18 September 2022

I recently started using a couple of fully-mechanical Nikon AI-S lenses with my Canon M50 Mark II body. Since I already had the Canon EF-to-M adapter, I decided to do a double adaption, using thin F-to-EF adapters for the Nikon lenses, effectively converting them into EF lenses, and then mounting them on the EF adapter.

Since I was adapting these lenses to EF, I had the option of using either chipped adapters or unchipped adapters. Using chipped adapters held the possibility of recording the lens focal length, the lens maximum aperture, and the shooting aperture in the EXIF data.

However, getting chipped adapters to work correctly on certain bodies — including mine — is not straightforward. This essay explains the issue and some possible solutions.

Chipped EF Adapters

A chipped adapter has electrical contacts backed by a microprocessor and enables electronic communication with the body. Of course, unlike a real EF lens, it has no control over the lens aperture.

A FotoFocus chipped F-to-EF adapter showing the EF side with the contacts.

Why would you want such communication? There are three reasons: enabling focus confirmation on a Canon EF or EF-S body, enabling the focus guide feature on a Canon RF body, and recording EXIF data.

Focus Confirmation

When you use manual focus with a EF or EF-S lens on a Canon EF or EF-S body, the phase-detection focus sensor in the optical viewfinder activates when you half-press the shutter button. This means that you can place a focus point on a subject, adjust the focus manually, and then stop focusing when the focus point lights up and the body beeps. It’s very convenient.

However, this feature is only available with EF or EF-S lenses or, more generally, lenses that respond to the electronic communication from the body like EF or EF-S lenses. If the lens does not respond electronically, the body will not activate the focus sensor. Obviously, an unchipped adapter will not respond electronically and so the focus sensor will be inactive. However, the response from a chipped adapter is sufficient to activate the focus sensor.

Focus Guide

Similarly, the focus guide manual-focus aid on a Canon RF body is only activated when using an RF lens, a EF or EF-S lens, or a lens with a chipped adapter. It is not available when using a lens with an unchipped adapter.

Recording EXIF Data

When you use an unchipped adapter, the camera body often only records the shutter speed and the ISO. A few bodies will allow you to manually set the lens identity on the body.

However, you can program a chipped adapter to set the values of the focal length and the maximum aperture of the lens. The adapter communicates these values to the body, which then records them in the EXIF data. This can help keep track of the lens identity, facilitating the use of a tool like Lens Tagger to add a more precise identification of the lens to the EXIF data after shooting.

Furthermore, you can use a chipped adapter to record the shooting aperture. To achieve this, you use M or Av mode, select the shooting aperture mechanically on the lens, select the same aperture on the body too, and expose. The camera records the focal length, maximum aperture, and shooting aperture in the EXIF data.

This doesn’t work with an unchipped adapter, as the body will typically display the aperture as an invalid value (often f/0) and will not let you change it.

Metering Issues

With certain bodies, there are issues with metering that can cause overexposure. The explanation for this problem comes from considering the two ways in which cameras meter an exposure.

One method is stopped-down metering. The camera leaves the lens at the shooting aperture at all times, or at least closes it to the shooting aperture just before metering, and meters at the shooting aperture. This is typically used by DSLRs and mirrorless cameras when there is no communication with the lens, which facilitates the use of adapted mechanical lenses on these bodies.

If a body uses stopped-down metering, then it will correctly meter with a mechanical lens on a chipped adapter and with the shooting aperture set on the body. Everything should just work without having to take special measures.

The other method is wide-open or full-aperture metering. When not exposing, the camera leaves the lens at the maximum aperture. It meters at the maximum aperture, adjusts the exposure for the difference between the maximum aperture and the selected shooting aperture, stops down the lens to the shooting aperture just before the exposure, exposes, and then returns to the maximum aperture after the exposure. This method is used by later SLRs and by DSLRs. In particular, it is used by Canon EF DSLRs when there is communication with the lens.

If a body uses wide-open metering, then we can easily see what can go wrong. Consider a lens with a maximum aperture of f/1.4 lens being used at a shooting aperture of f/2.8 set on both the lens and the body. The body meters, expecting the lens to be open to its maximum aperture of f/1.4 but it is actually stopped-down to f/2.8. It adjusts the exposure by two stops to compensate for the difference between the maximum aperture of f/1.4 and the selected shooting aperture of f/2.8. When the exposure is taken, it commands the lens to stop down from f/1.4 to f/2.8, but of course the lens does not respond, and the body takes an exposure that is overexposed by two stops.

If your body uses wide-open metering, all is not lost. Let me now explain two methods to get correct metering.

Correct Metering and Not Recording the Shooting Aperture

If a body uses wide-open metering, then there is a fairly simple way to correct the metering problem. However, it comes at the cost of not correctly recording the shooting aperture.

First, note that if you set the aperture on the body to the maximum aperture of the lens, wide-open metering will work even if the lens is actually stopped down, since the body will not make any adjustment between the metered exposure and the shooting exposure.

One way to achieve this is to first mount the lens with the fastest maximum aperture, set the aperture on the body to the maximum aperture (in M or Av mode), and then make no further adjustments to the aperture on the body. As you change lenses, the body will automatically select the maximum aperture of the mounted lens, even as you swap between faster and slower lenses, and will meter correctly.

While this gives correct metering, it does not correctly record the shooting aperture. However, if you just want to record the lens focal length and the maximum aperture, this method is perfectly adequate.

Correct Metering and Recording the Shooting Aperture

If a body uses wide-open metering, there is a means to get correct metering and record the shooting aperture, but it’s perhaps not for everyone.

The method is essentially to manually adjust the lens aperture according to the body’s expectations. Each time you want to meter, start by setting the aperture on the body to the shooting aperture and the aperture on the lens to wide-open. Then, either set the shutter speed and ISO manually according to the body’s meter or use automatic metering and then lock the exposure by pressing the AE lock button. Finally, set the aperture on the lens to the shooting aperture, focus, and expose. (Of course, if you’re shooting wide-open, you can just meter and expose in one step.)

If you’re going to use this method, you probably will want to disable exposure simulation, otherwise when you stop down to the shooting aperture the electronic viewfinder or monitor will show a darker simulated exposure.

This procedure is slower and more error prone than simply half-pressing to meter. That said, one of the attractions of manual-focus lenses is being a direct part of the focusing process, even though it is slower than auto-focus. This procedure makes you a direct part of the metering process too, perhaps giving you more awareness of your shutter speed and ISO, and so it might well appeal for similar reasons.

I would note that the two styles of metering can be combined. If you need faster metering, you can set the shooting aperture on the body to the wide-open aperture and get instant metering at the cost of recording the incorrect shooting aperture. If you have more time, you can use the slower method and record the correct shooting aperture.

Bodies That Use Stopped-Down Metering

Stopped-down metering with EF lenses and chipped adapters is used by:

The reason this works is that the Metabones EF adapter in Advanced Mode emulates a native E-mount lens, and Sony E-mount bodies use stopped-down metering with native lenses.

With this combination, you can freely set the aperture on the body to the shooting aperture, have it recorded in the EXIF, and still have correct metering without taking special measures. (Furthermore, it is robust, in that even if you have an accidental mismatch between the shooting aperture set on the body and the lens, it will meter correctly.)

Bodies That Use Wide-Open Metering

Wide-open metering with EF lenses and chipped adapters is used by:

Here, the Canon bodies follow the standard EF protocol and so use wide-open metering. The Sigma MC-11 and Metabones adapters in Green mode both emulate A-mount lenses, and Sony bodies use wide-open metering with such lenses.

All of these combinations will have the metering problem I describe here and will have to use one of the work-arounds to get correct metering.

Conclusions

My interest in chipped adapters was not in enabling focus confirmation or focus guide, since my Canon M50 Mark II doesn’t have either. (It does offer focus peaking and magnification even when using unchipped adapters.) Rather, my interest was in recording EXIF data, and in particular the shooting aperture. I’ve been using Lens Slate for this, but it’s a bit of a faf.

The M50 Mark II with the Canon EF adapter uses wide-open metering when there is communication with the lens and stopped-down metering when there is no communication with the lens. A chipped adapter provides communication, and so the body uses wide-open metering. Therefore, in order to get correct metering and record the shooting aperture, I have to adopt a more complex metering procedure described above.

I typically use adapted lenses when I’m shooting for myself and deliberately slowing down the process. For me, then, I think adopting the more complex metering process will not a problem.

You may reach a different conclusion. However, I hope I’ve helped you understand chipped EF adapters, how they interact with the metering system of your body, how to get correct metering if your body uses wide-open metering, and whether they are suitable for your needs.

Acknowledgements

Thanks to DPReview user Ernst Dinkla for suggesting that I consider chipped adapters and to other users Larry Rexley, Sittatunga, Victor Engle, and Ernst Dinkla again for information on the metering behavior of various cameras and EF adapters.

Further Notes

Determining the Metering Method

How can you tell if a body uses wide-open or stopped-down metering with EF lenses? The easiest way is probably to mount a real EF lens. In Av mode, check the behavior of the lens aperture when the shooting aperture is set to, say, f/8. When you half-press the shutter button to focus and meter, if the lens stays wide-open, then the camera probably uses wide-open metering. However, if the lens stops-down to the shooting aperture, the body probably uses stopped-down metering.

FotoFocus Chipped Adapters

I tested a chipped F-to-EF adapter from FotoFocus, although I would anticipate that many other chipped adapters would show similar behavior. This adapter has a 9th generation EMF chip.

I had to use a Canon DSLR to program the focal length and maximum aperture, as my attempts to program it with my M50 Mark II failed. However, once programmed, my M50 Mark II did correctly read these parameters and record them to EXIF.

I was also able to program the focus micro adjustment, but my M50 Mark II did not record it. While of course mirrorless cameras do not need focus microadjustment, it might have been useful to distinguish between lenses with the same focal length and maximum aperture.

FotoFocus also have chipped adapters for Nikon F with an aperture lever for AF-G lenses, M42, Olympus OM, Pentax K, and Contax/Yashica C/Y mounts. The chips are also available separately, if you want to install them yourself. Chips and chipped adapters are also available from other brands, although I’m sure many are simply rebranded.

There are also chipped adapters for mounts that have shorter flange-focal distances than EF, such as Minolta SR/MC/MD and Canon FD. However, these adapters either prevent the lens from focusing at infinity or include a diverging lens to place the focal plane in the correct position for EF.