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F2.8 not equal F2.8 ?
Is it true that different zoom lenses will let through different amounts
of light because "...glass is not 100% transmissive, and that zooms use lots of elements, and that cheap prosumer glass isn't very high quality, and that coatings and finish and materials changes transmissivity..." ? In other would a cheap zoom lens opened at F2.8 let through the same amount of light as a better zoom lens at F3.5 for instance ? -- Alfred Molon ------------------------------ http://groups.yahoo.com/group/Olympus_405060/ Olympus 5050 resource - http://www.molon.de/5050.html Olympus 5060 resource - http://www.molon.de/5060.html |
Re: F2.8 not equal F2.8 ?
"Alfred Molon" <alfred_molon@yahooDELETE.com> wrote in message news:e76ae5d3d3618c4900e65924348258fe@news.meganet news.com... > Is it true that different zoom lenses will let through different amounts > of light because "...glass is not 100% transmissive, and that zooms use > lots of elements, and that cheap prosumer glass isn't very high quality, > and that coatings and finish and materials changes transmissivity..." ? > > In other would a cheap zoom lens opened at F2.8 let through the same > amount of light as a better zoom lens at F3.5 for instance ? > -- > > Alfred Molon > ------------------------------ > http://groups.yahoo.com/group/Olympus_405060/ > Olympus 5050 resource - http://www.molon.de/5050.html > Olympus 5060 resource - http://www.molon.de/5060.html All things being equal, and no missleading going on on the part of the lens maker f2.8 should represent f2.8 regardless of the transmissivity of the elements in the lens. In many cases with thru the lens metering there would not be a problem. But say and there are few examples any more aside from view cameras f x.x should be f x.x as such on each lens. But then take Sigma for example as well as Fuji with the pixel count on the imaging devices. I guess it all boils down like Clinton said it depends on what " if " means. The same can be said for shutters. If the exposure is calculated for a camera with a slow or fast shutter, or even the old mercury battery replacement being slightly under voltage the negative should come out OK. But in the case of extreemly slow or fast shutter you would be hard pressed to explain to someone how you froze the speeding auto at 1/30th. Just my thoughts about your question. |
Re: F2.8 not equal F2.8 ?
> Is it true that different zoom lenses will let through different amounts
> of light because "...glass is not 100% transmissive, and that zooms use > lots of elements, and that cheap prosumer glass isn't very high quality, > and that coatings and finish and materials changes transmissivity..." ? > > In other would a cheap zoom lens opened at F2.8 let through the same > amount of light as a better zoom lens at F3.5 for instance ? In principle, yes. The F number only says something about the physical dimensions of the lens, not its actual optical transmission. Dvid |
Re: F2.8 not equal F2.8 ?
On 2004-01-17, David J Taylor <david-taylor@blueyonder.co.uk.not-this-bit> wrote:
>> Is it true that different zoom lenses will let through different amounts >> of light because "...glass is not 100% transmissive, and that zooms use >> lots of elements, and that cheap prosumer glass isn't very high quality, >> and that coatings and finish and materials changes transmissivity..." ? >> >> In other would a cheap zoom lens opened at F2.8 let through the same >> amount of light as a better zoom lens at F3.5 for instance ? > > In principle, yes. The F number only says something about the physical > dimensions of the lens, not its actual optical transmission. I have been told that for camera equipment, the formulas for calculating the f-stop from dimensions is not valid, as f-stop in cameras are only related to light-transmission these days. Otherwise a lens with sunglass glass would always underexposure a picture. |
Re: F2.8 not equal F2.8 ?
"?" <?@?.?> wrote in message news:Tb8Ob.25163$VS4.774438@bgtnsc04-news.ops.worldnet.att.net... > > "Alfred Molon" <alfred_molon@yahooDELETE.com> wrote in message > news:e76ae5d3d3618c4900e65924348258fe@news.meganet news.com... > > Is it true that different zoom lenses will let through different amounts > > of light because "...glass is not 100% transmissive, and that zooms use > > lots of elements, and that cheap prosumer glass isn't very high quality, > > and that coatings and finish and materials changes transmissivity..." ? > > > > In other would a cheap zoom lens opened at F2.8 let through the same > > amount of light as a better zoom lens at F3.5 for instance ? > > -- > > > > Alfred Molon > > ------------------------------ > > http://groups.yahoo.com/group/Olympus_405060/ > > Olympus 5050 resource - http://www.molon.de/5050.html > > Olympus 5060 resource - http://www.molon.de/5060.html > > All things being equal, and no missleading going on on the part of the lens > maker f2.8 should represent f2.8 regardless of the transmissivity of the > elements in the lens. Incorrect. All lenses vary in brightness at the same f-stop, from a marginal difference, to more than a stop. There's no way around it, rated f-stop is only the size of the opening, it has nothing to do with number or quality of lens elements, or basic lens design. Sigma's DG lenses (see http://sigma-photo.com/html/zoom_intro.htm) are a great example. They DG lenses are (quite intentionally) designed to be brighter at the same f-stop with digital sensors, because not only is the glassof extremely high quality, but the basic design is such that the rays are more parallel when exiting the rear element. Same basic thing microlenses are used for, to capture more of the angled rays at the sensor's periphery, but Sigma's DG line builds this characteristic into the lenses themselves. Put a the 24-70 EX DG and 28-70 EX (non-DG) on the same camera and set the same f-stop, the DG will be about a third stop brighter at the s ame aperture and focal length than the otherwise fabulous non-DG lens. The 24-70 EX DG is about a half stop brighter than the 24-70 HF at the same aperture and focal length - a reflection of the superb value HF's $85 pricetag- even though the EX has 5 more elements, 14 vs. 9. In general, prosumer lenses are awful compared to even the cheapest D/SLR glass. The F707/717 would be one exception, on par with low to mid level D/SLR glass. But Fuji's f2.8 is not an exception, in fact the min ISO of 160 shows that it is particularly dim. Though dimness is the least of prosumer lens problems, CA and barrel distortion are borderline absurd on most prosumers. Take a peek at cracker jack box Fuji optics... http://www.pbase.com/image/25203605/original Notice anything about those perfectly straight columns as they rise? Not to mention visible CA, even without backlighting. Then again, with all the SuperCCD Bayer interpolation artifacts littering the image, the lens hardly matters. It's hard to decide what ruins the image most. That's prosumer Fuji optics at 35mm equivalent, have a look at superior 25mm equivalent EX DG glass in front of 10.3MP... http://www.pbase.com/image/24323811/original Granted, the 15-30 EX DG alone costs about the same as the S602. > In many cases with thru the lens metering there would > not be a problem. But say and there are few examples any more aside from > view cameras f x.x should be f x.x as such on each lens. > But then take Sigma for example as well as Fuji with the pixel count on the > imaging devices. I guess it all boils down like Clinton said it depends on > what " if " means. > The same can be said for shutters. If the exposure is calculated for a > camera with a slow or fast shutter, or even the old mercury battery > replacement being slightly under voltage the negative should come out OK. > But in the case of extreemly slow or fast shutter you would be hard pressed > to explain to someone how you froze the speeding auto at 1/30th. > > Just my thoughts about your question. > > |
Re: F2.8 not equal F2.8 ?
"George Preddy" <george_preddy@yahoo.com> schrieb im Newsbeitrag news:bubb3r$e6b$1@news1.kornet.net... > In general, prosumer lenses are awful compared to even the cheapest D/SLR > glass. The F707/717 would be one exception, on par with low to mid level > D/SLR glass. If understand you correctly, a Minolta DiMAGE A1's zoom with F2,8 is no F2,8 at least compared with a comparable 28-200/F2,8-3,5 zoom for a dSLR? |
Re: F2.8 not equal F2.8 ?
"Manfred Thaler" <mtbiggy@hotmail.com> wrote in message news:bube4q$7sk$01$1@news.t-online.com... > > "George Preddy" <george_preddy@yahoo.com> schrieb im Newsbeitrag > news:bubb3r$e6b$1@news1.kornet.net... > > In general, prosumer lenses are awful compared to even the cheapest D/SLR > > glass. The F707/717 would be one exception, on par with low to mid level > > D/SLR glass. > > If understand you correctly, a Minolta DiMAGE A1's zoom with F2,8 is no F2,8 > at least compared with a comparable 28-200/F2,8-3,5 zoom for a dSLR? You don't. |
Re: F2.8 not equal F2.8 ?
"George Preddy" <george_preddy@yahoo.com> wrote in message news:bubdpo$fcu$1@news1.kornet.net... > > "Manfred Thaler" <mtbiggy@hotmail.com> wrote in message > news:bube4q$7sk$01$1@news.t-online.com... > > > > "George Preddy" <george_preddy@yahoo.com> schrieb im Newsbeitrag > > news:bubb3r$e6b$1@news1.kornet.net... > > > In general, prosumer lenses are awful compared to even the cheapest > D/SLR > > > glass. The F707/717 would be one exception, on par with low to mid > level > > > D/SLR glass. > > > > If understand you correctly, a Minolta DiMAGE A1's zoom with F2,8 is no > F2,8 > > at least compared with a comparable 28-200/F2,8-3,5 zoom for a dSLR? > > You don't. There is no way to know without comparing directly. A cheap lens might actually be brighter but with terrible other qualities, while a very expensive lens might be slightly dimmer with otherwise superb qualities. In general, the better the lens, the brighter the glass, but you cannot apply generalizations to specific lenses. Here is a good example, conditions are absolutely identical between images. Flip back and forth in medium thumbnail view, using the next/previous hyperlink to compare brightness. The image parameters and lens used is noted next at the bottom... http://www.pbase.com/imageprocessing/lenscompare SPP measures the difference at 0.3 stops. |
Re: F2.8 not equal F2.8 ?
Added another set... 24-70 EX DG vs. 24-70 HF
http://www.pbase.com/imageprocessing/lenscompare Both shots at f5.6 and 0.25 secs = 0.4 EV difference. |
Re: F2.8 not equal F2.8 ?
If the metering is done TTL - it matters not a whit. If you use a hand
meter - you are probably within 1/6th of a stop of the actual transmission. In other words - don't sweat it. The only lenses that transmit seriously less light than the aperture claims are mirror lenses. -- http://www.chapelhillnoir.com home of The Camera-ist's Manifesto The Improved Links Pages are at http://www.chapelhillnoir.com/links/mlinks00.html A sample chapter from my novel "Haight-Ashbury" is at http://www.chapelhillnoir.com/writ/hait/hatitl.html "Alfred Molon" <alfred_molon@yahooDELETE.com> wrote in message news:e76ae5d3d3618c4900e65924348258fe@news.meganet news.com... > Is it true that different zoom lenses will let through different amounts > of light because "...glass is not 100% transmissive, and that zooms use > lots of elements, and that cheap prosumer glass isn't very high quality, > and that coatings and finish and materials changes transmissivity..." ? > > In other would a cheap zoom lens opened at F2.8 let through the same > amount of light as a better zoom lens at F3.5 for instance ? > -- > > Alfred Molon > ------------------------------ > http://groups.yahoo.com/group/Olympus_405060/ > Olympus 5050 resource - http://www.molon.de/5050.html > Olympus 5060 resource - http://www.molon.de/5060.html |
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