13
Nov
09

Photographic firsts

I recently posted two images on my photo blog, both of which represent firsts for me.  Since the photoblog is kind of minimalist, I didn’t write much about them there, but I thought I should maybe add some info about them here.

The first was taken using a zone plate, which I got ages ago but never used.  I got it last year at my birthday in a kit like this, which includes a device for holding photographic pinholes, the pinhole itself, and an adapter to make it fit my camera.  I had taken a few photos using the pinhole but never the zone plate.  I like the effect.  There are a couple of downsides to using either the pinhole or the zone plate, however.

First, these have incredibly narrow apertures, which means that, in order to get a correctly exposed image, you need a very long exposure or very high ISO setting.  I kept the ISO reasonably low but I used my tripod to give me the stability I needed for a long exposure.  I used a 1.3 second exposure, which, for a shot taken in the middle of the day, is really long.  This zone plate has f/56 (not 5.6, 56!), which is pretty wide for this type of device.  The pinhole I have is something like f/130, so it would require a much longer exposure.

Second, whereas taking photographs with traditional lenses is pretty forgiving when it comes to junk on your sensor, pinhole and zone plate photography is extremely unforgiving.  I had to do a bunch of spot removal in Lightroom to get rid of a bunch of ugly splotches on the image.  The image below is a 1:1 crop from an image I took of the same scene with the pinhole.  There are at least 4 spots that are clearly visible, though they vary in severity.  I had never noticed these spots before in shots taken using my normal lenses.  I guess if I want to do any more photography using my pinhole or zone plate, it’s probably time to have my sensor cleaned again.

Spots on my CCD

 

The most recent picture is my first foray into high dynamic range (HDR) photography.  I’ve been interested in this for a while but never really pursued it.  The point of HDR images is to make details visible in both the highlights and shadows of an image. Generally, both the camera sensor and any typical viewing medium (like a monitor or even printed photos) don’t have enough dynamic range to either properly capture or properly display details in both an image’s shadows and highlights.  There is just too much difference in brightness between the darkest parts and the lightest parts in a scene for the camera to capture everything or for it to all be faithfully reproduced on a monitor or print.  So some kind of workaround is necessary.

Due to the limitations of the camera’s sensor, capturing the details in both the highlights and shadows requires multiple images to be taken at different settings, a technique called exposure bracketing.  In the simplest case, exposure bracketing involves taking the following 3 photos: one that’s significantly underexposed (to capture details in the highlights), one that’s properly exposed, and one that’s significantly overexposed (to capture details in the shadows).  These images are then imported into a program on a computer that merges them to produce a composite image that has a much higher dynamic range than can be captured with a single exposure.  Unfortunately, this image also has a much higher dynamic range than can be displayed on a monitor or on a print, so another step is necessary.  This step is called tone mapping.

Tone mapping takes a HDR image that can’t be displayed and maps its brightness values back to a range of values that can be displayed.  When an image is captured, the darkest darks and the brightest brights are “clipped”, which means they’re simply cut off – detail in those areas is lost.  Taking multiple pictures of the same scene using different exposure settings gets back the data that was clipped.  Tone-mapping could simply clip the data again, however that would throw away the detail we want to preserve.  Instead, tone-mapping compresses the dynamic range, so that the details are preserved in both the highlights and shadows.  Modern tone mapping algorithms are actually quite a bit more complicated than simply compressing the dynamic range.  Rather, they operate on the data both globally and locally to try to maximize the extent to which details are visible in the image while simultaneously compressing the dynamic range to something that can be viewed on a monitor or print.  This often results in a very striking, though sometimes unnatural-looking image.

Yesterday I was looking through my to do list and I found a reminder to buy some software for making HDR before I graduate so I can take advantage of their (60%!!) educational discount.  Having just sold our exercise bike, I had some cash on-hand so I decided to go ahead and buy the software while I thought about it.  I bought Photomatix from HDRSoft for about $40 rather than the usual $100.  I remembered that I was out a month or two ago and for some reason decided to take some shots using exposure bracketing, so I looked through my Lightroom catalog and found a few sets of exposure bracketed images.  I picked the set that I liked best, exported it to Photomatix, created the HDR image, re-imported to Lightroom, fiddled a bit with saturation and noise reduction, and then exported from Lightroom to PixelPost.  Done.

Having a tripod makes HDR photography easier, so I’m looking forward to using my new tripod along with my new HDR software to produce some good looking images in the future.  Stay tuned.


4 Responses to “Photographic firsts”


  1. 1 lovebug35
    November 13, 2009 at 8:58 pm

    interesting.

  2. November 14, 2009 at 7:39 am

    I would think the focus would be soft but clearer on the zone plate image–I mean f/56 means

    The other thing that I’d point out is with a pin hole (and possibly zone plate–not sure) photo on a digital camera you should put some sort of filter or clear cover on it. Apparently–this is what Andy tells me–taking a photo charges the sensor and that can electrostatically attract dust particles to the sensor. It’s probably worth considering or looking up more info about that.

  3. November 14, 2009 at 7:43 am

    Oops. I mean to say that f/56 means the depth of field/ focus should cover a lot of the photo.

  4. 4 Colin
    November 14, 2009 at 12:58 pm

    I think the zone plate is fuzzy because it uses diffraction rather than cameras’ usual methods of focusing with a lens. It could also be that my zone plate isn’t great quality, which might account for how blurry it is. I don’t know.

    Yeah, I’ve heard things about dust problems with pinholes. I’m not sure if the spots on my sensor are dust or some type of lubricating oil used in the mirror assembly. The last time I had my sensor cleaned, the guy at Calumet said I had some oil splotches. Those are harder to remove than dust particles. My camera has a CCD-shake dust removal system but it has failed to remove these splotches, so either the system isn’t very effective at removing dust or they’re not dust. Anyway, I like the zone plate because there’s no physical hole. Therefore, dust has no direct path from outside the camera to the sensor.

    It seems like you could make a faux pinhole by taking a piece of glass and coating it with an opaque coating then removing a tiny circle of that coating. Perhaps people have done this. This might be hard to do, however, without scratching the glass where you want the light to come through.


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