Exhibit 5.1


                                  March , 2001


Zygo Corporation
Laurel Brook Road
Middlefield, CT 06455-0448


Dear Sirs:

         In connection with the Registration Statement on Form S-3, Registration
No. 333-53214 (the "Registration Statement"), filed by Zygo Corporation, a
Delaware corporation (the "Company"), under the Securities Act of 1933, as
amended (the "Act"), relating to the public offering of an aggregate of up to
3,312,000 shares of the Company's Common Stock, par value $0.10 per share (the
"Common Stock"), of which 2,932,000 shares of authorized but heretofore unissued
shares of Common Stock (including up to 432,000 shares of Common Stock which
will be purchased by the underwriters if the underwriters exercise the option
granted to them by the Company to cover over-allotments, if any) are being
offered by the Company and 380,000 presently issued and outstanding shares of
Common Stock are being offered severally by certain selling stockholders
(collectively, the "Selling Stockholders"), we, as counsel for the Company, have
examined such corporate records, other documents and questions of law as we have
considered necessary or appropriate for the purposes of this opinion. Our
opinion set forth below is limited to the General Corporation Law of the State
of Delaware.

         We assume that appropriate action will be taken, prior to the offer and
sale of the shares of Common Stock, to register and qualify such shares for sale
under applicable state and securities or "blue sky" laws.

         In our examination of the foregoing documents, we have assumed the
genuineness of all signature and the authenticity of all documents submitted to
us as originals, the conformity to original documents of all documents submitted
to us as certified or photostatic copies, and the authenticity of the originals
of such latter documents.

         Based on the foregoing, we advise you that in our opinion (i) the
shares of Common Stock being issued and sold by the Company have been duly and
validly authorized and, when issued and sold in the manner contemplated by the
Underwriting Agreement, a form of which has been filed as an exhibit to the
Registration Statement (the "Underwriting Agreement"), and upon receipt by the
Company of payment therefor as provided in the Underwriting Agreement, will be
legally issued, fully paid and non-assessable, and (ii) based upon
representations of the company and the selling stockholders, the shares of
Common Stock being sold by the Selling Stockholders have been duly and validly
authorized and are legally issued, fully paid and non-assessable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and the reference to this firm under the caption "Legal
Matters" in the prospectus contained therein. This consent is not to be
construed as an admission that we are a party whose consent is required to be
filed with the Registration Statement under the provisions of the Act or the
rules and regulations of the Securities and Exchange Commission promulgated
thereunder.

         The opinion expressed herein is solely for your benefit, and may be
relied upon only by you.

                                          Very truly yours,

                                          Fulbright & Jaworski L.L.P.