Flash on overcast day with ND Filter?

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torque22

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Have had a few issues where i take a shot on overcast days (totally overcast, low light) and have used flash with a diffuser close up portrait, head shot.
Due to being so close to the subject 24-105 @ 70mm with 1.3 crop, the flash slightly overpowers the image.

I have read some vague reports of people using an ND filter to eleviate this but i am not familiar with this process.:thinking:

Anyone care to explain this in detail.
 
It's not a technique that I've heard of but I would have thought that the flash will use more power to create the same amount of light (I assume you are using TTL and so it is calibrating on a pre-flash)
 
grumpybadger said:
It's not a technique that I've heard of but I would have thought that the flash will use more power to create the same amount of light (I assume you are using TTL and so it is calibrating on a pre-flash)
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Yes, i sort of agree.
but this process does appear to exist and i have only read vague comments about it, and would like to know more info.

The flash can only out put to a certain max power, but i think its the reflected light from being so close to the subject that causes the problem. The ND helps elimante more reflected light than the flash compensates for from the ttl metering or somthing like that....I don't know.

Thats why I am asking.
 
i have only done this by mistake, wasnt an ND was a CP filter, and this was the result, lens was 17-40 cant remember the focal length but it was close.

0601-145032-01.jpg
 
Soz - but the explanation sounds daft

You're just mixing ambient and flash - if you want the ambient to record slightly darker then a true exposure yet with the flash correct, then that's called 'dragging the shutter' - is that what you mean? It's easiest to use manual settings on both camera & flash, but you could try dialing-in more flash comp.

:shrug:

DD
 
DiddyDave said:
Soz - but the explanation sounds daft

You're just mixing ambient and flash - if you want the ambient to record slightly darker then a true exposure yet with the flash correct, then that's called 'dragging the shutter' - is that what you mean? It's easiest to use manual settings on both camera & flash, but you could try dialing-in more flash comp.

:shrug:

DD
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Its not an explanation, I have read vague reports about this process and want somone who understands it to explain it to me.

The ND helps elimante more reflected light than the flash compensates for from the ttl metering or somthing like that....I don't know.

Thats why I am asking.
 
I'm with DD on this. It makes no sense to me either. You stick an ND on and everything gets darker. You then have to correct for that by increasing the camera exposure for the background and/or boosting the flash and you're back to square one - or you get an underexposed image. If you want the flash to be less prominent then dial it down, but you will have to pick up the slack by increasing the ambient exposure. I can't see how an ND would help at all.

Where an ND might help is when you have bright conditions and want a shallow DOF but can't use or don't want a shutter speed faster than your sync speed. The ND will tone down the ambient, allowing you to open up the aperture without overexposing the background, and the flash will not be affected.

Maybe the clue was when you mentioned a diffuser. That does make sense. Take the flash off camera and/or add a softbox or bounce off a reflector/umbrella/ceiling/wall to get a soft light or less hot-spotty light.
 
You can get sets of Sunpak filters for the 444D / 30DX / 622 era flashguns. Included are ND and wide angle diffusers, both of which will cut the flash output when on a manual setting, which only goes down to 1/16th of full power with the small flashes.

Many current flashguns have a wide angle diffuser built in, so try that to cut the output before tracking down a filter kit or gel.
 
tdodd said:
I can't see how an ND would help at all.

I agree, but I have read vague comments about this on forums and want somone to explain it to me

Where an ND might help is when you have bright conditions and want a shallow DOF but can't use or don't want a shutter speed faster than your sync speed. The ND will tone down the ambient, allowing you to open up the aperture without overexposing the background, and the flash will not be affected.

I know this already

Maybe the clue was when you mentioned a diffuser. That does make sense. Take the flash off camera and/or add a softbox or bounce off a reflector/umbrella/ceiling/wall to get a soft light or less hot-spotty light.
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My question is not about off camera flash, I would like somone who knows of this process involving ND and flash to explain it to me, thats all.

Wish I had never asked the damm question.
 
I wasn't trying to be smart or anything but just explain the rationale for why it makes no sense to me. I imagine the reason nobody else here has explained it so far is because it doesn't make any sense to anybody here - yet.

Perhaps it would help if you could post some links to sites where you have seen this discussed. It would seem logical that that is the place to look for more answers.
 
Another aspect is that the flash metering (if used) won't work for extremes (close range, wide aperture, high ISO) and the conditions may also be outside the performance envelope for the flashgun even if used manually. Although torque22 says the conditions were dim, high speed sync may still have been required.

An ND lens filter would help when a wide aperture is used and the lowest ISO available results in a shutterspeed that's too high, reducing the available flash range; or the minimum flash output is too great when the subject is at close range. The flash could (should) also be taken off-camera.
 
As photon says, the first thing you want to be doing is taking the flash off the camera and use it in manual mode not ttl. You can then vary the distance between subject and light source and adjust the flash output manually to get the desired effect.
 
Nothing to do with the use of ND filters on flash or lens, but note the behaviour of this Canon flashgun:

In bright light, above EV 10, the 430EX provides automatic fill-in flash in Full Auto and P modes. In dim light, EV 10 and below, the flash provides the main light in Full Auto and P modes (the background may be dark). Av, Tv and M modes deliver automatic fill-in flash in any light, even at night (slow sync mode). Slow sync results in a natural balance between ambient light and flash.

If torque22 could let us know the equipment used, settings and conditions in as full detail as possible we could suggest workarounds.
 
My main reason for this post was to find out if anyone knew of the process using an ND filter and Flash in low light. If they did, could they explain it and outline the pro’s and con’s of this method.

Here is a scenario where the use of ND and flash is supposedly the solution.
Overcast day (low light), subject is moving about having fun with wind in her hair.
Using 40d hand held, 24-105 set at about 60-90mm with 580EXII. The required shots are full face close ups and head/shoulders.
 
The 580EX has a guide number of 58m at 105mm zoom and 100 ISO. Given your crop factor we'll assume the flash stays zoomed out to 105mm for all your shots. Given the lens you have I'm assuming f/4 as your aperture. That brings down the flash effective distance to 58/4 = 14.5m. I guess you're shooting at a range of about 2m, so at full strength the flash will completely overpower the subject. At 1/4 power the flash effective range will drop by half to 7.25m. At 1/16 power that will halve again to ~3.6m. At 1/64 power that will drop by another half to 1.8m. You're now roughly in the right zone. If your shooting distance is less than 2m then that's OK because at 1/128 power the effective range will be only 1.3m. If that's still too strong then manually zoom the flash to less than 105mm and you will spill light out further to the sides, out of shot, and just weaken the effective range further.

If you put any kind of modifier over the flash (apart from a Better Beamer) then of course it becomes weaker still. If you close down below f/4 then the flash also becomes weaker.

Is your problem that the flash is overpowering the subject or that you are getting hotspots on cheeks, nose, forehead etc.? If you post a sample image with EXIF intact I'm sure people could offer some suggestions. Whether they include the use of an ND filter, graduated or otherwise, I couldn't say, but certainly the ability to control the flash intensity is completely within your grasp, with or without filters..
 
Thank you for the well structured in depth reply and offer of help.

It’s nice when people offer work a rounds other than just saying your question is daft.

My question is still unanswered in as far as no one can explain the process of using ND with Flash in low light situations. Just to clarify once more, the ND would be fitted to the lens not the flash.
 
I guess you can have an "overcast" day where the sky is still killer bright, relative to the land, so a graduated ND filter will take the heat out of the sky, allowing you to then balance the ambient light to manageable levels. Here's an example where the sky was overcast, yet to hold the detail in the sky I had to severely underexpose the foreground. I did not have an NDG filter.

20071130_112150_0405_DPP.JPG


Here's how it looks when adjusted in software simply to give an exposure boost to approximately get the exposure OK for the foreground. When I did this in camera the sky was completely blown.

20071130_112150_0405_DPPa.JPG


Now I didn't need flash for this shot, but a graduated ND would have evened out the ambient light to make the exposure for this picture far easier to manage. the wiggly horizon is a bit of a killer for using an NDG but hopefully the example is made, nonetheless.

This isn't a great scene into which to plant a model to be lit by fill flash, but assuming that is what you wanted to do, with the ambient light better balanced between land and sky, you are then free to use the flash as you like to balance the lighting of your subject with the background. If you didn't have an NDG for this shot, and lit a model with flash, you'd end up with bright sky, miserably dim middle ground, and a well lit model.

So at the end of all that, I don't think there is any special technique or trickery in play. It is just a question of first sorting out the ambient conditions and then sorting out your subject and his/her/its lighting.

Then again, perhaps I have completely the wrong end of the stick. You did say initially you were using a 1.3X crop body, which I took to mean a 1D something or other, but now you say it is a 40D, which is a 1.6X cropper and probably puts you a bit further from your subject then I first estimated, so comfortably 2m rather than anything less. You've also sometimes said ND Grad and other times just ND, so I'm not really clear on what filter you are talking about. If it is a grad and goes on the lens then you're going to have a rather odd gradation of the flash light, with the top of the head lit less well than the chin/neck/chest etc.. It all seems very odd to me. If you were shooting from above your subject then I could understand why you might need a gradient on the flash illumination, so that the head/face, which is nearest the flash, is dimmed, and the body, which is further away, gets the full flash with the clear glass. But really I'm just guessing wildly here. A sample picture showing the problem you have at the moment would help, as would some links to these places where you have seen the technique mentioned.
 
tdodd said:
.......but certainly the ability to control the flash intensity is completely within your grasp, with or without filters..
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Probably the most useful (and concise) answer on this thread. tdodd has given a very frank and informative reply but I can only re-iterate what he stated above, you can control the output as long as you put some thought into it and as such you don't need to use ND filters.

torque22 said:
My question is still unanswered in as far as no one can explain the process of using ND with Flash in low light situations. Just to clarify once more, the ND would be fitted to the lens not the flash.
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I thought the problem was clear in your first post:

torque22 said:
.......Due to being so close to the subject 24-105 @ 70mm with 1.3 crop, the flash slightly overpowers the image.
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You've had plenty of helpful replies which in my opinion give good advice to help you take pictures without the flash overpowering the image but you appear to be dismissing them. :shrug:
 
Seems the word 'daft' caused annoyance - so apologies, it was the wrong word to use

Having read the rest, I'm still not sure what you're after :shrug: so again, apologies

I often use flash & ambient light, underexposing the ambient to then use flash at the 'correct' exposure giving a darker than appeared at the time background, but still recording detail to record venue, etc.

But soz, I'll have to bow out here as I just don't know what you're after - however, you presumably read it somewhere??? So perhaps a link would help stop me being a thicky and answer the 'damn question' !!!

DD
 
A brief article by someone who has used ND filters when flash is used, both on the lens and the flash: http://www.geocities.com/cokinfiltersystem/gray_nd.htm

From the quote in my post #16 we might expect the 580EXII to also produce a deer trapped in the headlights result in dim conditions on Full Auto and P settings (I've no personal experience of Canon gear) and the range could be under a metre with 60mm focal length, which may be outside the design envelope for the camera/flash metering combination and I would think overexpose with all other settings. At that range, manual settings would offer no advantage - they are just a limited set of the flash's overall capabilities. The only options are to increase the flash-to-subject range or reduce flash output sufficiently with a filter or other modifier.

In bright conditions at less close range, an ND filter on the lens can be of value when wide apertures are used on cameras with a lowest ISO limited to e.g. 200.
 
torque22 said:
Just to clarify once more, the ND would be fitted to the lens not the flash.
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Not clarification. You don't mention it's a grad until post #12 just ND and you don't mention it is fitted to the lens not the flash until this post. I wonder why people are struggling to understand what you are asking? :cautious:

If it is a grad then I guess you can fool part of the metering as it will be expecting an even response.

Tell you what, I'll make a note to remember not to try and be helpful to you in the future unless I 100% understand the answer to a question you haven't clearly asked.
 
I think the answer he is after is that the ND will reduce some of the ambient, and the flash provide the lighting for the main subject.

22 - don't foget that anything beyond the range of the flash will not be illuminated at all by the flash. So even trees/hedge whatever, if they are beyond the range of the flash setting you won't get any lighting effect on them from the flash, UNLESS they are very reflective, like sheet metal (car, motorcycle chromeowrk etc.)

Use the ND to tone down areas, use the flash to light other areas - maybe just the persons face - so hit the face with just enough flash and no more, the rest will gradually dim out like a vignette due to the ND effect.

DD was right - she basically said the same thing, just not in so many words! Ambient is being reduced (underexposed by a tad - whether by settings or use of an ND filter the effect is the same) and the flash is being used to pop the subject.
 
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