seeing the nega -- a means of birur or a din?

Is seeing something through a telescope the same as seeing it in person?  Is seeing though a microscope or through eyeglasses the same as seeing with one's own eyes?  Nafka mina for many halachos, e.g. seeing ervah, seeing ner chanukah in a window, electric light for havdalah, seeing moon through a window for kiddush levana, etc.

The gemara (Chulim 10b) discusses what the source for the din of chazakah is.  The gemara brings proof from our parsha:

מנא הא מלתא דאמור רבנן אוקי מילתא אחזקיה אמר רבי שמואל בר נחמני אמר ר' יונתן אמר קרא ויצא הכהן מן הבית אל פתח הבית והסגיר את הבית שבעת ימים דלמא אדנפיק ואתא בצר ליה שיעורא אלא לאו משום דאמרינן אוקי אחזקיה

When the kohen walks out of the house afflicted with a nega to declare it tamei, how does he know that the nega that he saw is still there?  Maybe in the few seconds or minutes it took for him to walk out the nega vanished?  It must be that we rely on chazakah.

Asks the Rogatchover (Shu"T #13): maybe the kohen took out a telescope or put on a better pair of glasses and can see that the nega is still there?  

Q.E.D. that seeing means seeing with your own two unaided eyes, not seeing through some instrument.

Yesh lachkor: is there a din that the kohen must see the nega in order to declare it tamei, or is seeing the nega just a means of birur to determine that the nega is actually there?

The Mishna in Negaim (3:1 and see Mishna Achrona there) tells us that only a kohen has the power to declare a nega tamei or tahor, but if the kohen is am ha'aretz and doesn't know the difference, he can be coached by a talmid chacham and told "Say tahor," or "Say tamei."  

Compare the Rambam's formulation with Rashi:

Rambam Hil Tzaraas 9:2

כיצד כהן שאינו יודע לראות החכם רואהו ואומר לו אמור טמא והכהן אומר טמא. אמור טהור והכהן אומר טהור

Rashi Archin 3a:

 שאינו בקי. י] והולך תלמיד חכם ישראל ורואה עמו ואומר לו אמור טמא והוא אומר טהור והוא אומר שהטומאה והטהרה תלויה במאמר הכהן והכי תניא בת"כ: 

The Rambam writes that החכם רואהו ואומר לו , the talmid chacham who is a yisrael sees the nega and just tells the kohen what to say. Rashi, however, writes הולך תלמיד חכם ישראל ורואה עמו , that the kohen has to actually see the nega along with the talmid chacham.  

According to the Rambam, seeing the nega is just a means of birur -- it is just a means to an end.  So long as somehow the kohen knows the nega is there, that's sufficient.  According to Rashi, there is a chiyuv for the kohen to actually see the nega, eyes on.  It's not about what he knows -- it's what he sees that matters.

The Rogatchover's proof should hinge on this machlokes.  If one assumes that all that is needed is birur, than a yisrael standing by the door and telling the kohen that the nega is still there, or the kohen himself seeing it though a telescope, should also work.  However, if actual seeing is required, then a telescope may not be sufficient.