Sigma lens design trickery?
Dec 9, 2015 10:25:47 #
GAH1944 wrote:
yes, and tires are a trick to make your car ride smoother, and they're all doing it
I KNEW IT! I KNEW IT! Those b*st**ds in Detroit (or is it Akron?)!!!!
The next tire innovation (I am going for a patent so keep this quiet) is based on the Kelso shoe (formerly the Earth Shoe)
The Shoe has a lower heel and higher toe. It is based on foot prints in the sand where the toe can be seen to be higher than the heel.
So I drove a car on the beach. THE TRACKS LEFT IN THE SAND WERE FLAT! So I am going to mass produce the first tire that is flat on four sides!!!
Maybe three sides since I kind of like geodesic domes and Bucky Fuller was the man!!!
Dec 9, 2015 10:25:57 #
flip1948 wrote:
I fully understand that however there is a difference here as this is purposely being done on lenses designed for full frame bodies.
It's more likely that they're just designing for the intended image circle and using extra elements, better choices of optical glass, more efficient aspheres, etc.-- all of which became more practical with improved optical design software and faster computers on which to run it.
But they could be doing what you say. If they are, and if they're smart, they're trimming those lenses away from the stop down in diameter and only keeping the glass necessary to form the image in the circle corresponding to the sensor diagonal. This will keep the lens' weight down and also help keep light from outside the useful field from entering the camera. It would be simple enough to define a field size, design a lens to use with it and then redefine the field size down and 'trim away' all the glass which is no longer needed at any focal length the lens can reach.
Dec 9, 2015 10:29:15 #
If you remember the 24-120 vr 3.5-? lens many said was a terrible lens. They say that because of its softness in the corners. I like the lens for a walk around lens. Personally I don't have a problem with it because when I frame the shot, I back off a little so I can latter crop the shot to what I want. Actually I do that with almost all of my lenses. Even some of the internet reviews of that lens refer to it being a good lens on a aspc camera. That's basically what Sigma appears to be doing with their art lenses. Getting to know your equipment is half the battle.
Dec 9, 2015 10:35:15 #
flip1948 wrote:
color=gray Let me preface this by saying I have l... (show quote)
FYI. The 50mm f2.8 El-Nikkor enlarging lens could theoretically be used with a 6x6 negative ... the edge projection with a 6x6-or-6x7 negative was marginal for enlarging, however.
.....The 50mm f4.0 El-Nikkor did not have the same coverage.
My preferred enlarging lens was an 80mm lens because it could be used with either 6x6 or 35mm negatives.
Dec 9, 2015 10:35:42 #
robertjerl wrote:
All lenses project a bigger circle than the sensor size, other wise you would have the corners of the frame cut off.
The edge (corner) illumination doesn't cut off anything like sharply unless you're dealing with a slow optical system. The faster the system, the more gradual the vignetting. (This effect is what lens reviewers are talking about when they mention the f# at which vignetting disappears.) The main reason that most lenses are designed to project an image circle larger than the diagonal of the sensor or film is to keep the vignetting manageable.
Dec 9, 2015 10:37:58 #
And of course, tilt-shift and view camera lenses are designed with image circles much larger than the intended format.
alfeng wrote:
FYI. The 50mm f2.8 El-Nikkor enlarging lens could theoretically be used with a 6x6 negative ... the edge projection with a 6x6-or-6x7 negative was marginal for enlarging, however.
.....The 50mm f4.0 El-Nikkor did not have the same coverage.
My preferred enlarging lens was an 80mm lens because it could be used with either 6x6 or 35mm negatives.
.....The 50mm f4.0 El-Nikkor did not have the same coverage.
My preferred enlarging lens was an 80mm lens because it could be used with either 6x6 or 35mm negatives.
Dec 9, 2015 14:37:36 #
Dec 9, 2015 14:52:14 #
Vargnel wrote:
Round lens, square sensor......mmmmm
Square or rectangular, inside a circle whose radius is comfortably larger than its diagonal.
Dec 9, 2015 15:47:40 #
flip1948 wrote:
...
In the review I read the author claimed that what Sigma is doing with these lenses is having them project an image circle that is larger than needed to fully cover the sensor. As a result the sensor effectively crops out the far edges and corners where you could expect image sharpness to fall off.
He also said that this is not being done by Sigma alone...that other lens makers are using the same trick. I remember he specifically mentioned Nikon and perhaps Canon.
...
In the review I read the author claimed that what Sigma is doing with these lenses is having them project an image circle that is larger than needed to fully cover the sensor. As a result the sensor effectively crops out the far edges and corners where you could expect image sharpness to fall off.
He also said that this is not being done by Sigma alone...that other lens makers are using the same trick. I remember he specifically mentioned Nikon and perhaps Canon.
I don't believe this is a new trick? Some old Pentax lenses from my film days did the same thing.
The approach works nicely but does (normally) add size, more glass and weight to the lens. Sigma has reintroduced the practice with good results... and a higher price tag.
bwa
Dec 9, 2015 15:51:11 #
flip1948 wrote:
I fully understand that however there is a difference here as this is purposely being done on lenses designed for full frame bodies.
Not so sure that it is a trick, but that possibly explains why the new Sigma lenses are so long... I am not sure as I have never handled one of the Art lenses.... Hey, if it works, then no harm no foul, not to mention a superior product.
Dec 9, 2015 15:56:36 #
flip1948 wrote:
I fully understand that however there is a difference here as this is purposely being done on lenses designed for full frame bodies.
Another way to achieve sharpness in a design is to reduce the optic size. Using the old Nikon 55mm f/2.8 as an example. This is an extremely sharp flat field lens. By using a lens design of only f/2.8 max aperture there is less light "bending" involved so a higher level of critical sharpness and flat field can be achieved.
You have to realize ALL lens makers are confined to, and limited by the laws of physics to achieve their goal. Sigma chose to produce a larger, more expensive lens to achieve their goal.
Dec 9, 2015 15:59:12 #
robertjerl wrote:
Only draw back, the lens will be a bit bigger and heavier.
Only draw back, the lens will be a bit bigger and heavier.
And, most likely cost a bit more ....
Dec 9, 2015 17:12:19 #
flip1948 wrote:
Let me preface this by saying I have looked at a n... (show quote)
Why is this a "trick?" What's wrong with this?
Dec 9, 2015 17:13:54 #
DirtFarmer wrote:
They're positioning themselves for future cameras with XLF sensors (Extra Large Frame)
Always fun to start a new rumor......
Always fun to start a new rumor......
I like that. ELF sensor. Oh the Pentax 645Z already has that.
Dec 10, 2015 02:59:29 #
Bram boy
Loc: Vancouver Island B.C. Canada
It all boils down to it's a better system that was used not tricker , it took
Some thinking on sigma's pert to come up with it . Why didn't nikon or
Canon , Olympus do it first . If it works all the more power ti sigma for
Doing it first . Can they patent that or can the rest do it now . ?
Some thinking on sigma's pert to come up with it . Why didn't nikon or
Canon , Olympus do it first . If it works all the more power ti sigma for
Doing it first . Can they patent that or can the rest do it now . ?
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