lens. One of the reasons some lenses are brutally expensive is that the designers have opted to make their lenses as sharp as possible (or diffraction limited) wide open so that one doesn't need to stop down to get better lens performance. The old way of designing lenses (especially fast ones) was to do the best design you could and aim for highest sharpness two stops down from maximum aperture. You see that in most of the "nifty-fifty" inexpensive normal focal length lenses. Lots of aberrations along with unsharp corners and edges when used wide open but then shaping up nicely by f5.6. Now, with high density sensors, you'll start to find that f5.6 also might become your new minimum f-stop which, for all intents and purposes means that your mediocre (wide open) lens has only one usable f-stop. The one right before diffraction sets in.

When you overlay the idea of Airy Disks and their effect on resolution based on sensor size with the quicker mathematically implied diffraction effects of denser sensors you can see why an image from a lower density sensor might look better on screen at normal magnifications  than the same lens used on the same scene but shot on a much higher resolution system. The difference is in acuity or perceived sharpness. Because at the diffraction limited point it's the edge effect that gets eroded. The contrast between tones is reduced which reduces our perception of the sharpness of the image.

What a weird conundrum but there it is. I started thinking about this when I started shooting a D7100 next to a D7000 and started finding the 7000 images (16 megapixel sensor) much sharper in appearance. At the pixel level the D7100 was sharper but on the screen the D7000 images were more appealing. And if the target is the screen then all of the theoretical information is just more noise.

There are really so many more things at work here than I understand when I compare images from different cameras. There are generational issues having to do with noise reduction and dynamic range that shift the results and out ideas of what constitutes "a good camera." But Sony has done something that seemed at the time driven by the needs of video but at the same time revelatory of what we can see when we strip away some other muddying factors which have served to make us want the higher megapixel cameras (=more DR and less overall noise). They recently introduced a full frame camera at 12 megapixels that combines the state of the art noise handling and beyond state of the art dynamic range on that sensor. Now the seat of the pants evaluation and the awarding of "best imaging" prizes to the highest megapixel cameras is called into question. It may be that there will be a trend back toward rational pixel density driven by the very need for quality that drove us in the other direction. They've changed the underlying quality of the sensors and that may allow us to go back to being able to stop down for sharpness and to skirt some of the constraints of the laws of physics as they apply to optical systems. And in the end benefit with both great looking files and far more flexibility in shooting and lens choice.

But, as I've said, I don't understand all the nuts and bolts of this and this article is an invitation for my smart readers to step in and flesh out the discussion with more facts and less conjecture. Have at it if you want to....



VSL waves (with sadness) goodbye to the K5600 Lighting HMIs. A wonderful continuous light source for portraits, video interviews and a lot more...

Luke.


I was sad when I finished boxing up the loaner HMI lights from K5600 and dropping them off at the local Federal Express office. I'd rally fallen for those lights and it will be hard to go back to using my studio flash systems for portraits again. 

The kit in question was a two light, compact kit with an open face 200 watt Joker HMI and a fresnel 200 watt Alpha HMI and their attendant ballasts. The Alpha is a focusable, lensed light source that gives one nice, soft edges when used as a background light. It's got a good beam range and it's quick and easy to use as an accent light. The open face light can accept a wide range of lenses on the front and do everything from mimicking the effect of a fresnel to doing a wide spread, a tight spread, and everything in between.  The ballasts for the lights were convincingly heavy duty with massive heat syncs and positive locks on the cable connections. 

But the really cool attribute of the lights was the solid quality of light they put out. And, for the electrical draw, the quantity of light you could bring to bear as well. 

I like soft lights for portraits. Nearly everything I do when lighting people has the light blasting through something or bouncing off something. I like the way the edges work when a big diffuser is used in close to a subject. I love controlling the contrast of the light by moving black flags closer or further away from the opposite side of the sitter's face. But most of all I like shooting at the narrow apertures and still being able to get good, non-stuttering focus. It's just more fun. 

While I can get 90% of the way to the look of the HMIs (the way I use them with diffusion) with fluorescent it's really the color purity and overall spectrum that's is the icing on the cake. The light from the HMIs seems as though you had the quality of electronic flash (when it comes to tone and color accuracy) but you were able to slow down light time and have the clean blast of light last---a long time. 

I love shooting with continuous lights because they eliminate the annoying and intrusive flash pop. Subjects get comfortable with continuous light quickly and the output of the small HMIs is not overwhelming. It's enough to get me a good shutter speed, aperture and ISO combo but way under the  "squint" threshold. Must be why they use them extensively on movie sets...

The portrait above is very conservative. It's a timeless style.  It's for an attorney and it's meant to be used for a number of different marketing constructs. During the course of our session we did three wardrobe changes and experimented with alternate poses. After I put up a web gallery of the images that made it through my selection process Luke narrowed down the assortment to four or five he really liked and I retouched and delivered them. The portrait was done with a 6x6 foot diffusion scrim to one side with the open face HMI coming through and the background is lit by the fresnel fixture, fired through some netting to match the main light exposure. It was done with a Nikon D7100 camera and the 85mm f1.8 lens.

It's been a week of "good-byes" here in the studio. First I severed my relationship with Samsung's shooting program and then I got the e-mail letting me know my mini-romance with the K5600 HMIs had come to an end. Funny how letting go of stuff can make one feel very unencumbered and free. I like it. Now I feel like diving into a whole new range of photographic subjects I've been interested in, like my favorite photographic books. 

In fact, I'm planning to do a series of smaller articles dedicated to one book per blog post. I need to get started on that. How about right now?

In the meantime I would love it if you would head over to Amazon.com and buy yourself a copy of my novel, The Lisbon Portfolio. I put a lot of hard work into it. It's not perfect but then few books are. By snagging a copy you'll be providing VSL some emotional support. It can be hard for creative people to let go of projects and put them out in public. Seeing them sell well is a happy thing. 

As an incentive to make giving yourself the book just a bit easier I'm dropping the price by $6.00 to a new price of $3.99. This new price will be good only through the holidays. The price will go up right after the New Year!  Get yours soon! Before they run out of the Kindle edition!!!