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Author Topic: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C  (Read 33714 times)

Albi86

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #90 on: April 19, 2013, 11:13:28 AM »
...

You are mixing two concepts that are unrelated.

If we talk about framing, then you're right. The smaller effective aperture is the reason why DoF is bigger on crop at a given aperture and angle of view (note that I didn't say focal length).

However, framing has nothing to do with light gathering. f-stops are a function of focal length, not angle of view. A 50mm is a 50mm on every camera. It's the angle of view that changes in relation to sensor size, not the focal length.

Another quote from Wikipedia:
Quote
A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A 200 mm focal length f/4 lens has an entrance pupil diameter of 50 mm. The 200 mm lens's entrance pupil is larger than that of the 100 mm lens, but given the same light transmission efficiency, both will produce the same illuminance at the focal plane when imaging a scene of a given luminance.
But to compare a crop lens, crop sensor combo to a FF lens, FF sensor combo, there's no point in comparing two with different framing - otherwise you'd be arguing this 18-35 crop lens is a direct equivalent of a 16-35 FF lens on FF.

You can compare what you want, as long as you it correctly. The way you do it is the way you can compare angles of view. This is fine as long as you don't make the mistake to consider angle of view = focal length and to put this value into a f/stop calculation.

To exaggerate, is a 100mm f5.6 large format lens with its huge image circle the same as a 100mm f5.6 lens and its tiny image circle on a compact? Is it wrong to compare lenses which give the same framing? Surely from a photographers point of view, they're two very different lenses?

Focal length is what it is. You can mount an old Zeiss for Hasselblad lens on your Canon camera and the focal length will not change. It would give you the same framing of a 100mm Canon lens.

Wikipedia doesn't take into account imaging circle in that equation you're quoting. The aperture of a lens is a bit like working out the speed of water in a hose pipe. The imaging circle is a bit like the diameter of the pipe. Widen the pipe and keep the speed the same, you get more coming through.

More flow, but not more pressure. Same with light: you get more light coming in in total, but the amount of light / surface of the sensor would be the same. Any extra light that comes in will not affect exposure.

Or think about it like this - imagine a photo taken with a FF lens and a FF sensor. Now you take that same photo and you crop out just the centre 40% - you've taken away 60% of the image - which is also 60% of the light that passed through that FF lens. You're left with only 40% of the light. That's what crop does. You need a faster lens on crop to make it capture the same amount of light in that smaller area.

Same as above. A smaller sensor is actually a smaller mouth to feed. This is why you can have compact cameras with 1" sensor and f/1.8 lenses.

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #90 on: April 19, 2013, 11:13:28 AM »

rs

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #91 on: April 19, 2013, 11:29:32 AM »
You can compare what you want, as long as you it correctly. The way you do it is the way you can compare angles of view. This is fine as long as you don't make the mistake to consider angle of view = focal length and to put this value into a f/stop calculation.
Angle of view is a combination of focal length and sensor size. If we're talking about two different sized sensors, to get the same angle of view, we have to adjust the focal length to suit.

Focal length is what it is. You can mount an old Zeiss for Hasselblad lens on your Canon camera and the focal length will not change. It would give you the same framing of a 100mm Canon lens.
You're looking at it the wrong way here - while the 100mm Zeiss frames the same as the 100mm Canon on the Canon SLR, it frames very different from how it would on the Hasselbald. On the Canon, you've cropped out a fair old proportion of the image circle, resulting in much of the light being cropped out and a narrower FoV.

More flow, but not more pressure. Same with light: you get more light coming in in total, but the amount of light / surface of the sensor would be the same. Any extra light that comes in will not affect exposure.
That's my exact point - the intensity of the light at any area of the sensor isn't greater, its just there's a bigger area of it, so in total more light is captured by the system.

Same as above. A smaller sensor is actually a smaller mouth to feed. This is why you can have compact cameras with 1" sensor and f/1.8 lenses.
Again, it looks like you've nearly got it here - it does need that faster aperture to make it equivalent.
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Albi86

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #92 on: April 19, 2013, 11:47:10 AM »

Angle of view is a combination of focal length and sensor size. If we're talking about two different sized sensors, to get the same angle of view, we have to adjust the focal length to suit.



Exactly. And you have to decide if we're talking about focal length or angle of view. You can't freely interchange the two concepts, because they are two different things. You can compare one to the other, but within limits.

Focal length is a property of the lens, and the lens alone. Whatever is a function of focal length, is not affected by the sensor in your camera, which - as you said - instead will affect the angle of view.

A Nikon 1 10mm f/2.8 lens will have an equivalent focal length (read: angle of view) of a 27mm lens on FF, but it will be nevertheless a 10mm lens. Assuming transmission is the same, the exposure would be the same for this lens and a 10mm F/2.8 lens on FF. The Nikon 1 lens can be smaller because the sensor is smaller. The total amount of light gathered by a FF will be more, but the amount of light hitting the sensor / surface of the sensor would be the same. You could mount the FF lens on the Nikon 1 and it would be the same - because the extra light will fall off the sensor. That's why exposure is not affected.

If you now transpose this concept to this lens, you will understand that exposure-wise a f/1.8 lens is a f/1.8 lens disregarding of the system. This, again, is because f-stops depend on focal length and focal length is a parameter of the lens and not of the camera.

insanitybeard

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #93 on: April 19, 2013, 12:41:29 PM »
Debate regarding the light gathering ability of this lens and equivalent DOF vs FF aside, I must admit this is an interesting lens. This is coming from somebody who up until this point has only considered Canon glass. Maybe it will give Canon a push to put out some more high quality and fast dedicated crop lenses of it's own. The implications of using this lens on a crop camera cannot be ignored, if it is good optically.
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AprilForever

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #94 on: April 19, 2013, 12:45:06 PM »
What makes this lens epic is that there is no equivalent FF lens. In very low light, this can focus when f2.8 cannot!!!
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Albi86

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #95 on: April 19, 2013, 12:49:44 PM »
What makes this lens epic is that there is no equivalent FF lens. In very low light, this can focus when f2.8 cannot!!!

+1

It's epic that it takes crop shooters where they've never been before.

Lee Jay

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #96 on: April 19, 2013, 02:07:41 PM »
What makes this lens epic is that there is no equivalent FF lens. In very low light, this can focus when f2.8 cannot!!!

No cameras I know of have f/1.8 AF sensors.  f/2.8 sensors "see" at f/2.8 regardless of the actual f-stop of the lens.  An f/1.4 lens is no brighter to f/2.8 AF sensors than an f/2.8 lens is.

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #96 on: April 19, 2013, 02:07:41 PM »

indigo9

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #97 on: April 19, 2013, 02:20:48 PM »

Exactly. And you have to decide if we're talking about focal length or angle of view. You can't freely interchange the two concepts, because they are two different things. You can compare one to the other, but within limits.

Sensor dimensions taken from: http://en.wikipedia.org/wiki/Full-frame_digital_SLR
FoV/Focal Length formulas: http://paulbourke.net/miscellaneous/lens/

Calculations:
(Using an 81mm lens here to be more accurate, 36/22.2 = 1.62 crop factor)

APSC sensor: 22.2mm width, focal length 50mm = 0.4369 radians = 25.0 degrees
Full Frame sensor: 36mm width, focal length 81mm = 0.4373 radians = 25.1 degrees

Focal length and Field of View are the same thing. The only reason they might not match in practice is because manufacturers don't quite tell the truth and the advertised focal length is slightly different from what they say (if it's 52mm, they're going to advertise it as a 50mm anyway)


A Nikon 1 10mm f/2.8 lens will have an equivalent focal length (read: angle of view) of a 27mm lens on FF, but it will be nevertheless a 10mm lens. Assuming transmission is the same, the exposure would be the same for this lens and a 10mm F/2.8 lens on FF.

A Nikon 1 10mm f/2.8 lens will have a pupil diameter of 3.57mm.

A 27mm f2.8 lens will have a pupil diameter of 9.64mm.

There are 2.7^2=7.3 times as many photons are coming through that 27mm lens as through the 10mm lens at the same f stop. Since the same proportion of those photons falling on the sensor is the same [same aspect ratios fitting in a circular aperture], the full frame sensor is receiving 7.3 times as many photons at the same f-stop.

The fact that one sensor is larger or smaller is completely irrelevant -- both sensors are covering the same proportion of the image circle (because we're talking about 35mm equivalent focal lengths here -- if you want to argue proportion of image circle covered then you need to do the comparisons using the same focal lengths -- see below)

The Nikon 1 lens can be smaller because the sensor is smaller. The total amount of light gathered by a FF will be more, but the amount of light hitting the sensor / surface of the sensor would be the same.

See above -- the amount of light (ie photons) hitting the sensor is most definitely not the same. The physical aperture size and the field of view are the only 2 things that control how many photons go through the lens.

You could mount the FF lens on the Nikon 1 and it would be the same - because the extra light will fall off the sensor.

Huh? A Nikon 1 sensor is 2.72x2.72 = 7.44 times smaller -- 87% of photons that would be hitting a FF sensor are being ignored. Assuming sensors are equivalent technology, at the same shutter speed the simple fact is that the Nikon 1 will have to amplify the signal coming off the sensor 7 times more than the full frame camera to get a proper exposure. How is this possibly equivalent?

That's why exposure is not affected.

More photons hitting the sensor = more electrons being excited = less amplification necessary to properly expose an image = less amplification of background sensor noise.

Note that I deliberately haven't mentioned ISO settings at all -- ISO settings are just calibrated labels to measure how much sensor signal amplification the camera needs to perform to properly expose a scene to a certain level, they are not an inherent property of the sensor itself. Go to dxomark and compare the SNR on a Canon 5D2 and a 60D -- the 60D is far noisier despite having a newer sensor, because ISO 1600 on a 60D actually means a lot more signal amplification than ISO 1600 on a 5D2. The ISO number itself is irrelevant, what is relevant is how much noise is amplified along with the useful signal.

If you now transpose this concept to this lens, you will understand that exposure-wise a f/1.8 lens is a f/1.8 lens disregarding of the system. This, again, is because f-stops depend on focal length and focal length is a parameter of the lens and not of the camera.

Yes, a f/1.8 lens is a f/1.8 lens regardless of the system. A f/1.8 lens on a full frame will perform better than a f/1.8 lens on crop with equivalent focal lengths though, and that's what the original question was.

Imagine that tomorrow I introduce a new camera system for amateur astronomers called "Super 100x35mm", sensor dimensions 360mm x 240mm, same ~4000x2800px resolution as a crop system. I stick 35mm-equivalent 50mm focal length lens on it, which for this system would be a 500m f/2.8. The pupil diameter of this lens is 178mm -- this pupil is 10 times wider than a full frame lens. According to the logic above, the fact that this pupil & sensor has 262 times more light gathering capability than a crop 32mm f/2.8 lens is irrelevant; "exposure-wise" all f/2.8 lenses are equivalent? Does this really sound sensible to you?

If that's the case, why are astronomy telescopes so wide?




The original question was whether a crop camera with a given lens at f/2.8 performs the same as an equivalent focal length f/2.8 full frame. The answer is no, for equivalent focal lengths at the same f-stop the full frame sensor receives a lot more light and so gives less noise. In light of that, rs is right -- the lens might be nice for someone like me who only owns a crop camera but if you care terribly about low light performance then you should be on full frame.


Native sensor ISO? Let's not open *that* can of worms
« Last Edit: April 19, 2013, 02:23:40 PM by indigo9 »

michi

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #98 on: April 19, 2013, 02:45:34 PM »
Lots of high tech talk I am not privy to understand or care to understand.  The lens however seems great.  Impressed with Sigma.  Unfortunately I have decided to go and stay with full frame.  If anything remotely similar was available for full frame, I would be all over it.

AdamJ

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #99 on: April 19, 2013, 04:04:47 PM »
There has been a lot of nonsense on this thread. It's pointless contributing now because the ones spreading the nonsense have entrenched themselves so deeply that they have no prospect of coming out of this with any dignity or credibility.


CarlTN

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #100 on: April 19, 2013, 04:33:27 PM »
There has been a lot of nonsense on this thread. It's pointless contributing now because the ones spreading the nonsense have entrenched themselves so deeply that they have no prospect of coming out of this with any dignity or credibility.

Let's not say these people have no dignity...that's personal and uncalled for.  They're simply sharing their opinion.

However, I agree...the discussion has turned rather silly it seems.  And there's nothing "epic" about this lens.  "Epic" is such a silly slang word these days, overused by teenage pop culture...it's time to retire it.

via google: ep·ic 

/ˈepik/

Noun

A long poem, typically derived from oral tradition, narrating the deeds and adventures of heroic or legendary figures or the history of...

http://www.merriam-webster.com/dictionary/epic

The word really does not apply.  There actually have been other fast zooms, such as Olympus' f/2.  Just because this is the first f/1.8 zoom, does not make it "epic".

I mean, the above exchanges seem to have to do with light intensity, etc.  A crop sensor uses only part of a full frame lens' image circle.  Since the lens in question, is designed for a smaller image circle, then it can't really be compared to a lens that is designed to output a larger image circle to a larger sensor.  Can it?  Sure, you can attempt to calculate, and approximate...but does it really matter as much as those above think it does?  No.

Let's just all go full frame, and forget crop sensors, especially for anything less than telephoto focal lengths (such as over 100mm).
 

AdamJ

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #101 on: April 19, 2013, 05:06:04 PM »
There has been a lot of nonsense on this thread. It's pointless contributing now because the ones spreading the nonsense have entrenched themselves so deeply that they have no prospect of coming out of this with any dignity or credibility.

Let's not say these people have no dignity...that's personal and uncalled for.  They're simply sharing their opinion.


Yes, I shouldn't have put it that way. Apologies.

(Although, describing what f/1.8 means - whether on FF or APS-C - ought to be a matter of fact, not opinion).
 
« Last Edit: April 19, 2013, 05:09:11 PM by AdamJ »

9VIII

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #102 on: April 19, 2013, 09:27:05 PM »

Exactly. And you have to decide if we're talking about focal length or angle of view. You can't freely interchange the two concepts, because they are two different things. You can compare one to the other, but within limits.

Sensor dimensions taken from: http://en.wikipedia.org/wiki/Full-frame_digital_SLR
FoV/Focal Length formulas: http://paulbourke.net/miscellaneous/lens/

Calculations:
(Using an 81mm lens here to be more accurate, 36/22.2 = 1.62 crop factor)

APSC sensor: 22.2mm width, focal length 50mm = 0.4369 radians = 25.0 degrees
Full Frame sensor: 36mm width, focal length 81mm = 0.4373 radians = 25.1 degrees

Focal length and Field of View are the same thing. The only reason they might not match in practice is because manufacturers don't quite tell the truth and the advertised focal length is slightly different from what they say (if it's 52mm, they're going to advertise it as a 50mm anyway)


A Nikon 1 10mm f/2.8 lens will have an equivalent focal length (read: angle of view) of a 27mm lens on FF, but it will be nevertheless a 10mm lens. Assuming transmission is the same, the exposure would be the same for this lens and a 10mm F/2.8 lens on FF.

A Nikon 1 10mm f/2.8 lens will have a pupil diameter of 3.57mm.

A 27mm f2.8 lens will have a pupil diameter of 9.64mm.

There are 2.7^2=7.3 times as many photons are coming through that 27mm lens as through the 10mm lens at the same f stop. Since the same proportion of those photons falling on the sensor is the same [same aspect ratios fitting in a circular aperture], the full frame sensor is receiving 7.3 times as many photons at the same f-stop.

The fact that one sensor is larger or smaller is completely irrelevant -- both sensors are covering the same proportion of the image circle (because we're talking about 35mm equivalent focal lengths here -- if you want to argue proportion of image circle covered then you need to do the comparisons using the same focal lengths -- see below)

The Nikon 1 lens can be smaller because the sensor is smaller. The total amount of light gathered by a FF will be more, but the amount of light hitting the sensor / surface of the sensor would be the same.

See above -- the amount of light (ie photons) hitting the sensor is most definitely not the same. The physical aperture size and the field of view are the only 2 things that control how many photons go through the lens.

You could mount the FF lens on the Nikon 1 and it would be the same - because the extra light will fall off the sensor.

Huh? A Nikon 1 sensor is 2.72x2.72 = 7.44 times smaller -- 87% of photons that would be hitting a FF sensor are being ignored. Assuming sensors are equivalent technology, at the same shutter speed the simple fact is that the Nikon 1 will have to amplify the signal coming off the sensor 7 times more than the full frame camera to get a proper exposure. How is this possibly equivalent?

That's why exposure is not affected.

More photons hitting the sensor = more electrons being excited = less amplification necessary to properly expose an image = less amplification of background sensor noise.

Note that I deliberately haven't mentioned ISO settings at all -- ISO settings are just calibrated labels to measure how much sensor signal amplification the camera needs to perform to properly expose a scene to a certain level, they are not an inherent property of the sensor itself. Go to dxomark and compare the SNR on a Canon 5D2 and a 60D -- the 60D is far noisier despite having a newer sensor, because ISO 1600 on a 60D actually means a lot more signal amplification than ISO 1600 on a 5D2. The ISO number itself is irrelevant, what is relevant is how much noise is amplified along with the useful signal.

If you now transpose this concept to this lens, you will understand that exposure-wise a f/1.8 lens is a f/1.8 lens disregarding of the system. This, again, is because f-stops depend on focal length and focal length is a parameter of the lens and not of the camera.

Yes, a f/1.8 lens is a f/1.8 lens regardless of the system. A f/1.8 lens on a full frame will perform better than a f/1.8 lens on crop with equivalent focal lengths though, and that's what the original question was.

Imagine that tomorrow I introduce a new camera system for amateur astronomers called "Super 100x35mm", sensor dimensions 360mm x 240mm, same ~4000x2800px resolution as a crop system. I stick 35mm-equivalent 50mm focal length lens on it, which for this system would be a 500m f/2.8. The pupil diameter of this lens is 178mm -- this pupil is 10 times wider than a full frame lens. According to the logic above, the fact that this pupil & sensor has 262 times more light gathering capability than a crop 32mm f/2.8 lens is irrelevant; "exposure-wise" all f/2.8 lenses are equivalent? Does this really sound sensible to you?

If that's the case, why are astronomy telescopes so wide?




The original question was whether a crop camera with a given lens at f/2.8 performs the same as an equivalent focal length f/2.8 full frame. The answer is no, for equivalent focal lengths at the same f-stop the full frame sensor receives a lot more light and so gives less noise. In light of that, rs is right -- the lens might be nice for someone like me who only owns a crop camera but if you care terribly about low light performance then you should be on full frame.


Native sensor ISO? Let's not open *that* can of worms


Then it gets interesting when you look at the Metabones Speed Booster. I have to wonder if those kinds of abilities have been an option all along in crop sensor lens design.
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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #102 on: April 19, 2013, 09:27:05 PM »

dilbert

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #103 on: April 19, 2013, 09:56:43 PM »
There are sample photos taken with this lens mounted on a 5D Mark II:

http://lcap.tistory.com/entry/Sigma-18-35mm-f18-with-5D-Mark-II

Radiating

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #104 on: April 19, 2013, 11:34:01 PM »
I can just imagine Canon & Nikon engineers staring at their screens in disbelief. Sigma engineers have managed to crack some code to lens making. I have the Sigma 35mm f/1.4, just tested the new Sigma 30mm f/1.4 and can't wait for this. Amazing lenses Sigma, now please give me a nice 50mm lens because I am not at all happy with my Canon 50mm. At least my Canon 85mm is great.

It's actually not difficult to make a lens like this any more than it is to make a 24-70mm f/2.8 lens for full frame.

Both will gather approximatly the same amount of light.

The amazing thing here is that Sigma has the motivation to make a lens like this. Canon have been sitting on their butts making ridiculous products for the recent past. T5i? WTF. 8-15mm L fisheye WTF?

Canon have dozens lenses that are 13 years old and a complete embarassment. I think Sigma just saw a moment of weakness and decided to obliterate the competition with these new products.

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Re: Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C
« Reply #104 on: April 19, 2013, 11:34:01 PM »