The noun "zoom" is a widely accepted short form of "zoom lens", but it does need some kind of determiner like "this size (of)", or one of the articles "a" or "the". So your first example is fine, but the other two require a determiner e.g. "With a zoom (of) this size".

In your case, the 'size' refers to the lens, not to how much lens zoom. @BillJ

Typically both together. Generally, camera lenses that have a substantial zoom capability are bulkier and heavier, perhaps requiring some kind of image stabilisation to compensate for camera shake arising from the larger size and weight. (And very long zooms need tripods for stability).

@BillJ: taking zoom as a short form of zoom lens (per your comment above) I do not see why you would think this is idiomatic: with this size of lens books.google.com/ngrams/… this size of box is avoided.

As an aside, nowadays zoom capability can be optical or digital, and zoom with modern cameras is a term that means 'zoom capability' not zoom lens.

@TRomano I can't believe you're questioning this. Photographers often call their zoom lenses "zooms", as opposed to "primes" (prime lenses) , or "wide angles" (wide-angle lenses), simple as that. As a keen amateur photographer myself, I can assure you that what I said is correct. (see also the noun def here: link. Image stabilisation is a must for long zooms (long zoom lenses) because of their weight. When talking to other photogs, I will describe my kit as consisting of a pro-SLR, two "zooms" (zoom lenses) and a "prime" ( prime lense).

@BillJ: Well, you'll have to believe that I am questioning two things. The example in OP's question is from a contemporary camera which offers "optical zoom" as distinct from "digital zoom". zoom in that phrase (and in the parlance of the world of digital cameras generally) is a capability, not a lens, although it requires a zoom lens if it is 'optical' zoom. And I am questioning the view that this size of zoom is "fine". answers.microsoft.com/en-us/surface/forum/surfwinrt-surfusin‌​g/… (a typical usage)

Here's another typical example where zoom is a capability: quora.com/Why-dont-GoPro-cameras-have-zoom The question in the title is idiomatic; it's not missing an article; it's not "headlinese" because it's a title.

@TRomano Gee, what a fuss. I'm aware of that particular camera and its zoom lens. You can call it "capability" if you like, but either way the NPs in the OP's examples should be determined. Btw, I carry two "zooms" (meaning "two zoom lenses") with me, not a zoom capability!

@BillJ: It's not a fuss. It's just pointing how the term zoom has evolved. Those who acquired their photography lingo pre-digital-age (as I did) use zoom to mean "zoom lens" whereas those who acquired their pic-taking lingo during the digital-age use it to mean 'zooming capability', and that difference is germane to OP's question.

I think you guys are probably off-topic! This is not a technical question. Both senses make sense, and context would dictate which is appropriate.

@Kinzle B: I'm not answering it as a technical question but as a linguistic one.

That's not true. In digital photography, especially in SLR photography, we talk of zoom lenses. Other than with digital zooms, it's the lens that does the work. The camera in question has a 20x optical zoom lens.

@BillJ: What's not true? And who is "we"?

That zoom in that phrase (and in the parlance of the world of digital cameras generally) is a capability, not a lens. I've told you several times that we talk of our zoom lenses, or just our "zooms". That is the parlance between photogs.

@KinzleB: Compare: Does the car have stick shift?

You don't say "Does this camera have zoom? You'd typically say "does this camera have a zoom lens", or just "a zoom".

@BillJ: And I've told you several times that there is a generational difference in the way the term is used (and have provided examples of such usage). My son is a photographer.

And I'm telling you that the NPs in the OP's example should be determined.

And I'm telling you that if zoom is perceived as a capability, it does not need to be determined (see the stick shift example in my comment above).

"With a zoom this size" is much better than "with zoom this size". Sorry if you can't see that.

"Zoom (lens)" and "zoom (capability)" are both NPs that should be determined, which is the answer to the OP's question.

a zoom capability of this size.... is not idiomatic, IMO. Capabilities don't come in sizes.

Well, you (not me) used the word "capability" as a reason for not determining the NPs . In any case "a zoom capability ..." sounds okay to me if one is talking about a camera with a digital zoom system.

I guess I'll never convince you that in the OP's examples, "With a zoom (of) this size" is preferable to "With zoom (of) this size".