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FORUMS Photography Talk by Genre Macro Talk
Thread started 16 Jan 2016 (Saturday) 18:57
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Bond paper diffuser

 
Lester ­ Wareham
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Apr 29, 2016 12:08 as a reply to post 17989076 |  #46

Interesting point about 2nd curtain, I'll have to experiment; now if I can just find some time!!


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Lester ­ Wareham
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Apr 29, 2016 12:10 as a reply to post 17989255 |  #47

Good example. This was what I was trying to say, lower contrast light often needs (and gives the opportunity for) more PP contrast. This is just as true of ambient light.


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Archibald
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Apr 29, 2016 18:26 |  #48

A-PeeR wrote in post #17989180 (external link)
I wondered about the flash pulse duration. Curious, how do you know what output level you are using with the 270EX? Do you control the output level by FEC applied in camera or is there some other way to do this? Please excuse my ignorance but I use the 430EXII or the 600EX-RT and manually dial in flash output on the unit.

My 270EX II is set on manual, and for full power. At macro range, and using the paper diffuser, that usually gives the right amount of light at f/11 and ISO 100 or 200. The camera is also on manual, at 1/250 sec.

White blossoms look way overexposed (on the LCD) at these settings, but afterwards in LR it turns out they are not clipped. So it is OK. I have diddled with exposure compensation (flash and regular) and it has no effect. Not sure why. Maybe because everything is on manual.

I have the 430 and 580 flashes but the heads are too high for a lens-mounted diffuser.


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Apr 29, 2016 18:50 |  #49

SteB wrote in post #17989255 (external link)
Without seeing the original images I can't say what the issue is. However, with my concave diffusion principles the image often comes out very low contrast out of camera, and can initially seem soft. I created a diffuser to produce this very low contrast lighting so I could use strong sharpening and microcontrast boosts in post-processing without it looking over-sharpened. This was to counteract the diffraction softening of using quite a small effective aperture. At 1:1 an nominal aperture of f11 i.e. the aperture shown on Canon DSLRs is actually an effective aperture of around f22, and well into the zone where diffraction softens the image.

Undiffused or less effectively diffused macro flash creates a type of natural sharpening. What I mean by this is that you get little bright bits with blown highlights, and deep black shadows. This gives high acutance i.e. apparent sharpness. In luminance values the white is close to 255 and the black close to 0. The problem with this if it's in your RAW file it's baked in. What's more if you try to apply more sharpening or microcontrast to counteract diffraction softening it will look horribly over-sharpened. This is the reason for using low contrast lighting. With what videographers call grading you can add contrast and processing to a low contrast image. Unfortunately you cannot undo high contrast in an image when the contrast is baked into your original exposure. It's the same for overall image and microcontrast. It is far easier to work on a low contrast image in post-processing, and then to finally adjust the contrast to taste.

What I'm saying is that with no flash diffusion for macro flash, or less effective diffusion that it looks sharper out of camera, but you can't do much with the image in post processing without it looking over-sharpened. Whilst these images look sharp at web size if you look at them at 100% view, they are lacking in image detail. By using low contrast but oblique lighting, and then additional sharpening and microcontrast boost in post processing, there is far more apparent detail at 100% view. Before applying this extra sharpening and contrast boost I use noise reduction software (Topaz DeNoise) to remove any image noise (this will act like a key for the sharpening and will create ugly sharpening artifacts.

There's a difference between low contrast oblique light and flat lighting, even if they look superficially similar before post-processing.

Flat lighting is lighting from the front. Here there are no shadows at all, and if there are small bumps i.e. texture, there is no highlight on one side, and a shadow below as you get in oblique lighting which brings out the texture in a photograph. Even increasing sharpening, microcontrast, and overall contrast will not re-create texture with flat frontal lighting.

However, with low contrast oblique lighting from say above, there are still micro shadows below texture and brighter highlights above, it's just that they're not visible yet in an unprocessed image. When you increase sharpening and micro contrast, with say wide pixel radius sharpening, along overall contrast boosts, this texture will become far more apparent.

It's easiest to illustrate it with this image, which I used to counteract mistaken criticisms that the lighting from my diffusion was flat. These are the same exposure of the same Ladybird taken with my concave diffusion. The image on the left has had a moderate amount of sharpening and boosting of the micro contrast, and overall contrast. The image on the right has had more sharpening, microcontrast boost, and overall contrast adjustments. Not how much more image detail is apparent, and notice how it has brought out far more of the texture of the subject, which would not have been possible if this was truly flat lighting.

QUOTED IMAGE
[IMAGE'S LINK: https://flic.kr/p/7VBV​gg] (external link)Sharpening comparison (external link) by Stephen Barlow (external link), on Flickr

What I cannot say without looking from a full resolution image or a crop from the out of camera exposure is if the images are soft i.e. the detail is blurred, low resolution, whether the image has flat shadowless lighting, or if the light is just low contrast (where better processing would bring out more detail). As I think I said earlier I have tried bond paper as a diffuser. However, I found it absorbed far too much light, so it is possible your flash is firing at nearly full power and not freezing motion. There is a way to test this. Whilst the 270EX does not have manual power ratios on the flash, with many Canon DSLRs you can go into the menu and find the external flash control panel. This allows you to adjust the power ratio in manual, so you can establish what power level your flash if firing at for a correct exposure i.e. if it is firing near full power.

If the diffuser is simply absorbing too much light then simply use velum paper or preferably diffuser gel in it's place. Both are easy to cut, and all you have to do is to use your bond paper diffuser as a template, draw around it with a pencil and cut a diffuser out of one of these other materials. Both velum paper and diffuser gel transmit far more light than bond paper, but they still have excellent diffusion characteristics even with a single thickness. Having said this, if your flash is firing straight through the diffuser at the subject, you might get a bright spot. So possibly you could just a double thickness with a gap, or just a double thickness where the centre of flash strikes the diffuser.

I still don't know if there might be motion blur in my examples. It is possible, I think. Somewhere on the Web IIRC it was stated that the flash duration of the 270 was 1.3 ms. That's 1/800 sec, slow enough that motion could be a factor.

I've got some vellum paper and will give that a try. With it, I should be able to reduce the flash power by a stop or two, shortening the flash duration.


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Apr 29, 2016 21:36 |  #50

OK, I tried some vellum paper, exact same convex fan shape as the bond paper was. Exposure-wise, the vellum gives a 2-stop advantage. But it does not soften the light as much. See comparison below.

It might still be OK.

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Dalantech
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Apr 30, 2016 04:01 |  #51

Archibald wrote in post #17990072 (external link)
OK, I tried some vellum paper, exact same convex fan shape as the bond paper was. Exposure-wise, the vellum gives a 2-stop advantage. But it does not soften the light as much. See comparison below.

It might still be OK.

The MT-24EX that I use is brutally harsh out of the box. One trick that I tried last year and have stuck with is to use a replacement wide angle diffusion panel for a standard camera flash. I cut it to size and hot glued it to the MT-24EX's flash heads. The 270EX has a built in wide angle diffuser, just extend the flash head all the way out. Have you tried it?


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Apr 30, 2016 10:47 |  #52

Dalantech wrote in post #17990229 (external link)
The MT-24EX that I use is brutally harsh out of the box. One trick that I tried last year and have stuck with is to use a replacement wide angle diffusion panel for a standard camera flash. I cut it to size and hot glued it to the MT-24EX's flash heads. The 270EX has a built in wide angle diffuser, just extend the flash head all the way out. Have you tried it?

I'm unable to find a pull-out diffuser on my 270EX II.

The flash already directs light in a wide angle. It spreads the light out very evenly, and the fan-shaped vellum diffuser that sits on my lens is evenly illuminated, to the extent that is possible with a curved surface. Using a pull-out diffuser or home-made diffuser right on the flash will only spread the light further and that light will be lost to the surroundings. The light hitting the vellum will be just as even as before, there will just be less of it.

Of course what happens at the flash head does not change the optical behavior of the fan-shaped diffuser.

The light that arrives at the vellum, regardless of diffusion or otherwise at the flash head, is directional. It all comes from the flash head. The vellum diffuser redirects the light but does not do so completely randomly. If it did, then we would have soft light at the subject coming evenly from all parts of the vellum. But the vellum isn't a strong-enough diffuser for that. Most of the light goes through with a relatively small change of direction.

Accordingly we have a hotspot and less-soft light arriving at the subject.

Bond paper diffuses much better giving much softer light, but there is also much less light.

Like everything in photography, there are compromises and trade-offs. For the softest light we need heavy diffusion, but that reduces the amount of light. Less diffusion gives much brighter light but it is not as soft.


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Dalantech
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Apr 30, 2016 14:25 |  #53

Archibald wrote in post #17990530 (external link)
I'm unable to find a pull-out diffuser on my 270EX II...

Hold on to the end of the flash, where the flash tube is, and pull...


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Apr 30, 2016 14:32 |  #54

Dalantech wrote in post #17990741 (external link)
Hold on to the end of the flash, where the flash tube is, and pull...

?

Do you own the 270EX II?


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Apr 30, 2016 14:33 |  #55

Archibald wrote in post #17990749 (external link)
?

Do you own the 270EX II?

Yes, Have my copy right in front of me. Pull... On... The... Flash... Head...


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Dalantech
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Apr 30, 2016 14:36 |  #56

Archibald wrote in post #17990749 (external link)
?

Do you own the 270EX II?

Bonus tip: If it was mounted on your camera you could point it toward the ceiling after extending it. Why is that relevant? You could mount it upside down, extend the flash head, and maybe get a better angle between the flash head the subject when the working distance is short...


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Apr 30, 2016 14:42 |  #57

Dalantech wrote in post #17990229 (external link)
The 270EX has a built in wide angle diffuser, just extend the flash head all the way out. Have you tried it?

Dalantech wrote in post #17990750 (external link)
Yes, Have my copy right in front of me. Pull... On... The... Flash... Head...

Are we talking about a diffuser?

??


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Apr 30, 2016 14:53 |  #58

The 270EX II does not have a built-in wide angle diffuser.

It does have a pull-out head that tilts, but that is something different.


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Dalantech
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Apr 30, 2016 16:00 |  #59

Archibald wrote in post #17990770 (external link)
The 270EX II does not have a built-in wide angle diffuser.

It does have a pull-out head that tilts, but that is something different.

That takes it from "normal" to wide angle...


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Dalantech
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Apr 30, 2016 16:05 |  #60

Archibald wrote in post #17990770 (external link)
The 270EX II does not have a built-in wide angle diffuser.

It does have a pull-out head that tilts, but that is something different.

LOL! It's obviously too late in my day :)

When you pull the flash head out it actually concentrates the light. My bad. I though it would work to help force the light to spread out. Doh!


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