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#21
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fast glass?
Danny wrote:
"MarkČ" mjmorgan(lowest even number wrote in message news5mwf.8789$V.3101@fed1read04... Danny wrote: "Charles" wrote in message ... In article , Danny wrote: Just a thought. Just a thought. Read a basic book about photography. Why is their always a smart-arse on every Usenet group? - don't you have a ****ing job to go to? It might have been a bit abrupt...but it certainly has a shred of truth to it, since this is a topic any general photography technique book would cover in some detail...but I understand your reaction to his less-than-tactful reply... For a better answer...see my original reply. I'm surprized others haven't listed these little items. They matter. Ah heck... Here's a RE-post of it (with a bit more added), just in case you lose your way. Some reaons: 1. Intentional limiting of/greater control of depth of field. 2. Bright viewfinder...not only helpful for manual focus, but just plain easier to accurately use in general. 3. Focus sensors work far better when you double, tripple or quadruple the light it has to work with (which applies to any/every shot, since the focus mechanism works PRIOR to stopping the bright lens down. 4. You can use very fast shutter speeds...which is often worth sacrificing a bit of lens-based sharpness. 5. With many camera bodies, certain focus sensors become active ONLY with lenses that are 2.8 or faster, simply due to the need for greater light gathering/sensitivity. That last one sounds interesting - are we talking digital bodies here? No. It has nothing to do with whether the body is digital or not...because the focus systems of SLRs and DSLRs work the same way. They don't focus with the sensor. They focus with sensors that bounce off the mirror just before it flips out fo the way for exposure of the film...or sensor. Come to that, how *do* you know that an A/F sensor is working properly? - is there more to it than simply seeing if the relevant focus point lights up? Yes. - I suppose there must be, because an *ist will illuminate all focus points, even with the lens cap on!..... It's a little more complicated than that. On several Canon bodies, for example, it has to do with whether certain sensor points act as vertical line-of-contrast sensors...or horizontal-line-of-contrast sensors...or...with brighter glass...cross-type sensors, which are sensitive to both vertical and horizontal lines of contrast. Even in cameras where the sensor itself doesn't change it's characteristics, more light ALWAYS means easier/quicker focus. An important example of this is focus-tracking moving objects, like birds or other fast-moving objects. In less-than-optimal lighting, its a very difficult thing for any body to do well, and every bit of light helps. If you compare a 5.6 lens to a 2.8 lens in this example (or any example), the body will have **four times** the light to work with by using the 2.8 lens instead of the 5.6. This is easily enough to make the difference between successful focus tracking...and utter failure...in many instances such as flying birds. Stick a 1.8 lens on there, and you're talking GREAT focus track ability. While it might be even nicer to have a 400mm f1.4 lens (f1.4 being an amazing 16 times the amount of light gathered by a 5.6 lens!), the size a 400mm lens would have to be to acheive this would be immense. So...you usually only find apertures that wide on normal lenses, such as 50mm. But don't discount the benefit of huge apertures on less-than-tele lenses! The wider you go, the larger the aperture you often need to the kind of blurred background you want in certain shots. Add to this that auto-focus AND manual focus are both made easier with bright viewfinders, and very real advantages of large aperture lenses become very apparent. Nuff on that, but I think you get the idea, right? It's not the silly waste many here have erroneously implied. Sure, there are those who might buy a big lens because they think it's cool...just like old geezers still by 200MPH Corvettes with no intention of driving over 65MPH...but that doesn't mean it's useless. To the contrary, it's actually useful to ANY photographer, simply because his camera body with perform better in the ways I've described. Hope this helped... -Mark |
#22
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fast glass?
Danny wrote:
"MarkČ" mjmorgan(lowest even number wrote in message news:K_lwf.8788$V.1281@fed1read04... Danny wrote: everyone seems to want 'fast glass' - f/2.8, 1.7, 1.4, etc, but I'm left wondering 'why' As most people know, lenses are not at their sharpest wide open - usually requiring f/7 - 9 (ish) before they attain their maximum potential. So why the fuss about 'fast' lenses?, and why pay the huge premiums to own them? Most of my own lenses are 2.8, with one at 1.7, and one at 1.4 - yet I invariably have to stop down in order to get a nicely sharp image, which sort of defeats the object of the 'fast glass', doesn't it? I mean, why pay three times the price for a 'fast' lens, when you only end up stopping it down? I've got a theory that it's the mania for bright lenses that's behind a lot of the 'focus fuss' that clogs up the various forums - perhaps people don't realise that you're just not going to get the same image quality out of wide open lens and are mistaking 'softness' for focus issues. Just a thought. Some reaons: 1. Intentional limiting depth of field. 2. Bright viewfinder...not only helpful for manual focus, but just plain easier to use with accuracy. 3. Focus sensors work far better when you double, tripple or quadruple the light it has to work with prior to actual exosure--regardless of the aperture you use for that exposure. 4. You can use very fast shutter speeds...which is often worth sacrificing a bit of lens-based sharpness. Number 3 sounds a viable reason in theory - but it presupposes that the camera itself doesn't have any A/F issues. I can only say that the Pentax f/1.4 A/F lenses are not noted for fast focus in low light. That's because AF focus speed is dependant upon 4 things. 1. AF sensor sensitivities (which are entirely body-based), which vary from hunting for horizontal, diagonal, vertial lines...or a combination of two or all three. 2. The speed and accuracy of the focus motor in each lens. 3. The nature of the object you're trying to auto-focus on (a smooth white wall with no texture will fool nearly any focus system unless it has the aid of either a projected pattern (like is eitted by many shoe flashes), or a distance measuring capability. 4. The relative motion of the subject, and the degree to which this motion disrupts the sensor's ability to identify lines of contrast (which it uses to focus on). 5. Theoretically...the sharpness of the lens glass itself. You could take the same lens, and get wildly different focus speed/accuracy from it depending on what camera body model it's sitting on. Try it in a shop! Stick a macro lens on a Canon Rebel XT...and focus it. Now stick that same lens onto a 1D Mark II. That SAME lens that hunted and missed on the Rebel XT with snap into focus almost instantly on a more sensitive body. In fact, many slower Pentax lenses are quicker to focus under the same conditions. There are many factors involved. See above. |
#23
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fast glass?
"Danny" wrote in message ... everyone seems to want 'fast glass' - f/2.8, 1.7, 1.4, etc, but I'm left wondering 'why' As most people know, lenses are not at their sharpest wide open - usually requiring f/7 - 9 (ish) before they attain their maximum potential. Only on consumer glass. Try getting yourself a Nikon 85/1.4, Nikon 135 f/2.0 DC , Nikon 60 micro, Canon 85/1.2 L , Canon 135 f/2.0 L and Canon 100 macro. Stop it down 1 stop and you can see the glass at their optimum aperture. Also sometimes the ambient lighting does not allow you to take photos at smaller aperture hence stopping down to 1.4 or 1.0 in some case ... give the extra speed. |
#24
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fast glass?
MarkČ wrote:
No. It has nothing to do with whether the body is digital or not...because the focus systems of SLRs and DSLRs work the same way. They don't focus with the sensor. Oops. That should read, "They don't focus using the IMAGE sensor... ....And I've added "[]" below... They focus with [Separate AF sensors] using redirected light that reflects off of the mirror just before it flips out fo the way for exposure of the film...or sensor. |
#25
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fast glass?
Danny wrote:
everyone seems to want 'fast glass' - f/2.8, 1.7, 1.4, etc, but I'm left wondering 'why' As most people know, lenses are not at their Give me f/1.8 or f/1.4 prime wide lens for my Pentax body, and I will be finally able to shoot sharp images of my little son indoors, with nice blured background and without harsh flash shadows. That's so simple. And no, I do not care about slight loss of sharpners, although SMC 31/1.8 is said to be very sharp lens. B. |
#26
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fast glass?
"MarkČ" mjmorgan(lowest even number wrote in message news:bNmwf.8790$V.2542@fed1read04... Danny wrote: "MarkČ" mjmorgan(lowest even number wrote in message news5mwf.8789$V.3101@fed1read04... Danny wrote: "Charles" wrote in message ... In article , Danny wrote: Just a thought. Just a thought. Read a basic book about photography. Why is their always a smart-arse on every Usenet group? - don't you have a ****ing job to go to? It might have been a bit abrupt...but it certainly has a shred of truth to it, since this is a topic any general photography technique book would cover in some detail...but I understand your reaction to his less-than-tactful reply... For a better answer...see my original reply. I'm surprized others haven't listed these little items. They matter. Ah heck... Here's a RE-post of it (with a bit more added), just in case you lose your way. Some reaons: 1. Intentional limiting of/greater control of depth of field. 2. Bright viewfinder...not only helpful for manual focus, but just plain easier to accurately use in general. 3. Focus sensors work far better when you double, tripple or quadruple the light it has to work with (which applies to any/every shot, since the focus mechanism works PRIOR to stopping the bright lens down. 4. You can use very fast shutter speeds...which is often worth sacrificing a bit of lens-based sharpness. 5. With many camera bodies, certain focus sensors become active ONLY with lenses that are 2.8 or faster, simply due to the need for greater light gathering/sensitivity. That last one sounds interesting - are we talking digital bodies here? No. It has nothing to do with whether the body is digital or not...because the focus systems of SLRs and DSLRs work the same way. They don't focus with the sensor. They focus with sensors that bounce off the mirror just before it flips out fo the way for exposure of the film...or sensor. Come to that, how *do* you know that an A/F sensor is working properly? - is there more to it than simply seeing if the relevant focus point lights up? Yes. - I suppose there must be, because an *ist will illuminate all focus points, even with the lens cap on!..... It's a little more complicated than that. On several Canon bodies, for example, it has to do with whether certain sensor points act as vertical line-of-contrast sensors...or horizontal-line-of-contrast sensors...or...with brighter glass...cross-type sensors, which are sensitive to both vertical and horizontal lines of contrast. Even in cameras where the sensor itself doesn't change it's characteristics, more light ALWAYS means easier/quicker focus. An important example of this is focus-tracking moving objects, like birds or other fast-moving objects. In less-than-optimal lighting, its a very difficult thing for any body to do well, and every bit of light helps. If you compare a 5.6 lens to a 2.8 lens in this example (or any example), the body will have **four times** the light to work with by using the 2.8 lens instead of the 5.6. This is easily enough to make the difference between successful focus tracking...and utter failure...in many instances such as flying birds. Stick a 1.8 lens on there, and you're talking GREAT focus track ability. While it might be even nicer to have a 400mm f1.4 lens (f1.4 being an amazing 16 times the amount of light gathered by a 5.6 lens!), the size a 400mm lens would have to be to acheive this would be immense. So...you usually only find apertures that wide on normal lenses, such as 50mm. But don't discount the benefit of huge apertures on less-than-tele lenses! The wider you go, the larger the aperture you often need to the kind of blurred background you want in certain shots. Add to this that auto-focus AND manual focus are both made easier with bright viewfinders, and very real advantages of large aperture lenses become very apparent. Nuff on that, but I think you get the idea, right? It's not the silly waste many here have erroneously implied. Sure, there are those who might buy a big lens because they think it's cool...just like old geezers still by 200MPH Corvettes with no intention of driving over 65MPH...but that doesn't mean it's useless. To the contrary, it's actually useful to ANY photographer, simply because his camera body with perform better in the ways I've described. Hope this helped... Yes it did, very interesting and informative - thanks for taking the trouble. |
#27
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fast glass?
"Danny" wrote in message ... everyone seems to want 'fast glass' - f/2.8, 1.7, 1.4, etc, but I'm left wondering 'why' As most people know, lenses are not at their sharpest wide open - usually requiring f/7 - 9 (ish) before they attain their maximum potential. So why the fuss about 'fast' lenses?, and why pay the huge premiums to own them? Most of my own lenses are 2.8, with one at 1.7, and one at 1.4 - yet I invariably have to stop down in order to get a nicely sharp image, which sort of defeats the object of the 'fast glass', doesn't it? I mean, why pay three times the price for a 'fast' lens, when you only end up stopping it down? I've got a theory that it's the mania for bright lenses that's behind a lot of the 'focus fuss' that clogs up the various forums - perhaps people don't realise that you're just not going to get the same image quality out of wide open lens and are mistaking 'softness' for focus issues. Just a thought. Simple, so you can get pictures in lower light. without flash. I have a Minolta back and some lenses. True my 28-200 takes a sharper picture at f4 (its best) than my 50mm f1.4, but in poor light the f1.4 will take a sharp shot without flash, when the f4 will blur due to subject or camera movement. In lower light the f1.4 will still shoot without flash, but the f4 would need a tripod. |
#28
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fast glass?
"Danny" wrote in message
... "Charles" wrote in message ... In article , Danny wrote: Why is their always a smart-arse on every Usenet group? I meant what I said. Read some basic photography books and you will understand why we need fast glass. OK. let's try again, shall we? I'm well aware why some people 'need' fast lenses, and those that do need them usually buy high quality optics (at high quality prices) that are up to the job. My point (perhaps not clearly made) is that the great mass of 'hobby' photographers are buying cheaper lenses that are unsharp at wide apertures, simply because an f/2.8 badge on a lens gives it more street cred than an f/5.6 - even though the cheap ".8 might very well have to be stopped down past the 'slower' lens in order to get a decently sharp image. I know - because I've been suckered by the manufacturers as well, and If I was buying them again I'd be far less impressed by the alleged maximum aperture, and concentrate on element quality and construction. btw, sorry for flying off the handle, I just assumed that you were taking the ****. Right off the top, an f2.8 lens will be sharper at f5.6 than an f5.6 lens will be at that aperture, as a general rule. Your statement that a lens is at its weakest wide open applies to all glass, no matter the maximum aperture. (I can think of no exceptions.) Second, you have more control over depth of field with a fast lens than one with a smaller max aperture. The ability to get a shallow DOF and blur backgrounds can be essential. Third, ability to get faster shutter speeds to capture movement in low light may be critical. Fourth, the suggestion that you read up on photography is a valid one. -- Skip Middleton http://www.shadowcatcherimagery.com |
#29
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fast glass?
"Danny" wrote in message ... "Charles" wrote in message ... In article , Danny wrote: Just a thought. Just a thought. Read a basic book about photography. Why is their always a smart-arse on every Usenet group? - don't you have a ****ing job to go to? I don't know why it is so hard to either ignore a post or give a real, useable, respectful answer. But anyways... I work as a photojournalist and frequently cover sporting events that are either indoors or conducted at night under lights. The last thing that they will allow you to do is pop a flash in their face. Also, the flash might expose the subject OK but the background will black out. And the subject will suffer from the flat direct flash. One could use super fast film and push it, but the negative effects from that would be much worse than the very slight loss of sharpness from shooting at f2.8. When I shoot basketball games I generally shoot 800 speed film or digital equivalent at f2.8 and 1/250. Any slower lens will not allow a decent shutter speed for stopping action. Also, the wide aperture is very cool for isolating your subject from the background when you do portraits. Remember, most fast lenses are considered pro grade and they are pretty sharp to begin with. The wide aperture does require accurate focusing. But my Nikkor 80-200 f2.8D seems to be sharper at f2.8 than my Nikkor 80-200 f3.5-5.6 is at f5.6. Remember, that is a very subjective non-scientific analyisis based on memory of anecdotal evidence, but I feel confident enough that I use my 2.8 way more than the 3.5-5.6. I only use the latter outdoors when weight becomes a factor. Sasquatch |
#30
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fast glass?
"Danny" wrote in message ... everyone seems to want 'fast glass' - f/2.8, 1.7, 1.4, etc, but I'm left wondering 'why' As most people know, lenses are not at their sharpest wide open - usually requiring f/7 - 9 (ish) before they attain their maximum potential. So why the fuss about 'fast' lenses?, and why pay the huge premiums to own them? Most of my own lenses are 2.8, with one at 1.7, and one at 1.4 - yet I invariably have to stop down in order to get a nicely sharp image, which sort of defeats the object of the 'fast glass', doesn't it? I mean, why pay three times the price for a 'fast' lens, when you only end up stopping it down? I've got a theory that it's the mania for bright lenses that's behind a lot of the 'focus fuss' that clogs up the various forums - perhaps people don't realise that you're just not going to get the same image quality out of wide open lens and are mistaking 'softness' for focus issues. Just a thought. Most lenses aren't their sharpest until stopped down a few stops...if you're starting with f/1.4 that "few stops" is probably f/4, if your lens starts at f/4 those same "few stops" are f/11...kinda limits you a bit, doesn't it? |
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