Exhibit 4.6

                              GCA CORPORATION

                           REGISTRATION AGREEMENT
                           ----------------------

          Registration Agreement,  dated as of September 1, 1987, among GCA
Corporation,  a Delaware corporation (the "Company"),  and Carl Zeiss, Inc.
("Zeiss").  Terms not  otherwise  defined  herein  shall  have the  meaning
ascribed to them in the Warrant Agreement.

                                 WITNESSETH
                                 ----------

          WHEREAS,  the  Company  and Zeiss  are  parties  to that  certain
Warrant Agreement of even date herewith (the "Warrant Agreement"), pursuant
to which the  Company  has  issued to Zeiss a warrant  (the  "Warrant")  to
purchase  500,000 shares of common stock,  $.01 par value per share, of the
Company (the "Common Stock"); and

          WHEREAS, the Warrant Agreement provides that Zeiss and subsequent
holders of the Warrant or portions thereof outstanding and unexercised from
time to time shall have  certain  registration  rights with  respect to the
Warrant Shares issuable pursuant to the exercise of the Warrant;

          NOW,  THEREFORE,  in  consideration  of the  premises  and of the
mutual  covenants  hereinafter  set forth,  the  Company and Zeiss agree as
follows:

          1.  Defined  Terms.  Capitalized  terms  used in this  Agreement,
unless separately defined herein,  shall have the meanings ascribed to such
terms in the Warrant Agreement.

          2. Demand  Registrations.  (a) At any time after the date hereof,
the  holder of the  Warrant  representing  the right to  purchase  at least
200,000  shares of Common  Stock of the  Company  or the holder of at least
200,000 Warrant Shares (equitably  adjusted to reflect stock splits,  stock
dividends,  combinations  or similar  events and  adjustments  pursuant  to
Section 4 of the Warrant) may request registration under the Securities Act
of 1933, as amended (the "Securities Act"), of all or part of their Warrant
Shares on Form S-1 or any other form available for the  registration of the
Warrant Shares ("Demand  Registrations"),  by written notice to the Company
of such request accompanied by the simultaneous  exercise of the Warrant to
the extent of not less than Twenty Thousand (20,000) shares of Common Stock
of the Company,  $.01 Par Value,  less the number of  previously  exercised
shares which have not been registered.  Within 10 days after receipt of any
such request,  the Company shall give written notice of such request to all
other holders of the Warrant and of the Warrant  Shares and shall,  subject
to the provisions of Section 2(c) hereof,  include in such registration all
Warrant  Shares  with  respect to which the Company  has  received  written
requests  for  inclusion  therein  within 30 days after the  receipt of the
Company's notice.

               (b) Subject to the  provisions of Section 2(a),  the Company
shall pay all  Registration  Expenses  (as  defined in Section 6 hereof) in
connection  with  each  such  registration.   The  Company  shall  pay  all
Registration  Expenses in connection with any  registration  initiated as a
Demand Registration, whether or not consummated.

               (c) In the  event  that  the  managing  underwriters  of the
requested Demand  Registration  advise the Company in writing that in their
judgment in order to effect an orderly  public  distribution  the number of
Warrant Shares proposed to be included in any such Demand Registration must
be limited,  the Company shall include in such registration only the number
of Warrant Shares which, in the opinion of such  underwriters,  can be sold
in an orderly public  distribution,  such limitation to be imposed pro rata
among the holders of the Warrant or of the Warrant Shares,  as the case may
be, who are  participating in such  registration on the basis of the amount
of such securities initially proposed to be registered by such holder.

               (d) The Company  shall not be obligated to effect any Demand
Registration  within  six  months  after the  effective  date of a previous
Demand  Registration or a previous  registration under which each holder of
Warrant  Shares  was  given  piggyback  rights  (and was able to  include a
minimum of 66-2/3% of the shares of Warrant  Shares  requested  by it to be
included in such  registration)  pursuant to Section 3 hereof.  The Company
may  postpone  for up to six months the  filing or the  effectiveness  of a
registration  statement for a Demand Registration if the Company reasonably
believes that such Demand Registration might reasonably be expected to have
an adverse  effect on any  proposal or plan by the Company to engage in any
acquisition  of assets  (other than in the ordinary  course of business) or
any merger,  consolidation,  tender  offer or similar  transaction.  If the
Company  elects  to  postpone  the  filing  or  effectiveness  of a  Demand
Registration,  it shall  promptly  notify each holder of the Warrant and of
Warrant Shares.

               (e)  The  holders  of  a  majority  of  the  Warrant  Shares
participating in any Demand Registration shall have the right to select the
investment banker(s) and manager(s) to administer the offering,  subject to
the Company's approval, which shall not be unreasonably withheld.

          3. Piggyback Registrations.  (a) Whenever the Company proposes to
register any of its equity  securities under the Securities Act (other than
pursuant to a Demand Registration) and the registration form to be used may
be  used  for  the   registration  of  the  Warrant  Shares  (a  "Piggyback
Registration"), the Company shall give prompt written notice to all holders
of the  Warrant  and of Warrant  Shares of its  intention  to effect such a
registration and shall include in such registration all Warrant Shares with
respect to which the Company has received  written  requests for  inclusion
therein within 30 days after the receipt of the Company's notice.

               (b) The  Registration  Expenses  of the  holders  of Warrant
Shares shall be paid by such holders in all Piggyback Registrations.

               (c) If a Piggyback  Registration is an underwritten  primary
registration on behalf of the Company, and the managing underwriters advise
the  Company in writing  that in their  judgment  the number of  securities
requested to be included in such  registration  must be limited in order to
effect an orderly  public  distribution,  the Company shall include in such
registration  (i) first,  the securities the Company proposes to sell, (ii)
second,  the Warrant Shares requested to be included in such  registration,
pro rata among the holders of such  securities  on the basis of the numbers
of shares  initially  proposed to be registered by such holders,  and (iii)
third, any other securities requested to be included in such registration.

               (d) If a Piggyback Registration is an underwritten secondary
registration  on behalf of holders of the Company's  securities  other than
the holders of the Warrant Shares, and the managing underwriters advise the
Company  in  writing  that in  their  judgment  the  number  of  securities
requested to be included in such  registration  must be limited in order to
effect an orderly  public  distribution,  the Company shall include in such
registration (i) first, the securities  requested to be included therein by
the holders  requesting such registration  (ii) second,  the Warrant Shares
requested to be included in such  registration,  pro rata among the holders
of such securities on the basis of the number of shares initially  proposed
to  registered  by such  holders,  and (iii)  third,  any other  securities
requested to be included in such registration.

          4. Holdback Agreements.  (a) Each holder of Warrant Shares agrees
not to effect any public sale or  distribution  of the Warrant Shares owned
by such holder, including,  without limitation,  sales pursuant to Rule 144
(or any similar rule then in effect),  during the 10 days prior to, and the
90  days  beginning  on,  the  effective  date of any  underwritten  Demand
Registration or any  underwritten  Piggyback  Registration in which Warrant
Shares  owned  by  such  holder  are  included  (except  as  part  of  such
underwritten  registration) unless the underwriters managing the registered
public offering otherwise agree.

               (b) The  Company  agrees not to effect  any  public  sale or
distribution of its equity securities,  or any securities  convertible into
or  exchangeable  or exercisable  for such  securities,  during the 10 days
prior to, and during the 90 days  beginning on, the  effective  date of any
underwritten Demand Registration or any underwritten Piggyback Registration
(except  as  part  of  such   underwritten   registration  or  pursuant  to
registrations  on Form S-8 or any successor  form) unless the  underwriters
managing the registered  public offering  otherwise agree.

          5. Registration  Procedures.  Whenever the holders of the Warrant
or of the  Warrant  Shares  have  requested  that  any  Warrant  Shares  be
registered  pursuant  to this  Agreement,  the  Company  shall use its best
efforts to effect the  registration  of such Warrant  Shares in  accordance
with the intended method of disposition  thereof,  and pursuant thereto the
Company shall as expeditiously as possible:

               (a)  prepare  and file  with  the  Securities  and  Exchange
Commission a registration statement with respect to such Warrant Shares and
use its best  efforts  to  cause  such  registration  statement  to  become
effective  (provided  that  before  filing  a  registration   statement  or
prospectus  or any  amendments  or  supplements  thereto,  the Company will
furnish to the counsel selected by the holders of a majority of the Warrant
Shares  requesting  such  registration  statement  copies of all  documents
proposed to be filed, which documents will be subject to the review of such
counsel);

               (b)  prepare  and file  with  the  Securities  and  Exchange
Commission such amendments and supplements to such  registration  statement
and the prospectus used in connection therewith as may be necessary to keep
such  registration  statement  effective  for a period of not less than 180
days and comply with the  provisions of the  Securities Act with respect to
the disposition of all securities  covered by such  registration  statement
during such period in accordance  with the intended  methods of disposition
by the sellers  thereof as set forth in such  registration  statement;

               (c) furnish to each seller of Warrant  Shares such number of
copies  of such  registration  statement,  each  amendment  and  supplement
thereto, the prospectus included in such registration  statement (including
each  preliminary  prospectus)  and such other documents as such seller may
reasonably  request in order to facilitate  the  disposition of the Warrant
Shares  owned by such  seller;

               (d) use its best efforts to register or qualify such Warrant
Shares under such other  securities or blue sky laws of such  jurisdictions
as any seller reasonably  requests and do any and all other acts and things
which may be  reasonably  necessary  or  advisable to enable such seller to
consummate  the  disposition  in such  jurisdictions  of the Warrant Shares
owned by such seller (provided that the Company will not be required to (i)
qualify  generally  to do business in any  jurisdiction  where it would not
otherwise  be  required  to qualify  but for this  subparagraph  (d),  (ii)
subject  itself to taxation in any such  jurisdiction  or (iii)  consent to
general  service  of  process in any such  jurisdiction);

               (e) notify  each seller of such  Warrant  Shares at any time
when a prospectus  relating  thereto is required to be delivered  under the
Securities  Act,  of the  occurrence  of any event as a result of which the
prospectus  included  in such  registration  statement  contains  an untrue
statement  of a  material  fact or  omits  any fact  necessary  to make the
statements  therein  not  misleading,   and  shall  prepare  in  sufficient
quantities  a  supplement  or  amendment  to such  prospectus  so that,  as
thereafter   delivered  to  the  purchaser  of  such  Warrant  Shares  such
prospectus shall not contain an untrue statement of a material fact or omit
to state any fact necessary to make the statements therein not misleading;

               (f) use its best efforts to cause all such Warrant Shares to
be listed on each securities exchange on which similar securities issued by
the Company are then listed, and provide a transfer agent and registrar for
such  securities  not  later  than  the  effective  date of the  applicable
registration statement;

               (g) in the case of an underwritten offering, enter into such
customary agreements (including  underwriting agreements in customary form)
and take all such other actions as the holders of a majority of the Warrant
Shares  being  sold or the  underwriters,  reasonably  request  in order to
expedite or facilitate the  disposition of such Warrant Shares  (including,
without limitation, effecting a stock split or a combination of shares);

               (h) make  available for  inspection by any seller of Warrant
Shares, any underwriter  participating in any disposition  pursuant to such
registration  statement,  and  any  attorney,  accountant  or  other  agent
retained  by any such  seller  or  underwriter,  all  financial  and  other
records,  pertinent corporate documents and properties of the Company,  and
cause  the  Company's  officers,   directors,   employees  and  independent
accountants  to supply all  information  reasonably  requested  by any such
seller, underwriter,  attorney, accountant or agent in connection with such
registration  statement;  and

               (i) use its best  efforts to obtain an  appropriate  opinion
from  the  Company's  counsel  and a  comfort  letter  from  the  Company's
independent  public accountants in customary from and covering such matters
of the type customarily  covered by opinions of Company counsel and comfort
letters  in similar  registrations  as the  holders  of a  majority  of the
Warrant Shares being sold  reasonably  request  (provided that such holders
constitute  the  holders of a majority  of the  securities  covered by such
registration agreement).

          If any such  registration  statement refers to any holder by name
or otherwise as the holder of any  securities  of the Company,  such holder
shall have the right to require (i) the insertion  therein of language,  in
form and substance  reasonably  satisfactory to such holder,  to the effect
that the holding by such holder of such  securities  is not to be construed
as a  recommendation  of  such  holder  of the  investment  quality  of the
Company's  securities  covered thereby and that such holding does not imply
that such holder will assist in meeting any future  financial  requirements
of the Company,  or (ii) in the event that such reference to such holder by
name or  otherwise  is not  required by the  Securities  Act or any similar
Federal  statute  then in force,  the  deletion  of the  reference  to such
holder.

          6.  Registration  Expenses.  (a)  All  expenses  incident  to the
Company's  performance  of or  compliance  with this  Agreement,  including
without limitation,  all registration and filing and listing fees, National
Association  of  Securities  Dealers,  Inc. fees and expenses of compliance
with securities or blue sky laws, printing expenses, messenger and delivery
expenses,  and fees and  disbursements  of  counsel  for the  Company,  all
independent  certified  public  accountants,  and  underwriters  (excluding
discounts  and   commissions)   (all  such  expenses  being  herein  called
"Registration  Expenses"),  shall be borne as provided  in this  Agreement,
except that the Company  shall,  in any event,  pay its  internal  expenses
(including,  without limitation,  all salaries and expenses of its officers
and employees  performing legal or accounting  duties),  the expense of any
annual audit or quarterly  review,  the expense of any liability  insurance
and the expenses and fees for listing the  securities  to be  registered on
each securities  exchange on which similar securities issued by the Company
are then listed.

               (b) In  connection  with each  Registration  initiated  as a
Demand Registration, the Company shall reimburse the holders of the Warrant
Shares  covered  by  such   registration   for  the  reasonable   fees  and
disbursements  of one law firm  chosen by the  holders of a majority of the
Warrant  Shares   included  in  such   registration.

               (c) To the extent Registration  Expenses are not required to
be  paid  by  the  Company,  each  holder  of  securities  included  in any
registration  hereunder shall pay the Registration Expense allocated to the
registration of such holder's securities so included,  and any Registration
Expenses  not so  allocable  shall be borne by all  sellers  of  securities
included in such  registration in proportion to the aggregate selling price
of the securities to be so registered.

          7. Indemnification.  (a) The Company agrees to indemnify,  to the
extent  permitted by law, each holder of the Warrant and of Warrant Shares,
its officers and directors and each Person who controls such holder (within
the meaning of the Securities Act),  against all losses,  claims,  damages,
liabilities and expenses caused by, resulting from, arising out of or based
upon any untrue or alleged  untrue  statement of material fact contained in
any  registration  statement,  prospectus or preliminary  prospectus or any
amendment thereof or supplement thereto or any omission or alleged omission
of a material fact  required to be stated  therein or necessary to make the
statements  therein not  misleading,  except insofar as the same are caused
by,  resulting  from,  arising  out of or based  upon or  contained  in any
information  furnished  in writing to the Company by such holder  expressly
for use  therein  or by such  holder's  failure  to  deliver  a copy of the
registration  statement or  prospectus  or any  amendments  or  supplements
thereto  after the Company  has  furnished  such  holder with a  sufficient
number of copies of the same. In connection with an underwritten  offering,
the Company shall indemnify such underwriters, their officers and directors
and each Person who controls such  underwriters  (within the meaning of the
Securities  Act) to the same extent as provided  above with  respect to the
indemnification of the holders of the Warrant and of Warrant Shares.

               (b) In connection with any registration  settlement in which
a holder of a Warrant  or of  Warrant  Shares is  participating,  each such
holder  shall  furnish  to the  Company  in writing  such  information  and
affidavits as the Company  reasonably  requests for use in connection  with
any such registration  statement or prospectus and, to the extent permitted
by law,  shall  indemnify  each  other  holder of a Warrant  and of Warrant
Shares,  the  Company,  its  directors  and  officers  and each  person who
controls the Company (within the meaning of the Securities Act) against any
losses,  claims,  damages,  liabilities and expenses  caused by,  resulting
from,  arising out of or based upon any untrue or alleged untrue  statement
of material fact  contained in the  registration  statement,  prospectus or
preliminary  prospectus or any amendment  thereof or supplement  thereto or
any omission or alleged  omission of a material  fact required to be stated
therein or necessary to make the  statements  therein not  misleading,  but
only to the extent that such untrue  statement  or omission is contained in
any  information  or  affidavit  so  furnished  in writing  by such  holder
expressly for use in the registration  statement;  provided,  however, that
the obligation to indemnify shall be several, not joint and several,  among
such holders of a Warrant and of Warrant  Shares and the  liability of each
such holder of a Warrant and of Warrant  Shares,  shall be in proportion to
and  limited to the net amount  received  by such  holder  from the sale of
Warrant  Shares  pursuant to such  registration  statement.

               (c) Any person entitled to  indemnification  hereunder shall
(i) give prompt written notice to the indemnifying  party of any claim with
respect  to  which  it  seeks  indemnification  and  (ii)  unless  in  such
indemnified party's reasonable judgment a conflict of interest between such
indemnified and indemnifying  parties may exist with respect to such claim,
permit  such  indemnifying  party to assume the  defense of such claim with
counsel  reasonably  satisfactory to the indemnified party. If such defense
is assumed,  the  indemnifying  party shall not be subject to any liability
for any settlement made by the  indemnified  party without its consent (but
such consent will not be unreasonably  withheld). An indemnifying party who
is not entitled  to, or elects not to,  assume the defense of a claim shall
not be  obligated to pay the fees and expenses of more than one counsel for
all parties  indemnified  by such  indemnifying  party with respect to such
claim,  unless  in the  reasonable  judgment  of any  indemnified  party  a
conflict of interest may exist between such indemnified party and any other
of such  indemnified  parties with  respect to such claim.  Failure to give
prompt  written  notice shall not release the  indemnifying  party from its
obligations hereunder.

               (d) To the  extent  permitted  by law,  the  indemnification
provided  for under this  Agreement  shall  remain in full force and effect
regardless  of any  investigation  made by or on behalf of the  indemnified
party or any officer,  director or controlling  person of such  indemnified
party  and  shall   survive  the  transfer  of   securities.

               (e) If the  indemnification  provided  for in or pursuant to
this Section 7 is due in accordance with the terms thereof,  but is for any
reason  unavailable  or  unenforceable  or  insufficient  in respect of any
losses, claims, damages,  liabilities or expenses referred to therein, then
each  applicable   indemnifying   party,  in  lieu  of  indemnifying   such
indemnified  party,  shall contribute to the amount paid or payable by such
indemnified person as a result of such losses, claims, damages, liabilities
or expenses in such  proportion as is  appropriate  to reflect the relative
fault of the  indemnifying  party  on the one  hand and of the  indemnified
party on the other in connection  with the  statements  or omissions  which
resulted in such losses, claims,  damages,  liabilities or expenses as well
as any other relevant equitable  considerations.  The relative fault of the
indemnifying  party on the one hand and of the  indemnified  person  on the
other shall be determined by reference to, among other things,  whether the
untrue or alleged  untrue  statement of a material  fact or the omission or
alleged  omission to state a material fact relates to information  supplied
by the  indemnifying  party or by the  indemnified  party,  by such party's
relative  intent,  knowledge,  access to  information  and  opportunity  to
correct or prevent  such  statement,  or  omission.  In no event  shall the
liability of any selling holder of Warrant Shares be greater in amount than
the amount of proceeds received by such holder upon such sale.

          8.  Participation  in  Underwritten  Registrations.  No holder of
Warrant  Shares may  participate  in any  registration  hereunder  which is
underwritten unless such holder (a) agrees to sell such holder's securities
on the basis  provided  in any  underwriting  arrangements  approved by the
Person or Persons entitled  hereunder to approve such  arrangements and (b)
completes and executes all questionnaires, powers of attorney, indemnities,
underwriting agreements and other documents require under the terms of such
underwriting arrangements.

          9.  Miscellaneous.  (a) Except as otherwise  provided herein, the
provisions of this  Agreement may be amended only with the written  consent
of the Company and the holders of a Warrant to purchase at least 50% of the
then unexercised Warrant Shares.

               (b) All covenants and  agreements in this Agreement by or on
behalf of any of the parties  hereto shall bind and inure to the benefit of
their  respective  successors and assigns whether so expressed or not. Each
successor  and  assign  shall  agree to be bound by the terms  hereof as if
originally  a  party  hereto.  In  addition,  whether  or not  any  express
assignment has been made,  the  provisions of this Agreement  which are for
the benefit of purchasers or holders of the Warrant Shares are also for the
benefit  of, and  enforceable  by, any  subsequent  holder of such  Warrant
Shares,  provided  that each such  transferee  shall agree in writing to by
bound by the terms and conditions of this Agreement.

               (c) Whenever  possible,  each  provision  of this  Agreement
shall be  interpreted  in such  manner as to be  effective  and valid under
applicable  law,  but if any  provision  of  this  Agreement  is held to be
prohibited  by or invalid under  applicable  law,  such  provision  will be
ineffective only to the extent of such  prohibition or invalidity,  without
invalidating  the remainder of such provision of this  Agreement.

               (d) This Agreement may be executed  simultaneously in two or
more counterparts,  each of which shall constitute an original,  but all of
which taken together shall  constitute one and the same Agreement.

               (e)  The  headings  of  this   Agreement  are  inserted  for
convenience only and do not constitute a part of this Agreement.

               (f) This Agreement shall be governed by the law of the State
of New York.

               (g) All notices  provided  for herein shall be given or made
by  certified  mail or hand  delivery,  mailed or delivered to the intended
recipient at the address  specified  below its name on the  signature  page
hereof; or as to any party, at such other address as shall be designated by
such party in a notice to each other party. Except as otherwise provided in
this Agreement,  all such communications  shall be deemed to have been duly
given when mailed or personally delivered.

               (h) The Company will not hereafter  enter into any agreement
with  respect  to its  securities  which is  inconsistent  with the  rights
granted  under this  Agreement  to the holders of Warrant  Shares.

               (i) Any  person  having  rights  under any  provisions  this
Agreement will be entitled to enforce such rights specifically,  to recover
damages  caused by reason of any breach of any provision of this  Agreement
and to exercise all other rights granted by law.

               (j) In any  action of  proceeding  brought  to  enforce  any
provision of this  Agreement,  or where any provision of such  Agreement is
validly  asserted  as a  defense,  the  successfully  party  shall  receive
attorneys fees in addition to any other available remedy.

          IN WITNESS  WHEREOF,  the parties have executed this Agreement as
of the date first written above.

                                    GCA CORPORATION



                                    By
                                      -------------------------------
                                       (Name and Title)
                                       7 Shattuck Road
                                       Andover, Massachusetts  01810
                                       Attention:  General Counsel


                                    CARL ZEISS, INC.



                                    By
                                      -------------------------------
                                       (Name and Title)
                                       1 Zeiss Drive
                                       Thornwood, New York  10549
                                       Attention:  Corporate Secretary