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Hans Sandstrom March 26th, 2012 02:33 AM

Aperture vs ISO
Having just gone from full automatic settings to manual I have a question regarding the combination of aperture vs ISO.
So is it preferable to always use the lowest possible ISO and compensate that with a low f-stop value or...?

Jon Fairhurst March 26th, 2012 10:29 AM

Re: Aperture vs ISO
On the 5D2, I strive to keep the ISO below 1250. You might choose 800 as the preferred limit on your camera, but the exact number depends on your personal preference. That gives you some flexibility. You might choose 100 ISO and a wide aperture for a romantic, shallow DOF shot, or you might choose 800 ISO or higher with a narrow aperture for a close focus shot to get adequate DOF.

It can also depend on your lens. The EF 85/1.8 is a bit milky wide open. Closing down to f/2.2 or so improves the image. Knowing the sweet spot of the camera and lens - as well as the look that you want - can guide your decisions.

For instance, I took a beautiful photo of the Washington State capitol building handheld at night with the 5D2 and 35L lens. I checked the settings and saw that I nailed it. The shutter was 1/40 (you generally want 1/focal_length for handheld photos of distant objects), the ISO was 1250 (my personal max), and the aperture was f/2.0 (which would have improved the lens from its f/1.4 maximum.) Taken together as a system - and properly exposed for the scene - I got as good a photo as I could without a tripod. (With a tripod, I would have shot a longer exposure at 100 ISO and f/8.)

A simple guideline is to set the minimum ISO in the daytime and the maximum, personal, ISO after the sun falls. Also, consider an ND filter for daytime shooting, such as ND 0.9, or three stops. By using those default guidelines, you can usually dial in a good exposure, with reasonable settings quickly.

Hans Sandstrom March 26th, 2012 12:21 PM

Re: Aperture vs ISO
Thanks Jon,

So far I only have the stock lens 18-55/3.5 and a Tamron 10-24/3.5. And I just bought a loupe for the LCD.

I now realise that my "theory" is not so good. Another question do you normally start by defining which ISO setting or which which aperture you'll need. Maybe a dumb question as it might depend on each situation?

After shooting a video in full automatic mode in Shanghai I now can see that manual settings is a must especially in the night shots...

...so from now I decided to shot only in manual mode

Jon Fairhurst March 26th, 2012 01:18 PM

Re: Aperture vs ISO

Moving to manual mode is the right decision. You will quickly gain experience that will allow you to estimate the best settings before you turn on the camera.

I would recommend that you get an EF 50/1.8, if not an EF 50/1.4 lens. (The 1.4 has a much better focus ring with a long, though somewhat loose, throw.) That will give you much more flexibility with your settings. Regarding aperture, you're very limited right now. Those lenses really tie your hands.

You need to know your lenses. Some (like the 24-105/4L IS or the 70-200/2.8 lenses) are beautiful wide open. Others, like the 85/1.8 need to be stopped down slightly for best results.

For sharpest performance with little light falloff in the corners, f/8 is generally ideal. As you stop down further, diffraction will soften the image slightly. How the lens performs at wide apertures depends on the lens.

Artistically, you might want shallow DOF, or you might want two objects on different planes in-focus. If this is the case, you start with the aperture. Sometimes the light is low, so you are forced to use a wide aperture. In bright sun without any ND filters, you might be forced to use a tight aperture. Having a fast lens and ND filters (I use an ND0.9 and a circular polarizer, which also cuts light) will give you the best flexibility.

With ISO, you always want the minimum setting, but not so small that you can't get a good exposure and not so large or small that you compromise your desired DOF. As I mentioned, start with 100 in daylight and 800, 1250, or 1600 (depending on your preference and the camera) under artificial lights. Fine tune from there.

With the 5D3, you get another two stops of light or so. 5000 ISO might be a reasonable limit(!) That not only allows one to shoot in near moonlight conditions, it allows one to shoot with deep focus in normal, artificial light conditions.

A decision chart might go like this...

1) Is it day? Use 100 ISO and add the ND filter. Night? 800+ ISO and remove the ND.
2) Do you want deep focus? Set the aperture tight to f/8 or f/11. Do you want shallow focus? Open to or near the maximum aperture of the lens. Do you have two items that you want in focus at the same time? Find the best aperture and make that your target.
3) Is the exposure too dark? Remove ND filters, raise the ISO to your limit, and open the aperture in that order.
4) Is the exposure too bright? Reduce the ISO to the minimum, add ND filters, and stop down the aperture in that order.

That pretty much summarizes my approach. With practice, the choices become second nature.

It's all about 1) getting a good exposure, 2) having an appropriate aperture to meet your artistic goals within the limits of the lens, and 3) keeping the ISO as low as possible and no higher than your max without overly compromising point #2.

But definitely consider a fast 50mm lens and an ND filter. They aren't expensive as camera gear goes, and they will give you much more control than you have today.

Hans Sandstrom March 26th, 2012 02:46 PM

Re: Aperture vs ISO
Wow, that was excactly what I needed.
Thank you so much for taking time to write this. Now I feel it's up to me to go out and practise.


Bruce Foreman March 27th, 2012 12:12 PM

Re: Aperture vs ISO

Originally Posted by Hans Sandstrom (Post 1723200)
Thanks Jon,

So far I only have the stock lens 18-55/3.5 and a Tamron 10-24/3.5. And I just bought a loupe for the LCD.

I now realise that my "theory" is not so good. Another question — do you normally start by defining which ISO setting or which which aperture you'll need. Maybe a dumb question as it might depend on each situation?

...so from now I decided to shot only in manual mode

Here's my methodic approach to settings in manual mode.

Shutter: In NTSC areas set this to 1/60th, in PAL areas 1/50th (so that if artificial light sources are in the scene the shutter speed will be a close match to power line frequency and this may avoid or reduce flickering or banding)

Aperture: Set for desired depth of field (zone of acceptable sharpness) effect.

ISO: Set to AUTO initially. This will be only temporary. If your display is set to display settings at the bottom of the LCD, a light press of the the shutter button will cause the ISO value the camera selects with ISO in AUTO to appear at the bottom of the LCD.

So, now press the ISO button and dial this value in manually. Exposure is now "locked" and will not "drift" as you pan around. If you're using a loupe you can adjust ISO up or down a bit to "tune" the exposure effect you want.

In bright daylight if you need to use larger apertures have ND filters handy. I have .6 and .9 for a 2 stop and 3 stop reduction respectively. "Stacked" I can get a 5 stop reduction.

At night the biggest limiting factor is the maximum apertures on your current lenses. I recommend the EF 28mm f1.8 USM lens and the EF 24mm f2.8 prime lenses for "night" work. The 28 is a "workhorse" that with the APS-C sensors will give you a "normal" perspective with spatial relationships working much like our eyes see. The f1.8 capability will help you keep the ISO down. The 24mm will give you slightly wider view and the f2.8 is often usable for night street scenes.

Assuming you use a Hoodman Cinema Pro Kit or something similar you can actually evaluate exposure visually on the LCD. Run some quick tests to see if you need to "monkey" with screen brightness, this will depend on how much your eyes adapt to lighting environments.

I found at night if the image on the LCD looked perfect through the loupe it was actually underexposed when I got it in the NLE to work with. The solution: Drop the LCD brightness down two notches (for me). How do you tell where to set it? Notice the grey scale to the right of the image shown (the last still you shot), set the screen brightness so you can see EACH STEP on that scale. Tonal values on the image should "look about right" also (it's a good idea to leave a daylight "snap" as the last still on the card for this reference.

Likewise in bright sun, even with the loupe, my eyes adjust to the brightness around me to the point I can't really see image tones well on the LCD. Kicking the LCD brightness up some until I can see all the gray scale steps and the still image displayed does the trick.

Important to remember to set that LCD back to midscale when you go back to a normal lighting level environment. REMEMBER, REMEMBER!!

I don't "obsess" about high ISO and noise (but that's just me), if you get a bit of noise it will likely not be visible in your final delivery format (DVD or rendered file), so if needed I go up to 1600 and even 3200.

I have the new Olympus OMD E-M5 on pre-order, initial testers with pre-production samples are reporting CLEAN ISO 6400 on stills. I've seen examples shot at ISO 12,800 I can easily live with. I'm still keeping the 60D though.

Jon Fairhurst March 27th, 2012 02:15 PM

Re: Aperture vs ISO
As I mentioned, ISO limits are personal. Some time ago, one poster refused to leave 100 ISO(!) I guess he had lots of lights available. Bruce is content with 3200 ISO. I'm uncomfortable beyond 1250 on the 5D2.

Over time, you'll get a feel for where your own limits are.

Regarding the Auto ISO and Exposure Lock, that can work, but it might lock too bright or too dark for a given scene. For instance, if a person is standing in front of a bright window, you might choose to expose high to see the face while accepting that you will blow out the background. Or maybe you want the person to be mysterious, so you expose low to show a silhouette. With Auto ISO, you have to push Exposure Lock at the right moment and might not get what you want. With full manual, you are in control and you will get the feedback to know which settings work in various situations. Each time you use manual, you learn.

One key is to learn the location of the ISO button by feel, so you can quickly adjust it. Same with the WB button. (I have those on the 5D2 anyway. I'm not sure about the other models.) Once you develop muscle memory for the buttons and have a feel for which settings deliver the desired results, you'll find manual mode to be quick and easy.

Brett Sherman March 28th, 2012 09:57 AM

Re: Aperture vs ISO
I'm not comfortable above 1250 either, but if the light isn't there it isn't there. Depending on the shooting situation added lights may not be possible or practical. Once you got the shutter and iris down all the way, you have no choice but to go higher with ISO. Noise can also be forgiven in some scenarios. I'd rather have noise then that deer in the headlight look you get from an on camera light. To each their own.

Jon Fairhurst March 28th, 2012 11:59 AM

Re: Aperture vs ISO
Exactly right, Brett.

Shooting above your personal ISO limit is sometimes required. I don't do the on-camera light or flash thing either. The main thing is to open the aperture to the max first.

I did a "found light" shoot with my son a while ago in a small town downtown at night. By directing him into the light from streetlamps and shop windows, I was able to shoot at f/2 or f/2.8 at 1250 ISO.

We haven't mentioned shutter speed, but that's the other variable.

Here's the "formula":

For normal, 24fps video, shoot at 1/50, except when under artificial lights in North America or other 60Hz power location. In that case, shoot at 1/60.

If the motion is low and you are starving for light, you can consider 1/30 on a tripod or with an ultrawide lens.

If you have lots of light and want a stuttery effect, increase the shutter speed.

For photos, generally shoot at 1/focal_length. For instance, with a 50mm lens, shoot at 1/50 or faster on a full frame cam. On a crop cam, your 50mm lens is an 80mm equivalent, so you can shoot at 1/80.

If your lens has IS, you can cut the shutter speed to about 25%. With the 100L IS, on a crop cam, you might shoot 1/160 without IS and 1/40 with it.

With an ultrawide, say 24mm on full frame, you could shoot 1/25, but this would be too slow if your subject is moving. For sports, you might want 1/250 to capture a runner. Or you might go with 1/25 or slower to capture the blur.

The 1/focal_length rule also breaks down when shooting items very close to the lens. With a wide landscape view, camera shake barely moves the image. However, if you are taking a photo of an object inches from the lens, your shake will move the object greatly. So, that 24mm lens might be fine at 1/25 for normal distances, but you might want 1/100 when using it like a macro.

Anyway, shutter is the other big variable.

On that night shoot, I was mostly using a 35mm f/2 lens, full frame, so I was shooting at a limit of 1/40, f/2, and 1250 ISO, so we needed to find enough light from the shop windows to make that work. As long as we stayed out of the deepest shadows, it worked fine. Had we been shooting video, I would have shot at 1/60. More light, a higher ISO or a faster lens would have been needed for that.

In practice, it was pretty easy. Because it was dark, I set 1250 ISO immediately, opened the lens wide, and set 1/focal_length. I also set a tungsten WB and let the unique colors from the windows do their thing. Before I even looked through the viewfinder, I was already very close. If I had more light than I needed in a given shot, I would reduce ISO - unless I wanted deeper focus. In that case, I would stop down aperture.

Back to the original post, definitely look to get a faster lens and ND to open up the full range of possibilities.

Bruce Foreman March 28th, 2012 01:17 PM

Re: Aperture vs ISO

Originally Posted by Jon Fairhurst (Post 1723438)
Regarding the Auto ISO and Exposure Lock, that can work, but it might lock too bright or too dark for a given scene. For instance, if a person is standing in front of a bright window, you might choose to expose high to see the face while accepting that you will blow out the background. Or maybe you want the person to be mysterious, so you expose low to show a silhouette.

Just to clarify...I don't use AUTO ISO in video work. I only set it there initially to see where the camera will set it, just as a possible starting point. Then I immediately dial that value in manually.

If the exposure effect looks like what I want I leave ISO there and exposure is locked for that scene.

But in the kind of scenarios Jon describes above, I'll press the ISO button and start going up (or down) until what I see on the LCD is what I want for that scene (a loupe is almost an absolute MUST for this)

I may only do the initial AUTO thing for the first scene setup. From there I often simply press the ISO button and start "dialing" while observing through the loupe. But I suggested the procedure I posted as a pretty good way to get started for those new to Canon manual settings in video. If they have a loupe and follow my steps it's almost "can't miss".

Without the loupe they kind of have to settle for not trying to visually judge exposure on the LCD (stop after manually dialing in the ISO setting AUTO selected) unless indoors where they can see the LCD better.

Nigel Barker March 29th, 2012 03:42 AM

Re: Aperture vs ISO
With the 5D2 we will shoot at up to ISO3200 & get great noise free footage provided (& this is really important) that the scene is correctly exposed. If you use a high ISO & it is still underexposed then it will look like crap & the only answer is to add light. When we shoot events with changing lighting conditions I will set ISO3200 & then just adjust the aperture to keep the exposure correct as this is easier than changing the ISO. BTW I don't think that anyone mentioned the dinky little exposure meter at the bottom of the LCD screen or viewfinder. This is pretty accurate provided that you realise that it only operates in what Cnon call evaluative mode meaning that it's an average of the whole scene so you need to point the camera at the important part of the scene you want to get exposed right before framing. The other slightly slower method is to do as the photographers do & use the histogram to check exposure. Take a still or short movie then play it back on the screen & press the INFO button until you have cycled round to displaying all the info including the histogram.

Craig Longman April 2nd, 2012 07:56 AM

Re: Aperture vs ISO
Does anyone have anything to comment on wrt variable ND filters? I've just recent switched from an XL-1 to a T2i, and my initial plan for outdoor shooting was to find the best aperture for the lens (or most appropriate for the desired effect), leave the ISO alone, and then essentially use the variable ND to get the exposure right.
This would be for outdoor or very brightly lit situations. Obviously, situations will demand playing with all the variables at one time or another, but is my plan of relying initially on the variable ND a horrible one, or doomed to failure?


Jon Onstot April 2nd, 2012 11:20 AM

Re: Aperture vs ISO
That's exactly how I shoot outdoors, Craig. I manually adjust all settings to achieve the look I want, then play with the VND filter until the exposure is right. With a little practice, it becomes second nature and is very fast. A high quality VND is a must.

Craig Longman April 2nd, 2012 02:11 PM

Re: Aperture vs ISO
Your comment on 'high quality' got me looking around. I had been going to order a Polaroid one, but very quickly found many complaints about it.
Prices seem to vary a lot, the choices from Canadian retailers seems to be Polaroid ~60, Cameron ~80 and Tiffen ~200.
B&H has a Genus (a name I think I remember) and a bunch I've never heard of: Fader, Light Craft and HiTech.
I did find reviews for both the Fader Mark II and the Light Craft Mark II and they both were fairly favourable. Not sure about the "HD" version... says it has "25% higher light transmission" which at first blush, seems counter productive. And it's almost twice the price.
Sigh, almost nothing in this business is just inexpensive, it's only ever cheap.

Jon Onstot April 2nd, 2012 04:26 PM

Re: Aperture vs ISO
No, good vnd filters aren't cheap. I own a Genus, which I've been happy with. I also recently bought a Heliopan, which is in the best in class, but it'll set you back a few pennies. The cheapest sour e is Foto Mayr - Fotofachversand seit 1983. Takes a while to ship from Germany, but service is good, and it's about 25% cheaper than U.S.

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