<PAGE>
 
                                                                   
                                                                EXHIBIT 8.1     
                          
                       [LETTERHEAD OF ROPES & GRAY]     
                                             
                                          January 7, 1999     
   
Summit Technology, Inc.     
   
21 Hickory Drive     
   
Waltham, MA 02451     
   
Ladies and Gentlemen:     
   
  We have acted as counsel to Summit Technology, Inc. ("Summit"), a
Massachusetts corporation, in connection with the planned transaction (the
"Merger") contemplated by the Agreement and Plan of Merger, dated as of October
1, 1998, by and among Summit, Alpine Acquisition Corp., a Delaware corporation
and a wholly-ownded subsidiary of Summit ("Merger Sub"), and Autonomous
Technologies Corporation, a Florida corporation ("Autonomous") (the "Merger
Agreement"). All capitalized terms used but not defined herein have the
meanings ascribed to them in the Merger Agreement.     
   
  For purposes of the opinion set forth below, we have reviewed and relied upon
the Merger Agreement, the Joint Proxy Statement and Prospectus included in the
Registration Statement on Form S-4 filed by Summit with the Securities and
Exchange Commission on January 7, 1999 (the "Proxy Statement"), and such other
documents, records and instruments as we have deemed necessary or appropriate
as a basis for our opinion. We have assumed without investigation or
verification that all statements contained in the foregoing documents are true,
correct, and complete as of the date hereof and will remain true, correct and
complete through the Effective Time; that no actions inconsistent with such
statements have occurred or will occur; that all such statements made "to the
best of the knowledge of" any persons or parties, or similarly qualified, are
true, correct and complete as if made without such qualification; and, as to
all matters in which a person or entity making a representation has represented
that such person or entity either is not a party to, does not have, or is not
aware of, any plan or intention, understanding or agreement, we have assumed
that there is in fact no such plan, intention, understanding or agreement.     
   
  We also have assumed that (i) the Merger will be consummated in accordance
with the Merger Agreement (including satisfaction of all covenants and
conditions to the obligations of the parties without amendment or waiver
thereof); (ii) all representations and warranties contained in the Merger
Agreement are true, correct, and complete in all respects; (iii) the Merger
will be effective as a merger under the applicable laws of Delaware and
Massachusetts; and (iv) if the Merger is not restructured as a fully taxable
Merger, (a) each of Summit, Autonomous and Merger Sub will deliver a tax
representation certificate satisfactory to Ropes & Gray and (b) each of Summit,
Autonomous and Merger Sub will comply with the reporting obligations with
respect to the Merger, if any, required under the Internal Revenue Code (the
"Code") and the Treasury regulations promulgated thereunder.     
<PAGE>
 
   
  Any inaccuracy in, or breach of, any of the aforementioned statements,
representations and assumptions and any change in applicable law after the date
hereof could adversely affect our opinion. No ruling has been sought from the
Internal Revenue Service by Summit, Autonomous or Merger Sub as to the federal
income tax consequences of any aspect of the Merger, and the Internal Revenue
Service is not bound by our opinion herein.     
   
  Based upon and subject to the foregoing as well as to the qualifications and
limitations set forth below, it is our opinion that the discussion under the
caption "Material Federal Income Tax Consequences of the Merger" in the Proxy
Statement constitutes the opinion of Ropes & Gray as to the material United
States federal income tax consequences generally applicable to Autonomous
stockholders in connection with the Merger.     
   
  No opinion is expressed as to any matter not specifically addressed above,
including the tax consequences of any of the transactions under any foreign,
state, or local tax law or the tax consequences of any other transactions
contemplated or entered into by Summit, Autonomous or Merger Sub in connection
with the transactions described above. Our opinion is based on current federal
income tax law and we do not undertake to advise you as to any changes in
federal income tax law after the date hereof that may affect our opinion.     
   
  This opinion is solely for your benefit, shall not inure to the benefit of
any other person, including without limitation any successor or assign of
Summit, whether by operation of law or otherwise, and is not to be used,
circulated, quoted or otherwise referred to for any purpose without our express
written permission.     
   
  We hereby consent to the filing with the Securities and Exchange Commission
of this opinion as an exhibit to the Proxy Statement.     
                                             
                                          Very truly yours,     
                                             
                                          /s/ Ropes & Gray     
                                             
                                          Ropes & Gray