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Thread: Large Format Focal Plane Meter - New Product

  1. #1

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    Large Format Focal Plane Meter - New Product

    Hi All,

    My interest is not so much photography as electronics. I am here both for a bit of advice and to shamelessly plug my product.

    I developed a focal plane meter for my father's 4x5 Sinar several years ago, as my hobby was electronics and I am an engineer by trade. I have since supplied a couple more to other large format photographers, and then decided to productionise the design and to consider marketing it.

    My question is whether people are interested in such a product at the price I can sensibly achieve (120, roughly US$160 or Euro 130), and whether people have any suggestions or comments on the design.

    It comprises a frame, which inserts into the camera in place of the usual film carrier, with a metering probe that can be seen through the ground glass and used to measure the brightness at any particular points of interest in the image. The general idea is that you can examine the brightness in highlights and shadows and adjust to an exposure such that any shadow or highlight detail of interest will be retained in the final print. My father, I think, was using Adams' zone system at the time I developed this and this type of meter is ideal for that purpose.

    I believe that meters of this type have previously been produced e.g. by Sinar, very sophisticated but also very expensive. This was intended as a low cost, basic (but still accurate and reliable) alternative.

    What do people think? Obviously a get rich quick system this isn't - the total world market would hardly keep someone in film for a year - but I thought it might be a useful product that people might be interested in.

    See more details at http://www.dlgelectronics.com

    Picture below - there is more at the link above. Please feel free to message me either here or via the link above.

    I would also be interested if anyone has any other ideas for useful photographic/optical electronics products.
    Click image for larger version. 

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    Thanks!

    Dave

  2. #2

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    Re: Large Format Focal Plane Meter - New Product

    You are correct about other, similar products having been made. Gossen made a couple, but I am not knowledgeable about the details. They worked with Luna-Pro, Ultra-Pro, and perhaps other models. At least one was simliar to your design and reads in front of the ground glass. I think they made other attachments that read the rear of the GG. Minolta made the Auto-Booster and Auto-Booster II that came with four attachments -- one of which read on the back of the groundglass. The Minolta ones work with several of their meters, are useable for ambient and flash light (depending on the meter), and show up occationally on EBAY for around $50 or less. There may be other devises out there, as well from Sekonic and others. But perhaps comparing your design to these others could be useful in modifications.

  3. #3

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    Re: Large Format Focal Plane Meter - New Product

    What about offering a version of your a probe that will attach to the photographer's already existing light meter? In the past I owned several Minolta AutoMeters that had that capability.

  4. #4
    Peter De Smidt's Avatar
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    Re: Large Format Focal Plane Meter - New Product

    Dave, probably the best use for this is for close-up photography, whether in the studio or otherwise. Not long ago I shot a small product in a light tent, and using a handheld meter, spot or otherwise, was a bit of a challenge.
    "Why can't we all just get along?" President Dale, Mars Attacks

  5. #5
    Do or do not. There is no try.
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    Re: Large Format Focal Plane Meter - New Product

    Dave, that looks like a very interesting product, with a price and weight that are competitive with available spotmeters. The 8-stop brightness range could be limiting in some circumstances, but I don't think this would be a show-stopper. I've downloaded the user manual and will give it a careful read. I'm also an electrical engineer by day, at least for two more weeks.

    Terry, I think trying to make it compatible with existing meters would be a lot of work because there are a lot of different meters out there. Dave would have to choose one or two, and then anyone who didn't own the one(s) he chose would be out of luck.

  6. #6

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    Re: Large Format Focal Plane Meter - New Product

    Thanks for your interest!

    xkaes - I am interested in the feasibility of metering off the ground glass directly, and did have a concept using a pen-like sensor that you could put against the glass and meter a small spot. My idea was for a fibre-optic leading from the tip of the "pen" so that the tip could be made quite small allowing metering of an area of 1mm^2 or even less. However, when metering in this way don't you get ambient light entering the back of the camera through the glass or reflected within the glass and introducing errors into the metering? You must have to use a hood for this sort of application especially when you have the sun behind you. However, if people like metering off the glass, and find that stray light is either not a significant problem or don't mind using a hood then this is something I will try to develop further.

    Terry - as Steve notes it would be difficult to make a probe compatible with existing meters as I rather suspect that they will interface differently both mechanically and electrically, so I would have to offer a wide range of them. Also, I am not sure if some of these meters would be calibrated to specific sensors.

    Peter - that's an impressive picture. I am not a photographer myself but I can appreciate the technical difficulty of taking photographs like this. My meter is intended for situations like this where you want to meter not so much the overall scene but (in this example) the dark and light stripes specifically, to bring both the light and dark stripes in the range that the film and print can sensibly reproduce with saturation. Looking at your image, it would require metering quite specific small areas on the image. The sensor size on mine is approximately 5mm. Would this be small enough to get it wholly in the dark or wholly in the light stripes here? What format did you use? With a 4x5 or larger I would think it would work.

    Steve, the eight stop brightness range can be changed - I could even mod my existing stock very easily - I would have to substitute a different scale in the indicator and change one resistor value (if you look at the circuit diagram in the manual you will see how straightforward this would be . The reason for a plus/minus four stop range was that I had understood that was sufficient to accommodate the intensity range that could be reproduced and that anything beyond that would be full black or full white. Bear in mind the intended usage of the meter was to set the meter for your intended whole-image exposure (you dial the exposure in on a knob on the meter) then poke around in the image with the metering probe to check that shadows and highlights fall within a +/- 3 or 4 stop range or whatever of that, then fine tune the exposure a stop or two as necessary to ensure you get the shadow or highlight detail you want to be reproduced in the photograph. However, as a non-photographer myself I am open to advice on whether a +/- 4 stop range around the nominal exposure is sufficient to capture the full reproducible range of the film.

    Thanks again, Dave.

  7. #7

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    Re: Large Format Focal Plane Meter - New Product

    Here's what info I've got FWIW:

    First, is the Minolta Booster II with the GG reader (attached) and the flexible incident reader attachment (great for tight spots). These will work with most Minolta meters as plug-ins.

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    Second, is the Minolta Booster II with the GG reader (attached) and connected to a Minolta Flash Meter II.

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    The next pictures are close-ups of the GG reader itself. It is 38mm long with an 18mm thread to attach to the Booster or Booster II. The front, that is placed on the GG, is a clear, 2mm thick, plastic plate with a diameter of 15mm. In the center of this plate is a 5mm section that reads the light. The metal tube is maybe 0.25mm away from the GG. The interior of the tube is aluminum, just like the outside -- not black.

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    Click image for larger version. 

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    I suppose some light could "get around" the spot that is read, but a dark cloth should take care of most of that. For me, the bigger deal is the GG, and the lens fall-off. The instructions basically say to take a regular reading of a gray card in the scene. Then take a reading on the ground glass of the same gray card. Basically, the "difference" between the two readings is used to adjust future readings on the ground glass. There is an "adjustment" dial on the Booster which is turned to achieve the same exposure obtained from the the non-GG reading.

    But, IMHO, the readings taken on the edges of the GG need to be adjusted for any light fall-off -- which varies with the f-stop -- as well asthe GG itself, which gets less light at the edges -- varies with the GG /fresnel used, even if there is no light fall-off.

  8. #8

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    Re: Large Format Focal Plane Meter - New Product

    Thanks xkaecs, that's actually very informative and tells me it is at least feasible to meter off the ground glass. I am not sure why readings should be lower at the edges and corners of the image unless there's any vignetting by the camera optics and in any case you should be metering the light that the film will actually see, unless there's some behaviour of the ground glass scattering for off-axis illumination. I have a physics degree and I can also get some support on this from someone with doctorate in optical scattering so between us we should be able to work out how to do it.

    I've got another product development just starting now so I'm a bit busy but I will get the optical scattering Ph.D lady started on looking into this one.

  9. #9

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    Re: Large Format Focal Plane Meter - New Product

    I'll give you any info I can, but it will be based on my current GG setup. It would have to be adjusted for each GG/Fresnel screen avaiable -- and there are a lot of them,

  10. #10

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    Re: Large Format Focal Plane Meter - New Product

    Quote Originally Posted by Dave Gooding View Post
    Thanks xkaecs, that's actually very informative and tells me it is at least feasible to meter off the ground glass. I am not sure why readings should be lower at the edges and corners of the image unless there's any vignetting by the camera optics and in any case you should be metering the light that the film will actually see, unless there's some behaviour of the ground glass scattering for off-axis illumination. I have a physics degree and I can also get some support on this from someone with doctorate in optical scattering so between us we should be able to work out how to do it.

    I've got another product development just starting now so I'm a bit busy but I will get the optical scattering Ph.D lady started on looking into this one.
    Maybe you should look at what Linhof did. They made a focusing metering bellows that attached directly to the ground glass back and had an eyepiece with a rubber collar and, originally a 2x and currently with a 4x loupe. The 4x unscrews and becomes a fixed 2x and a removable 2x pair of loupes. The rubber collar was made to fit the microscope adapter of a Gossen LunaPro meter. The bellows will compress enough so a meter reading the diameter of a quarter could be read at any point of the gg or it could be pulled back all the way to meter the entire gg or any portion of the gg.

    To meter properly the back had to have a Fresnel installed and, of course, the user had to determine how much light was absorbed and lost by the gg/Fresnel.

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