small aperture test
in [Digital Cameras]
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From: Bob Larter on 5 Nov 2009 08:39 Dudley Hanks wrote: > "Chris Malcolm" <cam(a)holyrood.ed.ac.uk> wrote in message > news:7ldt5gF3cimtaU1(a)mid.individual.net... >> Dudley Hanks <dhanks(a)blind-apertures.ca> wrote: >> >>> "David J Taylor" >>> <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in >>> message news:t6aIm.1501$Ym4.551(a)text.news.virginmedia.com... >>>> "Dudley Hanks" <> wrote in message >>>> news:4U9Im.50459$Db2.29545(a)edtnps83... >>>>> I've heard a lot about how the cropped sensor cameras are defraction >>>>> limited to around f/8 - f/11, so I thought I'd see what kind of an >>>>> image >>>>> my XSi puts out at a small aperture. >>>>> >>>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at >>>>> f/22, >>>>> with a shutter speed of 1 sec. >>>>> >>>>> How did it turn out? >>>>> >>>>> http://www.snaps.blind-apertures.ca/images/SmallWinterPortrait.jpg >>>>> (quick >>>>> download) >>>>> >>>>> http://www.snaps.blind-apertures.ca/images/SelfPortraitWinter.jpg >>>>> (full >>>>> size) >>>>> >>>>> Take Care, >>>>> Dudley >>>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I >>>> loathe), so there could be some diffraction visible, but I'm also not >>>> convinced that the subject didn't move within the 1 second exposure! >>>> >>>> Cheers, >>>> David >>> Thanks, David, I'll try it again with an inanimate object, or a faster >>> shutter speed. >>> I suppose, if the test is to be useful, I should also take an equivalent >>> pic >>> of the subject using a wider aperture so the two images can be compared. >> The diffraction limit of aperture is usually taken to be the last >> aperture in a decreasing series of sharper apertures, i.e., stopping >> down further makes the image softer because of diffraction. But that's >> not a fixed aperture, it depends on such things as the exact sensor >> pixel size (or crop factor) not just the nominal "1.5", on the >> resolution of the lens, and whether you're looking at the centre of >> the image or the edges or some compromise between the two. Why >> should it depend on those? Because the point at which an extra stop's >> worth of diffraction softening becomes larger than how much other >> kinds of lens aberration are being improved by stopping down obviously >> will depend on the size of those other errors. In other words better >> lenses will have larger sharpest apertures. >> >> I find for example on my Sony A350 that my general purpose zoom is >> usually sharpest at f8, but at its soft extremes that becomes f11, and >> my 50mm prime is sharpest at f5.6. >> >> This can only be established for your camera and each of your lenses >> by taking a comparative series of shots while varying the aperture. On >> zooms it may change with focal length. >> >> -- >> Chris Malcolm > > Thanks, Chris, that's good info to have. > > This is a pretty cheap lens, and I think its a bit soft to begin with. The 50mm/F1.8II is a surprisingly good lens for the money. I've taken a lot of excellent shots with mine, so please don't sell it short! I've since 'upgraded' to a 50mm/F1.4, but it's not as much of an improvement as you might expect from the price difference. -- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
From: Bob Larter on 5 Nov 2009 08:40 Better Info wrote: > On 4 Nov 2009 17:49:36 GMT, Chris Malcolm <cam(a)holyrood.ed.ac.uk> wrote: > >> Dudley Hanks <dhanks(a)blind-apertures.ca> wrote: >> >>> "David J Taylor" >>> <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in >>> message news:t6aIm.1501$Ym4.551(a)text.news.virginmedia.com... >>>> "Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545(a)edtnps83... >>>>> I've heard a lot about how the cropped sensor cameras are defraction >>>>> limited to around f/8 - f/11, so I thought I'd see what kind of an image >>>>> my XSi puts out at a small aperture. >>>>> >>>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22, >>>>> with a shutter speed of 1 sec. >>>>> >>>>> How did it turn out? >>>>> >>>>> http://www.snaps.blind-apertures.ca/images/SmallWinterPortrait.jpg (quick >>>>> download) >>>>> >>>>> http://www.snaps.blind-apertures.ca/images/SelfPortraitWinter.jpg (full >>>>> size) >>>>> >>>>> Take Care, >>>>> Dudley >>>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I >>>> loathe), so there could be some diffraction visible, but I'm also not >>>> convinced that the subject didn't move within the 1 second exposure! >>>> >>>> Cheers, >>>> David >>> Thanks, David, I'll try it again with an inanimate object, or a faster >>> shutter speed. >>> I suppose, if the test is to be useful, I should also take an equivalent pic >>> of the subject using a wider aperture so the two images can be compared. >> The diffraction limit of aperture is usually taken to be the last >> aperture in a decreasing series of sharper apertures, i.e., stopping >> down further makes the image softer because of diffraction. But that's >> not a fixed aperture, it depends on such things as the exact sensor >> pixel size (or crop factor) not just the nominal "1.5", on the >> resolution of the lens, and whether you're looking at the centre of >> the image or the edges or some compromise between the two. Why >> should it depend on those? Because the point at which an extra stop's >> worth of diffraction softening becomes larger than how much other >> kinds of lens aberration are being improved by stopping down obviously >> will depend on the size of those other errors. In other words better >> lenses will have larger sharpest apertures. >> >> I find for example on my Sony A350 that my general purpose zoom is >> usually sharpest at f8, but at its soft extremes that becomes f11, and >> my 50mm prime is sharpest at f5.6. >> >> This can only be established for your camera and each of your lenses >> by taking a comparative series of shots while varying the aperture. On >> zooms it may change with focal length. > > Your test won't work. Please, get back to us when you grow a clue. Bye! -- W . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^---------------------------------------------------------------
From: Bryan on 5 Nov 2009 09:08 Dudley Hanks wrote: > I've heard a lot about how the cropped sensor cameras are defraction limited > to around f/8 - f/11, so I thought I'd see what kind of an image my XSi puts > out at a small aperture. > > I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22, > with a shutter speed of 1 sec. > > How did it turn out? [...] > http://www.snaps.blind-apertures.ca/images/SelfPortraitWinter.jpg (full > size) I'll go farther than previous respondents: That photo, from a Canon XSi at f/22, is obviously not diffraction limited. The statements you'll hear of the diffraction limit assume everything else it practically optimal: rock-steady subject, tripod mount, perfect focus, and unless the claim is about a particular lens, they mean a laudably sharp one.
From: Martin Brown on 5 Nov 2009 09:26 Dudley Hanks wrote: > "David J Taylor" > <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in > message news:t6aIm.1501$Ym4.551(a)text.news.virginmedia.com... >> "Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545(a)edtnps83... >>> I've heard a lot about how the cropped sensor cameras are defraction >>> limited to around f/8 - f/11, so I thought I'd see what kind of an image >>> my XSi puts out at a small aperture. >>> >>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22, >>> with a shutter speed of 1 sec. >>> >>> How did it turn out? >>> >>> http://www.snaps.blind-apertures.ca/images/SmallWinterPortrait.jpg (quick >>> download) >>> >>> http://www.snaps.blind-apertures.ca/images/SelfPortraitWinter.jpg (full >>> size) >>> >>> Take Care, >>> Dudley >> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I >> loathe), so there could be some diffraction visible, but I'm also not >> convinced that the subject didn't move within the 1 second exposure! >> > Thanks, David, I'll try it again with an inanimate object, or a faster > shutter speed. > > I suppose, if the test is to be useful, I should also take an equivalent pic > of the subject using a wider aperture so the two images can be compared. If you are serious about being able to tell include a few ball bearings on black velvet in the picture composition. Specular highlights are about the easiest thing to see if an image is diffraction limited. Or you could just use a pinhole over the lens and a verry long exposure. Regards, Martin Brown
From: Dudley Hanks on 5 Nov 2009 11:30
"Bob Larter" <bobbylarter(a)gmail.com> wrote in message news:4af2c78c$1(a)dnews.tpgi.com.au... > Dudley Hanks wrote: >> "Chris Malcolm" <cam(a)holyrood.ed.ac.uk> wrote in message >> news:7ldt5gF3cimtaU1(a)mid.individual.net... >>> Dudley Hanks <dhanks(a)blind-apertures.ca> wrote: >>> >>>> "David J Taylor" >>>> <david-taylor(a)blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in >>>> message news:t6aIm.1501$Ym4.551(a)text.news.virginmedia.com... >>>>> "Dudley Hanks" <> wrote in message >>>>> news:4U9Im.50459$Db2.29545(a)edtnps83... >>>>>> I've heard a lot about how the cropped sensor cameras are defraction >>>>>> limited to around f/8 - f/11, so I thought I'd see what kind of an >>>>>> image >>>>>> my XSi puts out at a small aperture. >>>>>> >>>>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at >>>>>> f/22, >>>>>> with a shutter speed of 1 sec. >>>>>> >>>>>> How did it turn out? >>>>>> >>>>>> http://www.snaps.blind-apertures.ca/images/SmallWinterPortrait.jpg >>>>>> (quick >>>>>> download) >>>>>> >>>>>> http://www.snaps.blind-apertures.ca/images/SelfPortraitWinter.jpg >>>>>> (full >>>>>> size) >>>>>> >>>>>> Take Care, >>>>>> Dudley >>>>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I >>>>> loathe), so there could be some diffraction visible, but I'm also not >>>>> convinced that the subject didn't move within the 1 second exposure! >>>>> >>>>> Cheers, >>>>> David >>>> Thanks, David, I'll try it again with an inanimate object, or a faster >>>> shutter speed. >>>> I suppose, if the test is to be useful, I should also take an >>>> equivalent pic >>>> of the subject using a wider aperture so the two images can be >>>> compared. >>> The diffraction limit of aperture is usually taken to be the last >>> aperture in a decreasing series of sharper apertures, i.e., stopping >>> down further makes the image softer because of diffraction. But that's >>> not a fixed aperture, it depends on such things as the exact sensor >>> pixel size (or crop factor) not just the nominal "1.5", on the >>> resolution of the lens, and whether you're looking at the centre of >>> the image or the edges or some compromise between the two. Why >>> should it depend on those? Because the point at which an extra stop's >>> worth of diffraction softening becomes larger than how much other >>> kinds of lens aberration are being improved by stopping down obviously >>> will depend on the size of those other errors. In other words better >>> lenses will have larger sharpest apertures. >>> >>> I find for example on my Sony A350 that my general purpose zoom is >>> usually sharpest at f8, but at its soft extremes that becomes f11, and >>> my 50mm prime is sharpest at f5.6. >>> >>> This can only be established for your camera and each of your lenses >>> by taking a comparative series of shots while varying the aperture. On >>> zooms it may change with focal length. >>> >>> -- >>> Chris Malcolm >> >> Thanks, Chris, that's good info to have. >> >> This is a pretty cheap lens, and I think its a bit soft to begin with. > > The 50mm/F1.8II is a surprisingly good lens for the money. I've taken a > lot of excellent shots with mine, so please don't sell it short! > I've since 'upgraded' to a 50mm/F1.4, but it's not as much of an > improvement as you might expect from the price difference. Originally, I bought it for my Canon A2, but didn't use it a lot. I used it a bit for blurred background shots of the kids, flowers, etc. However, with the crop factor of the XSi, it's now a great portrait lens, and it still has a fairly respectable aperture when I add in my 2x converter, giving me a (35mm equiv) f/3.5 160mm lens. I'm finding myself falling back on it a lot these days. Take Care, Dudley |