NikonGear'23
Gear Talk => Camera Talk => Topic started by: MFloyd on December 02, 2016, 00:07:25
-
All is in the subject: where, with my old removable Nikon F focusing screens, the matte side is obviously directed towards the mirror box; some people I know, tell me that on a modern Nikon DSLR, the matte side is oriented towards the prism. The reason for this question is, if the latter is the case, cleaning of dust coming from the mirror bis would be less critical to clean, as you would rub a glass surface, rather than the very delicate matte surface.
Nikon F focusing screen:
(https://farm6.staticflickr.com/5580/31206892112_2c82371ee6_k.jpg)
-
The obvious solution would be to look into the mirror chamber .... Then it will be apparent the matte side, as before, is directed towards the mirror, i.e. the lower side of the screen.
One can only shudder by the thought of what kind of internal reflections would result if the assertions were correct.
Never try to clean the groundglass other than by carefully blowing. No physical contact should occur.
Dust on a focusing screen is in fact beneficial for manual focusing. It helps the eye align a focused plane of the 3-D aerial image to the plane of the screen.
-
Thank you Bjørn. This concurs with my observation and logic. But the person, on another forum, was so convincing that a big doubt arose in my mind.
I have no fear to (wet) clean a sensor, but I never touch a focusing screen, except with a mild manual blower.
-
Believe your own eyes first, then get a second opinion.
That guy obviously never considered what would happen if a shiny surface, aligned parallel to the optical axis, was receiving light inside the mirror chamber. The black flocking is there for a reason.
The "matte" surface serves the purpose of breaking up the aerial image. For the Nikon F, one had a few special screens that really were "shiny" glass on either side. The C screen comes to mind. It was used for parallax focusing with a 6X dedicated finder and had an etched cross for this purpose. Outside the realm of photomacrography and without a high magnification finder, one couldn't visually focus the image at all as nothing trained the eye to stick to the plane of focus.
-
I had to check my D800, as Bjørn's conclusion differed from my own memories.
I observed that the curved Fresnel condenser is on the bottom, the spray-frosted matte-finish plano surface is on the top.
Due to the lack of a controlled lighting setup and that fact that I wanted to keep the screen area of the camera minimally exposed to dust, I hurriedly shot this iPhone photo that doesn't show the different surfaces, but does show the orientation of the screen as it sits in the camera, including the side flanges and the handling tab.
-
Thank you Keith. I'm correct to say that you observe that the matte side of the screen is oriented towards the prism? But it also means that both sides: matte screen side and Fresnel side are both in synthetic, very scratch sensitive material ? Which results that the cleaning procedure (no physical contact) remains ?
Contrary to my old Nikon F type focusing screen, which has clearly a glass side (prism) and a matte side (mirror) in synthetic material.
-
The basic fact remains that the lower side, towards the mirror chamber, is matte (by Fresnel structure on the surface).
-
So everything falls in place: old screens: glass side & plastic side; new screens: all synthetic: focusing side towards prism; fresnel side towards mirror.
-
A constant in a world of change.
-
I like it: A constant in a world of change.
-
If one absolutely needed to clean a modern thin plastic screen, an ultrasonic bath is probably the only sure way to guarantee no cleaning artifacts. Considering how seldom most operators need to clean the screen, a new replacement screen is probably a reasonable choice if your old one is too scratched, grease-smeared, or damaged.
I have, in the distant past, tried cleaning the textured Fresnel surfaces of the old F/F2/F3 screens using a cotton Q-Tip and alcohol. The best I could ever achieve was changing the screen from horribly soiled to merely soiled.
I agree with Bjørn that a bit of dust or even scratches on the focusing surface can actually be helpful when fine focusing. Dust spots on the non-focusing surfaces of screen or prism are much more annoying to me, since they hover just slightly out of focus.