Don't wrap it. I'll eat it here.
Erik Ohlson: Det är inte klåk!
det är skit!
Pat Cullinan Jr: Richard,
For your sake please consult with a large-format pro or other grizzled adept about "the greater low-light ability that a larger sensor would otherwise give."
Len speed remains constant.
All the best,
Let's say that B = nA, where n is some fractional value < 1. Then nE amount of light energy will be falling on area B, and the brightness over area B will be nE/B = nE/nA = E/A, which is the same as the brightness over the larger area. This long-winded presentation shows that, although a larger area captures more light energy, the brightness remains the same vis-a-vis a smaller area. I hope no one's turning to stone over this.
The FF shooter shoots at 1.8, just like the APS-C shooter. The inherent speed of a lens doesn't change if you use it on a big or a small sensor. The angle of acceptance, or angular coverage, changes, but not the lens speed.
Imagine a large-format photog shooting a scene at 5.6 with 8x10 film. If he now changes the format to 5x7, he will shoot the scene at 5.6 also. The required exposure hasn't changed. Only the format has changed. What it boils down to is the fact that THE BRIGHTNESS OF THE IMAGE AT THE FOCAL PLANE DOESN'T DEPEND ON THE SIZE OF THE PIECE OF FILM YOU PUT THERE. Put that way, I guess it sounds more or less obvious.
"But, Pat, doesn't a larger format glom more light energy?"
Yes, it does, but that energy is shmeared over a bigger area, so there is no net gain in brightness of image.
Let's say we have E amount of light energy falling on an area A per unit time. Then the brightness of the image is measured by E/A. Now imagine a portion B of this area...
Pat Cullinan Jr: <quote>should provide the depth-of-field control and low-light image quality on an APS-C DSLR that you'd get using an F2.8 zoom on 35mm full-frame.</quote>
The aperture of a lens is quite independent of the format of the film or sensor. In other words, f/1.8 is f/1.8 whether the lens is placed before an APS-C sensor or a full-frame sensor. The intensity of the light striking the target is the same whether you have a small or a large target. The aperture is a function solely of the focal length and the entrance "pupil" (meaning the diameter of the circle of light you see when you look through the lens from the rear).
I hope everybody understands this, because otherwise you'll be making disadvantageous decisions or doing things wrong.
P.S. I meant 411.
Hate to say it, but what you're saying isn't entirely true. I understand what you're saying, though.
What you can do is
1) talk to a large-format photographer and ask about changing formats while using the same lens.
2) call me (because my PC is dying). 911, Brooklyn, Patrick Cullinan. I'll be glad to help. After 9 PM Eastern, any day but Sunday.
All the best,
You're right. I should have said "relative aperture" or "f-stop."
"Aperture" just-plain means entrance pupil, and is measured in mm, as you say.
I cordially recommend The Focal Encyclopedia of Photography, Michael R. Peres, Focal Press. The Kindle edition is up to the moment (2012). The print edition was published in 2007. The Focal Press website presents their complete offering (http://www.focalpress.com/).
[continued] It's called relative aperture because it relates the bigness of the lens opening to the focal length.
A reference for this is Sidney F. Ray, Applied Photographic Optics, London and Boston: Focal Press, 1988, ISBN 0-240-51226-X. This, however, is gruesome stuff! You can read an excerpt of Ch. 14, The Speed of a Lens, on p. 122 at http://books.google.com/books?id=cuzYl4hx-B8C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false. You can get the book for $70, delivered. Focal Press is the best. They've been publishing outstanding books for generations.
The DOF part is correct, but the part about "low-light image quality," which amounts to (maximum) aperture, isn't. The maximum aperture is called lens speed (http://en.wikipedia.org/wiki/Lens_speed). Imagine a lens casting an image on a wall. Light energy is falling on the wall at a certain rate (energy per second per unit area). This rate is called intensity. It's intensity that determines the photographic effect on the film or the sensor. The intensity is the same whether you put a small sensor or a large one on the wall. Or, suppose you're shooting a subject using a view camera with a 5.6 lens and 5x7 sheet film. Now suppose you want to shoot some subjects with 4x5 film. You're lens is still 5.6! The lens speed doesn't change. Speed depends only on the diameter of the lens (actually, the "entrance pupil") and the focal length. The Wikipedia article "F-number" gives the relation N = f/D, i.e., f-number (aperture) = focal length over entrance pupil.
Pretty ugly ring bokeh but very interesting nonetheless.
Are we talking about "onion ring" bokeh here? ;)
SteveCooper: does anybody have a clue as to the projected price on this lens? Isn't that going to be one of most important factors as to whether or not this lens sells well?
My "SWAG" is $2400. ["G" = "guess"]
[continued from above] As regards DOF, you're correct in saying that f/1.8 on APS-C correlates with f/2.8 on FF (1.8 x 1.5 = 2.7). Wikipedia on "Depth of field" says, "Many small-format digital SLR camera systems allow using many of the same lenses on both full-frame and 'cropped format' cameras. If, for the same focal length setting, the subject distance is adjusted to provide the same field of view at the subject, at the same f-number [1.8, e.g.] and final-image size, the smaller format has greater DOF." Meaning the FF will have less DOF, unless stopped down [to 2.8, e.g.] to achieve equal DOF. A full treatment is given in the article cited, under the heading "Relationship of DOF to format size."
<quote>should provide the depth-of-field control and low-light image quality on an APS-C DSLR that you'd get using an F2.8 zoom on 35mm full-frame.</quote>
Gesture: Does anyone else have APS-C sensor plus fixed zoom lens?
Correct -- 18.70 x 14.00 mm vs. 17.30 x 13 mm.
Canon's APS-C is 22.20 x 14.80 mm.
knize10: It will be made by Panasonic.
I heard a rumor it will be made by Acme Camera, Bayonne, N.J.
Pat Cullinan Jr: Not turning cartwheels here. Edge rez is not impressive. By me.
After seeing Mr. Horshak's photos (see his post above), I'm mitigating my opinion about this lens. His input has provided the additional data needed to form a more considered opinion. It's the IS that scores the win.
Horshack: If anyone is interested I have a gallery of hand-held shots with the Tamron on my D800, most shot indoors @ f/2.8 with a shutter speed of 1/13. I've made the full-size 36MP images available for viewing.
Thanks very much for making your studies available to us. I can see that edge resolution is too low for my palate, notably in landscape shots, but for some reason it seems less of an issue in other compositions -- in particular, your interior shots, and the canal shots. This may be a function of object distance. Although I would not use it for landscapes, I will now seriously consider it for interiors, specifically, poorly illuminated interiors -- I'll be photographing the American Museum of Natural History this season, God willing, and I think the IS feature clinches the deal -- the museum is dark! The Nikon contenders lack IS. That kills the deal for them.
Gordon Laing has a 3-way comparison of the Tamron, the spendy Nikon 24-70 2.8, and the "cheap" ($600) Nikon 24-85 3.5-4.5 at