Just how far has technology come? Smartphone vs DSLR Fluorescence Photography

If you're expecting to read this and figuring out how to take photos like this using your 4-6W lamp and your smartphone just turn off. Not possible 2015.

 

http://imgur.com/bqiJwqA

There are currently many things that prevent smartphones from being able to take proper fluorescent photos. This post will explain some of the nuances and how to best correct for them

  • Lack of long exposures. Most smartphones today only allow you to take exposures that are a fraction of a second long. The best I've seen is 1 second. I've seen a couple apps that advertise being able to control this but I had no success with this. It'd be great if you could just take a 10-20 second exposure on a phone!
  • Lack of aperture control. You don't want to allow any mineral photo to have an aperture of f/2 or however low your camera allows you to go. This will result in lost detail of your specimen. Unfortunately you don't have a choice. In order to properly compensate for the low light your phone has to do something!
  • Small sensor size. Smaller sensor = less light gathered.

However, there are things that one can do to take better photos with their smartphone of choice. Below is an outline of several things that will improve your photos despite your lack of proper photographic equipment.

  • Pick a smaller specimen. Less surface area to light up.
  • Bring your UV light source much closer. In the photo on the left I had my lamp about 2 inches away from the specimen with the photo taken at a 45° angle.
  • Stabilization. Either use a tripod or wedge your phone between something that'll keep it steady as soon as you tap the button.

 

Features to look for in a smartphone app:

  • Noise reduction stacking (?) Hard to phrase it as every company tends to give it a different name. I've seen it called night mode, smart stabilization, etc. Basically what this does is take multiple photos and stack the images to reduce ISO noise. You can tell your app is doing this when your phone stutters after taking the photo. In some cases it might show an animation to illustrate that several photos are being taken or have a processing bar.
  • ISO control. Go from high to low and see which one looks best. Be as greedy as possible and select the lowest ISO number you can get away with. The lower the number the more detail is in your photo.

Re: Just how far has technology come? Smartphone vs DSLR ...

Some very good tips here.  A couple of clarifications:

1.  Small vs large apertures:  "Depth of field" refers to how far in front and behind the focus point will still be in focus.  Rocks are, of course, three dimensional and have depth.  We want both the front and the back of the specimen to be in focus.  The smaller the f-stop the greater the front-to-back depth of field.  A large aperture, e.g. f2, will have a very shallow depth-of-field.  The resulting photograph will show the front surface of the specimen in focus, but the image will get progressively more blurry towards the back of the specimen.  A smaller f-stop, e.g. f16, has greater depth of field, so that more of the specimen will be in focus.  There are, however, ways to use large f-stops and still get a well-focused image.  For f-stops the larger the number, the smaller the aperture; f2 is a very large aperture, f22 a very small one.

2.  ISO control: ISO is a term that carried over from film photography.  It was an objective measure of how sensitive the film was to light.  Films with low ISO numbers were less to light than films with high ISO numbers.  Obviously, less sensitive films required more light and/or longer exposures and larger apertures than high ISO films.  As a rule, high ISO films produced grainer images than low ISO films.

In the digital world, ISO still indicates the relatively sensitivity to light.  However, obviously, we don't change sensors to accommodate lighting conditions like we used to do with film.  Instead, digital cameras vary the amount of gain -- the amplification applied to the signal produced by the sensor -- to approximate different light sensitivities.  The higher the gain, i.e. the higher the ISO number, the more visual noise is introduced into the image.  Better cameras with better sensors introduce less noise when applying gain.  Some cellphone cameras have fairly good sensors and electronics (my Samsung Galaxy Note 3 does an excellent job).  Noise (frequently called "color noise") looks a little like the grain found in film photography.  The more noise, the less distinct the image.

3.  Stacking:  There are two kinds of stacking: focus stacking and exposure stacking (exposure stacking is usually called HDR, for High Dynamic Range).  Though both techniques involve multiple exposures taken without moving the camera, the techniques and result are very different.

Focus stacking:  As noted above, large apertures have shallow depth of field, so that only part of the specimen is in focus.  Focus stacking entails taking multiple exposures at different focus points, moving from front to back or back to front.  The resulting set of images is combined, either in a camera that supports it or in post-processing software like Adobe Photoshop, so that only the in-focus parts of each exposure are used for the final composite image.  This is done automatically by the software.  The resulting image will show sharp focus throughout the image. 

HDR (exposure stacking):  This technique involves atking multiple exposures as different EVs (exposure values).  This can be done by varying the aperture, exposure time, ISO or all three.  As with focus stacking, the multiple images are then processed, either in the camera or in computer software, with only the corrected-exposed sections of each image used for the final composite.  This technique not only results in greater dynamic range in the final image (dynamic range refers to the range between full black and full white), but it will also provide far more accurate color.

I'm not aware of any cellphone cameras that can do focus stacking or HDR, but perhaps there are some apps out there that can do this.

I've seen some good UV photographs taken with smartphones but, generally, it will be difficult to approximate the best results produced by a DSLR with full manual control.  As the article author notes, the more UV light on the specimen, the better.  A tripod, or some other stablization mechanism, is critical to getting good UV photographs.

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