Why is the body open?

Started Feb 9, 2013 | Questions
Rexel99
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Why is the body open?
Feb 9, 2013

This applies to all removable-lens cameras (that I know of) but it just occurred to me...

Why is there a big hole in the body of the camera when you remove the lens?

Surely a piece of glass could be in that hole, in front of the mirror (behind the lens) to prevent dust getting in.

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Lee Jay
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Re: Why is the body open?
In reply to Rexel99, Feb 9, 2013

Rexel99 wrote:

This applies to all removable-lens cameras (that I know of) but it just occurred to me...

Why is there a big hole in the body of the camera when you remove the lens?

Surely a piece of glass could be in that hole, in front of the mirror (behind the lens) to prevent dust getting in.

That would alter the optical formula of the lens, as that flat piece of glass would become part of the lens system.  In fact, some lenses have a flat piece of glass in the rear on purpose as part of the optical formula.

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Deleted1929
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Re: Why is the body open?
In reply to Lee Jay, Feb 9, 2013

Also worth pointing out that a flat piece of glass at the rear of some lenses has actually been the cause of an optical problem ( a bright spot ) from the reflection of light from the sensor onto the flat rear element and back onto the sensor.

In any case that opening doesn't cause half as many problems as people think.  It's an advantage !

Cameras which are sealed ( like the RX-100 ) still get dust in them via other routes.  As you can't remove the lens to clean the sensor there is no easy way to deal with that.  On an system when you can remove the lens you can easily get at the dust with a simple rocket blower or more elaborate method.

It's like having a car with a sealed engine.  Great if nothing goes wrong, but think of all the simple things that can be fixed by the owner just by popping the hood !  ( Someone said they didn't like sports car analogies, so please note this is not specific to sports cars ! )

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GuyMcKie
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Re: Why is the body open?
In reply to Rexel99, Feb 9, 2013

It is possible to seal the mirror box. Sigma has done it, and maybe patented the design.

Sensor flare is usually the result of a curved rear lens element.

Many sensor dust problems are related with the internal design of the body. Small particles from the shutter blades or oil specs.

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Deleted1929
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Re: Why is the body open?
In reply to GuyMcKie, Feb 10, 2013

Sort of off topic, but anyway :

AFAIK the original Tamron Adaptall 90mm f2.5 is prone to what you refer to as sensor flare ( bright spot ) and that has a flat rear element.  Later models, which don't have that issue, have a curved rear element.  I suspect that a concave rear element would also have potential for this issue.  Presumably convex rear elements don't have this issue.

Of course coatings might also help with this, and we know coatings have improved a great deal over the years as well.

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Ray Maines
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Oh My Goodness ....
In reply to Rexel99, Feb 10, 2013

Rexel99 wrote:

Why is there a big hole in the body of the camera when you remove the lens?

Surely a piece of glass could be in that hole, in front of the mirror (behind the lens) to prevent dust getting in.

OMG: Buy a Rocket Blower and a Lens Pen and just move on. Be grateful you have a direct path to the sensor and pity the poor fools that have a fixed lens camera.

Sooner or later, every camera with a zoom lens will get something sticky (flower pollen?) on the sensor that won't shake off and those of us with a big hole in the front of our cameras will be able to take care of that problem. Count your blessings.

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tkbslc
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You just moved the target, didn't prevent dust
In reply to Rexel99, Feb 10, 2013

If you put a clear lens farther away from the lens, all you did was alter the part of the camera that you need to clean.   Dust will just collect on your little protection lens instead of back on the sensor.  Nothing has changed in terms of dust prevention, but you've significantly altered the design of the lens mount.

And FWIW, the top layer of the sensor is protection glass already.  The actual sensor is not exposed.

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Zone8
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Not all cameras are open when lenses removed!
In reply to Rexel99, Feb 10, 2013

I bought the Sigma DSLR SD9 when it first appeared, in 2003 and still using it without any problems.  The Sigma Forum was beseiged for several years by owners of other cameras telling us what a load of cr^p it was and how it would not last.  Mine is still working perfectly and produces some stunning images, as does the later added SD14.

My equally old Kodak full frame DCS14n also produces excellent quality images (in good lighting) but has one major problem - like most DSLRs, the body is open when changing lenses.  Dust is a major PITA.  In both Sigmas - the SD9 has been cleaned three times in the ten years and the SD14, once.  Both Sigmas (and later Sigma DSLRs) have a protective glass in the camera body opening - designed of course -, so no problems optically and certainly greatly reduces the incidence of needing to clean the sensor.

Many cameras "open" to the World, as it were, get most internal dust from both changing lenses AND from using zooms that can suck in dust when being zoomed.

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003tvd
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Re: Not all cameras are open when lenses removed!
In reply to Zone8, Feb 10, 2013

isn't there a filter in the body to protect the sensor? Low pass or something like that, engineered in to the system so as not to degrade performance? Am i dreaming this up?

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Peter A. Stavrakoglou
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Re: Not all cameras are open when lenses removed!
In reply to 003tvd, Feb 10, 2013

If you are asking about the Sigma DSLRs, the sensor is covered by a piece of glass and the dust protector that covers the opening of the body is also a UV filter.  For other DSLRs, there is a filter on the sensor that is a UV and AA filter.

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Peter A. Stavrakoglou
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Re: Why is the body open?
In reply to GuyMcKie, Feb 10, 2013

The Sigma dust protector is also the UV filter.

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donaldsc
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Re: Why is the body open?
In reply to Rexel99, Feb 10, 2013

Ignoring all the other problems, what will happen when you get some dust on your protective glass?  Maybe you want to put a 2nd piece of protective glass in front of the first one - etc., etc., etc.

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MaxTux
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glass/air surfaces are bad for your image health...
In reply to Rexel99, Feb 11, 2013

Rexel99 wrote:

Surely a piece of glass could be in that hole, in front of the mirror (behind the lens) to prevent dust getting in.

Because two more glass/air surfaces would further reduce the optical quality of any lens used with the camera. Lens designers are doing their utmost to keep the number of air-glass surfaces to the minimum possible: sometimes two glass elements of a lens are glued together just that exact reason. Old Tessar lens design was an early example: it was better than any similar 4-element lens mostly because the two rear elements were glued together (at that time, using something called "Canadian Balsam". Today they use Canadian Club).

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Leonard Migliore
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Not an adhesive
In reply to MaxTux, Feb 11, 2013

MaxTux wrote:

Old Tessar lens design was an early example: it was better than any similar 4-element lens mostly because the two rear elements were glued together (at that time, using something called "Canadian Balsam". Today they use Canadian Club).

MaxTux

Canadian Club is a lubricant, not an adhesive.

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Zone8
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Clarification - Sigma body filter also for UV and IR.
In reply to 003tvd, Feb 11, 2013

003tvd wrote: isn't there a filter in the body to protect the sensor? Low pass or something like that, engineered in to the system so as not to degrade performance? Am i dreaming this up?

No, the sensor has a protective glass cover, like (I believe) all sensors in cameras but the body insert filter (to keep inside free of dust in the main at least) can also be removed in the SD9 and SD-models to and including the SD14 to then allow for IR captures - a very simple and useful feature. This "protective" body filter that effectively seals the body interior for the models mentioned is also a filter for UV and IR rays.

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Zone8: Although I am a handsome genius, when I stand in front of a mirror, I vaguely recognise the ugly idjit standing on the other side!
LINK: For B+W with Epson 1400 (and other models) using black ink only PLUS other useful tips:
http://www.photosnowdonia.co.uk/ZPS/epson1400-B&W.htm
Cleaning DSLR Sensors, including Kodak DSLR Factory Cleaning method:
http://www.photosnowdonia.co.uk/ZPS/KodakDCS-sensorcleaning.htm
Solving back/front focus problems on Sigma and most other DSLRs
http://forums.dpreview.com/forums/read.asp?forum=1027&message=35565277
PDF format list of lenses you can print or download - covers Italian Flag YES/NO for DCS 14n but applies to others. http://www.photosnowdonia.co.uk/ZPS/ItiFlagLensList.pdf

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Roger99
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Re: You just moved the target, didn't prevent dust
In reply to tkbslc, Feb 11, 2013

tkbslc wrote:

If you put a clear lens farther away from the lens, all you did was alter the part of the camera that you need to clean. Dust will just collect on your little protection lens instead of back on the sensor. Nothing has changed in terms of dust prevention, but you've significantly altered the design of the lens mount.

And FWIW, the top layer of the sensor is protection glass already. The actual sensor is not exposed.

I think the guy has a point. If there were a glass well in the box sealing it you would have far less trouble getting the dust out. You wouldn't need to worry about what has accumulated in the mechanism out of your sight line and whatever dust did get in to that protection plane would be outside the plane of focus and so be far less of a problem. Changing lenses on site would be less of a worry. Only trouble I could see is that it would reduce how close the rear element of the lens could get to the sensor plane reducing ultra wide ranges but how much of a limitation would that be. Oh and of course the flat plane of glass would change the optical characteristics of the lens you put in front of it so you would probably be looking at a whole new system for this one modification.  The glass could even be removable and replaceable in the long run to deal with any issues with micro scratches on it.

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Skatterball
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Re: Why is the body open?
In reply to Rexel99, Feb 11, 2013

Well you wouldn't want a piece of glass flush with forward end of the "hole" because no lens would fit on the camera.

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Rexel99
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Re: You just moved the target, didn't prevent dust
In reply to Roger99, Feb 17, 2013

Thanks, I will take you answer as one of the few here that 'get' the idea I was describing.

Sure, I am not saying that any current DSLR would be able to fit an extra piece of glass in the hole, it would require something to be engineered into a new model to allow it to fit/work with all the other systems around it.. but it's just an idea.

If it was there it would (help) prevent dust getting into the mechanisms when changing lenses, it would be easy to clean if dust got on it (when changing lenses) and yes, it may have some detrimental effects on the path of light coming into the camera at that point. To help with that perhaps the mirror and sensor would not need as much surface protection as these would then be within a sealed unit...

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