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CP-16r viewfinder repair


Jay Young
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I have a Cinema Products CP-16r with fungus (or something?) on one of the internal elements of the viewfinder.

It appears to be on the second element of the viewing (eye) side, as it does not change focus with the ground glass.

 

Can anyone point me to a resource for proper disassembly? I have taken the thing apart but I CAN NOT seem to

be able to remove the prizim covers, unless there is some secret after the two screws are removed.

 

This is the one thing that does not seem to be covered in any of the available documentation.

Before I spend money to replace it, I want to try to clean it!

 

Thanks for any help you might have.

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Ok. after emailing WhitehouseAV, I used... liberal force and a big stick to pop the prisms off.

 

Turns out not to be mold but the silvering on the mirrors being eaten away.

 

Mirror resilvering time! At least the lens glass is good.

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  • 6 years later...

I figured I would add to this topic my own adventure into repairing a dodgy CP viewfinder.  Mine was pretty bad, unusable.  After trying many methods, including a big stick, I tried the persuasive approach... nail polish remover.  Worked a treat.  After removing the glass I discovered that mine too needed re-silvering.  I will be trying some Rust-oleum mirror effect spray paint in the coming days to see if I can repair my viewfinder.... they are pretty expensive second hand...

If I succeed I will add the results... I also emailed Jay to see how he faired with his attempt..

20220224_230724.jpg.opt423x341o0,0s423x341.jpg

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36 minutes ago, Gareth Blackstock said:

I will be trying some Rust-oleum mirror effect spray paint in the coming days to see if I can repair my viewfinder.... they are pretty expensive second hand...

20220224_230724.jpg.opt423x341o0,0s423x341.jpg

😬 please don't do that  - try to find a local vacuum deposition shop (some are small and coat mirrors for DIY telescope makers) or ask edmund optics if they're willing to coat your prism. (Masking the faces that you don't want to be coated)

Edited by David Sekanina
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Hello,

Thanks for the tip, no harm in emailing them... do you have experience in getting prisms recoated from edmunds optics? I will email and see if its a service they offer. So far with other businesses the result has been at least a few hundred for the job, or the job is too small and not worth the hassle...

I'll check edmunds though.

Thanks, Gareth 

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Check Australian telescope forums - if there are any, and see what companies they used to have their hand polished mirrors coated. I've asked Edmund to send me quotes for other custom jobs, but not recoating prisms.

 

Edit: I think I show my age - building your own telescope was a hobby amongst teens in the 70s and 80s. Today you probably just buy one.

Edited by David Sekanina
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Hello,

Well i did some research, seems diy telescope enthusiasts grind their own mirrors and send them away to get coated, quite a process.... and seems expensive, not the actual coating, but setting machinery, couriers, subcontracting it to another business, etc is very expensive. More than i paid for the camera... i found a glazier who could do it for $80 just to get started, a few weeks wait, and most likely cost more.

Soooo... i will try some rust-oleum mirror finish, the results from sceptical consumers is encouraging...

https://www.pinterest.com.au/pin/527836018827709534/

And if the images in the viewfinder are still not useable, then off to the glazier i go. 

It will be cool if it works though, the paint may help keep cameras in use for a little longer...

Ill keep you posted,

Gareth

 

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2 hours ago, Gareth Blackstock said:

Hello,

Well i did some research, seems diy telescope enthusiasts grind their own mirrors and send them away to get coated, quite a process.... and seems expensive, not the actual coating, but setting machinery, couriers, subcontracting it to another business, etc is very expensive. More than i paid for the camera... i found a glazier who could do it for $80 just to get started, a few weeks wait, and most likely cost more.

Soooo... i will try some rust-oleum mirror finish, the results from sceptical consumers is encouraging...

https://www.pinterest.com.au/pin/527836018827709534/

And if the images in the viewfinder are still not useable, then off to the glazier i go. 

It will be cool if it works though, the paint may help keep cameras in use for a little longer...

Ill keep you posted,

Gareth

 

I don't think a spray mirror paint would work at all... I am pretty sure the end result will be useless and you will need to use great effort to scrape the paint off the surface to be able to test another coating process on it.

 

There were processes in the old days to use aluminium or silver salts to diy coat glass surfaces with metallic silver or aluminium to make mirrors.  it is not as perfect surface than vacuum deposition but might be cheaper for you if you don't count your own workhours as an expense (which would make it more expensive than the vacuum process because takes more more time) .

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I am always willing to try non-destructive solutions to the problems I come across, and if the results are not useable, then simply using a mild solution to remove paint is hardly great effort.  I think scraping paint off a glass prism is likely to do far more damage than what i am attempting..

Admittedly, going to such lengths on a camera that is potentially a few chemical processes away from oxidising itself into a great display piece seems over doing it, but then time and effort expended is relative to what else I could be doing...  

I have been stuck in my house for 3 weeks now and am getting over covid myself, so I've plenty of time.  

I've already souped up all my son's remote control cars, am rust proofing and re-painting a 40 year old car trailer, I put a mezzanine in the rabbit hutch, and I am a few days away from braiding the dog....

So if the paint doesn't work I'll simply drop it off at the glazier, they will do the job, could be around $120 give or take.... as gathering aluminium and silver salts would be difficult in a small country town..

 

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  • 2 weeks later...

Well, time to report back with the results: Originally the issue is that the silver paint from the rear of the viewfinder prisms wears away after a number of years largely rendering the viewfinder useless.  After getting the prisms out as per the above simple method, I found that the adhesive round pad placed there by Cinema Products causes the silver paint to corrode, right in the middle of the prism.

I experimented with silver cellophane which appeared fine, but once the viewfinder was reassembled, the tiniest imperfections in the foil surface were magnified and therefore blurred the image seen in the viewfinder.  So that didn't work. 

Next I tried rust-oleum "mirror finish"  I have seen a few youtube videos of the results and was impressed enough to buy a can and try it myself.  While the prisms are very hard to replace, or simply non-existent as spare parts, I considered using spray paint as suitable as it would not damage the surface as nail polish remover is the easiest paint remover.

So, I set up a rig to hold the prisms and expose only the side I wanted painted, and after applying the spray paint, a minimum of 5 very thin coats, and around a minute between each, perhaps sooner on a warmer day, I was very impressed with the result. 

I considered that while the paint was drying the result was impressive, however, I wanted to wait until I could put the prisms back under magnification in the viewfinder before I got excited with the results. 

During re-assembly of the prisms I remembered one youtube video suggesting that even when dry, not to touch the paint as it will be stained with a finger print and require the spray paint to be removed and re-applied.  So, after re-assembly of the viewfinder I was very happy with the image in the viewfinder, to the extent that I struggled to notice ANY difference between the factory coating and the spray paint I had applied.

I have attached pictures to attempt to show the final result.  I firmly believe that using this spray paint to replace mirror silvering that has corroded is a great solution to an otherwise expensive repair, or even more expensive replacement of hard to find viewfinders.

01g.jpg

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In the above image you can see the spray paint repair in the left prism, it is a slightly lighter coloured silver.  The prism on the right is a different angle, and shows a very nice match.

The below image is an attempt to show the quality of the reflection compared to looking directly at the writing.

To the undressed eye the reflection looks pretty good, a little imperfection can still be seen. 

01e.jpg

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Now, they say the proof of the pudding is in the eating, so the below image is a picture from a smart phone looking through the viewfinder.  I tried to light the scene to best portray the result, and I think the image speaks for itself, clearly, rust-oleum "mirror finish" goes a very long way to repairing corroded silvering in prisms that are used in viewfinders.

As a note, I imagine there are numerous methods of replacing silvering from the back of mirrors, and perhaps those processes last longer and may offer a more professional result.  However, such methods may require the sort of expertise that is not common these days, or require expensive ingredients, or require specialised glazing skills.  Perhaps in the 80's and 90's when re-silvering was commonly offered by businesses, their services were cheaper and a better alternative to what I have done. 

Well that was then, and these days I think most people using old technology like cine cameras are not keen on spending large amounts of money on them unless they are making money with them.  

Doing this has saved me from purchasing a replacement viewfinder for around USD$200.

Untitled f.jpg

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Gareth,

There is still one more step in the process:  A projected image.  Or digital.

I 've read (on this forum), that film is harder to come by where you live, but you need to shoot a 100ft test roll (or other short end), to be absolutely certain that your hard work has paid off.  

Reversal footage of focus charts, newspaper pages, fine print etc., as well as the "usual suspects" indoors and outdoors, light and shadow etc. will show whether "lens focus" and "eye focus" agree.  Others with more/deeper technical experience can explain that aspect.

It may also be necessary to actually shoot negative and take it through the process you normally use (or purchased the camera for),  to be assured there are no failings anywhere.  

Remember, Thomas Edison said, I know ten thousand ways not to make a lightbulb."  At least you carried it through this far, so, "good luck."

 

Addendum: An eyepiece is selling on eBay for $295.  Ooouch.

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18 minutes ago, Eric Eader said:

Gareth,

There is still one more step in the process:  A projected image.  Or digital.

I 've read (on this forum), that film is harder to come by where you live, but you need to shoot a 100ft test roll (or other short end), to be absolutely certain that your hard work has paid off.  

Reversal footage of focus charts, newspaper pages, fine print etc., as well as the "usual suspects" indoors and outdoors, light and shadow etc. will show whether "lens focus" and "eye focus" agree.  Others with more/deeper technical experience can explain that aspect.

It may also be necessary to actually shoot negative and take it through the process you normally use (or purchased the camera for),  to be assured there are no failings anywhere.  

Remember, Thomas Edison said, I know ten thousand ways not to make a lightbulb."  At least you carried it through this far, so, "good luck."

 

Addendum: An eyepiece is selling on eBay for $295.  Ooouch.

I don't see any need for extensive film tests just because a viewfinder prism was repaired. It does not affect the ground glass distance in any way and thus it cannot affect the focus (except if the image is so poor quality that you cannot see focus point at all) 

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Aapo, 

You may be correct.  I am not a technician.  All I am suggesting is that the final "test of the pudding" is not just looking thru the viewfinder, but is running film thru the camera and completing whatever post processing of those images he plans on using BEFORE shooting something important with it.  I hope the OP is successful,  but I can envision --- rightly or wrongly--- a scenario where the film may not be in proper focus and it is out of an "abundance of caution" that I recommend testing.

If testing is not necessary,  why do 1st AC's and DP's test rental equipment and lab processes PRIOR to shooting their Projects?

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Thanks for the feedback guys.  I am pretty confident the image seen in the viewfinder will be replicated onto the film.  For a couple of reasons: As I am getting old and wear glasses now, I often rely on measuring tape to ensure my eyesight is not letting me down, even though I set my diopter to my eyes, I find myself relying on measuring distance and less on my eyes.  Also, as the layer of spray paint is the same as the original layer of silver paint, there should (in my limited knowledge of opticals laws) virtually no difference in the magnification of the image.  If there were imperfections in the spray paint, perhaps tiny puddles or craters, then yes the image would skew I think.

it is a good point about shooting footage before a big shoot, or with a camera with unknown history, I am thinking the common practice Eric is noting may relate to scratch tests, lens collimation, functions of the camera all working, tight spots in loading or magazines with light leaks, etc.  Perhaps some early film rental houses were fast and loose with maintenance to preserve profits in a tight time and it became film industry 'lore' to check cameras?

I am hoping that people reading this might dig out those buggered corroded viewfinders and have a go repairing the silvering... and perhaps get a camera happily running again...

Thanks guys..

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it is always good to shoot camera tests before a big project of course to catch possible film transport errors.

but the condition of the screw-on viewfinder piece does not affect the placement of the ground glass at all so it cannot cause focus issues on film. One would need to actually mode the ground glass inside the camera body itself to introduce focus issues into the viewing system which would affect the image on the film negative.

If there is something wrong with the screw-on viewfinder system one would see the ground glass blurry in the viewfinder and would need to adjust the viewfinder's diopter ring but that does not cause the ground glass inside the camera to physically move to different position

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