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WHAT’S ALL THIS, THEN?

Jim Talkington is a photographer in Cincinnati, Ohio who makes a living making pictures. In today’s world, that’s worth a few nods of respect. Further, he shares his wisdom at his blog, prophotolife.com.

How awesome that is, or how Jim honed his amazing time management skills, is not what I want to explore today. Jim posted an article comparing the quality of various bulbs as photographic lighting. As one of the bulbs was a compact fluorescent (CF) and as I recalled how CF bulbs emit light differently than natural light, I thought I’d post a comment.

That lead to a follow-up article in which Jim compared light from a CF vs. an incandescent bulb. That (only three paragraphs later) is the topic of my mental meandering today. I’ve taken the bulb-ball and I’ll share where I’ve run with it so far:

SPECTROGRAPHIC ANALYSIS
I thought I’d start at my comment: my recollection that CF bulbs emit light differently than “natural” sources of light - i.e. things that make light by being very hot. Some quick googling*extensive research* led me to a site full of spectrographic analyses of various sources of light:

Analysis of Sunlight
© The LED Museum^[1]

Analysis of Flame
© The LED Museum^[1]

Analysis of a 60W Incandescent
© The LED Museum^[1]

Analysis of a CF Bulb (5000K, 13W)
© The LED Museum^[1]

SOURCES OF LIGHT
Sunlight, flame and incandescent light are all governed by Planck’s Law of black-body radiation. They emit light at all wavelengths, with the peak changing according to temperature. Fluorescent bulbs work differently.

Wikipedia tells us that the gas within a fluorescent bulb is excited by electricity, causing light. Sadly, it’s mostly UV light, so the tube is coated on the inside with phosphors that absorb the UV radiation and emit visible radiation (some is converted to heat, but as we can touch fluorescent bulbs it’s not so bad). The mix of phosphors determines the visible light:

Fluorescent Lighting Spectrum from Wikipedia
Click for Explanation

Our Wikipedia page tells us “A typical “cool white” fluorescent lamp utiliz[es] two rare earth doped phosphors, Tb3+, Ce3+:LaPO4 for green and blue emission and Eu:Y2O3 for red.”

So unlike black-body radiation which throws light at all wavelengths, a fluorescent bulb throws most of its light at specific wavelengths. That’s not so bad, though, as those wavelengths are our favourites: the ones that the cone cells in our eyes enjoy; the ones that our camera’s Bayer filtered photosensors detect. The ones our TVs and monitors fling at us daily, namely: red, green and blue.

A PHOTOGRAPHER’S HOOT
In what way does all this matter to us as photographers, then? I suppose what matters most is how the bulb manufacturer chooses to mix their phosphors to make the light appear natural. It’s important to note that not all fluorescents are alike.

Look back at that Wikipedia page again. Note the spectrograph for the halophosphate bulb. “The color rendering ability of these older style lamps is quite poor” says the article. One of the graphs on the LED Museum page shows a “Dollar Store” CFL of this type, implying that they might be living among us today.

So, as photographers interested in using CF bulbs for lighting, we want to make sure we choose a bulb that uses the right phosphors in a mix that closely matches natural light. Looking at the results Jim posted in his comparison, I’d say that bulb he used does a pretty good job.

MY RESULTS
Jim did an excellent job of doing a well-controlled comparison. However, I can’t very well go writing an article about photography without taking any pictures myself, so I tried to replicate his results, to see what I could learn.

Unfortunately I don’t have a Gretag Macbeth^[2] colour checker chart. I did, however, find a “Stride Rite” shoebox at a friend’s house with a very colourful design (what can I say, this is a budget production). I set my camera on tripod in the basement with the shoebox 3-4 feet away. The lamp, scavenged along with 3 bulbs from around the house, I placed at camera right, about 1 foot away.

I shot RAW to avoid worrying about setting the white balance perfectly in-camera. I set the exposure at 1.3″, f/4.5, ISO 100 and took three frames: Frame 1 uses a Philips Marathon^TM 15W CF bulb whose light has a warm glow (sort of) matching an incandescent’s (3000K-ish); Frame 2 uses a Pur-Lite^[3] 15W CF bulb whose CCT seems to be around 5000K, producing a very white light (perhaps I should say, Pur Wite Lite?); Frame 3 uses a 60W^[4] incandescent.

In processing the results, I set the white balance from the white “S” in the lower right corner using UFRaw. In The Gimp, I used Colour : Auto : Normalize to stretch the brightness of the image to fit the maximum range. (I did this after I noticed from the histograms that the brightness didn’t turn out the same across all bulbs. 15W CF is *supposed* to be 60W equivalent) Finally, I used a “Difference” overlay to make the differences clear. Anyways, here are the results:

Combined Results

Col. 1: CF3k, CF bulb, low temp.
Col. 2: CF5k, CF bulb, “pur wite lite”
Col. 3: INC, Incandescent

Row 1: histograms for the raw pictures (before I normalized)
Row 2: the pictures before normalization
Row 3: the pictures after normalization
Row 4: Differences (CF3k vs. CF5k / CF5k vs. INC / INC vs. CF3k)

ANALYSIS

(*) There is a small but noticeable difference, which the “difference” overlay makes apparent.
(*) The difference between CF3k and CF5k is similar to the difference between INC and CF3k. This suggests to me a couple of possibilities:
(o) The differences between phosphors is just as significant (or insignificant) as between CF emissions and natural light emissions;
(o) My own image processing (either WB adjusts or normalizing) might be confusing matters;

LESSONS LEARNED

Instead of a final result, what I’ve done so far is a learning experience. In doing a better study of this I would change a few things:
(*) Reset the exposure between each type of bulb by using a voice activated grey card^[5]. Take a frame as long as the card’s there anyway, to be used for white balancing.
(*) Include more of each bulb type to act as a control. Perhaps the difference between a 60W and 100W incandescent is just as noticeable as between incandescents and fluorescents.
(*) Get a Gretag Macbeth colour checker chart, or at least have handy greyscales to check exposure and whitebalance against.
(*) Take better care in post-processing to be avoid introducing artifacts.

In the meantime, however, I believe that CF bulbs ought to be fine except for critical colour management scenarios I can’t even imagine. I suppose those involved in such scenarios know more about this than I ever will.

UPDATE #1: If you’re visiting from ProPhotoLife.com I’d just like to point out (before you waste your time) that the vast majority of this blog is not photo-related. Here’s a link to the few posts that are tagged ‘photography’, be ye inclined to explore further.

UPDATE #2: I did a bit more digging and posted another article which includes info on strobe light spectra, in case you’re curious.

So Nortel (Telecom company in Ottawa) has this bike tour they do every year to support children’s cancer charities. That’s right, you can help me give children a free cancer!

I’ve decided to join the 80k tour. For me this is a lot of biking, but based on my 140km trip last year, I believe I can do this - with a fair amount of grumbling and sore buttedness.

If you’re reading this and you don’t make a pledge to help me reach/surpass my goal then I will personally contact Trogdor the Burninator and put you on his burnination list. You do not want to be on that list.

CAPTAIN WE GET SIGNAL!!!
YOU HAVE NO CHANCE TO SURVIVE MAKE YOUR PLEDGE

Please pledge now or else I’ll be forced to make another post with more intarweb memes, like this:

MAH PLEDGE
I SHOWS YOU IT.

Be forewarned, this post has no pictures.

NO PICTURES!

YESTERDAY
So, yesterday evening after taking pictures for the Weekly Assignments, I went around to make sure I had everything I needed to bike to work this morning.

Warm gloves? Check.
Ski pants? Check.
Sweater? Check.
Panniers, loaded^[1]? Check.
Brain bucket? Check.

THIS MORNING

I get up. That was my first mistake. Grab some clothes. Fetch the bike from the shed and bring it ’round to the driveway. Strap the panniers and laptop on the bike. Lock the front door, stow the keys in a pannier pocket. Check front tire pressure. 40psi? Pump it up to 70. Check rear tire; it’s at 40psi, too. Pump it up. Remove pump.

Sssssssssssssss.

*sigh*

Put the pump and gauge away. Curse. Remove laptop; remove panniers; unlock door. Curse. Drag everything inside. Curse twice. Grab shower, start car, go to work. Bleah.

Tonight when I get home, I get to enjoy the fun of changing the rear tire tube. Yay.

Savage Chicken is an interesting cartoon:

© 2008 Doug Savage

I appreciate how simple and easy these *appear* to be even though the ideas, the essence of funny contained within each, take inspiration and talent to conceive and express.

Electric Theatre

Like Expanding Mind before it, Electric Theatre is a result of one of my photo assignments, this time on Anthropomorphism.

The cute little socket faces are a different take on the classic drama / comedy theatre masks.

That’s right: a sunburn.

I did not go on vacation to Acapulco Bay for the winter.

I did not even spend the day skiing down the side of Cheval Blanc at Mont St. Marie.

No, I got a sunburn from shoveling snow all day. There’s a toque-line across my forehead.

As I wrapped my scarf around my neck, pulled on my good winter gloves and donned my jacket, the thought never even occurred to me to slap on some suntan lotion. I mean, c’mon! Then again the thought “I’m going to be outside shoveling snow all day” was also absent.

Somewhere there is a “True Canadian” checklist, on which one of the items is “Sunburned while shoveling snow”.

Check.

For those playing along at home who might not be in the know, Ottawa got 56cm of snow this weekend. We’ve had 413cm so far this year. We’re on track to beat the 1970-71 record of 444.1cm.

I wrote a snow-oriented post late last December and I invite you to compare pictures with me:

Driveway in December

Driveway in March

Notice how:

• my house had a nice picture window in December?
  
• the adjoining neighbours had a first floor in December?
  
• the yellow “fire hydrant is here” stick can be seen in December?
  
• the snow in front of my car is only hood high in December? (see next picture if the detail through Hunnybear’s car windows isn’t clear enough for ya)

House in December

House in March

Notice how:

• there was a cat in the window in December, but there’s barely a window at all in March?
  
• we had a doorway in December?
  
• the yellow “fire hydrant is here” stick can be seen in December?
  
• the neighbours have a nice evergreen in front of their door in December?

Finally, let’s turn around and look across the street:

The Neighbour’s House

If anyone ever cuts it down, the tree in the neighbours’ yard is going to have a particularly noticeable ring for this season, I think. Especially note the height of the car in the driveway on the left.

For more wintry pictures of our house, visit my “Home” gallery at the Gnurple Photo Gallery. It includes pictures of the driveway before shoveling (the snow comes up to the mirrors on the side of my car) and even a couple of non-winter pictures of the house. Wow! Lawn!

I admit that I am less bloggy lately than I have been in the past.

Most of my spare time these days is going into a couple of photography projects.

Project 1

The first is the “Every Day Objects” game described here. The latest Every Day Object appears in the right-hand sidebar (clicking the image leads to my gallery), or just visit the gallery by clicking here. As of this writing there are 32 photos of 26 objects.

The game is being played in the Open Discussion forum at Gnurple Forums. Each day, M-F, I post one new object for forum members to guess at. My Friend Codie is also posting occasional EDOs. I admit she is better than I at making them hard to guess.

Some of my favourites:

Object 1

Object 12

Object 24

Anybody can view the forum, new members are welcomeencouraged to join. Please email me as I believe registration is disabled at the moment to keep spammers away.

Project 2

The second is a Weekly Assignment challenge. There have been three already. The assignment gallery is here where you can see what we’ve done so far. Right now it’s just Codie and I doing the assignments. We’re hoping to get other enthusiastic photographers on-board. We have a Wiki over here which lists and describes the assignments, and various other useful information about the project in general.

My favourite Weekly Assignment of my own, so far:

Expanding Mind

Taken for the “Doors and Windows” assignment.

My favourite Weekly Assignment of Codie’s:

Shadow Face

Taken for the “Shadows” assignment.


Photography Books

Last but not least, in the various photography-related sites I lurk around on the Intarweb, two books appear to be outstanding so I ordered them.

The first is The Moment It Clicks by Joe McNally. McNally is about as professional as professional photographers come, with a career in assignment photography working for Life, National Geographic, Sports Illustrated and other world-famous publications.

Each page gives a picture and some advice / a story to go with it. It’s a mix of technical advice, tricks of the trade, on-the-job wisdom, and all useful. His writing style makes you feel as if you were sitting at a bar with him telling these stories, kind of an informal at-ease style. Nonetheless each lesson is presented in a way that beautifully and clearly illustrates some not-so-obvious concepts in a way that makes you smack your head and say, “of course!”

If you’re an amateur photographer wondering what the world of professional photography is like while also looking for tips, this book is for you.

The second is Light: Science and Magic by Fil Hunter, Steven Biver and Paul Fuqua. It has a more formal, educational style to it. It would be at home on the desks of a photographic lighting classroom. The information flow is organized as an educational course would be, starting off with basic principles and moving into dealing with more complex lighting situations.

They advocate learning principles instead of memorizing recipes, an attitude that I subscribe to wholeheartedly. However, where other textbooks present information in a dry, educational format, the writing style here includes enough wit, humour and interesting examples to keep you interested and flipping pages for hours.

That’s it from me for now. Each of the photo galleries I listed above has RSS feeds if you want to subscribe and keep track of new entries.

Since starting the Every Day Objects game (see the prior post), I’ve been doing a lot of macrophotography. My favourite lens set-up is an OM Zuiko 28mm f/3.5 lens, mounted on a 25mm extension tube (EX-25) using the OM-to-Fourthirds adapter ring. The one that Olympus used to give for free to the first three people who asked very nicely on the second Tuesday after a blue moon (or whatever their algorithm was).

I became curious about my lens setup. Is this really macrophotography? According to Wikipedia, “… the classical definition is that the image projected on the ‘film plane’ (i.e film or a digital sensor) is close to the same size as the subject.” I have read on other sites that true macrophotography achieves a 1-to-1 ratio or better. I find the latter definition more appealing to my inner geek than anything sporting an “… is close to …” so that’s what I’m going with. I’ll leave it to the reader to figure out whether “more macro” means a higher magnification - what a microscope does - or not. Heh.

Macro With the 28mm Lens

The OM Zuiko lens’s focus ring works by changing the position of the front element. How does this affect us in macrophotography? With the extension tube, this hardly changes where the focal plane is at all, but it has a big impact on the field of view.

[ASIDE: For macrophotography, we usually focus by moving the object or the camera closer or farther from each other, not by turning the focus ring. In the 3-5x range (objects being 3-5x larger on the image plane than in real life), you would mount your camera on a platform which you move by turning a long bar with a very shallow thread to achieve focus.]

This lens has macro range which we know so far to be between “close-up” and “even more close-up”. I want to replace those wishy-washy phrases with real numbers. Apologies to any readers who were hoping for imaginary ones, i haven’t got any (badum-bum-pish, I’m here all week, try the fish).

Determining Macro-Factor

In order to find our macro-factor, we need to know the size of our image plane and the size of our object. For the latter we’ll use a scale (what normal people call a ruler, but which a professor at university very effectively drove into my brain is called a scale) marked in millimeters.

For the former, we must harness the infinite power of teh intarwebs. The Fourthirds standard says the sensor is 18 x 13.5mm with an imaging area of 17.3 x 13.0 mm. Done.

Image A: Focus Ring at Infinity

Here’s my scale taken with the lens set to its widest field of view (infinity focus) and then focused by placing the camera lens parallel to the scale, and moving the camera back and forth to achieve focus. I find the most accurate way to focus is to use Live View with the view set at 10x magnification - I knew Live View would come in handy someday.

Looking at the picture, we can see it is about 20mm wide, but I’d like to try and make that a bit more precise. To do so, I overlay a 10 pixel by 10 pixel grid on the image:

10 Pixel Grid

Here is a 100% zoom of the rulerscale (dammit!), with a 10 x 10 pixel grid overlaid. NOTE that this is taken from the left-most edge of the closer image (see below), not the wider image above.

I then determined how many pixels per millimeter at the left edge, center, and right edge, to the nearest 10 pixels. In Image A it was 180 pixels per millimeter all across.

Finally, using the left edge of each nearest millimeter mark, I counted the number of pixels to each edge of the frame, to the nearest 10 pixels. On the left edge, it’s 30 pixels, and on the right edge it’s 30 pixels as well.

1mm / 180px * 60px = 0.333mm + 20mm = 20.3mm^[1]

Image B: Focus Ring at Closest

Using the same techniques on this image, I get:

* 210 pixels per millimeter
* 30 pixels on the left edge
* 70 pixels on the right

1mm / 210px * 100px = 0.476mm + 17mm = 17.5mm

Conclusions

For the widest field of view:
17.3mm image area / (1mm / 180px * 60px + 20mm) = 0.85x macro^[2]

For the narrowest field of view:
17.3mm image area / (1mm / 210px * 100px + 17mm) = 0.99x macro

*so close*… sigh.

Confusions, a.k.a. Why Your Results May Be Different

Looking at the dimensions of the pictures I posted causes some confusion: the specs say that the camera produces pictures with a resoultion of 3648 x 2736 px, but my full-size images are 3720 x 2800 px.

Whiskey Tango Foxtrot, say you?

Being an all-linux guy, I use dcraw to process my raw photos. Why is dcraw producing images larger than the specified resolution? Dave Coffin, dcraw author, offers this explanation in his FAQ:

Why are dcraw output images larger than camera JPEGs?

    Any algorithm that combines each pixel with its neighbors is going
    to have problems near the edges. C code is cheap, so dcraw applies
    a different algorithm to edge pixels. Hardware logic is expensive,
    so cameras crop off the edge pixels after processing.

To understand why edge pixels are different, we need to know that the sensor is actually made up of colour-insensitive photosites covered by colour filters. Usually this is the Bayer pattern - though I don’t know what the E-510 in particular uses.

The E-510 specs, for some reason, list the same resolution for RAW files as for JPEGs. I don’t know what resolution Olympus’ software or any other Olympus Raw Format (ORF) to JPEG converter produces.

If we had done this test using JPEGs instead of RAW files, we’d've gotten a range of 0.87x - 1.01x because we’d be assuming the 17.3mm wide image area is 3648 px across, un-cropped. Now we’re reasonably sure it’s at least 3720, but we can’t really be sure of anything - did Olympus publish the 17.3mm “image area” width as the width of the area where pixels are, or where the 3,648 pixels which get used for JPEGs are? Are there other pixels beyond the 3720 we know about?

Am I wrong? Is it possible I do actually have a 1.0x macro factor? My measurements would have to be off by more than 30 pixels, or the width from Olympus by more than 0.05mm. Despite my poor technique and non-horizontal picture, I doubt I’m that far off.

The Grande Scheme of Thyngs

Exactly how close this set-up is to true macro doesn’t really matter, though it is fun to figure out (and useful in comparing to other lenses). What *does* matter is the image quality. After all, using a lens designed for 35mm film might mean poor image quality, even in perfectly focused situations, on the E-510’s smaller sensor.

Fortunately, that is not the case with this lens. I consistently see images coming from this lens + tube that have more crisp detail than I typically see from my other lenses. That might be because I can take the time to do a better focusing job in tabletop photography than the AF mechanism can in hand-held shooting, but at least I know this lens is great. (I haven’t tried non-macro photos as focusing is not optimal in the E-510’s small, non-focus-equipped viewfinder)

When studying the above images, keep in mind that the full-size version you get when you click them has not been sharpened at all, and it came from RAW files. As cameras always apply some in-camera sharpening algorithm to their processed JPEGs, it’d be unfair to compare them to other photos without taking this into account. As an aside, the E-510 lets you control in-camera JPEG sharpening, which is a unique and awesome, if not well-documented, feature.

Also keep in mind that the poor image quality at the edges of those photos is not a lens issue. In macro-photography we deal with very, very shallow depths of field - hence the need to focus by moving the camera with a shallow-threaded screw. I took a picture of a straight object, which means that the distance from the edges to the sensor is greater than in the middle, and in this case they lie outside the area of acceptable focus. If I’d bent the rul…, er, scale so that it formed an arc, I could have gotten the whole thing in focus.

(I suppose I could have composed the photos a lot better, too, more horizontal, closer to center, more attention to critical focus… but when you get right down to it, I’m lazy)

A new game begins over in the Gnurple Forums!

How it works:

• Someone posts a macro-photo of an everyday object.
  • The subject should be a common object that most people would recognize if they saw the whole thing.
    
    
  • The photog should try and compose the photo so that the subject is somewhat hard to guess, but not impossible. Ideally, when its identity is revealed by a shrewd guesser or (eventually) the photographer, players should smack their heads and yell, “DOH! OF COURSE!”

    Bonus points for artistic presentation.

  • Some alterations (e.g. photoshopping) like cropping, rotating, a little levels/curves, a little sharpening, etc. are OK as long as the final image accurately represents what was seen in the viewfinder.
• Post your guesses / answers as comments.
  
  
• Hints: ask for hints if you want. The photog is free to be devious and elusive with their hints, but must not lie.
  
  
• Updates: the photog should post a hint each day that the puzzle goes unanswered, and should post the solution after a week.
  
  
• Each object should be posted in its own topic, with something like “Every Day Objects - Object ” as the subject, to keep posting clutter down and make concurrent images easier.
  

Please feel free to register at the forum - just email me if it gives you any trouble - and join the game!

If you don’t want to join (boo!) you can head over to the EDO Album in my Photo Gallery and play by adding comments to the photos using the “Add Comment” link in the left sidebar.

The latest Every Day Object will show up over on the right sidebar of this blog, right underneath the Random Image.