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Thread: Brightness Box?

  1. #11
    xo-whiplock's Avatar
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    Quote Originally Posted by Bill Burk View Post
    The issue with daylight is that it fluctuates, as you said, it's not easily controlled. A 4700K Incandescent bulb, on the other hand, might be something you can control with a feedback circuit or voltage regulator. If I were setting up a standard box, I'd make it one brightness, a standard, and then modify its brightness outside the box on the bench. You could use the old GE meter to monitor the brightness inside the box.
    I like standards, without them we all would be lost... LOL Thank you. This makes the most sense to me as well. It would be much easier to use physical filters upon a standard light source, then trying to manage a variable light source accurately for a DIY project and limited resources. I'm thinking a set of ND filters to peg say 3 different points along the exposure trajectory and the final point being the standardized light source without a filter for the brightest point. My camera's service manual says to use a brightness box set to two different EV's, and use a 50% filter to do one of the adjustments/checks. These checks/adjustments would be for high brightness and low brightness adjustments. There are other checks that can be done as well, but without such a box, it seems useless to even open up a camera to try and fix or adjust its exposure meter. This is why I asked for suggestion/help in making one. So far, I'll have to make due with my computer monitor, but I may well look for a used/broken LED monitor to use as my base for creating the box I need later....

  2. #12

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    Dear XO! The color temperature of daylight changes but we want to calibrated light source to have a constant color temperature. Dichroic color head generally has 3200K lamp in there. With some Cyan and very little Magenta I can make it becomes a 4700K light source and it would stay that way constantly. I used the spyder2 with the HFHC software to measure color temperature and recheck by shooting the light source with a Nikon Coolpix with the color temp set to 4700K and see if the resulting image is gray.
    The filtrations setting which is monitor by the 3 sensors and displayed on the unit digital displays are very accurate. I make a note of the readings for this condition and later all I have to dial in the amount of filter that gives the same reading then the light is the same even if the bulb has aged and changed color and intensity.
    And then dial in equal amount of filter on all 3 channel would give it neutral density. Monitoring the actual brightness with an accurate spot meter as reference. (Well you must have an instrument that you can trust to be correct) so I would know how bright the light is.
    It works very well except that I only have 5 stops range. The unit has 180cc adjustment and that's 6 stop but I waisted some of the filtration to increase the color temperature.

    By the way I used it to check out the light meter on my Minolta SRT-101 and after checking it I decided not to use it. Even I supply the camera a constant 1.35v source via a regulated power supply. I can adjust the calibration resistor to make it read higher or lower but if it's correct at EV14 it's wrong at EV9 and vice versa so I decided to use the camera as a meterless camera rather than trying to get expensive battery for it.

  3. #13
    Bill Burk's Avatar
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    Chan Tran,

    Were you adjusting both variable resistors and also mechanical linkage? Sounds like a calibration dance that requires a few recursions until you get it to work...

    http://www.willegal.net/photo/photo-first_page.htm

  4. #14

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    Quote Originally Posted by Bill Burk View Post
    Chan Tran,

    Were you adjusting both variable resistors and also mechanical linkage? Sounds like a calibration dance that requires a few recursions until you get it to work...

    http://www.willegal.net/photo/photo-first_page.htm

    One of the resistors is for adjusting the battery check level so it's not important and can easily adjusted. The other is for the metering itself. I didn't do anything with the mechanical because unlike other camera the SRT-101 mechanical linkage is totally independent of the meter movement. It's quite an interesting design where I don't see in other camera. All user's adjustment like aperture, shutter speed, ISO would only move the mechanical pointer. The light intensity moves the meter movement.

  5. #15
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    I'm following but I got lost at setting up a color enlarger properly... never done it but I'm sure I could learn... Chan, you are like advanced class and I'm beginning basics class... LOL I get your point thought. You have a stable light source and it allowed you to determine that the meter in your SRT101 is not reliable, so you use it full manual... My XE-7 is kinds made to use the meter and it's such a nice camera, I wanted to make sure after having to part out my first one due to shutter at 1/1000th sec. not opening and causing unexposed frames for which I could not fix on my own, I use the slide resistor from it in another XE-7 that I broke the slide resistor on while doing a clean up and getting the slide resistor to read again. Once I put the replacement slide resistor in and tested and measured shutter speeds, I compared meter reading with my DSLR aimed at different EV's. Close enough, so I shot a test roll this morning and they all came out exposed properly. I'm a happy camper. Scanning negatives is what I'm working on now... I've ruled out VueScan due to output that is not as good as the Epson Scan software's output. Oh, and to not use digital ice... LOL. I have like 8 SRT's? 101's and a couple of 102's all with mirror lock up. My first GAS camera because they are so basic and good at being mechanical, and easy take the top off and unstick the meter needles from the foam... LOL. I'll be using one for micro stuff and maybe telescope... The XE-7 is my baby and I love winding and shooting it. I have a pretty good kit of Rokkor lenses, so I good to go. Just need to shoot more and practice. I don't think I'll be able to DIY a stable light source, other then the idea of using an LED monitor to do a basic not scientific check of the my camera's exposure meters. If something is way off, I'll have to send it in to keh.com or someplace like it to get it done right in a lab by a pro. I value my cameras, and I need to have the faith and trust in their operation before running film though them. Right now, I'm confident in my XE-7 to do me right, and my Canon QL17 GIII. These two will do me fine for now, and I'll work on checking the rest of my cameras as time permits. Thanks all for the feedback and assistance, info and education... Happy Easter Egg Day!

  6. #16

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    I use the Minolta dual scan IV for my film scanning. I always use it in manual exposure mode especially if I want to check the exposure on film. In auto mode the scanner software automatically correct for exposure error as well as doing the color balance for the shot. Which is great for quick scan but you would not know if your exposure is right on or not. Using manual exposure setting on my scanner I can easily tell if my film exposure is off and by how much.
    Your XE-7 is an automatic camera and it does call for using it in automode and thus the meter must work correctly. I used an SRT-101 for many years (The cameraless years) and didn't use its meter at all and had good exposures most of the time. I started having many bad exposures when I bought a spanking new Nikon F5 in 2002 and tried out it matrix metering system.

  7. #17

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    Kyoritsu used EV's 9, 12 & 15 The camera/meter is set for ASA 100 as a standard value.
    When changing levels the knob had a mechanical feel and sound to it more like changing ND filters not like rotating an electrical switch.
    The tester also allowed changing the "K" factor to a value used by the camera maker.

    While fiddling with the "K" knob there was a slight difference in brightness possibly in color temp.
    Heavily sedated for your protection.

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