spotmeter modification question

[h2oman]

I've been shooting LF for less than a year, all color transparencies. So far I have done OK using my DSLR as a light meter, but I want to give B&W a try, so have decided to buy a meter, probably a Pentax digital spotmeter. I have seen some for sale that say they have been Zone VI modified, or something like that. What does this mean, and do I need/want it?

If it helps you respond, I think I have a crude understanding of the zone system. As I understand it, I'd meter the darkest place I want detail, and set my exposure for two stops below that. (I'm assuming I have done a film test and know what the speed of my film is.) Then I'd meter the brightest area in which I want detail. If opening up two stops from that reading gives me the settings I got from the dark area, I would use normal development. If not, I'd need some + or - development.

That's about all I know, so that is what you are working with if you dare to reply!:D

[mikebarger]

OH my lord, people are 180 degrees apart on this question. Most either believe it's the best thing since sliced bread, or it's the biggest waste of money known to man.

Not many people in the middle on this question.

I have a Zone VI Pentax V, not digital. I've never had any other spot meter, this one works well for me. I got it for a fair price, used, many years ago and don't regret it.

Any better than a non-modifed Pentax V, I've not got not a clue.

Good luck on sorting this one out.

Mike

[Eric Woodbury]

Z6 modified means that the photo sensor has been modified with filters to balance the response for BW film. BW film sees strongly in the blue and green, fading quickly to the red. The silicon sensor in the Pentax and most other meters, is very red and near IR sensitive and not very blue sensitive. By filtering the sensor differently,the meter can give accurate readings through filters, etc, for BW film. This makes BW exposure much easier. It still works fine w/o the Z6 mod, you would need to make some mental adjustments when metering strong colors.

I believe the Z6 mod also includes some extra baffles to reduce flare.

The only other meter that I know that is made specifically for BW use is the Pocket Spot.

[Ron Marshall]

I have a non-modified Pentax digital, and am very happy with it. For me the additional cost for the modification would be a waste of money.

[Deane Johnson]

I've had all of them and I wouldn't be without the Zone VI modified analog Pentax V for b&w work.

[h2oman]

OK, Eric took care of the "What is it?" Thanks, Eric! And Mike gave me fair warning about what to expect after that...

If anyone else wants to give their 2 cents on the want/need question, I'd be happy to hear it. There have been two votes for the Pentax analog spotmeter. Are there any others I should consider? I'm assuming that for landscape work I want a spotmeter, especially if I'm interested in metering a bit of El Cap about 2000 feet up?!?

[Deane Johnson]

Are you doing something similar to the zone system, or are you just metering the scene overall?

[Turner Reich]

I have Zone IV and it is color corrected so foliage for example doesn't throw the readings off. I believe that is what Fred Picker had in mind when he had the physicist do the calibrations for the meters.

[h2oman]

I intend to use the zone system, metering parts of the scene.

[Peter De Smidt]

The ZVI meter is calibrated for Tri-x. Other films do not share Tri-x's spectral response. I have the ZVI meter, and I have no complaints, but if I were buying again, I'd buy a regular Pentax Digital.

[Eric Woodbury]

True, Z6 is supposedly calibrated for XXX, but most other films have the nearly the same response except to the T-grains have more red response and of course the late Tech Pan (even more red) and IR films. Ilford films have slightly more green response than Kodak films, but what's a 1/3 stop among friends.

Some can't be without Z6 mod, but I didn't want to pay the extra myself and lived without the mod until I designed the Pocket Spot. Without the mod, you use filter factors, with the mod you meter through the filters.

Yes, Waterman, you want a spot for what you are doing.

Have fun.

[Turner Reich]

I have wanted a Pocket Spot for, a long time, hope, I hope to own one sometime.

[C. D. Keth]

I'd just get the meter you want and don't worry about whatever modification that is. All a meter does is provide information, and any properly working meter can do that. What you want to do with the information is up to you.

[RichardRitter]

All films drop off at a average area in the light wave spectrum. Fred just wanted it to be TriX not much difference between Tri x, T max or any other film. Color drops off a little differently and the last value is in the same range as black and white.

Light meters on the other hand see light beyond this drop off point and see color wrong. The modification makes the meter respond to light the same way film does and gives it a color correction so you can meter through filters.

It just everyone thinks the meter is for black and white film only. Its not in order to meter through color filters it has to work with color film. I when the meter was being tested was the one doing the test and Paul had me do color along with the B & W film.

Anyway it does not matter any more the meters are not being made and every one who knows how the meter works is hanging on to the meter. I know there are grippers in Hollywood who own more then one meter one guy has 6. They use then for color motion picture film.

Best light meter came on the inside of the film box.

[Peter De Smidt]

As David Kachel pointed out years and years ago--in Darkroom and Creative Camera Techniques, I believe-- t-grain films and traditional films respond to filtration in different ways. For example, using a red filter will increase grayscale contrast with tri-x but lower it with tmx; and a green filter will lower contrast with tri-x but increase it with tmx. I'm not talking about blocking complimentary colors. Photographing a grayscale scene, such as the lower row of a Mac Beth color checker, will show the contrast changes. That said, as long as your meter is consistent, you can test it's response, and since you should test anyway to get your process under control, this isn't a big deal. If you're going to meter through filters, definitely test each film you use with something like the Color Checker.

[Renato Tonelli]

I think Richard answered the question but feel free to keep on splitting hairs :)
I use mine for both B&W and color and I use extensively for cinematography work. It's a shame they stopped making it.

[Drew Wiley]

Even panchromatic films differ somewhat in spectral response. Just look at the tech
sheets. But what if you wanted to use an orthopan like Fuji Neopan or Adox 25? The
meter would be relatively useless. Then there's true otho, infrared, and color film - which the meter would be miserable for. I have three of the unmodified Pentax digital
spotmeters (one is set aside as a calibration reference). This has worked well with every task I have thrown at it. A little practice with your favorite film is all it takes.
I am also a little suspicious of how the added filters inside the modified meters hold
true before fading or organic degredation.

[Kirk Gittings]

I own two of the modified and love them. Are my negatives any better since I invested in them (after 20 years with regular Pentax meters)? No. It is more convenient, in a time pinch, to be able to meter through filters.

[Drew Wiley]

Kirk - just curiosity, but since you work with both styles of the meter, are you actually
metering color work with the modified one? I can understand how this might work if
you're reading a gray card or analagous neutrals, but not otherwise. As I recall, the
original SPD sensor in the Pentax has a fairly symmetrical response with the peak around 550nm, similar to the peak of human eye sensitivity. Back when I tested a bunch of these, the Minolta spotmeter was actually a little more accurate for color
readings, but nowhere near as convenient as the Pentax. But what I notice now is that
there seems to be a lot of the modified Zone VI meters coming up for sale used, but
rarely the plain Pentax. This must imply something. An offhand observation, but it might make a difference to someone planning to purchase one of these. Thanks.

[Kirk Gittings]

Drew, yes. Well up to two years ago when I switched mainly to digital for my commercial work that is, which is pretty much the only color work I do. I used/use these meters for all my film work, color and b&w. In terms of sales, I'll bet there are 100 of the unmodified for every modified one out there. I can't explain why there are so many modified ones for sale. But see Richard Ritters statement above. He was part of the design and manufacture of these. I would take his work as gospel.

[mikebarger]

I had a drink with dinner tonight, so take that in to consideration.

Is someone "really" suggesting a Zone VI modified meter doesn't work with color?

Sure works well for me.

Mike

[Photomagica]

The Zone VI calibrated meters do a very good job. I have used two, a calibrated Pentax Digital and a Soligor Digital and both work well on B&W film and color, transparencies and negative. They solved the problem that silicon photo diode meters had roughly 20 years ago of excessive IR and red sensitivity.

There is a misleading opinion going around that since these meters were calibrated to approximate the spectral curve to Tri-X film, that makes them unsuitable to use with other emulsions. This is definitely not the case. I urge LF Forum members who may have heard this not to repeat it - especially if they have not personally done the testing. I have tested this very, very carefully and these meters work well with a broad range of color and B&W emulsions, including narrow dynamic range color emulsions like Velvia.

I have also used a recent, non Zone VI calibrated, Pentax Digital Spot Meter. I have not had the opportunity to test it against a calibrated unit, however its performance suggests that it now has good spectral calibration. Some time ago I visited a web site where the photographer had done extensive testing and established to his satisfaction that a current Pentax meter performed essentially the same as a Zone VI modified unit. Unfortunately I have not been able to relocate this site. Perhaps another LF Forum member can point us in that direction of this URL.

The way to safeguard yourself against metering problems is to apply good professional photography practice and, when you get a meter, do a series of tests using the emulsions you intend to use and subjects typical of those you intend to photograph. These tests will teach you a great deal about how the metered value translates into exposure on film. In addition I'd avoid older photo diode based meters unless they are Zone VI calibrated die to the IR/red sensitivity problem.
Cheers,
Bill Peters
Photomagica

[Photomagica]

The site that offers comparative testing of Pentax and Pentax Zone VI meters is:

http://www.butzi.net/articles/zone%20VI%20reprise.htm

[Arne Croell]

I have owned a Zone VI digital for many years and got a new unmodified one about 2 years ago (I needed a 2nd one since I stay in two places and have two 4x5 setups). I made some comparisons measuring through filters and with different lighting and different object colors. The one difference I found is the sensitivity to infrared (IR) which is measurably higher in the unmodified one. Measuring through a dark red filter (29) produced about a 1 stop difference between them, slightly higher values (up to 1/2 stop) where also apparent in the unmodified one when measuring new foliage. Neutral gray or other colors gave the same response for both meters. This was corroborated by the "remote control test": turn on the meter in a dark room, point a TV remote control into the meter and use the remote. The IR from the remote will trigger a response in the Pentax digital (the analog meter might be too slow for that?). That response to pure IR is consistently higher for the unmodified one (it is not zero even in the Zone VI modified one, though)

There is an easy way to "modify" one yourself, without opening the meter: Put a UV/IR filter for digital cameras in front. It needs to be an interference filter type that is based on coatings, not an IR absorption filter, otherwise it absorbs too much in the visible, too. Both Heliopan ("Digital" filter) and B+W (filter no. 486) make these, both the Heliopan and the B+W come in the 40.5 filter thread that fits the Pentax digital. The filter Leica brought out for the original M8 is in the same category. I used the Heliopan, and with it the response measuring through the dark red filter, to foliage, and to the "remote control test" was the same as the Zone VI. In my experience the light loss from the filter reduces the response overall by about 1/3 of a stop, which has to be taken to account for your EI.

[Bruce Barlow]

"There is a misleading opinion going around that since these meters were calibrated to approximate the spectral curve to Tri-X film, that makes them unsuitable to use with other emulsions. This is definitely not the case. I urge LF Forum members who may have heard this not to repeat it - especially if they have not personally done the testing. I have tested this very, very carefully and these meters work well with a broad range of color and B&W emulsions, including narrow dynamic range color emulsions like Velvia."

"Misleading statements" probably posted by those who have never had the joy of using a Zone VI modified Pentax Digital Meter.

Richard Ritter has several Hollywood cinematographers who routinely send him their modified meters (two or three at a time) to be calibrated against Richard's standard light source and matched to each other.

I think it's been a long time since a Hollywood feature was shot on Tri-X. I think these guys' careers depend on using tools that work.

An unmodified meter works just fine, and given that, to my understanding, Calumet no longer modifies meters, and they won't let Richard do it either, the question of whether to modify an existing meter is moot. Nevertheless, I'd still own an unmodified one, were I looking for a fine meter.

[Peter De Smidt]

I've owned and used my Zone VI PD spot meter as my main meter since the mid-1990s, a few years before Fred sold to Calumet. I also have access to a non-modified meter, and I've run my own tests. I like both meters. There seems to be a misleading opinion going around that if anyone says anything even slightly negative about the ZVI meter that they are spreading "misleading opinions."

[mikebarger]

I don't think slightly negative comments get the "spreading misleading opinions" tag.

I think it's these type of comments

"The meter would be relatively useless."

that get the misleading comment tag.

Mike

[Deane Johnson]

I suspect there are some who post opinions that are only theory, not something they have determined with actual comparison tests. In some cases, they may have never even used the product they are posting "fact" on.

[RichardRitter]

Deane you fit the nail on the head.

A Zone VI customer got a new camera never put a lens on the camera but told us it would take tilted pictures. Camera was not capable of taking a level picture. His state fact was the lens on the lens board was mount at a slight tilt.

So based on his theory I should be able to take a lens off a camera (properly mounted) turn it 180 degrees and the image would be right side up.

[mikebarger]

Richard,

Maybe Fred wasn't the salesman everybody says. Focussing right side up surely would have led to more sales. ;)

Mike

[neil poulsen]

An unmodified meter works just fine, and given that, to my understanding, Calumet no longer modifies meters, and they won't let Richard do it either, the question of whether to modify an existing meter is moot. Nevertheless, I'd still own an unmodified one, were I looking for a fine meter.

So, did Calumet provide any explanation as to why they won't permit Richard to perform the modification? Is there a patent on the modification, or is it a trademark thing?

[Bruce Barlow]

It's their decision to make, and their lawyers on staff. Just like reissuing the Zone VI videos on DVD. The specifics of it I don't know. Copyright for the videos, for sure. It's not dead forever - as I recall, Richard got some hope from the discussion with them.

But then one contemplates materials. I know Richard has some of the filter material, but he priced getting more, and the cost needed some of the Wall Street bailout money to pay for (in the thousands, as I recall), so Richard was not entierely unhappy with Calumet's decision, especially since Pentax no longert makes the meters (true? I think so). Investing heavily in materials to modify meters that basically only exist used is not a winning proposition.

So with neither permission nor affordable materials, Richard wisely decided to invest in making my 8x10 camera. Alice is still doing fine, by the way, and continuing to make a disproportionate number of keepers. Must be because I have two modified meters...

[John Bowen]

Bruce,

I found this http://www.pentaxwebstore.com/detail/PTX+36141
so Pentax does has some available for the bargain basement price of $750 (unmodified). I think I'll hang on to my modified digital and 2 modified analog meters.... Richard was kind enough to calibrate them so all 3 read identically.

[RichardRitter]

When I was testing the meters I needed a fixed value. It was to hold a Luna Pro over my head and take a reading. With the white done over the photo cell Zone V reading and one at the target.

If I ever said these words while at Zone VI I would of been fired. The Luna Pro was the easiest to use, no taking the reading and then placing the zone you want. It was a no brainer hold it over your head and a perfect Zone V reading. Just run the zone I test and go. Perfect meter for a beginner or anyone. Quick and easy no guest work. I used one up until a year ago have to replace it.

But I will not give up my spot meters either. I still use then allot. Most of the time I work without a meter.

[Helen Bach]

Just a couple of comments, possibly already known to most of you:

From what I can gather Sekonic and Gossen filter their current range of meters to have a spectral response not much different from the visual response - with slight bias towards the blue end. In practice I've noticed fewer colour-related problems with my Sekonic L-508, L-758 and Pentax Digital than with my Minolta Spot F. I haven't used my Sekonic 778 enough in those situations to judge how that performs. Of course if you have an incident meter you can avoid a lot of colour issues, unless the illumination is strongly coloured.

A quick glance at film spectral response curves can be misleading. As I've mentioned a few times, Kodak show equal energy curves and almost all other manufacturers show wedge spectrograms made in tungsten light. The two cannot be compared directly, nor can tungsten wedge spectrograms be compared directly with daylight wedge spectrograms. It's not easy to compare, say, Tri-X and HP5+ just by looking at the manufacturers' curves.

Best,
Helen

[Eric Woodbury]

...I'm assuming the human visual response. It, and probably all other living things, have a completely different response than any light meter. Perhaps they cover the same spectral band, but the human response, as an example, is very green dominant and weak in response to both blue and red. It doesn't seem that way to us, because it is all we know, but to measure it versus a normalize photo detector would be surprising. And with cones and rod, center and periperal vision, this all becomes more confusing.

The older Selenium light meter had a pretty good spectral response without filtration. The modern Silicon cell is weak at the blue and tails off to nothing in the UV. But from 400 to 970 nm it has a linearly increasing sensitivity and then from there tailing to near nothing by 1100 nm. It is the red and near IR that can throw off a meter. Most meters today have a near IR cutoff filter that looks bluish and cuts off all the 700 nm and above radiation. Meters that are further normalize to 'film' would have an additional or built into the IR cutoff filter, another more bluish filter. Getting the filter just right for XXX or HP5+ or others requires careful adjustment to the spectrum, cutting off most of the red and compensating for the Si diodes overall lack of sensitivity to the blue. Fortunately, these filters don't have to be perfect, since +/- 1/3 stop is well tolerated by film, giving an error band of at least +/- 20%.

Although having a custom made dichroic filter made for thousands of dollars is a great way to go (and you get something like 6ea 13" diameter filters typically, a lot of glass), there are other ways to build a 'custom' filter using scientific gels and/or glasses available in the market today.

Finally, I have found the best way to test such filters is to photograph a neutral target under neutral light. Take a baseline pic without a filter and then meter through the filters and expose one frame per each filter according to the meter. Develop the film and measure with a densitometer. All the frames should have the same density.

[Helen Bach]

The human visual response indeed. I would have said the photopic response, but as the meters for photographic use don't follow any standard curve it's a moot point whether it is the photopic or scotopic that it doesn't fit. It's a while since I last worked on meter modifications and when I look at the production meter curves they look more like flattened-out photopic curves rather than blue-biased ones. Not surprisingly they show slightly too much response to infrared radiation - which is noticeable in practice when metering dark objects that reflect IR, and is useful when using IR film, of course.

Best,
Helen

[Don7x17]

People tend to support what they have -- sometimes ignoring reality.
Here's Paul Butzi's excellent work showing the differences between an unmodified Pentax and a Zone VI modified meter:
http://www.butzi.net/articles/zone%20VI%20worth%20it.htm
The difference Paul saw between the two meters on the Macbeth Chart was RMS 0.18 to 0.3 stop, with maximum difference 1/3 (2/3 under tungsten lighting).

Preuming the relative inaccuracy of even copal shutters (another subject entirely), and the fact that you should be doing some film tests using the meter as basis...

Pauls Summary of Results reads "Despite the results I found (which was that there was no significant different between the unmodified Pentax Digital Spotmeter and the Zone VI modifed one in terms of color response, but that the Zone VI modifications worsened the meter's response in low light and increased meter flare) as far as I know, no one has attempted to perform any similar testing. (or, if they have, I haven't seen their results, although I've been watching).".......So, on the face of it, it appears that I have, in fact, performed the test recommended here, and my conclusion is that no one needs an modified meter"

http://www.butzi.net/articles/zone%20VI%20reprise.htm

Paul Butzi also covers the responses of Gittings and Ross. Please read the articles carefully -- they contain data. I also have seen no data other than Paul's. If someone has some actual test data with their own pair of meters, please post.

Give it a read and draw your own conclusions.

[RichardRitter]

People always fine ways to make life more complicated then it needs to be. Take the meter most people become very attached to the meter. The meter over time will start to give different reading then what is true. Battery starts to go dead. there is enough dirt on the different parts of the metering path to make a 1/2 stop difference or more, meter just goes out of adjustment the list goes on. On the bright side most people don't even know their meter is off or nonlinear after years of use they just assume it is something they are doing or just don't know.

Then there is the question of what is the right exposure for a given film and subject matter. Being that some of us with are years of experience in the darkroom can take a negative that is 2 stops off and make a decent image out of it.

[Kirk Gittings]

Paul Butzi also covers the responses of Gittings and Ross. Please read the articles carefully -- they contain data. I also have seen no data other than Paul's. If someone has some actual test data with their own pair of meters, please post.

FWIW, Actually my process was, as I remember it.... I had owned regular Pentax Spot meters for 25+ years and they worked fine and currently had a digital one. I came into possession of a modified one and, in testing it against to my unmodified one, found it different and superior allowing for pretty accurate metering through filters. As a result I had my original one modified too as a back up. Now as my testing was only for my own use, and not realizing that Paul was later going to make a federal case out of the issue and plaster it all over his website (thanks Paul I love you too!), I did not preserve my tests (granted they were not nearly as thorough as Paul's). I don't remember what the cost of the conversion was, but it was not insignificant (2-3 hundred dollars?). Certainly I would not have paid the money if my testing had not suggested an improvement and the modification of the original one did bring both meters to the same color response. I had had other Picker products that I thought were less than superb and was always a bit skeptical as to his claims.

But in all honesty, it is much ado about nothing really. Both meters do the job if they are calibrated properly and neither will if not. Keeping a meter calibrated is far more important than this issue.

[Deane Johnson]

I liked Fred Picker's response to various theories: "Show me the photographs".

[John Jarosz]

Actually my favorite was a newsletter he sent out with a big "TRY IT" stamped in red across the first page. He said the stamp was his response to the suggestion letters he received.

John

[Helen Bach]

Most of the work I did was because I was commissioned to do it or because I was just curious. None of it altered my general satisfaction with the results from unmodified meters.

Best,
Helen

[Drew Wiley]

I always assumed that Fred Picker was a bit of a snake oil salesman, but having used a
few of his gadgets for many years and reading some of the comments on this thread, I
guess I was wrong. But if you really want to get nitpicky just for fun, back when I was
testing spotmeters I figured I needed a decent gray card. I took several samples of
each brand gray card available and ran them through a spectrophotometer to create
a reflection curve. Not only were none 18% gray at the peak sensitivity of the meter,
but most weren't 18% anywhere - typically 5 to 15% or more off! And cards even from the same mfg varied from each other. And the peak reflection was all over the map. So I actually made a batch of paint that was true 18% across the whole visible spectrum and slightly into the UV and IR. Would be hell to try to duplicate this batch however, unless you've got a lot of free time with the right equipment. It was an informative project, but otherwise I guess we all just get used to our meters. I check my spotmeters annually to see that they're in synch with each other.

[Helen Bach]

I wonder how much the slight difference matters for metering. It may matter for colour correction.

Here are three curves for three cards.The Smethurst card is not a nominal 18% card, but a 14% card, for which there is a good case.

Best,
Helen

http://i215.photobucket.com/albums/cc155/hbphotobucket/Greycards2.png

[Bruce Barlow]

Actually my favorite was a newsletter he sent out with a big "TRY IT" stamped in red across the first page. He said the stamp was his response to the suggestion letters he received.

John

I bought that stamp for Fred. It was my idea. Another stamp said "Bull****" (except with the uncensored version), and the third said "It Doesn't Matter." These three seemed to answer 90% of Fred's mail. We had to take the "Bull****" one away from him when he proved he couldn't play nicely with other children.

I note Mr. Butzi's test addressed neither the stated reasons why the meter was developed, nor meter anything that anyone would choose to photograph in real life. I didn't read Kirk's stuff, but he's a lot closer to the mark. Say what you will about Fred (and I will, at length), but he created and tested things to use in real life, rightly understanding that many things were invented by folks in laboratories who never went out the door to understand the real world. I agree with Kirk, that in some cases the hype exceeded the delivery. But sometimes not.

It's like the review of a new enlarging paper that I read in a prominent magazine. The authors said that they specifically chose not to make enlargements of real pictures, and instead used step wedges and curves to determine that the paper "would probably make good looking prints." I wanted to cry, both for the poor methodology and the editorial boneheadedness of the magazine in printing the article. I had tested the paper with a real picture under controlled conditions and found it almost as good as the best papers I'd tested (12 others at that time).

Last I checked, photography was about photographs, not MacBeth charts, curves, and tests. Test for film speed, proofing time and development time and the world is a simple place. Elapsed testing time about a day, most of that waiting for things to dry.

And you would have to pry my modified meter and my Compensating Developing Timer out of my cold, dead hands. You'd find Alice, my Richard Ritter 9x10, underneath my rigor-mortised back, with her 355 G-Claron poking my lumbar region.

[Fred L]

I have an unmodified Pentax Digital. If I were shooting strictly black and white, let's say with no coloured filters, is there an advantage to the Zone VI modified over the one I have now ? If I understand things correctly, using coloured filters is where a Zone VI meter is better because it's corrected for metering through filters ?

thanks,

Fred

[Alan Curtis]

I had my Pentax modified in 1992 and I like being able to meter through the filters. More important is having the meter properly calibrated. I had Richard Ritter check mine several months ago, it was off, especially in low light. I was placing shadows in Zones III and IV but they were really in II and III. Modified or not get the meter calibrated.

[Fred L]

thanks Alan !

[Nathan Potter]

Anyone have a spectral curve for both modified and unmodified meters along the line of Helens grey cards above? I think you could get this by running the meters through a monochometer if there was sufficient light intensity to register an EV reading.

BTW if the silicon sensor in the Pentax is a pn junction type rather than a bulk silicon type the falloff in sensitivity in the UV is most likely due to UV photons not reaching the junction depletion region so failing to generate as many hole electron pairs as longer wavelength light. OTOH at longer wavelengths into the IR incoming photons can go right thru the depletion region again causing a falloff in response in the IR region. By widening the depletion region using higher bias the response at either end of the visible spectrum can be extended.

Anyone know the details of the sensor construction?

Nate Potter, Boston MA.

[Mark Sampson]

The explanation and the data, with curves, for the meter modifications was published in the Zone VI newsletter when the mods were introduced. I could dig them up,scan and post them, but I don't think that they would convince the unbelievers. Myself I thought enough of the idea to purchase a modified meter, and have used it successfully for 16 years or so. Would an unmodified meter have been as accurate? I'll never know. Does it matter? (The extra cost was amortized a long time ago.) Do I have a tool that I'm confident in using? Yes.

[Don7x17]

The explanation and the data, with curves, for the meter modifications was published in the Zone VI newsletter when the mods were introduced. I could dig them up,scan and post them, but I don't think that they would convince the unbelievers. Myself I thought enough of the idea to purchase a modified meter, and have used it successfully for 16 years or so. Would an unmodified meter have been as accurate? I'll never know. Does it matter? (The extra cost was amortized a long time ago.) Do I have a tool that I'm confident in using? Yes.

Recall that Calumet Photo has the copyright for these. Your lawyer will tell you that you cannot scan and post without permission...does not fall within "fair use" restrictions.

[Kirk Keyes]

And you would have to pry my modified meter and my Compensating Developing Timer out of my cold, dead hands.

Does it take longer to pry the timer from your hands when they are cold? ;^)

[Kirk Keyes]

I think you could get this by running the meters through a monochometer if there was sufficient light intensity to register an EV reading.

I can do this. I'm just waiting for someone to loan me a modified Spot V to compare with my unmodified Spot V.