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Archive 2010 · Flash Help

ukphotographer
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p.2 #1 · Flash Help

BrianO wrote:
ukphotographer wrote: ...I already fully explained it go and read it again.

I think you should read Chuck's post again; I think you're reading more into it than what he's saying.

HSS does reduce flash intensity, and it is therefore better suited for use with larger apertures than smaller ones. By using HSS, you can go to a higher shutter speed, which in turn allows a larger aperture without the ambient blowing out the highlights.

That's all Chuck said, though not so succinctly.

That's not all Chuck said, that was a reply. He obviously intends to use HSS yet has not calculated the loss of HSS and the reduction in aperture and shutterspeed. I didn't misread anything. Here's the quote again.

cgardner wrote:
Outside in sunlight one gets hamstrung by "Sunny 16" when using conventional flash. If the camera sync limit is 1/250th sec, an aperture of f/11 is needed to expose the sunlit highlights below clipping. That in turn makes it difficult to eliminate distracting outdoor backgrounds with shallow DOF.

The Canon coded optical system allows High Speed FP sync at any shutter speed in TTL or M modes. There's a overall reduction in power and range, but its ideally used with wide apertures of f/4 or wider which don't require as much flash power as an f/11 exposure would.

I explained that this was and still is wrong. His example of f11 @ 1/250s and the equivalent exposure @ 1/2000s f4 would result in more power being needed at f4 because of HSS - not a reduction.

Sep 11, 2010 at 11:05 AM

cgardner
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p.2 #2 · Flash Help

My main point was that HHS is a very useful feature when shooting outdoors with flash which is lost when simple radio triggers limited by x-sync are used, and if using HHS, it is best use it with the widest aperture possible because that's the task HHS was designed for.

I did err in stating less power is needed at f/4 vs f/11 in HHS mode. Mea Cupla. In HHS mode the flash acts as a continuous source and shutter speed affects flash exposure just as it does an ambient one. The flash starts pulsing just before the first curtain opens and continues for the 1/300th sec. or so it takes both shutter curtains to pass over the sensor. The curtains move at a constant speed across the sensor regardless of indicted shutter exposure, what changes is the latency or gap between the first and second curtain movement; as indicated speed decreases so does the width of the moving slit formed by the curtains.

In M mode the Canon flash shows the distance at which flash exposure is correct on the LCD display on the back. I've found it to be quite accurate for direct flash. Based on that range display a 580ex at the full 1/1 M power setting, with the flash zoom set at 50mm near the middle of the zoom range, has a max. range for single burst flash of 15 ft. at f/11 @ 1/250th @ ISO 100. When the camera is changed to f/8 @ 1/500th the flash switches to HSS mode (when HSS mode is enabled) and the range drops to 7ft. The transition to HHS cuts the effective range in half. Once in HSS mode opening the aperture and decreasing shutter to keep the net exposure the same has no effect on the indicated point of correct exposure, it remains at 7ft. The net amount of light reaching the sensor remains constant because as the aperture gets larger letting in more light the gap between the curtains gets smaller reducing the time it hits each part of the sensor.

Reversing the equation and looking at relative power levels at a constant distance, in HHS the max range is 7ft which indicates in HSS the flash is working at max. output at 7ft. regardless of shutter / aperture combo to obtain a net "Sunny 16" exposed background outdoors. In normal flash mode, at f/11 @ 1/250th @ ISO 100 a power level of 1/4 is needed to move the point of correct exposure from 15ft. to 7ft. So the flash is working at a 100% of its total capacity in HHS mode but only about 25% capacity in normal mode to expose correctly at 7ft. No real surprise there.... But once in HSS mode the power needed is a constant level regardless of equivalent shutter/aperture settings (where I erred previously).

Granted 7ft. might seem rather limiting for HSS, but that's for a single flash used indoors, not factoring in the affect of the brighter ambient light on the overall exposure outdoors or the use of more than one flash. In practice, if one knows how to use the ambient light effectively outdoors, the range of HSS is more than adequate in many situations, including outdoor portraits.

Outdoors where HHS is designed to be used the flash doesn't need to provide all the light on the face so the effective range in practical terms is greater than the 7ft. the flash display or indoor testing would indicate for a single flash. When lighting a portrait outdoors with my Canon flashes I use two of them in an overlapping pattern of key over neutral fill, just as I do indoors. I've never systematically tested the maximum effective range of my 580ex flash outdoors in HHS mode but from other tests such as this one LINK I had no problem obtaining a correctly exposed foreground from a distance of 10ft with a singe direct 580ex in HHS mode with direct flash and use dual flash with my foam modifiers with HHS within 10ft without any problems with exposure.

While this thread has taken a tangent into HSS don't lose sight of the fact I don't recommend hot shoe flash as the tool of first choice for serious portraits. The show stopper for hot shoe and serious portrait work is the lack of power to drive larger modifiers and the lack of modeling lights to guide placement. With studio flash control of the shadow tone is basically the same, via the lighting ratio, but larger modifiers will render skin highlights better with less specularity. I've learned to work around the shortcoming of power by using smaller modifiers for candid shots and informal portraits. But I know how to control perceived shadow softness with lighting ratio and deal with the consequences of specular highlights caused by the direct flash or small modifier during editing using a variety of retouching techniques.

Sep 11, 2010 at 06:52 PM

ukphotographer
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p.2 #3 · Flash Help

cgardner wrote:
I did err in stating less power is needed at f/4 vs f/11 in HHS mode.

That's only as I pointed out. Too many people look to HSS as the Holy Grail, and it's nothing of the sort, useful for sure, but not in the way that many people get built up to expect.

Sep 11, 2010 at 08:09 PM

ukphotographer
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p.2 #4 · Flash Help

BrianO wrote:

I think you should read Chuck's post again;

!!!

Sep 11, 2010 at 08:12 PM

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p.2 #5 · Flash Help

ukphotographer wrote:
BrianO wrote:

I think you should read Chuck's post again;

Sep 11, 2010 at 11:45 PM

ukphotographer
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p.2 #6 · Flash Help

BrianO wrote:
ukphotographer wrote:
BrianO wrote:

I think you should read Chuck's post again;

!!!

Laugh yourself silly, but in the first posts we were talking about flash intensity, not power input. In HSS mode, the intensity of Canon flash guns is less than in normal mode. This is indisputable.

I fail to see your contribution in this matter other than to stick your nose in.

I pointed out to Chuck that he was wrong and explained why, and you (surprise,surprise) decided to jump to his defense saying I misread his post.

I didn't misread Chucks post and he agreed with me.

All you are doing now is blowing hot air about a conversation I was not part of and although I'd love to argue the point with you, my time is more important.

Sep 12, 2010 at 09:44 AM

cgardner
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p.2 #7 · Flash Help

I for one have never said HHS was the "Holy Grail" but find its useful tool for creating non-distraction backgrounds and nice Bokeh in outdoor shots.

I usually shoot in ETTL mode with flash in normal and HSS but to did a couple of tests in M mode yesterday to better quantify performance of HSS with my 580ex. I like to expose for highlight detail in the brightest solid objects, which outdoors in sunlit tends to render everything else much darker than seen by eye because the camera sensor can't handle the contrast range like our eyes, brain and adaptive perception does.

I started with an ambient only baseline shot at 1/500th, exposed per the clipping warning, to keep the sunlit parts of the white towel -- my highlight detail proxy -- and found I needed a aperture of f/9 to keep the sunlit part below clipping. I then added a single direct 580ex flash at 1/1 power in HHS mode from a distance of 10ft. and got this result:

This image is copyrighted by the owner

I then moved in to 7ft and got this result...

This image is copyrighted by the owner

and this at 5ft.

This image is copyrighted by the owner

Not shown is the baseline test I did at 1/250th with normal flash. From 10ft. I had to dial the power down to below 1/4 to get a flash exposure in front which matched ambient exposed below clipping on the towel. At 10ft. the flash power in HSS mode wasn't adequate. At 5ft. the foreground matched the sunlit part almost exactly, but the ambience and 3D rendering of the natural rim light is lost resulting in a flat-overflashed look. 7ft. produced the most "normal" rendering. The foreground is underexposed relative to how an indoor shot would be exposed, but that is necessary to preserve the ambience of the backlighting from the sun and avoid a flat over-flashed look.

Next I tested with dual flash, opening the aperture more and allowing the sunlit parts to clip slightly and winding up at 1/500th @ f/5.6 for my baseline ambient only exposure:

This image is copyrighted by the owner

I placed the off camera 580ex flash set to 1/1 power 45° to the right at a distance of 6ft. and shot with Master/fill on the camera bracket from 10ft, also set at 1/1 power and got these results:

This image is copyrighted by the owner

I moved a bit closer for the shot at 1/2000th, but not intentionally.

7-10ft. is the range I typically shoot portraits from and the M mode full power range tests confirm my anecdotal experience using HHS outdoors; it works fine at those distances when used with direct flash. I've also used HSS outdoors for shallow DOF shots of things like flowers where the flashes were closer with no problems. I didn't have time to do a test with diffusion on the off camera light to tone down the specularity of the highlights, but have shot that way previously in ETTL with the off camera flash closer and gotten OK results.

A big reason I like to use HSS when feasible is because prior to switching to Canon in 2004 I had been using a Minolta D7Hi which has an electronic viewfinder and no sync limit with my pair of trusty Vivitar 285HVs. I got spoiled shooting with flash outdoors and never having to worry about the sync limit. For the first year I owned my 20D I continued to shoot with my pair of Vivitars. Being frugal I was reluctant to spend $800 to get the same basic flash solution I already had, but but after the creative freedom from x-sync I enjoyed with the Minolta is was a PITA to be shooting at f/8 outdoors with my new 2.8 L lenses and I bit the bullet. I was aware of the limited range of HSS and the of Canon's optical based wireless, but I'd been using Wein optical triggers on my Vivitars. I was quite skeptical about the ETTL ratios to the point of asking others to shoot and post some tests, but after getting the flashes and learning how the evaluative flash metering introduced in the 20D worked I found that overall the Canon flashes were much more effective than shooting in Manual mode with the Vivitars, which I still have and use occasionally.

There's a lot of things I don't like about Canon flash, but I've learned to deal with its shortcomings, including the limited range of HHS. I'd like to see the obsolete and poorly positioned mechanical contact hot shoe replaced with a TosLink style fiber optic connector between camera body and Master flash and a dedicated slave flash with a stand mount, barebulb, speedring and emovable tethered sensor. FWIW I'm hoping that someday Canon will produce a 1.6 or larger EF / EF-S mount camera body with an EVF instead of the flapping mirror and sync-bound FP shutter. There are pros and cons to EVF vs. optical, but the advantages for flash and exposure control outweigh them for me. HHS wouldn't be needed and outdoor photography with flash would be much simpler.

Sep 12, 2010 at 04:09 PM

ukphotographer
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p.2 #8 · Flash Help

cgardner wrote:
I for one have never said HHS was the "Holy Grail" but find its useful tool for creating non-distraction backgrounds and nice Bokeh in outdoor shots.

And I never implied that you did. However, saying that a flash at f4 in HSS would use less power than one at f11 at normal X sync is wrong and perpetuates the idea that HSS has some sort of hidden magic with reserve power you could call on, when it hasn't.

Your examples illustrate the lengths you need to go to to obtain acceptable results within the limits of HSS. Unless you specifically require the effect of wide apertures then utilising your flash within your camera's max sync speed will provide you with the maximum output, range and contribution / ratio against ambient from you flash.

Fill at 7 feet, Key at 5 feet. Full power. Zoomed to 68mm..That seems reasonable to me. ISO is irrelevant, as the ratio would remain constant.

2 speedlites at 10ft works too.

Of course, circumstances might allow zooming of the flash heads to increase range or relative output, and softboxes or other modifiers used properly will reduce range. Reduced range will also be incurred with the use of wide angle lenses and linked zoom speedlites unless they are overridden - just like using regular X sync.

Sep 12, 2010 at 05:13 PM

ScooberJake
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p.2 #9 · Flash Help

cgardner wrote:removable tethered sensor.

Oh how many of my problems would be solved! This could even be produced as an add on. What about a third party? It's basically a repeater, probably very similar to those used for relaying remote control signals to AV equipment, but at a different wavelength.

Come to think of it, since the Canon flashes can operate on IR as well as visual, I wonder if one of those would work?

Sep 13, 2010 at 09:10 PM

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