After a jury trial, the defendant was convicted of disseminating obscene matter in violation of G. L. c. 272, § 29, and fined $5,000.1 The conviction was *890based on a coin-operated film, “Seak’s Fullfillment,” which was available for viewing at the defendant’s store. The defendant appealed and we granted the application for direct appellate review. On appeal, the defendant contends that the complaint should have been dismissed because G. L. c. 272, § 29, is unconstitutional under arts. 1, 12, and 16 of the Declaration of Rights of the Massachusetts Constitution, and the First Amendment to the United States Constitution. The defendant also objects to several of the judge’s evidentiary rulings, and to portions of the jury instructions. We conclude that the defendant’s motion to dismiss the complaint was properly denied, but that the defendant must have a new trial because of the judge’s refusal to allow the defendant’s expert to testify about the artistic value of the film.

At the time of the defendant’s trial, G. L. c. 272, § 31, as amended through St. 1977, c. 917, §§ 4-6, provided that “matter is obscene if taken as a whole it (1) appeals to the prurient interest of the average person applying the contemporary standards of the commonwealth;2 (2) depicts or describes sexual conduct in a patently offensive way; and (3) lacks serious literary, artistic, political or scientific value.” We have held that “[a]lthough G. L. c. 272, § 31, expressly applies the Statewide standard only to questions of priirience, the Legislature clearly intended that the Commonwealth standard should apply also to questions of patent offensiveness.” Commonwealth v. 707 Main Corp., 371 Mass. 374, 385 (1976). See District Attorney for the *891N. Dist. v. Three Way Theatres Corp., 371 Mass. 391, 392-393 (1976).

1. The defendant first argues that the definition of “obscene matter” in § 31 is unconstitutionally vague because there are no contemporary standards of the Commonwealth. In particular, the defendant focuses on the “patently offensive” requirement. Since § 31 was based on Miller v. California, 413 U.S. 15, 24-25, 33-34 (1973), we see no merit in the defendant’s claim under the First Amendment. See Commonwealth v. Trainor, 374 Mass. 796, 798 (1978). In Commonwealth v. 707 Main Corp., supra at 383, we held that the statute “is not unconstitutionally vague in its proscription of dissemination of obscene matter, because its definitions of ‘obscene’ matter and ‘sexual conduct’ . . . provide reasonably ascertainable standards of guilt” (emphasis supplied). See District Attorney for the N. Dist. v. Three Way Theatres Corp., supra at 394; Commonwealth v. Thureson, 371 Mass. 387, 389 (1976). We again rejected a claim that the Massachusetts Constitution requires “greater specificity” in the statutory definition of obscenity in Commonwealth v. Trainor, 374 Mass. 796, 798-799 (1978). See Bunker Hill Distrib., Inc. v. District Attorney for the Suffolk Dist., 376 Mass. 142, 145-146 (1978).

However, in Commonwealth v. Trainor, supra at 800, we left open “resolution of any challenge to the statute by proof that there is no such thing as . . . ‘contemporary standards of the commonwealth’ .... [I]f such standards do not exist, the statute must fail for unconstitutional vagueness.” The defendant argues that there are no such standards because reaction to given material differs with viewer attitudes depending on such factors as sex, age, occupation, education, and life-style as well as on the setting within the community in which the material is available. In addition, the defendant notes that public tolerance of material shifts over time.

In Commonwealth v. Trainor, supra at 800, we rejected a similar challenge, concluding that “[t]he appellants have *892not met their heavy burden of demonstrating the unconstitutionality of the Commonwealth’s obscenity statutes. We are not persuaded that there is no rational basis for the Legislature to conclude that there are ascertainable Statewide standards, even though the citizens of the Commonwealth differ from each other in numerous ways, including upbringing, place of residence, age, education, religion, and sex.” We take this language to mean that proof that there are no Statewide standards of patent offensiveness requires more than the defendant’s bare allegations here that attitudes vary with individual differences among viewers.

The setting in which the material is available is relevant to the question of patent offensiveness. In Commonwealth v. Plank, 378 Mass. 465, 469 (1979), discussing nude dancing, we stated that “the issue of patent offensiveness is to be decided in context.” However, this does not indicate that Statewide standards do not exist, but rather that Statewide standards vary uniformly depending on the context in which the material is available. It is not unusual for the legal reasonableness of a defendant’s conduct to depend on the circumstances in which the conduct occurred. Similarly, the fact that public tolerance shifts over time does not in itself show that there are no Statewide standards, so long as public tolerance shifts uniformly. The defendant has not made any arguments, other than those rejected in Trainor, to show that shifts in tolerance, if any, are not Statewide.

We reject the defendant’s argument that differing verdicts on numerous complaints against it involving allegedly comparable films reveal that there are no Statewide standards. See Smith v. United States, 431 U.S. 291, 309 (1977). Consistent verdicts in prosecutions under the same statute are not required, nor do we accept the defendant’s allegation that all the so called “adult” movies shown at its store were comparable. Moreover, several factors may influence a jury’s verdict, such as the knowledge requirement of G. L. c. 272, § 29.

*893We believe that our prior decisions establish that the definition of obscenity in G. L. c. 272, § 31, is not unconstitutionally vague under the Declaration of Rights or the First Amendment, and we once again “see no reason to change that conclusion at this time.” Commonwealth v. Trainor, 374 Mass. 796, 799 (1978). As to the issue left open in Trainor, we find the defendant’s proof insufficient to meet their “heavy burden” of showing that Statewide standards do not exist.3

We reaffirm our holding that the Commonwealth need not introduce extrinsic evidence of Statewide standards, but rather can rely on the material itself to prove that the material is obscene. Commonwealth v. Trainor, supra, and cases cited. The practice does not unconstitutionally relieve the Commonwealth of its burden of proof. See District Attorney for the N. Dist. v. Three Way Theatres Corp., 371 Mass. 391, 394 (1976), citing Kaplan v. California, 413 U.S. 115, 121 (1973). Nor does it allow the jury to make findings not supported by the evidence. “ [T]he trier of fact may draw on his own knowledge of normative views in his own community in applying statutorily prescribed community standards.” District Attorney for the N. Dist. v. Three Way Theatres Corp., supra.

2. The defendant’s contention that we should construe § 29 to require knowledge of the legal obscenity of the materials disseminated is also quickly decided. We have al*894ready rejected this argument, and held that the Commonwealth must prove only that the defendant had knowledge of the contents and general character of the material. Commonwealth v. Rosenberg, 379 Mass. 334, 338-339 (1979). Commonwealth v. Trainor, 374 Mass. 796, 800-801 (1978). Commonwealth v. Thureson, 371 Mass. 387, 389-390 (1976). See Hamling v. United States, 418 U.S. 87, 120-123 (1974). General Laws c. 272, § 31, as appearing in St. 1974, c. 430, § 12, defines “knowing” for purposes of § 29 as “a general awareness of the character of the matter.” The statutory definition fully comports with Federal and State constitutional due process requirements. Hamling v. United States, supra at 123. Commonwealth v. Trainor, supra at 801. Commonwealth v. 707 Main Corp., 371 Mass. 374, 383 (1976).

3. We now turn to the defendant’s objections to the conduct of its trial. The defendant first argues that the judge erred in refusing to allow the defendant’s expert, Professor Charles Blinderman, to testify. Defense counsel stated that Professor Blinderman’s testimony was offered as to contemporary community standards and as to the question of the serious artistic, social, political, and scientific value of the film. The record indicates that the judge’s ruling was based on his view that Professor Blinderman was not qualified as an expert in either area. Although the focus of discussion just prior to the ruling was on Professor Blinderman’s qualifications to testify as to contemporary Commonwealth standards, the judge ruled that “I am not going to allow Professor Blinderman to testify in this case,” and defense counsel had clearly stated that Professor Blinderman’s testimony was also offered as to serious artistic, social, political, and scientific value.

At the outset, we reject the Commonwealth’s argument that the defendant cannot successfully appeal the exclusion of Professor Blinderman’s testimony because it did not make an offer of proof as to his testimony. “The failure to make an offer of proof when it is required is fatal” (emphasis supplied). Commonwealth v. Hubbard, 371 Mass. 160, 174 (1976), and cases cited. When testimony is excluded based *895on the judge’s determination that the putative expert is not qualified, no offer of proof is required. Newton Girl Scout Council, Inc. v. Massachusetts Turnpike Auth., 335 Mass. 189, 199 (1956), and cases cited.

Both this court and the United States Supreme Court have recognized that testimony by a qualified expert is relevant and important to a defense that material is not obscene. Kaplan v. California, 413 U.S. 115, 121 (1973) (defense should be free to introduce appropriate expert testimony). Commonwealth v. Trainor, 374 Mass. 796, 802 (1978). Thus in Kaplan, supra, the Court referred with approval to Justice Frankfurter’s concurring opinion in Smith v. California, 361 U.S. 147, 164-165 (1959), discussing “the right of one charged with obscenity — a right implicit in the very nature of the legal concept of obscenity — to enlighten the judgment of the . . . jury . . . regarding the prevailing literary and moral community standards and to do so through qualified experts .... [T]o exclude such expert testimony is in effect to exclude as irrelevant evidence that goes to the very essence of the defense and therefore to the constitutional safeguards of due process.” Moreover, the fact that the Commonwealth carries its burden of proof of obscenity by introducing the material alone, militates in favor of allowing a defendant the broadest scope in introducing expert testimony on obscenity. “Where the question is whether portrayals of sexual conduct are ‘obscene’ under the statutory definition, it would be a rare case in which testimony from a qualified expert should be excluded on the ground that it would not be helpful to the trier of fact.” Commonwealth v. Trainor, supra.4

“We have repeatedly stated that the question of an expert’s qualifications is for the trial judge, and his determination will be reversed only on an abuse of discretion or error *896as matter of law.” Commonwealth v. Boyd, 367 Mass. 169, 182 (1975), and cases cited. See Commonwealth v. Seit, 373 Mass. 83, 92 (1977); Campbell v. Thornton, 368 Mass. 528, 541 (1975). “The criterion of the judge is whether the witness possesses sufficient skill, knowledge or experience in the field of his testimony that the jury may receive appreciable assistance from it.” Commonwealth v. Boyd, supra. In light of the numerous possible reasons for a trial judge’s ruling that a witness is not qualified as an expert, we are reluctant to act on appeal solely on the basis of our independent opinion that a witness was qualified. Nevertheless, a trial judge’s broad discretion in ruling on the qualifications of an expert witness “is not without limits.” Edinburg v. Merry, 11 Mass. App. Ct. 775, 777 (1981), and cases cited. Moreover, because of the special concerns involved, we bring closer scrutiny to the exclusion of expert testimony proffered by the defense in an obscenity case. See Hewitt v. State Bd. of Censors, 243 Md. 574, 582 (1966).

In the instant case, we cannot think of any acceptable reason why Professor Blinderman was not qualified to testify as an expert on the artistic value of the film. Professor Blinderman’s undisputed testimony on voir dire was that he was a professor of English and an affiliate professor of biology at Clark University in Worcester, that he had been a professor there for twenty years, that he taught an evening division course surveying erotic art over the centuries, that he had taught a total of 100 students in this course, and was familiar with their views on erotic art, that the course dealt in part with the nature of erotic expression in the Commonwealth, that he also did independent investigation in the Worcester area to study erotic art, that in this connection he purchased some magazines from convenience stores, saw two films at the “Fine Arts Theater,” saw some videotapes from a Worcester store, and reviewed books from two Worcester bookstores, to get an idea of the availability and the nature of sexually explicit material in Worcester, that he had read several reports and treatises on pornography, and that, as a result of his professional training, experience, re*897search, study, and investigation, he was familiar with contemporary trends and attitudes toward the depiction of sexual conduct in Massachusetts. In these circumstances, we conclude that it was error to refuse to allow Professor Blinderman to testify about the artistic value of the film. We note that although credibility is a factor in ruling on the qualifications of an expert witness, Rubin v. Arlington, 327 Mass. 382, 384 (1951), there is no indication here that the judge disbelieved Professor Blinderman’s description of his qualifications. Indeed, in a case, such as this one, involving constitutional problems of free speech, it is reasonable to require that a trial judge who excludes expert testimony because he disbelieves the witness’ testimony as to qualifications should make a specific finding to that effect. The judge made no such finding here.

Because our foregoing conclusion requires a new trial, it is unnecessary for us to consider the further issue whether there also was error in the judge’s ruling that Professor Blinderman was not qualified to testify about Statewide contemporary standards. We observe only that the issue is closer than the artistic value issue, and that were we to rule on Professor Blinderman’s qualifications in the first instance, we might well be inclined to find that he was also qualified to testify about Statewide standards. In this connection, we stress that the fact that Professor Blinderman’s testimony was chiefly of familiarity with the Worcester area did not indicate that he was not qualified to testify as to Statewide standards, since the obscenity statute assumes that a uniform, Statewide standard exists. See Commonwealth v. Trainor, 374 Mass. 796, 805 (1978). Nor was Professor Blinderman unqualified solely because he had not conducted a valid public opinion poll or survey. An expert may be qualified to testify as to community standards based on relevant training, experience, research, study, and investigation. It is clear that Professor Blinderman’s asserted expertise did not rest solely on his knowledge of the views expressed by the students in his evening division class.

*8984. What we have said above is dispositive of the case at this time. Nevertheless, we discuss some of the defendant’s other claims because they are likely to recur at a retrial of this matter.

Prior to the trial, the judge granted a motion in limine by the Commonwealth requesting that the judge order “that the defendant refrain from arguing to the jury that because the films were viewed by consenting adults it constitutes either a defense or appropriate consideration for the jury in determining whether the defendant is guilty of dissemination of obscene matter.” “The purpose of a motion in limine is to prevent irrelevant, inadmissible or prejudicial matters from being admitted in evidence . . . and in granting such a motion, a judge has discretion similar to that which he has when deciding whether to admit or exclude evidence ...” (citations omitted). Commonwealth v. Lopez, 383 Mass. 497, 500 n.2 (1981).5

The parties correctly agree that the fact that the film was available only to consenting adults is not a defense to a charge of disseminating obscene matter under § 29. See Paris Adult Theatre I v. Slaton, 413 U.S. 49, 57 (1973); New Palm Gardens, Inc. v. Alcoholic Beverages Control Comm’n, 11 Mass. App. Ct. 785, 795-796 (1981); Commonwealth v. Kocinski, 11 Mass. App. Ct. 120, 123 n.5 (1981). However, the defendant argues that based on Commonwealth v. Plank, 378 Mass. 465, 469-470 (1979), it is an appropriate consideration on the issue of patent offensiveness. As indicated supra, we agree that “the issue of patent offensiveness is to be decided in context.” Commonwealth v. Plank, supra at 469. Our holding there that a nude dance was not obscene rested in part on the fact that “ [s]o far as appears, the dance took place on a stage in a ‘club’ before willing adult patrons” (emphasis supplied). Id.

*899The record indicates that the judge allowed the Commonwealth’s motion based on his view that the consenting adults issue was irrelevant. This was error, in so far as “the context” in which the allegedly obscene material was disseminated, including the fact that it was available to consenting adults, is an appropriate consideration in determining whether the material is obscene. However, we do not think that defense counsel’s inability to use the words, “consenting adults,” was prejudicial. In closing argument, defense counsel, without objection, made the following argument “What is patently offensive? Officer Dussault [the arresting officer] mentioned a drive-in theater that shows ‘X’ rated movies. Would it make a difference to you, as an average person ... if this film . . . [was] shown at the drive-in theater close to a highway? Would it make any difference to you if you went to a sex theater or Showcase Cinema or White City Cinema and went in and watched this film? Would that make a difference? Where is the place? The place has been here since at least 1976. It’s a place that deals with sexually explicit materials. There is no doubt about that. Take a look at the front of the store. They were there for viewing in booths in the back. One person per booth. Does that circumstance affect the average person’s view of what is patently offensive?” Defense counsel also stated that “ [t]here are, in the City of Worcester alone, many adult uses . . . they’re uses which restrict actions to adults and His Honor will tell you in this particular case you need not speculate as to minors. We’re talking strictly of the impact of these films on adults. Minors are not involved in this case and it has nothing to do with your consideration.” Moreover, the evidence given by Officer Phillip Dussault at trial was that the front of the United Books’ store was glass that was painted yellow, with a sign stating “No one under 21 allowed”; that the coin-operated films were available in booths in a room at the rear of the store; and that each booth had a door which, when shut, served as the screen for the coin-operated film. In these circumstances, we think the jury were adequately ap*900prised of the context in which “Seak’s Fullfillment” was available in determining whether it was patently offensive. Accordingly, the defendant was not prejudiced by its inability to refer to “consenting adults.”

The defendant also argues that the judge erred in granting a motion in limine by the Commonwealth requesting that the judge order “that the defendant refrain from making reference to an entertainment license granted by the city of Worcester for showing coin-operated films on the premises at United Book[s], Inc. ...” Whatever the relevance of the defendant’s license to the issues at bar, the fact of the license was fully presented to the jury by the parties’ stipulation, which was read to the jury, that “the defendant, United Books Inc. is a duly organized and existing Massachusetts corporation and at the time of this alleged offense, the defendant United Book[s], Inc. was duly licensed by the City of Worcester to offer coin operated films for viewing in each of the booths on the premises.”

Finally, the defendant raises two objections to the jury instructions. First, the defendant argues that the judge erred in declining to instruct the jury that the Commonwealth must prove each of the three statutory elements of obscenity beyond a reasonable doubt. The judge instructed the jury on the presumption of innocence and the Commonwealth’s burden of proof beyond a reasonable doubt. He stated that the Commonwealth must prove beyond a reasonable doubt that the material in evidence is obscene, that the defendant disseminated the material, and that the defendant knew it was obscene. He then listed the three statutory elements of obscenity, repeated them for emphasis, and described each element correctly in detail. In this situation, we think the defendant’s argument is properly rejected on the reasoning that “the [defendant] [is] not entitled to any particular instruction as long as the charge, as a whole, was adequate.” Commonwealth v. Sherry, 386 Mass. 682, 696 (1982), and cases cited.

The defendant also contends that since the judge instructed the jury that “obscene material is not protected by the *901first amendment,” the judge erred in refusing to give the jury an instruction requested by the defendant that the film was presumptively protected by the First Amendment until proved to be obscene. The judge’s instructions on obscenity, discussed supra, made it clear that the defendant was presumed to be innocent unless and until the Commonwealth proved beyond a reasonable doubt that the film was obscene. The instruction requested by the defendant would have added nothing of substance to the already adequate charge. Thus, the judge did not err in refusing to give the requested instruction. Commonwealth v. Sherry, supra. Roaden v. Kentucky, 413 U.S. 496 (1973), and Bantam Books, Inc. v. Sullivan, 372 U.S. 58 (1963), relied on by the defendant, are inapposite. Both cases deal with the more stringent procedures required when the government seizes books or films. Similarly, Miller v. California, 413 U.S. 15 (1973), stresses the need for a precise statutory definition of obscenity to avoid constitutional problems. These cases do not require that a judge explicitly instruct a jury in an obscenity case that the material at issue is presumptively protected by the First Amendment. An adequate charge on the elements of obscenity and the presumption of innocence is sufficient in this regard.

Judgment reversed.

Verdict set aside.

(concurring). I adhere to the views expressed in my dissent in Commonwealth v. Trainor, 374 Mass. 796, 807-811 (1978). Accepting the fact that my views did not prevail, I concur in this opinion.