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View Full Version : Sigma 10-20 or 12-24?


icecavern
04-01-2007, 17:47
Right I'm looking for a wide lens as I have a 24-70 but it's just not wide enough. Right now I can get a new Sigma 12-24mm f4.5-5.6 EX DG ASPHERICAL or a Sigma 10-20mm f/4-5.6 EX DC HSM for £299 but not sure which to go for. Any opinions on which would be the better lens?

Witch
04-01-2007, 17:54
I'm glad you posted this thread. Having convinced myself I'd made up my mind to the 12-24mm I'm now wavering again.

would I be right in assuming that you use Canon? If so, and you ever have any ambitions towards owning a 1 series then you should give serious consideration to the 12-24mm as the other won't work on F/F. However, (and the reason I'm now unsure) it's a nightmare trying to use any form of filter with the 12-24 from what I can gather. I'm swaying more and more towards the idea of buying that 10-20 now, and then changing if I ever need to, in the hope that by that stage Sigma will be making something wide to suit FF without using ND grads being so impractical.

Hopefully someone who uses, or have used, both, will chance along in a minute and give us some sensible assistance! :)

Muler
04-01-2007, 18:06
Seeing as icecavern ownsa D2X, i presume he plans to use it on his nikon. if im right, the 12-24mm is actually a full frame lens yes? there for it would actually be a 18-30mm on his d2x.

as for the 10-20mm, as its "DC", that'd mean you'd be getting the true 10-20mm on your d2x. by that i mean the lens its self is made for cropped sensors, so would really be a 10mm at 1.5xcrop, as the 12-24mm isnt made for cropped sensors, so it'd actually be a 18-30mm.

and it just so happens im selling a sigma 10-20mm nikon mount too!
might want a chat about that too mate. :thumbs:

Jonnyreb
04-01-2007, 18:13
the 10-20 is a DC lens, but this still means its only 10-20 on a 35mm camera or full frame sensor.

Although a canon man, my 10-20 is actually 16-32 on the 1.6x crop of my EOS 30d.

The 12-24 is really 12-24 on my full frame EOS 5d.

That being said, icecavern will still get a wider fov with the 10-20 as they stack up as 15-30 (for the 10-20) and 18-36 (for the 12-24).

From personal expierience, the 12-24 is a much better lens

Joe T
04-01-2007, 18:16
as for the 10-20mm, as its "DC", that'd mean you'd be getting the true 10-20mm on your d2x. by that i mean the lens its self is made for cropped sensors, so would really be a 10mm at 1.5xcrop, as the 12-24mm isnt made for cropped sensors, so it'd actually be a 18-30mm.


Incorrect Im afraid. DC lenses only fit on APS-C lenses, but the focal length is still as rated on the lens. Like other lenses on APS-C cameras the crop factor for the field of view still applies.

Witch
04-01-2007, 18:23
Seeing as icecavern ownsa D2X....

Hmmm, I've noticed that too, now!

:embarrassed:

Muler
04-01-2007, 18:26
Incorrect Im afraid. DC lenses only fit on APS-C lenses, but the focal length is still as rated on the lens. Like other lenses on APS-C cameras the crop factor for the field of view still applies.

i believe your refering to "DG" as aposed to "DC".

i quote from sigma themselves:

"DC (DC Lens)
These are special lenses designed so that the image circle matches the smaller size of the image sensor of most digital SLR cameras. Their specialized design gives these lenses the ideal properties for digital cameras, the compact and lightweight construction is an added bonus ! including compact and lightweight construction."

i could be very wrong, but im 99% im right

Joe T
04-01-2007, 18:31
Muler, there is nothing in that quote that suggests that they mark the focal length differently.

Yes, they produce a smaller image circle, but this does not affect the actual focal length of the lenses.

Joe T
04-01-2007, 18:33
See this for example:

50-150mm f/2.8 EX DC HSM
Ultra-fast telephoto zoom giving the popular 70-200mm focal length when used on DSLRs with APS-C size image sensors.

Muler
04-01-2007, 18:35
Muler, there is nothing in that quote that suggests that they mark the focal length differently.

Yes, they produce a smaller image circle, but this does not affect the actual focal length of the lenses.

well if its a smaller image circle, then it'd be in proportion with the smaller sensor?

Muler
04-01-2007, 18:37
See this for example:


not a clue then, i must be wrong

King_Boru
04-01-2007, 18:42
The crop factor still applies. I dont know the technical reasons behind it, it is confusing to say the least. DX, DC whatever, you still need to calculate the crop factor. So really, the 10-20 is a 15-30 replacement (the older full frame ultra wide-angle).

If somebody can explain it in lame man terms then please go ahead.

King.

Joe T
04-01-2007, 18:45
The only thing that DC means is that you cant fit it to a full frame (i.e. 35mm) camera, without serious vignetting.

Its the same as Nikons DX lenses or Canons EF-S. Although with some of these there are more reasons why you shouldnt fit them.

Consider the lenses used for Medium format photography. These have the same focal lengths as lenses designed for SLR photography, but because the image sensor (in this the medium-format film) is so large than a 150mm lens becomes a wideangle lens.

Joe T
04-01-2007, 18:47
icecavern, back to your original point.

I would discount the Sigma 12-24, due to the filter issue. Its also quite an old lens now.

The two lenses I would be looking at are the Sigma 10-20 (as you mentioned) and the Tokina 12-24. It is hard to pick between these two, as they are both excellent lenses.

If your budget can stretch to the Nikkor 12-24, then I would get that tbh.

mij
04-01-2007, 18:57
Here begineth the sermon:

Focal length is a physical property of a lens and has nothing to do with the size of the sensor of film behind it. Technically it is the distance from the rear nodal lens element and the image plane, the sensor of film.

A 50mm lens on a 35mm camera will give a smaller angle of view than a 50mm on a 645 medium format camera. Similarly on a camera with an APS-C sized sensor the angle of view will be smaller than the 35mm camera.

It makes no difference whether it is a "full frame" lens or an EF-S/DX/DC/Di II lens, the focal length remains the same and so if you want to know the 35mm equivalent field of view on your camera you will need to multiply it by the appropriate factor of your sensor size. Always.

There is only one system of measuring a lenses focal length and what that number means to the field of view will depend purely on the sensor or film size you are using, not on the the size of the image circle cast by the lens.

A 50mm full frame lens on a Nikon DSLR will give you an equivalent field of view as a 75mm lens on a 35mm camera.

A 50mm DX lens on a Nikon DSLR will give you an equivalent field of view as a 75mm lens on a 35mm camera.

I repeat the point because it is commonly misunderstood.

It is also worth noting that it the 50mm lens on a Nikon DSLR will not give the same image as a 75mm lens on a 35mm camera because the focal length effects the depth of field as well as the angle of view. The smaller the focal length the greater depth of field.

Or to put it another way:

A 50mm lens on a Nikon DSLR gives the same depth of field as a 50mm lens on a 35mm camera, but has a smaller angle of view.

A 50mm lens on a Nikon DSLR gives the same angle of view as a 75mm lens on a 35mm camera, but has a greater depth of field.

Michael.

Joe T
04-01-2007, 19:00
^^^ Thats what I meant :p

Thanks Michael :)

mij
04-01-2007, 19:03
In answer to the original question, the difference of 2mm on a wide angle lens can be dramatic, the 10-20mm also has HSM (Sigma's equivalent to Nikon's Silent Wave motor). Unless you need the 20-24mm range I would suggest going with this model.

The benefit of the 12-24 is that it is, I believe, the widest rectilinear (non-fisheye) lens available for 35mm cameras and so if you plan on using it with a film camera too then it would be a good choice. You can use a 10-20mm lens on a 35mm camera but it will give you noticeable fisheye style vignetting, though this might be artistically desirable.

Michael.

mij
04-01-2007, 19:04
^^^ Thats what I meant :p

Thanks Michael :)

No problem, if I had not spent so long typing it out and noticed you had already explained I would not have bothered!

Michael.

King_Boru
04-01-2007, 19:09
Thanks. Nice to have it explained,... I knew t was something along thse lines but was never certain enough to open my gob.

King.

Ross
04-01-2007, 20:29
I have both, the 12-24 is sharper but lacks front fitting filters and also the wideness of the 10-20. It's also a good deal heavier.

RichardtheSane
04-01-2007, 20:54
I have gone from a 10mm to a 12mm (widest) lens.
tbh I have not noticed the difference as much as I thought I would. they are both bloody wide!

icecavern
04-01-2007, 21:24
This is the problem, everyone prefers the one they have, very few people have compared both :(

It'll be a Nikon fitment one, wish I could afford the Nikon 12-24 but that's out of the question unfortunately :(

Maybe I'll toss a coin lol

TG.
05-01-2007, 00:00
Here begineth the sermon:

Focal length is a physical property of a lens and has nothing to do with the size of the sensor of film behind it. Technically it is the distance from the rear nodal lens element and the image plane, the sensor of film.

A 50mm lens on a 35mm camera will give a smaller angle of view than a 50mm on a 645 medium format camera. Similarly on a camera with an APS-C sized sensor the angle of view will be smaller than the 35mm camera.

It makes no difference whether it is a "full frame" lens or an EF-S/DX/DC/Di II lens, the focal length remains the same and so if you want to know the 35mm equivalent field of view on your camera you will need to multiply it by the appropriate factor of your sensor size. Always.

There is only one system of measuring a lenses focal length and what that number means to the field of view will depend purely on the sensor or film size you are using, not on the the size of the image circle cast by the lens.

A 50mm full frame lens on a Nikon DSLR will give you an equivalent field of view as a 75mm lens on a 35mm camera.

A 50mm DX lens on a Nikon DSLR will give you an equivalent field of view as a 75mm lens on a 35mm camera.

I repeat the point because it is commonly misunderstood.

It is also worth noting that it the 50mm lens on a Nikon DSLR will not give the same image as a 75mm lens on a 35mm camera because the focal length effects the depth of field as well as the angle of view. The smaller the focal length the greater depth of field.

Or to put it another way:

A 50mm lens on a Nikon DSLR gives the same depth of field as a 50mm lens on a 35mm camera, but has a smaller angle of view.

A 50mm lens on a Nikon DSLR gives the same angle of view as a 75mm lens on a 35mm camera, but has a greater depth of field.

Michael.


thanks for explaining this as i bought it up on another thread regarding the sigma 17-70mm lens, which king boro explained a little about, but this is a bit more in dept, i was also under the impression that the sigma dc lense's gave the true field of view on a nikon DSLR, so that being the case that they don't what is the point of them ? and why are they different to any other len's you may buy ? as on the sigma website they advertised as digital camera lense's only :thinking:

Joe T
05-01-2007, 05:58
Like I said above, they are designed for digital cameras (APS-C sized sensors) and only give an image circle that fits such a sensor. ON a 35mm 'full frame' they will cause vignetting.

The smaller image circle means that hte lenses can be physically smaller and lighter.

Muler
05-01-2007, 15:53
Like I said above, they are designed for digital cameras (APS-C sized sensors) and only give an image circle that fits such a sensor. ON a 35mm 'full frame' they will cause vignetting.

The smaller image circle means that hte lenses can be physically smaller and lighter.

kind of stupid though, as i'd love to use a 10mm on my camera

Joe T
05-01-2007, 16:01
kind of stupid though, as i'd love to use a 10mm on my camera

Thats just it. 10mm full-frame non-fisheye lens is almost impossible to manufacture, and if it did it would be very very expensive indeed!

Fisheye lenses of this size are available, such as the Nikkor 10.5mm fisheye.

Im not sure that producing smaller and lighter lenses for smaller sensors is particularly stupid :shrug:

Muler
05-01-2007, 16:22
the 10.5mm is for cropped sensors though isnt it?

King_Boru
05-01-2007, 16:29
Im not sure that producing smaller and lighter lenses for smaller sensors is particularly stupid :shrug:

Agree with you there! Was using a Sigma 50-150 f2.8 the other week and it was great. Has the same coverage as a 70-200 f2.8 FF and weighs so so so much less.

TG.
05-01-2007, 16:49
kind of stupid though, as i'd love to use a 10mm on my camera


i'm guessing what muler means is kind of stupid saying it's a 10-20mm len's when it's not, well at least on a DSLR it's not unless you have a full frame sensor, it's kind of deceiving really, i mean if i would have bought the sigma 10-20mm len's to use on my D50 that's what i would expect to be getting, when in reality i'm not, if that makes sense :shrug:

Joe T
05-01-2007, 17:06
You are still getting a focal length of 10mm!!! You just get a different angle of view than if you are using film!!!

TG.
05-01-2007, 17:21
You are still getting a focal length of 10mm!!! You just get a different angle of view than if you are using film!!!


which i guess means a cropped view, so the only way around it is to have a full frame sensor ?

King_Boru
05-01-2007, 17:27
which i guess means a cropped view, so the only way around it is to have a full frame sensor ?

Read up and read it 3 or 4 times. It will make sense.

mij
06-01-2007, 02:10
i'm guessing what muler means is kind of stupid saying it's a 10-20mm len's when it's not, well at least on a DSLR it's not unless you have a full frame sensor

The thing to remember about focal length is that it is only a measurement of one aspect of the lens, the effect it has on the image you record is down to the sensor or film size, not the focal length. A 10-20mm lens is always going to be a 10-20mm lens whatever sized sensor or film is behind it, and whether the image it casts is larger or smaller than it can record.

On medium and large format systems 50mm is considered a wide, on a 35mm camera it is "normal", for a DSLR with an APS-C sensor it is a short telephoto, while on a digital compact camera it was would be a very long telephoto. The one thing they all have in common is that they the focal length is 50mm regardless.

I think the biggest sources of confusion about focal length comes from DSLR cameras being a successor to 35mm film, and in most cases retaining the same lens mounts and so lens compatibility, that people try to relate the focal length to a 35mm system giving it two meanings. This is why there was never confusion about the different effects of a focal length between other systems, because they were treated as separate and not compared in the same way.

It also does not help that even amongst DSLR cameras there is not one standard sensor size: Nikon ones are 2/3rds the size of a 35mm frame, Canon uses 5/8ths the size, while Four-Thirds system sensors are half the size. And that is just a rounded average. The 35mm equivalent field of view for Sigma's 10-20mm lens is 15-30mm on a Nikon, 16-32mm on a Canon, and 20-40mm on a Four-Thirds camera.

It would be confusing enough to consumers to have to understand two different systems of measuring lenses if Nikon and Canon used the 35mm equivalent figures for their DX and EF-S lens ranges. For companies like Sigma they would need to use different names for each mount they support.

Thankfully that manufacturers always giving the correct focal length is something that actually helps us because we do not have to worry about such things. A 50mm lens on a D80, for example, will give the same view whether it is a DX or DC lens or not. It would be a lot more confusing if you had two 50mm lensed and had to start wondering whether one is normal and the other a telephoto.

As far as I am aware the Sigma 12-24mm lens is the largest rectilinear (non-fisheye) lens you can get for a 35mm frame camera. A 10mm lens on this format would, as Joe said, be extremely expensive and suffer distortion problems.

Unless you need to work in both APS-C and 35mm systems the best advice is to ignore the 35mm equivalent numbers and just learn what the difference is between different focal lengths on your camera. Then if you do need to relate to a 35mm size, say while reading an article talking about film camera, you can convert in the other direction from that into the system you know and use by dividing the focal length by 2/3rds (for Nikon).

35mm is not in anyway "normal" or "right" that everything else should be considered a variant of, it is just one of many different sized systems used in photography, and there is no need to always think and relate in 35mm terms.

Michael.

Joe T
06-01-2007, 07:51
:agree: 100%

Thanks Michael. :)

Woodsy
07-01-2007, 10:16
Well said mij. Totally agreed

One begs the question though, aside from the debate about focal lengths and sensor sizes, which lens produces the better image? (assuming one photographer uses the same lenses; lets not get into a debate about what takes the better image, kit / photographer.)


Is one lens sharper than the other? Do either cause vignetting? Is there a massive price difference? Lets get down to the meat of the matter :D

Jonnyreb
07-01-2007, 10:21
from personal experience the 12-24mm is a far superior lens. imo the extra £100 is worth every penny.

icecavern
07-01-2007, 12:39
from personal experience the 12-24mm is a far superior lens. imo the extra £100 is worth every penny.

They are both available at the same price right now ( £299 ) which is why I asked for peoples opinions between them.

Jonnyreb
07-01-2007, 12:41
They are both available at the same price right now ( £299 ) which is why I asked for peoples opinions between them.

No doubt then, in my mind, the 12-24 is hands down winner. Whish i'd waited a while :bonk:

icecavern
07-01-2007, 14:00
The only thing really between them is the 10-20 is HSM and the 12-24 isn't as far as I can see.

Jonnyreb
07-01-2007, 14:04
The only thing really between them is the 10-20 is HSM and the 12-24 isn't as far as I can see.

They're both HSM - my copies anyway!!!

Muler
07-01-2007, 14:06
the 12-24mm does have HSM from what i know

icecavern
07-01-2007, 14:07
Reading it again it might well have yes http://www.cameraworld.co.uk/ViewProdDetails.asp?prod_code=51410&Prod_name=Sigma+12%2D24mm+f4%2E5%2D5%2E6+EX+DG+ASP HERICAL&CAT_CODE=2&SUBCAT_CODE=203

Muler
07-01-2007, 14:11
btw, correct me if im wrong, but you'd be getting 20degrees more view out of the 10-20mm if i calculated it properly, which now i think about it is quite conciderable

Witch
07-01-2007, 16:29
Oh heck - that price drop on the 12-24mm isn't helping my decision any!

The ONE thing putting me off just buying that one now is the issue of filters. I'm expecting to mainly use the lens for landscapey-type stuff, so how does one get around the issue of filters?

*edit* the 10-20 is available for £269.99 from OneStop.

Jonnyreb
07-01-2007, 16:53
Oh heck - that price drop on the 12-24mm isn't helping my decision any!

The ONE thing putting me off just buying that one now is the issue of filters. I'm expecting to mainly use the lens for landscapey-type stuff, so how does one get around the issue of filters?

*edit* the 10-20 is available for £269.99 from OneStop.

the 12-24 has a 2 part lens cap. There is a filter thread on the tubular section that can accommodate a screw in filter (or Lee / Cokin with adapter). On your 30d this will probably not obscure any of fov....

Jonnyreb
07-01-2007, 16:56
the 12-24 has a 2 part lens cap. There is a filter thread on the tubular section that can accommodate a screw in filter (or Lee / Cokin with adapter). On your 30d this will probably not obscure any of fov....

UPDATE: just checked - no vignetting leaving the tubular section on, on the 30d. Horror story on the 5d but there you go.

mij
07-01-2007, 16:57
To complicate matters further, the Sigma 10-20mm is only £271.34 with free next day delivery from jessops.com if you use one of the 10% off codes (Camera Price Buster's code of CPB10PC or Quidco's code of QUIDCOTEN). And if you go through quidco.com you will qualify for roughly £7 cashback too.

For those who do not know, quidco.com is a co-operative type site which offers cashback via selected retailers. It is just like using affiliate links except that instead of the site owner keeping all the money earned it is shared back with their users.

They do charge a £5 annual fee, but this is taken from your earnings with them so if you make less than £5 then you just get nothing but are no worse off than had you not used their links. It can also take quite a while for the payment to be made to Quidco by the retailer.

As Jessops offer 3% back on the ex-VAT price, if you buy the 10-20mm lens from them this way then you will still get just under £2 back even after paying the admin fee.

More details here:
http://quidco.com/jessops/

Michael.

Witch
07-01-2007, 17:59
UPDATE: just checked - no vignetting leaving the tubular section on, on the 30d. Horror story on the 5d but there you go.

Hmmm...now I have a quandary then.

My reason for getting the 12-24 over the other was an aim in the long term to end up heading along the 1-series route. I guess the question I have to ask myself is whether there will be vignetting on a 1.3x sensor or not. :thinking:

On the filter front - I'd be looking at having to invest in the Cokin x-pro range
presumably?

I think I'm closer than I was to a decision!

Jonnyreb
07-01-2007, 18:07
Hmmm...now I have a quandary then.

My reason for getting the 12-24 over the other was an aim in the long term to end up heading along the 1-series route. I guess the question I have to ask myself is whether there will be vignetting on a 1.3x sensor or not. :thinking:

On the filter front - I'd be looking at having to invest in the Cokin x-pro range
presumably?

I think I'm closer than I was to a decision!

You'd certainly need the x over the p range. I really couldn't tell you how a 1.3 crop may be affected but i suspect that there could be some vignetting at 12mm.

I believe Joe suggested earlier in this thread that there was an alternative 12-24 to the Sigma - whether that was Nikon only i can't remember.

What i can say is that lens flare is incredibly well controlled and on the 5d i've been combining shots in CS2 for the ND grad effect.......

Witch
07-01-2007, 18:23
Yes it was Nikon only Jon.

Right - decision made - 12-24. I'll ring cameraworld tomorrow and see if they can get me one into Chelmsford for Saturday! :thumbs:

Jonnyreb
07-01-2007, 18:27
Hope it works out for you - I'm still thoroughly enjoying mine! Good luck and happy shooting :thumbs:

Witch
07-01-2007, 18:55
Cheers! I was determined to get the lens before we go away at Easter and at that price I can't justify waiting! Might have to take the EOS500 and some film along for the ride now, don't you think!

Jonnyreb
07-01-2007, 18:57
Definately - a whole visual feast coming your way :clap:

Woodsy
07-01-2007, 20:46
Good stuff matey.

Post some pictures that you have taken with it at some point as well, would be nice to see some results of your shiney new purchase :D

icecavern
08-01-2007, 09:48
Yes it was Nikon only Jon.

Right - decision made - 12-24. I'll ring cameraworld tomorrow and see if they can get me one into Chelmsford for Saturday! :thumbs:

They don't have any left in Nikon fit, hope you're not too late on Canon fit too :(

icecavern
08-01-2007, 09:49
To complicate matters further, the Sigma 10-20mm is only £271.34 with free next day delivery from jessops.com if you use one of the 10% off codes (Camera Price Buster's code of CPB10PC or Quidco's code of QUIDCOTEN).

Michael.

The 10-20 is £370 on Jessops site though :shrug:

King_Boru
08-01-2007, 10:34
Good choice, if you still use film then a lens which can cover full frame without serious vignetting is a good investment.

mij
08-01-2007, 10:49
The 10-20 is £370 on Jessops site though :shrug:

Ooh, nasty Jessops (http://www.jessops.com/Products/SearchResults.aspx?searchword=sigma+10-20mm), they really make Nikon users pay for that extra 2° angle of view! It is only £301.49 for the Canon mount, all the other systems cost £370. Not that they have any in stock anyway.

Michael.

HIMUPNORTH
08-01-2007, 11:47
I have been following this thread as I have a EOS5D and three 35mm EOS bodies and was wanting to go wider than my current 15mm widest lens.

Can I give some nods first;

Mij - great posts explaining focal lengths and their meanings. Although I knew most of this you also expanded on some technical differences that I was not aware of and did so in interesting and educational style. Thanks!

JohnnyReb - As you are on the same system your posts have answered some of my queries regarding Sigma lenses. Thanks also.

I had considered all of the following lenses:
Sigma's 10-20mm f/4-5.6
Sigma’s 12-24mm f/4.5-5.6 EX
Canon’s 10-22mm f/3.5-4.5
Tamron’s 11-18mm f/4.5-5.6
Tokina AT-X 124 AF Pro DX 12-24mm f/4

And as far as I am aware they are all designed for smaller sensor sizes and some won't even fit a full frame sensor Canon. The exception being the Sigma’s 12-24mm f/4.5-5.6 EX which seems to be the only one that will fit a full frame Canon DSLR and will provide a (fairly) unencumbered view.

Am I correct? Are there others that I have missed? Has anyone used a mount convertor and added another make? If so was it successful?

Jas
08-01-2007, 14:59
All contributors,

many thanks for the insights. I has originally logged on to ask a similar question....does anyone have the nikon 12-24? I wanted to know if there are any filter issues i need to worry about before buying. I currently use Cokin p filters.

Jas

dazzajl
08-01-2007, 15:35
Am I correct? Are there others that I have missed?

That's pretty much it I think. I looked around back in the middle of last year and the sigma 12-24 was the only option for a 1.3x's or full frame canon.

It's not a bad lens but it does fall way shot of something like a canon 17-40 in terms of resolution. Also, it's huge, rather heavy and slowish if you're wanting to use the auto focus. Not that slow AF is much of an issue at the wide lens. Shoot at f8 and the DoF will go from the edge of the world right into about 14 inches.

Witch
08-01-2007, 18:00
They don't have any left in Nikon fit, hope you're not too late on Canon fit too :(

I hope so too - e-mailed them this morning but no response. I'll call tomorrow.

*edit*

Dirty rats - the price has now gone back to £438 - not too impressed as when I mailed this morning it was still at £299.00

That complicates things a bit. Not so sure again now.

TG.
09-01-2007, 16:59
The thing to remember about focal length is that it is only a measurement of one aspect of the lens, the effect it has on the image you record is down to the sensor or film size, not the focal length. A 10-20mm lens is always going to be a 10-20mm lens whatever sized sensor or film is behind it, and whether the image it casts is larger or smaller than it can record.

On medium and large format systems 50mm is considered a wide, on a 35mm camera it is "normal", for a DSLR with an APS-C sensor it is a short telephoto, while on a digital compact camera it was would be a very long telephoto. The one thing they all have in common is that they the focal length is 50mm regardless.

I think the biggest sources of confusion about focal length comes from DSLR cameras being a successor to 35mm film, and in most cases retaining the same lens mounts and so lens compatibility, that people try to relate the focal length to a 35mm system giving it two meanings. This is why there was never confusion about the different effects of a focal length between other systems, because they were treated as separate and not compared in the same way.

It also does not help that even amongst DSLR cameras there is not one standard sensor size: Nikon ones are 2/3rds the size of a 35mm frame, Canon uses 5/8ths the size, while Four-Thirds system sensors are half the size. And that is just a rounded average. The 35mm equivalent field of view for Sigma's 10-20mm lens is 15-30mm on a Nikon, 16-32mm on a Canon, and 20-40mm on a Four-Thirds camera.

It would be confusing enough to consumers to have to understand two different systems of measuring lenses if Nikon and Canon used the 35mm equivalent figures for their DX and EF-S lens ranges. For companies like Sigma they would need to use different names for each mount they support.

Thankfully that manufacturers always giving the correct focal length is something that actually helps us because we do not have to worry about such things. A 50mm lens on a D80, for example, will give the same view whether it is a DX or DC lens or not. It would be a lot more confusing if you had two 50mm lensed and had to start wondering whether one is normal and the other a telephoto.

As far as I am aware the Sigma 12-24mm lens is the largest rectilinear (non-fisheye) lens you can get for a 35mm frame camera. A 10mm lens on this format would, as Joe said, be extremely expensive and suffer distortion problems.

Unless you need to work in both APS-C and 35mm systems the best advice is to ignore the 35mm equivalent numbers and just learn what the difference is between different focal lengths on your camera. Then if you do need to relate to a 35mm size, say while reading an article talking about film camera, you can convert in the other direction from that into the system you know and use by dividing the focal length by 2/3rds (for Nikon).

35mm is not in anyway "normal" or "right" that everything else should be considered a variant of, it is just one of many different sized systems used in photography, and there is no need to always think and relate in 35mm terms.

Michael.



thanks michael, very well explained, after reading it several times i think it's finally sunk in now :bonk: :D

DiddyDave
11-01-2007, 08:25
Hi all, first ever comment...

If you're using the best possible quality camera (here by Nikon) you need to buy the best quality lens too - this is a game of 'weakest-link' and I found my D2Xs really punished what had been perfectly good lenses on my D100. So it's no option IMO it has to be the Nikon 12-24 as it's the best.

Canon people I know with the 5D or higher had the same problem and now only use L lenses

The 12-24 is a '18-36' equivalent on the D2x BTW even though it's a DX lens. The DX bit simply means as the image size produced can be smaller than for 'full frame' cameras, the lens itself is smaller/lighter than it otherwise would be