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Message |
    
Jxsoriano
Tinkerer
Username: Jxsoriano
Post Number: 3
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 28, 2006 - 11:57 am: | 
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I need suggestions on the best way to clean a focus screen from a Canon SLR. It has stuck some old pieces from mirror foam. |
Ethostech
Tinkerer
Username: Ethostech
Post Number: 14
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 29, 2006 - 07:38 am: |
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Respectfully - you need to post more information.
To know the Model of the Canon SLR would be useful.
It is a proposition to remove the focusing screen on some models - but absolutely not on others. |
Jxsoriano
Tinkerer
Username: Jxsoriano
Post Number: 4
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 29, 2006 - 12:23 pm: |
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It is a Canon FT QL
Thanks. |
Glenn
Tinkerer
Username: Glenn
Post Number: 62
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 29, 2006 - 08:06 pm: |
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There is plenty of information in the archive on this problem. The basics are as follows: Blow all the loose bits off with an air blower. Then using a cotton bud (Q-Tip) moistened with Ronsonol (Naphtha/Lighter Fluid), gently wipe the exposed surface of the screen along the long side once - ie left to right. Do not reuse the cotton bud and never make more than one pass with moist bud. Repeat, using a new moistened cotton bud for every pass, until the sticky degraded foam is removed.
Do not use a 'scrubbing' action on the screen and do not saturate the cotton bud. If you flood the surface with naphtha it can run onto the upper-side of the screen, This can lead to 'oily' marks being left as the solvent evaporates. On the FT, the only way to clean the upper surface of the screen is to remove the pentaprism. |
Ethostech
Tinkerer
Username: Ethostech
Post Number: 16
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 30, 2006 - 07:30 am: |
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Wow! Sorry - I would argue against Glenn's directions - but I don't want to get into a slanging match. I will just say that the fresnel screens are acrylic and any sort of spirit - even pure petroleum spirit or alcohol isn't a good idea. I have been that route and learned the hard way. A cotton-bud moistened with Windex - and applied according to Glenn's directions - is a safer bet.
Glenn's mileage may differ however and I respect his entitlement to a contrary view. It could also be that all fresnels are not equal. |
Glenn
Tinkerer
Username: Glenn
Post Number: 63
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 30, 2006 - 09:58 am: |
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Just for the record; I have cleaned literally dozens of CANON screens over the last 30 odd years. All have been cleaned with naphtha - sometimes followed with a washing up liquid/water wash, if out of camera. I have even used the solvent in an ultrasonic bath to clean some very dirty T90 screens.
Assuming 'Windex' is a water based cleaner and the degradation products of the foam being non soluble in water, I'll stick to my very tested method for Canon manufactured products. As I only 'fiddle' with Canon kit, this will be no hardship. |
Jxsoriano
Tinkerer
Username: Jxsoriano
Post Number: 5
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 02, 2006 - 06:42 am: |
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Can you give me advice on the best way to remove the screen completely to clean it?
Thanks, |
Glenn
Tinkerer
Username: Glenn
Post Number: 65
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 02, 2006 - 07:22 pm: |
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The top plate is easily removed, just remove wind on lever, shutter speed dial, rewind knob and battery 'door'. Remove the screws in the front plate and remove plate, now remove all top plate retaining screws.
The next bit is the tricky part as you have to remove the eyepiece, pentaprism, meter galvo and then the screen retaining frame. You are likely to come across quite a bit of degraded foam light seal also.The foam will need cleaning off and replacing. The disassembly is quite logical and straight forward - just remove the visible screws, but does need one to take care - especially if you are not to bend the meter needle. Also note the position of any shims under the screen retainer. Check the focus after reassembly using a piece of ground glass/draughting film on the film gate.
Take care also when you remove the prism retainers. I have come across some early FT prisms on which the protective black paint has started to loose adhesion. The paint will fall off with the slightest touch/knock. |
