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Author Topic: High ISO with medium format  (Read 2085 times)

Neil Williams

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High ISO with medium format
« on: April 29, 2018, 04:44:47 pm »

Guys
I have a question; When shooting in low light with a 100 megapixel CMOS digital back, what would you say is a maximum ISO to shoot at without sacrificing the dynamic range?

So to add some meat to this question I will be taking my Hasselblad H6D100c with me on Safari. As I am sure your aware the best light and action on safari is normally early morning or late afternoon meaning the need for higher than base ISO-64. I am thinking bumping it up to ISO800 but wondered what you guys thought about that especially if you have got any real practical experience of shooting the H6D100c at higher than base ISO.

I have seen Ming Thene shooting at ISO12800 in Malaysia with great results but that was people not vast landscapes with moving subjects.

Thoughts and comments most welcome

Neil
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ErikKaffehr

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Re: High ISO with medium format
« Reply #1 on: April 30, 2018, 03:21:01 pm »

Correction, I have written 1600 ISO but meant 16000 ISO, sorry.

Hi,

You always loose dynamic range when increasing ISO. But, you may have plenty of DR, so it may not matter.

What really happens when you increase ISO is that the image gets noisier. Why it gets noisier? Because it captures less photons. If you have a sensor twice the size, it will capture twice the number of photons at a given exposure.

So, if you have a 54x40 mm sensor, it would have an area that is 54x40/(24x36) -> 2.5X times the area of an 24x36 mm sensor. So, you would be able to use 2.5X higher ISO settings on 54x40 mm compared to 24x36 mm.

So, if 6400 ISO works with 24x36 mm, you would be able to use 1600 16000 ISO on 54x36 mm and get similar results. That applies as long as the underlying technology is similar. We are not so far from quantum limits now, so great leaps in performance are not really possible without radically new technology.

I would be cautious about using very high ISOs. I have shot ISO 6400 on my A7rII, in good light. recently and found that I got workable results. But, it is always better to keep ISO low.Photons are building the image and you want to capture all photons you can get.

Modern sensors are pretty much ISO-less, meaning that you get essentially the same result if you rise ISO five steps as you would get keeping ISO at base and underexpose five stops and adjust in LR/Photoshop/C1.

Some modern sensors have "dual gain conversion", a neat trick to get a cleaner signal at some certain ISO. Some of Sony's 24x36 MP sensors have this feature, kicking in at 640 ISO. That means that you get better results setting say 800 ISO than using 100 ISO and underexposing three stops. But, The H6D100C does not have that feature.

Best regards
Erik


« Last Edit: May 01, 2018, 02:15:36 am by ErikKaffehr »
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Neil Williams

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Re: High ISO with medium format
« Reply #2 on: April 30, 2018, 03:35:38 pm »

Hi,


So, if you have a 54x40 mm sensor, it would have an area that is 54x40/(24x36) -> 2.5X times the area of an 24x36 mm sensor. So, you would be able to use 2.5X higher ISO settings on 54x40 mm compared to 24x36 mm.

So, if 6400 ISO works with 24x36 mm, you would be able to use 1600 ISO on 54x36 mm and get similar results.



Best regards
Erik
Erik
Something isn't jiving........what you wrote is with a bigger sensor you can use higher ISO but your example shows less.....which way is it??

Neil
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Jim Kasson

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Re: High ISO with medium format
« Reply #3 on: April 30, 2018, 03:53:02 pm »

"So, if 6400 ISO works with 24x36 mm, you would be able to use 1600 ISO on 54x36 mm and get similar results. "

I think Erik meant: "So, if 1600 ISO works with 24x36 mm, you would be able to use 4000 ISO on 54x36 mm and get similar results."

Or maybe, "So, if 6400 ISO works with 24x36 mm, you would be able to use 16000 ISO on 54x36 mm and get similar results."

Jim

Neil Williams

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Re: High ISO with medium format
« Reply #4 on: April 30, 2018, 04:02:46 pm »

"So, if 6400 ISO works with 24x36 mm, you would be able to use 1600 ISO on 54x36 mm and get similar results. "

I think Erik meant: "So, if 1600 ISO works with 24x36 mm, you would be able to use 4000 ISO on 54x36 mm and get similar results."

Or maybe, "So, if 6400 ISO works with 24x36 mm, you would be able to use 16000 ISO on 54x36 mm and get similar results."

Jim
Thats more like it Jim
Thanks

Neil
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Neil Williams

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Re: High ISO with medium format
« Reply #5 on: April 30, 2018, 04:12:26 pm »

I just remembered I took a few pictures of my pal at ISO 1600 using my H6D100c Here is a right out of camera 100% crop shot at ISO1600.....not bad considering

Neil
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Neil Williams

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Re: High ISO with medium format
« Reply #6 on: April 30, 2018, 04:40:34 pm »

Here is a very quick PP of the above picture


Hopefully I can find wildebeest as pretty in September :) :) :)

Neil
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EricV

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Re: High ISO with medium format
« Reply #7 on: April 30, 2018, 05:47:00 pm »

If you are shooting in a low light situation, with exposure limited by shutter speed (to capture movement) or f/stop (for depth of field), such that you cannot provide full exposure at base ISO, then you have already lost dynamic range, regardless of ISO setting.  Deep shadows will be noisier than if there was more light.  The loss of dynamic range may or may not be significant.  You could go out into your yard and capture images of grass in sunlight and shadow, at various under-exposure settings (compensating by increasing ISO), to see where you find shadow noise becomes unacceptable.  This will tell you how much light you need for your images, or how much under-exposure you can tolerate.  You can interpret this as maximum acceptable ISO if you like, but it is really a statement about light level. 
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jduncan

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Re: High ISO with medium format
« Reply #8 on: May 01, 2018, 05:35:02 pm »

I just remembered I took a few pictures of my pal at ISO 1600 using my H6D100c Here is a right out of camera 100% crop shot at ISO1600.....not bad considering

Neil


Hi,
When the H4D-40 was announced and review,  everybody was talking about how it could do 1600 ISO and focus "fast", and the killer price. It was such a compelling machine.  Today we have results like this one and some forum member is asking about Medium format and ISO  around 10K.  We could move to an era were more and more photographers use MF as a secondary or primary camera.  Price still a barrier, but it's going down.

Best regards,
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BJL

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High ISO with medium format; “equivalence” fails on read noise
« Reply #9 on: May 02, 2018, 09:48:04 am »

I have a quibble with Erik’s discussion of equivalent settings between different formats. I agree that the exposure index (“ISO”) needed is 2.5x higher than in 35mm format (like from 800 to 2000) and the total photon count will be the same, so about the same photon shot noise effect. But read noise will likely be worse with the larger sensor, for the reasons shown by the effectiveness of DR-Pix technology.

Basically, the higher EI means that photosites are filled to a smaller fraction of their full well capacity, and that fraction determines the output voltage from a photosite, and the lower voltage means that subsequent read noise is a larger fraction of the signal value: lower signal to noise ratio. The effect is greatest in shadows, where read noise is a larger fraction of total noise.

By the way, some dynamic range measures obscure this: counting unused stops of “potential” DR above any level actually present in a high EI scene can obscure the more relevant measure of how many stops there are between the main subject “midtone placement” and the noise floor below.
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