My MT-24EX flash diffuser

When I purchased my insect macrophotography rig two summers ago, I already knew that one of the biggest challenges I would face (besides a steep learning curve) was lighting.  While it is possible to do insect macrophotography using only natural light, this generally requires the use of a tripod and reflector for all but the largest of insects.  Unfortunately, such devices aren’t very practical for field photographs of the tiger beetles that I have come to enjoy stalking (and I already have enough to carry as it is without adding such incumbrances).  Supplemental flash lighting is a more attractive alternative for me – not only does it minimize the amount of equipment I must carry, but the high shutter speeds and small apertures it allows are perfect for ‘freezing’ subjects prone to quick movements while maintaining good depth-of-field. There are many flash units to choose from, but I went with the Canon MT-24EX Macro Twin Lite Flash for its dual light sources (eliminating the “flatness” of a traditional ring flash) and lightweight, front-of-lens mounted bracket (no need for heavy bracket extenders).  Combined with Canon’s 100mm f/2.8 (up to 1X magnification) or MP-E 65mm (1-5X magnification) macro lens, this flash unit has become quite popular in recent years for insect macrophotography. 

The problem with flash, of course, is the harsh, unnatural light that it produces.  With natural lighting, illumination comes from all directions, while with flash it is essentially unidirectional.  This is especially problematic with beetles, many of which have a smooth, shiny integument that reflects the flash to produce strong specular highlights.  Diffusion and maximizing the apparent size of the light source are key to achieving good results with flash units, and a variety of diffusers are commonly used to achieve this. Unfortunately, the small size of the MT-24EX flash heads and their placement at the front of the lens creates some unique challenges for diffusing their light.  The only commercially available diffusers for the MT-24EX (that I’m aware of) are the Stofen OM-24XSET, which are translucent plastic caps that fit over the unit heads.  I used these during my first season of photography, and while better than nothing they still leave much to be desired.  The problem is that they do nothing to increase the apparent size of the light source, and it is an even worse problem with the 100mm lens than the 65mm because of its longer working distance.  Much better results have been achieved by Kurt (Up Close with Nature) with his concave foam diffuser and Alex (Myrmecos) with his tracing paper diffuser.  Unfortunately, these diffusers only work with short focal length lenses such as the 65mm, while it is the 100mm lens that I use most often for tiger beetles (1.0-1.5X range).  For most of this past season, I tried a Gary Fong Puffer + Sto-Fen combo diffuser based on an idea by Dalantech, but again that setup seemed only slightly better than Sto-Fens alone with the 100mm.  As the season progressed, I continued to mull over various contraptions and ideas to extend the flash heads out in front of the lens to increase apparent light size.  Most of those ideas were expensive and bulky, but at the end of the season I came up with an idea that seemed like it might work and went with it.  The following photographs are the first iteration of that idea.

Canon MT-24EX flash and 100mm macro lens with DIY oversized concave diffuser.

The diffuser is a larger version of Kurt’s do-it-yourself (DIY) concave diffuser.  It uses thick polypropylene foam (used as padding in cardboard shipping boxes) that is sturdy enough to hold its shape but flexible enough to curl back and over the top of the flash heads, essentially forming a large “soft box” in front of both flash heads.

Diffuser is ultralight and lays almost flat when not installed - easily carried in camera backpack.

I cut the bottom inch off of a a 1,000-mL polypropylene beaker (the prototype used a 500-mL beaker, but that was too small).  I then cut the center out of the beaker bottom so that the hole size matched the lens opening of the flash head bracket, and then cut the beaker bottom in half.  This forms a sturdy but translucent, semi-circular frame to hold the polypropylene foam against the flash head bracket on the front of the lens.  The piece of foam measures 21″ (front) x 7″ (back) x 9″ (front to back) and is attached to the polypropylene frame using hot glue.

Flash heads extended forward w/ Kaiser shoes. Thin polypropylene foam layer taped over flash head.

I also used Kaiser shoes to extend the flash heads a little further forward in front of the lens, and I taped a small piece of thin polypropylene foam over front of each flash head to provide some initial diffusion.  This helps to increase the apparent light size by reducing the distance between the flash heads and the subject.  I snugged the pivot screw on the Kaiser shoes just enough to hold the flash head in place but still allow me to adjust their aim.

Diffuser attaches to front of flash bracket using Velcro strips.

The diffuser frame is attached to the front of the flash head bracket using pieces of Velcro strips.  It’s not a tight, sturdy connection, but so far I have not had any problems with the diffuser falling off.  This system allows me to quickly and easily switch out similar diffusers of different sizes (I have a smaller one that I made for the 65mm lens).

Diffuser attached to flash bracket.

Diffuser is curled back and corners attached to back of flash heads using Velcro.

Pieces of Velcro strip are also attached the corners of the diffuser and the back of the flash heads to hold the diffuser foam in position after attaching the bracket to the flash head bracket.

Diffuser in position and ready for use.

Diffuser remains properly positioned regardless of flash head position or lens changes.

I have since added additional Velcro strips along the front edge of the foam to allow it to be pulled back closer to the flash heads, depending on the distance to subject. 

One nice thing about this diffuser is that it does also work with the 65mm lens as long as there is nothing to get in the way of the diffuser.  It is simply a matter of angling the flash heads back closer to the lens and adjusting their aim according to the subject distance, then pulling the foam layer back closer toward them.  Or, just swap out with a smaller version.  When detached, the diffuser can be folded to lay flat in the backpack.

Of course, the proof is in the pudding, and none of this means anything if it doesn’t actually do the job.  I’m now immersed in the depths of a Midwestern winter, so I haven’t yet had a chance to test the diffuser in the field.  I have, however, done a fair amount of testing here in the laboratory using both live and dead insects and have been quite pleased with the results so far.  Those photographs can be seen in the following posts.  This coming season I’ll put it to the test in the field to see if it actually has the usability and durability that I have hoping for.

Copyright © Ted C. MacRae 2010

20 thoughts on “My MT-24EX flash diffuser

  1. think the cup diffuser should work event with longer focal length, but it still work best for shorter focal length ..

    thanks for Stephen [] for his great effort to come out with both concave and cup diffuser …

    • Stephen’s concave diffuser looks different from Kurt’s. Is that what you use?

      I like his comparison shots between the concave diffuser, Sto-Fen diffusers, and bare flash heads – the difference is dramatic.

  2. Good stuff! I’ve been trying milky plastic to reduce the flash blowout on some of my IR camera traps, but am definitely gonna have to try some of this poly foam. Could be just what the photographer ordered.

  3. An elegant solution. I’m just concerned that the open-back of the diffuser will result in a loss of light intensity, which may lead to some problems with freezing subject movement. Besides, the flash blow-back may singe your eye-brows…

    Can’t you experiment by letting some of your captive tiger beetles loose in your living room and then photographing them? This will allow you to give us an up-date on the effectiveness sooner.


    • Flash blowback should be no worse with this than with the concave or tracing paper diffusers which are also open back designs. Camera aperature and shutter speed are set manually with the flash set on E-TTL, so if anything short battery life might be more of a problem (depending on the opacity of the foam used) than subject movement. I do cinch the foam up tighter now than is shown in the photos – there are additional Velcro pieces along the top edge that allow the foam to be curled further back over the flash heads. I did this to create ~1 cm spacing between the foam and the flash heads, but a secondary result is that the back isn’t so open either – perhaps this will cut down on light loss a bit also.

      Action shots will have to wait until spring – the tiger beetles are fast asleep!

  4. Ted, thanks so much for posting this. I have just bought a MT-24EX and spent a long time searching for dyi diffusers to use with the 100mm lens, when I finally came across this post of yours. Excelent! I built mine today, with minor adaptations, and it worked like a charm.

    What I did different:

    1) Instead of the beaker, I used the transparent lid from those bulk CD packages (similar to this one:

    2) I did not cut this piece exactly in half, but left a little more of the plastic towards teh bottom. Thus, the adapter fits more tightly around the flash’s part that goes over the lens and needs no velcro strips to keep it in place.

    3) I took apart two old scratched UV filters, one 58mm and another 77mm, and glued their mounts together with the threads facing outwards. I then screwed the 58mm part on the flash’s thread and this serves as an extra lock to keep the plastic adapter in place (see this drawing, imagine the larger blue ring as the 77mm filter and the larger green ring as the 58mm filter, both without the glass parts).

    4) I have not used any velcro yet, I am getting along with masking tape so far.

    Thanks again, cheers from Brazil 🙂

    • Sounds intriguing, but I can’t figure out how the two filter rings work to hold the diffuser in place. For my part, I’m less concerned about a secure attachment for the diffuser (and it has never fallen off once in place) than convenience in switching between the 100mm and 65mm lenses (each with their own diffuser setup). Anyway, thanks for the comments.
      Um abraço!

  5. Thank you for posting this. I am just becoming interested in macro photography and I just recently bought the MT-24EX for use with the 65mm lens. I recently used a Puffer diffuser on my Canon T3i’s popup flash just to start exploring the difference between undiffused and diffused flash photos, and I think the Puffer does better results with flash photos. I’m going to move on to the MT-24EX and experimenting with your diffuser setup and the one by John Kimbler. I’m really new to macro photography so I’m sure it will take me a couple years to become good at it. It helps to start with the same flash techiques used by pros like yourself.

    • Hi Bob – thanks for your comment. I am by no means a pro – just an entomologist with a camera and 2 years of experimentation under my belt. My diffuser is a synthesis of ideas I’ve gotten from other photographers who always seem to produce great photos – Alex Wild and Kurt (orionmystery) are the two I follow most closely, but there are others as well. It works great with the 100mm macro but not so well with the 65mm – for the latter I go back and forth between a small concave diffuser with double-layered polypropylene and a Puffer+Sto-Fen combination. I’m currently working on a setup that actually combines those two types of diffusers, but in a way that minimizes light loss so I can get the fastest possible flash pulse time (resulting in maximum sharpness). I’ll post results once I’ve tested it out.

      Good luck with your efforts!

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