350d boot from cf card

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Re: 350d boot from cf card
« Reply #430 on: 27 / October / 2012, 14:41:57 »
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I'm back after a month reporting that, thanks to a friend, my 350D is working again.  :xmas He substituted the broken shutter with one of another dead 350d. CHDK is still working and I'll try to update to the last version.

I've also made some testing, measuring gain and read noise from 100 to 3200 ISO. I remember to have read that 3200 ISO is not a true sensitivity, since the amplifier gain is the same of 1600 ISO and only the values are doubled via internal software. But from the measurements, the gain at 3200 is a factor 2 different from 1600, so it seems that 3200 ISO is a real sensitivity. Any comment?

Re: 350d boot from cf card
« Reply #431 on: 27 / October / 2012, 15:24:58 »
I'm trying the new version, very nice the EAEB function with a large number of frames!

But I've found that it does not work very well:
- not working with "M" mode.
- working with AV, but this imply that if the subject changes brightness, the sequence will not be correct.

Any idea to get a continuous sequence of increasing exposure times?

Re: 350d boot from cf card
« Reply #432 on: 27 / October / 2012, 15:53:17 »
the 3200 is software pushed, so there shouldn't be a difference.
According to my measurements of gain, 3200 ISO should be real. Do you have any source for your statement?

Re: 350d boot from cf card
« Reply #433 on: 27 / October / 2012, 16:10:16 »
According to my measurements of gain, 3200 ISO should be real. Do you have any source for your statement?

According to my investigations with the 400D, internal codes for ISO values follow a 1/8 EV sequence, and the highest code accepted by the camera is 1600 + 7/8 EV; trying to set ISO to 3200 (using the code that really corresponds to ISO-3200) produces broken images. Then, if you have a look at 16-bit histograms of the resulting images, you'll notice gaps in all extended / intermediate ISOs; these gaps indicate that the image was pushed by software. And the pattern of those gaps in a (supposed) ISO-3200 image do not correspond to a ISO-3200 image.


Re: 350d boot from cf card
« Reply #434 on: 27 / October / 2012, 16:59:24 »
According to my investigations with the 400D, internal codes for ISO values follow a 1/8 EV sequence, and the highest code accepted by the camera is 1600 + 7/8 EV; trying to set ISO to 3200 (using the code that really corresponds to ISO-3200) produces broken images. Then, if you have a look at 16-bit histograms of the resulting images, you'll notice gaps in all extended / intermediate ISOs; these gaps indicate that the image was pushed by software. And the pattern of those gaps in a (supposed) ISO-3200 image do not correspond to a ISO-3200 image.
Thanks for your reply Eduperez! Your point is very good, and now I've verified on my images the presence of the gaps in the histogram at 3200 ISO, as you wrote.
So the conclusion should be that the image at 3200 ISO is obtained from an image at 1600 ISO that is multiplied by 2.
Ok, this was also my thought, but I'm wondering why the measured gain at 3200 ISO is not the one at 1600 ISO. Here are my gain measurements on a 350D: http://www.astrosurf.com/comolli/strum154.png

Re: 350d boot from cf card
« Reply #435 on: 27 / October / 2012, 17:17:11 »
I'm back after a month reporting that, thanks to a friend, my 350D is working again.  :xmas He substituted the broken shutter with one of another dead 350d.
good to hear you have a working cam again :)
was this the first time that you had to replace the shutter?

Re: 350d boot from cf card
« Reply #436 on: 27 / October / 2012, 17:24:15 »
good to hear you have a working cam again :)
was this the first time that you had to replace the shutter?
Thanks! Yes, first time. At 158k shots I cannot ask more...

Re: 350d boot from cf card
« Reply #437 on: 27 / October / 2012, 17:32:51 »
definitely not, the rating for the 350D is 50k


Re: 350d boot from cf card
« Reply #438 on: 28 / October / 2012, 04:28:15 »
@   eduperez: in addition to my other reply, I've looked at the histograms of:
350D: 3200 and all intermediate 1/3 stops have gaps in the histogram
5D (old): 3200 has gaps, but all intermediate 1/3 stops no. (3200 is extended sensitivity, enabled by standard custom funtions)
60D: all sensitivities have no gaps, also the extended one at 12800 ISO.

So it seems to be no rule for understanding what is true and what is software. Any idea?

Re: 350d boot from cf card
« Reply #439 on: 28 / October / 2012, 05:55:46 »
since the 350D's 3200 is enabled by a hidden custom function, and the 20D goes to true 1600, and extended 3200 with custom function I've always assumed the 350d would be the same.

if the 350d had true iso 3200 that would be quite an anachronism. even the 450D and the 40D only go to 1600.

 

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