View Full Version : Calibration vs. Consistency

24-Aug-2014, 02:06
I was using my Pentax digital spot meter yesterday and got to thinking about the fact that I've never had it calibrated or even tuned up in over twenty five years and thus have no way of knowing if it is accurate. Let's say, for the sake of argument, that it is many stops off of some absolute standard and that what it reads as EV 12 is really EV 9. Since I use the same meter for all my exposures and have determined my own exposure indexes and development times for various films based on this meter's readings, what good would getting it calibrated do? It seems to me that as long as the meter is able to read relative values accurately--a six stop scene brightness range meters as a six stop scene brightness range--then all is good.

So I was wondering: is calibration of photographic measuring devices important, or is it better to use consistently functioning equipment in the same manner every time?


Regular Rod
24-Aug-2014, 02:22
Consistency beats everything when it comes to getting the results you want. Once you are there why move?


N Dhananjay
24-Aug-2014, 05:10
In my opinion, a lot of this has to do with chasing a level of accuracy and control that is neither there nor entirely necessary (at least within the range of our typical use). Consider print control - no matter how much you try to be accurate and control things, there will always be variation - some random and some systematic. Timers come with some range of random error, your ability to have the print in the developer for precisely 60/90/120/whatever seconds comes with some random error. Developer composition changes systematically through a printing session - as you put more paper through the developer, bromide accumulates in the developer which should have the same effect as adding a restrainer. Over a long enough printing session, you might be puzzled by why your printing paper seems to be growing slower, especially if you print the same negative at the start and the end of a really long printing session. And of course you change - you are probably more tired at the end of a printing session than at the beginning but your judgment may be better because it is in the zone and you are in a state of flow.

Things drift - you can either compensate your process or get things routinely checked or use some combination of both. Some things are more sensitive/susceptible to vagaries than others. It is probably not a bad idea to have light meters checked occasionally because they sometimes take falls or bumps and occasional maintenance is just some insurance against catastrophic failure at some uncertain future point (or maybe I am more clumsy than most). And if you really want to get obsessive about it, you can calibrate your meter against some standard before and after servicing to factor in the necessary adjustment to your process. Although given vagaries in our metering skills and visualization, I am not sure this really achieves anything. The final limiting factor is human - even if we had perfect unchanging materials, we change in subtle and unsubtle ways, both in the short term and the long term. Once we reach an acceptable level of accuracy, chasing accuracy beyond that is mostly pointless - there are other things our energy could be spent on in an effort to improve our photography.

Cheers, DJ

24-Aug-2014, 11:46
Consistency beats everything when it comes to getting the results you want. Once you are there why move?


Amen, brother!

24-Aug-2014, 16:03
Jonathan based on your great images both your calibration and consistency are correct - for you. Your calibration is your eye and that seems very accurate.

24-Aug-2014, 16:58
Jonathan based on your great images both your calibration and consistency are correct - for you. Your calibration is your eye and that seems very accurate.

Thanks. My approach is certainly based more on feel than objective standards. Almost all of my shutters are old and slow and out of whack, so I have learned to deal with a certain amount of "slop" in my exposures which I attempt to compensate for during processing. If we're able to get the results we want I suppose the method doesn't matter too much. I'm not looking to change my way of working, but I was curious how other people use and maintain their equipment.


24-Aug-2014, 17:46
Since I use the same meter for all my exposures and have determined my own exposure indexes

Seems like you have calibrated it.

Bruce Osgood
24-Aug-2014, 19:32
I've seen your work. Your meter ain't broke..... dont fix it.

Regular Rod
25-Aug-2014, 03:57
i've seen your work. Your meter ain't broke..... Dont fix it.



Darin Boville
25-Aug-2014, 08:56
The Zone System is valuable largely for just this reason. It introduced a consistent, repeatable process where before there was usually a great deal of haphazardness. All the rest of the Zone System methodology is just fine tuning. :)


Michael E
25-Aug-2014, 09:21
Calibration is important if more than one person uses this meter or if you use more than one meter. I use a spot meter and an incident (flash) meter, both Sekonic. Both have their own purpose, but it is good to have one as backup for the other. Then I want to be sure to get accurate readings at the same film speed setting.


Drew Wiley
26-Aug-2014, 12:02
These meters are not only calibrated to an objective standard, but to internal linearity as well. They periodically need to be tested and recalibrated. You might just
get accustomed to a certain reading error; but if the linearity is appreciably off, so too is your Zone System assumptions or whatever. My custom was to keep a
brand new Pentax digital spotmeter in the lab which was never used for anything other than checking my user ones. Once one of these showed a discrepancy with
any of the others, over their entire range, it was time to send them in for recalibration, which averaged about once a decade. Eventually in the not too distant
future I'll have to enlist that spare meter into regular duty, cause one of my old ones is getting pretty rickety, even though it still reads true. Or maybe I'll find a deal on another new one - but ya already know, these things don't go cheaply these days. Even when I also used a Minolta Spotmeter F in the studio, it exactly
matched the Pentax meters over the full range. I found Pentax more convenient to use in general. But at least this demonstrated that these two brands were
originally calibrated to the same strict standard.

26-Aug-2014, 12:17
Drew, that's a good point about "internal linearity." I do occasionally check my three meters--Gossen Luna Pro F, Minolta Flashmeter V, and the Pentax--against each other, both in absolute measurement and in relative terms. Not very scientific, I know, but if all three agree within half a stop or so (which they usually do) I figure I'm doing OK.

Calibration also opens up a huge rabbit hole in my case because so many of my shutters are not functioning at 100%. Even if my meters were magically made perfectly accurate, I would then feed those readings into a given shutter that might be off 20-30% at certain speeds (not to mention my use of the "Galli shutter" which introduces human error into the equation). If I were to have my meters calibrated I would also need to have my shutters cleaned and tested, and that seems a fool's errand with all of the old Compurs and Ilexes I have. If I shot transparencies I might be singing a different tune, but LF B&W has a generous amount of exposure latitude built-in, or at least enough to smooth out the ripples caused by my uncalibrated gear.


Drew Wiley
26-Aug-2014, 12:35
I keep a shutter tester on hand in the lab too. But my own habits were standardized around transparencies and I've kinda stuck with it. I find that kind of precision
very useful when dealing with Ektar too, which is a bit more finicky than most color neg films. It's also helpful when trying to squeeze in the bottom rung of shadow
detail using steep-toed films, which I often find myself doing, given the extreme contrasts of lighting I often encounter in the mtns, desert, or even in the redwoods
when the sun comes out. But black and white work is a lot more forgiving in general. I will admit that.

Bruce Watson
26-Aug-2014, 18:41
Since I use the same meter for all my exposures and have determined my own exposure indexes and development times for various films based on this meter's readings, what good would getting it calibrated do?

Calibrating your meter would probably be of little value to you, and it would necessitate retesting for your personal EI and development times again.

What you've found is the difference between accuracy and precision. They aren't interchangeable concepts as you've shown.

This is why I run my Jobo at 19.4 degrees. Because it needs calibrating; it's not accurate. But it's quite precise. Every batch of film I run comes out just like the last batch. Since it's not really broken...

Drew Wiley
27-Aug-2014, 10:00
Why calibrate, Bruce? Because if it has already started drifting from its original setting, it's going to gradually keep drifting. If it ever needs actual repair, it will have
to recalibrated anyway. And if someone happens to need a spare meter, it's important to match them. And as meters drift, they might not do it symmetrically. It
might remain accurate at one point and not somewhere else in the overall range. One damn box of color sheet film can cost more than the price of recalibrating a
Pentax meter.

Kirk Gittings
27-Aug-2014, 10:06
If you are going to recalibrate make sure you do a reading off of a consistently lit subject before you send it in so you can compare it when it comes back. Then your exp/dev processes may just need a film ASA adjustment in exposure to keep rolling. I have it done every few years whether I have noticed a problem or not.

28-Aug-2014, 23:10
I had a very similar conversation with someone I bought a lens off. When I received it the times were off, you could tell without having it tested. I sent an email to him complaining he did not mention this in his listing. He wrote back and said that each photographer gets to know their lens initmately and adjusts exposure settings accordingly to get the desired result. This is the same theory to your point about your light meter.

I minimise the use of my light meter, often taking just one reading then putting it away and tend to be guided intuitively from that point based on what I know from experience. This was recommended by F.C.Tilney, a fine arts historian and pictorialist photographer from the early 20th century.