Whats the point of fast lens

Discussion in 'Portraits and Fashion' started by john caetano photos, Dec 14, 2009.

  1. Ok, I know there awesome and great for shallow DOF, but here's my problem.
    When i shoot more then 1 person, there is always one out of focus. I even try shooting at F4 sometimes and to me they still come out soft. I shoot with both a 50 1.8 and 35 1.8. Usually keep torso and heads within frame (relatively close). Any tips? There's no point in fast lens if i can't make these portraits sharp.
  2. Hi John, a fast lens allows you the option of reducing depth of field, not increasing it.
    Since dop for a given focal length, ISO and apeture is a direct function of shutter speed, fast lenses also allow for higher shutter speeds. This can be an advantage in low light or stopping action. But there is no free lunch, you pay for this in dof.
    Cheers, JJ
  3. F4 is pretty shallow for group shots, Try F8 or smaller to start. F4 would be okay for a single person in the shot.
  4. Even when you'll be stopping down during the actual exposure (say, f/8 on a group), don't forget that the faster lens is wide open while you're composing. It makes for a brighter viewfinder, and allows your camera's AF system to work better on low-contrast subjects or in dim light before those strobes go off.
  5. Wow really? I usually shoot F2 for single portraits and try to stop a bit further for groups (2+ people)
    So then low F numbers are not good for portraits....so then there's no point in fast lens for portraits...(mean this in most cases not all)
  6. Matt that makes sense...there's one point... Thanks
  7. John: spend 10 minutes running various scenarios through this online DoF calculater (it's easy, promise). You'll quickly get a sense over how deep a puddle of workable depth of field you've got with your existing lenses used at various apertures and working distacnes from your subjects.

    Ther's nothing at all wrong with shooting close to wide open on, say, a pair of people. But you've got to get their eyes in a plane that's parallel with your camera's sensor. This can be logistically difficult with groups of people (or can result in some really bland compositions if you're not careful), so the compromise to shooting stopped-down makes plenty of sense for many portraits.

    On the other hand, you can work with a fast prime at a longer focal length (85, or 105, etc) to get back farther from your subjects, and greatly change the DoF recipe (see that calculator, again, for some thought experiments).

    I like using my 70-200/2.8 wide open for people, when I can, but using it at 85mm and f/2.8 is a lot different than using an f/1.4 or f/1.8 85mm prime wide open. Remember: it's all about planes and keeping the things you want in focus in that plane.
  8. Thanks Matt for the tool, I will get playing with it for study. I have seen it and know exactly what you mean, just don't understand how people shoot portraits wide open and get so much in focus (unless they are photoshopping it. For example, i'm seen a photo where there was a person totally in focus crisp sharp but everything else was clearly out of focus....just can't understand that.
  9. [[i'm seen a photo where there was a person totally in focus crisp sharp but everything else was clearly out of focus....just can't understand that.]]
    If your background is sufficiently far away, then you can easily have everything else out-of-focus.
    The DoF calculator will be able to direct you to an appropriate focal length, subject distance, aperture combination.
  10. Hi John,
    A low number, say f2.8 gives very narrow DOP with a longer lens. We would get a sharp face and out of focus background by shooting the face at this low f number. If we went to f8 and made the same image, the background would now appear much more in focus.
    If you have a very fast lens, say an 85mm f1.2, and you shoot at f1.2, the dop for a typical head-shot style portrait is maybe 1 or 2 inches. If the eyes are in focus, the end of the nose won't be.
    Why do we want fast lenses?
    1) Brighter viewfinder image. A fast lens lets in more light so you can see through the viewfinder more easily.
    2) Ability to make images with very narrow DOP. We often use narrow DOP to make our subject stand-off from the background more. See attached flower image. The background grass is very busy so I used f4.0 to make it go blurred or out of focus. This makes the flower stand out more.
    3) To increase shutter speed and stop action. If you shoot at F2.8, the shutter speed for the same shot will be faster than if you shoot at f8.
    4) To allow photography in lower light. If we shoot at f2.8, we have much more light than if we shoot at f8. So if it's dark, we may want to let in as much light as we can.
    5) Fast lenses tend to be a bit better made than the equivalent slower lenses. The canon 50 F1.2 is much more sturdy than the Canon 50 f1.8.
    6) Fast lenses tend to give the out of focus areas in an image a nicer, more appealing look. Not always, but there is a tendency here.
    I hope this helps. Cheers, JJ
  11. They are, not there!
  12. You have to run the numbers, John. There's always a sweet spot - positioning your subject, relative to the backdrop, and you, relative to the subject makes the most diference. If you get those things right, you might have a perfect 2-foot-deep area of workable DoF (just enough to get a person looking nicely in focus) while throwing the background well and truly out of focus.
  13. Shooting and seeing in low light.
  14. Even stopped down, fast lenses generally give better color and contrast compared to slower lenses. Plus, if you're shooting wide angle lenses like a 24/1.4, the entire group (two rows of people) is sharp at f/3.5 with the 5DII at the full 21 MP setting. If I tried this with the 24-70/2.8 lens it wouldn't be very sharp at f/3.5 - I'd need to go to about 26mm and stop down to about f/5.6.
  15. Yea i kinda get how DOF works, but then again maybe not exactly how length and f #'s work. I know the closer to the subject you are, the shallower the DOF, and vice versa...i guess what is borthering me is I see photos out there that i try to shoot at the same specs and don't get nearly the same DOF that i seen in other photos....maybe there is something i'm missing though...IDK
    Also another thing is buying fast lens and not being able to take advantage of the low F #s because of how shallow it can sometimes be (this depends of course on the type of shot i'm taking). So my guess is, should i shoot farther away from subjects and crop is post to use low F #s and fast shutter speeds?
  16. You are using some very wide lenses for portrait work. That forces you to be very close to the subject to fill the frame and that is why your depth of field is so shallow. If the person moves a little bit they could be leaning into or out of focus. F/5.6 or F/8 is a good place to start if you are hand holding the camera or outdoors using a 50mm lens. A studio setup allows much more control but outdoors you need to be flexible. You can't move the tree or the wall you are trying to use as a prop or backdrop. You have to be creative with your feet.
    On a 35mm camera, 105mm is a fantastic length for portraits of people. There is a reason for this: It allows you go get some distance between you and the subject. The longer lens will have less depth of field for a given f/number but the distance between you and the subject will make up for it. But the background will need to be farther away. No free lunch.
    Also, be careful about going wider than 50mm for portraits. A wide angle lens can give your subject a fat face or big nose. Don't shoot large people with a wide angle lens if you are trying to flatter them at all.
  17. John does this apply to a DX formatted camera? My 50mm acts as a 75mm in a 35mm format camera.
  18. When I shoot group/party photos with flash, I use manual mode (sometimes aperture priority) and set aperture to at least 6.3 or smaller and set shutter to allow some existing light to expose but a fast enough shutter to prevent blur.
    Be aware that the further you are from subjects, the deeper the DOF.
    Fast primes used wide open are best for single person portraits since DOF is VERY shallow:
    Here's a shot from my Canon 85MM 1.2
    and another: Canon 85MM 1.2 portrait
    Check out F stop settings on group portraits here :
  19. Just because a fast lens can shoot at a wider aperture doesn't mean you always want to be using it. Some of the best lenses have a max aperture of f/1.4, and when you need f/1.4, you need one of those lenses. Most of the time, however, you can get by just fine with a f/2.8 zoom, because you don't need 1.4 that often.
    The truth stands, however, that the most research and the best materials and manufacturing goes into the fast glass. Those f/1.4 lenses are sharper than the f/1.8, f/2, and f/2.8 counterparts. If you stop down to f/2.8 and compare it to a f/2.8 lens, the f/1.4 lens will usually win out in terms of sharpness (resolution, clarity, color, distortion, and everything else, too). Of course there are many exceptions to the rule, but those don't disprove my point.
  20. [i guess what is borthering me is I see photos out there that i try to shoot at the same specs and don't get nearly the same DOF that i seen in other photos....maybe there is something i'm missing though...]
    Don't forget to take into account the size of the sensor. The bigger the sensor, the shallower the DOF. Plus, the smaller the sensor, the more the image is cropped, making the lens seem longer.
    Good Luck!
  21. Hi John,
    Your DX sensor makes the angle of view on a 50mm lens look like a 75mm, but it's still a 50mm lens. The depth of field is based on the actual focal length of the lens. Your small sensor is only taking a picture out of the center of the lens, but it's not changing the way the lens works. I know this is confusing. Think of it this way: You are taking a picture with a 50mm lens and your camera is cropping the image circle. Nothing else changes. You just aren't using the outer area of the lens but the lens still works the same way it always did on every other regard.
    Very fine portraits can be made with a 50mm lens. It just requires a more critical approach because you are standing so close to fill the frame with a head shot that the depth of field will really get short. This can be used to great effect if you know what to expect.
    Portraits don't have to be razor sharp, and with all but a very few subjects you don't want a razor sharp portrait. Human beings just don't look good close up. No woman wants to see her pores. A good portrait lens is actually a little soft. A very good trick if you don't have a soft filter is to stretch panty hose over the lens when photographing a woman over 30. (Old school. Now everyone uses $1000 worth of photoshop to mimic two dollars worth of pantyhose.) Soft is good everywhere on earth except Photo.net. Sharpness in a portrait shows off a great photographer (to other photographers) but I doubt you'll sell many portraits to women that way.
    A lot of people will tell you to go buy some ridiculously expensive lens to get low light portraits. I say you will be miles ahead to really learn how light works and how best to use it. High end gear will come with time. Until you know exactly where your gear is letting you down you don't need it. In fact, for half the price of a single piece of high end glass you could get a complete used Medium Format rig that will blow away anything you can do with a DX camera anyway. Digital is awesome and the resolution / image quality are there now, but when it comes to tonality there is no replacement for displacement.
    My Pentax K20d with 70mm Limited prime lens is a wonder to behold. I love it in every way. But my 30 year old Bronica 6x4.5 with a three dollar roll of film in it is in a whole other class. I don't care what pixel peepers say. Both look awesome on a monitor, but prints don't lie.
    This site is a treasure trove when it comes to learning lighting. It's a very fun site, too. :
  22. John C: just to help you visualize things, here's a shot taken with a 50mm lens:
    I was just a few feet (perhaps six or seven feet, actually) from the subject. This lens was used at f/2 that particular moment, because I wanted to throw the busy background well out of focus, but wanted a touch more DoF than I would have had if I'd used the lens wide open at f/1.4. Using it at f/2 still blurred the background plenty, but it allowed me to get more than just his ear or one eyelash in focus. You'll notice, though, that his shoulders are stlill a bit out of focus - which is fine with me, since this was about his face.

    Now, if I'd wanted his shoulders and all to be in perfect focus, I could have stopped down further ... but I'd risk pulling the background more into focus. The other option would have been to throw on a longer lens, step back further, and keep is body in focus will still keeping the background well out. But that extra working distance isn't always an option. Or, sometimes it's your only option. You really do have to just do it, in order to internalize a sense of how these things can work for and against you.
  23. A fisheye at f/2.8 depending on the distance will have most every thing is focus. All I am stating is that the focal length also makes a difference.
  24. I may have a similar question to John's.

    What confuses me about DOF is that when I see portraits taken with a 70-200 f/2.8 at 200mm 2.8 which, I assume, has a really shallow DOF, the background is all nicely blurred out, yes, but the person (in some cases, persons) is all in perfect focus--eyes, nose, body etc.

    However, when I take pictures using my 50mm f/1.8 wide open which effectively should have a less shallow DOF than a 200mm at 2.8, I easily get some parts of the person's body/face OOF.

    Is there a certain optimal combination for focal length and aperture that causes this or is it just a matter of good composition and camera positioning?
  25. Matt, just trying to learn more so upon which part of the face did you focus and what focus mode did you use?
  26. The relationships between the distance to the subject, the distance to the background, and the aperture used all interact (in some surprisingly complex ways, sometimes) to create different workable focal plane depths, Benson. The DoF calculator mentioned above lets you see how that plays out, instantly, as you change one or more of those variables. You can't really say that the 70-200/2.8 has more or less DoF than the 50/1.8 when each are used wide open ... because they are and can be used in very different ways, and that changes the math.
  27. Ray: I used (as I almost always do), single-point focus with the center focus point in a D300. I usually have the camera in AF-S (single servo mode) rather than AF-C (continuous focus mode) when my subjects aren't running around on me. So in this case, I focused on his eye (the one closest to me), and then slightly recomposed before releasing the shutter.

    You can tell that his eye, sideburns, and ear are all in the same plane of focus, more or less. The nearest corner of his hat brim is just out of focus on THIS side of the plane, and the far corner of the brim is just out of focus PAST the plane. We're talking in inches, here, but as long as you get the eye(s) in focus, the viewer isn't distracted by that fall-off in focus. Miss the eye, and the image just looks ... wrong. Unless you have an editorial/compositional reason for that, of course.
  28. You guys have all did a awesome job at providing feedback and i am truly appreciated. I need to take all this info and practice. Last night i took the camera and tried shooting at different F #s and also different lengths and had a hard time really seeing the difference but i did. I just need to keep at it and see how the differences will affect it all.
    Thanks again for all your time and thoughts
  29. One more point: fast lenses do more accurate autofocus and will autofocus in light where slower lenses will just seek.
  30. John: to make it easier to see, consider practicing along something like a chain link fence or brick wall. Anything that has a repeating pattern. Shoot it at an angle so that it's clear what is and what isn't in focus.

    For example, I just grabbed these two shots for you, along a wooden fence. I stayed in one place, focused on the same thing, and shot in AP mode, so that as I changed aperture, the camera adjusted shutter speed to keep the exposure more or less the same.

    This is with a 50mm lens from about the same distance that you'd shoot a 3/4 portrait.
  31. John, I strongly suggest you take a beginning photo class at your local community college. You will then learn some about Depth of Field and how aperture and distance effect it. Your remarks about of fast lens for portraits are simply made out of ignorance. Another example....fast lens-blurred background, not photoshop [​IMG]
  32. I also wanted to say that everything Matt says is nonsense....no just kidding:) Everything he said is really good. A good book for general understanding is Upton's "Photography" a general textbook that covers a lot of areas including lens length, depth of field, etc. Here's another link that may be useful, it also shows how to calculate DOF for a lens type and length. http://www.cambridgeincolour.com/tutorials/depth-of-field.htm and has a little more explanation of DOF, what it is, what it does and how it works.
    Good luck - don't sell those fast lenses yet!
  33. The other option would have been to throw on a longer lens, step back further, and keep is body in focus will still keeping the background well out.​
    This is what I'm talking about, Matt. But as you said, it is very complex. Dang, if only longer fast lenses we're priced as the 50 1.8.
  34. Matt, thank you for your response. It was very helpful.
  35. Dang, if only longer fast lenses we're priced as the 50 1.8.​
    The 85 f/1.8 is not too terribly much more expensive. If you can put up with manual focus (and lack of metering with most digital cameras), you can get 105 f/2.5 or f/2.8, and 135 f/2.8 for not too much money, too.
  36. Dang, if only longer fast lenses we're priced as the 50 1.8.​
    The 85 f/1.8 is not too terribly much more expensive. If you can put up with manual focus (and lack of metering with most digital cameras), you can get 105 f/2.5 or f/2.8, and 135 f/2.8 for not too much money, too.
  37. Benson, the issue there is distance. DOF is a based on a combination of Focal Length, Aperture and Focus Distance. So if you have a 200mm lens set to f/2.8 and you shoot someone's portrait from 20 feet away, you might get a beautifully out of focus background and a perfectly in-focus face. Shooting the same person with a 50mm lens set to f/2.8 and framed the same you will need to be maybe 3 feet away. The 50mm lens will resolve the background with less blur than the 200mm lens because of the focal length. However, the subject will be partially blurry, maybe nose out of focus, because of the much closer distance. So:
    Smaller aperture number at the same distance and focal length, means narrower depth of field.
    Closer focus distance to the subject at the same aperture and same focal length, means narrower depth of field.
    Longer focal length with the same subject distance and same focal length means narrower depth of field.
    And of course all of the opposites apply.
  38. john c-please read this reply and the next. there is one point about fast lenses that has nothing to do with shooting in dim light. and that is that lenses begin to reach thier sharpest range about 2 stops closed down from wideopen. the lens may or may not be completely in the best performing range bjt it should be close. with said at wide open or near it a lens lets in a lot of light, BUT that lens is not performing at it best in terms of color and sharpness. lens perform thier best betwenn f5.6 and f11.0, though f4 on some may be very good. however, that range is modified by have to be about the 2 stops from wide open. so a lens that is a f1.4 wideopen with start to perform at or beyond f2.8 but with a lens that has a wideopen of f2.8, the user must shoot at f5.6 or smaller to get past the 2 stop from wide open limit. by the way this does not mean that good lenses shooting at less that 2 stops from the wideopen plus stops make bad images, but they can do much better beyond the 2 stops from wideopen.
    it should be noted that because of the crop factor in dslrs, lens focal lengths that once were considered great for portraits now may not be able to be used.
  39. in 35mm terms portraits used lenses from 70-80 to 135mm. the former were the full or 3/4 body shots while the 135mm was for face only. when taking portraits the distances were always in the 10-12 maybe 15ft range in the studio. when one wanted a different type of portrait you simply changed lenses. you did not move the camera to subject distance. if you did and went closer the nose ended up as very pronounced, if you went farther then the face had a very flat one dimensional appearance.
    macro lenses are not used for portraits simply because they see too much facial features; no one is going to thank you with every wrinkle or pimple or imperfection shown in all their glory. The image will just not be flattering. if a macro lens is used then you should plan on plenty of pp time to get the bad features back out. it is far simpler to simply use a kit lens size, or a lens similar, that is a 16 to 50 for the 3/4 shots and if desired switch to a 70-200 zoom used at 70 for the face only, which is 105mm, if not tight enough zoom to 90 which is 135mm. but in all this keep the subject distance at the 10-12 to 15ft distance.
    for your info-
    portraits were done in the studio by pros using, in 35mm terms, about 70mm to 135mm. the distance was fixed you were shooting from 10-12ft. at that distance the 70 gave the 3/4 body shot while the 135 gave a face only. in c sensor the 70mm becomes 47mm while the 135mm becomes 91mm. the distances used were to keep the face and body from distorting from a natural appearance. For digital the f1.4 50mm lenses becomes a very good portrait lens. It can also double a lowlight lens.
  40. WOW...so much info it's overwhelming.
    Anyways I kinda wanted to point out with of course more playing and reading, I do understand about DOF when it comes to Aperture #'s, but I guess what I need to practice more on is how F #s, Distance, and focal lengths (which is kinda like getting closer or farther from the subject) comes into play. I have a slim understanding but can't quite master it on the floor yet when it comes to knowing what will happen before taking the shot.
    I guess what I need to do in order to solve my problem if I want to continue to use small F #s is to back up in order to keep multiple faces in sharp focus and then crop in post. If not an option then stop down to get the desired results. (Of course the reason I state to use low apertures is when i need faster shutter speeds and don't feel like bumping up the ISO any higher)
    Anyways thanks for all the info guys/gals, going to reread it a few times to get it into my head.

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