IRE Scale on Pentax Spotmeter V : LUSENET : Large format photography : One Thread

I have had the opportunity to get out this weekend with my new Spotmeter V - first weekend without gales and rain for weeks ! I have used the meter in the standard way by setting the needle value lined up with the arrow and reading a combination of shutter/aperture. I also have tried using the IRE scale by metering off the deepest black that I want detail in and setting that value to 1, likewise highlights to 10. Using the IRE gives quite different values to using, say an incident meter. Has anyone else been using the IRE scale for metering for B & W and/or colo(u)r, if so are there any tips/advice - it seems quite a useful and potentially powerful tool.



-- David Tolcher (, February 16, 2002


Dave: You are quite right, this is one of the most powerful tools available for light metering, IMO much of it thanks to the IRE scale. I would like to change over to one of the new Incident/spot meters but their lack of the IRE scale has deterred me. I have been using the IRE scale in the Pentax Digital Spot meter for many years with excellent results for color. There are occassions when I prefer incident readings but those are less than about 1 out 4. I find that Zone 10 in the IRE produces a complete wash-out of highlights and as highlight detail in objects is always important I avoid Zone 10 and usually stay between 9 and 10 for the whitest whites. The whitest white or darkest black are not always conveniently available therefore, learning where you would want to place the zones for various objects is useful. You can do that by comparing incident with reflected meter readings when the conditions lend themselves to so doing. The 10 zones in the IRE scale cover a 5 EV range. Some color films do not have quite that range, and with those you could reach the darkest black before Zone 1. As with color work I am most concerned with highlights, I have not investigated the other end of the scale thoroughly enough to render a knowledgeable opinion. Zone VI has made an opus out of re-calibrating this meter but for my color work I have never seen the need. -From other postings I gather that other notable photographers who do B&W, among them John Sexton also do not. The Pentax Digital Spot Meter is a very mature product that has been on the market for many years and evidently Pentax has not seen the need for modifying it either.

-- Julio Fernandez (, February 17, 2002.

David & Julio,

I am a Pentax Digital Spotmeter junkie also - mine is the Zone VI modified though ... in Austyralia it's cheaper to purchase the Zone VI from Calumet than to buy a local untouched Pentax meter.

The most useful modification to the Zone VI version is the addition of a 'Zone Scale' which covers the IRE (Institute of Radio Engineers) scale and makes subject tone placements with analog simplicity - just like the rest of the scales.

In B&W the important markers, for me, are Zone II and Zone VIII. These correspond to 1/3 stop down from IRE '1' and 2/3 up from IRE 10. They are my outer limits.

With E6 stock I work on having a 4-stop window for magazine reproduction and so my shadow marker is half way between IRE 1 & 2 and my highlight marker is about IRE 8.5 (assuming the index mark between 8 & 10 is '9').

The 5-stop range of the IRE scale indicates the latitude of reversal films and movie films used for TV broadcasting (1:32 contrast ratio).

The further advantages of the Zone VI modifications are of questionable value. I have never compared my Pentax with an unmodifed Pentax but I do have a Minolter Spotmeter F for working with flash. Flare, Infra-Red and colour sensitivity track equally well.

The result of one testI did with the Pentax Zone VI and B&W contrats filters indicated that exposure readings were accurate within +/-1/3 stop with all filters except the 25 Red where it reads exactly 1-stop dark. These was determined on T-Max 100 and Delta 100 with a densitometer.

By determining exposure by aligning the subject brightness range within the capabilities of the END method of reproduction I find I never ever use an incident meter. I have a gorgeous bakelite Spectra-Combi 500 that was once my comrade in arms on every non-flash shoot which now sits proudly on a shelf in my equipment safe.

Happy days, guys,

Walter Glover

-- Walter Glover (, February 17, 2002.

Walter: Many thanks for your informative posting which shed more light into the IRE use and the Zone VI modification and elicit further discussion.

For example, if you take an incident reading at a location by a thickly branched cedar hedge and get EV 15, (then set the 15 in the EV dial by the red pointer in the Pentax SM) then take a spot meter reading from the hedge at a suitable distance and get EV 14, you then find that the 14 of the spot meter EV falls in front of IRE 'zone' 2. Similarly, whatever spot EV readings you get of other hedges or trees having similar color and reflectivity, you would place those in IRE zone 2 and get proper exposures. For me that works. OK, Calumet has a different scale overlapped over the IRE scale, so instead of IRE 'zone'2 you would read some other number; So what? Am I wrong in thinking that the Calumet scale fits better into the Adams lingo and the processes used in B&W but that it is totally redundant for color work in as much as the IRE scale works equally well? Also, since color transparency films may have a different exposure range than B&W and the films used in cinematography, those benchmarks, i.e. Zone VII for light and Zone II for dark that Walter refers to, is it not true that those benchmarks will need to be re-positioned accordingly, no? If so, weather you do it in Adams/ Calumet Zone lingo or IRE 'zone' lingo seems immaterial but for color work, the Calumet participation seems more hindrance than help. For my colour work IRE zones have worked very well. Have I been missing something?

Walter, I would appreciate your views on these questions/opinions. Thanks.

-- Julio Fernandez (, February 18, 2002.


The Zone VI overlay scale is simply a visual clue that makes tonal placement a little more intuitive. As I said, for B&W work I consider Zone II my low value limit and Zone VIII (not Zone VII as you quoted) my high value limit. Where I actually place a tone within that range is a matter of my interpretation and, hence, previsualisation of the scene.

For "Colour Transparency For Publication" work I operate within a 4-stop scale from Zone III to Zone VII, again determing Zone placement according to my preferred evaluation of the scene. Colour Negative I never use and so I have no end-reference points to suggest. Likewise digital capture is terra nullius for me.

How you choose to identify the reference points on the meter scale is up to you. The Zone VI tone scales are available as a separate item and can be stuck on any Pentax meter. You can use points and intermediate points on the IRE scale. Or you can take a screwdriver and scratch marks into the metal at one-stop intervals. It matters not.

What will lead to unnecessary confusion and possibly stifle the benefits of spotmetering technique is the comparison with single-reading incident meter techniques. It is a frustrating ordeal to try and get any two meters to track together; it is impossible to get two meters using different metering techniques to ever even talk to each other. It seems you are using the incident reading to validate the spot reading - it can't and won't. Place your trust in one meter or the other and in one technique.

Phil Davis in his weighty tome "Beyond The Zone System" discusses an incident meter metering technique that involves taking two incident readings - to quote it in detail here would be a digression but I suggest you get hold of a copy and read it for the enlightenment his theory affords. This does take the capabilities of the materials into account and the reflectance of matter in the real world. I am sure it works for many but I prefer the spotmeter my 4 or 6 stop window.

I have distilled my technique over many years and many thousands of colour and black & white exposures into a quick and abbreviated system the techniques of which are less important than the fact that I stick to using one piece of apparatus and one basic frame of reference - remove as many of the variables as possible and focus on the task at hand.

Much of the discussion on this and other Forums, particularly in regard to exposure and the Zone System, is centred on the rendering of tones as they appear in the real world rather than the interpretation of tones in the hope of providing a personal expression through tone placement . Validating your spot reading with an incident reading is striving towards the literal and forsaking the expressive, in my view.

Does this shed any light (no pun intended) on your quandry?

Walter Glover

-- Walter Glover (, February 18, 2002.

Walter: Thanks for your answers to my questions and the suggestions contained therein. You have indeed added more 'light' to the issues. It seems I conveyed the idea of using two metering systems, - incident/spot, on an ongoing basis, however I meant to indicate that by a comparative method involving incident and spot readings, I have made a chart that includes several objects which fit at various 'zones' in the IRE scale and that allows me to place the spot meter readings on their proper locations on the IRE scale. No matter, you have provided well reasoned arguments which I need to study in more detail and also, I need to study the book reference you provided.

I must also add Walter, that your kind of interaction in this forum is one of the reasons that makes it so valuable and such a pleasure. Thanks again!

-- Julio Fernandez (, February 18, 2002.


Sinar publish a brochure "Sinar Info 30 - Measuring Photography For Offset Reproduction". This brochure explains right through to scanning and offset printing the needs for and effects of correct tonal range placement - if you can obtain a copy I suggest that it is highly informative reading.

Thank you for expression of appreciation, you are very kind.

Walter Glover

-- Walter Glover (, February 19, 2002.

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