What advantage does EX give over APO?

[urycyon]

If I am primarily interested in sharpness and color aberration, and less interested (in relation to cost) in focus speed, lens build, and other non actual image related factors.
In a wide angle lens I'm not quite as concerned with fucus speed or f-stop, but I want a very sharp image. So will I see a difference in an image shot with an EX lens (with APO) and an image shot with a similar APO lens?

Steve- always looking at bang for buck

[HoodedOne]

Since you mention EX, I believe you´re thinking of buying a Sigma lens.
WEll EX just means that it looks nicer than non-Ex lenses.
If you want a good wide angle lens from sigma, look for the DG (Digital Generation) lenses. The DG lenses are specially designed for use with a digital camera.

cheers

[CyberDyneSystems]

I think that saying that EX lenses "look nicer" is an over simplification. :)

It is the same as saying that "L" lenses are "White"... :D

The EX lenses were introduced as Sigma's "Thuroghbred" lens stable. Most fo the "EX"series are totally new designs. They incorporate a number of improvements that you have mentioned including HSM motos,. and "SLD" lenses etc. They are built tougher with lasting finish.. and they all weigh a lot! :D

I understand that a select few "EX" lenses were around before the EX line existed,.. they simply were good enough to "become" EX lenses.

In some other cases and existing Sigma "APO" lens was redesigned and re-launched as an EX.
I do not know all the changes that went into such redesigns,. but I can give you my first hand expeirence with one lens.

The Sigma 500mm f/4.5 APO,.. was redesigned and reissued as the Sigma 500mm f/4.5 EX HSM.

The two lenses are identical on paper as far as optics go,. (except the "SLD" thing? ) but the tow lenses look qute different so it easy to tell them apart.

Well I had opurtunity to try the old design and I now own the new EX.

There is a WORLD of difference between the two in desighn, function, ergonomics, speed, and visual quality!

The old APO felt and functioned like a piece of junk! I hated this lens. (Fortunately I had experience with other EX lenses so I was not put off Sigma alltogether by this lens)

The EX 500mm is lite years ahead. It is so much better I can even explain it.

Optically I have very few examples of the old 500mm APO,. but it's images did not blow me away. They were marginally better than my 50-500mm zoom at 500mm. But not enough to impress me.

the 500mm EX on th other hand,. the image quality is simply stunning!

[urycyon]

So what exactly does DG mean? Does it have less performance on the edges since it will be used with a focal factor crop, to build it cheaper? Sigma's site gives no details.

Sigma wide angle EX lenses, maximum angles:

Lens--------------------35mm angle--------1.6 focal fac. crop
--------------------------in degrees-----------in degrees
12-24-----------------------122----------------97
14---------------------------114----------------89
15-30-----------------------110----------------84
17-35-----------------------104----------------75

[urycyon]

I found some info on the DG designation on Sigma's site.
I don't understand it though. Why does this light distribution matter to digital cameras, but not 35mm?
From Sigma site:
Q: Some Sigma lenses are designated "DG". What does this mean?

A: The DG designation applied to certain newer Sigma lenses (mostly wideangle and wide zoom type lenses) indicates that the lens is especially suited for use with digital SLR cameras. The DG lenses feature improved (more even) light distribution from image center to edge, especially at maximum aperture, compared to conventional fast wideangle lenses. This is important in digital photography, but is also useful in 35mm photography, especially when slide film is used. Also, the shorter focal lengths are desirable, because most digital SLR cameras have image sensors whose dimensions are considerably smaller than a 35mm negative (usually by a factor of 1.3X to 1.7X), making the lens' angle of view equivalent to that of a longer lens on a 35mm cameras.

[BrettD]

The only difference I can think of with regards to this is that I think digital sensors are more sensitive to vignetting (dark corners).

Think of the CCD/CMOS bucket analogy, light hitting the center pixels is comming from directly above (the bucket) but as we approach the corner pixels, the angle of the light entering the bucket increases, so some of it is wasted as it hits the walls instead of the sensitive bottom.

Of course it isn't really a bucket, but the angle is important because the bayer array (representing the top of the bucket) is above the photosites.

Maybe sigma's DG lenses do something to minimize the angle of light hitting the corner pixels ??? via a larger rear element???

Please read the above as the speculation that is is :-)


Brett D

[DonCoon]

Take a look at PhotoZones Lens tests and you'll find that Sigma's EX lenses are almost always rated higher than non-EX lenses in any category. There are a few exceptions and a few EX dogs but it's clear than EX glass is Sigma's "L" glass.

http://www.photozone.de/2Equipment/easytxt.htm

[urycyon]

The sigma EX 12-24 should be very similar to the nikkor AF-S DX 12-24. Here is a link with test shots of it, shot with a D100 which has a focal factor of 1.5.
http://www.nikonownersclub.com/benefits/benefits/website_review_2.php
The only place I know of where you can get the sigma 12-24 yet is Adorama, and they are only taking preorders, at 650.00, the msrp.

[DonCoon]

urycyon wrote:
The sigma EX 12-24 should be very similar to the nikkor AF-S DX 12-24. Here is a link with test shots of it, shot with a D100 which has a focal factor of 1.5.
http://www.nikonownersclub.com/benefits/benefits/website_review_2.php
The only place I know of where you can get the sigma 12-24 yet is Adorama, and they are only taking preorders, at 650.00, the msrp.

About the only things they have in common are 12-24mm and a minimum aperture of f22.

The nikkor is F/4; the Sigma is f-4.5-5.6. The size, weight, and lens construction* aren't similar.

*Sigma = 16 Elements/12 groups (4 SLD glass)
Nikkor = 11 Elements/7 groups (2 ED glass)

[urycyon]

But the advantage of the Sigma is it is a full frame lens capable of being used with a 35 mm camera.
The nikon is only full frame with the focal factor of a prosumer digital.

[DaveG]

urycyon wrote:
If I am primarily interested in sharpness and color aberration, and less interested (in relation to cost) in focus speed, lens build, and other non actual image related factors.
In a wide angle lens I'm not quite as concerned with fucus speed or f-stop, but I want a very sharp image. So will I see a difference in an image shot with an EX lens (with APO) and an image shot with a similar APO lens?

Steve- always looking at bang for buck

I would say that in the Sigma line you'd want the best lens they sell, so you'd start with the EX series. But EX doesn't mean anything specific and it doesn't exist outside of Sigma.

APO is an abreviation for apochromatic and most lens makers have some in their lineup. APO refers to all three colours of light falling on the same plane and should give better colour fidelity than non APO lenses. So an EX lens may be an APO and an APO may not be an EX.

I don't think that APO has much to do with sharpness, although it's equally important to the final image. I do think that if I was looking for straight out image quaility I'd select a prime lens - not a zoom - and make sure that I had one mother of a tripod.

[ron chappel]

The DG lenses are indeed optimised to deal with problems that digital sensors may have.This must be a "just in case" design for use with any sensor that was likely to come along because the canon CMOS and nikon/pentax CCD have zero problems with vignetting.
So basically these designs are just not needed now,and certainly won't be in future either.