Need help with TTL!!

[CThomas817]

So I have been doing portrait photography for a few years, either natural light or in studio with strobes. I recently ventured out to expand my services to event photography, and oh man I am struggling with TTL. I'm on a Nikon D850 and I use an SB900 with a Gary Fong Lightsphere diffuser if ceilings are not low enough to bounce. I've tried both TTL and TTL BL and my images are always several stops underexposed, so even exposure comp is not enough. I end up manually setting exposure for every shot as I make my way around the event and it's so time-inefficient.

The pre-flash is going off so I would think it's getting the exposure reading but ‍. Any advice would be great.

 

[Derrel]

The first thing I would suggest: switch the flash to A mode. pick an ISO level and an f-stop on the flash. Set the same f-stop on the lens. Pick an ISO such as 400,do your shot and,if needed, change either the ISO or the f-stop to get the correct exposure. This is a much older method that predates TTL flash control.

 

[Soocom1]

What your describing is the effect of the inverse square law.
Light diminishes the further from the subject.

The TTL system is reading the amount of light coming through the lens from an object a given distance away and is following the rules established by the camera's software. A goodly amount of that light is actually from the relfected light near you and the meter is reading that exposure level.
Derrel is correct with the exposure level action and one trick with modern digital is (only if possible ahead of time) to use a white flash card exposed at the light levels of the area and use that shot to generate a profile in post process to either balance the exposure or bring it up or down.

Read up on recipratory failure.

 

[CThomas817]

The first thing I was sugges to A mode. pick an Isolevel and and f-stop on the flash. Set the same f-stop on the lens. Pick an ISO such as 400 do you do shot change either the ISO or the f-stop to get the correct exposure this is a much older method that predates TTL flash control .

Will this change with distance to the subject though? One shot might be 5 feet from the subject while the next might be 15 feet away

 

[CThomas817]

What your describing is the effect of the inverse square law.
Light diminishes the further from the subject.

The TTL system is reading the amount of light coming through the lens from an object a given distance away and is following the rules established by the camera's software. A goodly amount of that light is actually from the relfected light near you and the meter is reading that exposure level.
Derrel is correct with the exposure level action and one trick with modern digital is (only if possible ahead of time) to use a white flash card exposed at the light levels of the area and use that shot to generate a profile in post process to either balance the exposure or bring it up or down.

Read up on recipratory failure.

Thanks, I will try this with the flash card for sure.

 

[tirediron]

Will this change with distance to the subject though? One shot might be 5 feet from the subject while the next might be 15 feet away

As mentioned, the inverse square law is what's at work. Simply put, the law states that the intensity of light is reduced in inverse proportion as the square of the distance between camera and subject is increased. That is, if a subject is 5' away from the camera and you need f8 (all other settings remain unchanged), if the subject is moved to 10', then then only 1/4 of the light will reach it, and therefore the exposure needs to be increased. The correct exposure would be f4.

 

[Soocom1]

One additional point.

If you have a spot meter, take a reading of an object at 5 feet and take a photo with those settings Do the same for 10, 20 and of possible 30 feet shooting an image at those settings.

Then take a toilet paper roll tube, paint the inside black and hold that over the sensor pointed at the subject at the 30 feet. The reading will drop and the exposure will be either near, at or over because the reading in the meter is only the direct light from the subject. Not the additional light reflected from everything between you and the subject.

With the flash attached the camera is reading the exposure as if from 5 feet away. PLUS the compensation from the flash giving a higher reading and voila...under exposure.

 

[Derrel]

There are three common ways to control the speed light-- 1)TTL or through the lens metering 2) Auto mode 3) manual
Mode

In Auto mode flash you typically set the flash to a specific aperture and a sensor on the flash automatically gives you more or less light as needed for that aperture,across a wide range of distances. This was the method of automatic flash control that was in common use before TTL was invented in the late 1970s.

A sensor on the flash( on the flash!) automatically gives you more or less light as needed, across a wide range of distances. Auto mode flash has been perfected for about 50 years or more. It is based upon setting the flash to A specific output level that is correlated with a specific f-stop, and typically a flash has two automatic f-stops, one wide, and then other medium or small. very sophisticated flashes will sometimes have three or four or five or even seven f/stop settings. But typically you have only two f/stops.

The flash has a sensor and it quickly reads,during the flash, the amount of light that comes back to the camera and it squelches the flash once enough light has been received. This happens at literally, the speed of light.

This method uses very simple technology that works extremely well. The newer TTL protocol is not working for you and I think you'll find it it is much easier to rely upon a more proven technology which is called auto flash.

Whenever you have a flash problem it is good to tell the specific camera model and flash model so that other people can troubleshoot your issue using online resources.

Even though I have been shooting TTL flash since the 1980s I actually prefer Auto flash. There are times when TTL Flash leads to extreme variation, but my experience is that the older technology is more consistent and is much easier to make corrections with

Manual flash is typically very labor-intensive, and it is a pain in the ass to shoot an event where you have to constantly adjust the lens aperture.