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07-10-2017, 01:16 AM   #1
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Which ISO uses camera??

I shoot quite often with TAv setting and flash.
I choose camera shutter speed and aperture manually (i.e. 5.6/160, flash in P-TTL), so camera adjusts its ISO setting accordingly.
Problem is I do *NOT* know which ISO setting is set by camera, all I know the ISO (in viewfinder/top LCD) is 'Auto'.
That's ridiculous info from Pentax
The result is some disastrous photos with surprised-me high ISO (mostly indoors, in dim rooms, or outdoors at twilight/sunset time), as K-3 is *VERY* bad with high ISO.
I do not want to limit upper ISO in auto mode through camera menu, what I want is just to KNOW which ISO is set by camera.
Otherwise shooting is like not knowing your auto aperture or auto shutter speed
C'mon Ricoh Pentax, let's upgrade the K-3 firmware...

07-10-2017, 01:54 AM - 1 Like   #2
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The ISO will show in the view finder, when you focus on your subject. If it's to high you can make shutter and aperture changes until it gets to where you want.
07-10-2017, 02:32 AM   #3
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choose Manual mode and fix low ISO value...
07-10-2017, 02:50 AM   #4
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QuoteOriginally posted by KiloHotelphoto Quote
The ISO will show in the view finder, when you focus on your subject. If it's to high you can make shutter and aperture changes until it gets to where you want.
Not with Pentax AF-540FGZ flash when gets switched-on (when red 'ready' light gets on), 'ISO number' gets into 'ISO Auto'.
Your way you would need to switch off and on your flash before every shot.


-----
QuoteOriginally posted by amodali Quote
choose Manual mode and fix low ISO value.
Manual mode is not convenient for fill-in flash.


Last edited by Prakticant; 07-10-2017 at 02:57 AM.
07-10-2017, 03:04 AM   #5
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Go into your settings and limit AUTO-ISO to 6400. If the camera is selecting something higher it is metering incorrectly unless you're shooting in complete darkness. Much better to push in post than resurrect blown high ISO RAW files.

With flash, I generally set the camera to manual with a conservative ISO, and the flash to either AUTO or P-TTL, while resolving to do some heavy lifting in Lightroom.
07-10-2017, 04:12 AM - 1 Like   #6
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Sadly, you may be asking for the impossible.

With TAv and P-TTL, the camera does not know the ISO it will use until after the P-TTL preflash. The camera may know the ISO required by the ambient light level but until it does the pre-flash, it doesn't know how the ISO might change (drop) because of the flash's contribution to the lighting.
07-10-2017, 04:23 AM   #7
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You can set the ISO range for Auto in the menu settings, it's listed in your manual or you can download a copy from Pentax/Ricoh, under support
07-10-2017, 07:25 AM   #8
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QuoteOriginally posted by photoptimist Quote
With TAv and P-TTL, the camera does not know the ISO it will use until after the P-TTL preflash. The camera may know the ISO required by the ambient light level but until it does the pre-flash, it doesn't know how the ISO might change because of the flash's contribution to the lighting.
That's interesting, as the other forum user says opposite:

QuoteOriginally posted by TheOneAndOnlyJH Quote
Just to reiterate, avoid auto ISO since the camera calculates ISO without taking flash into account and results in less than optimal exposure settings. (Means no TAv or full Auto)
https://www.pentaxforums.com/forums/172-pentax-k-3/242556-k-3-delay-when-usin...ml#post4034148

So question is:

How Pentax K-3 calculates ISO with TAv and strobe (fill-in flash)??

07-10-2017, 09:28 AM - 2 Likes   #9
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QuoteOriginally posted by Prakticant Quote
That's interesting, as the other forum user says opposite:


https://www.pentaxforums.com/forums/172-pentax-k-3/242556-k-3-delay-when-usin...ml#post4034148

So question is:

How Pentax K-3 calculates ISO with TAv and strobe (fill-in flash)??

You have the camera and the flash in hand. The behavior of the two in TAv and other auto exposure modes using auto-ISO should be plain and should take less time to figure out than interacting on this thread. If need be, the manuals for both the camera and the flash are available at:

Operation Manuals Download : Support & Service | RICOH IMAGING

Sorry if this response sounds a little curt, but whether you think it lame or not, the camera cannot appropriately calculate the ISO until it does the pre-flash. A little manual flash work with ISO as the variable will quickly help you figure out why. If you need full control over aperture, shutter speed, and ISO for PTTL flash work on the K-3, the solution is M mode with manual ISO.

BTW...photoptimist is correct and the other guy, not so much. That being said, I fully agree that auto-ISO is not a good thing.


Steve

(...another strong proof that auto-ISO is evil...)

Last edited by stevebrot; 07-10-2017 at 09:34 AM.
07-10-2017, 09:34 AM   #10
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QuoteOriginally posted by Prakticant Quote
That's interesting, as the other forum user says opposite:


https://www.pentaxforums.com/forums/172-pentax-k-3/242556-k-3-delay-when-usin...ml#post4034148

So question is:

How Pentax K-3 calculates ISO with TAv and strobe (fill-in flash)??
Autoexposure software can be extremely complicated and I doubt anyone has reverse engineered Pentax's firmware to see exactly how they compute AE for P-TTL. P-TTL is an especially complex scenario which is a function of the pattern of ambient lighting, the pattern of object distances to the flash, the max & min power settings of the flash, auto-ISO range, and a bunch of scene analysis algorithms that try to create a "pleasing" image.

Overall, though, the algorithm probably looks like this:

1. Measure the ambient light (this gets a baseline ISO which is the highest ISO the camera might use)

2. When the user hits the shutter button, fire the preflash and measure the change in light level across the scene (this provides data for computing how scene illumination changes as a function of flash power)

3. Calculate optimal flash power (find the flash power setting that: creates uniform illumination, gets the lowest possible auto-ISO, does not exceed full power, does not blow out highlights, does not exceed the highest-acceptable auto-ISO)

4. Calculate the ISO needed with that flash setting (which will be anywhere between: the lowest auto-ISO value and either the ambient ISO or maximum auto-ISO which ever is lower)

5. Take the picture with the calculated flash and ISO settings.

The point is that until the camera does the preflash, it does not know the best flash power setting to use or the ISO.
07-10-2017, 09:39 AM   #11
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QuoteOriginally posted by photoptimist Quote
With TAv and P-TTL, the camera does not know the ISO it will use until after the P-TTL preflash. The camera may know the ISO required by the ambient light level but until it does the pre-flash, it doesn't know how the ISO might change (drop) because of the flash's contribution to the lighting.
The key is that the flash is fairly limited in terms of the attenuation* it can apply and as the ISO climbs, the ability to attenuate approaches zero. There was a similar question recently where the user was upset because they were not allowed the combination of high ISO, wide aperture, and P-TTL flash with the AF 540 FGZ on the K-1.


Steve

* I prefer the term "attenuation" over "power" in this context in that the flash is actually quenched time-wise to vary output (low power = short duration) rather than there being a difference in brightness.

Last edited by stevebrot; 07-10-2017 at 09:57 AM.
07-10-2017, 09:42 AM - 1 Like   #12
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I'm afraid I have to say that using Auto-ISO with any sort of flash situation is a poor technique. The variables involved in creating the required creative and technical mix of ambient /flash exposure balance requires a knowledgable human mind to make to make the needed judgments andi impose technical constraints on the settings. .... This is in order to ensure that the settings are conducive to the environment, ambient light level, flash to subject distances, bounce angles, focal length/need for steadiness etc....

A fixed ISO considering these aspects is the best starting point for every flash photograph..... Then choose either M camera mode or Av depending on the static or dynamic nature of things.
07-10-2017, 09:54 AM   #13
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QuoteOriginally posted by Prakticant Quote
The result is some disastrous photos with surprised-me high ISO (mostly indoors, in dim rooms, or outdoors at twilight/sunset time), as K-3 is *VERY* bad with high ISO.
I do not want to limit upper ISO in auto mode through camera menu, what I want is just to KNOW which ISO is set by camera.
I don't see how knowing the ISO would help with the situations you describe. The fact that high ISO was calculated indicates that your chosen aperture was too small for the distance and available flash output to balance very scant available light. Things were easier in the olden days where the slide calculator on the back of the flash clearly showed the working range at various combinations of ISO and aperture.


Steve
07-10-2017, 09:57 AM   #14
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QuoteOriginally posted by mcgregni Quote
A fixed ISO considering these aspects is the best starting point for every flash photograph..... Then choose either M camera mode or Av depending on the static or dynamic nature of things.
Yep! Fix the ISO and the aperture and everything falls into place with the photographer having a high degree of control over the degree of fill and a certain amount of foreknowledge as to when things simply will not work.


Steve
07-10-2017, 12:14 PM   #15
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QuoteOriginally posted by Prakticant Quote
That's interesting, as the other forum user says opposite:
www.pentaxforums.com/forums/172-pentax-k-3/242556-k-3-delay-when-using-flash.html#post4034148
So question is:
How Pentax K-3 calculates ISO with TAv and strobe (fill-in flash)??
Reading that again I have to admit I worded that very poorly when I wrote it. (I've edited that post to correct it.) What I was trying to say is that auto-ISO chooses an ISO setting without seeing the actual flash that will fire when the picture is taken. It does use the pre-flash in it's calculations, but all decisions are made before the main flash. I don't know if it's due to poor calculations or differences in how the pre-flash and main flash illuminate the subject / room, but I find it often chooses very high ISO and greatly under-utilizes the flash power available when I would rather use higher flash power and lower ISO. I believe this might be more exaggerated in darker settings with less reflective surfaces, but I learned very quickly to avoid auto-ISO when using flash and haven't looked back since.

QuoteOriginally posted by mcgregni Quote
I'm afraid I have to say that using Auto-ISO with any sort of flash situation is a poor technique. The variables involved in creating the required creative and technical mix of ambient /flash exposure balance requires a knowledgable human mind to make to make the needed judgments and impose technical constraints on the settings. .... This is in order to ensure that the settings are conducive to the environment, ambient light level, flash to subject distances, bounce angles, focal length/need for steadiness etc....

A fixed ISO considering these aspects is the best starting point for every flash photograph..... Then choose either M camera mode or Av depending on the static or dynamic nature of things.
I agree with this. The K-3 is a very smart camera, but it does have it limits, and it can't (always) read my mind.
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