Stop down metering on canon EMF chip?

1kgcoffee · Joined: 16 May 2014 Posts: 51

So it turns out the reason I have been taking so many overexposed images in Av mode with the EMF adapter, is because the camera (a canon) assumes the aperture is wide open when metering. If I understand correctly, you need to turn down exposure compensation an equal number of stops for the camera to meter correctly if the aperture is set to anything smaller than wide open. For example, if I set the aperture to F5.6 and max is 1.8, I need to reduce exposure compensation two stops

This seems cumbersome. Is there a way for the camera to assume the camera is operating in stop down mode all the time, while still being able to record the aperture value as allowed by the EMF chip? It seems that this is only permitted when the aperture is set to max, or 00

drjs · Joined: 25 Feb 2013 Posts: 484 Location: USA

The only way I find it working properly is to set aperture in camera, followed by ooen physical aperture to max, half press shutter to lock exposure, then physically stop down the lens. I found this method so cumbersome, I stopped using EMF adapters. Now I moved to Sony, I stopped worrying over focus confirmation chips and just stick with focus peaking.

RSalles · Posted: Tue Aug 05, 2014 9:47 am Post subject:

Hi,

Will only work out with a chip that register the max correct aperture of the lens. That's what I have in dozen of lens, speaking of a lot of different chips I tried out,

Cheers,

Renato

PhantomLord · Joined: 08 Apr 2013 Posts: 472 Location: Szczecin, Poland

Hi coffee

Well on my Canon 600d it works like this:
EMF chip installed - in camera aperture in Av or in M mode set to it's 'widest position' it's allowed or programmed and than I could stop down the lens itself and it's measured without a problem.
For instance I have Jupiter 37A 135mm/3.5 lens, I programmed the chip that the widest aperture is f/3.5 so to shoot I set camera to M or Av mode, make sure that in camera f/3.5 is set up and than I could close lens to f/8 for example and shoot with perfect metering. Key is to set the widest aperture in camera and whatever you desire on lens.

The problem is if you for example set the lens on f/5.6 and at the same time you set in camera f/5.6 as well - than you will end up with completely messed up photo.

It's completely logic as camera thinks the lens is wide open during the metering. And if you set the aperture on camera to the wide open setting and stop down the lens to, let's say f/8, the camera will be thinking the lens is wide open and will adjust exposure for that amount of light that is coming through the lens in this example at f/8.
If you however set in camera aperture to f/8 setting and lens to f/8 as well camera thinks like that the lens during the exposure will be stopped down to f/8 but in fact at the time of making measurements it assumes the lens is wide open. However because our lens is stopped to f/8 at the time of measure, the camera gets improper readout, because it assumes the lens is wide open and will be stopped to f/8 at the time of exposure, so it set longer exposure time which results in completely overexposured photos.

Summing up:
On Canon DSLR with absolutely every chip you've to set up the wide open aperture in camera and than you could stop down the lens as you wish without a problem with metering. That's all.

Hope you get the idea Smile

, if not, please write in this topic or send me a PM.

Cheers
Mateusz

PhantomLord · Joined: 08 Apr 2013 Posts: 472 Location: Szczecin, Poland

"Is there a way for the camera to assume the camera is operating in stop down mode all the time, while still being able to record the aperture value as allowed by the EMF chip?"

Really sorry, I made fool of myself not reading your post to the end.

Well...if you would like to record f/stop in EXIF then it's the only reasonable way drjs told about locking exposure (not by going to focus peaking, which sucks in my opinion Wink

).

I was at similar point as you are, but well...I heard somewhere that photography is more about making good photographs than wondering what aperture did you used. I could bet with you that if you will be hanging your photos in the gallery you would not be printing book of EXIF next to each photo Wink

And if you need f/stops to be recorded for example during lens testing, than a piece of paper and a pencil is absolutely fantastic combination.

Cheers
Mateusz

visualopsins · Expire: 2025-04-11

Here's the manual for EMF chip: http://emfphoto.com/forum/index.php?board=1.0

1kgcoffee · Joined: 16 May 2014 Posts: 51

Thanks for the responses!