8-K

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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM 8-K

                                 Current Report
                     Pursuant to Section 13 or 15(d) of the
                         Securities Exchange Act of 1934


       Date of Report (Date of Earliest Event Reported): September 5, 2007



                               COGNEX CORPORATION
- --------------------------------------------------------------------------------
               (Exact name of registrant as specified in charter)


       Massachusetts                    0-17869                  04-2713778
- -----------------------------   ------------------------     -------------------
(State or other jurisdiction    (Commission File Number)      (I.R.S. Employer
       of incorporation)                                     Identification No.)


                                One Vision Drive
                        Natick, Massachusetts 01760-2059
          (Address, including zip code, of principal executive offices)


                                 (508) 650-3000
              (Registrant's telephone number, including area code)


          (Former name or former address, if changed since last report)


Check the appropriate box below if the Form 8-K filing is intended to
simultaneously satisfy the filing obligation of the registrant under any of the
following provisions:

|_|  Written communications pursuant to Rule 425 under the Securities Act (17
     CFR 230.425)
|_|  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR
     240.14a-12)
|_|  Pre-commencement communications pursuant to Rule 14d-2(b) under the
     Exchange Act (17 CFR 240.14d-2(b))
|_|  Pre-commencement communications pursuant to Rule 13e-4(c) under the
     Exchange Act (17 CFR 240.13e-4(c))

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Item 4.01 Changes in Registrant's Certifying Accountant

On September 5, 2007,  Ernst & Young LLP ("Ernst & Young") was dismissed and, on
September 7, 2007,  Grant  Thornton LLP ("Grant  Thornton") was appointed as the
independent registered public accounting firm for Cognex Corporation ("Cognex").
The decision to change auditors was unanimously  approved by the Audit Committee
of the Board of Directors.

The reports of Ernst & Young on the financial statements of Cognex for the years
ended  December  31,  2006 and 2005  did not  contain  any  adverse  opinion  or
disclaimer of opinion,  nor were they  qualified or modified as to  uncertainty,
audit scope or accounting principles.

During  Cognex's  fiscal  years  ended  December  31,  2006  and  2005,  and the
subsequent interim period through September 5, 2007, there were no disagreements
with  Ernst &  Young  on any  matter  of  accounting  principles  or  practices,
financial  statement   disclosure,   or  auditing  scope  or  procedure,   which
disagreements,  if not resolved to the satisfaction of Ernst & Young, would have
caused  Ernst  &  Young  to  make   reference  to  the  subject  matter  of  the
disagreements  in connection  with its reports.  None of the  reportable  events
described in Item  304(a)(1)(v)  of  Regulation  S-K occurred  during the fiscal
years ended December 31, 2006 and 2005, or the subsequent interim period through
September 5, 2007.

During the fiscal  years ended  December 31, 2006 and 2005,  and the  subsequent
interim  period  through  September  5, 2007,  Cognex did not consult with Grant
Thornton  regarding  either (i) the  application  of accounting  principles to a
specified  transaction,  either  completed  or  proposed;  or the  type of audit
opinion that might be rendered on Cognex's financial  statements,  and neither a
written  report was  provided  to Cognex  nor oral  advice  provided  that Grant
Thornton  concluded was an important  factor  considered by Cognex in reaching a
decision as to any accounting,  auditing or financial  reporting  issue; or (ii)
any  matter  that was  either the  subject  of a  disagreement,  as that term is
defined in Item 304(a)(1)(iv) of Regulation S-K and the related instructions, or
a reportable event, as that term is described in Item 304(a)(1)(v) of Regulation
S-K.

Cognex  has  provided  a copy of the  foregoing  statements  to  Ernst &  Young.
Attached as Exhibit 16.1 is Ernst & Young's letter to the SEC,  dated  September
10, 2007, stating its agreement with these statements.

Item 9.01 Financial Statements and Exhibits

(d)  Exhibits

Exhibit No.       Description
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16.1              Letter from Ernst & Young regarding change in certifying
                  accountant.




                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                                           COGNEX CORPORATION

Dated: September 10, 2007                  By: /s/ Richard A. Morin
                                           ------------------------
                                           Richard A. Morin
                                           Senior Vice President of Finance,
                                           Chief Financial Officer and Treasurer

EX-16.1

                                                                    Exhibit 16.1


September 10, 2007

Securities and Exchange Commission
100 F Street, N.E
Washington, DC 20549

Gentlemen:

We have read Item 4.01 of Form 8-K dated September 10, 2007, of Cognex
Corporation and are in agreement with the statements contained in paragraphs 1,
2 and 3 on page 2 therein, except that we have no knowledge of circumstances
regarding the appointment of Grant Thornton as the Company's Independent
Auditors. We have no basis to agree or disagree with other statements of the
registrant contained therein.


                                                       /s/ Ernst & Young LLP
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                                                       Ernst & Young LLP