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FORUMS Photography Talk by Genre Macro Talk 
Thread started 02 Jan 2018 (Tuesday) 06:53
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Lets talk about light

 
Dalantech
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Post edited 2 months ago by Dalantech. (2 edits in all)
     
Jan 02, 2018 06:53 |  #1

I've got a lot of reservations about starting this thread, but I voiced them on my blog (external link) and it might make for another topic of discussion if someone wants to talk about what I wrote in another thread. I felt that mentioning my reservations is warranted cause many of you have some strong opinions about light, and not everything that I'm going to mention in this thread can necessarily be quantified. Funny thing about macro is that it seems to attract a lot of really intelligent people. Unfortunately most of them can't wrap their heads around anything that cannot be measured in a lab and successful tested. An example is that I like diffused light that looks "feathered". Do I know what that light looks like when I see it? Yup. Can I accurately describe it to you? Would be tough in a forum post, especially since I don't feather my light by rotating the flash away from the subject. We're also not going to get into a discussion about the best way to diffuse a light source because it's too style dependent. I'd love to be able to use studio lights and huge soft boxes. Unfortunately it's a little tough to hand hold that kind of gear and chase after hyperactive subjects...

Note: The 1/focal length rule for determining the slowest shutter speed for hand holding a lens breaks down at 1x and higher magnification. You actually need much faster shutter speeds for shooting macro because motion as little as half the width of a pixel is enough to amplify diffraction. When shooting with the flash as your primary light source for the subject the duration of the flash becomes your "shutter speed". Although not as obvious as stopping a balloon in mid pop, or a bullet as it passes through an apple, flash based macro is a form of flash based stop motion photography. The more control you have over movement (yours and the subject) and the shorter the flash duration the sharper your images are going to be. A lot of the image softness that is blamed on diffraction is really just motion amplified diffraction, or what I like to call "macro motion blur". It won't look like traditional motion blur, but it will rob you of sharpness like diffraction does.

Let's start off by looking at a common mistake that I see people making, especially people who are struggling with the bright spot in the specular highlights (external link) that a flash tube can make. I was speaking with a shooter several years back who had solved the hot spot problem by cutting a hole in a white opaque plastic cutting board and mounting it to the front of his lens. I couldn't find an actual photo of it, but the light quality looked something like this:

Edit: The original image link no longer works. I'll update this post with a suitable replacement if I find one.

On the surface that might seem pretty good. No small central hot spot and light that looks pretty soft, at least from what I can tell looking at the reflection on the table. But the guy who was using it to diffuse his flash for macro complained about slow flash recycle times, and that his images seemed under exposed above 1x. The problem was that the cutting board was doing a better job of blocking the light than diffusing it, and his flash was firing close to or at full power most of the time. I think that this cutting board is a good example of a material that will diffuse a flash, but just because it can diffuse the light that doesn't mean that you should use it.

Lens mounted diffusers can be pretty effective, provide the flash is actually pointed toward the subject and not just camera mounted and firing straight ahead. Here's an example of one made by John Hallmen, although it could use some improvements.

IMAGE: https://farm8.staticflickr.com/7362/15744475133_5d9f975b00_z.jpg
IMAGE LINK: https://flic.kr/p/pZhx​VP  (external link) DIY Lamp shade macro diffuser (external link) by John Hallmén (external link), on Flickr

The general idea is to use the diffuser to shade the subject, so that the flash is the primary light source. You can then "walk the shutter" (decrease the shutter speed) to expose for the natural light in the background. One way to improve his design it to place something over the flash that will force any reflected light off of the back of the diffuser to go out the front. It would also prevent ambient light from coming though the diffuser (easier to make the flash the only light source on the subject). If you click on the image you'll get John's Flickr post with his list of pros and cons on using that diffuser. Also here's an example of what I mean by using the flash as the primary light source on the subject:

IMAGE: https://farm4.staticflickr.com/3872/15161185541_eac535636e_z.jpg
IMAGE LINK: https://flic.kr/p/p6K3​fH  (external link) Image One (external link) by John Kimbler (external link), on Flickr

While shooting that bee the flash didn't fire and you can see that the critter is almost a silhouette. I have the camera set to expose for the background (although a little under exposed). So I can use the flash to expose the subject and it's shorter than the shutter speed duration help to freeze motion.

IMAGE: https://farm6.staticflickr.com/5582/14977606198_ea18758e52_z.jpg
IMAGE LINK: https://flic.kr/p/oPw9​vC  (external link) Image Two (external link) by John Kimbler (external link), on Flickr

A camera mounted flash, with a lens mounted diffuser, will work (example here (external link)) and the light will be feathered because the flash isn't pointed directly at the subject. But since the flash is firing straight ahead it's not very efficient and you might run into problems keeping your flash duration short enough to freeze motion.

Ring flashes -just say no. They are very convenient and easy to use. But the light will look flat because the flash heads are too parallel to the lens, and because a ring flash almost wraps completely around the lens. So even when using ratio control to make one flash head brighter than the other the resulting light can still look pretty flat. Here's an example of the light "quality" that I was getting with a Canon MR-14EX over 10 years ago.

IMAGE: https://farm1.staticflickr.com/208/444988371_31739b1962_z.jpg
IMAGE LINK: https://flic.kr/p/FjFx​i  (external link) Bee at twice life size series 1-2 (external link) by John Kimbler (external link), on Flickr

For some of you the light in that image is gonna be acceptable, but for me it's not. Even with a 4:1 ratio difference between the two flash heads the light still looks flat, and the specular highlight is pretty ugly. I have seen some attempts at adding a diffuser to a ring flash, as well as trying to mount one by not connecting it to the end of a lens. But unless you're a dentist, who needs to photograph a patient's teeth, you're better off with any other light source.

I'm going to end this post here, with more to come later if you all want to continue this discussion. Keep in mind that I'm leaning more toward looking into light quality and diffuser efficiency, since both can effect the amount of detail that you can get in an image. Here's a pretty good example of what I'm currently getting with my light, although I'm constantly looking to improve it:

IMAGE: https://farm2.staticflickr.com/1716/25937312566_b430443d71_z.jpg
IMAGE LINK: https://flic.kr/p/FvZv​of  (external link) Newborn Blue Mason Bee I (external link) by John Kimbler (external link), on Flickr

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Left ­ Handed ­ Brisket
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Jan 02, 2018 07:22 |  #2

So, what is your light in that final image?


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Dalantech
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Jan 02, 2018 07:48 |  #3

Left Handed Brisket wrote in post #18531499 (external link)
So, what is your light in that final image?

That's Canon's MT-24EX with a home made diffuser. Currently using the MT-26EX-RT but I've only taken a single image with it so far, although the diffusion should actually be a little better. I use twin flashes cause I like to hand hold the lens, and I set up the lights like a portrait photographer (one as the key and the other as the fill). It fits my style of shooting and the look and feel that I want for my images.


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JasonC007
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Jan 02, 2018 12:01 |  #4

All good stuff.

You know my thoughts on diffusion and in simple terms this diagram explains that, which I find is working very well, especially considering the limiations of 3d printing. With this in mind it is possible to have very thin diffusers which do not block much light but still evens the light out across the diffusion face, which is why my diffusers only lose 1 stop of light allowing for faster flash speeds. If I could could improve the print process or manufacture these another way I could get them thinner and more even.



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Dalantech
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Jan 02, 2018 14:25 |  #5

The light on that hoverfly looks really good!


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Dalantech
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Post edited 3 months ago by Dalantech.
     
Jan 09, 2018 12:54 |  #6

Part II Diffusion Materials

I might take some heat for this one, since we're all pretty much experimenters and we like to try a lot of different things. Not trying to generate controversy, but honestly want to open up a dialog and maybe help someone solve a lighting problem or two. So with that in mind let's get started.

Yogurt containers are great! For holding, transporting, and displaying yogurt. Can you use one to diffuse a flash? Sure. Will you get an odd color cast to your light that's difficult, if not impossible, to fix in post? It can happen. Some food grade plastics are designed to protect products from certain wave lengths of light, and that's why some of them shouldn't be used for photographic diffusion. I've played with a lot of off the shelf plastics and for the price of a movie ticket, popcorn, and a soda you can get a gel diffuser pack (external link) and experiment with a range of diffusion grades. You can even experiment with modifying the color cast of your light with color correction filters (external link).

Just because you can use something to diffuse a flash that doesn't mean that you should...

Note: One of the things that I do is set my camera style to "Neutral". Even if you shoot RAW (and I do) you shouldn't let the camera do any post processing. Also make sure that the RAW editor that you use is also set to neutral, and even if you've taken shots in the past you can always set the camera style to neutral in the editor. Why? So when you look at your images you are seeing the scene just like the camera's sensor "saw" it. Then as you make adjustments to your lighting you can really see what kind of effect your changes are having on the color and contrast in your photos. Why spend a lot of time in post making changes to the quality of your light when you don't have to?...


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Jan 10, 2018 04:10 |  #7

How Light Creates Emotion in Photography. (external link)


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Jan 10, 2018 04:59 |  #8

Good stuff. Thanks for sharing.




  
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Dalantech
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Jan 10, 2018 05:35 |  #9

While I'm in the mood to post links I'd me negligent if I didn't mention Strobist (external link). Lots of tutorials on flash photography, and although not macro specific articles like Apparent Light Size (external link) helped me to wrap my head around diffusion.


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Jan 12, 2018 06:09 |  #10

Interesting discussion, did anyone see Lord V's diffuser tester on flickr today?
Here is a link to it as it is not my image
https://www.flickr.com …92/in/faves-14586608@N08/ (external link)




  
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Post edited 3 months ago by Wilt. (2 edits in all)
     
Jan 12, 2018 11:18 |  #11

Dalantech wrote in post #18537194 (external link)
Part II Diffusion Materials...

Yogurt containers are great! For holding, transporting, and displaying yogurt. Can you use one to diffuse a flash? Sure. Will you get an odd color cast to your light that's difficult, if not impossible, to fix in post? It can happen. Some food grade plastics are designed to protect products from certain wave lengths of light, and that's why some of them shouldn't be used for photographic diffusion. I've played with a lot of off the shelf plastics and for the price of a movie ticket, popcorn, and a soda you can get a gel diffuser pack (external link) and experiment with a range of diffusion grades. You can even experiment with modifying the color cast of your light with color correction filters (external link). .

Food container as 'diffusion' ... http://photography-on-the.net …showthread.php?​p=17737659

...I did this to spoof the expensive $50 tupperware offered on the market, but it certainly could be applied to bugs, too! :lol:


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Dalantech
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Jan 14, 2018 11:59 |  #12

davholla wrote in post #18539232 (external link)
Interesting discussion, did anyone see Lord V's diffuser tester on flickr today?
Here is a link to it as it is not my image
https://www.flickr.com …92/in/faves-14586608@N08/ (external link)

Anything that's shiny and has curved surfaces makes a good diffusion test subject. I like what Brian is using!


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Dalantech
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Post edited 3 months ago by Dalantech.
     
Jan 14, 2018 12:01 |  #13

Wilt wrote in post #18539374 (external link)
Food container as 'diffusion' ... http://photography-on-the.net …showthread.php?​p=17737659

...I did this to spoof the expensive $50 tupperware offered on the market, but it certainly could be applied to bugs, too! :lol:

Not saying that it doesn't work, only that sometimes the result aren't optimal. You could have gotten good diffusion simply by pointing your bare flash at the ceiling ;)


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Jan 14, 2018 12:31 |  #14

Due to the apparent light size principle (external link) diffusion gets better when the diffuser gets larger relative to the subject. So you can make your diffuser bigger, get it closer to the subject, or both to get better diffusion. For macro it's best to work on your diffusion at 1x or lower magnification, because if your light is good at low mag then it will only get better as the magnification goes up (due to the decrease in working distance). Apparent light size is also the reason why I think that short focal length lenses are better for flash based macro. The working distance of a long focal length macro lens can work against you when you're trying to get good diffusion.

This is kinda hard to demonstrate without setting my camera on a tripod and moving the flash around, but I think you can still see a difference in the specular highlights in these two images. Tech Specs: Canon 80D (F11, 1/125, ISO 200 due to Highlight Tone Priority) + a Canon EF-S 60mm macro lens + 25mm of extension tubes + a diffused MT-26EX-RT (both flash heads on the Canon flash mount, E-TTL metering, 0 FEC, second curtain sync).

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IMAGE: https://i.imgur.com/KtzE8Tol.jpg

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Jan 18, 2018 03:56 |  #15

Here's another good article, this time on Histograms (external link). Personally I always have the RGB histogram enabled on my camera display and typically expose to the right for the red channel.


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Lets talk about light
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