Haven't come across this before.

[Sorarse]

I recently found an old 24mm FD lens in my 'photography' cupboard, so thought I would give it a go on my 40D with the use of an EF-FD convertor.

Obviously there is no autofocus, and the aperture has to be set manually, but here's the strange thing; at f/4.0 exposure is spot on. If I open up the aperture to f/2.8 the image is underexposed by about 1/3 stop. Conversely if I close the aperture down from f/4.0, the resulting photos are overexposed by 1/3 stop for each subsequent stop of aperture. By the time I get to f/22 I am having to dial in -1 2/3 of exposure compensation to get a correct exposure.

As this lens is being used in what is effectively 'stopped down' photography, I'm surprised the camera can't work out correctly how much light is being passed at the various aperture settings other than f/4.0.

Just wondered if anyone had experienced anything similar.

[PhotosGuy]

I've never noticed that problem using my Nikkors on the 20D, but I use this for exposure.
Need an exposure crutch? (http://photography-on-the.net/forum/showthread.php?t=89123)

[JCH77Yanks]

I guess that's where the electronics of the modern lens comes into play... Although "wide open" during metering, an EF lens will communicate w/ the camera and the "brains" of the camera will give a reading according to the aperture info given by the lens. I guess that since there is no base info given from the FD lens, and less light is passed through while the lens is stopped down, the body wants to give a "proper exposure" reading. That's just my guess, though.

[Sorarse]

Have spoken to Canon and all they could say was the problem is there because I am using an incompatible lens. Well I knew that before I phoned them.

I think what they are really saying is that the 40D is incapable of working in stopped down metering mode, which my old A1 and T90 were able to do. Two steps forward and one step backwards.

It's not a problem now that I am aware of it, as long as I remember that I need to make an appropriate exposure compensation based on whatever aperture I set the lens to.

[Moppie]

Or you could meter wide open (which is what the camera does with an EF lens on) then stop down to take the photo (which is what the camera does with an EF lens on). :cool:

[440roadrunner]

I have a NUMBER of old manual lenses which I play with, and all I can say is,

welcome to the lashed-up world of adapted manual lenses. I have some lenses that pretty much meter correctly through their 'greater' aperture range, and others that for inexplixable causes, simply uh, don't.

About all you can do is play with it until you learn the quirks, and note them.

One reason I even discovered this problem was in the process of trying to chart the "sweet spot" of some of them, shooting in AV, on a tripod, I just kept stopping down and shooting. At some point, at least some lenses go awry on metering.

[Sorarse]

All good advice guys. I've already discovered that it exposes correctly if I set the aperture to f/4.0, and it's just a case of making alterations based on the reading at f/4.0 if I want to take a picture at any other aperture.

[440roadrunner]

Or you could meter wide open (which is what the camera does with an EF lens on) then stop down to take the photo (which is what the camera does with an EF lens on). :cool:


This won't help. There is no interconnection between the camera/meter and the lens. The EF lenses tweek the meter "as if it" were stopped down by communicating the stop setting to the camera. Here, you must actually meter with the manual lens already stopped down

[Moppie]

Set the aperture on the camera to the one you plan to shoot with on the lens.
Crank the lens wide open and meter, then stop it down and shoot.

Then you will know if it is the lens not stopping down in equal stops, or the camera having trouble metering through a stopped down lens.

[440roadrunner]

Set the aperture on the camera to the one you plan to shoot with on the lens.
Crank the lens wide open and meter, then stop it down and shoot.

Then you will know if it is the lens not stopping down in equal stops, or the camera having trouble metering through a stopped down lens.

You are confused, somewhere. He is speaking of an FD lens, a manual lens, which has NO communication with the camera. The camera defaults to something like F0.0 with no AF chip, or on mine F1.8 aperture when using an AF chip. In theory, for example if you were in Av, the meter "should" check the light through the lens, check the ISO setting, and compute the shutter speed based on the light through the lens. Most of the time it works out close, but for some reason, some apertures, and some lenses, it simply doesn't

With no electronic lens mounted, you cannot set the aperture on the camera. With an AF chip, it may read something else, but you still cannot adjust it.

[Moppie]

Yip, my mistake. For some reason I though you could still let the Aperture when shooting in M.

However, if the camera meters accurately wide open, you can still meter wide open, compensate and stop down.

[Sorarse]

Yip, my mistake. For some reason I though you could still let the Aperture when shooting in M.

However, if the camera meters accurately wide open, you can still meter wide open, compensate and stop down.

That's pretty much what I am doing, though with this particular lens accurate metering occurs when the lens is stopped down to f/4.0.

It underexposes at f/2.8 and overexposes at f/5.6 and higher.

[PhotosGuy]

It underexposes at f/2.8 and overexposes at f/5.6 and higher. So why not use the link I gave you & meter at the aperture you're going to use?

[Sorarse]

So why not use the link I gave you & meter at the aperture you're going to use?

Because I tend to learn by doing rather than reading. I have had a look at your link, and whilst I am sure there is some very good advice in there, I found it too wordy.

Now that I have discovered that there is a problem with this particular lens, I have now worked out how to compensate for the various readings I am getting when I use the lens at any aperture other than f/4.0.

Please don't think that I am knocking the information in your link, it's just that I have been taking photographs for more than 30 years now, and have a rough idea of the correlation between the various elements that go to make a correct exposure.

The reason for me posting originally was that with my 35mm film cameras (A1 and T90) I was quite used to taking photos in stopped down metering mode, and was quite surprised to find that the 40D wasn't capable of doing that.

[Quad]

A lensbaby does the same thing on my 5D it is fine wide open but will overexpose if I put in a smaller aperture and use AV. Theoretically it should be able to meter and set the correct shutter speed but it doesn't and it doesn't with consistency.

[440roadrunner]

Actually, Derek, I believe that one of my EF/ EF-S lenses, and it MAY be my kit lens, does some of the same thing, just not as bad as some of the old manuals.

Once again, I was shooting from a tripod, in Av, just stopping down and looking for the "sweet spot." At some point during the series, the exposure gets a little off. This seems to be a metering problem, plain and simple, IE it doesn't seem to matter whether you are in Av or M, the meter is simply off at some apertures. It seems to vary with different lenses. The worst of course, are my old manuals. I BELEIVE it's my old Tamron Adaptall-2 SP 17mm is the worst. At small apertures, you simply have to play to get the exposure correct, or they come out VERY overexposed.

[E-K]

Doesn't this kind of make sense? The meter sits on the eye side of the focus screen. Focus screens can impact metering (e.g. that's why you need to set it in the custom settings on camera's that officially support it). I know from experience that the OEM screen on my XT stays comparatively brighter as I stop down compared to the 3rd party one. From that you can conclude that metering needs to apply a corrective curve based on aperture. Since the camera doesn't know the aperture, it has to assume an aperture (say f/4).

Is this happening with the OEM screen or a 3rd party one?

e-k