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  1. #1
    Junior Member

    Question ISO changes

    Hi, I have a small problem that to be honest could be user error I go to the local Parkrun on a Saturday to photograph the runners, have never noticed this problem before but this morning but while I was there my ISO kept changing drastically from one shot to the next. today I had my camera set at shutter priority 1/2500, f/2.8 and ISO on auto: sensitivity 100, maximum sensitivity 2500. I won't go into a long story so I'll make it short. The sun was over my right shoulder and as I took a shot of a runner, shutter and aperture stayed the same in all the shots I took this morning but occasionally the ISO went from 250 up to 2500 yet the weather conditions stayed the same. I didn't move from where I was stood and I tried to take each shot as the runner came to it in the same place so the lighting didn't change. I'm hoping someone can help me by explaining why it would do this?.
    Lens was a 70-200mm and the focal length I used was 200mm.

    thanks for any help


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  2. #2
    Senior Member
    JH Foto's Avatar

    Re: ISO changes

    Hello and welcome........................................One of our experts will be along shortly to answer your question.
    I have an advanced degree in procrastination and another one in paranoia.

  3. #3
    Senior Member

    Re: ISO changes

    Well...If you're in shutter priority at 1/2500, f/2.8 and ISO on auto:... the shutter won't change (that's what shutter priority means)

    if there isn't enough light and the aperture is at f2.8... and that's the fastest your lens can go... it can't open any wider... so it won't change

    That only leaves one of the 3 legs of the exposure triangle that can change... the ISO... which you have at auto (that means it changes to accommodate the exposure)

    Sounds like your camera was doing exactly what you had it set to do...


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  4. #4
    Senior Member
    Horoscope Fish's Avatar

    Re: ISO changes

    Quote Originally Posted by uksweetheart View Post
    Hi, I have a small problem that to be honest could be user error I go to the local Parkrun on a Saturday to photograph the runners, have never noticed this problem before but this morning but while I was there my ISO kept changing drastically from one shot to the next. today I had my camera set at shutter priority 1/2500, f/2.8 and ISO on auto: sensitivity 100, maximum sensitivity 2500. I won't go into a long story so I'll make it short. The sun was over my right shoulder and as I took a shot of a runner, shutter and aperture stayed the same in all the shots I took this morning but occasionally the ISO went from 250 up to 2500 yet the weather conditions stayed the same. I didn't move from where I was stood and I tried to take each shot as the runner came to it in the same place so the lighting didn't change. I'm hoping someone can help me by explaining why it would do this?.
    Lens was a 70-200mm and the focal length I used was 200mm.

    thanks for any help
    Your post doesn't say but I'm guessing you were using Matrix metering? With Matrix enabled even small adjustments in the ambient light, and where the light appears in the frame, can cause big changes in how the shot is exposed. With the shutter speed and aperture dialed in and with the sun at your back as you shoot, this sort of behavior doesn't seem that odd to me. Consider also that going from ISO250 to ISO2500 is only what...three and a half stops? (It's too early here for reciprocity, someone correct me if I'm wrong).
    ~ Paul
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  5. #5
    Senior Member
    Challenge Team
    cwgrizz's Avatar

    Re: ISO changes

    Welcome to the forum. To add to what @FredKingston said, I am going to ask what metering mode you have the camera set at? Spot, Center-weighted or Matrix. If for example, you have it set to Spot metering and each runner has on different colored clothes, then the darker the clothes the more exposure the camera would feel was needed thus the only parameter left to change would be the ISO which would be raised. That is just a guess from the way you described your shooting situation.

    Edit: @Horoscope Fish is saying almost the same thing only in the opposite direction with the metering settings.
    Last edited by cwgrizz; 11-19-2016 at 05:35 PM.
    Thanks/Like Blacktop, Don Kuykendall Thanks/liked this post
     
    Walt

    D750; D7100; D5300;
    18-55mm f/3.5-5.6 G II VR; AF-S VR 70-300mm f/4.5-5.6 G IF-ED; Tokina 11-16mm f2.8 (IF) DX II; 200-500mm f5.6E ED VR; AF-S VR 24-120mm f/4G ED; TC14E II



  6. #6
    Senior Member
    Challenge Team
    Blacktop's Avatar

    Re: ISO changes

    Quote Originally Posted by uksweetheart View Post
    Hi, I have a small problem that to be honest could be user error I go to the local Parkrun on a Saturday to photograph the runners, have never noticed this problem before but this morning but while I was there my ISO kept changing drastically from one shot to the next. today I had my camera set at shutter priority 1/2500, f/2.8 and ISO on auto: sensitivity 100, maximum sensitivity 2500. I won't go into a long story so I'll make it short. The sun was over my right shoulder and as I took a shot of a runner, shutter and aperture stayed the same in all the shots I took this morning but occasionally the ISO went from 250 up to 2500 yet the weather conditions stayed the same. I didn't move from where I was stood and I tried to take each shot as the runner came to it in the same place so the lighting didn't change. I'm hoping someone can help me by explaining why it would do this?.
    Lens was a 70-200mm and the focal length I used was 200mm.

    thanks for any help
    Just to add to what @FredKingston correctly explained.

    It also depends on your metering mode as well. Lets say that the light didn't change at all, but one runner was wearing a light colored jersey, and the other was wearing dark.
    The camera will try and expose for those colors differently (especially in spot metering mode). So if you're in auto Iso and shutter priority, it will change your ISO to try and accommodate.

    I also have a suspicion that the light did change somewhat but you didn't notice. It does not take a lot.
    Nikkor 20mm f/2.8 AF-D
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  7. #7
    Senior Member
    Challenge Team
    Blacktop's Avatar

    Re: ISO changes

    Wow @cwgrizz. We typed the same thing at the same time.
    Nikkor 20mm f/2.8 AF-D
    Nikkor 28-105mm f/3.5-4.5-D
    Nikkor 50mm f/1.8-D
    Nikkor 24-120mm f/4 VR
    Nikkor 70-200mm F/2.8 VR I
    Nikkor 200-500mm f/5.6 VR
    Pete's Flickr... Blacktop's Photo and a Song .... Blacktops 365

  8. #8
    Senior Member
    Challenge Team
    cwgrizz's Avatar

    Re: ISO changes

    Quote Originally Posted by Blacktop View Post
    Wow @cwgrizz. We typed the same thing at the same time.
    I guess whether under the hood or in the driver's seat, we think the same. Ha!
    Thanks/Like Blacktop Thanks/liked this post
     
    Walt

    D750; D7100; D5300;
    18-55mm f/3.5-5.6 G II VR; AF-S VR 70-300mm f/4.5-5.6 G IF-ED; Tokina 11-16mm f2.8 (IF) DX II; 200-500mm f5.6E ED VR; AF-S VR 24-120mm f/4G ED; TC14E II



  9. #9
    Senior Member
    WayneF's Avatar

    Re: ISO changes

    Standing in "same place" ought not to change a front lighting or rear lighting situation, and perhaps not even change shade from trees and such... but subject colors certainly affect metering, and also, clouds do tend to drift past now and then, causing temporary shade. Maybe examine the shadows your subjects are casting on the ground... that is a very good indication of lighting level.
    Last edited by WayneF; 11-19-2016 at 06:31 PM.

  10. #10
    Senior Member
    Dawg Pics's Avatar

    Re: ISO changes

    I didn't know about this issue.
    Can you post a couple pics so I can do some more learning?
    "You doesn't have to call me Dawg Pics. You can call me Carolyn or you can call me Sue or you can call me Suzie or you can call me Suzie-Q or you can call me Carol or you can call me Carolyn Sue, but you doesn't have to call me Dawg Pics.

    "Remember to gaze up at the night sky because there is a little bit of the cosmos in each of us."

    Um yeahhhh, I shoot a lot of pics of my dogs.
    D500 (DOB 05/26/17), D300, D80, SB-800





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