Why is there not a protective glass element that is between the lens and shutter in a SLR?

Question

With the danger of dust on all SLR cameras, it only seems logical that adding a simple glass element that went between the lens and shutter (mounted on the camera) would both protect the camera's interior and sensor from any intrusive particulate matter.

Logically thinking, I don't think it should effect the picture quality at all, seeing how we have glass sky filters already.

There are a couple of questions that I have:

Are there any cameras that currently have this feature?

Would implementing this feature detract from the normal function of a camera?

Is this in any way impractical?

To clarify, the blue region is where the question refers to.

Asked by Dylansq

Answer

Image quality and possibly expense

Introducing yet another element in front of the sensor will degrade quality of the pictures, and for various reasons.

a) being outside of protection of the shutter will mean that it is constantly in contact with the air and dust. This will mean it will require more constant cleaning than a sensor would. How often do you clean the mirror inside your SLR? Hardly ever because you know it won't show up on photos. How often are you going to clean this extra piece of glass?

b) The placement of being between the lens and the sensor will mean that any dust on the glass would be spread over a larger area of the sensor, degrading quality. We probably all know what an example of dust on the 'sensor' looks like. That dust is on the protective glass right in front of the sensor, so only really covers the few pixels directly under. Being on glass in front of this would cause a larger smudge to be affected by the dust.

c) CA, diffraction, and all of those other nasty things. You have just had the light of your subject travelling through an expensive lens filled with precision glass. That nice white L lens you bought has scored amazingly well on sharpness and contrast tests. Now, however all that precision engineered light is passing at a steep angle through a cheap piece of glass placed in front of your sensor. Unless they spend a lot of money developing some very good quality coated glass, it is unlikely that it will not effect the quality of your photo. And depending on what lens you have, and the angles of incidence that the light from it is hitting this glass, will likely change how the glass effects it. To make none of this happen, you would need multi-element glass, or effectively another lens inside the camera, which would increase cost and give you even more to need to maintain and clean.

Also, in the placement where you put the glass, it might not fit with all lenses. I know some rear lens elements protrude more into the body with others, and I don't have any measurements, but at a guess some have been designed to only just narrowly miss the mirror as it flips up. Putting this glass in the way would mean these lenses no longer fit those cameras.

To summarise, it's not practical, and would degrade image quality. The sensor already has filtered glass on it that can be cleaned, and that is protected by a shutter that opens when it needs to to minimise contact with the air. Introducing an extra glass element removes this simplicity and makes the whole process of keeping things clean more difficult.

Answered by Dreamager

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Does shooting my photos in RAW and converting them help to correct small spots of dust on the lens?

Question

I have found a statement on one of Russian sites:

They (photographs) often shoot in RAW, and it, in turn, removes various small spots in the form of dust on the lens when converting.

Is it true? If yes, how to do this (what converter does this)?

Asked by garik

Answer

That statement from the Russian site is misleading. Shooting in raw format doesn't have any relevance to spot removal. You can remove dust spots just as easily with any other format of image.

There are multiple ways of clearing dust spots:

• Capture NX uses a healing brush
• Lightroom 4 (and below) use the spot removal healing brush
• Photoshop uses a spot removal tool similar to Lightroom

Basically it's just a cloning/healing procedure. But the best fix for dust spots is to clean your sensor.

Answered by nwcs

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How do I clean the external forward-facing glass on my lens?

Question

How do I clean the external forward-facing glass on my lens?

Over the last year or so of use it has accumulated a little dust and a translucent smear mark. Nothing serious, but I'd like to remove them nevertheless. The lens in question is a Sigma AF 17-50mm f/2.8 EX DC HSM OS and has a flat external forward-facing glass element (e.g. see here).

I've never cleaned any camera equipment before, so pitch this to a novice audience please.

Asked by fmark

Answer

Assuming you're just talking about the front element - I use these disposable Zeiss wipes. They do better than a lens pen (which handles dust ok, but doesn't do smudges nearly as well) and a box of 200 will last a long, long time with hobby level use. My local Walmart sells the box of 200 for under 4 dollars in the camera and the optometrist section. They won't harm the coatings on the element and do an excellent job.

Answered by rfusca

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What is the “Dust-Off Reference Photo” on a Nikon DSLR?

Question

I have seen this in my D700 menu and just saw it again on Nikon's tech sheet for the new D4. Is this the same tech that Minolta is using to clean their sensor of dust or is it something else? How does it work and what does it do?

Answer

No it's not for cleaning dust off the sensor, although there is an anti-dust feature that basically shakes off dust.

The dust-off reference feature has you take a shot of a featureless wall, piece of paper, overcast sky. You load that image into Capture NX2 software, and it then determines where dust spots (darker areas) are, and it then can automatically fix those areas in future images you take.

It would be nice if cameras could do this processing in-camera, but I'm not aware of any that do.

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Dust-like speck visible every few pictures — is it dust, or worse?

Question

I seem to have to dust-like speck on my Sony Cybershot S950's lens, but it appears randomly every few pictures. Could something be going bad internally?

Answer

That sure looks like sensor dust, for which I'd recommend seeing the answers in the Best way to clean a DSLR sensor thread. The spot may appear "randomly" because it only appears when you're using a narrow aperture.

That said, it seems you don't have a dSLR, thus no interchangeable lenses which are what usually causes the situation where dust can get inside the camera body. I suppose it's possible that dust got inside the camera through some other way although I think that's a fairly rare occurrence.

If the camera is still under warranty, it's worth a call to the manufacturer.

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Where is this dust located on my sensor?

Question

I have a really nasty looking piece of dust on my 550D's sensor, situated in the top right-hand corner of each image I take with anything higher than f/11. I am going to get a decent sensor cleaning kit, but I'd like to know which corner of the sensor should I focus on to get rid of this annoying particle?

In other words, does a lens flip the incoming light from left to right and turn it upside down? I think that's correct, so that means the answer in this diagram will be A, correct?

And before anyone asks - yes, I will clean the entire sensor while I'm in there, but this will help me focus on this particular (pun intended) problem. Thanks in advance!

Answer

(A) is indeed the correct answer (he said, remembering well the reflex finders sans prism that he's used over the years, which didn't flip the image right-to-left and made panning a bitch).

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How can I find a point & shoot camera which will not be dust-cursed?

Question

All my "point and shoot" cameras always end with noticeable dust in the lens (usually just after the warranty expiration), and although they otherwise work fine, I'm forced to buy another one.

I think that the dust enters inside the moving zoom elements, so searching on the web I've read about the so called "beach cameras" that are made to prevent the sand to enter inside, but the picture quality is ugly compared to other point & shoot cameras.

Are there "beach cameras" with acceptable quality?

I do need an handy point & shoot; I'm not interested in a "cleanable" dSLR. The last one lasted just one year, and having bought it in Japan, the warranty is out of question.

Answer

First, any waterproof camera will do. Those are completely sealed against dust, moisture, water, snow, etc.

The constraint on the lens they use means limited flexibility and certainly lower quality than standard cameras of a similar size. Among those, the best one I've seen so far is the Nikon Coolpix AW100 which I reviewed here. Do look at the sample gallery because for small prints, the quality is certainly acceptable in decent light.

You have to compromise somewhere, if the quality of any of those is not good enough. I suggest you learn to be more careful with your cameras. Store it in a well-sealed bag, clean it often, etc. I have owned some cameras for years and never seen more than a few specs of dust inside a fixed-lens camera. The DSLRs on the other hand get their share but it depends on the climate.

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How do I clean dust in a Sony A55 SLT?

Question

I am pretty sure I have dust inside of my Sony a55 SLT (Single Lens Translucent). However I'm not sure how to get rid of it or where exactly it is. I think it could be either on the translucent mirror or the sensor itself. It's in the same place each time, but mostly occurs on images with a high f number (e.g. F22 etc)

An example image (cropped):

Would a general sensor cleaning kit remove the dust form the translucent mirror part?

I'm unsure of what to do as it's not a conventional mirror like in SLR cameras.

Any recommendations on a good cleaning kit? To be honest I'm slightly scared about it all as I don't want to destroy my camera!

Answer

You have dust on the sensor. The higher the F-stop the more noticeable they are.

To get to it you have to release the small latch at the base of the translucent mirror and lift it manually.

If that happens rarely, I recommend you have it done in a store. The charge about $25 and they have a lot of practice doing it. Some stores here even do it for free if you bought the camera there.

The other option is to do it yourself using a wet-clean solution. The one I use is from VisibleDust. You need to buy a small bottle of liquid and some compatible swabs. The swabs get used once and are disposed of after. One set of swabs plus liquid cost about $80. You'll be able to clean a dozen times or so with this.

Avoid using a blower, compressed air or anything similar. It usually only puts more dust on the sensor, even those with filters on the intake are only marginally better.

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How weather resistant is the Canon EOS 7D?

Question

Canon states that the 7D is weather resistant and built to resist water and dust.

There is even a blog which shows a EOS 7D covered in snow, during a field trip. But reading trough the comments of this blog post, there are many cases of people who are desperate because their 7D broke due to damage by rain or water(even with a class L lens attached).

So, my questions:

• Are there any experiences regarding the Canon EOS 7D and heavy rain, snow or splash water?
• Can I be sure that my equipment will survive a photo shoot in the rain or in a very dusty location?

Answer

Unfortunately, very few camera models specify the amount of resistance as anything measurable.

Water and dust resistance, as specified by Canon, means very little. If it said waterproof and dustproof that would be a stronger statement. I also feel lawyers got involved somewhere in the writing of these things. For example, some Nikon manuals say 'resistant to dust and casual humidity'. Again, it has very little meaning.

The 7D falls among those cameras with vaguely specified resistance. Unfortunately, you have to try to find out. The 7D I used was subjected to snow without any problems. Actually, falling snow rarely is a problem even for non-weather-sealed camera as long as you wipe it off before you go into an environment where it would melt. I have no experience with a 7D under rain.

To be sure about your equipment's resistance you have to try it and even there, bring a backup. I used a Pentax K-7 in a shoot during a sand-storm and it worked perfectly. When I got to the hotel, I rinsed it under the tap for a minute or so to clean it. The polarizer I had though took a beating and I could hear sand in it between the rings for weeks after. It probably saved my lens though :) On the other hand, it took less than 15s for a Canon Rebel (not sure which model, probably XSi) to stop working completely in the storm. Canon asked for $150 or so to clean the sand out.

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Dust on the sensor, should I be worried?

Question

I did a 30 second long shot without the lens and checked the sensor and saw some dust on my sensor (even though camera has sensor cleaning). I didn't see any defects on photos yet, but is it something to consider and take actions ASAP?

Answer

Dust on your sensor happens to many of us, its not the end of the world.

If you're not seeing it on photos, I definitely wouldn't take drastic action. Order something like this rocket blower, set your camera to mirror lockup, and gently try to blow the dust off. You can also look at gentle liquid cleaning solutions.

If you are unable to remove the dust yourself and it becomes apparent in your photos, consider having your camera professionally cleaned by a shop or the manufacturer.

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Is it normal for there to be tiny dust particles in a new lens?

Question

I'm the owner of a new Canon 550D with a Canon 18-135mm IS lens.

While looking into the lens, I noticed what I think are two tiny dust particles (I would say smaller than 1mm) behind the first glass of the lens, that can be seen from the front and from the back, but I'm not sure if this can be noticed in the pictures. Given that I've paid some considerable money for this lens, is this something normal I can expect a new lens to have?

Apart from that (I think it might be unrelated) I also see two dots in the view finder. They are not related to this dust and, at least, I'm sure they are not visible in any pictures, but is this also something I can expect?

Answer

While I wouldn't really worry too much about dust in the lens actually effecting image quality, I would say that is still not normal, and I would probably return a brand new lens if it came with any dust inside.

Here is a good example of how bad a lens can get before image quality suffers - Dirty Lens Article

As for the dust you see through the viewfinder, that could actually be in the viewfinder - which I wouldn't worry about, or it could be farther down the lightpath - such as on the actual image sensor. If you just bought a brand new camera and it had dust on the sensor right out of the box, I would guess that it wasn't brand new and someone took it for a test drive or two prior to you purchasing it. I would return for a new camera in that case.

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