CHDK Spotmeter

[kuku]

Hi - I know its an old thread but I found nothing about it on the forum,and I think someone can use this fork to get the lightmeter functionality to chdk: http://code.google.com/p/chdk-lm/

[towolf]

The patch that dean0 posted is lost and the link to chdk-lm on GoogleCode gives me permission denied error 403.

Wouldn’t it be possible to make a pure lua light meter script? I mean Lua can draw widgets too, no?

[towolf]

To reply to myself,

with pure Lua scripting you can only make a [admin: avoid swearing please] light meter. Lua doesn’t give you arithmetic functions like log2 since it’s all integer based. So either you display stuff in the awkward APEX96 values and require input parameters in those of you have to resort to crummy lookup tables.

I’ve compared the EV measured values with my analogue Gossen and my digital Sekonic and it matches pretty well. Hence I conclude that it could be done in C code where you can work with decimal numbers, which is necessary since I want to meter outside of the normal range as well.

My pinhole camera has an aperture of f/500 and I'd like to directly meter for this stop and get the proper exposure time, not the other way around. The aperture is fixed obviously. Giving me time in seconds would be sufficient.

Since my Gossen’s scale goes up to f/90 only this would make things easier. I could add a compensation for reciprocity failure as well, since that varies from film to film. But that is usually and exponent to e and hence again requires floating point math.

Here’s an example: http://pinhole.stanford.edu/phcalc3.htm . I would like to implement a subset of that in the camera.

[fudgey]

Here's a copy of the attachment that must have gone missing in one of the forum changes..

[pelrun]

It would not be too hard to implement a fixed-point library for Lua; it's certainly been done a few times before in other contexts.

[outslider]

Walking on Internet I've found someday a CHDK-based project that was designed to work as a light-meter. But I can't find it now... I even don't remember the name of the project. I'll try to find it.

[an0n]

Walking on Internet I've found someday a CHDK-based project that was designed to work as a light-meter. But I can't find it now... I even don't remember the name of the project. I'll try to find it.

Is this what you were looking for ?
 http://chdk.setepontos.com/index.php?PHPSESSID=7973386aacdc6fb7e1b409702af56bbb&topic=5348.msg51863#msg51863

[towolf]

An0n, I had started from scratch and then discovered the script you linked to and modified it, but the limitation I’ve given above emerged.

I got to the point of having a script that gave me power of two times in seconds, which is not precise enough. Any other solution working with fixed point were either too cryptic to use or would require a pocket calculator to convert to human values. I didn’t want to look at implementing fixed-point math.

Thanks, fudgey, BTW.

[outslider]

Walking on Internet I've found someday a CHDK-based project that was designed to work as a light-meter. But I can't find it now... I even don't remember the name of the project. I'll try to find it.

Is this what you were looking for ?
 http://chdk.setepontos.com/index.php?PHPSESSID=7973386aacdc6fb7e1b409702af56bbb&topic=5348.msg51863#msg51863

No I mean CHDK-fork. Maybe it was the same that Kuku posted above...

[Microfunguy]

Luminance and chroma spotmeter http://stereo.jpn.org/eng/sdm/ubasic.htm#ub11

[towolf]

Luminance and chroma spotmeter http://stereo.jpn.org/eng/sdm/ubasic.htm#ub11

Quote there: The values are read from the live-image buffer and the correlation with the real scene values is not known.

This might have an academic interest, but it’s not useful for photography. The thing is, I can display the measured fractional EV with the OSD, and that looks good. I just need to do some simple math with it and provide some comvenient ways to change metering settings. This is what the OP did in C.

I just need to find the time to look into this stuff, merge it and then do my modifications. I’m sure adding a light meter mode with calculations is much more useful in a camera than playing reversi.

[Microfunguy]

I’m sure adding a light meter mode with calculations is much more useful in a camera than playing reversi.

That is what I like to hear, it is also my philosophy.

However, there will always be people who like chrome-plated car parts or 'go faster' stripes.

Someone has to provide for them !

[fudgey]

Oh, this is definitely related, right?

https://github.com/pronvit/chdk-lm

[towolf]

Oh, this is definitely related, right?

https://github.com/pronvit/chdk-lm

Yes, that's the github version of the dead Google Code hg repo.
But this is just a an exported CHDK tree with no information and no diffs.

From what I could glean, this works like a an additional OSD overlay, basically a table with settings. But it could be more. Just diffing this with the current trunk gives too many changes.

On Google you can see a .doc file related to this, but it's inaccessible.