Use a DSLR to calculate exposure? [Archive] - Large Format Photography Forum

Jon Warwick

4-Sep-2008, 07:46

I've started to use a 5x4 camera, mainly using Acros 100 film (given it has minimal reciprocity issues, and I typically photograph architecture at night).

I suddenly thought that maybe it makes sense to use my Digital SLR (a recent one, the Canon 40D) to get an accurate exposure reading. The main benefit that I can see is that I can check a whole load of various exposures on the DSLR's rear viewing screen to chose which one is the best-balanced and the most accurate for the scene in front of me.

I haven't yet had the opportunity to use this "technique" in terms of using whatever exposure appears to produce the most accurate image on my DSLR's rear viewing screen and simply using that shutter & aperture combination on the 5x4.

Does anyone use this "technique"? Does it work in reality, or am I missing something?

Frank Petronio

4-Sep-2008, 08:54

I use a dslr too, I use the histogram mostly to judge the exposure but I also factor in some experience and common sense. I understand that my technique is less than optimal compared to a carefully set-up and controlled Zone System approach using a Densitometer to establish film speed and careful consistent custom development. But I use one type of film (Tri-X) developed consistently but without any customization by a good commercial lab (Praus, www.4photolab.com). And it works just fine. Maybe I am missing the optimal exposure by half a stop but I screwed up that much even back in the day when I had my own darkroom and my official authorized Pentax 1-degree spot meter ;-)

I did rate the Tri-X at 320 and while I do chimp and consider the preview image, I try to discipline myself to value the histogram more than other factors. Still it is nice to see the digital preview to see if you want to push or pull the exposure value for a special treatment of high or low key scenes. I won't use Polaroid anymore since it will soon be impossible to get or too expensive for all but the most important scenes, so I went cold turkey and eliminated it from my workflow.

In any event, you just need to shoot and test, and maybe you adjust your film ISO or fudge some other way.

As far as tonal range, while the dslr may be more limited, the center of the dslr tonal range is usually where I want my film to be too. If the extreme shadows or highlights plug that's usually OK but I can always cheat a stop if I want to be sure to capture one or the other. But that is experience and practice working....

The dslr also helps me decide whether a set-up is worthy and it definitely helps me loosen up portrait subjects. When I switch to the large format camera after shooting with the dslr, my subjects always seem to "rise to the occasion" because they know the big film is special.

Also the Nikon metering is especially good when you are in a hurry...

Of course if you follow the dogma here you absolutely must have a Pentax Digital Spot along with your Chamonix/Arca-Swiss and Schneider 110-XL in order to make a decent photograph ;-)

roteague

4-Sep-2008, 08:57

Does anyone use this "technique"? Does it work in reality, or am I missing something?

I don't find it works well at all. However, I use my Nikon F6 at times as a light meter, Nikon DSLRs tend to underexpose too much. It also allows me to shoot 35mm of the same scene.

Kirk Gittings

4-Sep-2008, 09:01

The only real problem is that proper DSLR exposure, or ETTR (expose to the right, pushing the right shoulder of the histogram as far as you can to the right without clipping the highlights, this approach minimizes shadow noise), is more like shooting chromes (in a general sense) than B&W negatives (expose for the shadows, develop for the highlights, with B&W and a DSLR pin the important deep shadows slightly above clipping on the left and see how far the highlights fall and adjust development accordingly-this involves some experience and some guesswork). So as long as you can switch your brain back and forth between the two paradigms you can do alright. BUT it is not nearly as accurate approach as using a good spot meter and the Zone System or BTZS. To me the approaches are so different that I treat them as distinct paradigms.

roteague

4-Sep-2008, 10:16

BUT it is not nearly as accurate approach as using a good spot meter

That bears repeating ....

Frank Petronio

4-Sep-2008, 11:32

Nothing personal to Kirk or Robert but I disagree that a spot meter is somehow more accurate than a good DSLR. I think they are speaking more out of the large format dogma and tradition here.... If anything the meter of a modern dslr (at least a Nikon) is going to be more sensitive and probably respond in a more even-handed (linear) fashion than a 35-year old Pentax design. As far as measuring light, I think the modern mid-level digicam has to be at least as accurate as a light meter.

I'm not saying that taking an "average" meter reading off a dslr is anymore usable than taking an EV (exposure value units of one stop) value off your Pentax is. But for somebody who is new to this and hasn't gone through the Zone System yet (or ever) it seems to me that his tools are just fine -- it's how you interpret the values the camera or meter gives you. Handing someone a spot meter and knowing the EV without their having a grounding in the theory behind the Zone system doesn't help them make a more accurate exposure.

Use the camera. Shoot a couple of sheets, adjust as needed. It will become second nature if you actually try.... Why waste $300 on a spot meter if you have a more accurate, useful, and versatile tool right at hand?

Besides, most Zone System shooters usually shoot just bright enough to hold the highlights and let the shadows fall where they may, which is relatively simple. I know some of you do pull developments but I bet it is a very small minority.

gevalia

4-Sep-2008, 12:24

Scott Kathe

4-Sep-2008, 12:39

I found that in low light situations, that exposure was off between the DSLR and Luna Pro - taking into account reciprocity of course. For me this held true with both Acros 100 (ei 50) and TMAX 400 (ei 200).

I think you mean the exposure was off when you compare the DSLR image and film shot using the exposure calculated from the LunaPro. The meter in the DSLR and LunaPro should give you the same results. If not the LunaPro could need to be calibrated. The only reason I bring this up is because last year my film was consistently underexposed by about a stop with low light levels and my LunaPro SBC needed to be calibrated. Now it works great!

Secondly, I though Acros 100 had very good long exposure characteristics and you don't have to worry about reciprocity till about 2 minutes.

Scott

Marko

4-Sep-2008, 13:57

I really hope I don't sound like the idiot here but, isn't DSLR ISO completely different then analog ISO? When I started with 4x5 a whopping 6 months ago, I initially used my D80 as a crutch (my term, no offense intended) when I was training myself on the Zone system with my used Luna Pro. I found that in low light situations, that exposure was off between the DSLR and Luna Pro - taking into account reciprocity of course. For me this held true with both Acros 100 (ei 50) and TMAX 400 (ei 200).

Remember, as a beginner, my 2 cents adjusted for inflation are worthless.

ISO is ISO, there's no such thing as "analog" or "digital" ISO.

At the very basic level, both a traditional light meter and a DSLR are built around a light sensitive silicon chip, which is a fairly linear device.

Reciprocity failure, on the other hand, is a "feature" of film.

I see absolutely no reason why a DSLR could not be used as a pretty capable light meter, provided that one knows how to calibrate and use it in the first place. And while at it, it is also a very inexpensive substitute for Polaroids too.

Ron Bose

4-Sep-2008, 14:14

You need to expose a few sheets and learn how to get nicely exposed negatives. To do this you need a consistent meter, IMHO an incident meter is better than a DSLRs TTL Matrix metered 'intelligent' digital sensor optimised meter.

The incident meter doesn't try to compensate, the evaluative matrix metering does, so your readings won't be consistent.

A spot reflective meter is also more consistent 'if you know how to use it'. In other words, you can select an 18% (or 13%) gray item in every one of your images and meter off it.

I know photographers who can meter accurately in their heads, based on the heaviness and length of a shadow. Metering isn't that tricky, but a DSLR tries to think for you and over evaluates and therefore over or under compensates.

Marko

4-Sep-2008, 15:20

Metering isn't that tricky, but a DSLR tries to think for you and over evaluates and therefore over or under compensates.

Any decent DSLR has a full manual mode (and a bunch of semi-manual ones), nobody's forcing you to use the Mickey Mouse mode if you don't want to.

Some newer ones even come with a spot meter.

Ron Bose

4-Sep-2008, 15:55

roteague

4-Sep-2008, 17:31

Nothing personal to Kirk or Robert but I disagree that a spot meter is somehow more accurate than a good DSLR. I think they are speaking more out of the large format dogma and tradition here....

The problem isn't the quality of the meter itself; all meters do the same basic job - read 18% grey. The issue comes from the way the camera's software interprets and presents the results. The DSLR interpets the results to suit the needs of digital photography; they don't present the user with the raw meter reading like a spot meter does.

However, I can't, through lack of experience, say whether that is true when using the DSLR in spot meter mode. I've only used a DSLR in matrix mode. I also have no experience with Canon or other DSLRs - only Nikon.

Based upon my experience, my F6 has a more accurate metering system for shooting transparency film than my D200. However, I get better results from using a spot meter simply because it is easier to make a determination of where and how to employ split neutral density filters with one. I should point out that I do use my Nikon F6 as a meter in situations where the light is changing too fast to use a spot meter.

Stephen Benskin

4-Sep-2008, 18:11

ISO is ISO, there's no such thing as "analog" or "digital" ISO.

Actually, there is a difference. In fact, there is also a difference in parameters for B&W negative, color negative, and transparencies. One of the major factors for digital is noise. They all use, however, the same exposure formula, and from that point of view, all exposure meters should be the same in theory.

In reality, a big difference between using a light meter and a camera's meter is that the camera's meter incorporates the lens and lens barrel which in almost all cases will be very different than large format lenses and bellows extension.

Frank Petronio

4-Sep-2008, 18:55

I don't disagree with most of the above, but the reason I keep coming back is to respond to the original question: Yes you can use a dslr -- it will work. Perhaps getting a spot meter down the road is a good idea -- but not having a spot meter isn't going to hinder you from making excellent photos. It works for me. Enough so that I think a spot meter isn't worth carrying....

My exposures are NOT perfect -- I'm off by a half a stop quite often, maybe over a stop sometimes in extreme lighting situations... it's not the end of the world (in most cases). I've watched enough other photographers in the field to realize that even devout Zone System practitioners often don't do any better.

We ought to remember that newbie photographers need a little more encouragement and not be overwhelmed by "needing" this and that. They don't!

Kirk Gittings

4-Sep-2008, 19:00

Frank, once a few years ago I decided to go for a recreational drive and landscape shoot. I wanted to make some good images but I also wanted to work on some inconsistencies in my negative exposure. I really worked the ZS on that trip and came away with the most perfect negatives I have ever made.........also the most perfectly boring negatives I had ever made. They were way too methodical, there was no spark in them.

Alan Davenport

4-Sep-2008, 19:10

Correct exposure isn't that complicated a thing, nor is the concept of using zones to place your exposure. You don't need to delve into the "Zone System" very deeply either, because the idea of zones is only a tiny part and a simple concept at that. Yes, a DSLR can substitute for a light meter, and if you have the DSLR and want to save the cost of a meter that's fine. But please, let's try to avoid claims that a DSLR is somehow superior to a standalone meter, when we all know it just ain't so.

Besides, 4x5 film don't got no histogram nohow.

Marko

4-Sep-2008, 19:15

Hi Marko,
I'm not talking about the stupid modes (night, portrait, landscape), I'm talking Aperture priority.

Matrix metering and other evaluative metering systems will interpret the scene and judge an exposure based on the light that falls on it's multi-zone pattern sensor. You 'may' be able to defeat this by using spot mode ? I guess it depends on Canon/Nikon/Pentax/etc.

When I first got my incident light meter then a true-spot meter I realised how simple metering light was.

Even spending 50 bucks on a cheap Sekonic or Gossen will help your understanding of the whole process. Of course, YMMV :-)

In anycase, if I want to shoot digital, that's all I'll bring, if I want to shoot film, digital stays home ...

Hey Ron,

Understanding the process is not the issue here, I believe. It is whether you can use a DSLR as a substitute for a dedicated light meter.

The answer is, yes you can. The process is not the same, but the results are PROVIDED THAT you do understand what either of the instruments in question are telling you.

That being said, I do own a dedicated spot meter, not because I don't trust the DSLR but because I want to use the entire process. And I usually do bring both with me.

Here is a set of images that I posted before in a similar discussion. I set up a 4x5 and used my DSLR to measure the scene and take one of the shots. Then I recalculated the exposure to account for the difference between the digital sensor and the film I was using and shot the same scene on a sheet of film.

http://48pixels.com/images/fdcomp/dch_071118.jpg

I also measured the same scene with the spotmeter and that reading was about 1/2 f-stop different from my calculation.

Did any of you film shooters who say this can't be done actually give it a shot?

Frank Petronio

4-Sep-2008, 19:23

And Marko, which is the "correct" exposure? lol

Marko

4-Sep-2008, 19:25

Actually, there is a difference. In fact, there is also a difference in parameters for B&W negative, color negative, and transparencies. One of the major factors for digital is noise. They all use, however, the same exposure formula, and from that point of view, all exposure meters should be the same in theory.

In reality, a big difference between using a light meter and a camera's meter is that the camera's meter incorporates the lens and lens barrel which in almost all cases will be very different than large format lenses and bellows extension.

Stephen, those parameters are inherent to the light sensitive medium (film or sensor) used, not the meter itself.

The same meter will always show the same reading for the same light falling on the same scene, regardless of what is in the back of your camera. It is up to you to interpret what it's telling you.

Again, different meters will show different readings, some times slightly some times significantly, that is why we calibrate a meter to each combination of film and developer. Or for each sensor in case of a DSLR. Once calibrated, though, the results should be reliable and repeatable, regardless of the brand or type.

But please, let's try to avoid claims that a DSLR is somehow superior to a standalone meter, when we all know it just ain't so.

Besides, 4x5 film don't got no histogram nohow.

It doesn't got no needle or LCD either... ;)

Nobody's claiming a DSLR is superior to the standalone meter, all we're saying is that it can be its equal provided proper calibration and operator's skill.

Marko

4-Sep-2008, 19:32

And Marko, which is the "correct" exposure? lol

Now, that's a political question and you know by now that I am not overly politically correct... ;)

Ron Bose

4-Sep-2008, 20:08

My exposures are NOT perfect -- I'm off by a half a stop quite often, maybe over a stop sometimes in extreme lighting situations... it's not the end of the world (in most cases). I've watched enough other photographers in the field to realize that even devout Zone System practitioners often don't do any better.

We ought to remember that newbie photographers need a little more encouragement and not be overwhelmed by "needing" this and that. They don't!

Frank,
If you asked the question I'd say go for it, you have the experience to know what to do with a meter reading from your camera and how to compensate due to your years of experience and great results ... I also agree that you don't need to be a follower of the Zone System to get good exposures.

Marko, you asked which image was which. Again, I'd say that an experienced photographer who understands how either type of metering works and how to interprete it, compensate, then dial it into your lens will get the right exposure.

I know enough about how different shades of grey are present in my scene and what I need to do to get enough of them on the neg so I can make a half-decent print.

To be brutally honest, all I do is find something near 18% grey and meter, then look at the darkest spot I want detail in, meter and then make sure that the two point to the same exposure values. This to me was enough to start with and then you go from there ...

I'm not the greatest photographer here, far from it and having said all of this I dream of the day I can make images like Frank :-)

Stephen Benskin

4-Sep-2008, 20:12

Marko,

If you notice my response was to the false statement that ISO for analog is the same for digital. The ISO standard for film or digital has only to do with the materials. There's a separate ISO standard for light meters, and even then, the actual parameters on exposure aren't listed in any standard. You have to go back to the original scientific papers for tha

Here's a hint about exposure. The basic exposure constant is P = 8 mc. This is what your light meter and the exposure formula look for before factoring in shutter speed which is applied through the exposure calculator. You can find more in Connelly, D., Calibration Levels of Films and Exposure Devices, Journal of Photographic Science, Vol. 16, 1968.

And the part about using a digital camera for an exposure meter, Edward Weston never used a meter. In fact, meters weren't that universally used until the fifties. Many people used exposure charts and calculators. There's an ISO standard based on the research of Loyd Jones that is said to be so accurate, if used properly, that if your light meter disagrees with the data from the standard, your meter is probably wrong.

Let's not forget that disposable cameras produce acceptable results in a majority of situations and they not only don't have meters, they have a fixed aperture and shutter. Really, most of the time exposure isn't a big deal. It's when you encounter the more extreme or unusual situations where the difficulties lie.

Steve

argos33

5-Sep-2008, 00:44

I have used a DSLR to meter for LF slide film with great results. Yes the two are obviously different, but if you can experiment enough to be able to compensate for that difference you should be fine.

Jon Warwick

5-Sep-2008, 02:01

Thanks for the replies so far.

I fully agree that the DSLR will get confused by some lighting situations if not thoughtfully used.

However, as already mentionned by a few people above, perhaps the main benefit of using the DSLR will be "cheap polaroids".

I'll be taking a hand-held meter along too. By applying its readings onto my DSLR (which will be in manual mode) and taking a photo with the DSLR, I'm hoping that the DSLR preview screen will effectively act as a reliable substitute for taking a polaroid.

Ben Calwell

5-Sep-2008, 05:01

The importance of the histogram has been mentioned. Maybe I don't understand it completely, but I've never understood why looking at the histogram is important. Can't most experienced photographers, with the help of their exposure meters, simply look at a scene and tell which parts of it are likely to be overexposed or underexposed? I don't need a histogram to tell me that. What can a histogram tell me that I don't already know?

Kirk Gittings

5-Sep-2008, 06:05

Ben see this on ETTR exposure:

http://www.luminous-landscape.com/tutorials/expose-right.shtml

D. Bryant

5-Sep-2008, 06:41