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I own a canon 550d and i am begineer photographer .

I am wondering if we need to take any extra precautions while changing lenses to avoid dust getting into the sensor region . Also, Whenever I swichoff the camera I see "sensor cleaning" message. What kind of cleaning does it do? When using at water bodies , does it pose a severe risk if slight mist creeps into the body when changing lenses? What is the risk if Sensor region is directly exposed to Sun light ?What kind of precautions do we need to take generally?

Try to be quick while changing the lens. Also keep the camera face down when you change it.

Whatever lens change has to be done, do it inside your house/hotel room. I would never risk changing my lens outside. Water body or coffee shop, its a strict no-no.

It is Canon 550D with 18-55 kit lens,nomal mounting.Point to be noted,I was not using any tripod.

Sensor cleaning: the sensor is provided with a film/ coating that vibrates at ultrasonic frequencies to shake off any dust thats settled on it.
Mist entering cam: the mist will not land on the sensor. The mist (spray) may fall on reflex mirror. Never touch this mirror - its a first surface mirror (reflecting coating on top surface). Let the droplets evaorate in a dust free environment. Below the mirror you will find shutter curtains in closed position. So usually mist spray will not reach the sensor unless mirror is locked up and shutter is opened.

I have used my 400D in some really bad rains in Bandipur (caught unprepared) and the cam survived, despite not being weather sealed. Reinforced my trust in Canon.

Sensor exposed to sun:
No issues as long as you dont have a lens fitted, and focussing the sun, and using slow shutter. Just sunlight falling directly on sensor for few seconds does no harm.

I have used my Canon 300v (film), 400D, and 7D in really harsh conditions (-40©) and the cam n lenses worked very well :)

Ok, thanks. Never knew Canon supplies kit lenses with this kind of inferior optical quality with 550D. I was under the impression that mine was worse!

How to check this?Are you telling the lens is faulty?
So how can I get this checked?

I took this one with same lens,but used flash

I am not saying that the lens is faulty. Most of the kit lenses coming with entry level SLRs are not so good in optical quality. I want to replace my kitty, seriously contemplating on getting an f/2.8 17-70mm or so. But the kit lens that came with my A35 isn't that bad when it comes to chromatic aberration.

Every lense has a "sweet spot". That is the aperture and distance where the aberrations are minimal, so that you will get crisp photographs with minimal distortion/chromatic aberration. Find the spot and all your photographs will come out perfect (well nearly so).

Where the professional lenses excel is in the wide range of minimal distortion and better performance wide open, some thing which lower cost lenses compromise on, but for the price you pay, the low cost lenses are perfect if you know their limitations.

Kit lenses are usually hopeless - genuine waste of a good body if you dont upgrade optics. For general purpose shooting, go with a 18~135. If you want even better quality pics, and dont mind losing a bit on tele end, buy the fantastic 15~85. I have the 15~85 on my 7D all the time. Very nice superwide end and decent tele end.

White-rabbit, I read your previous posts now - UV filter is a good protection for the front element of the lens, but a poor quality one can degrade image quality. Please stop using it on kit lens. Use a good UV filter on expensive lenses in dusty conditions / near beaches where you might get salty sea spray. Dont forget to remove the UV filter for important shoots.

Commercially available macro lens kits may not provide good results, esp. higher magnifications. They produce visible chromatic aberration and focal plane distortion. Get a set of lens reversal rings and adapters that help you fit the lens reversed on your cam. You need to judge and use manual exposure as there is no aperture control on electronic lenses. Need to have a still subject and camera. You will be amazed at the results you get by reversing a 50mm lens :)

Hey Aroy you just generalized it, but it's true what you're saying.

Anyway, silly me thinks that I've got a better kitty here because never have i seen so much distortions with it; wide open, closed down, or somewhere in between. Gonna post some samples when I fix my router :(

True... Kit lenses come with a lot of variation in quality. My 18~55 was decent till it fell out of my camera bag. After that it started to produce hopeless chromatic aberration. My friends kit lens had this chromatic aberration straight out of the box.

Most of the older lenses, and the current professional ones have a metal barrel, with rings to hold the glass elements. So the lenses can be precisely aligned to give the designed performance. That also makes it easy for the glass elements to be changed and alignment adjusted. Unfortunately that comes at a steep price.

In general the low cost lenses are designed for mass production and use plastic barrels where the lense elements are fixed once and for all, extremely difficult to adjust the elements. Hence you get a wide variation in quality/performance.

In case you are particular, you should test a few lenses (if the shop permits) and then choose one which gives the best performance. There are a number of articles on the net on this particular topic which you can peruse.

Very true. My Minolta 70-210mm is still in perfect condition even after me opening it up couple of times to clean fungus. It has a metal body and glass elements are fixed in it with high precision and you can't go wrong with alignment when you put elements back. You can refer to my older post here in this thread for pictures on the lens surgery that was done at home.

Those lenses are truly brilliant. You can directly use them on Sony DSLR body in manual mode. They are heavy and well built.

Wish to share some pics.

1) Shot in the Basilica Notre Dame in Montreal - one of the oldest in North America. Its interiors are completely built of wood. I attempted several times to get a good image and was not satisfied with the results. I got frustrated and started walking out, and just when I was about to exit - I just turned around, took this pic and left. I realized that I got a good image only after I reviewed this image on my lappy at home - lesson - never delete a pic until you see it on your comp :)

The original RAW file was about 17MB, and its compressed to 679kb - so lot of detail is lost - but you can still see the beauty of this basilica.



2) Macro of a Ball Point - the ball is of just 0.5 mm diameter! achieved with 50mm f1.8 lens mounted with lens reversal ring.



3) A spider that was about 6~7mm long was captured with a 100mm Macro USM lens. The spider was extremely difficult to spot - blended well with tree bark. The scene was lit with a Canon EX520 II Speedlite (off camera). The green ones with orange legs around this spider may be the young ones - not sure though.



4) How important is a high end cam to get a decent pic? Debatable point - but like some members have mentioned earlier in the thread - there is a sweet spot for every lens - and cam. If we understand the limitations of our devices and operate with in their "sweet spot" zone, we can still get decent pics I think.
Here is a pic from my Nokia 5800 Xpressmusic post processed on Gimp:



I am thrilled to see so many BHPians sharing info on photography clap: