Lessons from experiments

This post is about post an image that I didn’t manage to get.  So far.       

We’ve put up a number of nest-boxes in the garden and we usually have a couple of them successfully hosting birds each year.  Often blue tits.  Earlier this summer I decided to see if I could photograph the comings and goings to one of the occupied boxes that I was watching as I cleaned my teeth in the mornings.  

It was no real problem to get the adults flying in and out of a nest box mounted about 16’ up in this Scots Pine.  The tree is a bit further than I’d like for ideal photography but I can shoot from my bedroom window across to the tree with a long lens.  Trouble is, the resulting photos of the birds going in and out of the nest box are really not that interesting.  I wanted to do something a little more and decided to have a crack at getting the birds fully in flight approaching or leaving the nest.  How hard could that be?  After all, the parents were regularly visiting the nest every few minutes and tended to follow a regular path.  So I decided to aim to try and photo the birds side lit by the morning light against a fairly dark foliage background that was in shade.  

How hard?  Well as it happens, pretty difficult.  Over a period of a week I took nearly 2000 photos.  About ten had barely usable images; none were really good.  Of that bunch the one below was about the best.  Given that this was about the lowest hit rate I’ve ever had, I though it would be useful to reflect on this and share the experience.

OK, let’s have a look at this.  On the positive side:

- It’s centred in the frame (well, it is after a little cropping) and the bluetit has some of the quality of subject lighting I was aiming for. 

- The motion is frozen using 1/5000 sec shutter.

- The underlying quality of the image is pretty amazing given that the ISO is 3200.   

On the negative:

- It’s out of focus (too close focussed by about 2”).  That’s enough to matter; so it’s basically unusable.

- It’s too backlit, there is insufficient main (key) subject lighting and no eye catchlight, which makes it all a bit flat.  The sun never would come round enough to light this position from the front. (Many birds seem to favour north’ish facing nest boxes in shade - I guess they try to avoid cooking the chicks in a sunlit box).  

- It’s not the most interesting image with the wings partly closed.  I had a few better ones of wings spread but those were embarrassingly out of focus, with movement blur (i.e. lower shutter speeds) or only partly in frame.  

There is some useful stuff to learn here:

- Flightpath: I thought the parent birds followed regular flightpaths.  Well they did but here they were not exact, there were several of them and they would vary these over a period of time.  So I just had to be patient until they were flying in sequence on my chosen path.  More unfortunate was that they shifted on this flightpath particular path a bit vertically (i.e. out of centre frame) so I often missed the path or got lots of bits of birds at top or bottom of frame.  They also shifted a bit horizontally so that they were out of focus - as in the image here.  

- Utter speed of these bluetits - they are fast*.  My camera fires at six fps.  Most images where I’d got on the flightpath, I’d have one frame of a sequence with a bird in it but I never had two sequential frames with birds in.  At first I though that using a 6 fps rather than 8, 10 or 12fps camera was the issue (excuse for a new pro body - where is that Nikon D400???).  In practice I don’t think this is so, I did a bit of maths I don’t think it would and have made that big a difference.  I’d really have needed not twice but three times (i.e. 18 plus fps**) or much more (I’m thinking 30 fps) to be confident that a bird would certainly and regularly end up centre frame if I nailed the flightpath and focus.  DSLRs cannot do this at present but some mirrorless cameras can.  

- Flightpath and speed #2.  The combination of the above two problems meant it was near impossible spotting incoming birds and to release the shutter.  By the time I knew they were incoming (and I wasn’t looking through the viewfinder at all - it was all set up on a tripod) I’d missed the chance; essentially that means I had about 1/4 to 1/2 second warning.  All the shots I actually captured a bird on were outgoing from the nest where I could see the parent emerge about 2 feet to the right of the framed area. (Hence the photo has the bird carrying a dropping rather than a juicy caterpillar!)  I basically had to release the shutter just as the bird was emerging from the nest box hole.  Even then, the bird could pause or dive out at indeterminate rates so that I could never judge if it would end up being framed by one of the sequence of shots.  

- Not enough light.  The D7200 is good enough to be able to get very usable photos at ISO 3200 but I really like to use a maximum of 800 - 1600. Ideally 400.  Nevertheless, it’s still not sensitive enough because I needed a shutter speed of about 1/4000 to freeze the action and that meant an aperture of 5.6.  The lens is easily good enough to be used wide open at 5.6 but here the depth of field is way to narrow given those flightpath variations. So, I simply need more light - that’s a problem in the UK.  Light is in surprisingly short supply even on a bright summer day.  

So, my thoughts on this:   

-  Let’s start with the lens and working distance.  I’m pretty happy with the area framed.  (The shown image is cropped from the original by about 25%).  It’s small enough to get a decent size image of the flying bird but big enough to allow some framing error as the bird flies through - it’s a compromise decision.  However, it’s obvious to me that a long telephoto and big f-stop just gives too little depth of field to work with.  This job needs a much shorter lens and a much closer working distance.  I’d probably be looking at 50mm, perhaps 100mm on my crop frame camera.  

- And a much higher f-stop.  Let’s say between f/11 and f/16 to give a better depth of field.  That should still leave the background somewhat out of focus - it’s a long way back.

- And a lower ISO setting.  Max of 800 but I’d prefer 400.  

With this sorted out I now only have one issue.  Light.  I’ve effectively cut down on light coming to the sensor by 5-6 stops with the above steps.  In short, using available light, the picture will now be almost completely black.  

- This means having to use flash to illuminate and freeze the bird.  This is a massive departure.  It will need several synced and gel corrected flashguns (at least two in front and one behind to light the bird and get a sufficiently short duration.  There is a further complication.  I’ll need to find a different time of day to take the shot.  This is because I need to reverse the illumination.  I need the background illuminated by some natural light so that it gives an image when using a 1/250 shutter or less (the camera’s flash max sync speed) and I need the bird in the foreground unlit so I don’t get a blurred streak and I can freeze it with the very short flash pulse.  

Basically, to get this photo is going to take a completely different technique to the one I was using.  It’s one that I’m not that practised with and is even harder to set up correctly (not to mention this nest box is 15’ above the ground and I can’t move a 100’ tree closer to my window).  But I know can look fantastic when done well - even with a bluetit!  Roll on next spring.  Starting point will be to remount the nest boxes this autumn to a place I can safely get a camera and flash rig to.   

Sometimes you can figure out how to do something by looking at  why what you’re trying is not working.  


* How fast? Well, I estimated from the photos that they are flying at about 3.5 m/s (i.e. about 15 kph or 10mph).  That doesn’t sound too bad except that the area framed by the camera is only about 30-35cm wide.  They can get through that in 1/10 sec.  So I had a number of complete misses with preceding and following frames having birds too close to the frame edge.  

** A 10fps camera would give assurance of getting a bird somewhere in frame but a lot would be cropped or too near edges.  This is pretty much what I had anyway with a few missed thrown in.   20fps (hence the 18fps min estimate to make a real difference) would mean one at edge of one frame would be more or less centred on the next one.  30fps would pretty much ensure getting a bird in the middle half of the frame if its aligned and focussed on the flightpath.