TTL vs Manual difference?

[AgentOrange76]

Im playing with some macro shots and not used flash much in the past

I have the camera in manual mode, Iso 160, 1/250th f20

I have the Godox TT685 Flash camera mounted.

If I shoot with the flash in Manual at 1/1 power which is as high as it goes im getting shadowing in the shot. The bottom of image drops away into partial shadow with the magnolia wall 18inch behind more grey to blue looking which i assume is the light not projecting far enough?

If I set the flash to TTL this shadow effect is not present, its more evenly lit and the wall more magnolia coloured so assume that the light is projecting further

Now if 1/1 is max power how can TTL produce more power or the effect of doing so? I dont appear to be able to change any other setting on the flash unit that has any effect

SO to save my sanity what is occuring to create this diference?

 

[ancient_mariner]

I wonder if TTL is overriding your manual settings somehow, an you're seeing a mix of flash and ambient.

 

[Sky]

At a higher power the light fall-off is more noticeable.

 

[Phil V]

At a higher power the light fall-off is more noticeable.

This^
the TTL flash is attempting to balance with the ambient, and by using lower power, the shadows are less harsh and the falloff is less.

Where you think you’re seeing ‘more’ light in TTL, it’s actually the opposite.

 

[mike weeks]

Im playing with some macro shots and not used flash much in the past

I have the camera in manual mode, Iso 160, 1/250th f20

I have the Godox TT685 Flash camera mounted.

If I shoot with the flash in Manual at 1/1 power which is as high as it goes im getting shadowing in the shot. The bottom of image drops away into partial shadow with the magnolia wall 18inch behind more grey to blue looking which i assume is the light not projecting far enough?

If I set the flash to TTL this shadow effect is not present, its more evenly lit and the wall more magnolia coloured so assume that the light is projecting further

Now if 1/1 is max power how can TTL produce more power or the effect of doing so? I dont appear to be able to change any other setting on the flash unit that has any effect

SO to save my sanity what is occuring to create this diference?

Best thing is to post the images, pictures paint a thousand words

Mike

 

[AgentOrange76]

This^
the TTL flash is attempting to balance with the ambient, and by using lower power, the shadows are less harsh and the falloff is less.

Where you think you’re seeing ‘more’ light in TTL, it’s actually the opposite.

That made perfect sense until i tried to replicate it, I reduce the power by 1/3rd increments in manual mode and just get less and less light falling onto the background.
So what does TTL control if the camera is manually set up and how would you replicate what it does.

Ill add a couple of images in a bit to show the diference.

I can live with the TTL but i would rather do things manually if possible as I better understand how to use it.

 

[Phil V]

That made perfect sense until i tried to replicate it, I reduce the power by 1/3rd increments in manual mode and just get less and less light falling onto the background.
So what does TTL control if the camera is manually set up and how would you replicate what it does.

Ill add a couple of images in a bit to show the diference.

I can live with the TTL but i would rather do things manually if possible as I better understand how to use it.

I’d say you’re not dialling it down anywhere near enough. I’d start at 1/4 power and see how it looks.

Depending on the specifics in the camera algorithm and the amount of light TTL will try to only ‘fill’ the shadows (ie be the secondary light source) until the light levels drop too low for hand held photography, at which point the flash becomes the primary light source.

The core principal of learning flash is that you have to remember you are managing 2 separate exposures. And that’s true whether you pop up a flash on a compact camera or are using 6 flash heads in a pro studio.

And once you have that in mind, the next realisation is that a camera mounted flashgun pointed straight ahead is the worst possible main light source. Lighting isn’t about the highlights, it’s about the shadows, shadows show form - so the worst possible light is small from the camera position, because all it does is create a hard shadow directly behind your subject.

 

[Sky]

TTL has it's place, but I'd suggest you forget it for the time being and concentrate on manual as you will get more consistent results. IMO TTL will just confuse you.

I just had a quick look on YouTube and I think Gavin gives a good demo here:

View: https://youtu.be/VXztfw4aG_o

 

[AgentOrange76]

So this is 2 images the first using TTL flash and the second Manual , the more i dial the flash down the darker the background goes
I started with 1/1 then dropped by 0.3 steps to 1/2 then tried 1/4 and 1/8.
Id rather use manual as i then know where im at but by accident took a shot with TTL that gave a better/diferent result but cant replicate it using a manual set up

 

[mike weeks]

Remember that metering mode will affect the results with TTL

 

[Sky]

That doesn't give us a lot to go on unfortunately as there is no EXIF information.

How much light was there in the room? As Toni suggested, the TTL could be exposing for the ambient and mixing the two.

In manual, take a picture without the flash. The picture should be completely black because it's underexposed - if it's not, stop down to around f8 and make sure it is.

Now switch the flash on and try again. Adjust the flash output until you get the exposure you want on the plant - ignore the background.

 

[Phil V]

So this is 2 images the first using TTL flash and the second Manual , the more i dial the flash down the darker the background goes
I started with 1/1 then dropped by 0.3 steps to 1/2 then tried 1/4 and 1/8.
Id rather use manual as i then know where im at but by accident took a shot with TTL that gave a better/diferent result but cant replicate it using a manual set up

Of course you can.
Start by finding out what the camera settings were on the TTL shot, then dial them in and experiment with the flash power.

you do though need to a knows that what’s happening in the TTL shot is the ambient is giving you the exposure you like on that background. And you keep assuming it’s the flash, despite information to the contrary.

like I said - you need to remember whether you’re using manual or TTL, you are juggling two separate exposures.

 

[sk66]

At a higher power the light fall-off is more noticeable.

At a higher power falloff happens over a greater distance... it's slower/more gradual. When the light is at a shorter distance to the subject the fallof is greater/faster (and the power should be lower)

Now if 1/1 is max power how can TTL produce more power or the effect of doing so? I dont appear to be able to change any other setting on the flash unit that has any effect

SO to save my sanity what is occuring to create this diference?

I think the flash must be switching into HSS when you go to TTL... it looks like 1/250 is extended sync; which is why you get the gradation towards the bottom in manual (it's *almost out of sync enough to generate a black bar). But 1/250 is also still close enough w/in x-sync that you don't get the typical loss of power due to being in HSS (the flash pulses layer/build).

 

[sk66]

Start by finding out what the camera settings were on the TTL shot, then dial them in and experiment with the flash power.

I believe he's saying the camera settings were set full manual and the same...

 

[AgentOrange76]

Thanks, 1/250th is the sync speed for the XT3 so will try a slightly slower speed to see if that changes anything

 

[AgentOrange76]

y

I believe he's saying the camera settings were set full manual and the same...

Yep,
Camera settings are fixed, fully manual and not changed
All i am doing is switching the flash from manual flash 1/1 power to TTL its a single button press which on the first time was accidental. From the settings shown on the flash's screen there is nothing diferent to the manual use.

 

[sk66]

Thanks, 1/250th is the sync speed for the XT3 so will try a slightly slower speed to see if that changes anything

It's the max sync speed; and seems a little overrated IMO. You could disable FP in your camera's sync settings (and/or the flash?) to isolate that factor. The only other possibility is that your settings are not actually fully manual and the ISO is increasing because the TTL metering is sensing underexposure.

 

[Phil V]

y
Yep,
Camera settings are fixed, fully manual and not changed
All i am doing is switching the flash from manual flash 1/1 power to TTL its a single button press which on the first time was accidental. From the settings shown on the flash's screen there is nothing diferent to the manual use.

JPG or raw, what processing was done on import.

 

[AgentOrange76]

Images posted were shot in Raw, imported into Capture one and exported straight out as jpeg.

 

[Phil V]

Images posted were shot in Raw, imported into Capture one and exported straight out as jpeg.

This is illogical.

In the TTL image the background is lit only by the ambient.

In the Manual image the upper half of the background is lit by the flash, the lower part has no flash (ergo only ambient) so the ‘dark’ portion should look exactly the same on both images if all the camera settings were the same. ie the dark portion would be lighter and a different colour.

Is there a chance that your ‘full manual’ has auto ISO, and is therefore not full manual?

could you post the exif?

 

[ancient_mariner]

I have to agree with Phil on this - regardless of apparent settings, there was some kind of autoexposure at work for the TTL shot.

 

[J Veitch]

I'm wondering if there could be auto ISO in the mix too - might be missed?

 

[AgentOrange76]

On the XT3 I have the lens switch set to manual aperture, then set it with the ring on the lens.
If i set the ISO dial to A (auto) I can then use a command dial to set the ISO to a fixed value. As a test I have also set the dial to 160 (base ISO)
Shutter speed is set with the other dial set to T which allows a second comand dial to set the speed. As a test I also set this to 1/250.

The same difference occurs either way,

So with TTL the exif says Flash Flash, with Manual the Exif says Flash No FLash. But the flash goes off with both shots.

 

[AgentOrange76]

 

[sk66]

Well, that settles it then... it is either the TTL flash firing in HSS (and layering), or it could be (probably is) a timing offset/error for the manual flash exposure...

I hadn't thought of the manual flash timing before, nor can I think of an obvious cause. But the TTL image knows the flash was used and the manual image doesn't. That means the manual flash exposure must have been in "dumb mode" (center pin only, or a dumb trigger used?). Which I would think makes a timing issue likely. The manual image looks most like tail sync that fired too early to me... I just hadn't completely realized it before.

 

[Phil V]

Well, that settles it then... it is either the TTL flash firing in HSS (and layering), or it could be (probably is) a timing offset/error for the manual flash exposure...

I hadn't thought of the manual flash timing before, nor can I think of an obvious cause. But the TTL image knows the flash was used and the manual image doesn't. That means the manual flash exposure must have been in "dumb mode" (center pin only, or a dumb trigger used?). Which I would think makes a timing issue likely. The manual image looks most like tail sync that fired too early to me... I just hadn't completely realized it before.

The flash is camera mounted. (first post)

But it does to me look like the problem could be SS related.

I’d got to the point I was going to try to recreate the problem, but I don’t think I’ve got a camera that sync’s so fast.

@AgentOrange76, the next thing I’d do is drop the shutter speed, unless there’s a good reason for using max sync, i generally go at least half a stop below

 

[mike weeks]

To really understand it needs 3 images, no flash, manual flash and TTL

Not surprised by the EXIF saying no flash as you have set to manual - that term probably means no TTL control, I have seen exif flash differences between Godox and Nikon flashes doing the same thing on the same body

You also need to set manual white balance for the tests as TTL is probably setting flash as wb but manual is using ambient wb

 

[mike weeks]

There is also a firmware update fir the X-T3 available https://fujifilm-x.com/en-gb/support/download/firmware/cameras/x-t3/

 

[AgentOrange76]

The flash is camera mounted. (first post)

But it does to me look like the problem could be SS related.

I’d got to the point I was going to try to recreate the problem, but I don’t think I’ve got a camera that sync’s so fast.

@AgentOrange76, the next thing I’d do is drop the shutter speed, unless there’s a good reason for using max sync, i generally go at least half a stop below

Ok so re-shot at 1/125th as thats the next dial setting and I want to eliminate any variable that may be a result of using the command dials instead to set speed.
The Manual image is brighter but have moved closer.
1st pair is with auto WB
2nd Pair with cloudy WB
3rd Pair WB set to 10000k

 

[sk66]

Ok so re-shot at 1/125th as thats the next dial setting and I want to eliminate any variable that may be a result of using the command dials instead to set speed.

I don't see any issue with those.

 

[AgentOrange76]

I don't see any issue with those.

nothing wrong but the Manual flash version brighter than the TTL version, I can naturally turn down the flash manually given the same camera and flash settings should they not be identicle?

 

[sk66]

should they not be identicle?

No, not necessarily and not normally. The TTL mode adjusts the flash power based upon the flash metering (preflashes, and some menu settings typically). The manual flash just dumps whatever it is set to; right or wrong it doesn't care... that's your job to figure out the exposure.

 

[AgentOrange76]

No, not necessarily and not normally. The TTL mode adjusts the flash power based upon the flash metering (preflashes, and some menu settings typically). The manual flash just dumps whatever it is set to; right or wrong it doesn't care... that's your job to figure out the exposure.

Ok, thanks. that makes sense, at least the initial issue is resolved, ill play with the SS using the command dials and see how I goes

 

[Phil V]

nothing wrong but the Manual flash version brighter than the TTL version, I can naturally turn down the flash manually given the same camera and flash settings should they not be identicle?

The manual flash versions are overexposed, if you turn fown the flash power you should find a setting that looks identical to the ETTL one.

Now to address the elephant in the room, your on camera flash doesn’t even cover the subject, to do this properly you need to get the flash off camera, but a quick and dirty trick is to zoom the flash to max length, twist the head almost 90 degrees and bounce it off a white card fairly close. That’ll give you a 10” light source that doesn’t have a lens covering it.

 

[Phil V]

Ok, thanks. that makes sense, at least the initial issue is resolved, ill play with the SS using the command dials and see how I goes

Adjusting the SS doesn’t change flash power (unless in ETTL at really high power - but that’s a whole other discussion).

Only aperture or flash power change flash exposure below sync speed (as per my first post re understanding that you’re balancing 2 separate exposures).

 

[mike weeks]

Adjusting the SS doesn’t change flash power

It actually can do in a a manner of speaking but it very limited circumstances and maybe not noticed by all.

If the flash duration is longer than the shutter speed then some of the flash power will be lost compared to using a lower shutter speed. My Nikons generally all have a flash sync speed of 1/250 but my Godox AD600 has a t0.1 of I think 1/220s, so technically there but a bugger to spot.

Where it does become noticeable is with leaf shutters such as my Fuji F100V which will happily sync at 1/2000 and there are whole articles on tuning the flash for optimum settings

Mike

 

[HoppyUK]

It actually can do in a a manner of speaking but it very limited circumstances and maybe not noticed by all.

If the flash duration is longer than the shutter speed then some of the flash power will be lost compared to using a lower shutter speed. My Nikons generally all have a flash sync speed of 1/250 but my Godox AD600 has a t0.1 of I think 1/220s, so technically there but a bugger to spot.

Where it does become noticeable is with leaf shutters such as my Fuji F100V which will happily sync at 1/2000 and there are whole articles on tuning the flash for optimum settings

Mike

It's not the actual shutter speed that matters, it's the length of time the sensor is fully uncovered - which is the shutter speed minus the shutter travel time. That's typically 1/300sec or so, meaning that in practise the x-sync window is roughly 1/500sec (at 1/200-250sec shutter speed). That's what commonly causes slight darkening at the bottom* of the frame when shooting at max x-sync speed with a tardy flash duration which is often in the 1/200-300sec range these days at full power.

Fortunately, while the total flash duration might be quite long, most of the light is emitted right at the start so the effect is minimal and often passes unnoticed, especially when shooting in daylight but it's definitely there. Easy to check - shoot a plain wall at max x-sync with the flash at full power and note uneven coverage, then reduce the shutter speed to say 1/125sec and the darkening will disappear. Or, stay at max x-sync speed and reduce the flash duration substantially by turning down the power to say quarter output (bump up ISO to compensate) and again there will be no darkening. I don't think I'm alone in using 1/125sec as my default x-sync speed unless I really need to go faster.

I wish Godox would pay more attention to this, as it's important when you need every drop of power working in bright daylight at max x-sync. Profoto has a slight advantage here, though the new Godox AD100Pro does rather better with a full power t.1 flash duration of 1/450sec from memory.

*can be at the top of the frame with some mirrorless cameras where the shutter runs bottom-to-top, as opposed from top-to-bottom with DSLRs.

 

[Garry Edwards]

*can be at the top of the frame with some mirrorless cameras where the shutter runs bottom-to-top, as opposed from top-to-bottom with DSLRs.

Or just turn the camera upside-down, I don't care what people think of me when they see me doing that

 

[AgentOrange76]

The manual flash versions are overexposed, if you turn fown the flash power you should find a setting that looks identical to the ETTL one.

Now to address the elephant in the room, your on camera flash doesn’t even cover the subject, to do this properly you need to get the flash off camera, but a quick and dirty trick is to zoom the flash to max length, twist the head almost 90 degrees and bounce it off a white card fairly close. That’ll give you a 10” light source that doesn’t have a lens covering it.

Now thats a tip and a half. My lack of flash knowledge, I expected manual set flash ans TTL set flash with the same setting to be the same or at least close.

Adjusting the SS doesn’t change flash power (unless in ETTL at really high power - but that’s a whole other discussion).

Only aperture or flash power change flash exposure below sync speed (as per my first post re understanding that you’re balancing 2 separate exposures).

Kind of knew that but what I meant is that by using the command dial I can set a SS between 1/250th and 1/125 to see at what point the original issue stops

 

[Phil V]

Now thats a tip and a half. My lack of flash knowledge, I expected manual set flash ans TTL set flash with the same setting to be the same or at least close.

When the flash is set to manual, it’s your job to set the correct amount of flash power. Just leaving it on full gives a full power flash, which might be overexposed. TTL flash will give you the correct exposure (within the limits we expect any auto mode to be ‘correct’).

Kind of knew that but what I meant is that by using the command dial I can set a SS between 1/250th and 1/125 to see at what point the original issue stops

Ah: I can see why you might care, but I’m a pragmatic kinda guy, and as such I tend to just set a SS below sync that I know is reliable and crack on with shooting.

As I said, from a picture taking point of view, I’m more concerned with the nature and direction of the light, rather than the power, which is very simple to control.