Using tiny apertures - Part 1, Background

 I re-started photography in 2007 after a gap of more than 30 years and started photographing insects, spiders, snails etc using a close-up lens on a small (1/2.3") sensor bridge camera. Since then I have continued using close-up lenses for invertebrates, both on newer small sensor bridge cameras and also micro four thirds cameras (with a 45-175mm camera lens) and an APS-C dSLR (with a 55-250mm camera lens). I have moved back and forth between these setups for years, mainly between bridge and micro four thirds, unable to decide which was best; each has its own merits and problems for what I want to do. (I'll talk about flowers etc another time, which have taken me on a different path.)

In order to get as much depth of field as I could for insects etc I used minimum apertures; f/8 on the bridge cameras and f/22 on the micro four thirds cameras. On the dSLR minimum aperture varied from f/22 at 55mm focal length to f/32 at 250mm focal length.

Used with a close-up lens, these apertures gave me very similar depth of field on all three types of camera, which was enough to get images like this with single shots (i.e. not focus stacking). 

From time to time I experimented with other approaches, including various combinations of macro lenses, extension tubes, teleconverters and reversed lenses, some of which let me get greater depth of field than I could with my close-up lens setups by using smaller effective apertures than I could with my close-up lens setups.

None of it worked to my satisfaction. For example, for the kit I tested I found that:

• Macro lenses either didn't let me use autofocus, or if they did it got so slow and unreliable as the magnification increased that it wasn't worth using. With my close-up lens setups I had autofocus that was responsive and accurate, and which especially with the bridge and micro four thirds setups let me use a very small focus area which allowed me to place the plane of focus pretty much exactly where I wanted it. Manual focus was in contrast very hit and miss, especially with subjects that were moving around.
• Macro lenses gave softer images at minimum aperture than close-up lenses
• A setup that let me use a tiny aperture (I tested an effective f-number of around f/132) gave images that were so soft as to be not usable.
• Using extension tubes would mean opening up the camera out in the field to change between them depending on scene/subject size. This would risk getting dust etc on the sensor. When using small apertures this matters greatly as dust shows up very clearly, especially with the fairly strong post processing I used.
• Teleconverters were promising as they provided greater magnification at the same minimum working distance or the same magnification as without them but with a greater working distance. However, a 1.4X teleconverter softened images a bit and a 2X teleconverter softened them more.
• When reversing lenses that didn't have a manual aperture control, I could only control the aperture with a procedure that was slow, fiddly and opened up the camera to dust etc. Alternatively, I could use a device that let me change the aperture in the normal way, but this caused very bad flare. Or I could use a legacy lens with manual aperture control, but none of the ones I tried worked well in my hands.
• Most of these setups were big, heavy and awkward to use.
• None of these setups gave me noticeably better image quality  than my close-up lens setups for the single-capture large depth of field shots that I typically go for. (This may seem surprising. Why wouldn't proper, very sharp, macro lenses give me better results? I think because of softness and loss of detail caused by diffraction. With the apertures I was using the excellent sharpness of the high quality lenses got blurred away by the large amount of diffraction softening.)

So, I kept coming back to my close-up lens setups. 

This left me with an unresolved problem; small subjects. I had only very limited success with small subjects such as fruit flies, springtails, barkflies and barkfly nymphs, mites and tics, which were often around 2 to 3mm long and sometimes 1mm or less. 

 

This problem had been nagging away at me for a long time. Most of my invertebrate subjects are what I think of as middle sized, or occasionally large, and over the years I slowly progressed, for example as my post processing improved. What I had never been satisfied with, and seemed unable to make meaningful progress with, was small subjects like this springtail, which was probably around  two millimetres long. 

Very occasionally I would get an image like this, but the capture failure rate was huge and when one did work the processing effort could be disproportionate. (I had repeated attempts over several years trying to get something usable out of this one.) It was extremely difficult to enough depth of field for my taste, and I had to keep the subject smaller in the frame than I would have liked. It was all pretty disheartening and for the most part I ignored small subjects like this.

So how did I end up using a big, heavy, manual focus setup which used a macro lens and not just one but two teleconverters, both of the 2X variety, using effective apertures even smaller than the f/132 that I had shown was unusable, and using this setup to photograph subjects as small as 2mm or so long as they moved around quite fast, with a fairly high success rate?

That is what the next few posts will be about.