differences in metering with different cameras?

sineadw

Hi all. Myself and Buzz Lightyear did a studio shoot yesterday. We had the lights metered using an external meter and all was looking perfect with Buzz's camera (A Nikon - D60 I think?), yet it was blowing out a bit with mine - a 5D mk I. And on the histogram - not on the backscreen. All other things were the same - ISO, aperture, shutter speed, EFL.. Any idea why this would be? It didn't make that much difference - I just had to stop down on the aperture. I'm just curious as to why thered be as much as a two stop discrepancy in some instances.

waits for 'because canon are crap' comments.. :rolleyes:

kumate_champ07

what kind of metering were u using? perhaps it was spot metering for the external and evaluative for your canon?

sineadw

The metering was external - using a separate light meter so we weren't going by the metering on either camera - just what the meter gave both of us, read from each light individually... The test shots were blowing out on me.

ThOnda

The lens. You had different lenses with different amount of elements, lenses and thickness of the glass (plastic). Even different amount of transitions from air to lens (and back) causes reflections in which you can loose light.

So you have cheaper lens with less elements or better lens with lenses made from better materials

But I may be more than wrong, of course.

DaireQuinlan

That's kinda wierd all right. You'd probably expect a little bit of a differance in practice I guess because of the vagaries of the individual cameras, lens mounted etc etc but it shouldn't amount to anything really noticeable. 2 stops sounds crazy. Did you have exposure compensation dialled in on your camera ? You double checked that everything else was the same between the bodies ? Were you shooting from the same angle ? That might make a bit of a differance to the highlights.

ThOnda

Just an idea - if you were shooting closer to the subject, that would also increase the amount of light recorded by the sensor. That would happen if he had used longer focal length than you for the same framing in the viewfinder.

CabanSail

Tis is quite a puzzle.

The Exposure Compensation will not affect things as it works on the internal meter, which you were not using.

Both camera's would be set on full manual. The Shutter Speed is irrelevant as the exposure time is set by the speed of the lights. So the only variables are Aperture & ISO.

Two stops is quite a difference, one sensor is seeing only a quarter of the light of the other.

Buzz didn't have a CPL Filter on by mistake?

CabanSail

ThOnda wrote: »

Just an idea - if you were shooting closer to the subject, that would also increase the amount of light recorded by the sensor. That would happen if he had used longer focal length than you for the same framing in the viewfinder.

That should not be a factor either as the light meter is reading incident light rather than reflected light.

DaireQuinlan

ThOnda wrote: »

Just an idea - if you were shooting closer to the subject, that would also increase the amount of light recorded by the sensor. That would happen if he had used longer focal length than you for the same framing in the viewfinder.

Nah, that wouldn't make any differance. Ideally to meter these things you'd use a flash meter to take an incident reading at the subject position pointing toward the camera. This is your metering for that point regardless of whether you're 1 foot or 10 feet away.

ThOnda

Let me disagree. The light goes from the source to the object. And is metered there. And then it is reflected and goes to the camera. And still, the light is receding with the root of the distance also between the reflected surface and the camera.

The CPL is also good hint, never thought about it (not having CPL for any of my recent lenses).

DaireQuinlan

ThOnda wrote: »

Let me disagree. The light goes from the source to the object. And is metered there. And then it is reflected and goes to the camera. And still, the light is receding with the root of the distance also between the reflected surface and the camera.

Trust me, thonda, that's not the way it works. Just as an experiment, try spot metering a wall across the room from you. Now walk up to the wall and spot meter the same place. You'll get the same reading. By your theory above you ought to get a higher reading the closer you get to the wall.

DaireQuinlan

I got it ! Everytime sinead went to take a shot, buzz stood in front of one of the lights :-)

nilhg

sineadw wrote: »

Hi all. Myself and Buzz Lightyear did a studio shoot yesterday. We had the lights metered using an external meter and all was looking perfect with Buzz's camera (A Nikon - D60 I think?), yet it was blowing out a bit with mine - a 5D mk I. And on the histogram - not on the backscreen. All other things were the same - ISO, aperture, shutter speed, EFL.. Any idea why this would be? It didn't make that much difference - I just had to stop down on the aperture. I'm just curious as to why thered be as much as a two stop discrepancy in some instances.

waits for 'because canon are crap' comments.. :rolleyes:

Just trying to think this through, you say the EFL was the same, so both cameras were side by side with lenses set to give the same field of view? That would rule out ThOnda's theory. I'm just wondering if any sort of in camera processing could account for the differences? A side effect of something like Nikon's D Lighting?

It would be interesting to see the images with full exif.

sineadw

Nope - no CPL, all manual and we were both using decent primes so I can't see the lenses making any real difference even if that were to be a factor. Odd, huh?

I thought maybe there'd be a bit of a difference in the sensors, but I was surprised at the different light getting in. It seemed to be my body that was at fault too - buzz's was spot on with the metering for the lights. I've never had a problem in the studio before though?

Buzz Lightyear

sineadw wrote: »

(A Nikon - D60 I think?)

D80 actually . Either way we were both shooting manual. The light meter gave us a reading of say f8 for the subject. I dialed in F8 and got a correctly exposed image, however Sineads D5 was being blown out by the same settings. Very bizare ! She ended up shooting at about F11 to achieve the same on screen exposure as myself. Her ISO was equal, as was the shutter speed.

So on manual there should have been no difference - except if she had dialed in exposure compensation at some stage, which with it not being my camera I couldn't immediately tell.

Daire - shooting from the exact same spot.
Cabansail - As for a filter - I was shooting mainly with my 50 without a filter, however it was Sinead who was getting blown.

sineadw

nilhg wrote: »

Just trying to think this through, you say the EFL was the same, so both cameras were side by side with lenses set to give the same field of view? That would rule out ThOnda's theory. I'm just wondering if any sort of in camera processing could account for the differences? A side effect of something like Nikon's D Lighting?

It would be interesting to see the images with full exif.

Mine's full frame, but I was shooting with longer lenses. We were both shooting raw so nothing in camera should have impacted that much? Am I right there? Don't know what D lighting is...

sineadw

Don't think I can dial in exposure compensation in Manual Mode?

kumate_champ07

ThOnda wrote: »

The lens. You had different lenses with different amount of elements, lenses and thickness of the glass (plastic). Even different amount of transitions from air to lens (and back) causes reflections in which you can loose light.

So you have cheaper lens with less elements or better lens with lenses made from better materials

But I may be more than wrong, of course.

the rated f stop for each lens would take that into account wouldnt it? or is the f stop just the size of the aperture/diaphragm relative to the focal length and not necessarily exactly how much light is transmitted thru it?

ThOnda

F-stop is just geometrical value, not considering optical properties of the materials of the optical elements.

Buzz Lightyear

ThOnda wrote: »

F-stop is just geometrical value, not considering optical properties of the materials of the optical elements.

F-stop maybe only a geometrical value, however unless you've bought your lens from Penny's or Dunnes Stores, they should be calibrated to allow a certain amount of light through the opening (aperature). So unless Sinead's Canon lens's were a monday morning jobbie, I can't see that being a factor ...

kumate_champ07

DaireQuinlan wrote: »

Trust me, thonda, that's not the way it works. Just as an experiment, try spot metering a wall across the room from you. Now walk up to the wall and spot meter the same place. You'll get the same reading. By your theory above you ought to get a higher reading the closer you get to the wall.

that would explain how we dont have total darkness being so far away from the sun!

kumate_champ07

have you had the 5d long? the jog wheel at the back might be set for exposure compensation. u can accidentally rub off it and change the settings. there should be a custom function to switch it off

if u both had f8 and f11 then thats only 1 stop off?

CabanSail

Exposure Compensation is an offset to the Metering in the camera, so as neither meters were being used it cannot be a factor.

The Nikons have 200 ISO as minimum (but you can reduce that down to 100 ISO)
The Canons have 100 ISO as minimum.

Are you sure both ISO's were the same?

Buzz Lightyear

CabanSail wrote: »

Exposure Compensation is an offset to the Metering in the camera, so as neither meters were being used it cannot be a factor.

The Nikons have 200 ISO as minimum (but you can reduce that down to 100 ISO)
The Canons have 100 ISO as minimum.

Are you sure both ISO's were the same?

My D80 has ISO 100 as min and was set for that and correctly exposed. I know Sineads 5D was set the same. It has to be a custom setting somewhere - only I don't know the Canon kit.

I know on the D80 you can set the exposure comp even when in manual. Sinead's checked her users manual and it's not possible with the 5D

Confusus still reins

kumate_champ07

CabanSail wrote: »

Exposure Compensation is an offset to the Metering in the camera, so as neither meters were being used it cannot be a factor.

so if u use full manual and enter the shutter speed u cant use exposure compensation also? i know it wouldnt be done but cant the setting be changed while in manual mode?

AnCatDubh

Go back to the quality of the lens (glass/plastic/optics/construction) for a minute - anecdotally and without as scientific a setup as has been posted here, I have found a significant difference between two lenses which I have - different brands. With same camera at f2.8 on both, and identical settings in so far as I can remember - IIRC the shutter speed drops significantly on one. One's a Tamron, the other is a Pentax prime. The Tamron drops the shutter speed. I always assumed it was the quality of the Pentax over the Tamron.

sineadw

I was using the Canon 85mm 1.8 USM, the Canon 50mm 1.4 USM and the Canon 135mm L, so no problem with quality. And nope - you can't use exposure compensation in manual mode - moving the wheel just changes the aperture. Manual is manual on the 5D - changing the settings simply changes the shutter speed or aperture.

100 ISO *definitely* - I can drop to 50 though

AFAIR (and I may not be remembering correctly - we were shooting for 11 hours all told :eek: ) the differences seemed to grow more when the lights were toned down and we were working with a higher aperture. So one stop difference when I was up around 11 or 16 but almost two stops when Philip was down at 2.8. Philip am I remembering that correctly?

Its all just out of curiosity really.. I'm happy with the shots. We can't put them up for comparison as yet though as they're for an album cover and the client has asked us not to publish anything until it's released..

DaireQuinlan

Buzz Lightyear wrote: »

F-stop maybe only a geometrical value, however unless you've bought your lens from Penny's or Dunnes Stores, they should be calibrated to allow a certain amount of light through the opening (aperature). So unless Sinead's Canon lens's were a monday morning jobbie, I can't see that being a factor ...

I used to think this aswell. We had some discussion about this ages ago here. Look up the difference between F-Stops and T-Stops. F-Stops are purely geometrical. T-stops are f-stops with the transmissive quality of the lens taken into account. T-stops are used in the film and motion picture industry (I think it was Hugh_C who illuminated the issue originally, he's got a background in the film industry IIRC). With modern lenses its not really an issue any more. I think the conclusion was that modern zooms don't lose anything more than maybe 1/3rd of a stop, primes even less, so in practice its not really anything to worry about. In any case the lenses on each of the cameras would be affected similarly.

DaireQuinlan

Actually, I'd be interested in seeing what would happen without the added variable of having strobes going off. IE take a meter reading with the external meter in daylight and take the shot with the metered readings and see what the exposure is like.

Morrisseeee

One was a Nikon and the other was a Canon, so they're bound to disagree !!! :pac::D:p

stcstc

does the D80 actually do iso 100, some of the nikons start at 200 and have a approx for 100 in lo1 i think its called

It not something like that that causeing it is it?

AnCatDubh

Morrisseeee wrote: »

One was a Nikon and the other was a Canon, so they're bound to disagree !!! :pac::D:p

True, but what's puzzling me is that the light meter should have been the referee in all of this. My basic understanding would be a correct meter reading followed would render a correct exposure.

CabanSail

Just out of curiosity, what Shutter Speeds did you use?

stcstc

ah think tony is onto something

is it to do with sync speed, my understanding is the nikons can sync slightly quicker than the canons

DaireQuinlan

stcstc wrote: »

ah think tony is onto something

is it to do with sync speed, my understanding is the nikons can sync slightly quicker than the canons

Presuming they were both shooting at or below their respective camera's sync speeds it shouldn't make a difference. If Sinead was shooting at above the canons sync then there'd more than likely be banding or something on the image, or half under exposed/half correctly exposed or something. I don't think anything could conspire to make it OVER exposed.

OTOH I was just thinking if sinead was shooting at long enough shutter speeds to allow the ambient make a significant contribution, but buzz wasn't then that would definately make a difference. And this difference would also decrease as she stopped down (ensuring that the ambient contribution would drop off as the aperture was closed up). I don't know what the situation in the studio was though.

-edit- just a quick google, both (5d, d80) seem to have max 1/200 sync. -edit-

sineadw

It was at 125th of a sec for both of us, so sync speed shouldn't be an issue. I did try higher shutter speeds at one stage to get a bigger aperture for a longer DoF, but got a dark line at the side of the image. 125 is fine though. So I don't think it was that.

I'm curious as to whether my shutter speeds are calibrated correctly though? I did think that maybe the camera is giving slightly longer exposures than it's saying? It was over-exposing slightly on all lenses so my understanding would be that it therefore couldn't be an error in aperture readings? Is there any way I could check that?

Daire - would the strobes not take away any variables in ambient light and give a more consistent reading? I would have thought they'd cancel out potential variables in ambient light, rather than create them. We did notice when shooting low key though that the ambient light sources in the room - the celiing lights, the light from the hallway, were visible in the shot.

DaireQuinlan

sineadw wrote: »

It was at 125th of a sec for both of us, so sync speed shouldn't be an issue. I did try higher shutter speeds at one stage to get a bigger aperture for a longer DoF, but got a dark line at the side of the image. 125 is fine though. So I don't think it was that.

Thats a classic sign of shooting over your flash sync. If you shoot at your flash sync speed, the moment the flash fires (typically just as the first shutter curtain has cleared the frame) the second curtain won't have begun to cross the frame. Any faster speed and there's no point at which the frame is completely clear, the second curtain will already be in the frame. At the fastest speeds the amount of the frame exposed at any one instant is only a thin slit.

Daire - would the strobes not take away any variables in ambient light and give a more consistent reading? I would have thought they'd cancel out potential variables in ambient light, rather than create them. We did notice when shooting low key though that the ambient light sources in the room - the celiing lights, the light from the hallway, were visible in the shot.

Your flash and your ambient will be two independent components of the exposure. If you were indoors in a studio with no windows or anything, and you were shooting at 1/125 at f/8 or f/16 then yeah I'd say the ambient component would be pretty negligible. Think about it like this, if the flash hadn't gone off at all, and you still get some sort of image (underexposed though it may be) then you'll have some ambient element to the image.

Buzz Lightyear

sineadw wrote: »

AFAIR (and I may not be remembering correctly - we were shooting for 11 hours all told :eek: ) the differences seemed to grow more when the lights were toned down and we were working with a higher aperture. So one stop difference when I was up around 11 or 16 but almost two stops when Philip was down at 2.8. Philip am I remembering that correctly?

Only getting back into this now - I'd no bb up in leitrim

Just checked my camera. I was shooting most of the day in F11 @ ISO100, 1/125. I cannot recall any major issues about exposure until we changed to shallow dof for one shoot and low key early in the evening. I had dropped to F4.5 for both of these (and obviously adjusted the lighting to suit). I do recall it being an issue then, even up to the last shoot at F8.

DaireQuinlan wrote: »

Presuming they were both shooting at or below their respective camera's sync speeds it shouldn't make a difference. If Sinead was shooting at above the canons sync then there'd more than likely be banding or something on the image, or half under exposed/half correctly exposed or something. I don't think anything could conspire to make it OVER exposed.

If either of us pushed our syncs we got banding - indicating that we had exceeded the sync speed. For both of us that was over 1/200.

DaireQuinlan wrote: »

OTOH I was just thinking if sinead was shooting at long enough shutter speeds to allow the ambient make a significant contribution, but buzz wasn't then that would definately make a difference. And this difference would also decrease as she stopped down (ensuring that the ambient contribution would drop off as the aperture was closed up). I don't know what the situation in the studio was though.

The ambient light from the overhead fluorescent gave us an extra dimension during test shots with MY model - who's images are not under any restriction (except for maybe a kitb :eek:). This was during the low key test shots where lighting was directional, however we have no comparrision shots for this as Sinead was pouting and posing .
The ambient lighting in this case was directly overhead, and made a definitive contribution at f4.5. This flourescent was however switch off once we copped and didn't interfere with the main shoot.

I'll need to check with Sinead on timings and f's to do a retrospective comparision to see where the lighting became an issue.

CabanSail

sineadw wrote: »

It was at 125th of a sec for both of us, so sync speed shouldn't be an issue. I did try higher shutter speeds at one stage to get a bigger aperture for a longer DoF, but got a dark line at the side of the image. 125 is fine though.

Using studio lights the shutter speed is almost irrelevant as the exposure time comes from the duration of the flash alone. So 1/125th is as good as any speed. This breaks down if you want to do something fancy with ambient light etc.

I can only think of reasons why you can get underexposure compared to the Flash Meter rather than over exposure.

Morrisseeee

Interesting thread/puzzle. I've no experience with this indoor, flash, ambient lighting set-up, but as a newbie lookin in on this, can I ask a few Q's ? (Chastise me if I'm tallkin a load of cobblers :pac::D)
Does everything have to be proportional ? because Sinead has a full frame sensor/lens, whereas Buzz has a 1.5 crop sensor/lens.

Set Up:

Cameras: Full frame, 1.5crop.
Lenses: ?, ?
Speed of shutter: same (?)
Speed of Flash: same (?)
ISO: same

If the flash lights up the subject for X speed, but then ambient light kicks in for the remainder of the (shutter open) time, if its longer than flash speed, then won't the full frame sensor (bigger FOV) pick up more light and hense give a blow out ?

DaireQuinlan

Morrisseeee wrote: »

won't the full frame sensor (bigger FOV) pick up more light and hense give a blow out ?

no

CabanSail

Morrisseeee wrote: »

Interesting thread/puzzle. I've no experience with this indoor, flash, ambient lighting set-up, but as a newbie lookin in on this, can I ask a few Q's ? (Chastise me if I'm tallkin a load of cobblers :pac::D)
Does everything have to be proportional ? because Sinead has a full frame sensor/lens, whereas Buzz has a 1.5 crop sensor/lens.

Set Up:

Cameras: Full frame, 1.5crop.
Lenses: ?, ?
Speed of shutter: same (?)
Speed of Flash: same (?)
ISO: same

If the flash lights up the subject for X speed, but then ambient light kicks in for the remainder of the (shutter open) time, if its longer than flash speed, then won't the full frame sensor (bigger FOV) pick up more light and hense give a blow out ?

The size of sensor is irrelevant. Exposure is dictated by the Aperture (f stop) & the time of the exposure (normally shutter speed, but duration of flash in this case) A Studio should be set up so that the ambient light is insignificant & does not register. This can be confirmed by doing an exposure & not firing the strobes, the frame should be completely black.

The sensor size has to be matched to a lens that has an adequate circle of illumination. So the crop factor will not make any difference.

The meter is reading incident light, which is the amount of light falling on the subject, as opposed to the in camera meter which is reading reflected light.

The exposure is adjusted by use of the Aperture, which also varies DOF, or by the output power or distance from the strobes.

It is such a simple set up that it allows just about any camera to work well that will fire the strobes.

Morrisseeee

no

&
Ah......

The sensor size has to be matched to a lens that has an adequate circle of illumination

.......OK, 50 lashes, detention & 100 lines for morrisseeee !

sineadw

I don't think it'd make any real difference anyway, but I was using roughly the same equivalent focal length anyway - when Buzz had the 50mm on I had the 85mm, and so on...

emul

How were you connected to the studio lighting? Wireless? Sync cable? Could either have caused the issue?

Buzz Lightyear

emul wrote: »

How were you connected to the studio lighting? Wireless? Sync cable? Could either have caused the issue?

We were using wireless triggers - same one just swapping around in turns. However it'd make no difference as we're both within sync timing.

We'll just have to compare shots when we meet next and see if something strikes us as obvious, cos so far no one, including us, has a clue as to what might have caused this ....

soccerc

Buzz Lightyear wrote: »

We were using wireless triggers - same one just swapping around in turns. However it'd make no difference as we're both within sync timing.

We'll just have to compare shots when we meet next and see if something strikes us as obvious, cos so far no one, including us, has a clue as to what might have caused this ....

Could you both post exif data of the offending and ok shot?