hunz
Established
The 23mm lens is equiv to a 34.5mm FF lens, what about the f-stop? is it also multiplied by 1.5? so an f-stop equivalent of f3.0?
Chris101
summicronia
Depends on how you are interpreting f-stop. Used to calculate exposure, it's the same, crop factor doesn't change the f-stop.
If you are using the f-stop to determine the depth of field, then yes, use a larger f-number. However since depth of field is somewhat subjective the exact amount of change must be determined by your own experience. Multiplying by 1.5 gets you in the right ballpark.
gavinlg
Veteran
The x100 23mm lens is equivalent to a 35mm f2.8 in levels of focal length and depth of field. Add a stop to the F-stop to get the FF equiv.
However in actual terms, f2 is f2. So it is still letting in the same amount as an FF f2 lens, just the Depth of field will be a little bit more.
hunz
Established
hunz
Established
Spyro
Well-known
I dont think dof can be so accurately measured hunz, these calcs are just an indication. There is an equation but it has a factor in it which is subjective and set arbitrarily by each lens maker. BTW I saw some zeiss otus shots today, I could swear judging from the look of the photos that it seemed almost a whole stop faster than it really is. Bokeh does look different from different lenses of the same spec, how do you measure that?
Anyway I think the take out is the x100/s doesnt have a whole lot of "dof" to play with, just enough to make annoying when you miss focus
Anyway I think the take out is the x100/s doesnt have a whole lot of "dof" to play with, just enough to make annoying when you miss focus
Wiyum
Established
I saw some zeiss otus shots today, I could swear judging from the look of the photos that it seemed almost a whole stop faster than it really is. Bokeh does look different from different lenses of the same spec, how do you measure that?
Anyway I think the take out is the x100/s doesnt have a whole lot of "dof" to play with, just enough to make annoying when you miss focus
I haven't looked much at samples from the Otus, but this is entirely unsurprising to me, as the Otus is supposed to be descended from Zeiss' own Master Primes for cinema. Those lenses I have a fair amount of experience with, and they're so incredibly sharp at the plane of focus that they appear to lack any depth of field at all... apparent focus rolls off very quickly. Areas of the image that on another lens might be considered sharp don't appear to be, simply by virtue of contrast with the sharpest part of the image. Which makes them a useful tool, but also frankly a liability in some regards. It will be interesting to see if some Otus users have the same "complaint."
But back to topic, I find that the x100s has plenty of opportunities for controlling depth of field. I've never felt as though I wanted more separation and couldn't achieve it. So that, too, is subjective.
The interesting comparison will be to the A7/A7r with the Zeiss 35mm/2.8 lens. Especially on the 24mp, AA-filtered A7.
Jockos
Well-known
I think you'd look at the "circle of confusion", and then match it towards your arbitrary standard of acceptable sharpness (in a magnification vs. enlargement ratio).
http://en.wikipedia.org/wiki/Circle_of_confusion
aizan
Veteran
there are things going on with DOF and bokeh that we mere mortals don't know about. ctein had a column on TOP a while ago about this topic. remember how the 35mm summicron pre-asph has more DOF at the same apertures than the ASPH? it's not as simple as multiplying the f-stop by the crop factor.
rivercityrocker
Well-known
DoF is consistent across all focal lengths according to aperture size and focus distance. There's no way that the 35 cron Pre-ASPH can have more DoF than the ASPH unless it has a physically smaller aperture.
Bokeh is just a buzzword that started to get thrown around in the late 90's. All it's meant to describe is the characteristics of the out of focus areas, not the amount. There's no way to get "more" bokeh or "less" bokeh.
Bokeh. It being defined has been one of the worse things to happen to bokehography, I mean photography. (jokes, sort of)
Wiyum
Established
This is true on paper, but not in practice. The reason is that the calculation of depth of field is a formula that relies upon a number for circle of confusion. Circle of confusion is itself a highly subjective thing, and can vary for a number of reasons, including format size, exhibition size, viewing distance in exhibition, and yes, the lens used. As regards that 'cron, it is likely that the appropriate circle of confusion for the pre-ASPH is different from that of the ASPH.
These differences are observable without too much difficulty, and have little to nothing to do with bokeh.
aizan
Veteran
there are a couple comparisons on the internet that illustrate what i'm talking about. one is from "jim" something and another was posted here on rff. i don't remember who did that one, but the photos were taken in the gardens around an old building. that would save the $3k+ you'd need to do the test yourself. if you have different lenses with the same specs, you could try it out too!
unixrevolution
Well-known
In my opinion, the idea of "Equivalent F/number for depth of field" is hogwash. Because the amount of depth of field you get from a lens is dependent on distance, f/number and focal length, and because you run into infinity sooner on a shorter lens than a longer one, you can only calculate the true equivalence for any one given working (or focusing) distance. Close up, the 23mm f/2 may act like a 35/2.8, but on the edge of the 23's hyperfocal distance, it'll be sharp to infinity or to a very long distance out where the 35 just won't.
There is no equivalence, there is no conversion. It just doesn't work.
There is no equivalence, there is no conversion. It just doesn't work.
rivercityrocker
Well-known
The circle of confusion isn't really subjective. It has a mathematical equation as well.
Rather than explain it in detail here, there's a good resource online that explains it very well.
http://www.rags-int-inc.com/PhotoTechStuff/DoF/
Wiyum
Established
It is comforting to think it is so; to me as much as anyone, truly. But I have seen firsthand the proof that it isn't so. We shot the same set of tests with an old 50mm Zeiss Standard, a still-quite-old 50mm Zeiss Superspeed, a roughly new 50mm Zeiss Ultraprime, a then not-on-the-market brand new 50mm Zeiss Masterprime, and a relatively-new 50mm Cooke S4. Sure, cinematography instead of photography, but optics are optics. We had a model at the point of focus and a model in the foreground and another in the background twice as far further from focus as the foreground model was near (the rough formulation of depth of field). All lenses were freshly collimated and shimmed by a reliable rental house, Clairmont Camera.
In identical circumstances, different lenses produced results that in some cases did and in other cases did not yield adequate depth of field to hold the three models. We tested 1.9/2.0/2.1, 2.8, and 4.0. We tested two different planes of precise focus. We tested numerous distances for the foreground and background models. And those models became acceptably sharp at different distances on different lenses. And as we (28 of us) filled out our reports watching the tests, there was not universal agreement as to when they became sharp. So yes, subjective. Certain things were universally held to be (there was clear consensus on the Masterprime having the least apparent depth of field by some margin, for example). But there was plenty of subjectivity at play, and clear differences between different vintages of lenses (again, four of the five were Zeiss).
As I said, I'd love it if it were true that math could answer all of these questions, let all lenses be equal and that be that. But it simply isn't true. I've seen it, projected on a sizable screen from answer-printed 35mm motion picture film. Believe it or don't; I know what I've seen firsthand.
Chris101
summicronia
It's even simpler that that. The circle of confusion depends on several factors outside of normal geometric optics. First and easiest to explain is the size of the observed image and the degree to which it is enlarged. Second is the distance the image is from the viewer. These can still be understood geometrically. Then come the tougher aspects - the sharpness of the lens overall. If a lens is extremely sharp, the sharp parts and blurry parts will be distinct, vs a lens that in generally soft, so the transition between sharp to blurred is not so easy to see where it happens. And finally there is the visual acuity of the viewer. If everything is kind of blurry, and the viewer has good 'blur interpretation' then the 'in acceptable focus' part will be larger.
So while it is possible to determine a circle of confusion for a lens that only depends on aperture and focal length, the perceived depth of field can vary depending on these other, physiological and psychological parameters, which are not so easily measured.
So while it is possible to determine a circle of confusion for a lens that only depends on aperture and focal length, the perceived depth of field can vary depending on these other, physiological and psychological parameters, which are not so easily measured.
Wiyum
Established
Yes, I tried to make these exact points above, but upon resistance felt it necessary to go back to the origin of my own understanding of how confusing a circle of confusion can be.