The article deals with the analysis of ethical issues arising from «invisible» qualitative technique used to study hard-to-reach communities such as religious organizations. Only bottom-level entry and covert context can provide access to these communities; this, in turn, contradicts the key ethical principle of sociologist-to obtain informed consent from respondent. The author examines in detail the use of the method of participant observation according to the «ethics code». However, the direct access and informed consent question the possibility to acquire reliable and transparent data. The fieldwork paradox forces the researcher to find compromise between the ethical issue and the «invisible» technique. Two basic strategies with their strong and weak points are considered in the paper: «I see you» strategy and «invisible» strategy. The author pays special attention to the context disclosure procedures and the censorship of the study results made by respondents.