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550d sensor native sensitivity?

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Charles Brepsant
550d sensor native sensitivity?
on Nov 10, 2010 at 11:28:29 pm

Hello,

I have read in several places that the 550d has a "native sensitivity range of ISO 100 to 1600".

My question is, how can a sensor have more than one native ISO sensitivity, since from what i understood going up in ISO is equivalent to increasing the gain, i.e. multiplying sensor readout values by constants ?

Or am i completely misunderstanding things ?

Confused...

Charles.


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Noah Kadner
Re: 550d sensor native sensitivity?
on Nov 10, 2010 at 11:40:58 pm

Doubt it's much higher than a 160-320 or so equivalent

Noah

Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Canon 5D Mark II and 7D.


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Steve Crow
Re: 550d sensor native sensitivity?
on Nov 11, 2010 at 2:19:12 am

I think what they might be referring to is that some ISO settings are consider "native" as in built into the camera firmware and hardware while the rest are somewhat artificial and are created by the camera software - sort of like the difference between optical and digital zoom.

So they are saying that their lowest NATIVE ISO is 100 and their highest native ISO is 1600 - aprox half of the ISOs found within that range are therefore NOT native.

That's my guess-timate of interpreting their marketing speak.

Naturally you are going to ask next what the native ISOs are and I don't have an answer for you as this is not info Canon is exactly upfront about giving its users. Here is a discussion on the topic for the Canon 7D but you can find other sources with a Google search:

http://wetpixel.com/i.php/full/canon-7d-video-iso-sweet-spots/


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Noah Kadner
Re: 550d sensor native sensitivity?
on Nov 11, 2010 at 4:16:14 pm

Yeah a more important question is at what ISO does the image become unusable.

Noah

Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Canon 5D Mark II and 7D.


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Michael Sacci
Re: 550d sensor native sensitivity?
on Nov 11, 2010 at 4:49:13 pm

Of course the list of best ISO for the 7D is useless to 550D/T2i users because we are fixed to full stop ISO and not 1/3s like the 7D can do.

But this is one place where video camera to DSLR isn't a direct path. While gain and ISO settings are similar to one another the DSLR handles the upping of the light sensitivity much better. You would never gain up 18dB on any video camera and except low noise but with a DSLR you can shoot with 800 and even 1600 on some cameras and get very good results.

For the 550/T2i I think that 800 ISO is the max unless you can live with a good bit of noise.


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Charles Brepsant
Re: 550d sensor native sensitivity?
on Nov 11, 2010 at 4:50:46 pm

Thanks a lot for the answers, especially for the website indication, really interesting. He did the same tests with the 550d and it turns out there's a big difference between 7d and 550d. While 7d manages in some "sweet ISO spots" (multiples of ISO 160) to lower noise dramatically, the 550d's noise levels are much higher than most of the 7d's sweet spots. I've done some tests of my own on the 550d and they indicate the same. It seems though that ISO 100 and 200 do not have such a big difference, which is good to know.

The question of when does the ISO become unusable is a good one.. Especially since from what i understood it depends a lot on exposure, no ?

I was once shooting a low light situation in a rather dark room, and when i came to post, i was amazed to find out that some of my shots had come out with such a level of detail it was simply astonishing. The blacks were black and the middle tones were beautifully rendered. Other shots with same ISO (i think) however were simply full of noise and horrendous. Problem is i didn't think to check the settings used on camera while shooting, and since there are no shooting informations attached to videos once on computer (or are there????), i cannot know what were my settings.

My point is, say we want to shoot a scene where everything is dark except a character's face for example. If i expose correctly for that person's face (through spot metering), and for that i need to push my ISO up, say 800 or 1600, will i get a nice picture since what is correctly exposed is the person's face ? Will the blacks be crushed even in high ISO ? Otherwise should we crush them in post ? (Btw, what is the best method of crushing the blacks in post, levels ?)

I'm going to do some tests when i get the time anyway, but if anybody knows something t'would be great if he would share !

Cheers,
Charles.


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Peter Burger
Re: 550d sensor native sensitivity?
on Nov 12, 2010 at 7:35:00 am

Hello, Charles!

All of the exif-info are stored in the thumbnail of the corresponding clip. So with an exif-viewer you can easily get all of the info on the camera settings used for that clip.

For any kind of contrast or colour change I find curves more useful than levels, but of course you can use levels as well.


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Charles Brepsant
Re: 550d sensor native sensitivity?
on Nov 12, 2010 at 1:23:47 pm

Amazing, i was searching all over the place for that simple thing ! Thank you Peter !

Unfortunately I looked for the exif informations of the clip(s) i was talking about, and realized my .THM files were not there... Stupid me.
But now i know.

Thanks for the tip on the curves also. The question remains if you can get proper blacks & low noise while being in high ISO by properly exposing, with spot metering or other... Or am i completely misunderstanding things ?


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Peter Burger
Re: 550d sensor native sensitivity?
on Nov 12, 2010 at 3:59:04 pm

Glad if I helped!

High ISO is a a problem... I try to avoid going higher than 800, so a fast lens was/is the only solution for me.
Shooting flat helps quite a bit. You could play around with the Marvel cinegamma style: http://marvelsfilm.wordpress.com/2009/10/19/canon-7d-picture-style-with-cin...

There's a lot of information about shooting flat here on the cow. Other great resources: http://www.prolost.com and http://www.dslrhd.com


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Michael Sacci
Re: 550d sensor native sensitivity?
on Nov 12, 2010 at 11:03:22 pm

I think most people agree 800 is the usable limit on this camera (higher on others) but the noise really shows up if you underexpose the frame and then try to lift the blacks and mids in post. A well exposed frame will give you a better chance of getting it so it is usable.

I would say that a properly exposed frame at 800 will look better than a corrected frame of 400 that was underexposed.


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