ASA Tests Anyone ?

[dracul]

Hello everyone. I am a newbie here. I noticed no one has tests lower then 320 asa and was wondering if shooting a 100 asa for example would get sharper images in general?
Can anyone comment and post some footage or stills if possible?

 

[Andrew M.]

320 or 100 is just meta-data info.
Will not influence the RAW itself.
However it changes how RAW is displayed on your screen.

 

[Mark Crabtree]

Iso

Iso

The sensor will clip at a certain point above 100 percent. Somewhere between 110 and 120 I have heard. Rating at 100 gets your highlights closer to the clip point (or beyond) but you will get less noise. The dynamic range is reduced when you over expose and when you under expose. That's why it is so important to test.

 

[dracul]

well, thank you for the replies gentleman. Being a film guy you sort of lost me.
I thought setting the camera at say 100 asa means you need more light in general but will result in sharper less noisy images. Ussually with digital still cameras same rule applies and doing this will get you sharper images. I guess i need a newbie guide explanation to red cinematography. Can someone point me in the right direction.

 

[Brook Willard]

Imagine an exposure range of -50 and +50 around 320 ASA. These numbers aren't stops, they're just magic made up numbers for the sake of this discussion.

Black is -50, your shadows live at -25, normal lives at 0 and decently exposed lives at +25. +50 is clipped... gone forever.

So you move to... 100ASA.

Now your deepest [originally black] shadows are at -25 [Hey, I can see them!], your shadows live at 0 [look great, low noise!], your normal lives at +25 [looks great, so clear!] and your decently exposed lives at... +50. Crap.

All exposing at a lower ISO on the RED does is shift a window of exposure. Lets say you're at a 2.8 at 320. If you go to 160, you essentially opened up to a 2.0. That's it. It'd look overexposed at 320, but not at 160. Your shadows would have a stop more light, but your highlights would clip a stop sooner.

Go the other way. You're at a 2.8 at 320. You go to 640... so now you're at a 4.0. You've underexposed everything by a stop. Now the highlights may not have clipped at all, but the shadows will have less light and - accordingly - more noise when you boost the exposure.

That's how the ASA on the RED works. It's just a metadata-related change. It has nothing to do with any sensor-side changes... at least not as of today [build 14]. Nobody knows if it will change in the future.

Now.

If you expose the image by a meter ["my meter says to put it at a 2.8, so put it at a 2.8"], then the exposure will never be perfect.

If you judge your exposure by a histogram or using the false color meter, you'll always have a better time placing your exposure. The "best" digital exposure is one that is as overexposed as possible WITHOUT clipping. Clipping means gone. Forever.

In a low contrast situation with no hot highlights, you may be able to open up another stop or so from the metered exposure. This may put your native ASA for that shot at 160 or so. Now that doesn't mean the camera is a 160 ASA camera and it doesn't mean the 320 ASA exposure would be wrong. It just means that you're using the digital tool in the best way possible - giving it as much as possible without clipping.

Go the other way. You're in a super contrasty situation with lots of highlights. You want to save those highlights so you stop down. You've essentially changed that shot's native ASA to... maybe... 640. Does that mean the image is underexposed? Will it be noisier? Not necessarily. It just means that you are placing your exposure based on what you want to save and what you're willing to let go. What if the shadows look too dark on the monitor? Will you be able to save them? Why wait until post to find out - point a light at them. Ultimately, if it looks good on the monitor, it'll look great on the RAW file.

I hope this helps. There have been threads upon threads about exposing properly with the RED [and digital cameras in general].

 

[dracul]

Imagine an exposure range of -50 and +50 around 320 ASA. These numbers aren't stops, they're just magic made up numbers for the sake of this discussion.

Black is -50, your shadows live at -25, normal lives at 0 and decently exposed lives at +25. +50 is clipped... gone forever.

So you move to... 100ASA.

Now your deepest [originally black] shadows are at -25 [Hey, I can see them!], your shadows live at 0 [look great, low noise!], your normal lives at +25 [looks great, so clear!] and your decently exposed lives at... +50. Crap.

All exposing at a lower ISO on the RED does is shift a window of exposure. Lets say you're at a 2.8 at 320. If you go to 160, you essentially opened up to a 2.0. That's it. It'd look overexposed at 320, but not at 160. Your shadows would have a stop more light, but your highlights would clip a stop sooner.

Go the other way. You're at a 2.8 at 320. You go to 640... so now you're at a 4.0. You've underexposed everything by a stop. Now the highlights may not have clipped at all, but the shadows will have less light and - accordingly - more noise when you boost the exposure.

That's how the ASA on the RED works. It's just a metadata-related change. It has nothing to do with any sensor-side changes... at least not as of today [build 14]. Nobody knows if it will change in the future.

Now.

If you expose the image by a meter ["my meter says to put it at a 2.8, so put it at a 2.8"], then the exposure will never be perfect.

If you judge your exposure by a histogram or using the false color meter, you'll always have a better time placing your exposure. The "best" digital exposure is one that is as overexposed as possible WITHOUT clipping. Clipping means gone. Forever.

In a low contrast situation with no hot highlights, you may be able to open up another stop or so from the metered exposure. This may put your native ASA for that shot at 160 or so. Now that doesn't mean the camera is a 160 ASA camera and it doesn't mean the 320 ASA exposure would be wrong. It just means that you're using the digital tool in the best way possible - giving it as much as possible without clipping.

Go the other way. You're in a super contrasty situation with lots of highlights. You want to save those highlights so you stop down. You've essentially changed that shot's native ASA to... maybe... 640. Does that mean the image is underexposed? Will it be noisier? Not necessarily. It just means that you are placing your exposure based on what you want to save and what you're willing to let go. What if the shadows look too dark on the monitor? Will you be able to save them? Why wait until post to find out - point a light at them. Ultimately, if it looks good on the monitor, it'll look great on the RAW file.

I hope this helps. There have been threads upon threads about exposing properly with the RED [and digital cameras in general].

yes, it has helped . thank you and I will search for those exposure threads.

 

[Jeremy Neish]

Brook -
Best... RED ASA... Explanation... Ever...!

I've tried to explain this to DP's on several occasions and they really struggle, I'm printing this out and including it in my rental kit.

 

[dracul]

The "best" digital exposure is one that is as overexposed as possible WITHOUT clipping. Clipping means gone. Forever

I assume by this you mean to not underexpose any part of the image. Another words just like film you want to expose normal and over then print it down. If you have not underexposed in film you retain maximum detail in shadows since you are using all the grains. Is this what can be done with red?
Can i expose the shadows normal , the normal say equivalent of 2 stops over and then just bring it down in post?

 

[Joel Kaye]

The "best" digital exposure is one that is as overexposed as possible WITHOUT clipping. Clipping means gone. Forever

I assume by this you mean to not underexpose any part of the image.

It's more like shooting reversal film. So it's the opposite of what you'd do with a negative. Once something has clipped to white it's gone. You'll have to judge from scene to scene whether or not to let anything clip.

 

[Patrick Tresch]

ASA rating

ASA rating

This thread is very tricky.

I'm not yet done with all my testings on REDONE. But ASA rating is an art with REDONE as it depends on what criterions you base your rating... ASA rating has also to do with managing the shadows area and the noise (nice one BTW). The sensitivity of the sensor is also determined by its response in R/G and B channels. You will have much more noise in a 320 ASA shot @ 2500k (white balance for 2500) as the blue channel (wich is the weakest until now (build 14)) has a lot of noise, than shooting @ 320 ASA @ 7000k.

I determined that shooting @100 asa is a error as it would clip informations at about 70% of signal (not quite understood what hapened to it...). So I would't go slower than +-250 ASA.

I love this camera in underexposure. Some shots done at 2500 and 5000 ASA in low contrast situations showed spectacular results. Noise can have very different response on how you handle it in post (REDCINE, I didn't test Scratch yet...). When I do have a shot @ 5000 ASA I first boost asa in REDCINE to 2000 asa (max.) enven If Jim said : !!!USE CURVES!!!! because using curves don't let you work precisely in this spectrum of the signal (the cuvre window in REDCINE is way too small to manage tiny changes). When boosting asa you have to keep an eye on what effect it has on the highlights and recover them (if possible)...

So determing asa of this camera is a much different story than only reading a Lab prescription and over expose 1/3 stop...:wink:

ASA rating is not metadata handling but determining a look and taking creative decisions.

See you.

Pat

 

[Brook Willard]

Can i expose the shadows normal , the normal say equivalent of 2 stops over and then just bring it down in post?

Assuming you have not clipped anything that you expect to keep... yes. That's exactly it.

But it's one hell of a flat lighting environment that will allow for two stops of overexposure on the lens barrel without any clipping.

 

[Brook Willard]

Brook -
Best... RED ASA... Explanation... Ever...!

I've tried to explain this to DP's on several occasions and they really struggle, I'm printing this out and including it in my rental kit.

I'm flattered. I would've spent more time on it if I knew it was going somewhere.

I once wrote a similar explanation of RED exposure in another thread... it was about twice as long and included a few more examples. But if this one's clear enough for you... I hope it helps.

 

[dracul]

Assuming you have not clipped anything that you expect to keep... yes. That's exactly it.

But it's one hell of a flat lighting environment that will allow for two stops of overexposure on the lens barrel without any clipping.

why do you say that? you would still maintain a 2 stop contrast range. 2 stops over for key or normal and normal exposure for the shadows. Then process everything darker equivalent of 2 stops darker in post.

 

[David Mullen ASC]

2-stop over for restoring to a normal look in post is rather risky, especially for a digital camera. Things only another stop over two (i.e. three stops over) will start to clip, and there are bound to be objects in the frame lighter in tone than the face, so while your two-stop overexposed face may hold some detail (shiny bits may already be clipping) other areas will really be clipped and you'll be unable to recover any detail there.

With a digital camera, overexposing to reduce noise has to be weighed against the loss of highlight detail from clipping. If the RED has a base sensitivity of 320 ASA, overexposing subjects in general by two stops is like rating it as 80 ASA, and that means you will be losing a lot of highlight information, anything lighter than fleshtone / light grey will be clipped probably. You have to remember that a typical scene has details that are lighter in tone than faces.

Whereas due to the enormous overexposure latitude of negative film, you can to some extent "expose for the shadows and print for the highlights" it doesn't work that way for digital cameras because you don't have that much headroom. You should find an ASA rating that gives you a noise level you like, then expose normally for that rating, watching your shadows and highlights to make sure important detail is being captured at both ends. Once you clip a highlight in digital, it's gone.

And a two-stop contrast range between highlights and shadows is somewhat flat, boring, conservative lighting. You would have a hard time color-correcting something that evenly-lit to look more contrasty and shadowy. Three stops difference would look richer.