Simple strobe question (I hope!) from a simple person..

[stiebs]

OK, I've done the search, and read the threads, and I'm still a little confused. I've done a fair amount of out-of-water photography, both film and digital, however I am in no way whatsoever versed in the art of low-light photography.

I use my Sony DSC-P5 with the Sony marinepack for underwater shots, and as expected, if I'm to be taking any presentable photos I will need to invest in a strobe.

When talking about TTL flashes, does this imply that the camera needs a remote flash connector to be able to use them?

I know I need to use a slave strobe. I understand that the S&S and Ike strobes have a slave sensor, either built into the strobe or as an extra wired (or wireless) add-on.

My understanding of TTL flashes is that they shut off at just the right time. Now, the slave sensor fires the flash at the right time, but does is kill the flash too, or is manual setting also necessary?

The DSC-P5 does not have a pre-flash, so I think I'm OK there.

When it comes down to it, I can buy for example, a Ikelite D-50 with sensor, or an S&S YS-90, and I'll be ready to go. Oh, I'll probably need some mounting gear too...

Am I right, or have I missed out something?

 

[Dee]

With TTL, the camera 'reads' the light needed for the photo and quenches the strobe when that requirement is met.

Personally, I don't care for TTL. I much prefer making my own decisions about exposure settings on a shot by shot basis rather than an umbrella exposure.

I'm not good at explaining technical stuff so Scorpionfish or others can be of more help!

 

[Finesse]

Couldn't have said it any better or clearer !!!

Personally, I don't care for TTL. I much prefer making my own decisions about exposure settings on a shot by shot basis rather than an umbrella exposure.

And I too agree on TTL versus manual .... and with instant feedback with digital you can always retake the shot......well that is if your subject hasn’t scurried off....and If I may add to this when using this "TTL/Automatic mode" ...ambient light, especially at shallow depth, can really screw up your exposure/pictures and “fake out” or trick the strobe and the light it delivers or needs to deliver.

 

[stiebs]

Hmm, OK..

So I think I've got it all under control then. Doesn't really matter what strobe I use, as long as its a slave which is triggered from "seeing" my camera's in built flash.

Ikelite claims on their website that their use of a remote sensor is more reliable than the S&S strobes which (from what I can tell) have their sensor built into the main housing.

Is this a proper description of the two designs, and if so, are Ikelite's claims of superiority properly founded?

My camera housing is clear, so I presume it would be best to diffuse the built-in flash, but still allow enough light to escape from the side of the housing for the sensor to pick up on it?

 

[Dee]

Of course, you can expect Ikelite to make such claims! But there are an awful lot of S&S users, myself included, who are perfectly satisfied. I have read more than a few people discussing ways to improve the Ikelite's sensors ability...altering the diffuser panel to help the sensor 'capture' more of the internal flash is just one. The Ike sensor is a seperate cylindrical shaped piece that is aimed at the housing, picking up the internal flash from the side to trigger it. The S&S YS90DX fiber optic cable is very securely attached over the front of the housing diffuser panel and picks up the internal flash straight on for triggering. I haven't heard of anyone having any trouble with it the S&S connection.

To me, the S&S is a cleaner system in that you don't have to worry about the sensor getting moved and losing the signal. The S&S fiber optic cable coils neatly out of the way and is forgotten about. Although I prefer the S&S YS90DX, the Ikelite is also an excellent product but I don't think their claim to being superior is founded.

 

[JeromeYep]

This S&S vs Ikelite business has been done to death. If you want you can read about it (2 pages worth) in this thread (I think somewhere in between, the members kind of lost the thread a bit):

http://www.scubaboard.com/showthread.php?s=&threadid=13761

Both flashes have their advantages and disavantages - boils down to personal choice and application.

And TTL or not to TTL - boils down to personal choice and application again - TTL can work quite well so lets not scoff at it - some of the best photographs taken by pros are in TTL mode.

Instead, with the P5, you might want to look at how your camera makes an exposure i.e. determins the shutter speed and aperture before and while taking making the exposure before making a decision on what strobe to buy.

Just a few thoughts to keep in mind:
1. The P5 is a full auto camera - so it has to, at some stage, determine what shutter speed and aperture to shoot at. I don't know how the P5 works but a lot cameras in full auto and forced flash mode always fix the aperture and shutter speed according to the ambient light before the exposure begins. And sadly, in low light conditions, the camera picks the slowest shutter speed and/or widest aperture settings...

Keeping this in mind have you considered a continous light source rather than a strobe? Granted you might not get the power of a strobe but some of the lights coming out these days have good colour temperature ratings that might just suit your application.

Might be worth experimenting in low light conditions and observing your exposure data before commiting to a lighting system. I read somewhere that there have been some reports that the algorithm the camera (P5) uses is not good for low light conditions, which is why they sell an underwater video light as an accessory in Japan.

Also a lot of people I know who use the P5 use a continous light source rather than a strobe, and they seem very pleased with it.

2. The P5 gets it's exposure feedback through a sensor in the front of the camera and not through the lens - so whatever the lighting system you choose make sure you don't block it with anything (including those fibre optic cabled slave sensors that you have to stick in front of the camera).

Sorry, probably confused you more... :bonk:

 

[JeromeYep]

Ok, here's a post I found on another forum which might put your mind to ease at least as far as Ikelite goes; it's someone with P5 and a marine pack:

--snip--
Thought you might find this interesting…I have just begun experimenting with a Sony DSC-P5 and Ikelite DS-50 in combination. Couldn't find any of the pictures mentioned but you'll get the idea:

So far I have had it in the pool for an hour, which convinced me that it is essential to block off the internal camera flash. The pool water was cloudy and produced a result just like the classic backscatter shots you see in the textbooks, because the internal flash faces straight ahead. There were unacceptable levels of backscatter for any shot over about 1 foot. Thanks to INUZUKA.m and others I realized it would be very easy to fix. In fact even easier than I thought, I just taped black cardboard over the flash itself (so it could go inside the housing). I took pictures above water in a dark-ish room with the flash on (but taped) to convince myself that I had essentially eliminated any light output from the flash.

Next thing I wanted to convince myself of was that the slave would still fire with this arrangement – it did – the sensor is extremely sensitive even on Minimum. Then I wanted to convice myself that the DS-50 in combination with this camera was indeed handling the TTL exposure. It definitely IS. I have posted some samples below. The last 4 shots show this

1. DS-50 in TTL mode, internal flash on but taped off
Looks great!
2. Strobe OFF, internal flash on but taped off
Good, no light from flash.. should eliminate the backscatter
3. Strobe in Manual mode, internal flash on but taped off
Way overexposed! Proves the TTL is working
4. Strobe OFF, internal flash untaped
For reference

Thanks Ikelite. The strobe works great with this camera.
--snip--

This would be similar with the DS125.

 

[stiebs]

Thanks for the info Jerome

I'm certainly not looking for a S&S vs Ike debate. It hasn't taken me very long to figure out that there are a number of posters here that just love waiting for a gear debate to crop up.

Personally, I like the look of the S&S ones better, and my LDS stocks them. (But they don't seem to know a great deal about them. Or to be fair, they don't know a great deal about using them with digital cams :think: )

Anyhoo..
The information that you've given me is exactly the stuff that I haven't been able to find out. Very useful. In above water low light, the camera seems to like f2.8 at 1/40, not matter what exposure level or ISO I choose. I must admit that I haven't recorded its thoughts underwater, and I've only taken it out 3 or 4 times.

Maybe a strobe complimented by a continuous light source to fool the camera? Or will the two light sources interfere with eachother too much? (Besides, I didn't really want to buy two lights, and I don't think my UK400 will suffice for photography)

 

[stiebs]

You must have posted that snipped post as I was typing my other reply!

Now... that's exactly the sort of story I was after! Maybe if I was a bit more serious about my photography then the P5 is not quite the answer I am looking for. But for my hobbyist intentions looks like the DS-125 or YS-90. But taking the wallet into consideration, maybe the DS-50 or YS-60 will have to do :ko:

 

[JeromeYep]

Froop,

OK, borrowed my girlfriend's camera and did a few quick tests in low light
conditions. We can then reverse engineer and see how the camera works:

The aperture range of the lens is 2.8 - 5.6 (surprisingly short range but it's
not rated as a fast lens and the DOF for digital cameras are quite good compared
to film cameras)

The F4.5 is the widest aperture it could open at that focal length I used - I tried to
keep a distance and use a subject similar in size to what you would do
underwater.

The photos with Forced Flash OFF had this data:

F4.5 1/30; Auto ISO 250
F4.5 1/30; +2.0 EV; Auto ISO 320
F4.5 1/80; -2.0 EV; Auto ISO 160
F4.5 1/30; Force ISO 100
F4.5 1/40; Force ISO 400

Increase the ambient light:

F4.5 1/80; Auto ISO 120
F4.5 1/100; Auto ISO 100


From the the data I think we can conclude that in low light conditions the P5:
- uses the widest aperture at that focal length;
- tries to do a shutter-priority type exposure: so it tries to keep the fastest
speed possible and won't go below 1/30;
- and does a balancing act with the ISO value if it is set to 'Auto' i.e. increases it if the shutter speed is slow;
- if you use the exposure compensation it changes the shutter speed and ISO to
compensate but leaves the aperture wide as possible; and
- if you force the ISO it just varies the shutter speed to get the correct
exposure.

Ok, the interesting bit: Forced Flash ON

F4.5 1 1/60; Force Flash; Auto ISO 100
F4.5 1/60; +2.0 EV; Force Flash; Auto ISO 100
F4.5 1/80; -2.0 EV; Force Flash; Auto ISO 100
F4.5 1/60; Force Flash High; Auto ISO 100
F4.5 1/60; Force Flash Low; Auto ISO 100

And increase the ambient light:

F4.5 1/80; Force Flash; Auto ISO 100

Hmmm...

- throws open the aperture as WIDE as possible;
- locks the ISO to 100; and
- and varies the shutter speed with 1/40 the slowest shutterspeed for forced flash and synchro

Notice how it doesn't change the exposure setting even if you set the flash to High or Low - just makes the image brighter or dimmer. My guess from that is that it's controlling how long and not how much it fires the flash. Interestingly, it uses the duration of the normal intensity in high or low, and since the aperture, shutter and ISO are the same, it results in a brighter or darker image. It's the camera's way of saying 'OK, if you set me to high or low intensity you must be trying to manually force more or less light into the picture RELATIVE to taking an AUTO exposure with the flash intensity set to NORMAL'.

If you cover the photocell window on the front of the camera and take a picture with the flash it takes a darker image BUT doesn't change F, Shutter or ISO - so it must be varying the flash output duration.

Strange thing is it takes a darker image - thought it'd be the opposite - the flash would do a 'full dump' and the image would be over exposed.

So, what will it do with an external slave strobe? I can only guess with the data that (I stress on GUESS):

- it will use the widest aperture possible;
- use ISO 100 unless forced to another setting;
- set a variable shutter speed according to the ambient light; and
- vary the duration of the flash to get the correct exposure

So if you have a TTL capable strobe and slave (like the Ikelite DS series) the camera will do the above. The internal flash will tell the the slave to fire the slave strobe. The camera will vary the duration of the internal flash and the photocell window will monitor the amount of light coming back from the subject. When the cell thinks the correct exposure has been reached it will quench the internal flash, consequently the slave will quench the external strobe. The cell doesn't know or care which flash or strobe the light is coming from - it'll just quench the internal flash when it thinks the correct exposure has been reached for an AUTO exposure with the internal flash set to NORMAL.

What happens with a manual slave strobe (like the S&S, Inon and to some degree the Ikelite)? The events are exactly the same upto the point where the cell will quench the internal flash when the correct exposure is reached. But because it's in manual mode the slave won't quench the slave strobe. The problem occurs when you dump too much or too little slave strobe light (using the manual power settings) for that exposure setting.

Too much power: The photocell says enough light has been received and quenches the internal flash, but because it's not TTL the slave sensor won't quench the slave strobe. It just continues to dump the amount of light it has been manually set to deliver. And your picture is over exposed. So you say why doesn't the shutter close and prevent over exposure? The strobe will dump all the light it's set to deliver in less time than when the shutter is open to ensure shutter/flash synchronisation. That's the only way it ensures that the entire frame receives the light evenly when the shutter is open. To give you an idea a 100 watt strobe will deliver 100 watts of power (it's full power) in about 1/300s.

Too little power (presuming you have the internal flash blocked to avoid back scatter): the amount of light bouncing off the subject isn't enough and your picture is underexposed.

So in manual slave mode you control the intensity (power) of the slave strobe for a particular exposure setting and not the camera controlling the duration of the flash.

Conclusion:
TTL or not to TTL:
From the above data we can presume the P5 will work with a TTL or manual strobe. What you choose depends on personal preference. My advice is don't ignore TTL - especially if you're a beginner. Taking good photos in manual takes practice and skill - and that digital advantage of seeing the result immediately - good tool for learning quickly - but useless if that shy, once-in-a-lifetime critter you were trying to shoot has vanished and all you got was whiteness (or blackness) because your manual setting was incorrect or you took too much time to setup! If you choose the path of manual then make sure you have finer power increments, like the Sea and Sea YS90 - though some people claim 1/8, 1/4, 1/2 and full of the Ikelite DS125 are sufficient. With the Ikelite you can get manual slaves that will allow you to dial up finer increments even if the strobe itself doesn't. Who knows, Ike may even come out with a slave that does both.

TTL or manual aside choose a strobe that will give you enough power for your application (read the specs please - not the strobe model number). Choose a strobe that gives you the angle of coverage for your application. Choose a strobe that has the colour temperature for your application. Choose a strobe that will allow you to expand should you upgrade your camera (preflash compatiblity etc.). Cycle time - the Ikelite recharges in 1s - faster than your internal flash will - so there's no real issue there. Battery life - how many flashes per charge. Ofcourse price will also be a consideration. I look at strobes as a long term investment - so spend wisely.

Another important feature I consider is an aiming light - specially if you're a beginner. Ok, you can strap a UW light on a strobe that doesn't have one - but do you really want to if you had a choice of an integrated one....?

What is a bit of concern here is the P5 itself - the fact that it is full auto and tends to set the widest aperture available and slow shutter speeds of 1/60. Apart from that it's a great camera - small, easy to use and stylish (including the marine pack).