Photographing insects: lenses

Last week I was asked about what objective I use when photographing live insects in the field. I do not always use the same objective, so I will describe the two I most frequently use. Neither do I use what would be the most suitable or state-of-the-art optics.

The camera (Olympus E-M1 mk I)

The camera I use is a mirrorless micro four-thirds camera, which has a smaller sensor than “full frame” cameras. The small sensor has two advantages for this type of photography: an objective of a given focal lens is equivalent to twice the focal length in a full-frame camera. This camera has also effective image stabilisation.

I am rather lazy so I almost never take a tripod to the field and hand hold the camera. Consequently, for macro photography I always enable image stabilisation and very frequently continuous focus. For handheld macro photography continuous focus helps even for static objects as it tracks the inevitable movements of the camera. This is because in many cases depth of (focus) field is only a few millimetres.

Insects can move fast on their own and/or the plants they are standing on may move in the wind. When magnification is high, a shift as small as a millimetre may ruin an image. The number of “hits” tends to be low even when working carefully. One needs to take hundreds of photographs and later select the few worth keeping.

Macro objective (50 mm prime)

The macro objective I own is a Zuiko Digital 50 mm f/2.0 macro for Four Thirds cameras, of Pro grade. Optically is very good, but its age and using it adapted means that focus is very slow. The focal length is equivalent to 100 mm. It can reach 1:2 magnification without use of a macro extension tube and 1:1 magnification with a 25 mm long extension tube, which I also own.

Being a prime (fixed focal length) and in its time being considered the sharpest lens available from any brand, it can produce incredibly good images… as long as the insects are tame and patient. With this focal length if the insects are rather small one has to get very near and and frequently wait for a couple of second until the camera locks focus.

Because of the rather low light level, it would have been difficult to take this image with an objective of longer focal length.

Image taken with the camera handheld, using the Zuiko 50 mm f/2.0 macro objective.
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Crop from the image above showing the detail.

The 50 mm f/2 macro works well together with the 2 x tele converter.

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Zuiko 50 mm f/2.0 macro + 2 x tele converter EC-20
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Detail from the image above.

The current M.Zuiko 60 mm f/2.8 micro-four-thirds macro objective with faster focusing and very good resolution would be better for this task. It also weights a lot less.

The advantage of working at close range is that one can hold a flash (or LED light) in one hand and the camera in the other. In the times of low ISO films this was one of the best ways of photographing insects, in which case one would focus by moving the camera very slowly and triggering the shutter some fraction of a second before perfect focus. If the light level is low (cloudy or sun low in the sky) the handheld use of a tele objective as described below becomes  very difficult if not impossible.

Tele objective (50-200 mm zoom)

The tele zoom I own is a Zuiko Digital 50-200 mm f/2.8-3.5 SWD for Four Thirds cameras, of Pro grade. Not up to current state of the start in focusing speed but more than fast enough for anything that is not flying. This is the objective I most frequently use for insect photography. To be able to reach high enough magnification, I use in combination with either a tele-converter or the 25 mm macro extension tube.

Image quality with the extension tube is excellent, although not on par with the 50 mm macro described above. With the Olympus 1.4 x tele converter image quality is what I consider good enough, while with the Olympus 2.0 x tele converter only marginally. This last combination is also difficult to use without a tripod. The tele-converter with less magnification provides a maximum focal length of 280 mm, which is equivalent to 560 mm in a full-frame camera. The tele converter with more magnification provides a maximum focal length of 400 mm, which is equivalent to 800 mm in a full-frame camera. The advantage of using a tele converter is that the minimum focusing distance is retained in spite of the increased focal length.

So, what I currently use most frequently for insects is the 50-200 mm tele zoom with the 1.4 x tele converter. It does not provide the best possible image quality but it allows me to obtain more good images as I disturb the insects much less, which allows more time for framing, focusing and for multiple takes of a given subject. This weights about 1.5 kg, has a minimum focusing distance of 1.10 m giving a field of view of xx times xx mm.

In full summer sunlight, the tele zoom plus a tele converter works well.

_6140578-09
Zuiko 50-200 mm f/2.8-3.5 SWD + 1.4 x tele converter EC-14
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Detail crop of the image above.
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Zuiko 50-200 mm f/2.8-3.5 SWD + 2 x Tele Converter EC-20
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Detail from the image above.

The tele zoom with an extension tube can be used to advantage, but the working distance is decreased.

If you have a camera with a bigger sensor, then if you want to be able to dispense of a tripod, you will need to use a shorter tele objective than the equivalent focal length of what I am using.


All illustrations, text and measurements are of my own authorship, and copyrighted.

(c) 2017 Pedro J. Aphalo


 

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Macro extension tubes (lens mount)


This is the third of three instalments on the comparison of three sets of macro extension tubes for MFT cameras: Macro extension tubes (description)Macro extension tubes (glare), and Macro extension tubes (lens mount).


Disclaimer: I have no connection to any of the suppliers of the items compared in this test. I bought them from different on-line sellers. Although some of the products I bought have serious design flaws I have tested only one copy of each, bought in July 2017 (Kenko), June 2017 (COMIX), October 2015 (PIXCO). The items in production at the time you read this post may be of an updated design or quality. It is also necessary to be aware that in the case of some Chinese brands, cheap and expensive versions of an item may exist.


As yesterday’s tests showed that the 45 mm f/1.8 general-purpose prime lens had, when used at high magnification, rather bad performance in the corners and edges of the image, I used the M.Zuiko 60 mm f/2.8 macro for the two tests described here.

In the second and third tests, described in this post, my aim was to test the lens mounts, first for light leaks, and second for mechanical fit.

For the second test the two LEDs were positioned one on each side of the tubes at the position of the mount between the two tubes in each pair. The lens cap on the lens, and room in almost darkness except for the two LEDs. Camera set to ISO 25600 and exposure time 10 s (f/11, but this is irrelevant as the lens cap was on and no light passing through the lens). The results of this test were good. The mounts in all three sets did not allow light through.

For the third and fourth tests both LEDs were positioned pointing downwards towards the target. The camera was as before carefully levelled and I assessed whether any gross focus problems were visible in the images. To my eyes, there were none. It should be remembered, though, that with the lens pointing downwards, the possible effect of the weight of the lens on axial misalignment was minimised. I do see slight overall softness with the COMIX tubes, but it is likely to be caused by internal reflections, still degrading image quality in a situation where glare was not expected, as no strong off-axis light source was included in the setup.

Kenko 10 + 16 mm
M.Zuiko 60 mm f/2.8 and Kenko 10 + 16 mm automatic extension tubes. Diaphragm at f/2.8.
Pixco 10 + 16 mm
M.Zuiko 60 mm f/2.8 and Pixco 10 + 16 mm automatic extension tubes. Diaphragm at f/2.8.
COMIX 10 + 16 mm
M.Zuiko 60 mm f/2.8 and COMIX 10 + 16 mm automatic extension tubes. Diaphragm at f/2.8.

Differences in sharpness anyway are very small and not detectable reliably with this simple test. The slight softness due to glare, seems to be a small but consistent effect under this test.

In the last test I looked at the play in the mounts. Inserting two tubes between camera and lens, add three new possible sources for play and misalignment. Tubes are used to increase image magnification, and consequently also decrease depth of field. For this test I simply very gently push the lens while keeping the tripod as steady as possible.

I was not sure on how to show how play in the mounts affects the image when working at rather high magnification, so I recorded a short video (hosted at YouTube because of wordpress.com free account restrictions), while moving the objective by softly pushing it and moving in the mount while keeping the camera and the photographed SD card adapter still (there was slight vibration due to camera shake, but it was very little compared to how much the play in the mount displaced the image projected on the camera sensor). To give an idea of how much play there was, by lightly pushing the lens “nose” it was possible to move it by a few millimetres while keeping the camera steady.

While the Kenko and PIXCO tubes have little play in the mounts, not causing trouble, the COMIX set has an awful lot of play, so much as to make this set of tubes completely useless. The surface of the mounts in the PIXCO is rough, while in the Kenko ones smoth, and in the COMIX shinny and smooth. When a lens is mounted on the PIXCO adapter a gentle grinding vibration and noise are felt. The surface of the tube has developed some use marks, so it could potentially be a source of dust particles.


CONCLUSION: Extension tubes are hollow tubes, but they still differ dramatically in how usable they are! The amount of play in the mounts of the COMIX tubes is so extreme and the springs so weak as to make them unable to keep any objective at a repeatable position, which is a requirement for successful macro photography. Do take this into account when buying cheap pieces of optical equipment.


All illustrations, text and measurements are of my own authorship, and copyrighted.

(c) 2017 Pedro J. Aphalo


 

Macro extension tubes (glare)


This is the second of three instalments on the comparison of three sets of macro extension tubes for MFT cameras: Macro extension tubes (description)Macro extension tubes (glare), and Macro extension tubes (lens mount).


Disclaimer: I have no connection to any of the suppliers of the items compared in this test. I bought them from different on-line sellers. Although some of the products I bought have serious design flaws I have tested only one copy of each, bought in July 2017 (Kenko), June 2017 (COMIX), October 2015 (PIXCO). The items in production at the time you read this post may be of an updated design and different quality. It is also necessary to be aware that in the case of some Chinese brands, cheap and expensive versions of an item may exist.


I did some tests today. I expected some differences, but not as large as I found. Some test conditions were rather extreme, but they dramatically show that although extension tubes are just hollow tubes, they are not all equal on their effect on image quality. It is frequently said that lens adaptors and extension tubes devoid of “glass” will not deteriorate image quality. It is also rather frequently said that there is no reason to buy expensive adaptors and extension tubes instead of very cheap ones from eBay, Aliexpress or similar sites. This is not to say that all cheap tube sets are extremely bad, some are good enough taking into consideration how little one pays for them, and may be good enough for occasional use. The tests will also give you same idea of what to look for in photographs when choosing an item to buy.

I run the tests indoors in a darkened room, with the camera on a tripod, mounted on a focusing rail. The light sources, two white LEDs, were firmly attached to the same rail by means of two “magic arms and a magic ball”. The camera shutter was triggered remotely. The camera used was an Olympus E-M1 with an M.Zuiko 45 mm f/1.8 prime lens considered to be one of the best available for Micro Four Thirds. Warm white LEDs use were NICHIA CRI=92 type NS6L183AT-H1, driven with constant current of 700 mA. The test target was an SD card adaptor on a matt grey card with 18% reflectance (Novoflex maxi Zebra card, A4) as as to minimize reflections from the table surface.

For the first test one LED was positioned pointing downwards towards the target. A second identical LED was positioned pointing sideways and upwards towards the rim of lens at an angle of approximately 45 degrees but in such a way that it was just outside the image frame, i.e. the LED was not visible through the camera viewfinder. First a close up of this set up.

_9112093 I tested several different diaphragm settings, I show here first those obtained at f/1.8 and below those obtained at f/8.0.

Kenko 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/1.8 with Kenko 10 + 16 mm automatic extension tubes. Auto exposure.
Pixco 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/1.8 with Pixco 10 + 16 mm automatic extension tubes. Auto exposure.
Comix 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/1.8 with Comix 10 + 16 mm automatic extension tubes. Auto exposure.

At f/1.8 the Kenko extension tubes together with the M.Zuiko lens suffer from mild glare. This is a very good performance given the setup used in the test. Contrast is decreased but the image usable. The very cheap Pixco tubes, are not as good as the Kenko ones but probably fine in many normal use cases. The mid-priced COMIX are a joke (pun intended).

The differences at f/8 need some explanation: even though at f/8 the glare is better controlled with all tubes, but exposure is way off. I think what is going on is that the camera is measuring EV with the open diaphragm, but reciprocity between f-value and shutter speed fails as the glare gets better controlled at f/8. So, the camera auto exposure system gets mislead by the strong reflections!

Kenko 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/8.0 with Kenko10 + 16 mm automatic extension tubes. Auto exposure. The black shadow is one of the find from the LED heat sink, not an artefact caused by the tubes or lens.
Pixco 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/8.0 with Pixco10 + 16 mm automatic extension tubes. Auto exposure.
Comix 10 + 16 mm
M.Zuiko 45mm f/1.8 at f/8.0 with Comix 10 + 16 mm automatic extension tubes. Auto exposure.

Note: In the photos the SD card adapter accidentally moved. This does not affect the test as the LEDs were attached to the camera and the SD card adapter on a table. Although I did not take another set of images, I moved the LED away from the objective and then returned it to a similar position and checked that the difference between the Kenko and COMIX extension tubes was the same as during the first round. Also during the first round I tested the Kenko tubes twice to make sure that the LED had not moved. There is an out-of-focus fin from the LED heat sink in the image top right region.


CONCLUSION: Extension tubes are hollow tubes, but they may still differ dramatically in how much or little they degrade image quality in actual use! Take this into account when buying cheap pieces of optical equipment.


All illustrations, text and measurements are of my own authorship, and copyrighted.

(c) 2017 Pedro J. Aphalo


 

Macro extension tubes (description)


This is the first of three instalments on the comparison of three sets of macro extension tubes for MFT cameras: Macro extension tubes (description)Macro extension tubes (glare), and Macro extension tubes (lens mount).


Disclaimer: I have no connection to any of the suppliers of the items compared in this test. I bought them from different on-line sellers. Although some of the products I bought have serious design flaws I have tested only one copy of each, bought in July 2017 (Kenko), June 2017 (COMIX), October 2015 (PIXCO). The items in production at the time you read this post may be of an updated design and different quality. It is also necessary to be aware that in the case of some Chinese brands, cheap and expensive versions of an item may exist.


Neither Olympus nor Panasonic sell macro extension tubes for Micro Four Thirds lens mount. There are several third party alternatives. I have bought three of them, I will describe here my experience using or trying to use them. In eBay photographs they all look rather similar, and the three sets I bought consisted of two tubes, with lengths of 10 mm and 16 mm. As I will describe bellow, there are major differences. The sets I own are Kenko “Extension Tube Set DG for Micro 4/3” (100 € to 140 €, Kenko Tokina, Japan), COMIX CM-ME-AFMM (35 € to 55 €, Commlite, China), PIXCO “Extension Tube Set DG  for Micro 4/3” (15 € to 20 €, PIXCO, China).

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The three sets of macro extension tubes.

One thing worth noting is that the set from Kenko is the only one of the three that displays the official Micro Four Thirds logo printed on the tubes and in the packaging and manual. This should ensure that the mount dimensions and placement of electrical contacts are within specifications, and the tubes widely compatible with Micro Four Thirds cameras and objectives. The body and lens/camera mounts are made of metal, and the inner surfaces are flat black, giving rise to very weak reflections. The set is rather hefty weighting 116 g. The mounts have very slight rotational play, but almost none along the lens axis.

The cheapest set, the one from PIXCO has a plastic body and metal lens/camera mounts. It is very light weight at 50 g. The inside shows an attempt to reduce reflections by means of a surface with fine ribs similar to those in the Kenko, the the surface is not as matt, giving rise to some diffuse reflections. The mounts have a bit more rotational play than in the Kenko, but no major problem with axial play. The location of electrical contacts is good enough and the rotational play small enough to make the set of tubes fully functional. However, what I dislike is that the metal used in the lens and camera mounts seems to be rather soft, and its surface rough. Mounting or dismounting a lens produces a grinding sound, which quickly results in visible mark on the lens mounts of the tubes. So, it is of rather poor quality as one could expect from its price, but is fully functional (at least under light use).

What could seem like a bargain, the COMIX tubes, very nicely packaged, including a nice small pouch for storage, turned out to be those of worse in use. Looked at casually they seem identical to the Kenko ones. The body of the tubes is plastic, but mounts are made from metal with a nice and smooth finish. Even the location of screws and the shape of the levers used for unlocking the mounted lens are almost the same as in the Kenko. On inspection they are light, weighting 59 g. On looking at the inside, I was surprised to see that the surface is smooth and shinny, just plain black plastic. On use, another unwelcome surprise: there is considerable rotational play together with a very important axial play. Electrical contacts do work in spite of axial play, but axial play as a result of the weight of the attached lens should cause under normal use a misalignment of the focus plane on the sensor (like in a tilt lens or a tilt adaptor). The dimensions of the mount are clearly not within reasonable tolerances and the metal springs way too weak to keep even light weight objectives in the required position and alignment. In other words, a nice looking set of tubes that is in practice non-functional.

Why is a matt black ribbed interior surface important? By changing the objective to sensor distance we project the image from further away. Consequently part of the light hits the inner walls of the tube. Reflections cause flare and can drastically decrease image contrast. Being macro extension tubes just tubes, one could think that as long as the camera and lens remain connected, the same lens using difference tubes should result in images of the same quality. This is not necessarily true, because both misalignment and  internal reflections can deteriorate image quality.

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The three sets of extension tubes, from left to right, Kenko, PIXCO and COMIX. The secondary light source was behind the tubes and slightly above, to avoid artefacts a large source was used: a 27″ computer monitor. The secondary light source used to test for reflections was at a shallow angle trying to simulate possible reflections in actual use.

All illustrations, text and measurements are of my own authorship, and copyrighted.

(c) 2017 Pedro J. Aphalo


 

Focus stacking

The image shown below is a close up of the adaxial  (upper) epidermis of a fallen sycamore (Acer platanoides) leaf. The image is an example of the use of focus stacking. Seventeen images were captured in sequence. After each individual image was captured, focus was slightly shifted. In each individual image only a part of the leaf surface is sharp, by merging the 17 images, retaining only the sharpest portion of each, an image with the full frame in perfect focus was obtained. Obtaining this kind of series of images is called focus bracketing while the image processing yielding the merged image is called focus stacking.

Acer platanoides
Autumn leaf from a sycamore tree (Acer platanoides)

I have produced an animation of the sequence of images at lower resolution. In this case, even though the object photographed is rather shallow, focus stacking still helps. The next two examples are of ‘deeper’ objects for which the advantage of using this method is even more dramatic.

The images of the leaf were captured with an Olympus E-M1 camera mounted on a tripod and tethered through USB to a computer and controlled with the free program Olympus Capture. The merged images and animation were generated with Helicon Focus using RAW images for the workflow. The merged RAW image was edited in Adobe Lightroom and JPEG files at reduced resolution produced for this post. In this example the focus shift between images was done with the objective, the uncertainty of the magnification is small because the object is shallow.

When working at high magnification an alternative approach is to change the distance between the camera and the object using a motorized focusing rail. This approach ensures that the magnification at different depths into the object remains constant. An example of the use of this approach can be seen below. For this final image a stack of 21 images was merged.

Aphids on barrel medic (Medicago truncatula)

I have produced an animation of the stacking process at lower resolution.

The images of the aphids were captured with an Olympus E-M1 camera mounted on a copy stand with a SatckShot motorized rail attached. The merged images and animation were generated with Helicon Focus using RAW images for the workflow. The merged RAW image was edited in Adobe Lightroom and JPEG files at reduced resolution produced for this post. In this example the focus shift between images was done by displacing the camera while keeping the focus setting on the objective unchanged.

The third example is not a macro image, however, photographing a plant from above and obtaining an image with the whole plant and the soil in focus, is difficult without focus stacking.

Barrel medic (Medicago truncatula)

I have produced an animation of the stacking process at lower resolution.

The images of the Medicago truncatula plant were captured with a Nikon D7000 camera mounted on a copy stand with a SatckShot motorized rail atatched. The merged images and animation were generated with Helicon Focus using RAW images for the workflow. The merged RAW image was edited in Adobe Lightroom and JPEG files at reduced resolution produced for this post. In this example the focus shift between images was done by displacing the camera while keeping the focus setting on the objective unchanged.

With good luck and perseverance it is also possible to obtain small series of focus-bracketed images when hand holding the camera by very slowly shifting one’s position forward while taking a series of images at high speed (several frames per second when working at high magnification).

I have here demonstrated focus stacking in macro and close up photography. It is equally useful in micro photography. It is also frequently used in product photography of static objects. In addition it can be used for landscape photography, but image processing may need some manual intervention as frequently some objects like leaves and branches which move are at different positions in the different images being merged.


I have used Helicon Focus, a specialised program for automated focus stacking, image alignment and merging, however, Adobe Photoshop can also be used. A diverse collection of impressive examples are available at the Helicon Focus web site  and in their Flickr group.


Conclusion: When the depth of field is not enough to include the whole object of interest, focus stacking provides a way for producing the desired images. In addition, use of focus stacking and aperture settings allows a more clear transition between in-focus and out-of-focus regions.


All illustrations, text and measurements are of my own authorship, and copyrighted.

(c) 2015-2017 Pedro J. Aphalo