Issue with OM-1 RAW Files?

[AliGW]

Is anyone with an OM-1 finding that RAW images, once opened in Develop Mode, flick from correct exposure to over exposed by at least one stop? I am noticing this with every image at the moment. I do not shoot JPEG - RAW only - and the thumbnails in ACDSee look right. Attached is what the same RAW file looks like in Viewer and then Develop Mode. It seems more pronounced with image taken using AEL (exposure lock).

With my Olympus E-1 Mk III images would flatten slightly in Develop Mode, but I never had this issue of an image massively over exposing. To be clear, it's not the fact that the image doesn't look the same in Develop Mode, it's the extent of the difference,

[AliGW]

I have found that the pronounced over-exposure only seems to happen with RAW files whose ISO is lower than 200.

[Regor250]

The flickering comes from ACDSee switching from the embedded JPEG to the RAW unprocessed file. Below ISO 200, the file is basically overexposed in camera and then given a negative EV correction (ISO100 = +1EV @ ISO200 with -1EV applied in post-processing) , hence the reduced dynamic range. ACDSee is giving us (I have an OM-1 too) the uncorrected version @ base ISO200, I am guessing. I'm also guessing that the reverse is different because over ISO 200, the captured light signal can be amplified, whereas below 200 it can not be reduced for whatever technical reason, hence why it is below ISO200 referred to as ISO L100, and L80 rather than ISO100, and 80.

[AliGW]

Sounds probable, and I have set my default ISO at 200 now, which seems to obviate the issue. I do wonder at the change, though, as ISO 100 on the E1 Mk III was never an issue.

[Greyfox]

Sounds probable, and I have set my default ISO at 200 now, which seems to obviate the issue. I do wonder at the change, though, as ISO 100 on the E1 Mk III was never an issue.

From my reading, the native ISO range for the OM-1 is 200 to 102,400, but can be expanded down to ISO 80. The base sensitivity at 200 is higher than the older models, but the high end has been increased (said to be by about 2 stops). There is a lot of on line discussion about the ISO on the OM-1 in photographic forums.

I don't have an OM-1, but on checking I found that nearly all of the OM-1 images I've downloaded along the way for testing (other than those specifically chosen for high ISO) happen to be ISO 200.

[AliGW]

This is currently with the tech team - I shall report here if there is any progress.

[PeterA]

The flickering comes from ACDSee switching from the embedded JPEG to the RAW unprocessed file. Below ISO 200, the file is basically overexposed in camera and then given a negative EV correction (ISO100 = +1EV @ ISO200 with -1EV applied in post-processing) , hence the reduced dynamic range. ACDSee is giving us (I have an OM-1 too) the uncorrected version @ base ISO200, I am guessing. I'm also guessing that the reverse is different because over ISO 200, the captured light signal can be amplified, whereas below 200 it can not be reduced for whatever technical reason, hence why it is below ISO200 referred to as ISO L100, and L80 rather than ISO100, and 80.

You may find the video by Thomas Eisl of interest OM System OM-1 – Image Noise Expert Guide and In-Depth Knowledge - YouTube. In it he explains that the OM-1 has 3 Analogue to Digital converters (ADCs) that operate at different ISOs. My guess is that your issue may be related to how the ADCs work, but the advice is useful background to choosing one's ISO.