Designing an Alt Process Meter, Input Wanted

Hi, Matt from Reveni Labs here.

I'm interested in designing a light meter for alternative process work, after hearing that the LIGHTMEASURE PPM2 was no longer produced. It doesn't appear there is anything that caters to alt process users specifically.

I don't have any experience with alternative processes, so I'm wondering if people would give me insights on what kind of features they'd like to have in a meter that would help them with their alt process work.

I have a list (in no particular order) of features currently on my mind:

- UV light measuring, for realtime and integrative UV readings, displayed in watts (uW,mW) per metre (centimetre) squared, and joules per metre squared.
- Visible light measuring, possibly filtered to just blue/green for ortho materials?
- Remote sensor head which can be used on or off the main meter body, for attaching to the front of a camera when doing long integrating exposures.
- Temperature/humidity sensor
- Output ports to control items like UV exposure box, enlarger, electronic shutter, relay-connected lightbulbs. Control done via an external relay or other low-voltage control method such as LED driver with an enable function. Possibly 433MHz wireless outlet control.
- Beeper/exposure level alarm

Other abilities

- Measuring UV transmittance of negatives
- Graphical plot of light levels during an exposure
- Remaining exposure time estimator
- Simple densitometer
- Enlarger exposure meter
- UV light box meter / controller. Could compensate for fluorescent UV bulbs which have slow turn-on times and ramp to maximum brightness

Other general features

- Aluminum construction
- Colour LCD screen, possibly, or OLED screen for the best outdoor viewability
- Rechargeable battery
- USB-C update feautres
- Relatively small and lightweight


Like I said, I don't have any alt process experience firsthand, so I'd like to hear about difficulties that people have with their work and what kind of things would be useful for them in a device like I have described. I'm interested in hearing what people have to say.

- Matt

Reveni-matt said:

It doesn't appear there is anything that caters to alt process users specifically.

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Yes, there is.
@Ian Leake himself can tell you all about it. It also appears to have virtually all the features you're looking to add.

In the long list of features you've identified, I feel the most crucial question (and the one that's virtually impossible to answer) remains unasked - i.e. 'what is UV'?
For each feature, I'd suggest to have a clear understanding of why, how and in what case they might be used, and also what the potential drawbacks might be. I see a lot of stuff going on that I don't immediately recognize as being of great utility in alt. printing, or if it's potentially useful, would be challenging to implement in such a way that it actually does something useful.

Thanks for your reply @koraks

I wasn't aware of this. I think probably because it's not really described as a meter, more of a process controller, and doesn't appear to be intended for use outside of the darkroom. I was envisioning a handheld device with darkroom features included essentially as a bonus.

I feel the most crucial question (and the one that's virtually impossible to answer) remains unasked - i.e. 'what is UV'?

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I don't follow. Do you mean literally? Or do you mean the more specific spectral sensitivity of materials to UVA, UVB, UVC? Any materials (especially homemade ones) will need to be calibrated via testing to determine their specific sensitivities, the user won't be able to escape that fact.

My list of features is speculative. Some of these features are free (software) or nearly free to implement. Some are optional which the user would not need to spend money on if they did not wish to use them, like various switchable output controls.

I saw your original message before you edited it, and I think you felt you were being harsh but I suspect what you wrote represents your true feelings. I don't have direct experience but I don't think that's relevant. I have no interest in getting into wet plate or tintype photography, and wouldn't want to do so just to gain insights I could get from talking with an experienced practitioner. The majority of engineers design equipment they have no personal or direct interest in using. I design light meters, I have experience in the field, I can design a specialized product for the niche-in-a-niche which alt process photography is. I'm asking for insight from people who care about alt process, asking what would make their lives easier, not telling them what would make their lives easier. The goal is a collaborative process to create something that would benefit the community.

Reveni-matt said:

I have no interest in getting into wet plate or tintype photography, and wouldn't want to do so just to gain insights I could get from talking with an experienced practitioner. The majority of engineers design equipment they have no personal or direct interest in using. I design light meters, I have experience in the field, I can design a specialized product for the niche-in-a-niche which alt process photography is. I'm asking for insight from people who care about alt process, asking what would make their lives easier, not telling them what would make their lives easier. The goal is a collaborative process to create something that would benefit the community.

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This describes typical product engineering process. That's why focus groups, subject-matter expert consultation/involvement, alpha/beta testing, and user experience testing is important. This thread seems like part of a normal product engineering process.

I was hesitant to jump into this thread because I'm not sure about exactly what it is you're trying to accomplish, but I'll toss out a couple of, perhaps unrelated, thoughts:

1. For those of us who shoot dry glass plates, I would LOVE a meter that provided me an accurate combined exposure reading for ambient light level + UV. Don't know if that would even be possible, but it sure would beat the gyrations I go through to "best guess" my exposure.

2. If this combo unit you envision could act as a densitometer measuring both standard white light (for those negs developed in standard developers) or UV (negs destined for pt/pd printing), this would be a huge benefit for film testing.

Please ignore, if these ideas don't apply. Thank you.

Reveni-matt said:

I don't follow. Do you mean literally? Or do you mean the more specific spectral sensitivity of materials to UVA, UVB, UVC? Any materials (especially homemade ones) will need to be calibrated via testing to determine their specific sensitivities, the user won't be able to escape that fact.

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The point is that in choosing a sensor and whatever optical arrangement it's part of, you'll be making a pretty fundamental choice w.r.t. the spectral sensitivity of the device. I think it's a good idea to be aware of this as well as the implications it has. The 'easy' answer is that whatever option you go for, there's always a downside.

Reveni-matt said:

I saw your original message before you edited it, and I think you felt you were being harsh

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That's correct.

Reveni-matt said:

I have no interest in getting into wet plate or tintype photography, and wouldn't want to do so just to gain insights I could get from talking with an experienced practitioner.

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I understand. I'm with @BrianShaw on this; it's part of a normal, commercial new product development process such as the one you're engaging in. That's all I'll say about it at this moment.
Edit: except that using a meter for wet plate/tintype photography is exceedingly unlikely to offer any benefit. It's a bit like Jack Sparrow waving his compass.

Alan9940 said:

I was hesitant to jump into this thread because I'm not sure about exactly what it is you're trying to accomplish, but I'll toss out a couple of, perhaps unrelated, thoughts:

1. For those of us who shoot dry glass plates, I would LOVE a meter that provided me an accurate combined exposure reading for ambient light level + UV. Don't know if that would even be possible, but it sure would beat the gyrations I go through to "best guess" my exposure.

2. If this combo unit you envision could act as a densitometer measuring both standard white light (for those negs developed in standard developers) or UV (negs destined for pt/pd printing), this would be a huge benefit for film testing.

Please ignore, if these ideas don't apply. Thank you.

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Hi Alan, these ideas absolutely apply. This meter would be able to meter an instant visible + UV light level as well as a cumulative reading during exposure to allow you to achieve a consistent "dose". The same hardware can measure the transmittance through a piece of film by measuring the light source intensity with and without the film in the way.

koraks said:

using a meter for wet plate/tintype photography is exceedingly unlikely to offer any benefit

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Would you be willing to explain why? I can't come up with a reason why it wouldn't help. My research shows that wet plate, tintype, daguerrotype, and many printing processes are near UV/Violet/Blue sensitive. Using a cumulative meter during the exposure would give good control over any weather-induced fluctuations. This article shows an interesting homemade solar UV meter being used.

Reveni-matt said:

This article shows an interesting homemade solar UV meter being used.

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It's used for cyanotype there. That's a whole different ballgame than wet plate. Also, try that meter in various lighting conditions and see how it goes. I'd be surprised you get consistent exposures even if the sun is used as the light source but in conditions varying from noon daylight to light overcast to shade, for instance.

The issue is in what I said earlier about 'what is UV'.
This is something you run into and realize if you do the testing with the processes involved and various light sources. That's why I think it's a good idea to familiarize yourself with the application. And I personally do think that's how innovative businesses generate value - by offering solutions based on intimate familiarity with the application field. Having a chat on a forum with some people can help a bit, but it's not a substitute for actual hands-on empirical research. And yes, you can ask people to write a tome about how they think it works, but...what's in it for them?
Btw, if you spend some time reading posts on UV exposure systems here on Photrio as well as on various websites you can piece together a reasonably usable story. Even so, I think hands-on experience would help as it'll give you the necessary absorptive capacity to make sense of the (incompletely encoded) empirical results of others.

koraks said:

It's used for cyanotype there. That's a whole different ballgame than wet plate. Also, try that meter in various lighting conditions and see how it goes. I'd be surprised you get consistent exposures even if the sun is used as the light source but in conditions varying from noon daylight to light overcast to shade, for instance.

The issue is in what I said earlier about 'what is UV'.
This is something you run into and realize if you do the testing with the processes involved and various light sources. That's why I think it's a good idea to familiarize yourself with the application. And I personally do think that's how innovative businesses generate value - by offering solutions based on intimate familiarity with the application field. Having a chat on a forum with some people can help a bit, but it's not a substitute for actual hands-on empirical research. And yes, you can ask people to write a tome about how they think it works, but...what's in it for them?
Btw, if you spend some time reading posts on UV exposure systems here on Photrio as well as on various websites you can piece together a reasonably usable story. Even so, I think hands-on experience would help as it'll give you the necessary absorptive capacity to make sense of the (incompletely encoded) empirical results of others.

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Part of my issue is that I need to explore the marketability of such a device, and try to determine why such a thing doesn't already exist in the market. Empirical testing on my part would be less of an issue if I had built the strong sense there is a market for the device. Even if I had decades of experience in this exact discipline, I would still need to check that other people were interested in the product in the same way I was. Right from the start, the development process for a one-off hobby item versus something intended to be produced in the hundreds, is very different.

What anyone who gives me insights freely might expect, is that the item they wish to buy will come into existence. If they were really keen, I'd probably involve them in beta testing and give them a free production version of the meter.

Reveni-matt said:

Part of my issue is that I need to explore the marketability of such a device, and try to determine why such a thing doesn't already exist in the market. Empirical testing on my part would be less of an issue if I had built the strong sense there is a market for the device.

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Such are the woes of running a business!

Good luck with your project.

Different alternative processes respond to different wavelengths of UV light in different ways.

Would it be practical economical and/or desired to have a meter that could differentiate between the amount of UV at 365 compared to the amount of 395 for example?

What will be the range of sensitivity in the UV range will your sensor be?

Vaughn said:

Different alternative processes respond to different wavelengths of UV light in different ways.

Would it be practical economical and/or desired to have a meter that could differentiate between the amount of UV at 365 compared to the amount of 395 for example?

What will be the range of sensitivity in the UV range will your sensor be?

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This is one of the things I have not determined yet.

Solar UV is around 94% UVA and 6% UVB. UVB is sub-320nm, I'm unsure how sensitive photographic materials are to those short wavelengths.

I'm unsure if a meter that can clearly differentiate between 365nm and 395nm is useful or cost-prohibitive. From what I have seen, individual testing is the only way to determine the characteristics of your materials, and the meter can only reduce/eliminate some variables, but not all.

Solar UV index levels are around 25mW/m^2 per unit, reaching a maximum of about 400mW/m^2 at high altitudes near the equator. The maximum for the meter could be 10 to 100x that fairly easily, for use with powerful UV lights in darkroom exposure boxes. Reaching a high maximum reading is generally much easier than reaching a low minimum reading.