Wednesday, July 18, 2018

Variable damselfly (Coenagrion pulchellum)


The Variable Damselfly is an uncommon species which occurs in widely scattered colonies throughout Britain but it can be abundant where it occurs. This picture was taken at Baston Fen in South Lincolnshire - a well known and good site for the species - on 3 July 2018.

Variable Damselfly male (Canon 80D, 100mm macro, F11, 1/250s, ISO 400)
I have seen the species at a few other sites in the region around Peterborough, but most consist and abundant at Baston Fen. In general, I would say it looks a bit daintier and darker than the very common Azure Damselfly (C. puella) with which it tends to occur. Males are fairly easily separated: the mark on the 2nd abdominal segment is typically shaped like a wineglass in C. pulchellum (but like a tumbler in C. puella - i.e. "U" shaped and not connected to the basal black band of the segment); the antihumeral stripes (the pale stripes running longitudinal down the thorax) are interrupted in C. pulchellum (broader and continuous in C. puella) and the 9th abdominal segment is mostly black with only a narrow, basal blue stripe (9th segment half or more blue in C. puella). However these features are quite variable (hence the name - Variable Damselfly!) especially the shape of the mark on the 2nd abdominal segment of the male.

Comparison

Tuesday, July 17, 2018

High ISO, available light insect shots

Conditions in the garden this afternoon were warm but overcast. I was taking some available light pictures of insects coming to Marjoram flowers (Oreganum vulgare). I was trying to maintain a fairly high shutter speed (1/400 - 1/500) because I was hand holding the camera with a 100mm macro lens and at an aperture of F6.3 or F8. To achieve this, I had to let the ISO go quite high.

Gatekeeper on Marjoram (100mm Macro on Canon 80D, 1/500s, F6.3, ISO 4000)
Here is an example of a shot of a Gatekeeper taken at ISO 4000 (1/500s, F6.3). This is a somewhat cropped version (3675 x 3090) of the RAW file (Canon's .CR2 file format - 6000 x 4000) as rendered into GIMP 2.10.2 by the default settings of nufraw. Whilst noise is evident on close examination, I think the image is quite usable and is pretty impressive for ISO 4000.

Friday, July 13, 2018

Digitising old slides using an Ohnar zoom slide duplicator

I have loads of old 35mm slides, mostly from my days of film photography using the Olympus OM2 system, but also some even older. There are some good wildlife photographs here as well as stuff of historical, family and personal significance. Over the years, I have used a number of means of capturing these including a CanoScan III film scanner, a "Compact Digital Film Scanner" from Jessop's and a 35mm holder for a flatbed scanner. None of these have been particularly satisfactory and none of them work with my current hardware.

Be that as it may, there are times when I want to recover images from my old slide collections. So I have recently tried yet another approach: I have an old device - an "Ohnar Zoom Slide Duplicator" by Bush & Meissner Ltd.

I don't remember when I bought this, but probably in the 1980s. It is designed to fit on a 35mm SLR camera using a T2 mount - and mine has an Olympus T2 mount, so clearly dates from my Olympus OM2 days. The 35mm negative or slide goes in the holder (at the right hand end in the photo above) and the whole device is pointed at some bright light source (e.g. an electronic flash). The holder has a translucent white diffuser built in. The holder allows the slide to be moved from side to side and can be moved up and down and rotated. The device also has a built in 1 - 2.5x zoom. So it is possible to photograph the whole slide or any portion of it.

A problem is that this device was designed for use on a 35mm SLR. I expect that it would deliver an image of the whole 35mm frame when on a full frame DSLR body but, mounted on a crop sensor DSLR such as my Canon 80D, the minimum magnification is effectively 1.6x (the body's crop factor) and it is not possible for me to capture the whole frame.

In practice, it mounted easily enough using a Canon T2 mount. I find that a good exposure is only achieved by trial and error, which when using a DSLR, is not a problem. I simply inserted a slide, pointed one of my Yongnuo 560 III flash guns at the diffuser, put everything on manual, set the ISO to 100, shutter speed to 1./250 (the flash sync speed of this body) and then took a series of trial shots, adjusting the flash power each time until I got an acceptable histogram. I find that the density of slides varies quite a bit, so the flash power needed for a good exposure varies by at least a stop either way between different slides, but typically around 1/16th power.

The main problem I have encountered with all of these devices (and this is no exception!) is that they tend to significantly increase the contrast of the image. Even using the best method and exposure, the resolution and dynamic range of 35mm colour slides are not actually very good compared to what we have become accustomed to with modern digital images, so the resulting images are rather disappointing whatever the capture device.

Sunday, July 08, 2018

Courtship of Poecilobothrus nobilitatus (Dolichopodidae)

The Dolichopodid fly Poecilobothrus nobilitatus is a common species which can be abundant in the right conditions. It likes the shallow, muddy edges of pools and streams and even muddy puddles in dappled shade. Dolichopodids (long legged flies) have extravagant external male genitalia, they are typically colourful with metallic green and blue colours and iridescent eyes and the legs of males are often ornamented. In this particular species, the males, which are about 5-6 mm long, have the wings blackened over the outer half and milky white tips.

Poecilobothrus nobilitatus male
 Females are usually a bit duller and lack ornamentation. In this species, the wings are not coloured.

Poecilobothrus nobilitatus female
During courtship, Dolichopodid males semaphore with there ornamented legs, or in this case, their coloured wings. In this species, courtship takes place on the surface of wet mud or water. At the start of a courtship bout, the male approaches a female and and waves its wings in short bursts when a few centimeters away, it then jumps over the female and repeats from the other side. If the female shows any interest, the second phase involves the male hovering in a short, wavering flight, in front of and to either side of the female.

There is a small pond in my garden in the shade of a Scot's Pine tree. This obviously provides the right conditions for P. nobilitatus and large numbers are present at the moment - and courting furiously.

Poecilobothrus on the pond - these are mostly females
 I wanted to try and photograph this courtship behaviour, but I knew it would be difficult. The flies are small and, to get a good image, would need a reproduction ratio close to 1:1, which means getting quite close. At these short distances, the rapid movements involved would make it very difficult to capture. In these circumstances, electronic flash provides sufficient illumination to achieve the small apertures necessary for the depth of field and also the short duration of the flash has a chance of freezing the movements.

Photos were taken using a 100mm macro lens at around f16. The main illumination was from Canon MT-24 dual flash with a Yongnuo 560 III providing background illumination. A Yongnuo RF605C radio unit was used to trigger the background flash. The Canon 80D camera was set in manual mode and the flash power set as low as possible - around 1/8 or 1/16 power. This reduces the flash duration allowing for high speed imaging. The maximum flash sync speed for this camera is 1/250th sec, so the shutter speed was set to 1/250 or 1/200th. At 100 ISO, f16 and 1/250 sec, the available light level would lead to underexposure of about 4-5 stops, so the exposure is totally due to the flash, therefore the camera's shutter speed is irrelevant (providing the shutter is fully open when the flash fires).


Male (right) approaching a female (left) wing waving

Male wing waving

Male leaping over a female

Wednesday, April 25, 2018

Flies in flight


The hoverfly Epistrophe eligans male in flight (F11, 1/1000s, ISO 1600, 100mm Macro)
Taking pictures of flies in flight is rather challenging. Hoverflies are a little easier than some others because they hover in one place for a few seconds at a time. Males are territorial and tend to repeatedly return to a similar air space. Epistrophe eligans is a common, early spring species in which the males lek. A group of males tends to form a loose cluster around the end of a branch and jostle for position. These were taken at a reproduction ratio between 1:1 and 1:2 so, even with a 100mm macro, it is still necessary to get pretty close to the fly to focus. Auto-focus is of little use in this situation. It is better to switch to manual focus and focus by rocking backwards and forwards. A small aperture is necessary to get enough depth of field. These wee taken at F11. A fast shutter speed is also necessary to stop motion of both the fly and the camera. Even in bright sunshine, a high ISO will be necessary. So the camera (Canon 80D) was set in manual mode (M) with 1/1000s and F11 dialled in and the ISO set to "Auto". I used high speed shooting mode to take brief bursts of shots when the fly came into focus through the viewfinder.

The Beefly, Bombylius major, is another common early spring species that hovers, although not as persistently as a hoverfly. The following shot was taken using similar techniques.

Bombylius major (F8, 1/1000s, ISO 2500, 100mm macro)

Friday, April 20, 2018

Kowa TSN-PA8 for DSLR digiscoping

I have previously written about digiscoping using a 50mm lens on the DSLR camera body. However, an alternative is to mount the camera body directly on the telescope, using the telescope's optics as the lens system. My scope is a Kowa TSN-823M, which is a fairly old scope that is no longer in production. Kowa have offered an adapter of this type (TSN-PA7) for their current 'scopes, but their adapter for the legacy range of 'scopes - including mine, is a bit more recent. This is the TSN-PA8.
TSN-PA8 mounted on the 'scope eyepiece with Canon 60D fitted.
The adapter is in two parts: a collar that screws on to the accessory mounting thread around the eyepiece aperture of the telescope and a tube which fits over the eyepiece, slips onto the collar and is held in place by a pair of screws. The camera is mounted using a T2 mount which screws on to the outer end of this tube.
from left to right, telescope with the eyepiece removed, collar, tube and the Canon T2 mount at the bottom
The outer end of the tube is closed by a piece of coated, optical glass which covers the eyepiece and prevents any muck, dust or moisture which might be on it from getting into the mirror box of the camera and hence on to the sensor. This was added to the PA7 adapter about 2015 (and it became the PA7A) but, as far as I know, has always been a feature of the PA8.
The assembled mount in position over the eyepiece. Note the optical glass covering the end of the eyepiece to prevent anything getting into the mirror box of the camera.
The cut-outs on the side of the tube allow access to the eyepiece's zoom ring so that you can still operate the zoom whilst the camera and adapter are in place.
Ports in the side of the tube allow access to the eyepiece zoom ring.
Overall, it is a well made and well designed, if rather expensive, piece of kit and does the job of mounting a DSLR on the 'scope very well. It is fairly quick and easy to fit. Swap the camera lens for the adapter, slip it over the eyepiece and do up the two securing screws and you are ready to go. The camera can be oriented either horizontally, in landscape mode or vertically, in portrait mode, just by loosening the screws and twisting and, unlike my previous DSLR digiscoping setups, the zoom function is accessible whilst the camera is mounted.

In use, the usual problems of digiscoping remain. Firstly, the field of view is very small, so finding your target is often quite difficult and it can be rather tricky to keep a moving subject in view. Secondly, the magnification is considerable and the whole setup rather cumbersome, so camera shake is a big problem. It needs a pretty fast shutter speed and you really want to trigger the shutter without touching the shutter button. I usually use either the 2 second delay timer or the Canon RS-60E3 remote shutter release. I find one difference with my previous digiscoping attempts is that I don't get any vignetting, even at the lowest zoom magnification setting.

According to info on the Kowa web site, at minimum magnification this set up is roughly equivalent to a 1200mm, F12 lens on a 35mm camera and a maximum zoom a 2900mm lens at F34. On an APS-C sensor camera like mine, you need to multiply these focal lengths by 1.6x to appreciate the sort of reach you get.

Exposure Settings

At these very small apertures, even on a bright day, a pretty high ISO is needed to get a decent shutter speed. I usually try to stick to 1/1000s to counter subject movement and camera shake, so the ISO rarely goes below 1600. I put the camera in manual mode (M), set the shutter speed to 1/1000s and select Auto ISO. I generally find I have to dial in between minus one and minus one and two third stops compensation to get a correct exposure, otherwise the metering system seems to over-expose everything. I am not sure why this should be so.

Focusing is, of course, manual and done with the telescopes focus knob. If the subject is fairly static, live view is very useful for adjusting the focus accurately. I use as much magnification as I can get on live view to critically set the focus. Otherwise, make sure that the dioptre setting on the viewfinder is properly adjusted for your eyes before you start and focus as best you can visually, through the viewfinder. You don't get a lot of depth of field, so I generally take a series of shots, adjusting the focus each time - unless I have been able to set it up accurately on a static subject using live view.

Results

These examples are derived from straight RAW shots taken using my Canon 80D on the setup described, at minimum zoom unless otherwise stated.
Gadwall female, 1/1000s, ISO 2000, -1⅓ exposure compensation

Great Spotted Woodpecker on feeder, 1/1000s, ISO 6400, -1⅓ exposure compensation
These two shots of a coot were taken seconds apart, the first at minimum zoom and the second at maximum.
Coot at minimum zoom, , 1/1000s, ISO 1600, -1⅓ exposure compensation
same Coot at maximum zoom, , 1/1000s, ISO 5000, -1⅓ exposure compensation
I find that shots taken at higher zoom levels are always rather soft. I think this is because diffraction becomes a very significant issue at such tiny apertures.

This shot of a  Heron catching a fish illustrates the problems of capturing action with such a cumbersome setup and without the benefits of auto-focus. Here, I haven't got the focus quite right - I think the plane of maximum sharpness is just in front of the bird and, despite the fast shutter speed,  camera movement is obvious (I think I jabbed at the shutter button with my finger to try and capture the moment!).
Heron catching a fish, 1/1000s, ISO 2000, -1 stops exposure compensation

Thursday, April 19, 2018

Long term review of Manfrotto 701RC2 fluid video tripod head

I bought my 701RC2 on 8th Feb 2006 for £83.94. A quick web search shows that, whilst it is no longer listed on the Manfrotto web site and is, therefore, presumably no longer in production, there are still sites offering it for sale new (and at prices less that I paid for it 12 years ago).
Manfrotto 701RC2
I have used it both for my birdwatching telescope and for photography continuously and it does the job well. The movement is smooth, it locks into place easily and tightening the pan and tilt screws do not alter the 'scopes position appreciably. It is rated for 4kg, so it has no problem with either my 'scope or camera with a long lens.

One of the features I like is the built in spirit level. Whilst it has obvious benefits for photography, I also find it quite useful when birdwatching. If I am sea watching or at somewhere like a large reservoir, I like to level up the tripod so that I can pan the 'scope round in a wide arc without having to constantly readjust the tilt. Having a spirit level built into the base of the tripod head is therefore, very handy.

Spirit level
Another feature which I have more mixed feelings about is the sliding top plate. This allows the quick release plate to be moved backwards and forwards by +/- 20 mm. You loosen off a screw and the whole plate slides backwards and forwards.

Scale for the sliding quick release plate.
In theory, this is a nice idea. It allows you to balance the head nicely for different gear so that the tilt mechanism stays where you put it without having to tighten it up hard. In practice, it is not so good. Firstly, the travel is not sufficient to properly balance the gear I normally use. My telescope (Kowa 823) tends to be a bit back heavy - so it will tend to tip backwards unless the tilt screw is well tightened. So, I slide the plate all the way forwards - which is nearly enough to balance it but not quite! In contrast, my Canon 80D with the 100-400mm lens at full zoom is decidedly front heavy and the plate won't slide back nearly far enough to counter this. Secondly, it is impossible to tighten up the locking mechanism on the sliding plate sufficiently to stop it sliding. Tighten it up as much as you can and it will still moves relatively easily. The reason is easy to see: the tightening mechanism consists of a little rectangular plate which is pressed against the side rail of the sliding plate by tightening the screw. But the area of contact is only 20mm long and it is metal on metal, so not much friction.

Tightening mechanism: top - the screw removed, bottom - the plate and screw.

This can get quite annoying since, I have it set up as best I can for whatever gear I am using, but as soon as you carry it about for a bit, the plate slides to one end or the other and isn't in the right place for the next time you stop.

It has been a fairly robust piece of kit and is still in good, functioning condition after 12 years, if with a bit of chipped paint here and there. Spares are available from the Manfrotto spares web site and I have had to avail myself on a couple of occasions. I managed to lose the long handle on my way back from one trip abroad (it was disassembled for carriage) and I managed to break the head off the pan tightening screw on another occasion. In both cases I got the necessary parts with no problem, but they are rather pricey!

All in all, it has been a very good tripod head and I continue to use it. The one thing I would change is the sliding quick release mount. It needs the locking mechanism modifying so that it locks in place positively and, ideally, needs a bit more travel.