Best F-Stop range to shoot between?

C

ChrisA

Member
I've heard that due to most lenses having a 'sweet spot', shooting using F-stops around F4-F8 with a Dvx will produce a sharper/higher quality image compared to both extremes of the iris (fully open/almost closed).

However I recently read that when James Longley shot the documentary Iraq In Fragments using a Dvx (then blown up to 35mm), he kept the iris wide open the whole time and used the Nd filters/ shutter speed to control exposure. (I think the theory being let as much light into the sensors as possible)

Both seem to make sense but also obviously contradict each other, I'd be interested to hear others opinions on this.
 
Wow, is there really a difference to tell between the two ugafan?

I didn't know that!

Chris,

If you have the iris at 3-5.6, it will decrease the noise a lot. If you leave the iris open, or closed, you will get more noise then normal.
 
Robbie Comeau said:
If you have the iris at 3-5.6, it will decrease the noise a lot. If you leave the iris open, or closed, you will get more noise then normal.
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No.

Open iris (assuming there is enough light) will give you a slightly softer picture especially at the corners, and a shallower depth of field. f/4.8-5.6 seems to be the sharpest. Way down to f/16 your picture will become noticeable softer as diffraction comes into play.

Low light aside, the iris has nothing to do with noise in the DVX.
 
That's not what I heard. I heard if you have it open, you get more noise. That's why I try to shoot close to 4 and 5.
 
Don't know. But, I would assume that people who are shooting wide open are probably not shooting with enough light to begin with, hence the noisier picture.

Don't know how iris would effect noise... never heard of that before, but I guess it could be possible. Just don't know how it could be possible.

Later,
Jason
 
Quick and dirty test. All settings on the DVX are 0 except Master Ped which is at -5, Cinelike-D, Norm Matrix, 24pA.

Even after white balancing that cast is still there. I don't know what it is. Take a look though at the sharpness gained at f/6.8 over wide open (wood grain). If there is more noise, you would never notice it from shot to shot. I don't think there is more noticeable in these pictures. Straight out of the camera.

f/1.6 (Wide Open w/ 1/8th ND)
1202353860.jpg


f/6.8
1202353907.jpg
 
Barry Green said in his DVX book that f5.6 is the sweet spot. I forget the reason, but I'll reread it tonight.
 
Robbie Comeau said:
That's not what I heard. I heard if you have it open, you get more noise. That's why I try to shoot close to 4 and 5.
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Robbie Comeau said:
.....................If you have the iris at 3-5.6, it will decrease the noise a lot. If you leave the iris open, or closed, you will get more noise then normal.
Click to expand...


Generally speaking, it is never a good idea to accept or give advice based upon "what I heard". You are in the right area but noise is not the issue.
Noise is the result of electronic gain or lack of light, or both. It can also be the result of sharpening. Will your image look softer at extreme ends of the iris range?...yes---for different reasons.
The optimal f-stop range is f4.8--f11 and William Robinette's screen grabs nicely confirm it. The sharpest f-stop setting is f5.6. It has to do with the resolution ability of your camera lense, not noise (assuming you have proper exposure).
I'm just a beginner myself so all of this is based upon what I have read from someone with experience (and i'm still learning). See Barry's book, pages 28,29.
 
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I guess case closed. I just remember a post on here, saying "Why do you get more noise when you shoot open" an I thought it was from Wiliam robinette!

I don't know.
 
gco said:
The optimal f-stop range is f4.8--f11 and William Robinette's screen grabs nicely confirm it. The sharpest f-stop setting is f5.6. It has to do with the resolution ability of your camera lense, not noise (assuming you have proper exposure).
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Are William's screen grabs available online?
 
I'll go ahead and be the nerd in the room...

A lot of this talk about optimal f/stops has a lot to do with longitudinal chromatic aberration.

Basically, in a nut shell, not all the wavelengths of light passing threw the lens are focused on the same plane at very wide open f/stops. By increasing your depth of field via a tighter f/stop, you can increase your sharpness.

It looks sharper because more of the light is actually focused on the focal plane.
Typically, the green channel is spot on no mater what f/stop, and that makes some sense. It's the most important channel. It's always the cleanest, so a lower quality lens better make sure that channel is always performing spot on.

Look carefully at some footage shot wide open with high contrast edges. I guarantee you will see some hazy colored edges. If you isolate the red and blue channels, they will be badly out of focus. You see the colored edges because of LATERAL chromatic aberration. Thats a bit different. The different wavelengths of light are basically not lined up perfectly. You can compensate for it in post if you know how, and I do personally.
 
cardmaverick said:
I'll go ahead and be the nerd in the room...
A lot of this talk about optimal f/stops has a lot to do with longitudinal chromatic aberration.
Basically, in a nut shell, not all the wavelengths of light passing threw the lens are focused on the same plane at very wide open f/stops. By increasing your depth of field via a tighter f/stop, you can increase your sharpness.
It looks sharper because more of the light is actually focused on the focal plane.
Typically, the green channel is spot on no mater what f/stop, and that makes some sense. It's the most important channel. It's always the cleanest, so a lower quality lens better make sure that channel is always performing spot on.
Look carefully at some footage shot wide open with high contrast edges. I guarantee you will see some hazy colored edges. If you isolate the red and blue channels, they will be badly out of focus. You see the colored edges because of LATERAL chromatic aberration. Thats a bit different. The different wavelengths of light are basically not lined up perfectly. You can compensate for it in post if you know how, and I do personally.
Click to expand...

Ok, that actually makes sense to me Chris. If I am understanding you correctly, chromatic aberration (lateral that is) occurs at wide open iris because red and blue channels are not resolving cleanly in the focal plane?... and this manifests itself in the form of blurry, color bleedy edges?. Might this also occur beyond the sweet spot of 5.6 at the closed end? I knew that diffraction (bending of light) at the closed end occurs and causes soft images but it would seem to follow that chromatic aberration might occur as well at the closed end. I haven't actually noticed because I never close down anywhere near f16. Just wondering out loud here. Also does the term "lateral" differentiate from another type of chromatic aberration or just refer to bleeding edges?
 
gco said:
Ok, that actually makes sense to me Chris. If I am understanding you correctly, chromatic aberration (lateral that is) occurs at wide open iris because red and blue channels are not resolving cleanly in the focal plane?... and this manifests itself in the form of blurry, color bleedy edges?. Might this also occur beyond the sweet spot of 5.6 at the closed end? I knew that diffraction (bending of light) at the closed end occurs and causes soft images but it would seem to follow that chromatic aberration might occur as well at the closed end. I haven't actually noticed because I never close down anywhere near f16. Just wondering out loud here. Also does the term "lateral" differentiate from another type of chromatic aberration or just refer to bleeding edges?
Click to expand...

Lateral CA is strictly mis alignment, and it can happen at any f/stop or focal length, though my personal studies with the DVX Leica lens have shown that it shifts around depending on what focal length you are on. I'm not sure about where its perfect just yet.

Longitudinal is strictly out of focus channels (to be more technical, not all wavelengths of light clearly focused on the focal plane). By stopping down, you can help negate this effect.
 
I don't know if there's another thread about this, but lets say your using a 35mm adapter, do you have to adjust both f-stops on the DVX lense and on the SLR lens that has been attached to reach optimal quality or do you just worry about the SLR lens.
 
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