[Kobayashi.K]

Kobayashi....
I have wrecked a focus screen with IPA and also seen IPA react super badly with a plastic camera case and auto winder bith Chinon. Until the Chinon I had never seen it react badly with basic plastic finishes but on the Chinon it took the shine right out of the plastic and turned it to a matt finish.

Thanks @Astro-Baby, I have already made a note of it. I'm beginning to think it is perhaps the matt coating that is reacting badly (if we assume the info on the MIR web site is correct). Perhaps when OP has a new screen he could do a test with IPA on the glossy side of the old screen, to see if it degrades too.

[Astro-Baby]

I have seen the glossy side of a Fujica screen survive some IPA but the matt side was wrecked. The matt side of a screen is finely ground producing a kind of frosted effect. The finely ground surface means the plastic particles are so fine they melt quicker under a hit of IPA.

[Kobayashi.K]

I have seen the glossy side of a Fujica screen survive some IPA but the matt side was wrecked. The matt side of a screen is finely ground producing a kind of frosted effect. The finely ground surface means the plastic particles are so fine they melt quicker under a hit of IPA.

That is a plausible explanation, and it would happen to all sorts of plastic screens from different brands.

[gofour3]

That is a plausible explanation, and it would happen to all sorts of plastic screens from different brands.

I checked a LX brochure I have and it mentions the focusing screen coating:

"Each screen is specially treated with a newly created Pentax coating which enhances light transmission and ensures the brightest possible viewfinder image."

So it looks like this unique "Pentax coating" is what's getting messed up with IPA.

Phil.

[Kobayashi.K]

I checked a LX brochure I have and it mentions the focusing screen coating:

"Each screen is specially treated with a newly created Pentax coating which enhances light transmission and ensures the brightest possible viewfinder image."

So it looks like this unique "Pentax coating" is what's getting messed up with IPA.

Phil.

Interesting, so the info I found on the MIR page mentioned in my post #11 is correct.

However, @Astro-Baby sees the same effect on screens from other brands. We humans tend to think in OR functions, but it could well be a combination of factors. What we have learned though is that using IPA on a focusing screen is not recommended.

I still think an ultrasonic bath with a suitable solvent might be worth trying out. A model with adjustable power, temperature and time. Perhaps with a cleaner for prosthesis that is used by dentists (Emag EM070), and a provision to keep the screen separated from the bath's walls. This will cost more than a new screen, but it is also usable for other purposes.

p.s. The intended use of the ultrasonic bath is not for reversing the damage from IPA but for example when the screen it is polluted with a sticky seal during replacement, or a fingerprint.

[stevebrot]

Thanks @Astro-Baby, I have already made a note of it. I'm beginning to think it is perhaps the matt coating that is reacting badly (if we assume the info on the MIR web site is correct). Perhaps when OP has a new screen he could do a test with IPA on the glossy side of the old screen, to see if it degrades too.

I am thinking that it is dissolving the ridges of the Fresnel field. In regards to optical coating, I think you may be misreading the MIR site. As for the OP doing testing with a fresh screen, perhaps that might be something you might undertake.


Steve

[Kobayashi.K]

I am thinking that it is dissolving the ridges of the Fresnel field. In regards to optical coating, I think you may be misreading the MIR site. As for the OP doing testing with a fresh screen, perhaps that might be something you might undertake.
Steve

It's a guess how the screen is actually made with this little information, and how the damage is done. But the info from Phil also points to a coating. The important conclusion for this thread is not to use IPA.

[Fluegel]

As a sidenote, isopropyl alcohol and other alcohols are very hygroscopic. So if you theoretically could get a 99% pure alcohol, and when you open the bottle and pour it into a bath it immediately absorbs moisture from the air and you end up with 80% or less.

99% pure Alcohol does not exist, You can not get alcohol over 96% purity.

I sold a completely serviced excellent Hasselblad 500C/M body at an auction.
The buyer complained the focusing screen became useless after cleaning it with fluid.
He even tried to blame me for it.
Please do not use any fluid when cleaning focusing screens. The fluid, even water, will most likely destroy the focusing screen.

The Hasselblad camera manual warns about the use of fluids with screens.
Only use low pressure dry air.

[stevebrot]

It occurred to me that the former KatzEye Web site had an FAQ on care and cleaning of focus screens. I found the relevant page on the Wayback Machine at the link below.

cleaning - KatzEye Optics

A few years ago, I asked a camera repair guy friend about how to clean a screen and his answer was, aside from using a rocket blower, to bring the camera in and have him do it. A self-serving reply, but probably the path least likely to result in tears.


Steve

[g026r]

I am thinking that it is dissolving the ridges of the Fresnel field. In regards to optical coating, I think you may be misreading the MIR site. As for the OP doing testing with a fresh screen, perhaps that might be something you might undertake.

I'm inclined to agree it has little to do with any potential coating. If only because a few years ago I accidentally splashed some isopropyl on one of the late-model plastic Exakta screens, which resulted in something similar to the original photo.

[stevebrot]

"Each screen is specially treated with a newly created Pentax coating which enhances light transmission and ensures the brightest possible viewfinder image."

So it looks like this unique "Pentax coating" is what's getting messed up with IPA.

I might agree except for the abundance of reports on the Web regarding damage to screens in general from IPA. I was particularly saddened to see one regarding a ruined Maxwell screen.

Google is my friend and they showed me an old thread on this site as well as another link providing options and pointing out the hazards of screen cleaning.

To clean a focusing screen - PentaxForums.com

Focus Screen and Lens Cleaning Tips, Any Comments | Photo.net Photography Forums

Steve

[gofour3]

Found this cleaning info in the LX focusing screens leaflet that comes with each screen. This is the older version of the leaflet, another one I have is different.

Basically never touch or wipe the screen with anything and only use a blower.

Phil.

[monochrome]

Here’s a replacement SA-21 at KEH for $40. I’d email them to ensure it includes the plastic case and installation tool (tweezers).

Of course the postage will probably double that.

[Astro-Baby]

Yep would agree that in an ideal world and when spanking new screens should NEVER be touched and only blown or at the very worst VERY lightly brushed with a lens brush (bearing in mind that normally you wouldnt have the lid off the camera and be messing about in its guts so you would only be dealing with harder, shiny side of the screen ) BUT we are often dealing with bangers in the world of film cameras where the box might be 40 years old and screens can, very often, be covered in drek that aint going to blow away. Bits of decayed mirror bumper, cigararette smoke and oily deposits seem to be quite common. When faced with these I habe found that a soak in some luke warm water with just a spot of washing up liquid will work wonders, if pushed a light stroking with a very find sable brush ( and I do mean gently ) followed jpmwith a rinse down and then dried using a blower will often bring the screen, if not to new condition, to at least clean and usable state. Dont be tempted to put a hair dryer on it, the heat if its too hot will melt it and when its being soaked I put a very soft cloth in the bottom of the dish so the screen isnt scratched by the dish at all and exercise maximum care.

Its worked for me on two OMs and a four Minoltas.

[ProfessorBuzz]

99% pure Alcohol does not exist, You can not get alcohol over 96% purity.

In my experience, that is not the case. For example, MG Chemicals 99.9% pure anhydrous isopropyl alcohol which complies with several MIL and ANSI specifications.

This is an industrial chemical used in the electronics and optics industry. Moisure in the air will be absorbed, so handling is a factor.
Also, note that they have a chart of plastics compatibility, and indicate it should not be used when some coatings are present.

Data sheet here: https://www.mgchemicals.com/downloads/tds/tds-824-l.pdf

Please do not use any fluid when cleaning focusing screens.
...

Only use low pressure dry air.

Agreed - this is the best practice! Thanks for sharing your experience.