EXHIBIT 23.1

            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in this Annual Report (Form 10-K)
of Cognex Corporation of our report dated March 1, 2006, with respect to the
consolidated financial statements of Cognex Corporation and our report dated
March 1, 2006 with respect to Cognex Corporation management's assessment of the
effectiveness of internal control over financial reporting and the effectiveness
of internal control over financial reporting of Cognex Corporation, included in
the 2005 Annual Report to Shareholders of Cognex Corporation.

Our audits also included the financial statement schedule of Cognex Corporation
listed in Item 15(a). This schedule is the responsibility of Cognex
Corporation's management. Our responsibility is to express an opinion based on
our audits. In our opinion, as to which the date is March 1, 2006, the financial
statement schedule referred to above, when considered in relation to the basic
financial statements taken as a whole, presents fairly in all material respects
the information set forth therein.

We consent to the incorporation by reference in the Registration Statements on
Form S-8 (File Nos. 33-81150, 333-04621, 333-02151, 333-60807, 33-32815,
333-44824, 333-68158, 333-96961, 333-100709, and 333-126787) of Cognex
Corporation of our report dated March 1, 2006, with respect to the consolidated
financial statements of Cognex Corporation incorporated herein by reference, our
report dated March 1, 2006 with respect to Cognex Corporation management's
assessment of the effectiveness of internal control over financial reporting and
the effectiveness of internal control over financial reporting of Cognex
Corporation incorporated herein by reference, and our report included in the
preceding paragraph with respect to the financial statement schedule of Cognex
Corporation included in this Annual Report (Form 10-K) of Cognex Corporation.

/s/ Ernst & Young LLP

Boston, Massachusetts
March 1, 2006