Sigma 17-50 quick question.

I see some of the Sigma 17-50 lenses listed as having "FLD". Do they all have this feature but some sellers just don't list it in the item description?
Thanks.

FLD = 'F' Low Dispersion, a material claimed to have performance equivalent to fluorite glass (one of the best types) but at reduced cost. Sigma claims Its optical characteristics allow excellent correction for residual chromatic aberration, while its lower density compared to traditional optical glass allows lighter lenses. Sigma added this to (3) new lenses somewhere arounf early 2010.

If a seller doesn't list it I would as a minimum assume it isn't on the lens being sold or specifically ask.

By the way, prior to the FLD glass, there was a Sigma 18-50mm f/2.8 that was a decent lens. Some can be found for very reasonable prices.

So there are versions of this lens made with and without this feature?

Yes, but the older ones will be without. If in doubt ask for all the letter designations that appear on the front or rim of the lens. Things like OS HSM DG DC; these designations will help you track down what you are getting. I think the current version will have the FLD. From the Sigma website there is this Q&A.

Q2. I’ve recently seen a reference to FLD glass being used in Sigma lenses, is this different from ELD and SLD glass?
A. FLD ("F" Low Dispersion) glass is the highest level low dispersion glass available with extremely high light transmission. This glass has a performance equal to flourite glass which has a low refractive index and low dispersion compared to current optical glass. FLD glass offers superior optical performance, equal to flourite, at an affordable price.

ELD (Extraordinary Low Dispersion) glass has lower dispersion characteristics than SLD (Special Low Dispersion) glass, which Sigma has been using in its APO lenses (and some non-APO lenses as well) for many years now. It has other advantageous properties as well.

AFAIK all 17-50/2.8 OS have FLD ? Are you sure you're not thinking of 18-50/2.8

I'm just going by how I'm seeing the lens description from online retailers like Amazon, B&H etc. Some list it as having "FLD" and some don't, at least not in the initial item heading. I just want to make sure that if I buy one I get the latest version.
Thanks guys.

Sigma has also taken the opportunity to reveal a bit more about its new 'FLD' glass, which is used in several of the company's lens designs simultaneously unveiled at PMA. Standing for 'F' Low Dispersion, the material is claimed to have performance equivalent to fluorite glass, but at a more affordable price. Its optical characteristics apparently allow excellent correction for residual chromatic aberration, while its lower density compared to traditional optical glass allows lighter lenses. It's used in the company's new 70-200mm, 17-50mm and 8-16mm designs.

My lens' rim doesn't list "FLD", but the box it came with does have it. I am pretty sure Sigma hasn't had time to change the optical formula for the lens, given how recent it is. Meaning all of them must be using FLD glass.

The 17-50 EX DC OS HSM lens has FLD glass. FLD is just one of the types of glass used in that lens. Other Sigma lenses may or may not have that glass as needed but when a design on a specific lens has that glass, every lens of that specific model will have it. You didn't specify which specific model you were looking at and I'm not even sure there are other versions of the 17-50 or not.

I'm looking at the 17-50 2.8 EX DC OS HSM FLD. YIKES

There is only one sigma 17-50 and they all have FLD

This is a sigma

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