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09-09-2015, 01:50 AM   #31
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QuoteOriginally posted by coboren3 Quote
Is 0.95 f-Stop practical? Working exposure settings being what they are, a combination of quick shutter speeds and smaller f-Stops, where would there be a need to shoot wide open (@ f0.95). Depth of field would be very shallow in low light levels to use the faster shutter speeds.
Could be, sometimes. Have in mind that any lens would be quite soft at f/0,95. Don't expect super sharp images at that setting. Assume low resolution usage (web), about 2 Mp / Full HD sharpness and allow an unsharpness of n pixels in the Full HD image .(CoC = 24mm / (1920 / n) pixels = ..... mm). Play around with the DoF calculator.

n = 1 pixel CoC -> Hyperfocal distance is 200m, image is sharp from 100m to infinity
n = 2 pixel CoC -> Hyperfocal distance is 100m, image is sharp from 50m to infinity
n = 4 pixel CoC -> Hyperfocal distance is 50m, image is sharp from 25m to infinity

Calculate the focus depth at 5 or 10 meters focus distance:

n = 1 pixel CoC and focus at 5m -> DoF = 0,25 m
n = 2 pixel CoC and focus at 5m -> DoF = 0,5 m
n = 4 pixel CoC and focus at 5m -> DoF = 1 m
n = 1 pixel CoC and focus at 10m -> DoF = 1 m
n = 2 pixel CoC and focus at 10m -> DoF = 2 m
n = 4 pixel CoC and focus at 10m -> DoF = 4 m

Conclusion: f/0,95 is useful if your resolution requirements are low, focus distances are quite long or if you want extremely low DoF. Given the manual focus you have to select scenes that doesn't move much back or forward.

09-09-2015, 07:19 PM   #32
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QuoteOriginally posted by UncleVanya Quote
Maybe you need to define what you mean by linear - I'm not following you. Linear functions are plotted such that they can be represented by a simple line. The f numbers themselves aren't linear as far as I can tell, but the exposure values they represent are. Fundamentally the point I want to be sure we are all agreeing to is that 1/3rd of a stop is 1/3rd of a stop and has the same effect if made by going from 1.4 to 1.2 or from 4 to 3.5 or by changing shutter speed by 1/3rd of a stop.

Also as far as a half stop being significant - that's pretty relative given the huge dynamic range we are able to access in digital. Many would argue that in the digital world a half stop is mostly insignificant.

The Depth of Field difference between 1.4 and 1.2 may be very significant depending on the subject.
You were the one that brought in linear. The amount of light let in by the aperture is not linear. Leave depth of field out of the discussion regarding the amount of light. What I originally said is there is a big difference on the amount of light hitting a film plane or sensor plane in an f2 lens and an f1.4 lens.



Each full stop results in a factor of 2 in light intensity increase.
09-09-2015, 07:20 PM   #33
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QuoteOriginally posted by MorgothV8 Quote
F scale is log base square root 2.
Because of "rounding" 1.0 - 1.2 - 1.4 (half stops) seems linear.
But this should be in reality:
1 -- 2^0.25 = 1.2 -- 2^0.5 = 1.41 -- 2^0.75 = 1.7 -- 2^1 = 2.
Linear are exponents of "2" where full stop is increment +0.5

The same with ISO and so on.
Stop is 0.5 because exposition is proportional to aperture area which is proportional to f ^ 2.
The stops may be mostly linear, but the size of the opening is NOT. Hence, more light is let in.

09-09-2015, 11:30 PM   #34
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I never said they are linear.
I said they "seems to be linear" in range 1 - 1,2 - 1,4 due to "rounding"
but in reality it is:
1.0 - 1.1892... - 1.41421 - 1,68179... - 2 and so on....

09-10-2015, 09:04 AM   #35
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QuoteOriginally posted by Blue Quote
There is a big difference in the amount of light hitting the sensor/film plane with an F1.4 lens compared to an F2 lens. Like wise there is a lot more light hitting the sensor/film plane with an f1.2 lens compared to an f1.4. The reason for that is that it is not linear!
QuoteOriginally posted by Blue Quote
You were the one that brought in linear. The amount of light let in by the aperture is not linear. Leave depth of field out of the discussion regarding the amount of light. What I originally said is there is a big difference on the amount of light hitting a film plane or sensor plane in an f2 lens and an f1.4 lens.



Each full stop results in a factor of 2 in light intensity increase.
An increase of a factor of 2 is the definition of linear. The slope is not curved. Also you brought up linear in your post quoted above before I said anything about it. Lastly while you mentioned f/2 and f/1.4 I responded to the second part of the statement which was about 1.2 and 1.4 - you claimed there was a LOT more light in that case and that it wasn't linear. Linearity does not imply 1:1 - the ratio fo the numbers for f/stops are not in question here. The point I made is that f/1.2 is a mere 1/3 of a stop faster than f/1.4 - which is a very small difference.
09-10-2015, 10:52 AM   #36
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I don't see the appeal. It is much easier to make an image softer in post-processing than to make it sharper. It seems to me that image sharpness is the most important thing to photographers these days (or their critics, at least). To the viewer of a photograph, the effect of shallow depth of field and blurry bokeh is quite noticeable at f1.4 and f2, even on APS-C cameras (and that effect is enhanced in a sharper photograph). As Norm posted, using f1.4 lenses on FF cameras generates just as shallow of depth of field as moving from f1.4 to f1.0 on APS-C cameras. Under what kind of ambient light conditions does 1 stop faster aperture make possible better images than post-processing (either noise reduction or exposure compensation) is capable of? Why purchase a lens that can be made to work for some, but not all scenarios, when there are lenses available that work as good or better in all scenarios?

The only appeal I can see is that of a talisman. An object that confers some kind of magical property to its owner once it is mounted on a camera.
09-10-2015, 03:40 PM   #37
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QuoteOriginally posted by UncleVanya Quote
An increase of a factor of 2 is the definition of linear. The slope is not curved. Also you brought up linear in your post quoted above before I said anything about it. Lastly while you mentioned f/2 and f/1.4 I responded to the second part of the statement which was about 1.2 and 1.4 - you claimed there was a LOT more light in that case and that it wasn't linear. Linearity does not imply 1:1 - the ratio fo the numbers for f/stops are not in question here. The point I made is that f/1.2 is a mere 1/3 of a stop faster than f/1.4 - which is a very small difference.
The areas of those circles aren't linear. Calculate the area and graph it against the f-stop. When I mentioned linear, was referring to the area or amount of light, not the f stop number. You are the one that used the linear argument about f stops. Each stop doubles the amount of light which isn't really the definition of linear. Even the f-stops themselves are geometric and related to the power of the square root of 2.

Furthermore, my first post wasn't directed at you. However, the 1/3 of a stop in your example is a lot more light than a 1/3 of a stop between f8 and f11. As the lens is stopped down, each stop halves the intensity of light from the previous full stop. Are you trying to argue that amount of light increase from 1.4 to 1.2 isn't significant? However, you example is more like half a stop on some lenses given 1.2 falls between 1.4 and 1.


Last edited by Blue; 09-10-2015 at 04:12 PM.
09-10-2015, 03:59 PM   #38
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I used to shoot with a 50mm f0.9 lens on my RF camera. A carefully calibrated RF camera. No chimping, refocusing, and reshooting.

It is a very hard lens to use. Given the very narrow DOF, it is hard to focus up close even with a tripod. Sometimes you get lucky and hit what you are aiming at. Most of the time you are not. I have an image of the detail on my wedding band in a self portrait. I tried to focus on my face.

Its uses are limited. I ended up using it primarily for items at a greater distance or landscapes in low light with slower film. It was great for that. At almost three and a half times the weight of its f1.8 brother it got left home a lot. Also it had 72mm filters compared to its f1.8 brother with 40.5mm filters.
09-10-2015, 05:58 PM   #39
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QuoteOriginally posted by Blue Quote
The areas of those circles aren't linear. Calculate the area and graph it against the f-stop.
When I mentioned linear, was referring to the area or amount of light, not the f stop number. You are the one that used the linear argument about f stops. Each stop doubles the amount of light which isn't really the definition of linear. Even the f-stops themselves are geometric and related to the power of the square root of 2.
Linear simply means that the slope of the function is a line. That's it. Linear | Define Linear at Dictionary.com We are in violent agreement that a full f/stop is 2x the light and this relationship is true every time no matter which f/stops we are talking about.

QuoteOriginally posted by Blue Quote
Furthermore, my first post wasn't directed at you.
It is a discussion forum so I butted in with my opinion. That is sort of the point of these threads right? If not then PM's would be how we all got our replies to the OP and the interactive nature of the discussion would die.

QuoteOriginally posted by Blue Quote
However, the 1/3 of a stop in your example is a lot more light than a 1/3 of a stop between f8 and f11.
FIrst I don't know what you mean here. F/8 to F/11 is a full stop. I will assume you meant to type f/8 to f/9. In that case from a pure number of photons per second or any other objective means of measuring light, the increase from f/9 to f/8 and the increase from f/1.4 to f/1.2 - you are absolutely correct. However the ratio of the change is the same and the impact to exposure is the same. Obviously whatever shutter speed you select would cut the number of seconds by almost 32 times (for simplicity I am rounding to the whole stop) assuming the exposure was held the same, while at the same time nearly 32x more light per unit of time would be let in so the total number of photons delivered to the sensor in the exposure would be identical in either case - that's why we can trade shutter speed against aperture the way we do and nothing more complex is needed. My point which I tried to make in my original post was that no matter how much more light is let it - it is still just 1/3 of a stop.

QuoteOriginally posted by Blue Quote
As the lens is stopped down, each stop halves the intensity of light from the previous full stop. Are you trying to argue that amount of light increase from 1.4 to 1.2 isn't significant? However, you example is more like half a stop on some lenses given 1.2 falls between 1.4 and 1.
Nope we agree - but we disagree on the importance of that fact. Also your point about a half stop is true - manufacturers can lie. We know they do on Focal Length and F/stops at times. The f/1.4 could be more or less and the f/1.2 could also. I would think however that they would get creative and label it 1.1 or 1.15 or whatever it was to really show off with a lens that was faster than f/1.2.

The honest truth is that I think we are no longer talking about the lens and we are simply caught up in a web of semantics. We both understand exposure and the math we are just phrasing things differently and maybe typing poorly in our haste to try to explain.

My entire point is summed up as:

1/3 of a stop is 1/3 of a stop no matter how you slice it. ISO, Shutter Speed, Aperture - one of these can change and the others will follow in kind to balance unless you are intentionally adjusting the exposure. Super fast lenses are harder and harder to make because of the point you made - each f/stop requires 2x the light to make it through the lens - which gets really difficult. But in the end - the only thing you get from 1.4 to 1.2 is that 1/3 of a stop at least from an exposure perspective.
09-10-2015, 11:40 PM   #40
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Isn't 1.4 and 1.2 a half stop difference - not 1/3?
Anyway I don't care, because as I said - I bought 1,2 lens for soft contrast and coma - which may be counterintuitive for someone.
I just LIKE effect on 1,2 - dreamy soft, coma, lower contrast but still sharp.... just like Pentax 67 soft focus lenses
Even more: I'm using it with ND16 on Nikon FM2 in daylight....
09-11-2015, 08:52 AM   #41
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QuoteOriginally posted by MorgothV8 Quote
Isn't 1.4 and 1.2 a half stop difference - not 1/3?
Anyway I don't care, because as I said - I bought 1,2 lens for soft contrast and coma - which may be counterintuitive for someone.
I just LIKE effect on 1,2 - dreamy soft, coma, lower contrast but still sharp.... just like Pentax 67 soft focus lenses
Even more: I'm using it with ND16 on Nikon FM2 in daylight....
No disagreement here about the reasons. You buy for what you need and or want a lens to do.

As for 1/2 or 1/3 stops, the charts I find show it both ways - often on the same chart in different columns! I suspect as Blue pointed out there is some rounding and that 1.2x or 1.1x is the real 1/2 or 1/3 stop but that they are labeled this way for simplicity.
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