F/1.8 Zoom lens!!

[Sifor]

For a street photographer, the zoom range is incredibly useful. How many threads are there debating 28mm vs 35mm vs 50mm (FF equivalent) as the best street focal length. You get all three and everything in between at f1.8 with this lens.

Very good point - this could easily be the go to lens for street photographers..

Never know, this might just be the start of something new in fast zoom lenses...

[Lance B]

Sigma has also taken a big advancement leap with their Lens Dock technology, so that you can update latest firmware for the lens and adjust things like AF fine tune, but more specifically, AF fine tune at different zoom settings. Quite the innovation for a 3rd party lens maker:

http://www.sigma-global.com/en/lense...oduct/usb.html

Even though it doesn't list the 18-35 on the linked site for the Dock, it does mention it at the bottom of the info page for the 18-35.

http://www.sigma-global.com/en/lense...tml#features06

[WhoDo]

I stick my hand up as one, I don't believe that the APSC format is anywhere near dead yet and seeing as we own a couple of capable DX bodies to work with relatively cheap dedicated APSC lenses they make good sense as travel cameras.

Not sure these will qualify as "relatively cheap", Andrew, but I do take your point.

[cupic]

Some samples and results
http://lcap.tistory.com/entry/Sigma-...mm-f18-Preview

[ameerat42]

Ta for that, Cupic. So that where Sar NOP got the MTF charts from!
Am.

[Lance B]

Ta for that, Cupic. So that where Sar NOP got the MTF charts from!
Am.

I think he would have got it from here like everyone else:

http://www.sigma-global.com/en/lense.../features.html

[ameerat42]

Ta Lance. That day I couldn't find this. Now I can't get away from it!
m.

[arthurking83]

...... The fact is, wide angle lenses for APS C are not really smaller and I alluded to this when talking about the lens mount distance which was a leftover from the film days which meant that they have to have special lens designs so as to cause less vignetting and other factors .......

OK ... not really sure what you're referring to here Lance but lets put some figures into perspective here:

Sigma 30/1.4(APS-C only): Dimensions (Diameter x Length) φ74.2mm x 63.3mm
Nikon 35/1.4(Fullframe): Diameter x length Approximately 83 x 89.5 mm

APS-C a lot smaller(mainly in percentage terms)


Nikon 16-35/4VR: Diameter x length Approximately 82.5 x 125 mm
Tamron 17-50/2.8VC: LENGTH 94.5mm (no diameter given but filter diameter is 72mm, and the lens diameter looks to be very close to this .. maybe 2mm more)

Note that the Nikon lens is a much less extreme optic in that it's an f/4 .. one stop slower than the Tammy. Sigma's equivalent is about the same size as the Tammy.

At the ultra wide angle end of the scale, we get:

Tokina's 11-16/2.8: Dimensions 84x89mm
Nikon's 14-24/2.8: Dimensions 98x132mm


Pretty much as far as I can see .. the vast majority of APS-C only lenses are in fact on average about 15% smaller in physical dimensions(except weight) to their full frame counterparts.

Apart from the Sigma 50-150mm f/2.8, I doubt that we will ever see any lenses above about 50mm for APS-C sensored cameras(Nikon also has it's 85mm f/3.5 micro), as it appears to be a counterproductive exercise by the manufacturer.
Due to the extreme nature of the designs of wider angled lenses on an SLR format camera it makes sense for manufacturers to produce APS-C only(or 4/3's or mirrorless) lenses .. but once the lens design exceeds the 50mm focal length it seems to require much less in the way of design compromises .. so why limit the longer focal length lens to APS-C only when a larger market bekons!


So one of the not so commonly mentioned benefits of this lens(provided that it does perform as well as the specs say it will), is that a faster aperture zoom lens is possible at the wider end of the focal range and in a size that is relatively small!
Relatively small in comparison to similar focal length lenses with slower aperture values(i.e Nikon 16-35/4 17-35/2.8 , etc .. Canon 16-35/2.8 17-40/4 .. etc, etc) and this lens is an f/1.8!

I'm not sure where you're seeing this point that you've made that APS-C wide angle lenses are not smaller than full frame capable lenses of similar specs?

[Lance B]

OK ... not really sure what you're referring to here Lance but lets put some figures into perspective here:

Sigma 30/1.4(APS-C only): Dimensions (Diameter x Length) φ74.2mm x 63.3mm
Nikon 35/1.4(Fullframe): Diameter x length Approximately 83 x 89.5 mm

APS-C a lot smaller(mainly in percentage terms)


Nikon 16-35/4VR: Diameter x length Approximately 82.5 x 125 mm
Tamron 17-50/2.8VC: LENGTH 94.5mm (no diameter given but filter diameter is 72mm, and the lens diameter looks to be very close to this .. maybe 2mm more)

Note that the Nikon lens is a much less extreme optic in that it's an f/4 .. one stop slower than the Tammy. Sigma's equivalent is about the same size as the Tammy.

At the ultra wide angle end of the scale, we get:

Tokina's 11-16/2.8: Dimensions 84x89mm
Nikon's 14-24/2.8: Dimensions 98x132mm


Pretty much as far as I can see .. the vast majority of APS-C only lenses are in fact on average about 15% smaller in physical dimensions(except weight) to their full frame counterparts.

Apart from the Sigma 50-150mm f/2.8, I doubt that we will ever see any lenses above about 50mm for APS-C sensored cameras(Nikon also has it's 85mm f/3.5 micro), as it appears to be a counterproductive exercise by the manufacturer.
Due to the extreme nature of the designs of wider angled lenses on an SLR format camera it makes sense for manufacturers to produce APS-C only(or 4/3's or mirrorless) lenses .. but once the lens design exceeds the 50mm focal length it seems to require much less in the way of design compromises .. so why limit the longer focal length lens to APS-C only when a larger market bekons!


So one of the not so commonly mentioned benefits of this lens(provided that it does perform as well as the specs say it will), is that a faster aperture zoom lens is possible at the wider end of the focal range and in a size that is relatively small!
Relatively small in comparison to similar focal length lenses with slower aperture values(i.e Nikon 16-35/4 17-35/2.8 , etc .. Canon 16-35/2.8 17-40/4 .. etc, etc) and this lens is an f/1.8!

I'm not sure where you're seeing this point that you've made that APS-C wide angle lenses are not smaller than full frame capable lenses of similar specs?

You're not comparing equivalent FOV. You need to compare a 24mm APS C lens with a 35mm FF lens, or a 14mm APS C lens with a 20mm FF lens etc. Unfortunately, Nikon has made ver few DX only lenses and the ones they have made are not really a direct equivalent, ie, some having different max apertures and some don't have VR.

A reasonable comparision is possibly the Nikon 24-70 f2.8 and the 17-55 f2.8, where;

24-70 = 83mm x 133mm 900gms and 77mm filter thread
17-55 = 86mm x 111mm 755 gms and 77mm filter thread.

To me these lenses are not all that different considering that the APS C sensor is 50% smaller than that from the FF sensor. However, we don't really have an exact equivalent for the 24-70 in APS C as it would really need to be an f2 17-55 lens to be a real equivalent and just imagine how big that would be!

Unfortunately, there are not many real equivalent DX (APSC) Nikon lenses to fully compare, but there is one DX lens we can use, the 35mm f1.8 and can compare it to the Nikon 50mm f1.8G:

50mm f1.8G = 72mm x 52.5mm 185gms and 58mm filter
35mm f1.8 DX = 70mm x 52.5mm 200gms and 52mm filter.

As you can see, the DX lens is no smaller than the FX lens for an equivalent FOV and again, to be a real equivalent it should be an f1.2-f1.4 lens!

Luckily, Pentax has made some APS C only lenses for their DSLR's and yu can do a few direct comparisons, like:

FA20mm f2.8 (FF) = 70mm x 44mm 255gms and 67mm filter
DA14mm f2.8 (APS C) = 84mm x 69mm 420gms and 77 filter!

As you can see, the 14mm is quite a bit bigger than it's FF counterpart!

[arthurking83]

You're not comparing equivalent FOV. ......

Well, in this case you'll never be happy then.

Your original comment was:

".... Laws of physics dictate that whatever the focal length, the aperture is going to be the ratio of that focal length regardless of format .... "

focal length and the ratio.

And now you want FOV equivalence too.

As you may well know, this is impossible to achieve on two different formats.


I agree that there are some lenses that have been designed for the smaller format that don't necessarily come in a smaller physical form than their larger format equivalent cameras .. and to be honest the comparison between the Nikon 17-55 and their 24-70 is actually a lame one on two counts;

1. the 17-55 actually can cover the full 135 format at the longer focal lengths
2. the 17-55 should be compared to the more equivalent (old) 28-70/2.8 which are of a similar era of design!


Anyhow, I now have to bow out of a discussion I can no longer comprehend.

[Lance B]

Well, in this case you'll never be happy then.

Your original comment was:

".... Laws of physics dictate that whatever the focal length, the aperture is going to be the ratio of that focal length regardless of format .... "

focal length and the ratio.

And now you want FOV equivalence too.

What are you on about? I was always saying that you have to have FOV equivalence, as this whole discussion was about equivalence between APS C and FF. To make it fair on both formats, they have to be seen as equivalent in FOV ie focal length equivalents for FF and APS C, so a 14mm lens on APSC is equivalent to 21mm on FF which will give the same FOV, like a 35mm on APS C will give almost the same FOV as a 50mm on FF etc. I don't know why you would not think that I was somehow differentiating focal length and FOV.

What I said about ".... Laws of physics dictate that whatever the focal length, the aperture is going to be the ratio of that focal length regardless of format .... " is still exactly correct, the aperture is the ratio of focal length to actual aperture size and was relevent when considering that the equivalent APS C lens really needs to have a wide open aperture 1 stop faster than it's FF counterpart, so a 14mm f2.8 lens on APS C need only be 21mm f4 only FF for the same DOF wide open.

As you may well know, this is impossible to achieve on two different formats.

Really? 14mm FOV on APSC isn't the equivalent of 21mm FOV on FF? Last time I looked it was almost exactly the same FOV.

I agree that there are some lenses that have been designed for the smaller format that don't necessarily come in a smaller physical form than their larger format equivalent cameras .. and to be honest the comparison between the Nikon 17-55 and their 24-70 is actually a lame one on two counts;

1. the 17-55 actually can cover the full 135 format at the longer focal lengths

But it isn't because you get vignetting at the wider angles, how can that be construed as being designed to be used on FF???? It is not a FF lens!!! and cannot be considered as one, it is a DX lens, period and it was designed as one.

2. the 17-55 should be compared to the more equivalent (old) 28-70/2.8 which are of a similar era of design!

Rubbish and irrelevent. The Nikon 28-70 f2.8 was designed and first built in 1999. The Nikon 17-55 f2.8 was first designed and bult 2004, so was a whole 5 years later in development. The 24-70 f2.8 was only 2007, just 3 years after the 17-55, both designed in the digital era, so they are a lot closer in design to each other than the 28-70.

Anyhow, I now have to bow out of a discussion I can no longer comprehend.

I am sorry you can't follow simple logic and equivalence.

The Sigma 18-35 f1.8 APS C lens would be equivalent in FOV and focal length and max aperture to a 27mm-52mm f2.5 FF lens. Hardly a stressful design for FF.

[arthurking83]

FWIW: the Nikon 35/1.8 Dx lens has the ability to form an image almost over the entire full frame sensor .. even tho it's design is specific to the APS-C format.

If we take into account lenses that are designed more closely for their respective format sizes, we see that the majority of these lenses are smaller than their full frame equivalents.

Where you can quote examples where they are the same or larger, I can equally find more examples where they are smaller by a fair margin .. so the debate is only going to go round in an endless circle.

But what is important in these lenses is how much of an image circle they actually form!

It's obvious that for some manufacturers a specific level of quality is of paramount importance, and they design a specific lens in a specific manner.
This point doesn't mean that the APS-C lens isn't going to be smaller due to the laws if physics of lens requirements

That is, that the APS-C 35/1.8 is not smaller than the full frame 50/1.8 or f/2.0 of f/4 doesn't mean that it shouldn't be. The fact is that they can be(as exampled by Sigma's 30/1.4) and that the manufacturer simply hasn't troubled themselves with the size of the lens for APS-C.


Nikon do this themselves all the time too even with their full frame lenses.
For example again. Look at Nikon's f/2.8 prime lenses in the 24 - 60mm range and they're all a heck of a lot smaller than the Nikon 24-70/2.8 lens
Each one of those prime lenses in the F/2.8 range and between 24mm and 60mm(that I know of) are all a lot smaller than the zoom lens of equivalent focal length .. be that the 28-70 or 24-70mm

Do we at least agree on this?

If so, then what of the 14-24/2.8 vs the 14/2.8 prime lens.
Both of which are in fact quite close in physical size .. where the norm for zoom lenses is that they will generally be 2x or 3x large than a prime lens of similar focal length!
This is obviously a design consideration taken by a manufacturer in developing the lens ... in this instance size must have been of utmost importance to Nikon in the design of the 14-24/2.8.


What I'm afraid you are confusing with the laws of physics and lenses designed for the smaller format has in fact more to do with the design brief of the manufacturer.

As I've already said too tho.. up to a certain focal length point there is no point for a manufacturer to produce a lens specific to the APS-C format .. and by that I'm referring to most manufacturers except Olympus who only have vested interests in the 4/3rds format.

But for Sigma to produce an APS-C only 135mm f/2.8 is a wasted effort, as it seems to be almost as easy to make it encompass the full frame format anyhow .. and they'd be mad not to design it for both formats.

This focal length point appears to be roughly in the 50-100mm range as this is where lenses specific to the APS-C format cease to exist.

Except for the Sigma 50-150/2.8 which is a strange lens. Possibly a marketing exercise by Sigma .. or whatever.. this lens is strangely large for the physical specs it supposedly has.
It is as large as their 70-200/2.8(both lenses with OS) ... which in a theoretical sense makes absolutely no sense.
But if you read the test review for the 50-150/2.8, you can easily analyse the design compromises Sigma has made for this particular lens ...
Comments such as "The Sigma 50-150mm ƒ/2.8 OS is quite simply one of the sharpest zoom lenses we have had the opportunity to test ... " and " .... Stopping down the lens provides practically insignificant improvements in image sharpness: this lens is just excellent at every setting." clearly point to a design where no compromises existed in the ability of the lens!
This obviously precluded minimising the physical size in the design brief for that lens.

So, I think you have confused isolated instances of design compromises that a specific manufacturer has taken into account with the reality of lenses for the real world.

If this wasn't the case then the argument would be much more simple .. no lens designed for specifically for APS-C would exist in a smaller physical size than it's full frame counterpart .. and yet they do!

And this lens is one of those instances.
Why? because we know that to design a wide angle lens with a large aperture is increasingly hard. Forget FOV .. we're now referring strictly with the physical limitations of the lens design and focal lengths!

We know that a 18-35 with an aperture of f/4 is going to have a set physical dimension witnessed by the Nikon 16-35 .. and estimated with the Nikon 18-35/3.5-4.5 .. also the Nikon 17-35/2.8.
We know the sizes of these lenses they exist.
We also know from previous discussions that as the aperture is designed to be faster these lens types grow significantly.

Yet Sigma's new lens is physically smaller in every aspect. That the lens is not significantly smaller is a moot point .. the size of the aperture here is the important point .. it's supposedly 1 1/3stops faster than the slowest of the Nikon lenses mentioned.
Look at any other lens type where the aperture speed increases by 1 and 1/3 stop and the faster lens grows in size by at least 2x .. usually more.

I'm hoping that you're getting the picture here.
I fully understand what you're trying to express. But as already said .. you can't compare the lens designs in a strict manner the way you have due to the nature of the two formats.


Put simply if lens design was as simple as the theory of physics .. a 16-35mm f/4 lens should have a physical size of only 35mm length x 8.75 mm diameter.
Whereas the 18-35/1.8 should be 35mm length x 10mm diameter as maximums .. but this doesn't exist in the real world and the lenses real sizes are much more different as we know.

Yet the theoretically larger Sigma 18-35/1.8 is actually smaller than the Nikon 16-35/4 ... once again this is due to what the manufacturer determines to be of importance in the properties of the lens for it to be successful as a marketable product .... and this lens succeeds in proving that APS-C lenses can be made smaller if the manufacturer tried harder.

Going back to your argument that FOV equivalence needs to be factored into the equation, a quick look at the Olympus 300/2.8 compared to the Nikon 600/4 .. which by all accounts are theoretically equivalent.
The Olympus is significantly smaller than the 600 Nikon which provides FOV equivalence. But the two lenses can't really be compared as they are different lenses .. providing different levels of magnification.

You need to keep the argument restricted to one variable only when it comes to lenses for use on different formats. Once you jumble the argument up with two different variables, it becomes confusing and you get nowhere with it.



So what you are saying with respect to focal length FOV and aperture ratio is that a 14mm lens on APS-C provides the same magnification as a 21mm lens on full frame as well?

..... or is FOV the only possible measure that a lens is judged on?


Anyhow like I said.... with the introduction of multiple variables, it's difficult if not impossible to keep up with what you want to argue about .. it has nothing to do with logic.

Your logic will dictate that a 14mm lens on APS-C will provide not only the same FOV, but that it also has the same magnification as the 21mm lens on full frame.

This is logic that I don't understand then.

[Lance B]

FWIW: the Nikon 35/1.8 Dx lens has the ability to form an image almost over the entire full frame sensor .. even tho it's design is specific to the APS-C format.

If we take into account lenses that are designed more closely for their respective format sizes, we see that the majority of these lenses are smaller than their full frame equivalents.

Only if we take the tele end into consideration.

In my initial post in this thread, if you care to re-read it, I actually said: "but this was only realised at the longer focal lengths where, say a 200mm lens on FF is "equivalent" to a 135mm on APS C", so, I don't know why you are bringing this up. I did say a caveat, though, and this was that you actually need to factor in the 1 stop faster requirment of APS C to have the same wide open aperture DOF consideration as APS C has inherent 1 stop extra DOF due to the format size, I said: "However, if you want to get the same narrow DOF on APS C, you need to have the APS C lens one stop faster so, taking the example of the 200mm lens on FF and it was f4, then you require the 135mm lens to be f2.8 on APS negating the benefit of APS C somewhat. ". I don't think that is too difficult to understand, surely.

Where you can quote examples where they are the same or larger, I can equally find more examples where they are smaller by a fair margin .. so the debate is only going to go round in an endless circle.

I haven't seen too many, if any real equivalent AOS C lenses at the wide end that are smaller by any margin than their FF counterparts.

But what is important in these lenses is how much of an image circle they actually form!

Exactly! Now you're getting it!

It's obvious that for some manufacturers a specific level of quality is of paramount importance, and they design a specific lens in a specific manner.
This point doesn't mean that the APS-C lens isn't going to be smaller due to the laws if physics of lens requirements.

At the wide end, they basically are at least as big as their FF counterparts due to the design constraints of the old film camera lens mount that Canon/Nikon/Pentax etc used so as they didn't have to design a specific lens mount for APS C and therefore adopted the 35mm film lens mount. It is this very decision that has meant that they had to design the wide angle lenses in a specific way so as to avoid issues likelight drop off at the corners of the image circle and other desing considerations. For this reason, these wide angle lenses therefore did not realise the benefit of being smaller due to the sensor size. Do an internet serarch and you will see that I am correct in this matter. Olympus, however, did design their 4/3rds lens mount system from the ground up and they do have an advantage by generally beinfg able to desing smaller wide angle lenses than their FF conterparts (and APS C for that matter).

That is, that the APS-C 35/1.8 is not smaller than the full frame 50/1.8 or f/2.0 of f/4 doesn't mean that it shouldn't be.

Sorry, that is just plainly wrong. Why on earth would they desing the 35mm f1.8 lens so that it was bigger than required? There was no need to make it bigger to suit any other format as they already have a FF 35mm f1.8. No, they deigned the 35mm DX lens that size because it needed to be that size.

The fact is that they can be(as exampled by Sigma's 30/1.4) and that the manufacturer simply hasn't troubled themselves with the size of the lens for APS-C.

Really? The Sigma 30mm f1.4 is a APS C lens only and has a FOV of 45 degreees on APS C is 77mm x 59mm and weighs in at 430gms, the Nikon 50mm f1.4G (the closest equivalent for FF) has a FOV of 46 degrees (in otherwords almost the exact same FOV) on FF and is 74mm x 54mm and weighs in at 280gms. Seems as though the Sigma is larger to me.

Nikon do this themselves all the time too even with their full frame lenses.
For example again. Look at Nikon's f/2.8 prime lenses in the 24 - 60mm range and they're all a heck of a lot smaller than the Nikon 24-70/2.8 lens
Each one of those prime lenses in the F/2.8 range and between 24mm and 60mm(that I know of) are all a lot smaller than the zoom lens of equivalent focal length .. be that the 28-70 or 24-70mm.

Do we at least agree on this?

No, because it is a completely absurd comparison. You cannot compare a zoom with a prime.

If so, then what of the 14-24/2.8 vs the 14/2.8 prime lens.

Again, an absurd comparison.

Both of which are in fact quite close in physical size .. where the norm for zoom lenses is that they will generally be 2x or 3x large than a prime lens of similar focal length!
This is obviously a design consideration taken by a manufacturer in developing the lens ... in this instance size must have been of utmost importance to Nikon in the design of the 14-24/2.8.

Again, really? The Nikon 14mm f2.8 is 87mm x 87mm and 670gms, the Nikon 14-24 f2.8 is 98mm x 132mm and 10000gms! Quite a large difference if you ask em.

What I'm afraid you are confusing with the laws of physics and lenses designed for the smaller format has in fact more to do with the design brief of the manufacturer.

It seems as though I have pointed out that you are confusing the issue, not me. I have refuted each of your arguments.

As I've already said too tho.. up to a certain focal length point there is no point for a manufacturer to produce a lens specific to the APS-C format .. and by that I'm referring to most manufacturers except Olympus who only have vested interests in the 4/3rds format.

But for Sigma to produce an APS-C only 135mm f/2.8 is a wasted effort, as it seems to be almost as easy to make it encompass the full frame format anyhow .. and they'd be mad not to design it for both formats.

At the tele end, we are talking a different kettle of fish. If we think of the wide end, we need large fron elements in order to encompass the wide FOV. At the tele end, the laws of physics come into play with regards to focal length over aperture, so, if we have a 200mm f2.8 lens, it will require a front element of 200/2.8 = 72mm and this is regardless of format, ie whatever the size of the sensor, a 200mm lens will need a front element of at least 72mm. Therefore, to make a 200mm lens with an f2.8 aperture, it will be the same size regardless of format. The benefit for APS C, however, is that you can use a 135mm f2.8 lens to sort of be the equivalent of a 200mm f2.8 lens on FF. However, as I stated previously, to be a true equivalent, the 135mm APS C lens really needs to be a 135mm f2 lens if we consider the sytem as a whole and this means things like the DOF being narrower by 1 stop on FF and FF sensors having about 1 stop better ISO and DR when equivalent time frame release of sensors is considered (that's another discussion).

This focal length point appears to be roughly in the 50-100mm range as this is where lenses specific to the APS-C format cease to exist.

Because the laws of physics show that you can't make the lens smaller as the front element has to be what it has to be as I pointed out. The "advantage" is that you get to use a 135mm f2.8 lens on APS C as compared to 200mm f2.8 on FF, discounting the DOF considerations as also pined out above.

Except for the Sigma 50-150/2.8 which is a strange lens. Possibly a marketing exercise by Sigma .. or whatever.. this lens is strangely large for the physical specs it supposedly has.
It is as large as their 70-200/2.8(both lenses with OS) ... which in a theoretical sense makes absolutely no sense.
But if you read the test review for the 50-150/2.8, you can easily analyse the design compromises Sigma has made for this particular lens ...
Comments such as "The Sigma 50-150mm ƒ/2.8 OS is quite simply one of the sharpest zoom lenses we have had the opportunity to test ... " and " .... Stopping down the lens provides practically insignificant improvements in image sharpness: this lens is just excellent at every setting." clearly point to a design where no compromises existed in the ability of the lens!
This obviously precluded minimising the physical size in the design brief for that lens.

Not really relevent to the discussion.

So, I think you have confused isolated instances of design compromises that a specific manufacturer has taken into account with the reality of lenses for the real world.

LOL. It is not me that is confused. I have refuted all your theories. Do an internet search and you will see I am correct.

If this wasn't the case then the argument would be much more simple .. no lens designed for specifically for APS-C would exist in a smaller physical size than it's full frame counterpart .. and yet they do!

Basically only at the long end, which is what I said from my opening post in this thread (see my first responses in this post), and only if you take the equivalent in FOV/Focal Length disregarding DOF considerations with wide open aperture, ie, a 135mm f2 lens will not be smaller thana 200mm f2.8 lens. If we look at Canon's 135mm f2 lens it is 82.5mm x 112.0mm, 72mm filter size, 750g and their 200mm f2.8 lens is 83.2 x 136.2mm, 72mm filter size, 765g - so, you can see that they are almost identical in size! This means that on APS C, the 135mm f2 will have identical FOV and identical DOF when used wide open or one stop down etc to the 200mm f2.8 lens on FF.

And this lens is one of those instances.
Why? because we know that to design a wide angle lens with a large aperture is increasingly hard. Forget FOV .. we're now referring strictly with the physical limitations of the lens design and focal lengths!

You can't forget FOV as this is the resultant of focal length on a given sensor size!!

We know that a 18-35 with an aperture of f/4 is going to have a set physical dimension witnessed by the Nikon 16-35 .. and estimated with the Nikon 18-35/3.5-4.5 .. also the Nikon 17-35/2.8.
We know the sizes of these lenses they exist.
We also know from previous discussions that as the aperture is designed to be faster these lens types grow significantly.

Yes, and your point being? This is irrelevent unless you are comparing the APS C lens to the FF lens of the same FOV/focal length.

Yet Sigma's new lens is physically smaller in every aspect.

Compared to what? I do not know of a FF lens with the same zoomFOV/Focal Length with which to compare it to. It is an APS C lens with a variable focal length/variable FOV of 18-35 f1.8/76.5-44.2 degrees - this would need to be a FF equivalent of 27mm-52mm f2.5 and they are a rarity for FF in this range.

That the lens is not significantly smaller is a moot point .. the size of the aperture here is the important point .. it's supposedly 1 1/3stops faster than the slowest of the Nikon lenses mentioned.
Look at any other lens type where the aperture speed increases by 1 and 1/3 stop and the faster lens grows in size by at least 2x .. usually more.

Realistically, the FF equivalent is 27-52 f2.5, you have to remember the DOF considerations of APS C having 1 stop more DOF for each aperture. There is more to this discaussion that just the DOF considerations as it also ventures into APS C vs FF on things like high ISO noise, DR etc, but that is for another discussion. So, the aperture of the FF lens really only needs to be f2.5, ie f1.8 x 1.414 (square root of 2). To design a FF lens like this would be easy as it has basically already been done with many lenses from many manufacturers, 24-70 f2.8 is close enough to the f2.5 and yet covers a larger zoom range.

I'm hoping that you're getting the picture here.

That is really funny. I have a complete grasp of the situation, it is you that is missing the poiny. I have refuted all your arguments and proved them incorrect. As I say, do an internet search of this topic andyou will see I am correct.

quote]I fully understand what you're trying to express.[/quote]

If you understood, you wouldn't need to argue.

But as already said .. you can't compare the lens designs in a strict manner the way you have due to the nature of the two formats.

Well, actually you can and you must to have a level playing field. You cannot take one supposed advantage of one sytem yet ignore the disadvantages of that system.

Put simply if lens design was as simple as the theory of physics .. a 16-35mm f/4 lens should have a physical size of only 35mm length x 8.75 mm diameter.

I've said it once and I will say it again, it's a zoom. You cannot compare a zoom with a prime. SHEESH!! Bows head and shakes.

Whereas the 18-35/1.8 should be 35mm length x 10mm diameter as maximums .. but this doesn't exist in the real world and the lenses real sizes are much more different as we know.

Yet the theoretically larger Sigma 18-35/1.8 is actually smaller than the Nikon 16-35/4 ... once again this is due to what the manufacturer determines to be of importance in the properties of the lens for it to be successful as a marketable product .... and this lens succeeds in proving that APS-C lenses can be made smaller if the manufacturer tried harder.

I cannot believe that you are comaring a APS C lens to a FF lens of the same focal length when it is the FOV that needs to be compared. Quite unbelievable!! You have to compare the APS C 18-35 f1.8 lens to a FF lens of the same focal Length/ FOV and that would be a 27-52mm f2.5 lens!!! How many more times do I need to spell it out!!

[quote]Going back to your argument that FOV equivalence needs to be factored into the equation, a quick look at the Olympus 300/2.8 compared to the Nikon 600/4 .. which by all accounts are theoretically equivalent.
The Olympus is significantly smaller than the 600 Nikon which provides FOV equivalence. But the two lenses can't really be compared as they are different lenses .. providing different levels of magnification.

No, they do not they have the exact same FOV and almost the same magnification on their respective formats. Magnification difference only comes about by due to the different close focus of each lens and this is a design cinsideration by each manufacturere and nothing to do with the differing sensors. The difference, however, is very minimal to the point of being considered basically the same. The Oly 300 f2.8 has a minimum focus distance of 2.4mts, whereas the Nikon 600 has a close focus of 5mts, to be equal, the Oly would need to be 2.5mts due to the 2x conversion factor, and then you would find the magnification exactly the same. The thing you also need to remeber is that the 300 f2.8 lens from Olympus needs to be considered the equivalent of a 600mm f5.6 on FF due to it's 2x crop factor which is a 2 stop difference of the 4/3rds sensor.

This is why Olympus went with their top flight zooms as f2 lenses (which really should be f1.4 lenses) to equal the DOF considerations of a FF f2.8 lens. The Olympus f2 lenses, for DOF considerations (which bring into play the sensors for high ISO noise and DR), is really an f4 lens equivalent for FF and an f2.8 lens for APS C. DO the calculations yourself on the On-Line DOF calcualtor if you don't believe me:

http://www.dofmaster.com/dofjs.html

So a 100mm lens set at f2 and 10mts on an Olympus 4/3rds camera = .59mt total DOF. the "equivalent" 200mm lens set to f4 on FF at 10mts = the same .59mt total DOF.

You need to keep the argument restricted to one variable only when it comes to lenses for use on different formats. Once you jumble the argument up with two different variables, it becomes confusing and you get nowhere with it.

So what you are saying with respect to focal length FOV and aperture ratio is that a 14mm lens on APS-C provides the same magnification as a 21mm lens on full frame as well?

Magnification is a slightly different thing as that is a factor of subject to camera distance and/or close focus ability. What I am saying, and have been saying all along, is that FOV and focal length are linked for their respective formats. A 14mm APS C lens has the same or alomst identical FOV as a 21mm lens on FF. This is what you have to compare when comparing formats as well as maximum wide open aperture.

..... or is FOV the only possible measure that a lens is judged on?

FOV is a function of focal length on a given sensor size.

Anyhow like I said.... with the introduction of multiple variables, it's difficult if not impossible to keep up with what you want to argue about .. it has nothing to do with logic.

Seems logical to me and all the discussions I have read on the internet, a 14mm lens on APS C has the same FOV as that of a 21mm les on FF and yet the 14mm lens is physically larger. I pointed out many wide angle lenses that this applies to here as well, but they are just some of those that are out there when comparing equivalents. I'll go back to my oiginal point and that is, wide angle APS C lenses rarely give you a smaller lens when they equivalent FOV/focal length and aperures are compared. I also think you need to add the fact that they also need to be 1 stop faster for true equivalence. They are generally as big and in some cases larger than their FF counterparts.

Your logic will dictate that a 14mm lens on APS-C will provide not only the same FOV, but that it also has the same magnification as the 21mm lens on full frame.

Never said they give the same mginification as that is a slightly different thing as this is a factor of camera to subject distance and/or minimum focus, but if they are the same distcance form the respective cameras, then manification should be the same or near as damn it to each other.

This is logic that I don't understand then.

Then read what I have said and you will understand.

[ameerat42]

The latest news...

I've just heard that Σ are withdrawing this lens from sale due to the controversy it has generated.
(Apparently, L Tolstoy is seeking copyright infringement damages.)

...from the perpendicular universe