Posts Tagged ‘photography’

The Sigma 18-35mm f/1.8, firmware updates, and auto-focus

July 27, 2015

Here is the quick summary: the firmware update for the Canon mount Sigma 18-35mm f/1.8 (2014-8-22) did more than add support for the EOS C100, as claimed by Sigma. It also changed the lens ID from 137 to 150, and seems to have improved auto-focus accuracy, although not precision. Update: The auto-focus is as good as a Canon EF 85mm f/1.8.

I got one of Sigma’s 18-35mm f/1.8 lenses to go with a new Canon EOS 70D over a year ago. At a New Year’s event with a local band that includes a neighbor of mine, I took a bunch of pictures with this combination. The result seemed to work pretty well in spite of the low light at the outdoor venue. However, I have found that many images I have taken with the lens since then have not been in focus when using the optical viewfinder. This is a fairly common problem with Sigma lenses, although it doesn’t account for its early good performance. I’m guessing that at the New Year’s event most of the pictures had a deeper depth of field from focusing far enough away.

To deal with the problem, I got one of Sigma’s dock gizmos. I printed out a focus test page and made a table that I filled out with the adjustments needed. Every time I used the dock, the Sigma software asked about updating the lens firmware. I always refused because Sigma claims they just added support for a camera I don’t have. I don’t like to update things unless the update is actually beneficial. It is a way of limiting the chances of dealing with an update that breaks something.

Auto-focus calibration tool

Auto-focus calibration tool

The attempt at improving auto-focus didn’t go well. I got very contradictory results from two attempts, each starting from no adjustments, and neither improved the results. I figured the paper at a 45 degree angle was to blame, so I built a focus target out of Lego. When I cleared the adjustments on the lens before testing, I decided to update the lens firmware just to keep the software from incessantly asking about it. Every test I did with the Lego target suggested the lens was fine. Some tests with more common subjects suggest the accuracy is decent, but the precision still isn’t as good as with Canon lenses, so it is still a good idea to take several pictures and review them.

The software I use for keeping track of my photos, Digikam, did not at first identify this lens. Instead it called it lens 137; it has since been updated. I think the Canon protocol uses an 8-bit unsigned integer to identify the lens model, although now additional information like the focal length range is needed to identify a specific lens model. Since I updated the firmware, Digikam identifies the new images as being taken with lens 150.

I don’t know if this change from 137 to 150 is needed to make the lens work with the EOS C100. It is possible that the change will affect how the lens and camera work together. From what I’m seeing, it has a favorable effect on auto-focus performance with my EOS 70D. I don’t know why Sigma wouldn’t mention this, and I really don’t like the short list of changes common in the photographic industry for such updates. I have suspected that some changes are omitted from the public list of changes, and my experience with Sigma’s 18-35mm f/1.8 lens deepens that suspicion.

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LumiQuest softboxes and flash zoom settings

January 2, 2014

Oops: I made a common mistake when I wrote this post. The output of a flash is controlled as a fraction of maximum output energy, not power. Changing flash power can only change brightness reliably for photographic use if the duration of the output is constant, and that assumes constant power during the output. A camera sees more light as brighter, so flash energy is useful to control, while flash power is not. Power is energy over time. I haven’t bothered to correct the rest of the post.

It is good to have diffuse light for soft shadows. To that end, when I can’t aim the flash at a ceiling I use LumiQuest softtboxes because they aren’t super pricey (although there are cheap competitors from beyond the USA now), and they are very portable. This isn’t an advertisement for the product, though; I’m not getting paid. Instead, this is about an investigation I did into how to get the best results from the LumiQuest’s Softbox and Softbox LTp.

Happy Thanksgiving!

The LTp softbox is directly over the minifigs and very close

I got the LTp to help with some Thanksgiving dinner pictures of Lego minifigures. It is almost too large for something attached to a flash, and it did take a few tries to keep it from falling off. It was facing downward to be an overhead light, but that made falling extra easy.

I wanted the light to be as even as possible, so I used the pull-out light scattering lens of the flash. This put the flash’s zoom head into its 14mm setting, which is really just the 24mm setting with the lens applied. The lens is made of some plastic like material and absorbs some light, which was also helpful because otherwise the flash was too bright. The flash in question here is the Yongnuo YN568EX II, which is working out quite well for me, but that could be the topic of another post.

Brightness uniformity test

Brightness uniformity test

Afterwards, I wanted to investigate what works best with the LTp to make the softest shadows. It makes sense that the light will need to be uniformly bright across the light scattering surface of the softbox for the best results. I took pictures of the LTp with different flash zoom and power settings to get an idea of the uniformity. The exposure was the same for all pictures (f/16, 1/125sec, ISO 100). The resulting test is not indicative of overall brightness because most of the images have over-exposed areas. They do, however, clearly show that the 14mm flash zoom setting does provide the most uniform light over the surface provided by the LTp softbox. The 24mm setting isn’t much worse, but the 105mm setting looks like it should make the LTp perform the same as a much smaller softbox.

Next, I decided to see what effect this has on the quality of shadows. I put a cardboard tube on frosted glass so that I could photograph the shadow on the glass, and because I had the glass already setup. I later discovered that the shadow on the glass was sometimes filled in with light from the flash reflecting from other surfaces in the room which obscured what the shadow would have been with light only directly from the softbox. The test images also had a shadow cast by the tube onto itself, which turned out to be mostly immune to the problem. It made for small test images, but I think they worked out well.

Shadow quality test

Shadow quality test (take link for bigger view)

For a more complete test, I also tried my old LumiQuest Softbox (the one with a notch in what otherwise would be a rectangular light scattering surface), a bare flash, and a misused Sto-Fen Omni-Bounce. I varied the flash power, but not the exposure (f/4, 1/160sec, ISO 100) or distance between the flash and tube (about 740mm, or 29 inches). In all cases, the 14mm setting required quadrupling the flash power and the modifiers required doubling it. The bare flash at 24mm used 1/32 flash power. The 105mm flash zoom setting required changing flash power, but it wasn’t so consistent.

The results show that the LTp softbox responds more to the flash zoom setting than the other LumiQuest softbox I have. The LTp improves with the 14mm setting over the 24mm, but the loss of light from the flash’s scattering lens will sometimes make 14mm too dim. Other flashes may fare better, but I think most will be similar if they don’t use a glass scattering lens. Using the LTp with the 105mm setting makes it about as good as the non-LTp softbox at 14mm or 24mm.

The LumiQuest Softbox (non-LTp) produces shadows with a negligible difference with the 14mm and 24mm zoom settings, but does get worse at 105mm. The bare flash gives the expected shadows with hard edges, but it does seem to be very slightly softer at 105mm. This suggests the zooming action changes the uniformity of the brightness across the flash head.

Finally, I tried a Sto-Fen Omni-Bounce pointed directly at the tube. The Omni-Bounce is a light scattering device that doesn’t add much surface area like a softbox does. This makes it half of a light diffuser. The other half is supposed to be the ceiling and walls of the surrounding room. The little card included with the Omni-Bounce states that it should be pointed at the ceiling and not the subject. This test shows why. I have seen some people misuse their Omni-Bounce by pointing it directly at their subject while inside a convention center with high black ceilings, but that just results in wasting flash power.

CD-R Stack as a Background for Pictures

October 12, 2013
Background setup

Background setup and messy desk

I’ve been using a stack of CD-R’s as the background for several images of Lego minifigures. The CD-R’s are lit by flashlight (a silver Hexbright). In front of the flashlight is a color filter and a light scattering filter, both really intended to be used with a flash. The position of the CD-R’s and the two Star Wars minifigs in front are unchanged from the recent photo “Don’t let this happen to you”. The examples shown here all use the same color filter, but I also used violet and red-ish ones, as well as none at all.

The background result is affected by the relative position and orientation of the flashlight, CD-R stack, and camera. This makes using a flash in place of the flashlight really difficult. Also, I usually had the Hexbright at a low brightness setting, so it really was flashing, but it bothered the camera more than me. All of these positions and orientations provide lots of variables to play with to make a number of interesting effects for colorful abstract out-of-focus backgrounds.

Mom, I can see straight!

Mom, I can see straight!

Some of the light going through the CD-R’s makes nice vertical columns of highlights. There are four of these columns: one on either side of the central spindle pillar thingy (I don’t know what that is called), and two further away that seem to be reflections of the first two. Getting all four in the same picture is nearly impossible, but two is pretty easy and three isn’t difficult. Some prism-like effects are visible in those highlights, and the CD-R’s colors the light a bit green. I’ve got two or three bands of CD-R’s in the stack, so the exact shade of green varies a bit. I also looked at some DVD-R’s, but they are a boring white. I think I’ve got older ones that’ll color the light a bit red, but I haven’t tried.

With this setup, horizontal bands over a limited vertical distance can be shown where the light passes between the disks. As a result, these bands are not colored by the CD-R’s. They are visible just under Iron Man’s left arm in “Looking for trouble”. The light also reflects between the surfaces of adjacent disks; this seems to create an odd pattern that can result in curved swirly lines that are more easily seen by a camera than eyes. The curvy swirlies are seen in “Mom, I can see straight” to the left of the minifig. Some placements of the camera versus the CD-R stack avoid this effect and have clear horizontal lines with beveled edges as seen near the minifig in “An explorer in a strange place”.

Looking for trouble

Looking for trouble in front of CD-R’s

With the help of a light in front of the CD-R’s (I used an on-camera flash pointed at the ceiling and nearby wall), a single vertical column of reflected light can also be put in the background. The reflection highlights look distinctly different from the highlights of light passing through the CD-R’s. Instead of aperture shaped highlights, they have horizontal bands that seem to be sections of the aperture shape. Since this light comes from a different source, it is a simple matter to make it a different color. This shows up in “Looking for trouble” with Lego Iron Man (sans iron). I used a CTO filter on the flash attached to the camera to help make the helmet look more golden, and it shows up reflecting off the CD-R’s.

This guy

This guy

What I’m most fascinated by are some horizontal bands in my picture “This guy” (lower middle of frame next to the minifig; not visible in the little thumby here, best seen after taking the link and viewing the image full size). Even though the stack is well out of focus, there are a number of thin bands. I’m guessing that the banding of horizontal disks caused similar banding in the out-of-focus light which can be made into thin lines by how the light from different bands are superimposed on each other.

The top of the desk is glass, so I usually have a flash under it. The effect works a lot better than some of the scenes of the evil Kirk in “The Enemy Within”. It also helped tremendously with my “Looking for trouble” picture; one flash lit the face and the other lit the helmet.

I also made a video to show how the background can change, but it really doesn’t give a full demonstration.


False Steps

The Space Race as it might have been

keithlugcom.wordpress.com/

You Control The Action!

High Frontier

the space colony simulation game

Simple Climate

Straightforwardly explaining climate change, so you can read, react and then get on with your life.