USING THE MT-24EX ON ANY NON-58mm LENS

As you might have read on the main page (or the archives, depending on when you are reading this), here I will explain what I did to adapt the MT-24EX twin macrolite flash for all lenses with a filter size other than 58mm. In fact, this will allow the MT-24EX to be used with any lense with a filter screw.
Here's what you'll need:

  • 1 Canon macrolite adapter 72C
  • any kind of filter or screw guide for the lens you are planning to use
  • cyanoacrylic glue
  • epoxy putty
  • assorted metal files
  • sanding paper
  • black matt paint
  • matt transparent paint

Here's a little rundown on how the MT-24EX works: the main unit is attached to the camera hotshoe just like any other Canon Speedlite and the two lamps are attached to a frontal support unit. This frontal unit does not use the filter screw guide for support (probably due to its weight), but rather uses a snap-on mechanism to attach itself outside the lens filter, in the same way as lens hoods do. Without any adapter, the frontal unit of the MT-24EX can be used only with Canon lenses with a filter size of 58mm, like the MP-E, the 100mm macro, the 50mm macro, the EF-S 60mm macro or any genuine Canon lens with a 58mm filter, like the 18-55mm kit lens(*); as Canon has a fourth macro lens, the 180mm L with a filter size of 72mm, they thought to develop the 72C adaptor to allow usage of the MT-24EX with this lens. This adapter is nothing more that a outer 58mm guide attached to a 72mm screw filter.

(*) Yes, the MT-24EX ring can snap on the 18-55mm kit lens. The first time I was quite surprised too, but it made sense: Canon engineers would only need to design a single external guide ring for any kind of lens hood or equipment like the MT-24EX. However, due to the 18-55mm struture, it's basically impossible to confortably use the MT-24EX: the frontal ring rotates to focus, meaning that the MT-24EX will rotate too - and if this causes excessive strain on the 18-55mm structure, I don't know, I never tried after realizing the whole thing. Ah, yes, I have the first 18-55mm, found with a 300D, now the 350D and the 30D come with the 18-55mm II, but Canon stated it's only a cosmetic change, so I don't think situation for this lens will change too much.

Rear of the frontal unit of the MT-24EX. The four clamps are activated by a button on the top of the unit (not shown) and they are what keeps the collar from popping off the lens.

Front element of the Canon 100mm macro. The first indent is where the four clamps of the MT-24EX frontal unit go.

Frontal ring and Canon 100mm macro together. The light grey thing is the button I was speaking about before.

So, the task is very simple: adapting the 72C to your lens of choice, in my case a 17-85mm IS USM, a lens with a filter size of 67mm.
The task of ordering a 72C adaptor is easy, finding a 67mm screw guide is not. Well, it is, any cheap UV filter will do, but they are still costly and breaking their glass is not everyone might want to do. Unfortunately, after searching in various hardware stores I had to stick with a cheap filter for basic support: although finding 67mm screw guides is easy, it's not easy to find something that is useable with a photography lens: they are either too heavy, too big or they simply won't screw on the lens filter; so, bought a "cheap" (20 euros!) UV filter and started working.

A 67mm filter is just millimeters bigger than the 72C screw guide, so a little filing in required on both parts for better fitting. For a better handling, you'll might want to break the filter glass right away. Depending on the filter material, it can be "true" glass or a synthetic material. In the latter case, it's unlikely it will shatter in many parts like real glass would, but for safety it's better to wrap the filter in a small cloth first. Be careful - breaking the glass might require more force than you might think - plastic materials are quite sturdy: I used a metal chised normally used for bricks to break it down. Remove all shards and you are ready to go. The outer, reeded border of the filter is the best place to create a plain contact surface: it's already angled and easy to file, just be sure not to use too much strenght or you'll might end cutting the metal part of the filter in half - it's lightweight aluminium, afterall.
Place EXTREME caution in not damaging any of the screw guides.
Now file the 72C screw guide inner border to complement the filter filing and use cyanoacrylic glue to fix them. Be sure that the adapter and the filter and perfetcly aligned, you don't want to have the MT-24EX frontal unit pointing away from the subject: strange angles can also lead to excessinge wear on the lens structure, so be extra careful when aligning them - cyanoacrilic gel is expecially useful because it allows to move the glued parts around a bit before hardening. You can also use duct tape to temporarly fix them together and then use the glue to fix them once and for all.

Once the glue has completely dried, you'll might want to reinfoce the joint with any kind of tool you prefer - in my case, Tamiya epoxy putty. It's sturdy and light enough to sustain the adapter structure without adding too much weight on the whole thing. I added it on both the external and internal sides for precaution, and after complete drying, I sanded it to remove any excess putty both to make it look nicer and to reduce weight even more.

Last step is to paint it black.

Modified adapter, outer part.

Modified adapter, inner part. The putty there is rough because it's very difficult to sand it.

If you are using a large filter, like a 77mm for a 17-55mm IS USM or a 24-105mm IS USM, the job is easier as the filter will nicely go around the existing 72mm screw guide. You'll might want to reduce the original guide a bit so it won't come in contact with the lens front glass, but leave a small portion of it so you'll have a good starting point to place the 77mm filter exaclty in the center of the adapter. Adapting the 72C to a smaller filter size (58mm, for the excellent Sigma 105mm macro) does not stricly require to cut the original 72mm screw guide (you'll have 14mm of difference between the two) and is somewhat easier as you'll simply have to file the filter reeded head flat and glue it to the back side of the 72C adaptor.

So, here's the final result on the 17-85mm (at 85mm focal lenght):

Please note that wide-angle lenses will be able to capture the adaptor structure within their frame (even with cropped cameras like the 30D): on the 17-85mm IS USM, you'll get black parts from 17 to 24 mm and probably on full frame cameras (like the 5D) will be worse.

17-85mm@17mm on 1.6x crop camera (Canon 30D): adapter borders are very visible.

17-85mm@24mm on 1.6x crop camera (Canon 30D): still visible

17-85mm@35mm on 1.6x crop camera (Canon 30D): shadows on the corners, shooting RAW and reducing vignetting should take care of them.

17-85mm@50mm on 1.6x crop camera (Canon 30D): no more shadows.