Importance of auto-off on focus light?

I have determined that I should add a focus light to my camera rig.

I have read what articles I can find on the subject. All the articles recommend using a focus light (for the kinds of shooting I'm doing - normally, CFWA). But, none of them even talk about the feature that I see on some focus lights - where they automatically turn off when the strobes fire.

Is that feature just not important?

My thought is that if my focus light doesn't turn off, I'm going to (very often) have annoying backscatter showing up in my photos.

I also wonder how does the auto-off really work for people (like me) who are generally shutting in full manual mode? There is no strobe pre-flash, so would the auto-off actually do anything for me at all? Is that why so many focus lights don't seem to have an auto-off? Because it's useless for people shooting full manual (as I think most serious u/w photographers do)?

Some stuff that I read seemed to boil down to saying that I should use a focus light and that it would be so low power, relative to my strobes, that whatever it is illuminating won't really show up in the picture. A couple of articles said that if the focus light was creating a hot spot in the picture, turn up the shutter speed and turn up the strobe power to "drown out" the focus light.

My issue with that is that i usually set the aperture for my desired FOV, then the shutter speed to achieve the color of background that I want. I start with ISO set at its lowest. If the shutter speed ends up being too slow (for moving subjects, like sharks), then I increase the ISO and the shutter speed, in order to eliminate motion blur while preserving background color.

It seems like the advice regarding eliminating a focus light hot spot or backscatter will potentially throw off my ability to get the background color I want. I turn up the shutter speed and lose the backscatter, but the background goes dark. If I turn up the ISO, then the background comes back, but so does the hot spot or backscatter.

So, I'm back to wondering if I need a focus light with auto-off. And, if I do, will that require me to shoot TTL (to have a pre-flash) in order to actually make the auto-off work?

My favorite handheld dive lights have multiple brightness settings, so I can use one set to a pretty low output (200-ish lumens?). Or brighter, of course. And, they have a threaded hole (1/4-20? whatever is the standard tripod screw threading) on the underside of the body. I think I could mount one to my housing pretty easily. Maybe that's really all I need? No auto-off, but that's not a problem?

Thanks for any insights y'all can share on this.

This is a very good topic. I think the purpose of a focus light is to help you focus and depending on the camera you have this can be achieved most times without a focus light. With my current and past camera the camera will refuse to shoot with auto focus once I past the -3 Ev before then it would somehow focus or I would manual focus and use live view boost and shoot

However some cameras do a poor job at focussing and they need some help. Lately I have not been diving at all with a focus light as when I use autofocus either I have enough space or enough light and in those cases where I do not have that I use the strobe focus light that does have auto shut off and the focus light has a 40 degree angle so at least one of the strobes will be vaguely close to the subject to help the camera focus

If you use a focus light you just have to bring the camera to the point of focus which can be at -2/5 Ev this does not help black background situations unless you ca fire at 1/2000 then it does not matter anymore. Besides camera that struggle to focus tend to be compacts that can give you those speeds

I guess I might add, I'm shooting an Olympus OM-D E-M10 (yes, an old camera), the kit 14-42 lens, and a Nauticam WWL-1, with 2 x Inon Z240 strobes.

Often, I'm shooting sharks, inside a wreck, so it's dark (though you can see outside water in the shots through holes in the wreck).

I have thought about using the strobe focus lights, but they don't turn back on after the shot. I don't normally have time to keep turning them back on after every shot.

Also, I think that not only will a focus light help the camera, it will help me. Often, the image on the camera display is so dark that I can't tell with any real precision exactly what the composition is or exactly what spot it's focusing on. I'm thinking that a focus light will brighten up the image shown on the LCD display.

Regardless, the question from my OP remains: Is the auto-off feature on a focus light important for me to have? I *think* it's not, but I'd like to get some confirmation from someone who actually knows. I'm an amateur hack, at best, and I may be wrong in the way I have thought it through.

I use focusing lights while scuba diving and doing photography mainly for night photography and have not noticed an adverse effect from the light in my pix. I do tend to keep the brightness level of the light down but that is to get at least an hour of lighting.

I also use focusing lights for my salmon photography when it is dusk. This does help with focusing with DSLRs as they reach a point where focusing is not possible due to low light. As well focusing becomes slower when they become light-challenged. This point can be detected if I forgot to turn off focus assist in the camera menu (done this a couple of times!) as the "pilot" light will come on (Seacam strobes).

The "focus" light on your strobe is of little use as it has a narrow beam and one of the first rules of UW photography is don't point your strobe at your subject. Your focus light does not need to be very bright at all, I find a 350 lumen INON UW torch does a good job and with that low power level it's quite a few stops under you main exposure s just does not show up in the image. I have used such a ight mounted to the cold shoe with both the EM-5 Mkii and EM-1 MkII and it just works,

The "focus" light on your strobe is of little use as it has a narrow beam and one of the first rules of UW photography is don't point your strobe at your subject. Your focus light does not need to be very bright at all, I find a 350 lumen INON UW torch does a good job and with that low power level it's quite a few stops under you main exposure s just does not show up in the image. I have used such a ight mounted to the cold shoe with both the EM-5 Mkii and EM-1 MkII and it just works,

So, even with a lot of particulate in the water, it doesn't show up as backscatter in the image because of how little light the focus light is actually putting out?

I have no experience with a focus light without turn-off function, but what I can say is that when I turn the light off my Em5 has much bigger problems to focus when shooting macro. I use a Weefine Smart Focus 3000 (but any of the smart focus series would be ok) and I only use the red light mode as to not disturb or scare the animals. I only shoot in manual, but I've never had a red spot in my images. I assume that the detection is extremely fast and therefore the light turns off before exposure begins or at least within such a short amount of time, that the light doesn't affect the exposure.

I have no experience with a focus light without turn-off function, but what I can say is that when I turn the light off my Em5 has much bigger problems to focus when shooting macro. I use a Weefine Smart Focus 3000 (but any of the smart focus series would be ok) and I only use the red light mode as to not disturb or scare the animals. I only shoot in manual, but I've never had a red spot in my images. I assume that the detection is extremely fast and therefore the light turns off before exposure begins or at least within such a short amount of time, that the light doesn't affect the exposure.

I assume you are also using 1 or more strobes. So, maybe the auto-off IS so fast that that is why it doesn't affect the exposure. OR, maybe it's what I postulated above. The strobe(s) are so much brighter than the focus light that even though the focus light may be on during the exposure, it is completely drowned out by the much brighter strobe(s) and that is why you don't have a red spot or red tint in your photos?

And that is really the gist of my original post. Is auto-off of any use for people shooting on full Manual? Or will 2 lights, one with auto-off and one without, both yield exactly the same results (presuming both have the same output)?

Hey Stuart

Like many, I use a focus light sometimes when shooting macro with a Nikkor 105mm on an DX (so, crop frame) camera. Although the focusing on a D500 is very good, the light defintely helps in low light situations.

I've had two focussing lights: a Fixeye which definitely switched off when the strobe fired; and now a Sola Photo 800. Slightly embarrassingly I have no clue whether that switches off or not. The light from it can't be seen though in the images.

As for backscatter, generally focus lights are only used for macro so backscatter isn't an issue. So you are right, as Chris points out, the output is quite low anyway - nothing like the "blast" of light that a strobe emits and lights up particulate in the water column.

If you are shooting macro and the lens is struggling, a focus light really helps.

The "focus" light on your strobe is of little use as it has a narrow beam and one of the first rules of UW photography is don't point your strobe at your subject. Your focus light does not need to be very bright at all, I find a 350 lumen INON UW torch does a good job and with that low power level it's quite a few stops under you main exposure s just does not show up in the image. I have used such a ight mounted to the cold shoe with both the EM-5 Mkii and EM-1 MkII and it just works,

It becomes 40 degrees the field of view of a long lens is 20-30 degrees the focus light of the strobe will still increase brightness of the scene and make you shoot in fact one of the classic one strobe positioning is right on top of the port aiming forward straight in front

Moreover when you are really close and that is when your camera fails to focus you can aim the strobes to subject and there is no problem either

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As for the first question, whether the feature is important, I'd say "sometimes". I have a few pictures from a night dive, not macro, where I've used a red focus light and there are traces of red light in the picture. Not that disturbing, but you can see it at least if you know it's there.

I don't have the pictures here (am at work), but it's likely they are taken at a notably wide aperture. Stopping down might have helped.

certainly there are situations where you could make use of the focus light when shooting macro, however the OP specifically mentions CFWA where it may present some issues .

I'm also sure you could get the focus light to show if for some reason you shot high ISO and/or wide aperture, but that's not a normal situation in UW photography where the strobes are set to overpower ambient light. It could be an issue for example shooting a small sensor compact at f2 (quite common in such cameras like theTG5), but on a m43 I would think you'd mostly shoot around f8 at least if behind a dome port.

The explanation as to how the light is able to switch off is that the duration of the strobe exposure is much shorter than the shutter speed which sets the ambient light exposure. So if the light turns off for say1/8 of a second after receiving the signal to shut down, likely the light is only present for something around the duration of the strobe exposure, so a very short time compared to the total time the shutter is open.

Frankly it is almost impossible not to be able to focus with the WWL-1 and the 14-42

The WWL-1 makes the lens 5mm equivalent if you set it to focus manually at 20 cm you can do the entire dive without ever focussing again...

There is totally no need to use a focus light with a wide lens to shoot sharks inside a wreck as he does just focus on your hand set to manual and fire away

Unless you change the focal lenght drastically the WWL will make the camera take sharp pictures for the whole dive

The only situation where I can see an issue is long focal lengths of super small subjects clearly if the op prefers to focus each time then a focus light in a dark environment will be required and as you don't have black background the strobes will over power it as long as it is not red colour.

Furthermore if there is backscatter the focus light will make things worse and the camera go and focus hunt on the particles

certainly there are situations where you could make use of the focus light when shooting macro, however the OP specifically mentions CFWA where it may present some issues .

 

I'm also sure you could get the focus light to show if for some reason you shot high ISO and/or wide aperture, but that's not a normal situation in UW photography where the strobes are set to overpower ambient light. It could be an issue for example shooting a small sensor compact at f2 (quite common in such cameras like theTG5), but on a m43 I would think you'd mostly shoot around f8 at least if behind a dome port.

 

The explanation as to how the light is able to switch off is that the duration of the strobe exposure is much shorter than the shutter speed which sets the ambient light exposure. So if the light turns off for say1/8 of a second after receiving the signal to shut down, likely the light is only present for something around the duration of the strobe exposure, so a very short time compared to the total time the shutter is open.

With the crop factor of 2, I usually set up for CFWA with an aperture of 4 - 5.6, to achieve a DOF equivalent to a FF camera set at f/8 - f/11.

Regardless, what you're saying makes sense and is right in line with what I was thinking from my other reading.

The comment about the auto-off, though, is not making sense to me. The auto-off lights I'm talking about are ones that have an optical sensor to detect when to shut off. They detect a pre-flash and turn off for around 1 second. I can see how that would work. But, if you're shooting in Manual and there is no pre-flash, then it would be the actual flash that would trigger the focus light to turn off. Except, at that point, it's probably too late, isn't it? I'm guessing that a $99 focus light is not going to have fast enough electronics to turn off during the main flash event quickly enough that it doesn't affect the exposure at all.

Or is turning off right when the strobe fires (presuming a front curtain sync) quick enough to take the focus light out of the equation for exposure of the background?

Re-reading your post, I think that is what you're saying. The auto-off would mean the focus light turns off while the strobe is dumping, but then stays off for the duration of the time the shutter is open, and that is enough to eliminate any real concern over it creating backscatter. Yes?

Frankly it is almost impossible not to be able to focus with the WWL-1 and the 14-42

 

The WWL-1 makes the lens 5mm equivalent if you set it to focus manually at 20 cm you can do the entire dive without ever focussing again...

 

There is totally no need to use a focus light with a wide lens to shoot sharks inside a wreck as he does just focus on your hand set to manual and fire away

 

Unless you change the focal lenght drastically the WWL will make the camera take sharp pictures for the whole dive

 

The only situation where I can see an issue is long focal lengths of super small subjects clearly if the op prefers to focus each time then a focus light in a dark environment will be required and as you don't have black background the strobes will over power it as long as it is not red colour.

 

Furthermore if there is backscatter the focus light will make things worse and the camera go and focus hunt on the particles

Ah ha! Now THAT is some great info!

But, let me make sure I understand. During a typical dive for me (shooting sharks and wrecks) the distance to my subject (from the front of the lens) might be anywhere from, say 2 feet (~50cm?) to 10 feet (3 - 4m).

Are you suggesting that setting the focus manually to 20cm is going to give me truly sharp results over that whole range? For the sake of discussion, let's just assume I set an aperture of f/5.6.

i have never tried shooting with Manual focus. If that would work, that would be great. Eliminating focus lag and out of focus shots is the whole reason I was looking at getting a focus light.

 

Ah ha! Now THAT is some great info!

 

But, let me make sure I understand. During a typical dive for me (shooting sharks and wrecks) the distance to my subject (from the front of the lens) might be anywhere from, say 2 feet (~50cm?) to 10 feet (3 - 4m).

 

Are you suggesting that setting the focus manually to 20cm is going to give me truly sharp results over that whole range? For the sake of discussion, let's just assume I set an aperture of f/5.6.

 

i have never tried shooting with Manual focus. If that would work, that would be great. Eliminating focus lag and out of focus shots is the whole reason I was looking at getting a focus light.

This video has been taken focussing only once with the same lens as yours

https://www.youtube.com/watch?v=cxdPDUFrEQs

When you set your focus at one foot (not from the top of the WWL but from the top of the port so say 20 cm) then switch to manual focus anything between 20 cm and infinity will be in focus anyway there is very little difference between f/5.6 f/8 etc it only extends the focus right to the front of the glass just dont exceed f/11 as optical quality will drop due to diffraction

With the Z240 you can shoot at f/8 and iso 200 the sharpness is at its best and literally everything will be sharp

 

 

This video has been taken focussing only once with the same lens as yours

 

https://www.youtube.com/watch?v=cxdPDUFrEQs

 

When you set your focus at one foot (not from the top of the WWL but from the top of the port so say 20 cm) then switch to manual focus anything between 20 cm and infinity will be in focus anyway there is very little difference between f/5.6 f/8 etc it only extends the focus right to the front of the glass just dont exceed f/11 as optical quality will drop due to diffraction

 

With the Z240 you can shoot at f/8 and iso 200 the sharpness is at its best and literally everything will be sharp

Nice!

Thank you very much. This is great!

That video is awesome, by the way. I wish i could get that kind of ambient light and viz when I dive with the NC sand tiger sharks...

Anyway, one last question. I will need to preset my camera's focus before I put it in the housing. Doing that on dry land, what distance should I set the focus to? I imagine that 20cm under water, behind the WWL-1, translates to a different distance on land, with only the kit lens and no dome.

Someday, I will upgrade to a better camera and a better housing. But, for now, I have a Meikon housing and I cannot adjust the focus once the camera is in the housing.

 

Nice!

 

Thank you very much. This is great!

 

That video is awesome, by the way. I wish i could get that kind of ambient light and viz when I dive with the NC sand tiger sharks...

 

Anyway, one last question. I will need to preset my camera's focus before I put it in the housing. Doing that on dry land, what distance should I set the focus to? I imagine that 20cm under water, behind the WWL-1, translates to a different distance on land, with only the kit lens and no dome.

 

Someday, I will upgrade to a better camera and a better housing. But, for now, I have a Meikon housing and I cannot adjust the focus once the camera is in the housing.

I do it in water as the wwl is not a land lens

You dont need manual focus ring

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Focus in water on your hand fin etc is best then switch to manual or start in manual with push on

I do it in water as the wwl is not a land lens

You dont need manual focus ring

 

 

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Got it. Great. Thank you!

If you have the capability use back button focus, you can normally assign that to one of the function buttons, then you have the best of both worlds. Use the function button to focus then don't touch it again till you need to. That way if you find a subject that's really close you can focus on it if need be.