As a result of the recently overwhelming debateon the topic “DSLR vs. soap dish ”and my own thoughts on this topic, I decided to purchase a“ DSLR ”. It just turned out that my good friend in the States was selling his Canon Rebel XSI camera. I decided to buy this camera from him. I know him well and trust him. The situation has many advantages: cheaper than on ebay or amazon? additional bonuses in the form of a spare battery, a couple of capacious sd-cards, the seller’s responsibility that I know of and his careful handling of the equipment. However, in the situation of buying used "DSLRs" can be present cons, which one of my listeners kindly warned me about. He wrote me a voluminous letter in which he gave recommendations that are better to follow when trying to purchase a used camera. With his permission, I publish it here. I hope someone else helps. Add-ons are welcome in the comments.
I would like to give some “vital” necessary and most important tips when buying a used earpiece, that is, a used SLR camera and a couple of warnings for its initial use.

Appearance

In fact, it is very banal, but in my opinion one of the most important aspects when buying a used camera is its appearance. If you see that the camera is badly worn or there are some deep scratches on the case or, God forbid, twisted bolts, then run away! Mirror - creating gentle and careless handling of it (drop, shock) can bring down the exact focus and further negatively affect the output, in other words, the quality of your photos

Matrix

A CMOS sensor or just a matrix is ​​the heart of your SLR camera and is an integral part of checking when buying a used, and sometimes even a new DSLR. What is the main problem with the sensor? And the fact is that in comparison with simple “soap” cameras, the matrix in the mirror chamber is open to the outside world and is thus unprotected from dust, dirt and other “antiparticles” of the universe, which with pleasure settle on it and subsequently affect the output in the form of black dots or stripes in the frame. In fact, of course, you should not worry too much about this fact, since giants like Nikon and Kenon themselves are not yet able to solve this problem completely, so even buying a completely new SLR can safely count on a small amount of dust on the sensor. the word small is important since if the camera is used improperly for EVEN a short period of time, the SLR matrix can be very quickly hidden beyond recognition. And then another gross mistake is made, namely, an independent attempt to clean the sensor, which in 90% results in cloudy stains and scratches on a VERY sensitive upper layer of the sensor and in the future they try to quickly “fuse” the camera, that is, sell it! That's what I want to warn you against!

To do this, always be sure to take a test shot that will show you the status of the sensor. The test algorithm is as follows: the

camera is placed in the “M” mode (manual), the
focus switches on the lens to the manual focus mode, while the focus itself is absolutely unimportant.
The zoom lens is twisted to maximum. (for example, at 18-55, the zoom is placed at 55mm)

MOST IMPORTANT: the aperture is set as closed as possible (usually f34, f36, maximum on some lenses f22), the

shutter speed is set to 1/50 and the built-in flash in the camera turns on,
you photograph a completely white sheet of paper, at a distance of about 30-40 cm so that the frame is completely white.
And then the oil painting: you open the picture and see the dust content on the sensor! For convenience, it is advisable to play around with the levels in Photoshop, then the dust, in the form of black dots, will be visible even more clearly.

For example, a test shot should look like this:

Such a dust content on the sensor is quite normal and it is unlikely that you will ever see it in a photograph, unless of course you close the aperture to “crazy” values ​​like f22 or more. But this is another conversation ...

But if your test shot, God forbid, looks like this: www.cosmetic-jerid.de/test2.jpg , then the camera’s sensor is clearly “killed” and you should definitely not buy such a DSLR!
PS You say that in my cell there is a special system for cleaning dust from the sensor and it makes no sense to worry about its pollution?
Yes, I do not argue, a sensor cleaning system exists in almost all current SLR cameras! But, unfortunately, it is very inefficient and is mostly used by manufacturers only for commercial purposes!

Gate

The shutter of the SLR camera is the only mechanical thing in the camera and it is he who gives it the right to be called a SLR! Like any other mechanism, the shutter is not eternal and, unfortunately, 80% of the causes of all breakdowns of SLR cameras is the shutter. The life of the camera shutter varies by model. In budget DSLRs (Canon 1000d, 350d, 450d, 500d, 550d or Nikon d3000, d5000, d90), the shutter is approximately designed for 70 to 100 thousand shots. On more expensive models (Canon 40d, 50d, 7d, 5d or Nikon d300, d700), the shutter lives about 120-150 thousand shots. Well, on the professional, he can go too far for 300 tons of shots.
It is very important to know how many pictures the camera shutter has already “recaptured” before buying a used ear-mirror. I would not advise buying a budget DSLR with 50 thousand taken pictures, since she already has the cat in a bag disease.

Optics

It is worth paying special attention to the lens. He can tell you a lot about how a person used the camera. If the lens glasses are incredibly stained with fingerprints or even have scratches, then the camera was obviously used inaccurately and carelessly. However, a completely “licked” lens is also not very good. The constant, endless wiping of the lens can completely remove the thin spraying on the lens, which then adversely affects the quality of the pictures. The correct lens should be moderately dusty and reasonably clean. Here the golden mean is important.
In my opinion, these are the 4 most important aspects that must be observed when buying a used SLR camera. You can, of course, go even deeper, which, in my opinion, will ultimately discourage interest in buying a used DSLR. Yes, and buying second-hand goods, it is simply impossible to be 100% sure of its quality.
And
finally, a couple of important warnings when using the SLR camera for the first time: Changing the lens should take place quickly and, if possible, in an un dusty room. The body (camera) must be kept with the notch down during a lens change. This procedure is necessary to prevent dust from entering the sensor.
Do not just take off the lens and admire the insides of the camera. And especially taking pictures without a lens! This again is fraught with the fact that dust can get on the sensor and in the future leave unpleasant points in photos.
Try to handle optics carefully! Fingerprints on the lens glass are best removed with special pencils or special ones. microfiber fabrics. But you should not rub the lens on every occasion, since a little dust or fingerprints on the front glass of the lens will not affect the quality of the photo, but the erased thin special coating on the lens will make itself felt!
Always cover the lens with a protective cap after using the camera. This will prevent accidental damage or contamination of the lens.
Denis, I am always happy to help you and wish you good luck and many wonderful shots with your new SLR camera!
Regards
Andrew