why does the exposure change when i change lenses?

[WouldBe]

The convenience of TTL metering comes at a cost, though. It can and will be fooled by unusual subject tonalities. Attempting to shoot a black cat in white snow will probably result in noticeable underexposure. Wedding photographers have great trouble getting the exposure right when the bride is wearing a traditional white dress for similar reasons.

You would get the same problems with a hand held meter. The way I used to get around it was to set the aperture and shutter speed by (spot) metering on something neutral very close to the subject then moving the camera to get the angle I want and ignore what the meter says at that point.

 

[friedaweed]

Perplexed Frieda but most informative thread all round

 

[Hocus Eye.]

You would get the same problems with a hand held meter. The way I used to get around it was to set the aperture and shutter speed by (spot) metering on something neutral very close to the subject then moving the camera to get the angle I want and ignore what the meter says at that point.

WouldBe

You are right here.

In this case you are doing what is called a 'substitute reading' The 'something neutral' close to the subject is the same as doing what others on the thread would recognise as like a 'grey card' reading (the grey card reflects 18% of the light it receives). It was calculated many years ago that if all the tones of the average photograph were mixed up it would result in an 18% grey*. Here you are really doing an incident light reading without realising it. I used to use a green jacket that I often wore for getting correct exposures doing landscapes. Usually though landscapes are easy to expose for, because pointing down to the ground especially if it is grass or a tarmac road will sort this out. Similarly on a clear blue cloudless day the sky directly above you will also render an 18% grey. I was reminded of this by a post further up. I have used this method quite recently.

I am talking to you in this post because you are at last making sense.

*This is the orthodox view, however some writers claim that some cameras are calibrated to 36% grey. This is a stop difference. Isn't photography wonderful and simple?

 

[Herbsman.]

Right, I tested it last night and now there's no difference

So, either my aperture blades got stuck in the few photos I took where the problem occured, or, I changed the ISO or took the neutral density gels off my flashes and forgot. I'm sure I didn't change the ISO, and I'm sure I didn't take the gels off my flashes, so my lens could be occasionally malfunctioning (it's second hand and cost £60 and I've had it for years, so I wouldn't be surprised)

 

[Hocus Eye.]

Right, I tested it last night and now there's no difference

So, either my aperture blades got stuck in the few photos I took where the problem occured, or, I changed the ISO or took the neutral density gels off my flashes and forgot. I'm sure I didn't change the ISO, and I'm sure I didn't take the gels off my flashes, so my lens could be occasionally malfunctioning (it's second hand and cost £60 and I've had it for years, so I wouldn't be surprised)

Great, we can all stop wracking our brains about this one now. . Last night I thought of another possible reason for the problem but will leave it now as the problem doesn't exist it seems. PM me if it recurs.

 

[Herbsman.]

Go on, give it us!

 

[Hocus Eye.]

Herbsman check your PMs

 

[Wilson]

tell us all ya tightarsw ^

Right, I tested it last night and now there's no difference

So, either my aperture blades got stuck in the few photos I took where the problem occured, or, I changed the ISO or took the neutral density gels off my flashes and forgot. I'm sure I didn't change the ISO, and I'm sure I didn't take the gels off my flashes, so my lens could be occasionally malfunctioning (it's second hand and cost £60 and I've had it for years, so I wouldn't be surprised)

so i was right then, thanks

 

[cybertect]

So it's not because it's a different focal length then?

 

[Hocus Eye.]

tell us all ya tightarsw ^

Hi Wilson

Why not PM Herbsman to forward the PM I sent to him? It is however obviously irrelevant and wrong seeing that the problem has now disappeared. I just wanted to talk to Herbsman who understands things photographic (as evidently also do you) without having to repeatedly go through my post syllable by syllable to explain to another particular poster who shall be nameless who seems not to. If you PM Herbsman he can forward you my idea if he chooses to. The idea was was based on a bit of speculation about the lighting on his subject. which was not provided in the OP. My speculation/guesswork was wrong judging by the fact that the problem has gone away so it is not relevant to the original question or really to any others on this thread I would have thought apart from the mildly curious.

.