SL2 Exposure results wide variation

[hoppyman]

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I recently shot a project in window light 1600 ISO f/2 with the 35 Summicron. I saw a wide and unexpected variation in the DNG files shot to shot.
I experimented with different metering options combined with different focus methods, where understandably there will be variation in results.
However setting manual exposure (here) 1/320 f/2 with zero compensation set I saw a large difference in the results (no visible change in the available light).
The EXIF reports the settings unchanged shot to shot but the results are hugely different. These shots 3 seconds apart.
I hadn't seen this in a previous project with similar conditions.
I don't think I have made some basic error but (and I am a couple of thousand frames in with the SL2 so far) but I can't account for this so suggest away. My only speculation is about which shutter mode was operating (in hybrid).

Any suggestions/comments on a possible cause would be welcome.
No there was no solar eclipse or visible change in the light from window.

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[Exodies]

Dark matter?

[sebben]

Auto iso?

[spassig123]

I don't see any pictures.

Why?

Jochen

[spassig123]

vor 9 Stunden schrieb hoppyman:

However setting manual exposure (here) 1/320 f/2 with zero compensation set I saw a large difference in the results (no visible change in the available light).
 

What does zero compensation mean?

Jochen

[giampo]

I don't see the photos.

I myself did quite a lot of studio shoots with the SL2 but never experienced what you said.
Could be the flashes that are failing in some way? Maybe shooting too fast and not let them recharging completly? Only suppositions...

[Donzo98]

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10 hours ago, spassig123 said:

What does zero compensation mean?

Jochen

Pretty sure he/she means NO EXP COMP.

[spassig123]

vor 23 Minuten schrieb Donzo98:

Pretty sure he/she means NO EXP COMP.

Thanks for feedback.I‘m German. I don’t understand the technical reason . Can you give a link to manual?

Jochen

[hoppyman]

I thought I deleted all of this post content as I decided I should have investigated further before posting here.

this was available light from window predominating with reflector helping lighten a little from behind  and the room lights were on. 

no flash, fixed ISO of 1600,  1/320th f/2 EV0 that is, no exposure compensation set, centreweighted metering  And on rechecking Exposure mode was A not M but both frames identical settings,

same subject, angle etc. No visible difference in the light level in the room.

 2 frames three seconds apart with identical settings reported in EXIF but very large difference that looks like a couple of stops difference.

It sounds impossible so I thought I should keep investigating and thought I deleted the post content entirely.

EDIT: I have reconfirmed the identical settings I detailed. It has to have been fluctuating window light  ( moving light cloud) that I was not aware of.  I can see variations across the 600+ frames I shot and variations existed in both A  and M mode and something I am not aware of in my metering.

 

Edited February 25, 2020 by hoppyman

[hoppyman]

A further follow up as this remained visible when I thought it was deleted. Just in case anyone else might encounter this issue.

in A mode the identical exposure parameters can be explained if I locked AE as well as AF with back button and or shutter release at the first exposure and I did not notice the ambient light change.

My dealer also just reminded me that the Self-timer LED/AF assist light is also an exposure sensor. Inadvertently obscuring that or partly so will affect the exposure too. Easy for me to do when holding the camera even on tripod which it was.  That might explain a lot. Availability of an L module on baseplate should help me there.