As you guys know I am shooting with A75S which is Hassy mount using Rz67 Pro II using Digital Art adapter. I am generally extremely pleased with this combo and in love with my Aptus. The H1 is sitting on the studio shelf collecting dust and the old Rz is the money making machine. The only complain that i ever had for this digital solution is the lock of abilities to shoot in higher ISO. Recently I bought Nikon D3 to fill the gap for these rare occasion where I do not control the amount of light.
Quite camera but nowhere close to the level of image quality that I am spoiled with Aptus. I shot them in studio side by side and was struck with the sensitivity discrepancies. I long forgot about light meters since I always shoot tethered. But this time it was obvious that at ISO 200 on both cameras at the same shutter and aparture setting my Aptus was two full levels under expose as compare to D3. This started a series of experiments including my dusty H1.
I cannot find any explanation but here are the facts:
Aptus 75S installed on H1 is 1.3 levels more sensitive that the same Aptus installed on Rz67.
I checked all possible explanation eliminating synch problems and lens variations.
I shot at all ISO setting allowed by Aptus using a total of 9 different lenses from Hassy and Mamiya using shutters from 1/30 to 1/400 and including Rz mechanical shutter and two different Rz bodies.
I think I left nothing to chance and simply can not grasp the concept.
I even shot without lenses installed.
How can it be that the same back has a different sensitivity on different cameras. My ISO 200 on Rz 67 is actually ISO 80 on H1 and even closer to ISO 50 on Sekonic meter.
Can anyone offer explanation. Combine wisdom???? Please.
andre
http://andrenapier.com

I have never found discrepancies in the order like you have. I have noticed discrepancies that were in the order of around 1 stop maximum.

I always blamed those to the various lenses where f4 on one lens was slightly different than on another.

Why lenses? Because I found these differences also while using the same system, eg. Nikon lenses. I own about 30 lenses or so at the moment and most have small differences. Another thing is that the camera basically is just a box that attaches lenses to an imaging device.

2 stops difference is a big difference though. I wonder what others make of this.

On my 645AFD/II after calibrating the lightmeter on 18% gray the difference are in the 0.7 and 0.5 stops (depending on ISO) for some lenses there is a 0.2 difference.

I am sure there are people more expert in the science of F stops and light transmission that I am as my experience just comes from practical use . . .though . . . .

Without knowing the specifics, light souce, distance to subject, etc. I think what Andre is seeing is probably bellows factors and lens light transmission differernces.

An RZ really is a 6x7 camera reagardless of the capture device and like a 4x5 took approx. another stop of light compared to a 6x7, a 6x7can require another stop of light than a 645.

Unlike cinema lenses, still photography lenses are rarely accurate or better put the F stop rating is subject to the transmission value of the lens elements. In other words a lens may have a 2.8 aperture value but loose 9% of light in transmission, which once again is the reason most cinema lenses are rated at T stops vs. F stops.

Back in the film days I've compared Bronica, Contax, mamiya and Hasselblad all with the approx. same focal lengths and could see close to a full stop difference on transparency film.

Also back in the film days I use to have one client that wanted some sessions shot 6x7 instead of my standard 645 so when we moved from the Bronicas to the RZ we would just bump the packs up another 1 1/2 stops of power, depedning on the distance to subject.

With digital we usually don't notice the differences because we don't meter, factor in bellows factors or transmission loss . . . we just shoot to the computer or camera lcd and adjust, not really knowing that the light on the suject is F8 though the capture is F4..5

This is one of the reasons that comparisions between different formats is so difficult. Comparing a medium format back with a Canon would sound easy, but so much of it depends on the lens, the exposure at the capture device and the conversion process.

This is also one of the reasons that if your going to invest in medium format it's important you test the exact camera and back in the situations you work in.



JR

I think that indeed is the problem.
The knowledge of how metering works is slowly slipping away in a dark hole and people only know how to look at the histogram, which in my opinion tells you not a whole lot, expect how the distribution is of the keys.

When you really want to capture something the way it IS/WAS you really need to know how te meter and how to use/calibrate the meter.

I have to admit that I'm a big advocate for using meters and knowing how they work so what I answer is a bit colored

Well, I guess . . . I never really used meters, even in the film days, but Andre's question is more about why he's losing/gaining stops of light with the same back on different cameras.

I assume it's just falloff and the differences in light transmission between the different lens/cameras.

I know there is a lot of questions about comparisions between camera makes, backs, etc. but one thing that would be interesting is to take the 4 brands of backs and their newest cameras, all with an 80mm and compare the actual iso at the final exposure level.

In other words does an H3dII with an 80mm, f whatever and 200 iso exactly equal an AFI with an 80mm at the same f stop and iso same with the Phase and the Sinar.

That would be an interesting comparision.

JR

I don't think so.

One of the items on our advanced workshops is calibrating the lightmeter, you can see there is a difference between two identical cameras, sometimes up to 0.2 stops, also there is a difference between lenses, normally also within 0.3 stops.

Throw those two together and you can have half a stop difference with 2 identical cameras (other lenses).

Whatever, but I never used meters except for rare instances and I own 4. I don't think I've carried one in over 5 years.

Actually the reason I bought my last meter was one particular client never understood why I didn't do 45 meter readings so to appease them I would just point it and fire it a few times, then do what I always did, which is calculate the ratios with my instincts rather than a meter.

So far it's worked out prety well, but I've never taken a class in photography so maybe I missed something.

JR

You never missed something, it's like a workflow.
I teach to learn to use a meter, especially when shooting full manual with for example a RZ it's in my opinion almost impossible to make a good shot without a meter, on the other hand, when shooting digital you can of course due to the instant review, and if you know how fstops works you can adjust by eye probarbly, but to do that you have to understand how it works (and you probarbly know )

So it's not wrong not to use one, seeing your work that goes without saying
But I think it's important that people understand what goes on behind the meter.

When I have to teach a starting photographer to work in the studio I always teach them to meter, that why they know for 100% sure if something is done correctly, if a background is photographic black or not etc.

For me the meter is always with me, when I do a session I meter everything that I need to know and shoot, some people will do differently.
It all depends on the preference of the photographer and how long it will take to get to the end result.

I think Ive seen this as well it was in the middle of a very hectic shoot and I had forgotten to test it since but I noticed, and I know this sounds weird but, the Aptus on Rz with pocket wizard was a stop under than with cord sync and 1.6 stops under 645Afd. At first I thought it was lens calibration but the whole cord pocket wizard thing is freeky. I'll have to check it out further.

don't get me wrong I've done the meter thing and it's ok, if you want read numbers but photography is more than the correct numbers.

In fact I think one of the reasons people think digital looks digital is just because someone sits on the monitor with the eyedropper and keeps yelling out numbers like don't go over 255.

For some work, that's needed but in reality whites should be white, blow outs should blow out, blacks should collapse.

There is a certain point where intuitiveness should take over regardless of what the dial says and that's when it gets interesting.

Sometimes you just have to toss the numbers, grab the camera and spin it until it looks good and then you have something, but running numbers, clicking strobes back and forth 1/3 a stop just gets in the way.

JR

P.S. I should add I'm not that serious about this stuff. Actually I'm not that serious about much other than getting the photograph. I just write fast and I think I come across that way.

As Helmut Newton said, they're just little pictures.

Actually I think Helmut put it another way, but I'd have to x out 1/3 of it.

I hate it when people are doing the 255.255.255 thing.

I simply use the meter to set up everything before the model enters the scene, I already have the final picture in my mind and by measuring all the strobes I'm sure it gets there within bounds so I can adjust after seeing the "preview"

for me a good picture takes you, it gives you an emotion and technique is second place in that.

Thank you everybody.
James,
your explanation does make a lot of sense. I forgot this aspect completely. Thanks.

Frank,
What is a light meter?
Last time I used one was ..... in the previous millennium.
I shoot tethered. If I do not like what I see, I want like it even when I know the exact reading of reflected light ratios.
Generally since I shoot Rz WLF ( no meter ) I can predict the light up to 0.5 step first try in or out the studio. Kind of like never having a watch but knowing the time.
For Rz/A75s shooter - you can apply the famous "16 Rule". When outside on sunny summer day set your shooter to 1/125 sec and your aparture to......F4
Http://AndreNapier.com