x elements in x groups in lens descriptions
- Thread starter jann1033
- Start date
WOW... a great question and one I really had to research to answer.... here goes...
Element - each individual piece of glass in the lens
Group - Several elements optically cemented together to act as a single element.
(copied to the running dictionary)
A lens is composed of a number of glass parts, or elements, some standing alone and others optically cemented together forming groups, thus the statistics.
A lens might be made of of 5 elements in 5 groups, meaning that each element stands alone within the lens or it might be made of of 5 elements in 3 groups, meaning that at least one glass construct within the lens design comprises more than 1 chunk of glass. Possible combinations might be 1, 1 & 3 or 1, 2 & 2 -- both combinations allowing for 5 elements in 3 groups.
As to why, optics is a complex subject. Every time you bend light, as with any simple lens, most goes where you want it but some doesn't. Complex lens formulae comprising multiple convex, concave and aspheric elements are worked together using mathematical computer modeling (it used to be done by hand) in order to ensure that all the light gets to the same place -- your sensor -- and at the same time. In the process, the lens designer works out compromises for focal length, aperture, zoom ratio (if any), chromatic and spherical aberrations, pincushion and barrel distortions, coma, a host of other problems.
Groups and elements give you an idea as to the complexity of the optical formula of a lens -- not its quality.
(taken from http://forums.dpreview.com/forums/read.asp?forum=1030&message=21571821 )
Element - each individual piece of glass in the lens
Group - Several elements optically cemented together to act as a single element.
(copied to the running dictionary)
A lens is composed of a number of glass parts, or elements, some standing alone and others optically cemented together forming groups, thus the statistics.
A lens might be made of of 5 elements in 5 groups, meaning that each element stands alone within the lens or it might be made of of 5 elements in 3 groups, meaning that at least one glass construct within the lens design comprises more than 1 chunk of glass. Possible combinations might be 1, 1 & 3 or 1, 2 & 2 -- both combinations allowing for 5 elements in 3 groups.
As to why, optics is a complex subject. Every time you bend light, as with any simple lens, most goes where you want it but some doesn't. Complex lens formulae comprising multiple convex, concave and aspheric elements are worked together using mathematical computer modeling (it used to be done by hand) in order to ensure that all the light gets to the same place -- your sensor -- and at the same time. In the process, the lens designer works out compromises for focal length, aperture, zoom ratio (if any), chromatic and spherical aberrations, pincushion and barrel distortions, coma, a host of other problems.
Groups and elements give you an idea as to the complexity of the optical formula of a lens -- not its quality.
(taken from http://forums.dpreview.com/forums/read.asp?forum=1030&message=21571821 )
here is a picture that shows what elements and groups look like....
taken from http://www.sigmaphoto.com/images/Lenses ... _small.gif
taken from http://www.sigmaphoto.com/images/Lenses ... _small.gif
Blades is referring to the # of blades in an aperture ring.
Look here: http://www.themeparkphotos.us/html/aperture.html
Look at the second picture - you can kind of see the blades of the aperture ring. Usually the more blades you have, the closer to a true circle the center becomes, and that usually produces better "bokeh". At least to some people.
Look here: http://www.themeparkphotos.us/html/aperture.html
Look at the second picture - you can kind of see the blades of the aperture ring. Usually the more blades you have, the closer to a true circle the center becomes, and that usually produces better "bokeh". At least to some people.
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exactly as roger put it... the blades are what comprise the aperture itself. they open and close to change the size (the f/stop) and like he said generally the more the merrier. bokeh is a buzz word for background blur. nice bokeh is smooth, cheaper lenses are more jagged and not as smooth.
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speaking of bokeh...i was somewhat surprised to see how angular the actual areas of the water reflection were in this photo..i always read about the bokeh being good with this lens( 70-200 f4 canon)
maybe it's more talking about the normal background blur rather than a reflection like this?
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if you really want to get confused, read this article...
http://www.kenrockwell.com/tech/bokeh.htm
http://www.kenrockwell.com/tech/bokeh.htm
Jeff Fillmore
Member
The shape of the blades also makes a difference- rounded diaphragm opening = nice bokeh.
thanks for the link...i also found this one that has my lens in it but i'll have to check on my exif info and see what i shot the above photo at...i was thinking it was simply background blur but guessing i was wrong ( not a shock);D
http://www.rickdenney.com/bokeh_test.htm
http://www.rickdenney.com/bokeh_test.htm