I'm trying to learn shooting with off-camera flash outdoors. I'm using a Yongnuo YN560 IV flash and YN560-TX transmitter. I'm shooting in Manual on bright, sunny day. I tried using flash as fill to eliminate shadows on one side of a subject's face. Settings: 1/200 SS, f2.8, ISO 125. No matter how much I reduce the flash power the photo is overexposed. I'm assuming I must keep SS at 1/200 for flash sync purposes.
I want to maintain f2.8 to blur background.
What am I doing wrong?
Maybe the picture is already overexposed because of the sunlight? Then you do to the flash settings what you want, and it won't help you. Verify this first.
1/200 with 2.8 ISO 125 seems to be very bright for a sunny day. If you want the aperture open, and cannot go with shorter times because of the flash, you need to find another way to get rid of the extra light. Choose the smallest ISO you have (50?), but that won't help much either, then you need a ND filter (basically a dark sun-glass for the lens front). Make sure your shot comes out well without the flash before adding it in.
I'm shooting in Manual on bright, sunny day. ... Settings: 1/200 SS, f2.8, ISO 125.
Did you look at your meter? It was likely telling you that you were overexposed. Purely on the ambient. If you were shooting in sunny-16 conditions, with these settings, you'd be overexposed by four stops even without the flash. Throw the flash in, and you're overexposed by even more.
With fill flash, you're typically going for settings a stop or two lower than what you'd use for ambient, and then adding in flash to make your subject pop against a darker background.
I want to maintain f2.8 to blur background.
And you've just discovered why off-camera flash shooters will pay more to have HSS capability in their radio triggers and flashes. So they can shoot in bright light with thin depth of field and use a flash. This is one of the main drawbacks to having a cheapie manual-only flash setup that can't do TTL/HSS.
What am I doing wrong?
You're assuming you can use f/2.8 and 1/200s and get good exposure in bright sunlight. :) The problem is that with a manual flash like a YN-560, the 1/200s is a definite hard limit and your ISO is already as low as you can go. So to use f/2.8 you'll have to use some additional gear.
The easiest low-cost fix is to get neutral density (ND) filters for your camera lens. ND filters are like sunglasses for your lens. In this case, you probably need a four-stop or six-stop filter. This will bring the exposure back down into reasonable range, and still allow you to use a wider aperture setting with an 1/200s shutter speed.
You could also get a radio triggering setup that allows for HSS; e.g., a Godox X1T transmitter and a TT600, or a YN-685 and YN-622-TX. But HSS is also a game of diminishing returns—you lose more power than if you used an ND filter setup. But, OTOH, you actually get a faster shutter speed, so if you need to freeze action with a faster shutter speed, HSS will actually work, where an ND filter won't.
Avoid flash! Use photographic reflectors instead.
They provide very minimal harshness to the photo and a perfectly diffused light.
And because you won't be limited by the flash sync speed, you can use a higher shutter speed to allow your aperture to be wide open.
If you want to play further and can buy aditional equipment you can try to reduce the ammount of light entering the lens.
You can use neutral density filter(s) or two polarisation filters for that purpose.
You can stack the grey filters to get appropriate darkening with the same aperture settings (same focal depth). If you use polarisation filters they act like two bright neutral filters when aligned (parallel) but as "dark glass" when perpendicular. The darkening changes linearly with the misalignment.
Original purpose of polarisation filter is to reduce reflections from flat surfaces like water or glass by cropping off the light with different polarisation than the filter is. Drawback is, that the light is filtered by absorbtion. In our case drawback becomes a feature.
As already mentioned, the problem is not caused by the light of the flash itself contributing to the exposure; it's caused by the fact that firing the flash forces the camera to limit the shutter speed to the maximum sync speed - try shooting with the exact same settings (shutter speed, aperture, ISO), but without the flash, and you'll have the same overexposure.
You've got two options:
Here's another approach.
If the problem really is too much light from the flash unit, you can also try putting tissue paper over the flash. This will reduce and diffuse the light. You can use multiple layers until you get a good effect.
The guide number method of setting a flash exposure is primordial. We divided the guide number by the flash to subject distance. The guide number for this flash is 58 for 100 ISO set for use with a 105mm (For this application, OK to use regardless of lens mounted).As an example, flash to subject distance 10 feet then 58 ÷ 10 = 5.8, we set the f/number to f/5.6 (we round).
We can work this math backwards for synchro-sunlight work. Suppose the camera’s automation sets the camera at 1/200 of a second at f/2.8. We find the flash to subject distance by division thus 58 ÷2.8 = 20. This tells us that if we position the flash 20 feet from the subject, the light playing on the subject from the flash equals the sunlight exposure.
Let me add, I think it best if the flash is 1 f/stop subordinate. To accomplish, multiply distance by 1.4. This is the revised flash to subject distance. Thus 20 X 1.4 = 28 feet. This sets the lighting ratio at the “bread and butter” ratio of 3:1.
Published guide numbers are usually based on being indoors. You will need to experiment to find the guide number for this unit outdoor. Try 40.
