I've been trying to take pictures of spiders and insects at night, with a working distance of 8-10cm, with the actual photo being lit by flash. In order to (manually) focus, I have a single "warm white" LED stuck on the lens, which provides the minimal amount of light needed. Some of these critters are quite timid, though (Latrodectus in particular), so I'm wondering if there are best practices for making a focus-assist light for this purpose, considering things like:

  • Wavelength(s) that would be more/less alarming to bugs
  • Small point source vs. larger, lower intensity source
  • Duration - leave on while moving closer vs. wait until the last minute

Are there generally agreed-upon approaches to this?

EDIT: I should also mention that, in my case, I'm not using an optical viewfinder, which means that there's potential for using wavelengths that wouldn't normally be visually useful, as long as they register on the camera sensor well enough to produce useful output in the EVF.

  • \$\begingroup\$ I'd also be interested to hear the answer to this. In the daytime arachnids seem quite tolerant of nearby light and movement, but nocturnally they seem quite alarmed, which is pretty understandable. \$\endgroup\$
    – HamishKL
    Commented Mar 11, 2016 at 6:16
  • \$\begingroup\$ Stumbled across this and wanted to ask: would the AF Assist beam using something like the Canon ST-E2 work to help obtain focus or is a constant, broader amount of light required? \$\endgroup\$
    – OnBreak.
    Commented Jan 25, 2018 at 16:26
  • \$\begingroup\$ @Corey Not much info about the wavelength of the beam on that thing, but I'm guessing somewhere in the near-IR region. The intensity in that range needed to register on the sensor in a helpful way probably depends on the camera... which makes me realize that I didn't specify that I'm using an EVF/LCD in the question... I'll fix that. \$\endgroup\$ Commented Jan 25, 2018 at 20:57

1 Answer 1


I certainly won't pretend to be an expert in this area, however a few thoughts came to mind when I was considering why you have these issues.

1] I found this paper on the "Spectral Sensitivities of Wolf Spider Eyes" - there may be some interesting information in there that can be applied to other arachnids. For example, in one experiment it was shown that Wolf Spiders more frequently chose to rest in boxes bathed under red light. This was early on in the paper though and may not be accepted as scientific fact, so further reading would be advised! http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2225900/pdf/1.pdf

2] If we generally find that the arachnids and insects that you're shooting are averse to blasts of light during the night, can we further dim your focus-assist light with a piece of partially translucent tape?

3] I'm thinking about moonlight and assuming that most insects and arachnids aren't noticeably afraid of it. My guess is that the constant presence helps lower their sensitivity to it. There may be an analogy to be found in how you treat your duration as well as the general colour temperature of moonlight (around 4100 - 4150K, from what I just read).

I think the answer must lie somewhere in the fact that your auto-assist light is jarring to their senses in that it both comes on quickly and is relatively intense (read: bright) for the area they are hanging around in when you are shooting. I would expect someone walking with a flashlight swinging would cause a similar reaction were the beam to cross their eyes. It can be difficult to get any type of living creature to betray their natural survival instincts and reactions without conditioning, but some of these suggestions may help you ease or (in a perfect world) eliminate some of that external stimulus you are introducing.

(Again, I apologize that I'm not necessarily getting to the root of your question which is around best-practices... I'm not qualified to answer that! I simply noticed that your question was unanswered and wanted to give it a bit of thought.)

  • \$\begingroup\$ These are all points worth mentioning, and pretty much what I'm basing my current approach on, short of limiting the wavelengths of the focus light to the extreme low end of the visible spectrum. I don't enjoy trying to manually focus with pure red light, but maybe a combination of red and a smaller amount of "warm white" could be worth trying... \$\endgroup\$ Commented Mar 29, 2016 at 7:14

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