I'm wondering if you have your metering mode set for something other than matrix. Spot or center weighted can make your exposure vary by framing slightly different between shots. Also make sure bracketing is OFF, that can make you crazy. Exposure compensation is another possibility. Just throwing ideas out there without seeing pictures.
As for auto iso, you have your base set for 100 and its set to auto. So the camera will go as low as 100 and raise as needed to make a proper exposure. Not clear if you have a high end iso set. Looks like it doesn't matter for the shots described. There is another component to auto iso. That is the minimum shutter speed before the camera will bump up the iso. You either have it set to 1/30 or it is set to auto. Auto will pick the lowest shutter speed for the lens used. It would probably pick 1/30 for that lens. This means while in Aperture mode, the camera will try not to go lower than 1/30 before bumping the iso.
This is how the camera handles these shots in Aperture mode... Iso starts at 100. You set f16. The camera felt a need to slow the shutter speed for proper exposure. It stopped at 1/30. At that point it raised the iso to make a good exposure. Nothing (aperture, shutter and iso) is bottomed out so both shots should be exposed correctly. So I think it has to be one of the things I mentioned above, meter mode, bracketing and exp comp.
Side note, I don't like auto iso in shutter or aperture mode. It gets confusing. If I need auto iso, I shoot manual. Then I pick the aperture and the shutter speed and the camera adjusts iso to make it work. Its still automatic but i have control over my shutter and aperture. If I need to shoot in shutter or aperture mode, I turn off auto iso and set it manually.
Thank You so much nickt for reading my post so well.
Yes my metering is Center & will not change with my Non Cpu glass.
Yes set to auto iso & 100 iso for a start by the D7100 manual.
As to your side note. I believe that a jump to manual control is the only way I can continue to use my old Nikkor glass.
Just a small bit of my Digital journey. I started by ordering a used D7000 it arrived damaged, however I did gain some experience.
I was still unsure of what parts of my Nikkor glass would work on this Digital camera & what could damage it.
I mounted a 50mm F1.8 series E lens & took some shots all were dark so I bumped the iso up & observed a weird electronic interference
in the picture on the back screen.
I sent the D7000 back & accepted a D7100 with 850 shutter count, I have this camera now. So you can see how at this point I
am looking back at this and LMAO. One great thing happened to my glass collection was the like new Nikkor 105mm F2.8D micro this
is a fantastic lens I found online 2 mos ago..
The 105mm micro is an AF lens & it searches a lot in AF, however it takes great photos. I see a lot of Photographers have cameras in the D7000 series
so it must be something I am doing wrong. Thank you for reading & responding to my questions with understanding & really great advice.
nickt I see by your gallery we share a love of animals & Close up photography :encouragement: I'll get the bugs worked & be seeing you around the Forum.
Mike