[BruceBanner]

So, I don't always run & gun in Av mode with on camera flash (360II), but I did notice yesterday, under shall we say dim lighting conditions the shutter speed chosen was 1/50, turn the flash off and we get the ISO Auto settings for controlling the Shutter (Fast, Normal or Slow). I understand that the burst of flash likely freezes the subjects and that we shouldn't worry too much about ambience at around 1/50th, but I was just curious as to how Av with Flash works, how it comes to decide on a shutter speed (or lowest speed it's willing to drop too (which in this particular instance seemed like 1/50th for me). Furthermore I noticed that some manual glass like lensbaby ones (which are meant to work in Av mode predominantly) get a fixed 1/200 in Av mode with flash on and there's no budging it at all.

So yeah, just curious as to how the camera decides to settle on a shutter speed when flash is attached in Av mode, can we change it at all (so say 1/80 instead). I had a go at messing with Auto ISO Setttings to see if Fast, Normal or Slow (and change those parameters) affected flash when it was on, but it didn't seem to make a difference.

Cheers,

Bruce

[stevebrot]

we get the ISO Auto settings for controlling the Shutter (Fast, Normal or Slow)

Those three settings may not be doing what you think they do.

I understand that the burst of flash likely freezes the subjects and that we shouldn't worry too much about ambience at around 1/50th, but I was just curious as to how Av with Flash works

The exposure (shutter speed) is determined during the pre-flash. (Magic is used.)

On a more serious note, this sort of thing (automated balancing) is one of the strengths of P-TTL. You can override with a combination of EV comp and flash comp.


Steve

(...auto-ISO is evil...)

[stevebrot]

Furthermore I noticed that some manual glass like lensbaby ones (which are meant to work in Av mode predominantly) get a fixed 1/200 in Av mode with flash on and there's no budging it at all.

That is because lenses without mount contacts get no automation when using flash. You get the X speed and your selected manual aperture. M mode will get you control over shutter speed. Even with contacts, those that are not AF get a reduced feature set.


Steve

[stevebrot]

The exposure (shutter speed) is determined during the pre-flash. (Magic is used.)

OK...there is some nuance. The camera will tend to err towards minimizing subject blur and will keep shutter speed high. It may even bump ISO to do so. (Remember, auto-ISO is evil.) You can at least partially overcome this by enabling slow sync. Another thing you can do is shoot in M mode and use the EV scale to determine initial ambient exposure manually.


Steve

[BruceBanner]

Those three settings may not be doing what you think they do.



The exposure (shutter speed) is determined during the pre-flash. (Magic is used.)

On a more serious note, this sort of thing (automated balancing) is one of the strengths of P-TTL. You can override with a combination of EV comp and flash comp.


Steve

(...auto-ISO is evil...)

That is because lenses without mount contacts get no automation when using flash. You get the X speed and your selected manual aperture. M mode will get you control over shutter speed. Even with contacts, those that are not AF get a reduced feature set.


Steve

OK...there is some nuance. The camera will tend to err towards minimizing subject blur and will keep shutter speed high. It may even bump ISO to do so. (Remember, auto-ISO is evil.) You can at least partially overcome this by enabling slow sync. Another thing you can do is shoot in M mode and use the EV scale to determine initial ambient exposure manually.


Steve

Sorry, specifically I meant 'Auto ISO Parameters'. I change them depending on what the lowest shutter speed I think I can get away with for the task is acceptable before it bumps ISO up. So 'Slow' gives the slowest shutter speed, once you encounter this shutter speed only then will it increase ISO. So it's a way to control how the Auto ISO behaves. If you feel dropping to 1/60th in Av mode is too low, change it to 'Fast' where you might get 1/250th as your lowest shutter speed and it will adjust the ISO only once reaching that threshold.
The KP goes one step better than the K-1 and actually allows you to specify the exact shutter speed yourself, handy if 'Fast' is not fast enough, you can now have an Av mode whereby 1/1000 is the lowest shutter speed you'll encounter.

Of course this changes if you set your ISO range to say 100-3200, once you exceed 3200 it will then drop your shutter speeds below your 'wanted' lowest shutter speed.

I was curious that with the addition of adding flash if this logic is somewhat followed, so that perhaps a change of Fast, Slow or Normal might change where the shutter speed sits, but it doesn't appear to be doing that. Hence this thread, how does it decide on a shutter speed etc.

So for example, right now I have my K-1 with a DA 20-40 attached, I'm at 30mm and f3.5. The flash is off, my Auto ISO is set to Normal and my range 100-3200. With ISO in Auto mode I can see it's given me 1600 (for the location I am currently in, with a shutter speed of 1/50. So I know that 1/50 is the lowest this focal length wants to drop to before bumping ISO, I know this because Auto ISO is at 1600 (i.e. it's already raising it). If I toggle out of Auto ISO and now select 800 I get 1/25, I am basically overiding the Auto ISO Parameters.

What's kinda interesting is when we turn flash on (360II), it sets the shutter speed to 1/60 and puts me in Auto ISO mode, if I toggle out of Auto-ISO and set ISO to 100, 200, 400, 800, 1600 it stays at 1/60, only once I get to 3200 does it shift to 1/1000. I think this is what I was experiencing yesterday, it felt like for the room i was in whatever respectable ISO I selected the shutter speed did not budge (and I was at f3.5 and couldn't widen the aperture further). The idea of using 3200 ISO to get a little more shutter speed seemed ridiculous when flash was involved, indeed toggling off flash at this point (leaving ISO at 3200 meant my shutter speed stayed the same (1/100), so it made me kinda question what was the point of using flash at all, it didn't help lower ISO in that situation at all.

I just thought it was interesting, what the shutter speed was doing under Av mode, even when fixing and changing ISO. For a 'Av' mode it seemed to stay pretty fixed throughout a largish range (ISO 100-1600, no waivering in shutter speed when flash was attached). I guess the P-TTL system will adjust the power of flash output between those ranges (ISO 100 would get the most severe flash output, ISO 1600 the least), the issue is if you have EV compensation (-1EV) and were wanting to mix ambient light with the flash then you really needed to set the ISO to Auto for this to occur, otherwise fixing ISO and having no drop in shutter speed throughout 100-1600 results in a very different light balance between the two throughout. It's almost like Av mode somewhat 'goes out the window' when you add a flash on, it's really not 'Av mode' anymore when all 3 exposure triangles remain fixed from ISO 100-1600.



Also, to get back to the Lensbaby/Manual glass, when in Av mode and you have a flash attached, it slaps it to 1/200 right, but if you menu dive and change Flash Sync Speed (to something less than 1/200) it's still not reflected in Av mode (obviously is in X mode). And as you say in Manual mode you can adjust it, I was just curious as to where this 1/200 came from for Av mode when those kinda lenses were attached.


Up till now I have not messed around with Flash Sync settings much, P-TTL, HSS and Manual. Second Curtain I haven't had the need to try yet. I did use Tv mode to great success at a dance recently and dropped the shutter speed down to 1/5th but I had the flash in 'Normal' mode, ie first curtain? Whereby the flash fired first and then took longer to complete the shot. I tried it the other way around, but I found it harder to 'capture the moment' as the flash is firing after you see the moment you want to capture. I understand where it could be useful however, just thus far have not encountered the need for it. So when you say 'enabling slow sync' what exactly is this?

Thanks again Steve,

Bruce

[pschlute]

Have a look at Nigel's flash guides which give a detailed description of camera behaviour in each mode.

Slow speed sync is a flash mode you can only use in P or Av (and I think Sv). Normally in those modes when using flash the camera will choose a shutter speed with a limitation of 1/30 or 1/60 as the slowest depending on FL. It will try and balance the ambient and flash output to the scene, but wont go below the minimum shutter speed to avoid blur from elements in your picture lit by ambient light.. If you enable slow speed sync it will choose a slower shutter speed if the ambient light requires it.

Regarding your lensbaby, any lens that does not communicate its aperture and focus distance to the camera can lead to unexpected results when trying to use an auto mode like Av. if you add auto-ISO into the mix you are confusing things further.

There is a reason many flash users prefer Manual exposure mode when using a flash in P-TTL and that is it gives the greatest control and most consistent results.

[Paul the Sunman]

(Remember, auto-ISO is evil.)

Auto-ISO used to be evil. These days, with the K1, I can hardly tell that I've used high ISO in pp without really zooming in. Whilst being sensible with the shutter speed and depth of field I aim for, I refuse to twist myself in knots any more to avoid ISO 3200 or even ISO 6400. Trust the camera. TAv is my friend.

[BruceBanner]

Auto-ISO used to be evil. These days, with the K1, I can hardly tell that I've used high ISO in pp without really zooming in. Whilst being sensible with the shutter speed and depth of field I aim for, I refuse to twist myself in knots any more to avoid ISO 3200 or even ISO 6400. Trust the camera. TAv is my friend.

Yeah I do tend to stay away from 6400, 3200 is my cut off personally, I do use Av mode a lot but have ISO fixed more often than not, or restrained heavily. I think people forget that this is even a thing. Av mode for me is typically leaving only shutter speed to be decided (in combination with my EV compensation) and it's not without its constraints and specifics either (Auto ISO Parameters). I've even had my lower ISO value set to 400 so that I gain faster shutter speeds, it starts to feel awfully like being in Manual Mode with just that additional bit of support.

By the by, I'm on the Godox User Group on facebook and someone just posted this;

"Question for wedding photographers: A friend told me she second shot with another photographer at an indoor wedding reception and the lead photographer had his shutter speed at 1/40 (yes, 1/40, I assume obtain a lower ISO.) with on camera flash. My question is this possible without getting any motion blur? I thought your shutter speed had to be at least over 200 to avoid motion blur. My ISO last night was kicked to 5000 with a SS of around 1/200 to 1/250 with Godox on camera flash around 1/16. Is this this typical or am I missing something completely?"

It made me think, I mean I know why you can still get plenty successful shots at 1/40th of a second, I took a gazillion shots a couple of weeks ago at 1/4th and 1/5th of a second and the flash was still freezing the subject nice and sharp, like these examples;





but I wondered if perhaps that lead wedding photographer was also in Av mode and got given 1/40th lol, like... perhaps different systems pluck out different shutter speeds when on camera flash is used in Av mode. It must vary with different glass attached tho right? I just actually haven't tested it out properly but I think even using the HD DA 20-40 in av mode, adjusting the focal length made teh shutter speed go from 1/50th to 1/60th (with flash enabled), but then that is a 2.8-4 piece of glass. Just curious to know now if using a FA43/1.9 @f1.9 with on camera flash in Av mode sets the camera to the same shutter speed (1/50th) as say using the FA77/1.8 @1.8 etc. Because I noticed that the Auto ISO Parameter settings value given changes depending on the lens attached, it will give quicker lower shutter speeds for longer focal length glass than shorter (kinda like that rule in photography about not dropping below the shutter speed for the mm glass attached, 1/50th for 50mm, 1/100 for 100mm etc etc).

[pschlute]

It made me think, I mean I know why you can still get plenty successful shots at 1/40th of a second, I took a gazillion shots a couple of weeks ago at 1/4th and 1/5th of a second and the flash was still freezing the subject nice and sharp, like these examples

There is motion blur in your pictures. Look at the man behind the subject in the first picture and also the arms of the subject. Motion blur in both from the ambient part of your exposure, but the flash has frozen your subject as you would expect so you dont notice it.

Great pictures by the way.

[swanlefitte]

I still wonder from a previous thread if metering matters because the flash only affects the subject.
Also wondering if flash strength shows up in exif.

[kaseki]

...
Also wondering if flash strength shows up in exif.

I don't see it in the part of the exif that shows in Darktable. However, the concept suggests that a lot of info would be needed by the camera, all reported back to it by whatever array of flashes were present. To be useful, range, angle, divergence, gobo transmission/reflection, etc. would be needed. Or maybe each pre-flash would have to occur at a different time to infer these characteristics. If P-TTL were perfect, whatever the pre-flash showed as an EV relative to where the flash EV was set would determine a scale factor for all the flashes and the actual EV achieved would be the flash EV that was set. Only in cases where the flash power was inadequate would a measure of how far in EV units the flash missed the mark be useful, I think.

[stevebrot]

if you add auto-ISO into the mix you are confusing things further.

That is the reason for my persistent chant that "auto-iso is evil". How and when it ramps creates an element of uncertainty.


Steve

[stevebrot]

Also wondering if flash strength shows up in exif.

The camera only "knows" the intensity setting for on-board flash and even then, it may not be recorded in the EXIF. Pentax makernotes support for flash varies by body and about the only thing that is consistent is stuff related to basic dedication, i.e. external flash detected, external flash success, external flash fail, etc.. The actual communication between flash and body is minimal.

ExifTool's tag interpretation summary may provide some clarity:

Pentax Tags


Steve

[stevebrot]

Sorry, specifically I meant 'Auto ISO Parameters'. I change them depending on what the lowest shutter speed I think I can get away with for the task is acceptable before it bumps ISO up. So 'Slow' gives the slowest shutter speed, once you encounter this shutter speed only then will it increase ISO. So it's a way to control how the Auto ISO behaves. If you feel dropping to 1/60th in Av mode is too low, change it to 'Fast' where you might get 1/250th as your lowest shutter speed and it will adjust the ISO only once reaching that threshold.

Cool...I could not remember if you were part of that discussion way back when to hammer out the details of auto-ISO ramping.

The KP goes one step better than the K-1 and actually allows you to specify the exact shutter speed yourself, handy if 'Fast' is not fast enough, you can now have an Av mode whereby 1/1000 is the lowest shutter speed you'll encounter.

Truly? I will have to look that up. That one sounds like a deep pit for a noob to fall into.
Edit: I just took a look at the manual and without a KP in hand, it looks to be a deep, deep, pit...


Steve

[pschlute]

The KP goes one step better than the K-1 and actually allows you to specify the exact shutter speed yourself, handy if 'Fast' is not fast enough, you can now have an Av mode whereby 1/1000 is the lowest shutter speed you'll encounter.

Too complicated. Especially when the next time you wander out with your camera you have forgotten you changed that setting.

Exposure is not rocket science. There are three parameters. There are enough modes to accommodate you as long as you understand exposure. Adding a shutter speed limit in Av ?.....really !!