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john.l.barford
4-Jul-2017, 13:25
I have made a 4x5 camera using aluminium extrusions called makerbeam. I have bought one 150mm 4x5 lens and have made a couple more using binocular objective lenses and old prontor shutters from vintage bellows cameras. I decided to build a through the lens meter to more easily calculate the exposure reqiired for these home made lenses and also to more fully understand the effects of filters and bellows extension and just for the hell of it.
After huge amount of trial and even more error i have succeeded in making a resonably accurate meter which fulfills the above criteria.
I will publish details of the build if anyone is interested.
Let me know.

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Barry Kirsten
4-Jul-2017, 13:59
Very interested, John. There's a lot of diy-ers here, and I'm sure there would be a lot of interest. Thanks in advance.

Dan Fromm
4-Jul-2017, 14:32
Tell us about the camera and lenses too.

Jac@stafford.net
4-Jul-2017, 15:08
Post more! I am another DIY fan, and I haven't looked at makerbeam for some time.
And welcome!

ic-racer
4-Jul-2017, 15:57
I'd be interested in your calibration technique.
166875

Jac@stafford.net
4-Jul-2017, 16:42
So how do we measure 'nits'?

Dan Fromm
4-Jul-2017, 18:01
I'd be interested in your calibration technique.
166875

That's nice, also completely irrelevant.

ic-racer
4-Jul-2017, 18:23
That's nice, also completely irrelevant.

Since you responded, what is your "relevant" technique? Something that falls outside of empiric physics like most of your posts?

john.l.barford
5-Jul-2017, 03:18
I am having diffulculty downlooading pictures

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john.l.barford
5-Jul-2017, 03:24
Makerbeam camera

I am having diffulculty downlooading pictures

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https://uploads.tapatalk-cdn.com/20170705/104a151bdeeb1c3748789e315ee0441c.jpg

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john.l.barford
5-Jul-2017, 03:26
Tapatalk appears to only accept one photo at a time

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john.l.barford
5-Jul-2017, 04:12
Tapatalk appears to only accept one photo at a time

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I am seriously unimpressed with tapatalk

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Dan Fromm
5-Jul-2017, 06:26
Since you responded, what is your "relevant" technique? Something that falls outside of empiric physics like most of your posts?

Why do the calculations when meter, shoot, develop, measure film density will do?

I'm all for models and using them but direct measurement is, well, more direct.

Drew Bedo
5-Jul-2017, 07:50
Yes . . .please publish the Meter info.

I fooled around with this years ago trying to use photo cells from Radio Shack and a multimeter. Mounted ity all to a film holder (lots of Epoxy putty) and tried it out. Lack of linearity and other things lead me to realize that I didn't have the electrical engineering backround to get this done . . .and dropped the project.

john.l.barford
5-Jul-2017, 09:26
Through the lens metering .
To make this meter you will need.
1) A LUX METER. Plenty of these on e bay. You will need one where the sensor head is seperate from the meter joined to it by curled wire.
2) a solar cell roughly 4x5 inches (plenty of these on e bay)
3) an old 4x5 film holder
4) bits of wire

Glue the solar cell into the film holder.
Cut sensor off lux meter
Wire lux meter to solar cell
Put film holder in camera
Test
Match readings on lux meter to light meter readings
And type up conversion table.https://uploads.tapatalk-cdn.com/20170705/858cf273ac0f408363c68841e6b0fa39.jpg

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Dan Fromm
5-Jul-2017, 10:43
Cute. How well does it work in dim light?

john.l.barford
5-Jul-2017, 12:52
It is able tto cover all exposure values (EVs) from 1 to 16

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stevelmx5
5-Jul-2017, 15:31
Out of interest, how would having the lux meter behind the lens account for shutter speed? I understand you could set the desired aperture then open the shutter on bulb to get a lux reading but what conversion would you apply to get ISO/shutter?

Jody_S
5-Jul-2017, 22:42
Through the lens metering .
To make this meter you will need.
1) A LUX METER. Plenty of these on e bay. You will need one where the sensor head is seperate from the meter joined to it by curled wire.
2) a solar cell roughly 4x5 inches (plenty of these on e bay)
3) an old 4x5 film holder
4) bits of wire

Glue the solar cell into the film holder.
Cut sensor off lux meter
Wire lux meter to solar cell
Put film holder in camera
Test
Match readings on lux meter to light meter readings
And type up conversion table.

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FYI, any voltmeter will do if it's accurate in the 0-1.5V range. But an accurate volt meter might cost more than a cheap lux meter from China. Also, you could mount a smaller photovoltaic cell on a thin piece of spring steel, then you would have a through-the-lens 'spot' meter that will read specific areas of interest, that you can position by sliding it about in the holder.

john.l.barford
6-Jul-2017, 02:33
To calibrate the through the lens meter
I suggest that at first you use the lux meter
(before you chop off the end) and print out a LUX to EV conversion table from the net. Use the lux meter as an exposure meter and familiarise yourself with converting its readings to exposure values you are happy with.
Make the through the lens meter. the readings from this will not be the same as the lux meter they may be bigger or smaller this does not matter. For example the lux meter will read between 320 and 640 for an exposure value (EV) between 7 and 8 . If the through the lens meter reads, say, between 1280 and 2560 (too high) simply move all the lux readings on your table down a place.
Hope this helps

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john.l.barford
6-Jul-2017, 02:46
On the subject of spot or average meter readings with the through the lens meter.
I have explored the idea of placing lots of small solar cells in patterns then activating some of them and deactivating others to form a spot or average meter. There lies madness. If you wish to explore this area of metering i suggest that you make black card cutout masks to cover and uncover parts of the solar cell. Make sure that the area of the cutout portion is the same for every configuration you wish to try. Because some cells of the solar cells will now be covered you will need to recalibrate yor lux table. See previous article


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john.l.barford
6-Jul-2017, 03:22
When i first started messing about with the idea of building a through the lens meter the reasons for it were to more fully understand the effects of bellows extension on exposure, the effects of homemade filters and homemade lenses.
Bellows extension
Using the meter it is very simple to measure the light dropoff as the bellows extends. For example my 150mm lens needs about half a stop extra exposure at full extension.
Homemade filters
It is very easy to measure light reduction from a homemade filter giving cheap access to all sorts of filter gels.
Homemade lenses
I am making lenses from old binocular parts combined with shutters from old bellows cameras (plenty of these on ebay) the problem is that the iris does not match the lens. For example if i set f8 on the iris it is incorrect. Using the through the lens meter an accurate exposure can be easily measured.


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Dan Fromm
6-Jul-2017, 04:48
John, you've reinvented Horseman's exposure meter and the reasons for using it. See http://www.galerie-photo.com/horseman-4x5-exposure-meter.html

Kleiny41
6-Jul-2017, 05:49
I am definitely interested. That sounds fantastic!!