Confusion with long exposures not being over exposed.

[Bob Pringle]

I am  experimenting with  10-stop ND filter and an app to calculate exposure time, to get long exposure in daylight on Sony A7R5. If the app suggests an exposure time of 2 minutes I dial that in to the exposure time under Bulb Timer Settings. Exposure turns out fine. Then I thought, lets see what happens if I dial in an exposure time of 3 minutes. You would think it would be way over exposed, totally blown out, and it is when I try the same experiment on  my DSLR. However the shot comes out fine again. Tried various other timings to try to over expose, but shot always came out fine. Totally baffled.

[XKAES]

You need to be more specific.  What camera(s) are you using and what settings are you using.  How are you metering?

We are not sitting there with you looking at what you are doing.

[Cameratose]

Assuming all other settings remained the same:

3 minutes is about 1/2 stop more than 2 minutes. I wouldn't expect to see much difference. It doesn't matter that you're dealing with long exposures, the same basic photography rules apply. Try exposing for 5 minutes and see what happens.

[Zedster]

Digital sensors do not suffer from reciprocity failure in the way film does, they are linear. Cameratose's suggestion is the most likely. Also with such long exposures, there could be subtle changes in lighting levels between the two shots taken at seperate times, that the human eye could not perceive.