Sigma Announces 18-35 f/1.8 DC HSM Art for APS-C

[Wildfire]

Some people forget that F aperture is not (just) about bokeh, blur, etc. its about the amount of light which can reach the sensor. In that matter the F value is equivalent between FF and APS-C.

I don't think so. Aperture is about the diameter of the blade iris. The amount of light actually conveyed to the sensor is measured in T stops.

Regardless of the light transmission, an f/1.8 aperture will produce the same exposure at the same ISO and shutter speed whether full frame or crop. I think that's what he means.

[Hannes]

Now that was an unexpected announcement. Great one none the less and it makes massive amounts of sense for indoor shooting

[Mantanuska]

This is great for crop shooters.  However, before everyone gets excited over the f/1.8 bit, you have to remember that f/1.8 on a crop sensor is nothing like f/1.8 on a FF sensor.  This lens will give the same angle of view, image noise for given exposure parameters (*1), depth of field at a given AOV and subject distance (*2), etc. etc. etc. as a 28-50mm f/2.8 full frame lens.

In other words, if the lenses and sensors are perfect, this lens on a crop sensor would give identical results to a 28-50mm f/2.8 on a FF sensor. 

You mean identical DOF. f1.8 will still give more light on APS-C than f/2.8 on full frame.

[mrsfotografie]

18mm?  What the heck is it with these idiotic lens makers.  We've got the 17-55, 18-55, 18-135, 18-200, 18-270 and now 18-35.  What do we have that starts at 24mm-equivalent?  The only one I own - the 15-85IS.

f/1.8 sounds interesting, but not if it starts at 18mm!!!

Pass.

Copy that, it reminds me of the 19-35 I've used in the past on APS-C, not a very inspiring zoom range. Better get a 24 mm f/1.4 instead.

[rs]

This is great for crop shooters.  However, before everyone gets excited over the f/1.8 bit, you have to remember that f/1.8 on a crop sensor is nothing like f/1.8 on a FF sensor.  This lens will give the same angle of view, image noise for given exposure parameters (*1), depth of field at a given AOV and subject distance (*2), etc. etc. etc. as a 28-50mm f/2.8 full frame lens.

In other words, if the lenses and sensors are perfect, this lens on a crop sensor would give identical results to a 28-50mm f/2.8 on a FF sensor. 

You mean identical DOF. f1.8 will still give more light on APS-C than f/2.8 on full frame.

No. A FF sensor behind an f2.8 FF lens gathers 2.56x as much light as an f2.8 lens does on a 1.6x crop sensor due to the sensors 2.56x bigger surface area. If you only capture a fraction of all that FF f2.8 light by cropping it, well, the obvious happens from the light gathering point of view. The reason why using an f1.8 lens wide open on crop gives a brighter image than f2.8 on FF (when both are at the same ISO and shutter speed) is the amplification of the crop cameras sensor is 2.56x greater, at the expense of noise at any given ISO rating. In other words ISO 10,000 on crop is pretty much equal to ISO 25,600 on FF in terms of noise. So feel free to shoot smaller apertures on FF and use higher ISO's to get the same light gathering and noise.

The different amplification levels is a bit like how the Sony NEX 7 and the Sony SLT A77 both share an identical sensor, and give the same exposure with the same shutter speed, aperture and ISO, yet the SLT camera has a semi translucent mirror permanently in front of the sensor, acting like a neutral density filter you can't get rid of. Sony just cranked up the amplifier on the A77 a bit more to make it all seem good - at the expense of noise.

So f1.8 on a 1.6x crop is equivalent to f2.88 on FF in terms of both depth of field and light gathering.

I see this Sigma lens as being a crop alternative to the 24-70 II on FF in just the same way as the 17-55 IS is a crop alternative to the 24-105L on FF. Not quite as fast an effective aperture, and not as wide or as long effective focal lengths. Slightly worse on all fronts when compared to the FF equivalent, but none the less a nice string in the bow for crop sensor users. Lets hope it performs well optically, and I like the idea of an internal zoom on a lens covering the normal range, even if the zoom ring rotates the wrong way

[Kit.]

My point is, in the film days, only the cheapest kit zooms started at 28, and all the rest started at 24.

Actually, the only Canon's standard zoom starting at 24 "in the film days" was EF24-85/3.5-4.5 USM.

Then EF24-70/2.8L was introduced in 2002.

[Shane1.4]

Maybe I will get my 60d back out of my bag. That lens sounds awesome!

[Danielle]

That's pretty awesome. An f1.8 zoom finally. Not that I'll be buying a lens specifically for crop on a hurry but that's a great step in that direction none the less.

Go sigma. I love how tamron and sigma are stepping up.

[AdamJ]

This is great for crop shooters.  However, before everyone gets excited over the f/1.8 bit, you have to remember that f/1.8 on a crop sensor is nothing like f/1.8 on a FF sensor.  This lens will give the same angle of view, image noise for given exposure parameters (*1), depth of field at a given AOV and subject distance (*2), etc. etc. etc. as a 28-50mm f/2.8 full frame lens.

In other words, if the lenses and sensors are perfect, this lens on a crop sensor would give identical results to a 28-50mm f/2.8 on a FF sensor. 

You mean identical DOF. f1.8 will still give more light on APS-C than f/2.8 on full frame.

No. A FF sensor behind an f2.8 FF lens gathers 2.56x as much light as an f2.8 lens does on a 1.6x crop sensor due to the sensors 2.56x bigger surface area. If you only capture a fraction of all that FF f2.8 light by cropping it, well, the obvious happens from the light gathering point of view. The reason why using an f1.8 lens wide open on crop gives a brighter image than f2.8 on FF (when both are at the same ISO and shutter speed) is the amplification of the crop cameras sensor is 2.56x greater, at the expense of noise at any given ISO rating. In other words ISO 10,000 on crop is pretty much equal to ISO 25,600 on FF in terms of noise. So feel free to shoot smaller apertures on FF and use higher ISO's to get the same light gathering and noise.

The different amplification levels is a bit like how the Sony NEX 7 and the Sony SLT A77 both share an identical sensor, and give the same exposure with the same shutter speed, aperture and ISO, yet the SLT camera has a semi translucent mirror permanently in front of the sensor, acting like a neutral density filter you can't get rid of. Sony just cranked up the amplifier on the A77 a bit more to make it all seem good - at the expense of noise.

So f1.8 on a 1.6x crop is equivalent to f2.88 on FF in terms of both depth of field and light gathering.

Wuh? 

[citation needed]

[Wildfire]

The reason why using an f1.8 lens wide open on crop gives a brighter image than f2.8 on FF (when both are at the same ISO and shutter speed) is the amplification of the crop cameras sensor is 2.56x greater, at the expense of noise at any given ISO rating.

What? That's wrong.

A crop f/1.8 lens and a full frame f/1.8 lens will provide exactly the same exposure when used at the same shutter speed and ISO. The full frame exposure WILL NOT be brighter.

You're right about an FF f/2.8 lens having more light gathering ability than a crop f/1.8 lens, but all that light it gathers is spread over a larger sensor, which makes the exposure more than a full stop darker than if you had used an f/1.8 lens.

So in terms of exposure, a f/1.8 lens is brighter than an f/2.8 lens, regardless of sensor size. Sensor size does affect depth of field, but that's a different story.

[Mantanuska]

The reason why using an f1.8 lens wide open on crop gives a brighter image than f2.8 on FF (when both are at the same ISO and shutter speed) is the amplification of the crop cameras sensor is 2.56x greater, at the expense of noise at any given ISO rating.

What? That's wrong.

A crop f/1.8 lens and a full frame f/1.8 lens will provide exactly the same exposure when used at the same shutter speed and ISO. The full frame exposure WILL NOT be brighter.

You're right about an FF f/2.8 lens having more light gathering ability than a crop f/1.8 lens, but all that light it gathers is spread over a larger sensor, which makes the exposure more than a full stop darker than if you had used an f/1.8 lens.

So in terms of exposure, a f/1.8 lens is brighter than an f/2.8 lens, regardless of sensor size. Sensor size does affect depth of field, but that's a different story.

Exactly. Try it for yourself on a crop body and FF. f1.8 at 1/30 sec at 100 ISO will give you the same exposure on both cameras. FF will not be brighter.

[SwissBear]

this is f*** ****some!

all i hope is that the price is in the 3 digit range

[eml58]

I think what has happened is that Canon's pricing policies have become SO absurd that is has given some astute tech. and money managers at Sigma the ability to realize that they have a lot more wiggle room to make a great product and still be super competitive in price to big read. (it also shows how ridiculous Canon's pricing has become). I do not own a crop body either, but I do LOVE the appearance of this lens! Hope the IQ and price/performance ratio are right up there with the Sigma 35mm, f/1.4 that I own and absolutely love. This can be nothing but good for all of us! Can't wait to see what the next lens is in the new Art Line!!!!!!!

Yep, tend to agree with all that has been said here, I haven't a use for this Lens as I shoot FF, even my Lads both shoot FF (6D & 5DMK III), but it's the fact that Sigma will make this Lens that's such good News, it should make Canon/Nikon sit up & take note, as has been said, if Sigma can produce their Art Series Lenses going forward as well as they have done with the Art 35f/1.4 (Bought it, Love it, also own the Canon 35f/1.4, the Art is better I feel), then it should be good news for all of us, those that are happy to use non Canon lenses, and those that generally only use Canon lenses and are slowly heading to the poor house due to their personal addiction.

[Frage]

Some people forget that F aperture is not (just) about bokeh, blur, etc. its about the amount of light which can reach the sensor. In that matter the F value is equivalent between FF and APS-C.

I don't think so. Aperture is about the diameter of the blade iris. The amount of light actually conveyed to the sensor is measured in T stops.

Regardless of the light transmission, an f/1.8 aperture will produce the same exposure at the same ISO and shutter speed whether full frame or crop. I think that's what he means.

Thank you, that´s exactly what I wanted to say. My english is not good enough.

[TrumpetPower!]

The reason why using an f1.8 lens wide open on crop gives a brighter image than f2.8 on FF (when both are at the same ISO and shutter speed) is the amplification of the crop cameras sensor is 2.56x greater, at the expense of noise at any given ISO rating.

What? That's wrong.

A crop f/1.8 lens and a full frame f/1.8 lens will provide exactly the same exposure when used at the same shutter speed and ISO. The full frame exposure WILL NOT be brighter.

You're right about an FF f/2.8 lens having more light gathering ability than a crop f/1.8 lens, but all that light it gathers is spread over a larger sensor, which makes the exposure more than a full stop darker than if you had used an f/1.8 lens.

So in terms of exposure, a f/1.8 lens is brighter than an f/2.8 lens, regardless of sensor size. Sensor size does affect depth of field, but that's a different story.

Exactly. Try it for yourself on a crop body and FF. f1.8 at 1/30 sec at 100 ISO will give you the same exposure on both cameras. FF will not be brighter.

Within minor variation, yes, of course, you'll get the same exposure on both cameras.

The difference, though, is that there will be more noise / grain in the crop version, and the math works out such that the APS-C camera with a 30mm lens at f/1.8 @ 1/30 @ ISO 100 and the 135 camera with a 50mm lens at f/2.8 @ 1/30 @ ISO 260 will give you not only the same exposure, but also the same depth of field but still with less noise and more resolution (assuming the same film stock or pixel pitch).

That means that, with the full frame camera, you can shoot at f/1.8 @ 1/30 @ ISO 100 and get the image with shallower depth of field and much less noise, or you can shoot it at f/2.8 @ 1/60 @ ISO 320 and get the image with the same depth of field and the same noise but a faster shutter speed, or any of another number of variations.

So, basically, you're both right; you're just typing past each other....

It's well worth doing some experimentation in the matter. Set up a still life with controlled lighting and your camera on a tripod -- and don't touch the tripod. Shoot with different focal lengths at different apertures, whether with a zoom or different lenses. Crop them all to the same field of view and scale them all to the same pixel dimensions and compare the results. Figure out what you have to do to match depth of field from the one to the other, and observe what happens to the rest of the image. Be sure to also do a set with low light levels and high ISOs to compensate. (Don't just use a super fast shutter in bright light to get to the high ISOs; that doesn't tell you the whole story and it's not very representative of the real world).

Cheers,

b&