Document:

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                                                                     Exhibit 4.3

                        ACCENT OPTICAL TECHNOLOGIES, INC.
                                520 Clyde Avenue
                             Mountain View, CA 94043

                                                  Dated as of September 30, 2000

To Certain Securityholders of Accent
Optical Technologies, Inc.:

      Reference is made to that certain Securityholders Agreement dated as of
July 31, 2000 (the "Agreement") by and among JFI II, L.P., Peter M. Joost, Bruce
C. Rhine and Martha H. Rhine, David Johnson, as Trustee of the Rhine 2000
Children's Trust, Bio-Rad Laboratories, Inc., the initial additional
securityholders and the initial management securityholders. Section 4.1 of the
Agreement is hereby amended by deleting the reference to "60 days" in the
proviso at the end of such Section 4.1 and substituting in lieu thereof a
reference to "90 days". Except as specifically provided for by this letter, the
Agreement shall remain in full force and effect and is hereby ratified and
confirmed. This letter may be executed in any number of counterparts, each of
which will be an original, but all of which together will constitute one
instrument. If this letter expresses your understanding with respect to the
matters described herein, please sign this letter where indicated below and
return (i) a copy of such executed letter via facsimile to O'Melveny & Meyers
LLP, fax number (212) 326-2061, Attention: Brian Hutchings, and (ii) the
original of such executed letter via courier to O'Melveny & Myers LLP, 153 East
53rd Street, New York, NY 10022, Attention: Brian Hutchings.

                                               Very truly yours,

                                               ACCENT OPTICAL TECHNOLOGIES, INC.

                                               By:/s/ Bruce C. Rhine
                                                  ------------------------------
                                                  Name:  Bruce C. Rhine
                                                  Title: President
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ACKNOWLEDGED AND AGREED AS OF
THIS 20th DAY OF OCTOBER 2000:

JFI II, L.P.

By:  Joost Enterprises Corporation
Its: General Partner

       By:  /s/  Peter M. Joost
          ----------------------------
       Name:  Peter M. Joost
       Title: President

       /s/  Peter M. Joost
--------------------------------------
Peter M. Joost
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       /s/  Bruce C. Rhine
--------------------------------------
Bruce C. Rhine

       /s/  Martha H. Rhine
--------------------------------------
Martha H. Rhine
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       /s/  David Johnson
--------------------------------------
David Johnson, as Trustee of the Rhine
2000 Children's Trust
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BIO-RAD LABORATORIES, INC.

By:    /s/  Sanford S. Wadler
   -----------------------------------
Name:  Sanford S. Wadler
Title: Vice President
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       /s/  Stephen R. Blight
--------------------------------------
Stephen R. Blight
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       /s/  Gregory A. Kaiser
--------------------------------------
Gregory A. Kaiser
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       /s/  Brian R. Hale
--------------------------------------
Brian R. Hale
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       /s/  Gregory A. Kaiser
--------------------------------------
Gregory A. Kaiser<PAGE>
                                                                     Exhibit 4.4

                        ACCENT OPTICAL TECHNOLOGIES, INC.

                  AMENDMENT NO. 1 TO SECURITYHOLDERS AGREEMENT

     This Amendment No. 1 to Securityholders Agreement (this "Amendment") is
entered as of this 9th day of March, 2004, among Accent Optical Technologies,
Inc., a Delaware corporation (the "Company"); JFI II, L.P., a Texas limited
partnership; Peter M. Joost; Peter M. Joost and Lindsay M. Joost, Trustees U/T/A
Dated 04/11/02; Bruce C. Rhine and Martha H. Rhine, as joint tenants with a
right of survivorship; David Johnson, Trustee, The Rhine 2000 Children's Trust
Dated June 12, 2000; Bio-Rad Laboratories, Inc.; FSC Corp.; Bruce Crawford;
Brian Hale, Rajeev Mundhe, Gregory Kaiser and Reid Langrill. All capitalized
terms used but not defined herein shall have the meanings ascribed to such terms
in the Securityholders Agreement among the aforementioned persons and the other
parties thereto dated as of July 31, 2000 (the "Agreement").

     WHEREAS, Section 6.6(b) of the Agreement provides that the Agreement may be
amended or modified only by a writing signed by each of (i) the Company, (ii)
each of the Founders, (iii) Additional Securityholders holding at least 35% of
the aggregate number of Securities held by all Additional Securityholders, and
(iv) Management Securityholders holding at least 25% of the Securities then held
by all Management Securityholders on a fully diluted basis (together, the
"Required Parties");

     WHEREAS, the undersigned represent not less than the Required Parties and
wish to clarify certain provisions contained in the Agreement;

     NOW, THEREFORE, the parties hereby agree to amend the Agreement as follows:

     1.   Definitions. Section 1.1 of the Agreement is amended to amend and
restate the following definition:

          "Additional Securities" means all Securities which are issued by the
     Company at any time, other than (i) the Securities issued and outstanding
     on the date hereof, (ii) any Securities issued to all of the holders of
     Securities then outstanding on a proportionate basis, (iii) any Securities
     issued to one or more employees of the Company pursuant to and in
     accordance with any employee benefit plan, agreement or arrangement that
     has been approved by the Board, (iv) any Securities that are issued in
     connection with the acquisition by the Company or a subsidiary of the
     Company of any business (whether by acquisition of stock or assets) or any
     assets, (v) any Securities issued to any lender or other Person providing
     debt financing to the Company in a bona fide financing transaction approved
     by the Board, (vi) any Securities issued upon exercise, conversion or
     exchange of any other Securities, (vii) any Securities issued to a Person
     whose participation in the Company the Board determines in good faith,
     based on factors particular to the identity, nature or domicile of such
     person, would be an asset or benefit to the Company; (viii) any Securities
     issued in amounts less than $500,000 in any single transaction or related
     series of transactions; provided that the aggregate amount of all
     transactions under this clause (viii) shall not exceed $2,000,000; and (ix)
     any Securities issued or issuable in an Initial Public Offering.

<PAGE>

          2.   Section 3.2 of the Agreement is amended to add a new subsection
               3.2(g) as follows:

               (g) This Section 3.2 shall not apply to any Securities
          Transferred (or proposed to be Transferred) in connection with a
          Qualified Public Offering.

          3.   Section 5.1 of the Agreement is amended to amend and restate
               subsection 5.1(a) as follows:

               (a) This Agreement shall terminate and, except for Sections 3.4,
          6.2 and 6.4 through 6.15, shall be of no further force and effect and
          shall not be binding upon any party hereto as of immediately prior to
          the closing of a Qualified Public Offering. This Agreement shall
          terminate in full (A) upon the dissolution, liquidation or winding up
          of the Company, or (B) upon the approval of such termination by each
          Securityholder. In any event, all provisions of this Agreement shall
          terminate on December 31, 2025.

          4.   Section 6.7 of the Agreement is amended and restated in its
               entirety as follows:

         SECTION 6.7  NOTICES

               All notices, requests and other communications to any party
          hereunder shall be in writing (including telecopy or similar writing)
          and shall be given,

               (1)  if to the Company:

                Accent Optical Technologies, Inc.
                131 NW Hawthorne, Suite 207
                Bend, OR 97701
                Attn: President
                Telecopy: (541) 318-1966

               (2)  if to Additional Securityholders:

               The addresses set forth on Schedule I.

               (3) if to any Management Securityholder:

               The addresses set forth on Schedule II.

               (4)  if to JFI II:

               JFI  II, L.P.
               c/o Joost Enterprises Corporation
               555 California Street,
               Suite 5180
               San Francisco, CA 94104
               Attn: Peter M. Joost
               Telecopy: (415) 875-5609

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               (5)  if to Joost:

               Peter M. Joost
               c/o Joost Enterprises Corporation
               555 California Street, Suite 5180
               San Francisco, CA 94104
               Attn: Peter M. Joost
               Telecopy: (415) 875-5609

               (6)  if to Rhine:

               Bruce C. Rhine
               Martha H. Rhine
               55925 Hashknife Road
               Bend, OR 97707
               Attention: Bruce C. Rhine
               Telecopy: (541) 318-1966

               (7)  if to Rhine Trust:

                David Johnson, Trustee
                The Rhine Childrens' Family Trust
                298 Mt. Top Road
                Howard, PA 16841
                Telecopy: (570) 748-3711

               (8)  if to Bio-Rad:

               Bio-Rad Laboratories, Inc.
               1000 Alfred Nobel Drive
               Hercules, California 94547
               Attention: Sanford S. Wadler, Esq.
               Telecopy: (510) 741-5815

               or to such other address or telecopy number and with such other
          copies, as such party may hereafter specify for the purpose by notice
          to the other parties. Each such notice, request or other communication
          shall be effective (i) if given by telecopy, when such telecopy is
          transmitted to the telecopy number specified in this Section and
          evidence of receipt is received or (ii) if given by any other means,
          upon delivery or refusal of delivery at the address specified in this
          Section 6.7.

               5. Schedule III of the Agreement is amended to add a new Section
          8 as follows:

               SECTION 8. ASSIGNMENT OF REGISTRATION RIGHTS

               The rights to cause the Company to register Registrable
          Securities pursuant to this Schedule III may be assigned (but only
          with all related obligations) by a Securityholder to a Permitted
          Transferee or to another Transferee who, after such assignment or
          Transfer, holds at least a majority of the Registrable Securities
          originally held by such Securityholder, provided that (i) the Company
          is, within a reasonable time after such Transfer, furnished with
          written notice of the name and address of

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          such Transferee or assignee and the Securities with respect to which
          such registration rights are being assigned, and (ii) such Transferee
          or assignee agrees in writing to be bound by and subject to the terms
          and conditions of this Agreement as in effect at such time.

               6. Except as explicitly amended by this Amendment No. 1, all of
          the terms and conditions of the Agreement shall remain in full force
          and effect.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1
to Securityholders Agreement to be duly executed as of the date first written
above.

ACCENT OPTICAL TECHNOLOGIES, INC.        JFI II, L.P.

BY:  /s/                                 BY:  Joost Enterprises Corporation,
   -----------------------------              its General Partner

NAME  Bruce C. Rhine
     ---------------------------
                                         BY:  /s/
                                         ---------------------------------------
TITLE:   CEO                                   Peter M. Joost, President
      --------------------------

PETER M. JOOST AND LINDSAY M. JOOST,      BRUCE C. RHINE AND MARTHA H. TRUSTEES
DATED 04/11/02                            U/T/A RHINE, JWTROS

 /s/                                      /s/
-------------------------------          ---------------------------------------

 /s/                                      /s/
-------------------------------          ---------------------------------------
PETER M. JOOST                           BIO-RAD LABORATORIES, INC.

/s/
-------------------------------          BY:  /s/
                                         ---------------------------------------
DAVID JOHNSON, TRUSTEE, THE RHINE 2000
CHILDREN'S TRUST DATED JUNE 12, 2000     NAME:     Sanford Wadler
                                         ---------------------------------------

/s/                                      TITLE: Vice President and General
-------------------------------                 Counsel
                                         ---------------------------------------
FSC CORP.                                BRUCE CRAWFORD

BY:  /s/                                  /s/
   ----------------------------          ---------------------------------------

NAME:     John J. Quintal
     --------------------------

TITLE:    Vice President
      -------------------------

BRIAN HALE                               RAJEEV MUNDHE

 /s/                                      /s/
-------------------------------          ---------------------------------------

GREGORY KAISER                           REID LANGRILL

 /s/                                      /s/
-------------------------------          ---------------------------------------

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