Moths and Ultrasound

[MikeOxon]

Has anyone else noticed a problem when trying to photograph moths with a camera that uses an ultrasonic auto-focus (AF) system? I use a Nkon with AF-S lenses and many Canon lenses use a similar system.

I first noticed the effect when I tried to photograph a Burnet Companion, to show alongside photos of Dingy Skippers. Whereas the Dingy Skippers were not affected, the Burnet Companions always flew the instant I touched the shutter release to activate AF. I tried a few simple experiments,turning AF 'off' and 'on', and found that they responded up to distances of several feet. I eventually got my photos by using manual focus.

Seven Barrows, Lambourn, Berks - June 2008
Nikon D70 with 300mm AF-S, 1/500s@f/9.5 Manual focus

I am guessing that this is a result of the moth's anti-bat defences. I have no idea how other moth species are affected.

Mike

[P.J.Underwood]

I tried photographing a group of dogs this morning and they reacted as soon as I pressed the button.Was it the AF or shutter noise(which was very quiet?)
P.J.U.

[JohnR]

I find that I can't use Canon autofocus with butterflies in the field but I can with moths under a macro lens when taking voucher photos!

[dilettante]

No comment on your theory, but just to clarify that these systems don't use any sort of ultrasonic signal directed at the subject for autofocus. They still use purely optical and electronic means of focusing. The ultrasonic term refers to the ring motors used in the lenses. Which isn't to say that such motors don't inadvertently emit something (maybe just sound?) that disturbs butterflies or moths.

Sorry if I'm stating the obvious!

[MikeOxon]

The ultrasonic term refers to the ring motors used in the lenses

Perfectly correct and I didn't make this clear. I assume that these motors emit an ultrasonic whine as they operate. It was why I was surprised that the moth appeared to detect it at several feet distance. The moth flew at first touch on the shutter button, before the shutter itself fired.

Mike

[Dave McCormick]

I have not had much problem with moths or butterflies really, just the odd Meadow brown or Speckled Wood don't like the sound but I always had it down to the noise of the shutter as soon as I press the button they seem to fly away. Burnet moths (Six-Spot and Narrow Bordered-Five Spot) seem to fly away when I try and photograph them though, Silver Y I have a lot of problems with (ones I find during the day flying around, ones I catch in my traps are easy to photograph). Hawk-Moths I have nightmares photographing. Every humming-bird hawk moth I have ever seen (4) have all darted from my camera when I pressed the button and they disappeared never to be seen again, very frustrating when I don't see them that often. AF could be my problem too.

[55bloke]

I've only just seen this thread, and can confirm that I have often encountered this problem. I use a Canon SX10IS, and had an earlier model prior to this. I found using both that the autofocus seems to tip-off butterflies that I'd succeeded in getting close to, to my presence. It's b****y annoying!! Can't say I've figured out which species are most sensitive to whatever it is that gives the game away!

[MikeOxon]

I wonder if someone with both a bat detector and a camera with ultrasonic focus motor (Canon or Nikon AF-S) could look what sort of 'signature' the motor emits as it operates?

I'd be interested to see the results.

Mike

[JohnR]

I've posted the question in the Canon forum to see if anyone has any ideas. I think that I only experience the problem with zoom lenses on my Canon 7D.

[Mikhail]

I wonder if someone with both a bat detector and a camera with ultrasonic focus motor (Canon or Nikon AF-S) could look what sort of 'signature' the motor emits as it operates?

I'd be interested to see the results.

Mike

I have just carried out a test using my Canon 100mm IS macro on an EOS 60D with my bat detector, and can confirm that the motor produces a great deal of ultrasound over a broad frequency range, but particularly loud between 30 and 40kHz. The test came to a premature end when my bat detector batteries died.

Misha

[MikeOxon]

confirm that the motor produces a great deal of ultrasound over a broad frequency range

Many thanks for doing that test, Misha.

It seems to give some support to my theory that some moths, and perhaps butterflies too, 'hear' the sound from the focus motor and react accordingly!

My Tamron 90mm macro does not use an ultrasonic motor, and appears to be unaffected by this problem, but I cannot use my Nikon AF-S 70-300 zoom with several species - especially the Burnet Companion moth - unless I focus manually.

This may be a problem for many photographers - they're not just suffering from bad luck!!!

Mike

[55bloke]

This is fascinating, and certainly confirms what I've suspected for a long time. It would be really interesting to know which species are the most susceptible.

[JohnR]

I had the following reply from a post in the Canon forum which confirms what has been written here.

Does your lens have USM written on it (or HSM if it's a Sigma)? That stands for Ultra (or Hyper) Sonic Motor. So, yes, your lens does emit ultrasound. Now my ears are old, bent and knackered; but my bat-eared friend, who can hear quite a way into the ultrasound range, tells me that the frequencies she can hear from USM lenses are about the same as those used by the local bats (yes, she really can hear them).

[NickMorgan]

This is really interesting. I ofen have the same issue using my Canon ixus. I had always assumed that the camera used infrared for the autofocus and that was what the butterflies detected. I had never thought about ultrasound.

[legless2007]

what I find interesting, and will have to find out more about, is that the moths seem to take off when they hear the noise. The usual response of a moth to ultrasonic noise in flight is to drop suddenly to evade the predator (you can try this by rattling a bunch of keys when moths are flying). So taking off seems like a strange reaction to perceived "in flight" predator.

I must find out more about this.

Jo

[MikeOxon]

the moths seem to take off when they hear the noise

That is a very good point, Jo, which I had not thought about. As you say, it does not seem to be a 'sensible' reaction in the face of a flying predator! My link with bats was possibly a step too far, as bats emit a distinctive clicking sound. Perhaps it is just that the moths are sensitive to sounds in this frequency range (since it is potentially useful to them) and simply 'jump' at a loud noise. More experiments needed.

Mike

[legless2007]

Being a bit of a geek I've taken some time to look into hearing in moths (One of the joys of being an Open University student is full access to its outstanding online library).

Lots of work has been done on hearing in day flying moths (where predation from bats isn't a problem) and it seems that some species have completely lost hearing, but those species that communicate using ultrasonic sounds socially, for mate selection etc retain their hearing and are more likely to respond to ultrasound.

One study that was very interesting compared Trichodezia albovittata , a silent geometrid with Lycomorpha pholus a sound producing arctiid. Trichodezia albovittata has morphology similar to nocturnal geometrids but didn't react at all to ultrasound so it was suggested that the hearing is vestigial due to complete isolation from bats.Lycomorpha pholus seemed to have a lower sensitivity but it responded with evasive flight action when it was exposed to ultrasound. The suggestion is that while it wouldn't necessarily hear bat sounds it may communicate socially so the ears were still functional for that purpose.

Another study looking at nocturnal moths, which i'm trying to locate again, looked at a species where the female selects the male based on ultrasonic communication, she selects males that produce sounds based on the frequency they emit with those producing sounds less likely to be detected by bats more likely to be selected as its safer for her to 'reveal herself' if the male isn't advertising himself as dinner. There are males that do produce sounds in the bats' preferred range though, which is fascinating as you'd think with their increased susceptibility to predation and disadvantage in mate selection that trait would die out.

Its not completely relevant to the original discussion but i thought it was interesting enough to share, i'm becoming a little too absorbed in this subject while i'm waiting for butterfly weather!

Jo

[MikeOxon]

Fascinating stuff, Jo. Rainy days are always good for studying.

I remember reading somewhere (possibly New Scientist years ago) a theory that some moths send out ultrasound to confuse bats, in much the same way as aircraft use electronic countermeasures (ECM) to deflect radar-guided missiles! Having seen some of the extraordinary relationships between orchids and their pollinators, I am ready to believe that evolution is capable of anything. The truth, however, is much more likely to be that the moths use their ultrasound for communication, as you suggest.

Plenty more scope for study - if we ever see butterflies again, that is

Mike