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Roger shares his knowledge to be helpful and typically with the most successful procedure.Due to trial and error,those insights are quite viable.
Every effort I've ever seen by a novice on his first attempt to remove a focusing screen and clean it with any other means then air,resulting in a failed procedure...and frustration; in repeated attempts to remove marks or mineral spots or streaks from dried pure water.
There are vids on the net showing individuals using alcohol.Most importantly;one shouldn't attempt cleaning a focusing screen with wet cleaning solution and especially alcohol,since the focusing screen is not designed to get wet and usually results in stains,smudges or wipe mark stains.Once contaminated in such a way it will never be like its original exact pristine condition.
If one feels compelled to use a wet cleaning solution,here are a few viable options that have worked to some degree for experienced camera repair technicians.
Some use water with a few drops of mild dish soap in a 8oz. container and a two to three bath rinse,then a hot air blow across the surface...unless you know what your doing and have some experience,this method usually results in failure as well due to residual pure water spots or streaks.
The procedure is as follows:
1. get three clean foam cups, a bottle of distilled water, some dish soap(sensitivite skin ver), a roll of toilet paper(hehe) and a hair-dryer.
2. Drop three drop of soap in the first cup and fill it with distilled water.
3. Fill the remaining two cups with clean distilled water.
4. taking your plastic screen tweezers, grab your screen and soak it in the water for a good 30mins. This will allow the soap to break down the oils and residue that have built-up on on your screen.
5. Once it has soaked, you can carefully swish it around in the solution to help propagate the cleaning agent throughout the fine groves of the fresnel texture. Don't worry if the screen falls into the cup, the foam is not hard enough to affect the screen. Though fishing it could require care.
6. Carefully lifting the screen out of the water allow to drip dry and dip it in the first clear water rinse. Rinse and repeat until the screen shows no more signs of cleanser(soap colors) and shows rapid clear dissipation. However... do not allow it to dry out the air(it will leave residue stains).
Now here comes the hard part...
7. With the hair-dryer in one hand and your screen in the other, gently place the screen above the tissue roll so that the corner or edge of it is gently resting on the tissue, while blow drying the screen along the edges(not face on!). This will hopefully and with a little luck,force the water droplets off the screen and into the tissue quickly enough to dry without leaving residue marks.
The second alternative is film rinsing agent.Some consider film rinsing agent to be the cat's meow for wet cleaning a screen...
In place of the mild soap as in the above procedure, add a small portion of film rinsing agent. This is actually a very mild soap that is designed for modifying the surface tension of the rinse water so that it will not form droplets. The formation of droplets, regardless of size will ultimately lead to a spot because no matter how hard you try, you will never end up with pure water. There will always be some dissolved minerals in the water, even if it is carried over from the first rinse bath. The ring that these spots leave is due to the concentration of minerals as the droplet evaporates, but if you use a solution that is specifically designed NOT to permit this, the problem is avoided. The film rinsing agent is intended to achieve this and avoid spotting on the negatives. If it can result in clean negatives, it can result also in a clean focusing screen if done properly.
Sure,these may work as long as the individual is experienced and well versed in the procedure....and if one want's to practice it on some old focusing screens till one becomes proficient at the task...have at it...
Either using air only or buying a new focusing screen and carefully installing it after some practice with the old screen,is the simplest solution with the least frustration.
If one must remove the screen and use air,I prefer the screen tweezers.Once the screen is extracted for cleaning with the tweezers,grab the tweezers on the clamping end,to give extra pressure to hold the screen by the clip while blowing air across the surface.
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