Fresnel lens as a macro flash add-on?

DQE · Post by **DQE** » Thu Aug 16, 2012 1:56 pm

Is it possible that a Fresnel lens could be designed and producedas an add-on to a flash unit for macro photography? My hope is that converting the naked flash head into a highly dispersive light source could be accomplished somehow.

One of many issues is that the distance between the MT-24 flash heads in the subject is often only a few inches or cm. If one adds a Fresnel lens attachment, it wouldn't work if a significant number of inches/cm are needed between the flash head and the Fresnel lens. Maybe there would be a better chance if used with telephoto macro lenses such as Canon's 180mm macro lens?

I thought of this as I was using my "Better Beamer" Fresnel lens add-on for telephoto bird photography. Here, one places a thin plastic Fresnel lens maybe 6 inches from the flash head. It creates a much more concentrated spot of light at a substantial distance from the camera. This works much better than an unmodified flash for dim-light bird photography.

Probably we're much more limited by the effective size of the light source (in subtended angle terms) than by the diffuseness of the light source.

Here's a link to a mini-review of the Better Beamer unit:

http://www.digitalcamerareview.com/defa ... ewsID=3651

Oskar O · Post by **Oskar O** » Fri Aug 17, 2012 12:52 pm

A fresnel lens can definitely be used to modify the path of the light in the flash. Many flashes contain some sort of wide-angle diffuser, which while not usually a fresnel lens per se, does borrow the principle to diffuse the light.

That said, I'm not sure what you wish to accomplish. As I understand, the better beamer is used to focus the light so that it's in a narrower cone, thus being effective at a longer range. But in macro, power is not usually the problem (until powerful microscope objectives that is...)

Harold Gough · Post by **Harold Gough** » Fri Aug 17, 2012 1:11 pm

Perhaps it would be bulky and/or heavy?

Higher intensity would permit a shorter exposure.

Harold

DQE · Post by **DQE** » Fri Aug 17, 2012 4:16 pm

In thinking further about this, I believe I confused the role of a diffuser with that of a lens.

What I would l really like to have of course is something that would turn my MT-24 flash heads into effectively much larger diameter, highly diffuse light sources.

Naturally I also want light weight and high light throughput efficiency. While I am at it, I may as well wish for low cost too!

Hard to say if there is *any* role for Fresnel lenses in such a quest. At least the ones used in my Better Beamer unit are very lightweight and not too expensive.

Oskar O · Post by **Oskar O** » Sat Aug 18, 2012 1:21 pm

I see... a lens could of course be used to spread out the light, but at some point some diffuser is needed. But it shouldn't be impossible or anything; the area of the light source doesn't need to be that big if it's close to the subject, but some sort of distance between the flash bulb and final diffusing layer is needed to properly spread out the light. Haven't seen any product like this specifically for macro.

TheLostVertex · Post by **TheLostVertex** » Sun Aug 19, 2012 10:55 am

DQE wrote:...
What I would l really like to have of course is something that would turn my MT-24 flash heads into effectively much larger diameter, highly diffuse light sources.

Naturally I also want light weight and high light throughput efficiency. While I am at it, I may as well wish for low cost too!
...

Well, you can do that pretty effectively I think. Grab some stiff construction paper/cardboard, some tracing paper or drawing paper, tape, aluminum foil, and contact cement.

-Cut the paper or cardboard into a few of these (pardon the crude 10 second drawing)

-Glue the inside with aluminum foil cut to fit(shiny side up)
-Fold over the tabs at the bottom of each of the pieces then tape them all together so you have a pyramid shape with the port hole to fit over the flash head. The hole for the flash head should protrude out from the box for maximum light bounce-age.
-Add on your diffuser to the front of the device.
-Attach to the flash head

You can make it as deep or as shallow as you like, and as wide as you want. You can also change the diffusion material to what suits you. Cheap, light weight, high light output. Did I miss anything?

DQE · Post by **DQE** » Sun Aug 19, 2012 7:50 pm

One of the more interesting and apparently effective MT-24 mod rigs I've seen posted to the net is orionmystery's:

http://orionmystery.blogspot.com/2010/1 ... pdate.html

The concave dish reflector seems to work quite differently from the conventional diffused lightbox that is commonly used. My biggest worry about this design is the secondary flash diffusing surface that seems to be placed significantly in front of the lens. I may misunderstand, but it seems that it would interfere with high mag shots. Perhaps all that is necessary is to fold the sheet back somewhat.

I keep wondering if a computer-optimized design like orionmystery's design would be significantly more efficient...my guess is that there probably isn't that much room left for improvement.

ChrisR · Post by **ChrisR** » Mon Aug 20, 2012 1:13 am

Surely most of what matters is how big the light source appears to be, from the bug's position. I have a couple of cheap bought "pyramid" versions of diffusers like TheLostVertex has drawn, and they diffuse, but don't give as effectively large a diffuser as a wrap-around design like OrionMystery shows.

Couple of other factors (at least!) -
one is how you illuminate the diffuser. If you use a wrap-around then a single flash will cause a hot-spot, though it fades away quite nicely. If you have more flash sources, or a mirror surface to illuminate the diffuser from another angle, it'll give a more even light.
A second is the material you use. As a general diffuser, tissue paper seems to be pretty good. There are some special materials used in flat panel laptop displays designed to direct light out at right angles to their surface, which I haven't played with.

Also, if you, eg, put your bug in a tube of paper, then the lit parts of the paper work as a diffuser, and the unlit parts as a fill-in reflector, so you win twice.

DQE · Post by **DQE** » Mon Aug 20, 2012 5:30 am

ChrisR wrote:Surely most of what matters is how big the light source appears to be, from the bug's position. I have a couple of cheap bought "pyramid" versions of diffusers like TheLostVertex has drawn, and they diffuse, but don't give as effectively large a diffuser as a wrap-around design like OrionMystery shows.

I think that my biggest concern about my MT-24 flash heads, only diffused by somewhat spaced -away Fong Puffer diffusers, is the small angular subtense of the two individual illuminating light sources.

The wrap-around diffuser alone may even be enough to solve this problem, hopefully without eating too much more light. However, at present, my MT-24 flash heads not uncommonly bump against the flower/bush that bugs are on, and at 4-5x mag (MPE-65 lens) the flash heads sometimes bump against a flat wall at some shooting angles. As a result, I can't quite see how I could use a wrap-around diffuser on the front of my MT-24 attachment ring. I must be missing something since orionmystery uses it so extensively and with such great success.

Unfortunately, that I only do field macro, so studio solutions often can't be easily applied. It would be great if bugs would quietly and cooperatively place themselves inside a white cylinder.

------------
What I would most appreciate is if other bugs would follow the example of most crab spiders and quietly sit very still while I arrange myself, my camera, and even a full tripod-based rig!

Harold Gough · Post by **Harold Gough** » Mon Aug 20, 2012 5:50 am

This may have some potential:

http://www.ebay.co.uk/itm/Rogue-Flashbe ... 43ad07acc5

Harold

TheLostVertex · Post by **TheLostVertex** » Mon Aug 20, 2012 11:03 am

DQE wrote:... My biggest worry about this design is the secondary flash diffusing surface that seems to be placed significantly in front of the lens. I may misunderstand, but it seems that it would interfere with high mag shots. Perhaps all that is necessary is to fold the sheet back somewhat.

That was my first thought when viewing it as well. I would guess any object that are on a protruding surface would be fine. But it would likely run into issues where the is a back wall, or ceiling for the subject. I am sure that orionmystery could fill us in more clearly on its advantages and pitfalls in real use.

DQE wrote:I keep wondering if a computer-optimized design like orionmystery's design would be significantly more efficient...my guess is that there probably isn't that much room left for improvement.

My guess would be that peeling back the cone into more of a half lampshade would give more clearance. I am not sure if that would have a drastic effect on light.

Testing is the best way to proceed I think. OM's diffuser, a modified wider one, a softbox style like the instructions I posted, some phong diffusers, perhaps the flashbender panels, and of course bare flash. Let us know when you're done