Category Archives: photography

Moon Shot, take Ⅱ

The quarter moon offers much more contrast than a full moon, and this time I used a telephoto lens: Canon EF-S 55–250mm f/4–5.6 lens on its longest position.  I used the Canon 70D on a tripod, ISO 100, 1/160 at f/5.6 ×3 exposures.

Quarter Moon

It’s difficult to get focused, and about 1/3 of the bursts were out of focus even though I used the touch screen “Live View” to indicate what to focus on.

The lens has optical stabilization, but I suspect it’s turned off automatically if the steadiness of a tripod is detected, as that is a feature listed on some lenses. Unfortunately faster exposure times were subject to blurring anyway. I didn’t bother to use a remote shutter release, but that might help. I don’t know if this is (usual) vibration of the camera lens, or caused by atmospheric turbulence making the image move around. f/5.6 is the fastest aperture at the 250mm end of the zoom, which is also the size where diffraction starts to be noticeable.

Exposure-wise, 1/40 second still (only barely) has no clipping, so would be the optimum for ETTR to capture the most detail and least noise. 1/125 is the good-looking natural exposure, and at 1/640 it shows visible noise.

I improved the contrast by using the “highlight” slider as well as the overall “exposure” slider in Adobe Camera Raw. The difference between the limb and the terminator was still vastly different lighting, and bringing out better the rays of Kepler would darken the terminator and bring the shadow farther in to make more of a crescent than a quarter. So I used “curves”, leaving the darks alone and changing the contrast of the mid-to-bright.

The color is as-shot, with no white balance adjustment or B&W conversions.  The underexposed pictures came out brown, and the bright ones are very neutral.

I merged three exposures as follows:

  • Cancel all adjustments made in Lightroom while evaluating the exposures.  Noise reduction is turned all the way off, but sharpening is left as proper for the basic “developing”.
  • Transfer the burst to Photoshop as layers
  • Double the resolution
  • Auto-align the layers, specifying “reposition only”.  Leaving it on auto can make PS complain that it can’t find anything.
  • Use the stacking mode Median or Mean, whichever works better.  For longer bursts the Median gets rid of outliers, but for low-noise images Mean is more accurate.
  • Rasterize the stack.

The doubling of the resolution allows for alignment to half a pixel in the original images, and combining exposures this way actually increases resolution as well as removes noise.  With non-noisy images, the increase in clarity is due to the “dithering” of different exposures.

After combining the original exposures, then adjust the exposure, apply noise reduction, and so on.  This is easily done using Adobe Camera Raw as a (smart) filter in Photoshop.

Now sharpening is also done in the Adobe Camera Raw filter, at the same time as the other adjustments.  Because the resolution was doubled and the image is not pixel-sharp to begin with, a large radius value is warranted.  I set it to 3, which allows more aggressive processing without introducing fake detail from noise.

Shoot the Moon

A few days ago was the extra full moon in a calendar month.  This is sometimes called a blue moon, as a weaker form of the traditional term. July 2 and July 31 2015 were both full moons. Two full moons in the same calendar month occurred twice in 2012 and will occur twice again in 2018.

I took some pictures using my somewhat-new Sony α-6000 with the Sony 55–210 f/4.5–6.3 zoom lens.  This features image stabilization, and I hoped the auto-focus could lock on it.  I avoided the most extreme aperture setting so set f/5.0 and 1/250 second at the native (best quality) ISO 100.  The shots were hand-held.  Unfortunately,  I seem to have left the lens set to the short end of the range, not the long end, so this was essentially taken with a “normal” (not “telephoto”) focal length.

I also grabbed my Canon 70D, which was mounted on a tripod.  I attached the EF-S 55–250mm f/4–5.6 lens and tried that too.  Again, I backed off from the most extreme aperture setting and used f/4.5, which is brighter than the Sony.  Also again, I used the shortest (not the longest) focal length, so I would have been better off using a high-quality “normal” prime lens.

In both cases, in full manual mode, I set a variety of shutter speeds and shot bursts with each.  The in-camera metering and histogram is not useful because the black background overwhelms the data and the moon is actually very small in the frame.

Blue Moon #1

Blue Moon #2

I did notice that the underexposure warning overlay was standing off from the disk of the moon, and in Lightroom it was even clearer. The sky around the moon was not black but hazy. Presumably the atmosphere scatters light, enough to show in the exposure, even if it appears very clear by eye.

The histogram showed two distinct distributions, with the haze a few stops below the bright portion. I wondered if the dark shades of the haze were only in the dark sky, or if the dark areas on the moon also included these values. That would determine whether I truncated these darks and to to what extent. So I used a gradient map filter in Photoshop, setting different colors for the darkest darks, the next darks, and others. By moving the slider of the gradient editing tool I could set the split so that the background was “darkest” but any more would start showing the other color; then see if the dark shades on the moon were tagged as “darkest” or the other key color.

000453I found that a tiny amount in the Sea of Crises was in the same range as the background.  The Levels tool controls in the screenshot inset shows what I decided on. The “haze” is the lobe to the left, and it’s significantly below the main subject’s detail.  Only shadow areas that essentially go to black — don’t show any detail anyway — extend farther left than where the right lobe rises visibly from the zero value.

Even with the contrast and exposure levels set nicely, it’s hard to make out detail in the colorless image.  The earlier use of gradient mapping to find details inspired me to use the same tool again, for artistic purposes.  I used midnight blue for the darks and a warm-light color for the lights, but set yellow for the brightest values and adjusted the slider so the split between them was showing color contrast on the rays coming from Tycho Crater.

 Exposures

In both photos presented above, I stacked a burst of 3 shots and took the median of each pixel, to reduce noise.  Since this was ISO 100 with brightness in normal midtone range, I don’t think it did anything useful for the main subject, though it did improve the pixelization of the “haze” background (which is truncated from the final image anyway).  Before aligning the exposures I doubled the image size, as this will help with sub-pixel alignment differences.  The disk of the moon is only 250 to 275 pixels even after doubling: as I said, very small in the frame or about 3% of the height of the exposure.

Since the range of values (see histogram inset above) is a small portion of the exposure’s latitude, there is a large latitude in useful exposures possible.  I chose 1/250 f/5 for the Sony and 1/400 f/4.5 for the Canon, and applied the identical adjustments to each, so you can see they are the same EV.  A brighter exposure on the Canon, which is not overflowing the high end of the available capture range, was not nearly as good even though you would expect it to be less noisy and more nuanced.  Oddly, the size of the moon is different from exposure to exposure, so the zoom lens was not held fixed but moved.  Markedly more chromatic aberration and lower contrast (even after adjusting for the difference in exposure) could be due to the performance of the lens at different zoom settings?

Of the shots I took, the Canon (second picture above) is the clearest and sharpest.  If the lenses are equally good, the lower resolution and longer focal length of the Canon would be better, even though the two cancel out to give the same number of pixels.   A larger pixel pitch and larger projected image to match, covering the same number of pixels, should give better quality.  However I think any differences are dominated by lens performance.  It’s hard to tell exactly if it’s really “better” though because the best exposure in the Canon was actually a little smaller than the Sony, so it would look sharper due to that.

Conclusions

  1. shoot lots of exposures, even more than you would think you need.
  2. vary the settings, even beyond what you think is the right range and also change things you don’t think would matter.
  3. know your lenses.  Not only how the sharpness varies with f-stop, but are there any sweet spots or sour spots in the zoom?
  4. know how to operate everything by feel in the dark.  That includes reviewing images and zooming to inspect what you just shot with the camera’s screen.

This is also a striking example of how a good camera trounces what a cellphone can do.  People might be used to “selfies” and social media shots that are of very poor technical quality, and not really notice when a picture is better in that respect.  But when it comes to pictures that could not be taken at all with a smartphone camera, it’s a difference between getting the shot and having nothing useful at all.

It’s amazing that a small fist-sized compact camera can get hand-held pictures with the kind of close-up you have using binoculars.

 

Are different brands of camera flashes different?

On the Photography StackExchange site, I came across an interesting question: “Factoring out all features and just considering the Quality of the light, What is the difference between a very expensive flash and a average priced flash?

I was aware that people had posted opinions on general quality of manufacturing and durability in a professional-use situation and product lifetime, and I had decided to get one of each (one expensive, one cheap).  The only feature difference that I use is the secondary lamp on the high-end brand.  Since I have them, I thought I could easily compare the results.

The Test Shots

I shot the same picture using a Yongnuo YN568EXII (currently sold for $105) and a Metz 58AF2 ($400 for those versions still for sale).  I used a tripod with the flash mounted on-camera, and fully specified the exposure as ISO 100, 1/250 second at f/22. The flashes were set to use ETTL to determine the light output automatically, with the zoom head set to 70mm, and the secondary lamp on the Metz disabled.

The raw files can be downloaded via Dropbox.  IMG_4236 was taken using the Yongnuo, and IMG_4237 with the Metz.

RAW Data Analysis

chart-measurements

The green rectangles indicate some of the regions where measurements were taken: whole-chart, lightest, darkest, and grey-background.

To my surprise, the immediate appearance of the histogram on the camera showed striking differences!  The Metz showed a substantially broader range of tonal values, while the Yongnuo showed a narrow spike dominating the display.

To get a closer look, I used RawDigger, which will give information about the real recorded values in the RAW file without any kind of interpretation going on.

IMG_4236-Sel-1813-1257-1605x1135.x

Yongnuo whole chart measurement

IMG_4237-Sel-1813-1257-1605x1135.x

Metz whole-chart measurement

Where are these differences coming from?  I’ll report only the green values because the shapes of the histogram are the same in all channels.

For middle grey, the background border areas of the card, Yongnuo (Y) shows an average value of about 702 and σ (standard deviation) is 32.  For Metz (M), the average is 852 with σ 25.  The darkest and lightest (un-numbered) patches are 68–3013, while for M they range from 55½–2417, with similar variances on each brand.

For M, the brightest un-colored base paper is not the brightest value recorded! Patches 13-A through 19-B, (C,D)-13 (cyans), and (C,D)-15 (yellows) are all brighter in the green channel.  The brightest patches on M measure as 3142, where there is a visible spike at the right edge of the histogram.  In Y, those patches are 2895, a little less than full bright, as expected.

This might be due to uneven flash coverage: I found the wall around the chart was also brighter towards the upper-right on the M, so the base-paper patch happens to lie in the corner that received the least light.  On the other hand, the wall was more slightly brighter towards the top in the Y exposure.  Since the camera was in the same position and the flash height is only about 1cm different, any effects due to angle should be the same on both.

Looking at the R,G,B values of patch L8, it is clear that the color balance is different: the Y has more blue than the M.  In the histograms for the overall chart, the M shows double peaks in all three channels where the Y only has one.  In the red channel, one peak between EV −2 and −3 (about sample value 350) while in M there is a double peak around this value; for green the situation is similar between EV −1 and −2; and for blue the peak just right of EV −2 in the Y corresponds to just the (smaller) right part of the double-peak on either side of EV −2, in the M.  The blue channel also has another strong peak at EV −1 in the M that’s not present at all on Y.  Clearly the colors are responding differently.

The overall exposure seems darker in the M photo just looking at what comes up in RawDigger, though range of values (as seen on the histograms) is the same on each, and the specific value recorded for middle gray is the other way around.  For the wall to the right of the chart, the M is also a tiny amount brighter.  But for the lower-left of the exposure, the wall is significantly darker in the M if you just look at the average.

flash-chart-wall-R

flash-chart-wall-LL

The M exposure shows a lower average and a much lower σ, but the histogram pictures show fatter distributions on the M, and double peaks.  This is confusing and not immediately obvious why, but RawDigger changes horizontal scales when moving between exposures, and the choice of scale is not intuitive.  It appears that the exposure is about half a stop lower in this region for the M.

Without using careful measurements of the image pixel data, a side-by-side viewing appears to have a slight difference in exposure, but upon closer inspection only some things are exposed differently and the color balance is different.  This definitely counts as a difference.

Developed Data Analysis

Loading the files into Lightroom, I synchronized changes to the two exposures. I cropped the chart so the histogram is dominated by neutrals and shows a clear peak that should be lined up in all channels. I also corrected the perspective so it’s roughly rectangular, which will simplify the later overlay comparison. Sharpening and Noise Reduction were both turned off.

The process used is 2012 Adobe Standard, and no adjustments where made to exposure.

The White Balance was set using the eyedrop tool over a section of grey background. The image is rather noisy with the color varying from pixel to pixel, visible in the loupe-zoom of the tool. So I tried a few spots to make sure it was representative, and verified that the RGB values of the neutral patches were showing the same in each channel.

The same WB was applied to both exposures, and the other exposure was visibly different, showing a color cast.  Below are screen shots put together in a collage.  You can see the histogram in LightRoom indicates that the neutral peaks don’t line up.

wb-comparison

The Color Temperature of the two flashes are different, and neither matches the Flash preset color balance.  The setting above, taken for the Yongnuo, is a temperature of 6650 with tint +10.  The Metz is about 6072 with tint +14.

Next, I compare all the colored patches by cutting strips half as tall as the patches and alternating them from different exposures.  Below, each patch, e.g. the yellow in L15, has the bottom of the box shown from the Yongnuo exposure, and the top of the box from the Metz.  In addition, the left and right edges are painted in Photoshop as pure uniform grey.

stacked-charts

After adjusting the WB individually for each exposure as explained above, it was clear from this rendering that the brightness varied across the chart, in different ways for each exposure!  I used a (different) gradient exposure adjustment on each to approximate the uniform brightness of the grey background.

Ignoring the brightness completely by setting all the “B” values to 50% and leaving the “H” and “S” unchanged, we can better see the color differences without being overwhelmed by the illumination changes.

stacked-charts-hue

Colors with especially low saturation are lost, but this shows that the only color shift is subtle: Pure blue shifts in saturation, green shifts a little in hue value, and cyan does both.  This is not something that will be noticed, so in terms of color quality of the flash I would say there is no real difference.

Note that this uses the correct white balance adjustment for each flash, individually.  What about using both at the same time, so the light sources are mixed?

stacked-charts-WB-hues
This adds a yellowing of the mid to dark neutrals, and a hue shift in the magentas.   The lightest neutrals don’t have a visible difference, and I think that would be where it would be more bothersome.  I expect the overall effect is lost in the normal color casts you pick up from other objects in the room and whatever you are bouncing off or diffusing through.

Conclusions

Both flashes have non-uniform light beams that I believe are the dominant source of differences.  In particular, the apparent difference in exposure and the visibly different texturing of the wall is due, I conjecture, to the differences in illumination angles.  A difference in diffusion, or apparent size of the light source, can affect the modeling of textures especially when the flash is near the lens.  This deserves further research.

Although I saw the in-camera histogram was quite different with one seemingly offering more dynamic range in the exposure, and the reflected light curves are also rather different in some interesting ways, they both work to reproduce colors well.  (Assuming a silver-halide technology ANSI standard IT8 calibrating target contains pigments that respond to different spectra of light in a similar manner to real-world scenes, though it was produced with the intention of mimicking the response of various prints and films. But pigments and dies used for making prints are themselves expected to look right under different lighting conditions.)