Auto ISO Broke?

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Philth

Senior Member
I have a question with regards to Auto ISO. With my current settings, I have it set to max ISO of 3200, with a minimum shutter speed of 1/125. The ISO is set at 100 for minimum.

However, I noticed when shooting test objects this morning in every mode (P, S, A, etc.), the ISO would sometimes go to 6400 and my shutter speed would sometimes dip down to 1/40. I haven't noticed this before and am wondering if the latest firmware update (which I just did), has something to do with it?
 
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nmccamy

Senior Member
I just downloaded the D610 manual. We are talking about the D610, right? If so, it's in the latest manual.

I can't seem to copy\paste from the pdf, that's why I referred you to it.
 
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RockyNH_RIP

RockyNH_RIP

Senior Member
I thought he was shooting a 5100... It is in his profile and this is the D5100 section.. (Hey, I could be wrong) :)

It would not be the first time for me and surely not that last!

Pat in NH
 
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WayneF

Senior Member
Page numbers in D5100 manual has other issues anyway. There is a small Users Manual and a large Reference manual. My guess is the small Users manual ships with product, but the large Reference manual is needed (both are online). http://support.nikonusa.com/app/answers/detail/a_id/13948#Anchor-9
I'm thinking the small one was an experiment, they stopped it with the D5200. PDF manuals are a good thing though, they are searchable.

The Minimum Shutter Speed in the Auto ISO settings is NOT a minimum shutter speed. It is the Minimum before ISO will be raised (the threshold for Auto ISO). Then ISO is raised while holding at that shutter speed. If ISO is not enough to do it, THEN shutter speed is necessarily lowered more. It will try to obtain a proper exposure.
 
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nmccamy

Senior Member
Disregard what I said! I made a mistake. I was talking about the D610. I know nothing about the D5100. Sorry for my stupidity!
 
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Philth

Senior Member
WayneF said:
Page numbers in D5100 manual has other issues anyway. There is a small Users Manual and a large Reference manual. My guess is the small Users manual ships with product, but the large Reference manual is needed (both are online). http://support.nikonusa.com/app/answers/detail/a_id/13948#Anchor-9
I'm thinking the small one was an experiment, they stopped it with the D5200. PDF manuals are a good thing though, they are searchable.

The Minimum Shutter Speed in the Auto ISO settings is NOT a minimum shutter speed. It is the Minimum before ISO will be raised (the threshold for Auto ISO). Then ISO is raised while holding at that shutter speed. If ISO is not enough to do it, THEN shutter speed is necessarily lowered more. It will try to obtain a proper exposure.
Click to expand...

Thanks. I think I understand it. I opened the reference manual, and here is what is says about it:

When On is chosen, ISO sensitivity will automatically be adjusted if optimal exposure can not be achieved at the value selected by the user (ISO sensitivity is adjusted appropriately when the flash is used). The maximum value for auto ISO sensitivity can be selected using the Maximum sensitivity option in the Auto ISO sensitivity control menu (choose lower values to prevent noise (randomly-spaced bright pixels, fog, or lines); the minimum value for auto ISO sensitivity is automatically set to ISO 100). In modes P and A, sensitivity will only be adjusted if underexposure would result at the shutter speed selected for Minimum shutter speed (1/2000–1 s; in modes S and M, sensitivity will be adjusted for optimal exposure at the shutter speed selected by the user). Slower shutter speeds will be used only if optimum exposure can not be achieved at the ISO sensitivity value selected for Maximum sensitivity. If the ISO sensitivity selected by the user is higher than the value selected for Maximum sensitivity, the value selected for Maximum sensitivity will be used instead.
Click to expand...

I'm still not really sure when Auto ISO would be useful then. I thought that no matter what, the ISO would always stay within the range I had it set, with the shutter speed going no lower than what I had the minimum set at.
 
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WayneF

Senior Member
Philth said:
I'm still not really sure when Auto ISO would be useful then. I thought that no matter what, the ISO would always stay within the range I had it set, with the shutter speed going no lower than what I had the minimum set at.
Click to expand...


If if did that (shutter speed limit), it would be limited, causing unnecessary exposure failures. If you want a specific shutter speed, then set a specific shutter speed.

Camera A or P mode says to adjust shutter speed as necessary.
Auto ISO says to adjust ISO as necessary.

If both, it does both.

It is NOT a Minimum shutter speed. You set shutter speed elsewhere. This is in the Auto ISO settings, and it is the "minimum shutter speed" before ISO is adjusted upwards. A threshold setting. Just a matter of wording maybe.

The purpose is because Auto ISO must hit some physical limit before ISO is increased. For example, in camera S mode, the aperture hits its wide open value before ISO is increased. But A and P modes adjusting shutter speed, that shutter maximum is 30 seconds. This shutter setting in the Auto ISO menu just substitutes another more reasonable limit, so ISO can increase before shutter speed gets to the end at 30 seconds. Seriously. :) Call it Minimum Shutter Speed Before Adjusting ISO. It is in the Auto ISO menu.

I was surprised to hear it went higher than Maximum ISO, so I just ignored that, not knowing about it. I cannot see that, cannot duplicate it here. There would be no need, since shutter speed CAN drop to 30 seconds. I don't know what happens at 30 seconds?

Was this ISO in camera Manual mode? In camera Manual mode, I know ISO can go lower than Minimum ISO, if necessary for the exposure. It is still Auto ISO in camera Manual mode, but it cannot adjust shutter or aperture then to help do it (so the range is small, and it may take more liberties to pull it off).
 
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Horoscope Fish

Horoscope Fish

Senior Member
I don't know if this will help but just ran a test using my D7100... I use Auto ISO and shoot primarily in Aperture Priority mode so that's what my camera is set to use now...

I went into the menus and changed the Auto ISO settings as follows: Minimum ISO to 100. Maximum ISO to 200. Minimum shutter speed was set to 1/125s and I chose an aperture of f/8. It's very dark and cloudy outside right now so this deliberately set up an impossible situation for Auto ISO to manage. The camera behaved as I expected: It used ISO 200 but dropped the shutter speed to 1/40s. Under the circumstances something had to give and that was, obviously, the shutter speed. This is what I would expect Auto ISO to do. It went no higher than programmed, used the aperture I selected and dropped the shutter speed to maintain proper exposure.

Once I increased Maximum ISO to 6400, leaving all other settings the same, the shutter speed went to 1/125s but ISO increased to either 640 or 800 (I forget which). This is, again, what I would expect to happen. The Auto ISO feature tries to use my minimum shutter speed at the aperture I select and bumps the ISO to do that, but only as much as needed to meet the dialed in Minimum Shutter speed.

So, while I'm not sure who's understanding of Auto ISO is correct here, that's how it works for me on my D7100, and that's how I would expect it to work.

.....
 
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