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09-14-2015, 05:33 AM   #16
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B&H will probably be very accommodating if the flaw is as obvious in person as in your photos. Taking care of problems like this is how they made their reputation.

09-14-2015, 06:05 AM   #17
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QuoteOriginally posted by Lev Quote
I'm in real trouble, it's a second body which is about to be returned and I'm not sure what B&H will say
If it is otherwise in working condition, without any signs of abuse i'm sure it will be okay. Customer satisfaction is very important to companies like B&H.
09-14-2015, 06:43 AM   #18
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Happy to hear your last replies guys, as I've decided to not touch anything and just return it as it is. But the question, what it is really and how this thing ended up being there is killing me
09-14-2015, 07:05 AM   #19
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QuoteOriginally posted by Lev Quote
But the question, what it is really and how this thing ended up being there is killing me
Bubbles in glass and plastics are common and easy to provoke. Many decades ago the celebrated German Lens maker Carl Zeiss produced many lenses which had (unintentionally) bubbles in the glass - professionals at the time, considered the lenses with bubbles in the glass to be superior to lenses without bubbles.These days such a thing would spark more than a few angry posts about QC.I have to say, i'm surprised a bubble this big, and in such an obtrusive spot managed to escape notice.

09-14-2015, 07:23 AM   #20
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QuoteOriginally posted by Digitalis Quote
Bubbles in glass and plastics are common and easy to provoke. Many decades ago the celebrated German Lens maker Carl Zeiss produced many lenses which had (unintentionally) bubbles in the glass - professionals at the time, considered the lenses with bubbles in the glass to be superior to lenses without bubbles.These days such a thing would spark more than a few angry posts about QC.I have to say, i'm surprised a bubble this big, and in such an obtrusive spot managed to escape notice.
Are these bubbles tend to dissapear over the time or it stays forever? Difficult thing is that I can't determine if it is soft or hard object
09-14-2015, 07:43 AM   #21
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It's not a bubble, it's a conchoidal fracture.

These very commonly occur when glass is hit with a sharp blow. Controlled knowledge of these fracturing patterns is how our prehistoric ancestors created tools out of volcanic glass, aka obsidian.

The fact that it appears to be symmetric on either side tells me it took a sharp blow at one of the corners/seams of the pentaprism, which is actually composed of a number of smaller cemented simple prisms.

It's not going to go away over time, nor would it if were a bubble in the glass, and it certainly would be a QC issue if it left the factory with either a bubble or fracture of this size. As stated above, if you didn't drop the camera itself, then it probably was damaged during shipment and you didn't notice it at first

---------- Post added 09-14-15 at 08:12 AM ----------

Here are some annotations to your last pic showing what I mean:

Last edited by dcshooter; 09-14-2015 at 08:14 AM.
09-14-2015, 08:44 AM   #22
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QuoteOriginally posted by dcshooter Quote
It's not a bubble, it's a conchoidal fracture.

These very commonly occur when glass is hit with a sharp blow. Controlled knowledge of these fracturing patterns is how our prehistoric ancestors created tools out of volcanic glass, aka obsidian.

The fact that it appears to be symmetric on either side tells me it took a sharp blow at one of the corners/seams of the pentaprism, which is actually composed of a number of smaller cemented simple prisms.

It's not going to go away over time, nor would it if were a bubble in the glass, and it certainly would be a QC issue if it left the factory with either a bubble or fracture of this size. As stated above, if you didn't drop the camera itself, then it probably was damaged during shipment and you didn't notice it at first

---------- Post added 09-14-15 at 08:12 AM ----------

Here are some annotations to your last pic showing what I mean:
Great explanation - thanks for posting it.
09-14-2015, 09:27 AM   #23
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Somewhat unusual question but I have to make it, Is it somehow possible to damage that pentaprism area because of the lense vibration during focusing? My 55-300 giving a loud noise when its focusing, not so smoothly as my 16-85, just tell me that this is a funny question

09-14-2015, 11:15 AM   #24
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QuoteOriginally posted by rawr Quote
It could be a chip in the focussing screen glass introduced
View is clearly of the ocular glass, not the focusing screen.

Edit:
I stand corrected, dcshooter convincingly shows it as damage to the pentaprism visible at the ocular...

QuoteOriginally posted by dcshooter Quote
It's not a bubble, it's a conchoidal fracture.

Steve
09-14-2015, 11:16 AM   #25
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QuoteOriginally posted by Lev Quote
and I'm not sure what B&H will say
Show them the photo...they will accept and pay for the return.


Steve
09-15-2015, 12:06 AM   #26
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QuoteOriginally posted by dcshooter Quote
It's not a bubble, it's a conchoidal fracture.
Your conchordial fracture hypothesis has one glaring fault - the force required to cause this kind of fracture would have visibly dented the top of the pentaprism housing.

To quote the article you referenced: "conchoidal fracture is common in crystalline materials also if they have no cleavage"

Common materials for SLR prisms are N-BK7 or N-BaK4 - both have cleavage planes, Cubic for N-BK 7 and N-BaK 4*. I will admit that conchoidal fracture is certainly possible in these glass types as it is in all silicates.

From the referenced article: "Smoothly curving fracture surface develops when force is rapidly applied to brittle objects"

The Pentaprism housing on the Pentax K3 is very solid,which would indicate a tremendous amount of force was applied. However, according to the user, no such force has been applied to the camera. It is possible this could have occurred during shipping, or even assembly, but if that is the case, then it would be just as easy for a bubble to have been in the glass itself or the optical cement in other optical components used in the viewfinder. E.g Injection molded corrective poly carbonate components used at the eyepiece.




QuoteOriginally posted by Lev Quote
Is it somehow possible to damage that pentaprism area because of the lense vibration during focusing?
Unless you're are also using a jackhammer for a tripod, the answer to this is: No, the optical cement commonly used to build prisms and lenses are very strong.


*All optical,mechanical and chemical properties of these glass types are available from the 2014 Shott optical glass datasheets

Last edited by Digitalis; 09-15-2015 at 12:55 AM.
09-15-2015, 09:57 AM   #27
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QuoteOriginally posted by Digitalis Quote
this could have occurred during shipping, or even assembly
I would suggest that the fault was present before or during assembly and escaped detection. It is also possible that latent internal stress within the prism is at fault.

Regardless of the cause, it is not supposed to be like that and is probably covered under the camera warranty.


Steve
09-15-2015, 11:00 AM   #28
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Packed and sent back to B&H

Thank you all for your attension, help and support!! I really appreciate.
09-21-2015, 07:47 AM   #29
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Glass cleaves quite easily in conchoidal patterns and does not require tremendous or even direct force for that matter. Obsidian knappers commonly use soft materials like antler, horn, or wood tools with light blows or even non-percussive pressure (i.e. steady, not rapid) to achieve conchoidal fracturing at an angled edge, analagous to the peaked corner of a pentaprism.

See approximately 2:00 of this video:


For tiney fractures like this, pressure is even more likely than a highly percussive blow, which would usually lead to a larger spall.

QuoteOriginally posted by Digitalis Quote
Your conchordial fracture hypothesis has one glaring fault - the force required to cause this kind of fracture would have visibly dented the top of the pentaprism housing.

To quote the article you referenced: "conchoidal fracture is common in crystalline materials also if they have no cleavage"

Common materials for SLR prisms are N-BK7 or N-BaK4 - both have cleavage planes, Cubic for N-BK 7 and N-BaK 4*. I will admit that conchoidal fracture is certainly possible in these glass types as it is in all silicates.

From the referenced article: "Smoothly curving fracture surface develops when force is rapidly applied to brittle objects"

The Pentaprism housing on the Pentax K3 is very solid,which would indicate a tremendous amount of force was applied. However, according to the user, no such force has been applied to the camera. It is possible this could have occurred during shipping, or even assembly, but if that is the case, then it would be just as easy for a bubble to have been in the glass itself or the optical cement in other optical components used in the viewfinder. E.g Injection molded corrective poly carbonate components used at the eyepiece.






Unless you're are also using a jackhammer for a tripod, the answer to this is: No, the optical cement commonly used to build prisms and lenses are very strong.


*All optical,mechanical and chemical properties of these glass types are available from the 2014 Shott optical glass datasheets
09-21-2015, 01:23 PM   #30
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My dear friends....

B&H has replaced it! My third K-3 II body is on its way I'll kill myself if something go wrong....


I'm just looking at this picture and still wonder what happened, and how do you guys think where it happened? definitely upper portion but which corner, A or B?
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