At f/4 and equal focal length, is EF 24-70mm f/2.8L brighter than EF 24-70mm f/4L IS?

[hanhasgotqi]

Hi all,

I'd like to buy a standard zoom lens for a canon camera. Somebody told me recently that EF 24-70mm f/2.8L II USM would let in more light than EF 24-70mm f/4L IS USM at any f/number whatsoever.

He said that equally at f/8, for example, with the focal length both set at 60, the f/2.8 lens would have a bigger aperture than a f/4 lens, and gives people better image quality or a faster shutter speed.

I've never heard that before. Of course I understand EF 24-70mm f/2.8L II USM can open up 3 more stops than EF 24-70mm f/4L IS USM. However, below f/4, I always thought that at the same focal length, if the f/number is the same, then the aperture diameter by definition is the same, so the f/4 lens could function just as well as a f/2.8 lens. (If we disregard the IS inherent in the f/4 lens, that is)

Could someone please correct me if I'm wrong? Thank you in advance for your time!

Han

[PhotomanJohn]

The only difference you should notice is when looking through the viewfinder the image will be brighter with the f/2.8 lens. This is because prior to the exposure each lens will be set at its largest aperture. But there will be no difference in the exposure as each lens closes down to f/8 (or whatever the setting is) prior to the image being taken.

John

[DanK]

Welcome to CiC. Please add your location and real name to your profile. We use real names here, and locations often help people target their advice.

John has answered your main question. However, you also wrote:

Of course I understand EF 24-70mm f/2.8L II USM can open up 3 more stops than EF 24-70mm f/4L IS USM. However, below f/4, I always thought that at the same focal length, if the f/number is the same, then the aperture diameter by definition is the same,

The difference is one stop. One stop is a multiple of the square root of 2, approximately 1.4. 1.4 x 2.8 is approximately 4. Each stop doubles or halves the amount of light.

The f stop number is the ratio of focal length to aperture diameter. Going from f/4 to f/2.8 entails increasing the aperture by a multiple of 1.4 (approximately). But the area of a circle is pi x r^2, so increasing the diameter by a factor of 1.4 increases the area of the opening by 1.4^=2, and hence doubles the light reaching the sensor.

[rpcrowe]

Having the lens open to its maximum aperture and then close down instantaneously to the pre-selected f/stop sometimes confuses people.

When they hear that most crop cameras cannot maintain auto-focus at an f/stop smaller than f/5.6 (which means f/8/ f/11 and so on); they interpret that to mean that you cannot shoot a lens with an f/2.8 aperture when you are shooting stopped down to an aperture smaller then f/5.6.

Here is a quick history of DSLR lenses from the days of film:

The first types of DSLR lenses had to be manually closed to the shooting aperture and the manually opened again to focus...

Then came Pre-Set lenses. These lenses had to be manually stopped down but there was a detent which would allow you to pre-select an f/stop and then manually stop down to that f/stop without having to look at the lens. The aperture ring would stop at the f/stop you selected. This was quite an advancement. But, these manual lenses were still a PITA to work with because if you wanted to shoot at a small aperture, the image in the viewfinder would be really dark. Try the focus preview button on your DSLR to see what it is like shooting at f/16. Trying to follow focus was darn nearly impossible.

Then the big breakthrough came when lenses evolved to a point that allowed you to view and focus with the lens wide open and then would stop down to shoot and open back up automatically. These lenses were called "automatic lenses". That designation no longer applies because there are no more lenses being offered that need to be manually closed and opened, so the term automatic is no longer necessary. Also the term "automatic" would be confusing since most lenses of today are auto focus...

[Mike Buckley]

there are no more lenses being offered that need to be manually closed and opened, so the term automatic is no longer necessary.

While that's certainly almost always true, this recently released macro lens has no automatic aperture.

[rpcrowe]

While that's certainly almost always true, this recently released macro lens has no automatic aperture.

Totally correct, Mike... I forgot about that type of lens. Probably because, having used non-automatic diaphragm lenses years ago, I'd never think of returning to that type of lens today...

[Manfred M]

While that's certainly almost always true, this recently released macro lens has no automatic aperture.

So far as I know this is a budget lens, so the more that can be cut out, the lower the price.

Dedicated video lenses and large format camera lenses are also manual aperture control lenses, as are the Leica M lenses. Most mainstream (D)SLR camera lenses are not and have not been for the past 40 years.

[Mike Buckley]

Probably because, having used non-automatic diaphragm lenses years ago, I'd never think of returning to that type of lens today...

I'm very seriously thinking of that lens as a purchase for early next year. As Manfred pointed out, its cost is relatively low probably because it has no automatic aperture. Yet it also provides a 2:1 magnification. That seems like a reasonably good fit with my wants for macro work when photographing inanimate objects in my makeshift studio using a tripod to produce abstracts. I'm skeptical that I would be happy with it in any other situation despite the reviewer's praise even when hand holding the camera.

[hanhasgotqi]

John, Thank you for answering my question. And Dan, you are right, there is only one stop between f/2.8 and f/4. On my camera, the default setting for exposure level increment is 1/3 stop, so I see f/3 and f/3.5 before f/4 comes up. My mistake.

On a separate note, if anyone has used the EF 24-70mm f/2.8L and EF 24-70mm f/4L IS, may I ask how much a difference the IS makes in the latter lens? I am buying a lens for travel to remote Chinese villages, and most often will be shooting hand-held. I've shot some photos with a 60mm f/2.8 macro lens, and the depth of field at f/2.8 is too thin for my purpose: taking candid photos of villagers so I can record and analyze their teeth in post. For a scientific research of sort. I need all of their features to be sharp, not just the eyes, cheek bones, but teeth. At f/2.8, sometimes the teeth are blurry if a subject tilts his head. So I am leaning toward the EF 24-70mm f/4L IS.

In any case, thank you so much for clarifying the f/number confusion. Your time is much appreciated!

[Manfred M]

Han - lack of sharpness can be attributable to many things; for instance focusing error, shallow depth of field, camera shake.

You might wish to look at some of the tools on this site; such as the depth of field calculator;

https://www.cambridgeincolour.com/tu...calculator.htm

Normally a skilled shooter is not going to have too much trouble hand holding a 24-70mm lens, which is why neither Canon or Nikon have gone with image stabilization in their f/2.8 pro lenses. The 24-70mm is a full frame lens, so it is very much a wide angle to very short telephoto lens.

Frankly, if I were shooting primarily to analyze teeth, I would be taking head shots and would be using a 70 - 200mm lens and would be choosing the appropriate aperture (f/8 - f/11), fast shutter speeds (nothing less than 1/250th) and appropriate ISO and I would definitely be using IS to get these shots. I assume you are shooting "candidly" so that the subjects don't know that they are the subject of a study?

I think that for serious work, I would not do casual head shots; I would get an appropriate lens with a ring flash so that I get good, even and flat lighting on the teeth so that my results were constant from mouth to mouth. I believe Canon and Nikon have both built specialized packages for dental work recording (appropriate lenses and ring flash) and have marketed these specialty cameras to dentists.

[hanhasgotqi]

Great suggestion Manfred! Thank you very much! I need to work on my basics, bracing myself and controlling my breathing. And yes, the depth of field calculator is very helpful.

For previous shots with a 60mm 2.8 macro lens on a Canon 70D, I sometimes used shutter speeds 1/80 and 1/125, and the results were not sharp enough. I was shooting outside but it wasn't that bright. I will look into ring flashes.

I shouldn't have said "candid photos". I usually ask the permission of villagers to take their photos and ask them to show their teeth when I take head shots, but there is minimal setup. I meet them on the street, talk to them about my project, about their diets and just ask them if I can snap a few shots showing their teeth and facial structure. I have been using available light so far.

Great suggestions Manfred. I'm excited about improving my skills. Thank you again.

Han

[george013]

Han,
In contrary to Nikon, Canon 24-70 lenses have image stabilization I just read. It's called USM. If you want sharp images, you should seek for the best diaphragm, that seems to be 5.6 or 8. I allways have a look at Photozone.de. You can compare all these lenses.
George

[DanK]

In contrary to Nikon, Canon 24-70 lenses have image stabilization I just read. It's called USM.

No. USM is the type of focusing motor, not image stabilization. In Canon's system, image stabilization is called IS. The 24-70 f/4 has IS. I believe that neither of the 24-70 f/2.8 lenses does.

Han, I am puzzled by this:

I am buying a lens for travel to remote Chinese villages, and most often will be shooting hand-held. I've shot some photos with a 60mm f/2.8 macro lens, and the depth of field at f/2.8 is too thin for my purpose: taking candid photos of villagers so I can record and analyze their teeth in post. For a scientific research of sort. I need all of their features to be sharp, not just the eyes, cheek bones, but teeth. At f/2.8, sometimes the teeth are blurry if a subject tilts his head.

If 60 mm is giving you the distance you want from your subjects, and your only problem is that the depth of field is too narrow at f/2.8, why don't you just use a smaller aperture? At a given f/stop, the EF-S 60mm macro will give the same depth of field as any other lens set to 60mm. This is explained in the tutorial on depth of field on this site, https://www.cambridgeincolour.com/tu...h-of-field.htm.

I think the first step for me would be deciding how far away I want to be from the subjects. For candid work you might want to be farther away. That would determine which lens I would choose--both the focal length and the minimum focusing distance. On a crop sensor camera, I rarely shoot candids of people at less than f/4 because of the problem you mentioned--very narrow depth of field. The distance might also determine which flash you buy. Ring flashes are designed for close work, and I don't know their range. They might have enough range, but I would check.

[george013]

No. USM is the type of focusing motor, not image stabilization. In Canon's system, image stabilization is called IS. The 24-70 f/4 has IS. I believe that neither of the 24-70 f/2.8 lenses does.

Han, I am puzzled by this:



If 60 mm is giving you the distance you want from your subjects, and your only problem is that the depth of field is too narrow at f/2.8, why don't you just use a smaller aperture? At a given f/stop, the EF-S 60mm macro will give the same depth of field as any other lens set to 60mm. This is explained in the tutorial on depth of field on this site, https://www.cambridgeincolour.com/tu...h-of-field.htm.

I think the first step for me would be deciding how far away I want to be from the subjects. For candid work you might want to be farther away. That would determine which lens I would choose--both the focal length and the minimum focusing distance. On a crop sensor camera, I rarely shoot candids of people at less than f/4 because of the problem you mentioned--very narrow depth of field. The distance might also determine which flash you buy. Ring flashes are designed for close work, and I don't know their range. They might have enough range, but I would check.

You're right. Quickly reading I saw a gain of 3 stops I believe. For when he wants to have a overview of lenses for Canon http://www.photozone.de/canon_eos_ff

George

[hanhasgotqi]

No. USM is the type of focusing motor, not image stabilization. In Canon's system, image stabilization is called IS. The 24-70 f/4 has IS. I believe that neither of the 24-70 f/2.8 lenses does.

Han, I am puzzled by this:



If 60 mm is giving you the distance you want from your subjects, and your only problem is that the depth of field is too narrow at f/2.8, why don't you just use a smaller aperture? At a given f/stop, the EF-S 60mm macro will give the same depth of field as any other lens set to 60mm. This is explained in the tutorial on depth of field on this site, https://www.cambridgeincolour.com/tu...h-of-field.htm.

You are absolutely right Dan. The 60mm f/2.8 lens is adequate for my work. Negligible barrel/pincushion distortion, a decent distance from my subject, and good resolution.

My friend at home advised me to get a good zoom lens as well, just as a walk around lens. I am thinking of getting a L zoom lens with IS. The smog in Eastern China is pretty bad; we get less sunlight because of that. Sometimes it gets pretty dark during the day. Even outside, I often find myself bumping the ISO to 6400 (1/200, f/8 - f/11). Therefore I was wondering if an IS lens could help a little. The smog and dust in the air also prompted me to consider a L glass for its sealing. Mr. Manfred recommended the 70-200 zoom. I only have a 60mm f/2.8 macro at the moment (96mm equivalent). I have a gut feeling I need a standard zoom to cover the range when my 60mm f/2.8 is too long, like snapping photos inside villager's houses, documenting their home lives, etc.

Perhaps I should just save the money and roll with a 60mm prime, just to get a better understanding of composition. Any suggestion will be much appreciated guys!

Han

[DanK]

Han,

I think you should decide which purposes are most important for you right now, since no one lens will do all you want.

Given your issue with low light, I think IS makes sense. it offers no help at all when the subjects are moving, but it does help with shots of static subjects. The amount of help depends on the lens, many will give you a 3-stop advantage.

Re the 70-200 zooms: the Canon lenses in this range are very good, and the two that have IS are superb (f/4 and f/2.8 II). The f/2.8 is expensive and heavy, 1.49 kg. The f/4 is just over half the weight (760g) and cost, which is why I carry the f/4. However, neither one is what I would choose for either an outdoor walk-around for a crop or for indoor use. For indoor use, unless the spaces are very big, you will want something much shorter. The most common solution for indoors on a crop sensor camera is one of the many fairly lenses in the roughly 17-50 range. Tamron makes two, Sigma makes one or two, and Canon makes one. When I used a crop sensor camera, I used a Tamron 28-75 f/2.8, but it was often too long at the wide end even in US settings, which I am guessing are larger than many rooms in China.

These lenses will also work for a walk-around outdoors, with the disadvantage that they don't go very long. There are many options to deal with that. One is to add a telephoto zoom, such as the one of the Canon 70-200s, the Tamron competitor, or one of the slower and cheaper Canon zooms (55-250 and 70-300). Another option is to get a walk-around zoom with a larger zoom range. When I shot primarily with a crop, my standard outdoor walk-around was an EF-S 15-85, and there are other options.

Dan