27 replies to this topic

[Alex_Mustard]

Finally I have sorted out my pictures from yesterday's tests on high speed synch speed. All shot with a Nikon D70 with 10.5mm lens and a single Subtronic lens.

This main test was to see the effect of shutter speed on sunbursts. All shots were taken with the same aperture and flash power (Subtronic Alpha at 1/4 power). Shutter speed was increased, through the sequence, increasingly underexposing the background. Usually I would underexpose the background more than the control shot at 1/160th.



IMO the sunburst is poorest in the 1/180th image. I don't see big differences between the 1/500th and 1/1000th images.

[Alex_Mustard]

The next test I did was to demonstrate that it is the underexposure of high shutter speed, rather than the high shutter speed itself that is what produces the decent sunbursts.
In these shots as I sped up the shutter speed, I also openned up the aperture to keep the background light level close to constant. I also lowered the flashpower accordingly with the aperture.



IMO non of these shots are particularly better than the others.

[Alex_Mustard]

The final test was to look at the effect of fast shutter speeds on flash exposure. All these images were taken at 1/1000th. I actually increased the flash power from 1/4 to 1/2 to Full across these sequence - but there is no increase in strobe light in the images because these is not time for the strobe to discharge more than 1/4 of its power in the 1/1000th sec exposure.



The way to increase flash power in short exposures is to add more strobes - all giving out 1/4 of their light during the exposure. So if you wanna do lots of high shutter speed shots you need lots of strobes 2, 3 or 4, but they need not be on more than 1/4 power!!!

Alex

[kdietz]

Thanks Alex.......that was very informative and helpful

Karl

[MikeVeitch]

Thanks Alex, great test.

[UWphotoNewbie]

However if the camera doesn't think that the strobe is there. And the easiest way to duplicate this is to turn the strobe off (or block some contacts). Then it will fire the strobe at faster shutter speeds.

You don't have to "modify" the contacts to do this. At least in my Ikelite housing, the hotshoe for non TTL does not use all of the contacts and so therefore lets you choose any shutter speed you want. The high shutter speeds are controlled by an electronic shutter so you won't get a partial sync. Ike however reports that his strobes DS125 take about 1/250 s to discharge a full dump. So the effective sync speed is limited by the strobe not the camera if you want to get a full dump. Now if you use the fractional power settings you can get all of it at higher shutter speeds. There is also nothing wrong with cutting off the strobe by closing the shutter early if you are still getting enough light. With the shoot review shoot meathod of non TTL digital it matters little weather the strobe or the shutter cut off the light if the exposure is right.

Of course all of this changes when we go TTL. Then presumably Ike hooks up the other hotshoe pins and my D70 won't let me go past 1/500. At that point I'll want the camera to get all of the strobe flash that it asks for in the exposure in order for TTL to work reliably.

So there are upsides and downsides to the current TTL situation with dslrs.

[james]

Holy crap this is useful stuff Alex.

Mind if I split your images out into a separate thread and title it "High Speed Flasy Sync Tests?"

Cheers
James

[samplin]

Hi Gang
I have been following this thread. We shoot Little Leagues and I have 6 D70s.
We shoot them an Manual with Lumedyne strobes. We use the AS-15 to connect the PC tohousehold sync cord.

My findings with this set up were no matter where I put the shtter speed .. Even at 6000th the camera synced with the strobe.

I went outside and put the camera on F8 @ 250th Took a scene of half a wall and hald my backyard. Started at 250 and the wall and background were properly exposed. As I cranked up the shutter speed the background got darker and the wall stayed properly exposed. Went all the way to 8000 th and the same results. Background was Black.

There might be something in the connection when the camera sees a strobe attaches to it. Think if you put a SB800 on the shoe, the shutter wil not go higher than a 500th.

Not like the old focal plane shutters that would only sync at a 250th.. We even went as far to have our camera repair person lock the shutter speed at a 250 so there wasnt any chance of half a frame exposed .

This is the main reason we switched from the d100s to the D70s.

Joe

[UWphotoNewbie]

Wow! Thanks Alex great test.

I like the last one the best--f22 1/1000 and 1/1 flash.

Your conclusion also sits well with my general attitude toward life: More power...hrrrrgh hrrrrgh ....

[randapex]

Yes, thanks for you work Alex. The 1/4 power info is greatly appreciated. I'm still considering the photos. I'm pondering the somewhat disappointing (to me) results of the 10.5. It seems to have pushed the sun out to a relatively small part of the frame. Hmmm.
Rand

[herbko]

Yes, thanks for you work Alex. The 1/4 power info is greatly appreciated. I'm still considering the photos. I'm pondering the somewhat disappointing (to me) results of the 10.5. It seems to have pushed the sun out to a relatively small part of the frame. Hmmm.  
Rand

Keep in mind that 1/4 power @ 1/1000 is strobe dependent. I expect the Inon will deliver up to 1/2 at that speed.

[randapex]

I will, thanks Herb.

Rand

[Alex_Mustard]

You don't have to "modify" the contacts to do this. At least in my Ikelite housing, the hotshoe for non TTL does not use all of the contacts and so therefore lets you choose any shutter speed you want.

I agree that this is housing specific. The Subal D70 has all 5 wires already connected (well it looks that way) and therefore knows that there is a strobe attached. The D70 is much more friendly to older strobes that the D100 (and D1, D1x), which refuses to fire if you attach (with 5 wires) older strobes.

Alex

[Alex_Mustard]

Keep in mind that 1/4 power @ 1/1000 is strobe dependent. I expect the Inon will deliver up to 1/2 at that speed.

What we need is a way to get those "Lumedyne strobes" that Joe used on land. Those babies seem to be able to discharge fully within 1/8000th sec. Nice. Now we need to get them UW!!

Alex

[kdietz]

extension cord and emergency generator?

Karl

[james]

OK, It looks like I've successfully split the topic. Phew!

Cheers
James

[laz217]

Alex, Thanks for the insightful knowledge on the D70 and the higher shutter speed flash syncing mystery. It's ultimate goal still seems in question, though...

What are the best settings for capturing a jaw-dropping solar flare? As a couple of us discussed in a previous post, I believe there are a number of variables that go into producing that perfect sun flair that go beyond the physics of the camera. I'm surprised to find that the solar flares weren't more prominent in your crystal-clear, shallow water photos -- at least from what I can see in the images you posted.

Here's a what-if... And let me make something clear. I am one of those underwater photographers who knows the camera from an enormous amount of trial and error and not because of my vast knowledge on the physics of it all... While there's no doubt we have produced some great results at the super-high shutter speeds, I have an inkling feeling that we are overlooking something. What if instead of shooting at high-speed during mid day, we should instead be shooting during the early morning or late afternoon low-light, extreme light angle time of the day at a slow shutter speed with a higher aperture. Some of the more prominent light rays I see while diving are usually during those times.

Anyways... It just a zany thought of mine and one that I'll have to toy around with one of these days whenever I do a twilight dive or an early morning kayak trip. Your thoughts?

I'm pondering the somewhat disappointing (to me) results of the 10.5. It seems to have pushed the sun out to a relatively small part of the frame. Hmmm.  
Rand

Now.. Wasn't it easier when you used to use your 5050?

[MikeVeitch]

Yea Laz i agree with you about the early morning and late afternoon stuff. Much easier to get a good angle of sun at those times as it is coming at a low angle and creates great rays.
Although these are film i think you will agreed the high aperture and slower shutter does create a nice flare.
f16 90/sec
f16 60/sec
f8 250/sec

all 3 at about 8am

I used Nikonos max 90/sec for years and therefore had to shoot early morning or late afternoon so i am excited about trying things during the middle of the day with the new D70. If you look around my site you will see i have a preference for sunburst shots. Alex's tests make me giddy as a little girl when i think of the possibilities.
Can't wait to get the D70 underwater...

[Alex_Mustard]

I completely agree that the environmental conditions also contribute to the sunburst:
A choppy sea state breaks up the nice neat sunball and rays.
A glassy smooth surface with small undulations to refract the separate rays is best, IMO.
Evening and morning light underwater tends to be more dappled and warmer. But the contrast between the bright surface and dark water beneath is more pronounced.
Slightly murky water also helps to show the individual rays better.

Alex

[Detonate]

I'm pondering the somewhat disappointing (to me) results of the 10.5. It seems to have pushed the sun out to a relatively small part of the frame. Hmmm.  
Rand

Maybe you should just let me take that 10.5 off your hands for you.