So Sigma have been busy....

maninsuitcase said:
An odd lens this one. The price is attractive (this and a D5200 is about the same as body only on a D600), but I can't help but think that it's not what most people actually need.

Also 1.8 @ 18mm? What's that for? Night landscape shots is about all I can think of but even then at 1.8 DOF, even at 18mm is probably still an issue. 35 1.8 is more useful but the DX prime is pretty cheap and I would hazard a guess better optically.

Essentially they will sell a load to people who see the specs, but don't stop to think what will I use it for.
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Rubbish, IMVHO. Why not 18-35mm f1.8?

It's for APS-C so if you need the FF equiv it's 18-35 x 1.5/1.6=what used to be a very popular FF focal length at both ends and in between and the DoF will be FF equiv of 1.8 x 1.5/1.6 but the light gathering ability will be f1.8. Pretty good IMVHO.

IMVHO It's not a lens for people who don't know what they're doing, quite the opposite in fact. I see it as a lens for people who know exactly what they're doing who'll look at the spec and see a use for it and going by the one English language review I've read (I linked and quoted it earlier) it looks like it's a good lens and capable of good results.
 
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JonathanRyan said:
Have I got the sums right?

Isn't minimum diameter of the front optic focal length / maximum aperture?

There are other things to solve but that should mean a 24-70 1.8 could fit into the same size barrel as the current 2.8.
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It doesn't work like that :( Diameter of the front element is, usually, not directly related to the diameter of the actual aperture. It works out quite close with say a 50mm or 100mm prime, but if the same maths is applied to my 17-40mm f/4 zoom for example, it would be f/0.3 at 17mm.
 
Lez325 said:
I own a Sigma 24-70mm f2.8 and its NOT fixed at f2.8 - just has that option throughout the zoom range- I often shoot at f2.8 if I want a oof back ground

Les :thumbs:
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I don't get it or maybe i'm very uneducated.

I thought the Sigma 24-70 f2.8 you have is a fixed f2.8 aperture lens. Which means you can use f2.8 through out the whole range, and if lens like variable aperture it will say something like f2.8-f4 for example which means at the tele end you can only open it to f4 and f2.8 on the wide end.

By looking at this sigma 18-35 f1.8 i thought is a fixed f1.8 aperture.
 
f/1.8 on a crop will provide very similar DoF as f/2.8 on FF. As said a few posts above, the big benefit is light gathering ability vs FF rivals. An f/1.8 zoom on FF is possible, but the lens, especially the front elements would need to be massive.
 
badboy1984 said:
I don't get it or maybe i'm very uneducated.

I thought the Sigma 24-70 f2.8 you have is a fixed f2.8 aperture lens. Which means you can use f2.8 through out the whole range, and if lens like variable aperture it will say something like f2.8-f4 for example which means at the tele end you can only open it to f4 and f2.8 on the wide end.

By looking at this sigma 18-35 f1.8 i thought is a fixed f1.8 aperture.
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It means the maximum aperture at all focal lengths is f1.8 but you can stop it down to whatever you like e.g. f4, f12, etc.
Its not fixed in the sense that you cant change it at all, it means the maximum aperture is fixed throughout the focal lengths.
Is that what you meant?
 
This is exactly what i so confuse, i always thought the meaning of fixed aperture lens means you an set that particular aperture on all zoom range but have ability to stop down to whatever the lens can stop to.

aperture like f2.8-f4 is variable aperture where wide end can open up to f2.8 and the tele end can only open to f4. Any zoom can stop down from 2.8 - what ever and f4 - whatever as well.

Fixed aperture lens does not mean the aperture is fix at that particular value all the time.

So the sigma 24-70 f2.8 is a fix aperture lens and so is this 18-35 f1.8.
 
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AchimT said:
In which way was it off - the AF? After testing one, I ordered one now, and want to prepare myself for that. What should I look out for?
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The focus point was off, micro-adjusting on cam wasn't sufficient to correct it. Even on a tripod, testing on clear, contrasty subjects like bold text on white - it was focusing above where I aimed the AF point. They now have a usb dock that you can buy for £40, that will sort this issue out. But I had to send mine back, and got the last copy the store had. I wasn't happy, the store weren't happy, they wanted me to go deal with Sigma - no chance.
 
badboy1984 said:
I see where you guys coming from about maximum aperture. Nikon uses the term fixed aperture for their lens.

http://www.nikonusa.com/en/Learn-An...um-aperture-fixed-and-variable-apertures.html

So maximum aperture = fix aperture.
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No, the maximum aperture is just how wide open the lens can be; on a standard kit lens the maximum aperture is f3.5 at 18mm and f5.6 at 55mm. On the Sigma in question its maximum aperture is f1.8 throughout because its got a fixed aperture, therefore on the lens it only needs to say 18-35mm f1.8 as opposed to a variable aperture lens which might say 18-35mm f2.8-f4. All lenses have a maximum aperture, just some lenses it changes at different focal lengths.
 
I see what you mean but when a lens like 24-70 f2.8 many people call it fix aperture lens or constant aperture lens.

Lens like 18-55 f3.5-5.6 means is a variable aperture lens means max aperture it can open on the wide end is f3.5 and max zoom range is f5.6.

I do know what maximum aperture on the lens means.

What i'm trying to see is the lens 18-35 f1.8 is a fix aperture f1.8 lens or constant f1.8 lens. (of course this means the maximum aperture is f1.8).

I think we both talking about the same thing but in different terms.

After re-reading what i comment before about "max aperture = fix aperture", that is completely wrong. I thought you mean the lens with constant aperture is called "maximum aperture".

To sum it up all lens have maximum aperture,

lens like 18-55 f3.5-5.6 have variable aperture and lens like 24-70 f2.8 have fixed f2.8 aperture or constant f2.8 aperture.

I think it got confuse because someone earlier on the post ask whether the sigma lens have fixed aperture! What he really means is the lens is fixed at f1.8 and not allow to change, where my fix aperture terms means maximum aperture is f1.8 on all focal range but can stop down to whatever it can stop to.
 
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badboy1984 said:
This is exactly what i so confuse, i always thought the meaning of fixed aperture lens means you an set that particular aperture on all zoom range but have ability to stop down to whatever the lens can stop to.

aperture like f2.8-f4 is variable aperture where wide end can open up to f2.8 and the tele end can only open to f4. Any zoom can stop down from 2.8 - what ever and f4 - whatever as well.

Fixed aperture lens does not mean the aperture is fix at that particular value all the time.

So the sigma 24-70 f2.8 is a fix aperture lens and so is this 18-35 f1.8.
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Fixed aperture simply means that the aperture can be fixed across it's entire zoom range at it's brightest setting. If you set f/1.8 in-camera, it will remain "fixed", independent of zoom.
 
HoppyUK said:
It doesn't work like that :( Diameter of the front element is, usually, not directly related to the diameter of the actual aperture. It works out quite close with say a 50mm or 100mm prime, but if the same maths is applied to my 17-40mm f/4 zoom for example, it would be f/0.3 at 17mm.
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Ah OK. I assumed they were just standardising on a front optic size because the calc gave the minimum size. So both the 24-70 and 70-200 2.8s are 77mm lenses because, well, pros lose lens caps ;)

I suppose zooms are harder than you think. Which is why this lens is interesting.
 
Orville said:
Fixed aperture simply means that the aperture can be fixed across it's entire zoom range at it's brightest setting. If you set f/1.8 in-camera, it will remain "fixed", independent of zoom.
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I do understand what fix aperture means. All my lens is fix aperture or constant aperture if you want to called it.

I been telling off by someone for saying this sigma lens 18-35mm f1.8 is a fix aperture lens where someone mis-understood the term fix aperture (as in fix aperture and can't change).

All I want to mention is the terms i use for lens. fix aperture and variable aperture.

The reason why i arguing is someone said i'm wrong when i said the lens is fixed aperture.
 
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"Fixed" implies something which cannot be moved.

A "fixed maximum aperture" throughout the focal length range would be a less ambiguous way to describe this lens and also the likes of the Canon 24-70L and Nikon 24-70 AF-S lenses.

The likes of the 18-55mm kit lenses would then be described as having a "variable maximum aperture" throughout the focal length range.

If someone referred to a "fixed aperture", I would assume they we're talking about one which did not change at all.
 
badboy1984 said:
Isn't this means fixed f1.8 throughout all zoom range? Just like the 24-70 f2.8 but is 18-35 f1.8 instead.
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as hoppy said maximum , not fixed - it means that you can select all the way up to f1.8 at any focal length, but you can also select any other f stop - down to about f22 i think

Fixed appertures (ie those that can't be changed) are relatively rare on modern lenses - you tend to get them on miror lenses (usually f8 or f11) but not on most others

most cheap zooms vary their maximum apperture as they zoom - e.g they might be f4.5 at the wide end, but f5.6 at the long end - this sigma lens doesnt do that i.e it has a constant maximum apperture of f1.8
 
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Ok, i'm gonna say it one last time again. I understand the difference between "Fixed maximum aperture" lens and "Variable maximum aperture" lens.

I'm also sorry to confuse anyone regard the term "Fix aperture". I'm sure alot of people refer "fix aperture" lens to "fix maximum aperture" lens. Thats the way how i was taught.

I will say "Constant Aperture" lens for now on?

I only use the term that Nikon use as well.

If you read on the nikon site.

http://www.nikonusa.com/en/Learn-An...um-aperture-fixed-and-variable-apertures.html

"Fixed aperture lenses utilize more sophisticated lens elements than variable aperture ......... etc"
 
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The clue may be in the "usa" part of that url.

In any case, there are not many lenses that are truly fixed aperture in the literal sense (maybe the f8 body cap lens from Panasonic but they are an oddity!)
 
badboy1984 said:
Ok, i'm gonna say it one last time again. I understand the difference between "Fixed maximum aperture" lens and "Variable maximum aperture" lens.

I'm also sorry to confuse anyone regard the term "Fix aperture". I'm sure alot of people refer "fix aperture" lens to "fix maximum aperture" lens. Thats the way how i was taught.

I will say "Constant Aperture" lens for now on?

I only use the term that Nikon use as well.

If you read on the nikon site.

http://www.nikonusa.com/en/Learn-And-Explore/Article/gll2rs05/zoom-lens-maximum-aperture-fixed-and-variable-apertures.html

"Fixed aperture lenses utilize more sophisticated lens elements than variable aperture ......... etc"
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I didn't think it confusing. I always though constant aperture and fixed aperture were used to describe zooms like this.
 
boyfalldown said:
I didn't think it confusing. I always though constant aperture and fixed aperture were used to describe zooms like this.
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Thank You Hugh. Finally someone know what i was talking about without jumping to a bandwagon to tell me off ........

Thats the point i'm trying to say but many got confuse with the term and say i referring the lens having a aperture which is fixed and can't be change .......
 
badboy1984 said:
Thank You Hugh. Finally someone know what i was talking about without jumping to a bandwagon to tell me off ........

Thats the point i'm trying to say but many got confuse with the term and say i referring the lens having a aperture which is fixed and can't be change .......
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As an aside I didn't think there were any zooms you couldn't change - there are one or two fairly esoteric primes ( mirror lenses or body cap lenses) but afaik no zooms
 
Cagey75 said:
The focus point was off...
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Thanks, especially also for pointing us to that USB device. I ordered the lens yesterday, the USB dock is not yet available for the Nikon mount it seems, but I will get that one as well, if my lens shows any AF problems. Even with the dock, it is a very moderately priced lens.
 
AchimT said:
Thanks, especially also for pointing us to that USB device. I ordered the lens yesterday, the USB dock is not yet available for the Nikon mount it seems, but I will get that one as well, if my lens shows any AF problems. Even with the dock, it is a very moderately priced lens.
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I'm keeping an eye out for the dock. So if you spot it for nikon anywhere let me know ;)
 
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