What is ADI Flash metering?
What is ADI Flash metering? Comparing against Preflash-TTL metering – by M Sulhan Juman
I would like to welcome all the Sony Alpha Flash System users out there – new and current users. I’ve received some queries from fellow Sony Alpha flash users on the differences between the ADI flash metering and the TTL metering system. The ADI function – also known as Advance Distance Integration, is a feature that was introduced during the time when Minolta introduced this ADI functionality as an added feature to its then most advanced film camera the Dynax 7 (also known as Maxxum 7) film camera.
1. A little bit of History
The launch of the then Minolta Dynax 7 film camera saw the launch of some of the upgraded lenses and flashes that supported this ADI (Advance Distance Integration) feature – noted by the ‘D‘ notation on its lenses and the Flash model numbers. When the Dynax 7 was introduced, there were some new lenses and flashes that was launched along side such as the :
- Lens – Minolta 24-105mm f3.4-4.5 (D) – later rebadged to Konica Minolta – then Sony
- Lens – Minolta 75-300mm f4.5-5.6 (D) – later rebadged to Konica Minolta – then Sony
- Flash – Minolta 3600HS(D) – Designed for Film and able to support Pre-Flash TTL (P-TTL) required in Digital SLR systems
- Flash – Minolta 5600HS(D) – Designed for Film and able to support Pre-Flash TTL (P-TTL) required in Digital SLR systems
There were several lenses being upgraded and relaunched shortly after – featuring the new ADI functionality as part of its flash metering options.
2. Implementation of ADI
The ADI functionality is achieved by integrating encoders within the lens hardware to send-back actual focusing distance of subject back to the camera’s exposure computation system. This information is then used by the camera to compute the actual flash power that it is required to ensure that enough flash is fired to provide the right illumination of the subject at that given distance.
Typically, in older lenses that does not support ADI functionality, information that are fed back to the camera ONLY includes:
- the actual focal length information by means of focal length position encoder and
- the lens information data which resides in the ROM (Read Only Memory) within the lens itself.
This can be identified by the number of pinouts on the electrical contact points on the lens. However, in newer Konica Minolta lenses that supports the ADI functionality, they do carry the (D) notation on the lens itself. When Sony breathed new life to the Alpha mount system, some of the older lenses from the Konica Minolta era were upgraded to include the ADI functionality. The newer lenses that supports ADI functionality can be easily identified as they normally have 8 or more contacts on them.The image below shows the tow generations of lenses – left (older Minolta lens) & right (Konica Minolta era lens).
The (D) notation is printed on the newer pre-Sony, Minolta & Konica Minolta lenses which supported ADI functionality. When the Alpha mount camera system was taken over by Sony, Sony dropped the (D) annotation. I believe that Sony would eventually have ADI functionality on their new generation lenses – supported by the new generation DSLR and the SLT cameras.
Fig. 2 An example of the (D” annotation on the lens marking
3. ADI in action
The ADI functionality is a user selectable function under the flash settings menu on the camera. Allowing users to select between the Pre-Flash TTL and ADI metering. The ADI function is designed to give better illumination on subjects that may have high reflectance surfaces such as:
- shiny metallic surfaces and
- Shiny skin
- polished surfaces etc.
In these cases, when the flash head is pointed directly to the subject, there is a great tendency that the flash “highlight spot” may appear on the above mentioned surfaces within the frame and metering area of the camera. These reflected light will appear as bright spots within the metering zones. If the actual subject distance is unknown to the camera, the flashing will be metered based on the illumination as in the normal Preflash-TTL mode. This will result in a darkened under- exposed image. However, in the ADI mode, the actual camera to subject focusing distance is fed back to the metering system is used in the computation of the final flash to be fired which will then avoid under-exposure.
The examples below shows the results form a Preflash-TTL (P-TTL) versus the ADI (Advance Distance Integration) mode. In the test, a mirror was placed on the subject with the position of the flash visible through the lens (view finder/LCD). The Sony HVL-F43AM was used here on the Sony A77 for this test. The first shot was using the flash in Pre-Flash TTL mode.
Fig. 3 Under-exposed image due to presence of bright (reflected) flash illumination into frame (Preflash-TTL)
As seen from the above example, the ADI functionality actually comes handy in situations where bright high reflecting surfaces may be unavoidable.
The ADI functionality is a very useful feature that every photographer using the Sony Alpha flash system should be familiar with. This can also be use ful for portraitures, product photography and industrial photography applications. I personally use this often during our food photography andproduct shoots where foods are served in highly reflective bowls and containers.
Do have a go at trying out the ADI function and do share with us your experiences and feel free to write back to us should you have any questions on how to use the ADI functionality. Till then, thank you for checking out this little article.
Sulhan @ Alphastrobist