After this court’s opinion in Commonwealth v. Oakes, 401 Mass. 602 (1988), reversing the defendant’s conviction for violation of G. L. c. 272, § 29A (1986 ed.),1 because of constitutional overbreadth under the First Amendment, the Legislature amended G. L. c. 272, § 29A.2 As a result of the legislative amendment to G. L. c. 272, § 29A, and after oral argument, a plurality of the United States Supreme Court decided that the overbreadth issue was moot and remanded the case to us for further proceedings on the remaining “live” issue, an as-applied Federal constitutional attack on the statute. See Massachusetts v. Oakes, 109 S. Ct. 2633, 2639 (1989).3 For the reasons stated in this opinion, we affirm the defendant’s conviction.

*94Generally, a challenge to the constitutionality of a statute as applied should be preserved in a motion for a required finding of not guilty under Mass. R. Crim. P. 25, as amended, 389 Mass. 1107 (1983). See Commonwealth v. Jasmin, 396 Mass. 653, 655 (1986) (“a challenge to ... a statute as applied might properly be raised before trial, but it need not be raised until the Commonwealth has presented its evidence showing the circumstances in which the statute would be applied to a defendant”). See also Commonwealth v. 707 Main Corp., 371 Mass. 374, 383 (1976); Commonwealth v. Antobenedetto, 366 Mass. 51, 58-59 (1974). Although the defendant raised an as-applied challenge to the statute’s constitutionality in a pretrial motion to dismiss, he failed to preserve it at trial. He did not move for a required finding of not guilty. See Mass. R. Crim. P. 25 (a). He also did not ask for any limiting jury instructions. Thus, under our procedural rules, the defendant’s Federal constitutional as-applied challenge was not properly preserved.4 “[W]e recognize that we may consider issues on appeal not raised at trial, but our power to do so is rarely exercised, and is exercised only in response to a serious and obvious error creating *95a substantial risk of a miscarriage of justice.” Commonwealth v. Pares- Ramirez, 400 Mass. 604, 609 (1987). Commonwealth v. Freeman, 352 Mass. 556, 564 (1967). We conclude there is no substantial risk of a miscarriage of justice.

In determining whether the defendant’s claim that the former statute, G. L. c. 272, § 29A, is unconstitutional as applied to his conduct, we set forth the facts in the light most favorable to the Commonwealth. See Commonwealth v. Latimore, 378 Mass. 671, 676-677 (1979). See also Commonwealth v. Jasmin, 396 Mass. 653 (1986). In 1983 and 1984, the defendant took a series of photographs of his stepdaughter, who was then fourteen years old. At first, he photographed her in clothes. Next, he photographed her wearing bathing suits and “age-inappropriate” lingerie. Finally, he took approximately ten photographs of her, posed atop a bar in the basement of their home, wearing only bikini underpants and a red scarf. These photographs prominently featured the teenager’s uncovered breasts. The defendant suggested that these photographs would make her “big for Playboy magazine.” The defendant kept these photographs a secret from his then wife,5 the teenager’s mother. He kept them hidden, first in a locked safe and then in a false ceiling in the basement of the house. The teenager attempted to rip up the photographs and throw them away. When the defendant discovered her attempt to destroy the photographs, he demanded that she reassemble them. The defendant’s trial strategy (trial counsel is not counsel on appeal) was to deny that he took the photographs.

The defendant argues that his conviction cannot stand because the photographs are protected speech under the First Amendment to the United States Constitution. Contrary to the defendant’s argument, his conduct was not “pure” speech; contrary to the Commonwealth’s argument, it was not merely conduct. The activities for which the defendant was convicted were mixed speech and conduct, or expressive *96conduct. Commonwealth v. Oakes, supra at 603-604.6 See State v. Helgoth, 691 S.W.2d 281 (en banc) (Mo. 1985) (in child pornography prosecution, prohibited conduct may be assumed to contain “speech” as well as “non-speech” elements). Accord People v. Folk, 109 Misc. 2d 738 (N.Y. Crim. Ct. 1981); State v. Jordan, 665 P.2d 1280 (Utah), appeal dismissed, sub nom. Fullmer v. Utah, 464 U.S. 910 (1983). Cf. Payne v. Commonwealth, 623 S.W.2d 867, 872 (Ky. 1981), cert. denied, 456 U.S. 909 (1982).

Under current First Amendment analysis, “[t]he Government generally has a freer hand in restricting expressive conduct than it has in restricting the written or spoken word.” Texas v. Johnson, 109 S. Ct. 2533, 2540 (1989). When “‘speech’ and ‘nonspeech’ elements are combined in the same course of conduct, a sufficiently important governmental interest in regulating the nonspeech element can justify incidental limitations on First Amendment freedoms.” United States v. O’Brien, 391 U.S. 367, 376 (1968).

In order for a State to prevail under the rule in O’Brien, it must demonstrate that it has “asserted an interest in support of [the defendant’s] conviction that is unrelated to the suppression of expression.” Texas v. Johnson, supra at 2541.7 To justify the defendant’s conviction, the Commonwealth asserts an interest in protecting minors from exploitation. The Commonwealth’s interest in preventing the exploitation of children meets the O’Brien standard, id., because it is unre*97lated to the suppression of expression. Moreover, “[i]t is evident beyond the need for elaboration that a State’s interest in ‘safeguarding the physical and psychological well-being of a minor’ is ‘compelling.’ ” New York v. Ferber, 458 U.S. 747, 756-757 (1982), quoting Globe Newspaper Co. v. Superior Court, 457 U.S. 596, 607 (1982). The interest in protecting minors from exploitation falls within an area in which States traditionally have exercised the police power. See Prince v. Massachusetts, 321 U.S. 158, 170 (1944); State v. Jordan, 665 P.2d 1280, 1283 (Utah 1983).

The defendant’s conduct in posing his stepdaughter partially nude and photographing her is distinguishable from the dissemination of such photographs. For First Amendment purposes, the former is mixed speech and conduct, or expressive conduct; the latter is “pure” speech, and under Federal law is more fully protected than expressive conduct. “Regulations governing activities of distributors of child pornography may be viewed with greater constitutional scrutiny than those regulating activities of coercers and producers, because the latter are considered to regulate, primarily conduct and only incidentally speech.” United States v. Reedy, 632 F. Supp. 1415, 1418-1419 (W.D. Okla. 1986), aff'd, 845 F.2d 239 (10th Cir. 1988), cert. denied, 489 U.S. 1055 (1989). “The specific distinction to be made is between the use of children in the actual production of pornographic material and the ultimate dissemination of materials so produced.” State v. Helgoth, 691 S.W.2d 281, 284 (en banc) (Mo. 1985).

The Commonwealth’s evidence did not show any indication that the photographs would be distributed. Therefore, considerations peculiar to distributors are not involved in this case. Rather, the harm sought to be proscribed by § 29A is the conduct involved in photographing a child nude or semi-nude, not the photographs themselves.8 Thus, the fact that *98the pictures are not child pornography under New York v. Ferber, 458 U.S. 747 (1982), is irrelevant. What is made criminal under § 29A is photographing minors nude or semi-nude. Accordingly, under Federal constitutional law, the Commonwealth’s interest in protecting children permits the application of § 29A to the defendant’s conduct.

On remand from the United States Supreme Court, the defendant for the first time argues that the statute under which he was convicted violates art. 16 of the Massachusetts Declaration of Rights. Although the defendant stated in his pretrial motion to dismiss that the statute violated art. 16 of the Declaration of Rights, he never offered any argument to support his contention at any stage of the proceedings until the action, was remanded to us by the United States Supreme Court. The defendant now argues that art. 16 of the Declaration of Rights provides greater protection to a citizen than does the First Amendment to the United States Constitution. See, e.g., Commonwealth v. Sees, 374 Mass. 532 (1978). The Attorney General responds by noting that it has been this court’s policy not to decide cases on State constitutional grounds unless the State constitutional issue was raised at trial and is argued separately from any Federal claim. See Commonwealth v. Shine, 398 Mass. 641, 649 n.2 (1986); Commonwealth v. Acen, 396 Mass. 472, 473 n.2, appeal dismissed, 476 U.S. 1155 (1986); Matter of Roche, 381 Mass. 624, 629 n.7 (1980). See also Commonwealth v. McDonough, 400 Mass. 639, 647 n.12 (1987). Cf. Commonwealth v. Upton, 394 Mass. 363, 364 (1985) (discussing State law issue timely raised but not decided in Commonwealth v. Upton, 390 Mass. 562, 573-574 [1983]). We agree with the *99Attorney General that the defendant did not preserve this issue. We therefore do not reach or discuss it.9

Judgment affirmed.

(concurring, with whom Nolan and Lynch, JJ., join). I agree with the court that “under Federal constitutional law, the Commonwealth’s interest in protecting children permits the application of [G. L. c. 272,] § 29A to the defendant’s conduct.” Ante at 98. I agree that the conviction should be affirmed. I write separately only because in my view, the same view I expressed in Commonwealth v. Oakes, 401 Mass. 602, 605 (1988) (O’Connor, J., dissenting), vacated and remanded, 109 S. Ct. 2633, 2639 (1989), the court errs when it declares that “speech” requiring First Amendment analysis occurred in this case. The mere procuring or causing of a child to pose for photographs, not shown by the *100evidence nor even contended by the defendant to have been taken for display or distribution, is not speech. Conduct, of course, may constitute speech, but conduct that is not intended to communicate and that says nothing to anyone, as here, does not call for First Amendment-type analysis. The court relies primarily on State v. Helgoth, 691 S.W.2d 281 (en banc) (Mo. 1985), in support of its statement that the defendant’s actions in this case contain elements of speech. In fact, as I stated in my dissent in Oakes, supra at 609-610, Helgoth stands for the contrary proposition. In Helgoth, the defendant was convicted of taking posed photographs of a seventeen year old girl that focused on her uncovered breasts and vagina. The Supreme Court of Missouri stated that “the activity engaged in by the defendant and prohibited by the statute is distinctly conduct, as contrasted with speech. The offensive act is grounded in child abuse, and that is the epicenter of the case. The specific distinction to be made is between the use of children in the actual production of pornographic material and the ultimate dissemination of materials so produced.” Id. at 284. By stating otherwise in this case as to the defendant’s similar conduct, the court creates unwise precedent.