SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549



                                  SCHEDULE 13G
                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                                (AMENDMENT NO. )

                             Cyberoptics Corporation
                         ------------------------------
                                (NAME OF ISSUER)

                      COMMON STOCK, NO PAR VALUE PER SHARE
                   -------------------------------------------
                         (TITLE OF CLASS OF SECURITIES)

                                    232517102
                          ----------------------------
                                 (CUSIP NUMBER)

The  remainder  of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for any  subsequent  amendment  containing  information  which  would  alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act") or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
notes).






--------------------------------------------------------------
  1   NAME OF REPORTING PERSONS
      S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

      EQSF ADVISERS, INC.
      (EIN 13-3354359)

--------------------------------------------------------------
--------------------------------------------------------------
  2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
       (a)  [   ]

       (b)  [   ]
--------------------------------------------------------------
--------------------------------------------------------------
  3   SEC USE ONLY

--------------------------------------------------------------
--------------------------------------------------------------
  4   CITIZENSHIP OR PLACE OF ORGANIZATION

                  NEW YORK CORPORATION

--------------------------------------------------------------
--------------------------------------------------------------
                   5  SOLE VOTING POWER

                           451,000
   NUMBER OF
                 ---------------------------------------------
                 ---------------------------------------------
     SHARES        6  SHARED VOTING POWER
  BENEFICIALLY
    OWNED BY
                 ---------------------------------------------
                 ---------------------------------------------
      EACH         7  SOLE DISPOSITIVE POWER
   REPORTING
     PERSON                451,000

                 ---------------------------------------------
                 ---------------------------------------------
      WITH        8   SHARED DISPOSITIVE POWER


--------------------------------------------------------------
--------------------------------------------------------------
 9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON

           451,000

--------------------------------------------------------------
--------------------------------------------------------------
 10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
      CERTAIN SHARES*
             [    ]

--------------------------------------------------------------
--------------------------------------------------------------
  11     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

           5.67%

--------------------------------------------------------------
--------------------------------------------------------------
 12     TYPE OF REPORTING PERSON*

           IA

--------------------------------------------------------------

                *SEE INSTRUCTIONS BEFORE FILLING OUT!






--------------------------------------------------------------
  1   NAME OF REPORTING PERSONS
      S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

      M.J. WHITMAN ADVISERS, INC.
      (EIN 13-3686379)

--------------------------------------------------------------
--------------------------------------------------------------
  2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
       (a)  [   ]

       (b)  [   ]
--------------------------------------------------------------
--------------------------------------------------------------
  3   SEC USE ONLY

--------------------------------------------------------------
--------------------------------------------------------------
  4   CITIZENSHIP OR PLACE OF ORGANIZATION

                  NEW YORK CORPORATION

--------------------------------------------------------------
--------------------------------------------------------------
                   5  SOLE VOTING POWER

                          0
   NUMBER OF
                 ---------------------------------------------
                 ---------------------------------------------
     SHARES        6  SHARED VOTING POWER
  BENEFICIALLY
    OWNED BY                        NONE

                 ---------------------------------------------
                 ---------------------------------------------
      EACH         7  SOLE DISPOSITIVE POWER
   REPORTING
     PERSON               0

                 ---------------------------------------------
                 ---------------------------------------------
      WITH        8   SHARED DISPOSITIVE POWER

                                    NONE
--------------------------------------------------------------
--------------------------------------------------------------
 9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON

           0
--------------------------------------------------------------
--------------------------------------------------------------
 10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
      CERTAIN SHARES*
             [    ]

--------------------------------------------------------------
--------------------------------------------------------------
 11     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

           0
--------------------------------------------------------------
--------------------------------------------------------------
 12      TYPE OF REPORTING PERSON*

           IA
--------------------------------------------------------------

                *SEE INSTRUCTIONS BEFORE FILLING OUT!






--------------------------------------------------------------
  1   NAME OF REPORTING PERSONS
      S.S. OR I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

           MARTIN J. WHITMAN


--------------------------------------------------------------
--------------------------------------------------------------
  2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
       (a)   [   ]

       (b)   [   ]
--------------------------------------------------------------
--------------------------------------------------------------
  3   SEC USE ONLY

--------------------------------------------------------------
--------------------------------------------------------------
  4   CITIZENSHIP OR PLACE OF ORGANIZATION

           USA

--------------------------------------------------------------
--------------------------------------------------------------
                   5  SOLE VOTING POWER

   NUMBER OF               NONE  (SEE ITEM 4)
                 ---------------------------------------------
                 ---------------------------------------------
                   6  SHARED VOTING POWER
     SHARES
                           NONE
  BENEFICIALLY
    OWNED BY     ---------------------------------------------
                 ---------------------------------------------
      EACH         7  SOLE DISPOSITIVE POWER
   REPORTING               NONE  (SEE ITEM 4)

                 ---------------------------------------------
                 ---------------------------------------------
  PERSON WITH     8   SHARED DISPOSITIVE POWER

                           NONE
--------------------------------------------------------------
--------------------------------------------------------------
 9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
      PERSON

           -0-    (SEE ITEM 4)
--------------------------------------------------------------
--------------------------------------------------------------
 10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
      CERTAIN SHARES*
             [  ]

--------------------------------------------------------------
--------------------------------------------------------------
 11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

           -0-

--------------------------------------------------------------
--------------------------------------------------------------
 12   TYPE OF REPORTING PERSON*

           IN

--------------------------------------------------------------
                *SEE INSTRUCTIONS BEFORE FILLING OUT!

ITEM 1.

     (A) NAME OF ISSUER:
         ---------------
         Cyberoptics Corporation (the "Issuer").

     (B) ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES OR, IF NONE, RESIDENCE:
         -----------------------------------------------------------------------
           5900 Golden Hills Drive, Minneapolis, MN 55416
ITEM 2.

     (A) NAME OF PERSON FILING:

         This schedule is being jointly filed by EQSF Advisers,  Inc.
("EQSF"),   M.J.  Whitman  Advisers,  Inc.  ("MJWA")  and  Martin  J.
Whitman,   the  Chief   Executive   Officer  of  EQSF  and  MJWA  and
controlling  person  of EQSF and  MJWA.  (EQSF,  MJWA and  Martin  J.
Whitman  are  sometimes   collectively  referred  to  hereinafter  as
"Filer").  Attached  hereto  as an  exhibit  is a copy  of the  joint
Schedule 13G filing agreement among the reporting persons.

     (B) ADDRESS OF PRINCIPAL BUSINESS OFFICE:
         -------------------------------------
         The address of the principal  executive office of EQSF, MJWA
         and Mr. Whitman is:  767 Third Avenue, New York, New York 10017-2023.

     (C) CITIZENSHIP:
         ------------
         The  citizenship  or place  of  organization  of each of the  reporting
         persons is as follows:

         EQSF
         ----
         New York State Corporation.

         MJWA
         ----
         New York State Corporation.

         MARTIN J. WHITMAN
         -----------------
         United States Citizen.

     (D) TITLE OF CLASS OF SECURITIES:
         -----------------------------
        Common Stock, no par value per share.

     (E)  CUSIP NUMBER:
          -------------
          077347300

ITEM 3.IF THIS STATEMENT IS BEING FILED PURSUANT TO RULES 13D-1(B), OR 13D-2(B),
CHECK WHETHER THE PERSON FILING IS A:

         (E) Investment  Adviser  registered under section 203 of the INVESTMENT
             ADVISERS ACT OF 1940 (EQSF AND MJWA).

ITEM 4.  OWNERSHIP.

     (a)  & (b)EQSF beneficially owns 451,000 shares, or 5.67% of the class of
          securities of the issuer.

     (c)   (i) EQSF: 451,000

          (ii) Not applicable.

         (iii) EQSF: 451,000

          (iv) Not applicable.

     Mr. Whitman disclaims beneficial ownership of all such shares.

ITEM 5.  OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS.

         Not applicable.


ITEM 6.  OWNERSHIP  OF MORE THAN FIVE  PERCENT  ON BEHALF OF ANOTHER PERSON.

     Third Avenue Value Portfolio of the WRL Series Fund, an investment  company
registered  under the  Investment  Company Act of 1940, has the right to receive
dividends from, and the proceeds from the sale of, 82,500 of the shares reported
by EQSF,  Third  Avenue  Variable  Series  Trust of the  Third  Avenue  Variable
Portfolio,  an investment company registered under the Investment Company Act of
1940,  has the right to receive  dividends  from, and the proceeds from the sale
of, 90,600 of the shares reported by EQSF, Third Avenue Small Cap Value Fund, an
investment  company registered under the Investment Company Act of 1940, has the
right to receive  dividends  from, and the proceeds from the sale of, 198,500 of
the shares reported by EQSF, Style Select Small-Cap Value Series,  an investment
company  registered  under the Investment  Company Act of 1940, has the right to
receive dividends from, and the proceeds from the sale of, 67,400, of the shares
reported by EQSFk, and Legends Fund, an investment  company registered under the
Investment Company Act of 1940, has the right to receive dividends from, and the
proceeds  from the sale of,  12,000,  of the shares  reported  by EQSF.  Various
clients  for whom  MJWA acts as  investment  advisor  have the right to  receive
dividends from, and the proceeds of the sale of, the shares reported by MJWA.


ITEM 7.  IDENTIFICATION  AND  CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED
THE  SECURITY  BEING  REPORTED  ON BY THE  PARENT  HOLDING COMPANY.

         Not Applicable.

ITEM 8.  IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP.

         Not applicable.

ITEM 9.  NOTICE OF DISSOLUTION OF GROUP.

         Not applicable.

ITEM 10. CERTIFICATION.

         By  signing  below I  certify  that,  to the best of my  knowledge  and
belief, the securities referred to above were acquired in the ordinary course of
business  and were not acquired for the purpose of and do not have the effect of
changing or  influencing  the control of the issuer of such  securities and were
not acquired in connection  with or as a participant in any  transaction  having
such purposes or effect.








                                    SIGNATURE

         After reasonable  inquiry and to the best of my knowledge and belief, I
certify that the information  set forth in this statement is true,  complete and
correct.

                                 May 10, 2001
                                 --------------------------------
                                 (Date)




                                 EQSF ADVISERS, INC.

                                 BY:/S/ MARTIN J. WHITMAN
                                 ------------------------
                                 Martin J. Whitman
                                 Chairman, President and Chief Executive Officer

                                 M.J. WHITMAN ADVISERS, INC.

                                 BY:/S/  MARTIN J. WHITMAN
                                 ----------------------
                                 Martin J. Whitman
                                 Chairman and Chief Executive Officer

                                 /S/  MARTIN J. WHITMAN
                                 -----------------------
                                 Martin J. Whitman, President