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Prism shield - cover

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#1 Audrius

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Posted 24 July 2021 - 10:13 AM

Hello binoculars enthusiasts,

I am quit new at binoculars hobby, but I have already dismantled and cleaned number of binoculars. Could  You please share Your thoughts about prisms' black mat metal shield.

Why a lot of Porro-prism binoculars have just one shield (cover) on the prisms that are closer to the objective? It this fact only related to economical reasons? Or maybe it is just irrelevant to put the shield on the prism that is closer to the ocular? Of course cheap binoculars have none of these shields installed and these are not worth mentioning.

I have seen both prisms shielded on the one side when both prisms sit on the same removable shelf (very often this is a case then binoculars are collimated via prisms screws) for example KOMZ 6x24. Does this imply that both shielded prisms have better protection against straight light and thus superior to those binoculars with only single prism shield? Or there is another reason to install double prisms' shield due to construction features?

My question would be - is it worth putting the metal shield on all prisms in Porro-binoculars? Or it would be reasonably to leave as it is (there at present are only two shields).

I am pretty well aware of the advantages of blackening the edges of the prisms for further improvement, but it would be a different topic for a next time:)

 

Best Regards

Audrius

 



#2 csa/montana

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Posted 24 July 2021 - 10:22 AM

Moved to Binoculars, for better fit of topic.



#3 MrZoomZoom2017

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Posted 24 July 2021 - 11:28 AM

The rear/aft prisms have a minimal likelihood of light (reflected, stray, or otherwise) impinging on the exposed angled surfaces so adding light shields there would be of little to no benefit.  Having good baffling and non-reflective, darkened surfaces on the insides of the housing and other parts is important to keep light artifacts to a minimum.

 

Hope this helps.

 

Cheers,

Tim


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#4 Rich V.

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Posted 24 July 2021 - 11:58 AM

Some binoculars have black metal prism "tents" around both prisms, though,  The MS series binos come to mind.

 

Rich

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#5 MrZoomZoom2017

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Posted 24 July 2021 - 12:21 PM

Some binoculars have black metal prism "tents" around both prisms, though,  The MS series binos come to mind.

 

Rich

Wow Rich - nothing like a belt and suspenders - right lol.gif lol.gif lol.gif?  I like the side shielding on those as well - is the silicone adhesive factory or part of a restoration?  Wonder if any design employed 3-D hats, similar to those covers on miniature binos, to cover all exposed surfaces?

 

Even the highly regarded WWII B&L Mark 41 7x50 don't have aft prism shields...  Ummm - I stand corrected here - the cutaway image I have of the Mark 41 did not show the aft prism shields but it does appear from photos that shields are used on both forward and aft prisms.  Also, taking a look at NAVSHIPS 250-624-2, Manual for Overhaul and Repair of 7x50 Binoculars, (link:  https://www.brayebro...PS_250624-2.zip) shields are on both forward and aft prisms.  Sorry about that - blush.gif

 

Cheers,

Tim


Edited by MrZoomZoom2017, 24 July 2021 - 12:45 PM.


#6 Audrius

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Posted 24 July 2021 - 12:26 PM

The rear/aft prisms have a minimal likelihood of light (reflected, stray, or otherwise) impinging on the exposed angled surfaces so adding light shields there would be of little to no benefit.  Having good baffling and non-reflective, darkened surfaces on the insides of the housing and other parts is important to keep light artifacts to a minimum.

 

Hope this helps.

 

Cheers,

Tim

It seems very reasonable, since the first prism in light's path is already well covered from any light sources in its own chamber, while the second prism (which is physically closer to the objective) is directly exposed to the (angled) light directly from the objective and therefore requires shielding. Thank You for Your insights

 

Audrius 



#7 Rich V.

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Posted 24 July 2021 - 12:30 PM

No restoration; just looking under the hood to see inside.  Factory silicone adhesive.



#8 MrZoomZoom2017

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Posted 24 July 2021 - 12:30 PM

As Rich points out - there are examples where shields were/are used on both prisms.  Here is another example:  https://www.surpluss...item/B1223.html

 

Cheers,

Tim



#9 Audrius

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Posted 24 July 2021 - 12:33 PM

Some binoculars have black metal prism "tents" around both prisms, though,  The MS series binos come to mind.

 

Rich

thank You for sharing this great photo, that illustrates wonderful craftsmanship. I wish I could produce such shields that accommodate prism so perfectly. All high-end porro-binoculars should house these kind of treated prisms. I wonder was this a true case with expensive binocular when roof prisms were still limited in use due to technical capabilities of production. 



#10 Rich V.

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Posted 24 July 2021 - 12:42 PM

thank You for sharing this great photo, that illustrates wonderful craftsmanship. I wish I could produce such shields that accommodate prism so perfectly. All high-end porro-binoculars should house these kind of treated prisms. I wonder was this a true case with expensive binocular when roof prisms were still limited in use due to technical capabilities of production. 

No, example of current production KUO MS ED.  This one is the 16x70.



#11 Audrius

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Posted 24 July 2021 - 01:01 PM

No, example of current production KUO MS ED.  This one is the 16x70.

So it seems this manufacturer is very dedicated to the quality. I could also find some old WWII binoculars with both prism shielded:

 

And this is a single shield for soviet BPC 7x50 binoculars:

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#12 pat in los angeles basin

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Posted 24 July 2021 - 01:05 PM

About prism hats- are they there to shade the prisms from direct or ambient light. Out of curiosity, I check my table bino's  (mostly motley crew of classic 7x35 porros)  along with various 7x and 10 x stuff- all porros and found what I would consider the mass market big retailer stuff to NOT have hats and from the looks of the fact that if I tilt these same binos at an angle, can see much of  each forward prisms faces in a direct fashion- surely those would be the ones of the lower contrast or stray light protection? The 10xs had a longer focal length - and prim hats  and in both cases ,barely any of the prisms face (even if it didn't have the hat) were  vulnerable to direct light impingement. So ambient light hitting the prism might reduce contrast?  I might make an experiment with some soda can or cat food can aluminum (cuts easy with a scissors- very thin) after making a paper or cardboard mockup/ pattern to see if that might improve contrast a bit or perhaps keep the light  from hitting when viewing objects  that are tight proximity to a high intensity light source thus preventing some glare.   Pat


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