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Author Topic: Question on Leaf A75 high iso noise  (Read 4236 times)

BernardLanguillier

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Question on Leaf A75 high iso noise
« on: August 22, 2006, 01:11:12 am »

Dear Michael,

Thanks a lot for the P45 vs A75 field report, useful info as usual.

Regarding the noise of the A75 at 800 ISO, the 100% crop you provide doesn't seem too bad, although there is a clear drop of quality compared to lower ISOs.

I was wondering how the A75 at 800 ISO compares to a 1ds2 at 800 ISO when printing the image at say 17x22 inch?

Based on the 100% crop provided, my feeling is that both should be very close considering the advantage in resolution of the A75.

What is your view on this?

Best regards,
Bernard

ddolde

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Question on Leaf A75 high iso noise
« Reply #1 on: August 22, 2006, 01:54:47 am »

One thing this review does not address are the reports by many that the Leaf backs have a more "filmlike" image quality compared to the Phase One backs.

It would be interesting to see the same image shot with each camera side by side in more than just noise comparisons.  The images presented do look very good though in terms of that quality.
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Ray

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Question on Leaf A75 high iso noise
« Reply #2 on: August 22, 2006, 02:38:57 am »

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I was wondering how the A75 at 800 ISO compares to a 1ds2 at 800 ISO when printing the image at say 17x22 inch?

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Bernard, with all due respect, I think this is not the right question. The A75 has double the sensor size as the 1Ds2. A more relevant question would be, 'How does the A75 at ISO 800 compare with the 1Ds2 at ISO 400? Same exposure and same DoF in both situations.
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Quentin

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Question on Leaf A75 high iso noise
« Reply #3 on: August 22, 2006, 03:28:17 am »

One other possble issue concerns colour shifts that affect the Kodak chip in the P45 (and other Kodak-chipped backs) but not Dalsa chipped backs.  You probably would not notice this in the field, but it might be an issue in the studio, althugh I know there is a solution to it of course.

Quote
Bernard, with all due respect, I think this is not the right question. The A75 has double the sensor size as the 1Ds2. A more relevant question would be, 'How does the A75 at ISO 800 compare with the 1Ds2 at ISO 400? Same exposure and same DoF in both situations.
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BernardLanguillier

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Question on Leaf A75 high iso noise
« Reply #4 on: August 22, 2006, 03:29:32 am »

Quote
Bernard, with all due respect, I think this is not the right question. The A75 has double the sensor size as the 1Ds2. A more relevant question would be, 'How does the A75 at ISO 800 compare with the 1Ds2 at ISO 400? Same exposure and same DoF in both situations.
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Ray,

You might be right, but my question isn't originating from the technology, but from the usage of the image. The reason why I asked is that numerous people have stated in the past that the 1ds2 was good enough at 800 ISO to provide acceptable prints at A2 size, I am just wondering how well the A75 compares to that.

If I were to follow you on the technology route, I would say that the A75 has double the sensor size and double the pixel count, so that the size of each pixel is about the same, isn't it?

Assuming that it is twice worse than the 1ds2 in terms of noise per pixel, but that we pick a print size where only half the potential of the A75 is enough to achieve acceptable resolution, I feel that an A2 comparision makes sense from a practical standpoint.

Cheers,
Bernard

Ray

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Question on Leaf A75 high iso noise
« Reply #5 on: August 22, 2006, 08:30:47 pm »

Quote
.......the size of each pixel is about the same, isn't it?

Assuming that it is twice worse than the 1ds2 in terms of noise per pixel, but that we pick a print size where only half the potential of the A75 is enough to achieve acceptable resolution, I feel that an A2 comparision makes sense from a practical standpoint.
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Hi! Bernard,
Sorry to harp on this, but I feel it is something often overlooked when comparing different size sensors. This is also going to be relevant when comparing noise levels in the LX2 with other larger sensors.

You are right that the A75 pixel is about the same size as the 1Ds2 pixel, so maybe we should compare noise per pixel at ISO 800. But this really wouldn't tell us anything useful. The Canon D60 and 10D also have lower noise at the pixel level than the original 1Ds, but on equal size prints the greater number of pixels of the 1Ds more than makes up for that slight  pixel-level deficiency regarding noise.

I agree therefore that an A2 print comparison makes more sense. By the same token, the reason we use high ISOs is in order to get either greater DoF or to be able to use a faster shutter speed, therefore the comparison should be, whatever size prints we want to compare, between the 1Ds2 at ISO 400 and the A75 at ISO 800, which gives us the same DoF, the same shutter speed, but one stop wider aperture with the 1Ds2.

To do the job thoroughly, we should also first check the actual ISO values of both cameras because they rarely seem to be spot on. ISO 400 on the 20D, for example, is actually ISO 500.
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BernardLanguillier

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Question on Leaf A75 high iso noise
« Reply #6 on: August 22, 2006, 08:56:30 pm »

Quote
I agree therefore that an A2 print comparison makes more sense. By the same token, the reason we use high ISOs is in order to get either greater DoF or to be able to use a faster shutter speed, therefore the comparison should be, whatever size prints we want to compare, between the 1Ds2 at ISO 400 and the A75 at ISO 800, which gives us the same DoF, the same shutter speed, but one stop wider aperture with the 1Ds2.
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Ray,

I see your point.

The same should actually be done when comparing a 1ds2 with a D2x for instance.

Cheers,
Bernard

Ray

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Question on Leaf A75 high iso noise
« Reply #7 on: August 23, 2006, 12:32:22 am »

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The same should actually be done when comparing a 1ds2 with a D2x for instance.
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Bernard,
Indeed it should. I sometimes forget about such issues myself when I don't have BJL to remind me (what happened to BJL? Hope he's all right.)

I'm beginning to think that the thorough tests at dpreview deliberately avoid confornting these issues in order to generate controversy, although to be fair, they do sometimes mention the 'actual' ISO values as in the following chart.

[attachment=915:attachment]

I think you'd agree, the D2X with its 3 options of noise reduction, complicates the comparison. If you compare the D2X noise with full noise reduction on at ISO 800 with the 5D at ISO 1600 (which is actually ISO 2000), then the D2X is definitely less noisy, but at the expense of resolution loss. If you compare the D2X at ISO 3200 in standard mode, which uses a moderate amount of detail-destroying noise reduction, with the 20D at ISO 3200, we see that noise levels are about the same. The questions then arise, 'How does total image quality on equal size prints compare?' 'To what extent does the greater number of pixels (of the D2X)compensate for, perhaps, a more aggressive, resolution-reducing noise reduction?'

It seems to me that these important practical considerations are often skipped over far too readily.

[attachment=916:attachment]
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