Sigma 24-70 F2 OS

Talley wrote in post #16167034
A friend of mine who works at NASA, his boy has a friend on his baseball team who gets babysitted by this lady who has a nephew in florida that does top secret testing for the Sigma antartica team. He has been using this very lens for the past 4 years. It only weighs 5.3lbs but is filled with helium to reduce the "realistic weight" making it the same as a 40mm pancake.

Ya, this is more accurate lol.

My neighbor works with a guy who once dated this girl who had a thing with a guy who works at NASA, his boy has a friend on his baseball team who gets babysitted by this lady who has a nephew in florida that does top secret testing for the Sigma antartica team

might be related...

SMP_Homer wrote in post #16167044
the reason I can't see a f/2 with a 3x zoom is you don't see much in the way of a 2.8 zoom with more than 3x range
I always assumed technical reasons for lack of anything substantially more than 3x in a 2.8, and whatever those tech reasons are, will be magnified in a 2.0 zoom... i would be happy with a 24-48 (or call it 24-50 or whatever) in 2.0, but I really doubt we will see long 2.0 zooms...

Manufacturers do have faster zooms available (e.g. the Zeiss Master Zoom with a T/2.6 (so effective f/2.2+) with a 6.6x zoom range). However, that thing weighs 12kg and costs $60k used.

kasey wrote in post #16165799
Sounds like absolute bull.

One stop bigger requires 1.4 times in linear dimension (diameter) for the aperture. Assuming all else equal (assume the 77mm front filter size of the 24-70 mark I), we are taking about a front filter size around 110cm? Really? For a walkaround? We haven't even think about the weight!

People keep saying this. Does anyone have a good explanation of the actual physics involved?

I ask because it seems to me that there are lots of ways to get more light at the sensor which do not involve changing the size of the front element. Changing the curvature of the front element is one. Reducing losses due to internal reflection (better coatings, fewer elements) is another. Having a slightly shorter zoom range than advertised (which most lenses do to some degree) would be yet another. Of course front element size < filter size and if you narrow the gap there you can get away with making the lens (apparently) less large. Finally, you can accept a bit more vignetting.

Likewise, the actual size of the aperture itself seems to be only indirectly related to the size of the front element, though I'm less clear on the details there. It does not however seem that increasing the size of the front element necessarily requires a larger aperture. If for example the internal elements are of higher quality (less distortion around the edges, less light loss) then the aperture can be a bit larger without the elements being a bit larger.

Does anyone have a good reference on lens design which explains this?

Kolor-Pikker wrote in post #16167016
I can't see the logic at all, 24-70mm is a 100% walk around focal length range, but the lens will likely be huge and heavy, so who's it for?

Well, definitely not for weaklings and wimps. Sigma doesn't seem concerned about weight. Have you looked at how much the 120-300mm f/2.8 weighs? And then there's that crazy 500mm f/2.8...

Kolor-Pikker wrote in post #16167016
I can't see the logic at all, 24-70mm is a 100% walk around focal length range, but the lens will likely be huge and heavy, so who's it for? Would anyone really honestly take a 1.5kg standard zoom along for whatever?

It better be super sharp at f/2 as well, or again there is no point, when I could just use a prime instead, or use a smaller aperture (and thus may as well use a smaller lens altogether).

Enough people complained about the Brick's weight as it is.

every wedding photographer would buy one, myself included

Kolor-Pikker wrote in post #16167016
I can't see the logic at all, 24-70mm is a 100% walk around focal length range, but the lens will likely be huge and heavy, so who's it for? Would anyone really honestly take a 1.5kg standard zoom along for whatever?

It better be super sharp at f/2 as well, or again there is no point, when I could just use a prime instead, or use a smaller aperture (and thus may as well use a smaller lens altogether).

Enough people complained about the Brick's weight as it is.

I would imagine it would be a fantastic lens for wedding shooters given that it performs to standards of wedding photographers. I would put it on my list to buy. Weight does not matter to me so long as the lens is not so heavy I cannot handhold it. Something like this paired up with a 70-200 MkII would be a dream for weddings. I'd probably keep the S35 in my bag as well. That's all I'd need. Very interested in the lens as well as wanting to see if Sigma is going to release the rumored 135 1.8 OS

bespoke wrote in post #16167235
every wedding photographer would buy one, myself included

Sorry, but apparently there is a little-known law forbidding a 24-70mm to be used for anything other than as a walk-around lens. I trust you're in compliance and aren't using a 24-70mm for anything other than just walkin' around.

If the lens is reasonable in price, weight, and size... Sign me up! I really hope this is more than just a rumor!

melauer wrote in post #16167173
People keep saying this. Does anyone have a good explanation of the actual physics involved?

I ask because it seems to me that there are lots of ways to get more light at the sensor which do not involve changing the size of the front element. Changing the curvature of the front element is one. Reducing losses due to internal reflection (better coatings, fewer elements) is another. Having a slightly shorter zoom range than advertised (which most lenses do to some degree) would be yet another. Of course front element size < filter size and if you narrow the gap there you can get away with making the lens (apparently) less large. Finally, you can accept a bit more vignetting.

Likewise, the actual size of the aperture itself seems to be only indirectly related to the size of the front element, though I'm less clear on the details there. It does not however seem that increasing the size of the front element necessarily requires a larger aperture. If for example the internal elements are of higher quality (less distortion around the edges, less light loss) then the aperture can be a bit larger without the elements being a bit larger.

Does anyone have a good reference on lens design which explains this?

The f-numbers that we all know and love is calculated by dividing the focal length of the lens over the width of the entrance pupil of a lens. The entrance pupil is the optical image of the physical aperture stop as viewed from the front of the lens, and is limited in part by how big the front element is.

For instance, if the front element is 100mm in diameter, then when you look into the front of the lens at the aperture, the apparent size of the aperture (i.e. size of the entrance pupil) can only be at most 100mm. Hence, in most normal to telephoto designs, the size of the front element is directly related to the aperture (and focal length) of the lens.

This is true in practice - a theoretical 85mm f/1.2 should have an entrance pupil of 70.8mm, and the actual front element of the actual 85LII is approximately that wide (72mm front filter size). A theoretical 400mm f/2.8 should have a entrance pupil size of 143mm and the actual EF 400mm f/2.8L IS II has a lens hood diameter of 155mm (ET-155), which means that the front element should be about 145-150mm, again falling in line with our calculations. This breaks down somewhat when we talk about retrofocus designs (wide zooms like the 16-35 or 17-40, etc...), but that is another story for another time.

Having better coatings and such will improve the ultimate light transmission of a certain lens but has no effect on the the f-number. (If you are interested in the light transmission, then the T-number is what you should be looking up and what most cine lens manufacturers report).

A good reference on optical design is Hecht's Optics if you want to know more about this.

SMP_Homer wrote in post #16167044
the reason I can't see a f/2 with a 3x zoom is you don't see much in the way of a 2.8 zoom with more than 3x range
I always assumed technical reasons for lack of anything substantially more than 3x in a 2.8, and whatever those tech reasons are, will be magnified in a 2.0 zoom... i would be happy with a 24-48 (or call it 24-50 or whatever) in 2.0, but I really doubt we will see long 2.0 zooms...

The technical reason is simply that a zoom ratio of more than 3.3x is considered a "super zoom" and optical quality starts to quickly degrade past this point. It's not specifically about the aperture range.

Kolor-Pikker wrote in post #16167646
The technical reason is simply that a zoom ratio of more than 3.3x is considered a "super zoom" and optical quality starts to quickly degrade past this point. It's not specifically about the aperture range.

70-300L has good optics

the 28-300L has fairly good optics as well.

"Fairly good" isn't the same as "sharp as a prime at same focal length/aperture"
Yes, perhaps the 70-300 does have good optics, but the 70-200 has laser crisp optics with no distortion.
The 100-400 and 24-105 are also good lenses, but fairly flawed, with the former being on the soft side for a telephoto lens, and the latter having crazy amounts of distortion on the wide end (as do most super zooms).

Kolor-Pikker wrote in post #16167723
"Fairly good" isn't the same as "sharp as a prime at same focal length/aperture"
Yes, perhaps the 70-300 does have good optics, but the 70-200 has laser crisp optics with no distortion.
The 100-400 and 24-105 are also good lenses, but fairly flawed, with the former being on the soft side for a telephoto lens, and the latter having crazy amounts of distortion on the wide end (as do most super zooms).

well the 70-300 is a new lens with the latest optics, and it's pretty much on par with primes, just slower.

IMO, it's prime sharp wide open. You'de have to pixel peep to see the difference, and even then you might do a double take. If all 4x zooms were that sharp, I dont think there would be complaints about sharpness.

the 28-300 is also very good, considering it's a dated lens design.

I'm a believer of good optics. Good is good, and zoom factor doesnt really matter. Older optics were dumbed down because pixel levels were low. Now they're high and pixel peeping is a new art. Primes sharp wide open..... there was a thought that you have to stop down primes for really sharp photos..... not the case with newer primes.

frankchn wrote in post #16167556
The f-numbers that we all know and love is calculated by dividing the focal length of the lens over the width of the entrance pupil of a lens. The entrance pupil is the optical image of the physical aperture stop as viewed from the front of the lens, and is limited in part by how big the front element is.

For instance, if the front element is 100mm in diameter, then when you look into the front of the lens at the aperture, the apparent size of the aperture (i.e. size of the entrance pupil) can only be at most 100mm. Hence, in most normal to telephoto designs, the size of the front element is directly related to the aperture (and focal length) of the lens.

This is true in practice - a theoretical 85mm f/1.2 should have an entrance pupil of 70.8mm, and the actual front element of the actual 85LII is approximately that wide (72mm front filter size). A theoretical 400mm f/2.8 should have a entrance pupil size of 143mm and the actual EF 400mm f/2.8L IS II has a lens hood diameter of 155mm (ET-155), which means that the front element should be about 145-150mm, again falling in line with our calculations. This breaks down somewhat when we talk about retrofocus designs (wide zooms like the 16-35 or 17-40, etc...), but that is another story for another time.

Having better coatings and such will improve the ultimate light transmission of a certain lens but has no effect on the the f-number. (If you are interested in the light transmission, then the T-number is what you should be looking up and what most cine lens manufacturers report).

A good reference on optical design is Hecht's Optics if you want to know more about this.

Thanks, I will definitely look up Hecht's Optics.

Your point about T-stops is more-or-less why I bought this up. I get the feeling that people are arguing that the front element needs to have twice the area (or 1.4 times the radius) so that twice the light can pass through. As you said that's not an argument about f-stops, it's about T-stops.

I don't know hypothetically how small the front element of an f/2 or f/2.8 24-70 zoom can be. Maybe once I get to reading that book I'll figure it out. My point is that it does seem wrong to just extrapolate from the dimensions of existing lenses.

Surely modern lenses are built with larger front elements than are technically necessary for performance reasons. For example, the latest 24-70 2.8 zooms all take 82mm filters, but the original Canon 24-70 took 77mm filters. Knowing that, the question becomes how small those front elements can they be, and what other factors (e.g. a shorter "true" zoom range like 25-67mm, accepting more vignetting) might permit an f/2 zoom to be smaller than people think. Still huge no doubt, but not literally twice the size of a current f/2.8.