HELP with SX 40 ISO overrides !!

BaldTom

« on: 17 / May / 2012, 15:40:49 »

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I've been able to see that this model recognizes ISO from 10 to 51200, by looking in the detailed playback after making manual changes. This almost doubles the natural range on the camera.

In practice, the I-R value in miscellaneous follows the overide value that I had selected, but the I-M value appears 50-60% larger, and the detail in playback follows the latter number. If I set ISO to about 22,000 the I-M value is negative (and may be truncated because of the sign and space allowed).

I'd like to take advantage of this increased range as far as possible in the custom auto iso feature in CHDK.

I can't find instructions that cover the parameters in build 1825, firmware 100i, namely "second alternative minimum shutter" and "second alt max ISO." How should these be set in relationship to the first overrides chosen? The 2012 guide doesn't cover these parameters. What do they do?

The sx40 doesn't have a HI setting. Ignore choices for these, or set same as AUTO?

The camera seems to be picking slower shutter speeds than the constraints I've set. I'm not sure what I'm doing to cause this. Do the IS and User values affect this in some fashion?

For a scene with measured Ev of 8.5, and max ISO 3200, min shutter 1/500, IS=2, user =2, It holds at 800 ISO, f/2.7 and shutter goes to 1/50.

Also, why can't max ISO values override above 3200? This is the max value without CHDK.

There's something in the camera itself causing some of this, not CHDK. Without CHDK, Auto ISO goes to 3200 only in sports mode; all other modes seem to stop at 1600. I've read the Topic 7824 about ISO above 800, but I started a new one because it didn't address settings, etc. Hope this doesn't confuse things.

IN trying out various settings I occasionally get a lock-up and shut down.

Again, thanks for a wonderful product. Any help on any or all of this will be deeply appreciated.

« Last Edit: 18 / May / 2012, 10:47:31 by BaldTom »

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k5083

Re: HELP with SX 40 ISO overrides !!

« Reply #1 on: 25 / May / 2012, 09:21:58 »

I'm interested in the answers to your question as well. I'm more interested in the lower ISOs.

I haven't played with it as much, but my SX40 is crashing whenever I override the ISO to 50, 20, etc. Do I understand you to say you've had success with the manual override down to 10?

August

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BaldTom

Re: HELP with SX 40 ISO overrides !!

« Reply #2 on: 26 / May / 2012, 10:10:17 »

I've been able to snap an image all the way down to ISO set at 1 without crashing the camera. I don't think this is "success," because there is no noticeable difference in exposure over a series of photos.

In practice, setting ISO to 50 produces a noticeable step down in exposure. Here, the playback ISO is shown as 80. Setting ISO to 20 produces a playback ISO of 50, but in my case, I would not say I gained another full exposure step. Gaining about 2 steps is good! Its about the same on the high end. Show all the miscellaneous values while you are doing this to determine actual changes.

If you want low ISO sensitivity because of bright light, try engaging the ND filter.

The playback ISO numbers might be in the camera because of EXIF requirements, or part of Canon's corporate firmware that is used in other models.

It is important to use manual mode in checking the camera out for its capabilities. Also shut off i-contrast, etc. There is some parameter that is being overridden, in this case ISO, so I set this to 100 (the nearest)before engaging CHDK. The camera tends to "prefer" changes to shutter and/or aperture in ways I cannot figure out, but sometimes can compensate for the override.

Let us know what you find out. Thanks

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dvip

Re: HELP with SX 40 ISO overrides !!

« Reply #3 on: 26 / May / 2012, 18:23:00 »

Quote from: BaldTom on 26 / May / 2012, 10:10:17

In practice, setting ISO to 50 produces a noticeable step down in exposure. Here, the playback ISO is shown as 80.

I have never seen steps differences if I do this in my A590IS. I wonder if chdk ISO code is different in both cam.

I would like to use this with the A590IS since it doesn't have a built-in ND filter.

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philmoz

3445

Re: HELP with SX 40 ISO overrides !!

« Reply #4 on: 26 / May / 2012, 18:52:22 »

Quote from: BaldTom on 17 / May / 2012, 15:40:49

I've been able to see that this model recognizes ISO from 10 to 51200, by looking in the detailed playback after making manual changes. This almost doubles the natural range on the camera.

Unless Canon have made a drastic hardware change to the camera design then this is unlikely.

On my sx40 there is less than 1/8th of a stop extra below ISO 100 if you set the ISO override to 50 (real ISO, market ISO will be 80).
There is about the same above ISO 3200 is you set the override to 4000 (real, market = 6400).

Lower or higher values give no appreciable gain either way.

The EXIF data in the image will reflect the market ISO override value; but that doesn't mean the hardware supports this ISO.

If you're camera is capable of this extreme range please post some sample images showing the differences between the min & max Canon ISO and your min/max. I'd love to see what the noise is like at ISO 51200.

Phil.

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CHDK ports:
sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
g12 (1.00c, 1.00e, 1.00f & 1.00g)
sx130is (1.01d & 1.01f)
ixus310hs (1.00a & 1.01a)
sx40hs (1.00d, 1.00g & 1.00i)
g1x (1.00e, 1.00f & 1.00g)
g5x (1.00c, 1.01a, 1.01b)
g7x2 (1.01a, 1.01b, 1.10b)

k5083

Re: HELP with SX 40 ISO overrides !!

« Reply #5 on: 29 / May / 2012, 15:33:25 »

Quote from: BaldTom on 26 / May / 2012, 10:10:17

If you want low ISO sensitivity because of bright light, try engaging the ND filter.

This works on the SX40? I thought since it has an iris diaphragm there is no ND filter. Will try it. Right now I'm using an ND on the front of the lens in bright light; inside would be better!

August

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BaldTom

Re: HELP with SX 40 ISO overrides !!

« Reply #6 on: 29 / May / 2012, 21:14:13 »

August,

No ND filter on SX40. I should have checked it out first. Sorry!

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philmoz

3445

Re: HELP with SX 40 ISO overrides !!

« Reply #7 on: 30 / May / 2012, 05:28:05 »

Quote from: BaldTom on 29 / May / 2012, 21:14:13

August,

No ND filter on SX40. I should have checked it out first. Sorry!

Mine has a 2 stop ND filter built into the lens.
It can be enabled and disabled with the CHDK overrides.

Phil.

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k5083

Re: HELP with SX 40 ISO overrides !!

« Reply #8 on: 31 / May / 2012, 12:59:45 »

Phil, I think you may be right. At least, when I activated the option in the chdk menu, the camera's P mode did lengthen the shutter speed by a couple of stops without appearing to blow out the exposure. So maybe it has both an iris and the internal ND -- maybe for super high light situations? The blogosphere/forumosphere seems divided on whether this really exists. Needs a little more tinkering to find if it really works. If so, another great easter egg unlocked by CHDK.

August

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BaldTom

Re: HELP with SX 40 ISO overrides !!

« Reply #9 on: 05 / June / 2012, 12:37:36 »

Phil, you replied earlier,

"If you're camera is capable of this extreme range please post some sample images showing the differences between the min & max Canon ISO and your min/max. I'd love to see what the noise is like at ISO 51200."

I can't find any noticeable difference beyond the ranges you specified. I was led astray by the appearance of these (market values) in the camera's playback display.

Thanks for your patient help.

Do you have any suggestions on setting up the alternate shutter and ISO in the Custom auto ISO menu? Thanks

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