Hi everyone,
Lately I've been searching for a camera, and yesterday I found a Canon EOS 550D with 18 megapixels on sale. I went on the internet and made a research, I found some information but I'd like to know what you think about it. I am looking for a camera with a good macro shooting.
p.s if you have time, could you explain me what ISO is? ;)

Hi Olivia. It's a good camera. I bought one for my daughter and I know at least one PB member who uses it to very good effect. The 550D has been replaced by the 600D, which means it should be fairly cheap and/or include two "kit" lenses in the package. (A kit lens is a bit like the ink sold with a new printer - not much good, but at least it allows you to use the product straight out of the box.)

ISO is the rating for sensor sensitivity. The sensor records light just like film. When there isn't enough light - for example, at night or indoors - you can:
- use the flash (not always very well) to add light
- increase the aperture, i.e., widen the hole through which light passes in the lens when taking the picture, but there are downsides and limits
- lengthen the exposure time, i.e., keep the shutter open for longer, which runs the risk of subject and/or camera shake and blurriness
- increase the sensor's sensitivity by upping the ISO, which means the sensor records more light at a given aperture or speed. The sensor amplifies the light signal it records, but this also amplifies noise (graininess) in the image.

Most of us try a combination of aperture / speed combinations and try to keep the ISO down to a minimum. When using a flash, never set the ISO to more than 200.

ISO is just a name for an organisation. In film days light sensitivity was also measured as ASA/DIN. Before digital, you had to change film when changing shooting situations.

The base setting (before you fiddle with your Canon) is 100 ISO, which is fine for bright sunny days. You can either leave your 550D at auto ISO or change it to 200 for cloudy, 400-800 for low light situations such as dawn / dusk shots and indoors or boost it to 1600 and, I believe, 3200 for night shots. I suggest letting the camera choose the ISO (auto ISO). For your macro work, I advise not exceeding 800 because noise (grain) becomes visible at that point with a decent macro lens.

Compacts are notorious for poor high-ISO performance, mostly because they use tiny sensors whose components overheat in low light situations and cause noise. The 550D and Canon DSLRs in general have a good reputation for high ISO performance, so you needn't worry. I often shoot at 3200 ISO with my 5DII. At web resolution, there's no difference between that and 100 ISO. The latest high-end Canons and Nikons can shoot at 200000+ ISO in almost pitch-black situations!

Hope this helps.

Thank you so much for the ISO information! But I didn't really get if you said it was good or not, as I understood you said it was?
Thank you again

I use a Canon 550 D, a good choice not too expensive to start, easy to make shots of meadows, even without the macro lens. To understand the ISO, do as I do, handle it and you discover its potential

If you are serious about macro it might be worth the extra money for the 600D. It has an LCD display that can be flipped out and twisted around in almost any angle which is very useful if you shoot very close to the ground or other awkward angles.

But is it better also technically or is it only the LCD screen to change from the 550d to the 600d...

They are both technically very good. I think it comes down to how much you want to spend. Both will produce excellent images. There will be a lot to learn with each model. I have the 600d and I like it very much but if I couldn't afford the extra ££££ I would have been very happy to have the 550d.

My guess from your ISO question is that you are fairly new to digital SLR cameras. There will be a steep learning curve, and the 550d will be a perfect place to start.
.

Even for me, I still have not fully understood ISO . What I can suggest though is leaving ISO to auto and just play around with the flash, shutter and aperture. For my camera, as long as ISO is set to auto, it tries to minimise it as much as possible.

ISO gives you a third choice of control. We are used to using Aperture and Exposure. With ISO we can extend our range - it gives a huge amount of possibilities, particularly with DSLR where these days 400+ ISO still gives acceptable resolution.

@Olivia The sensor is the same in the 2 cameras so the image quality is the same. The 600 has a few more functions for beginners to help them modify the images without any basic photographic skills.

@jirehphotog You can simply imagine the ISO setting as a way of controlling the sensitivity of the camera to light. Of course, as in real life there is no free lunch so the higher you set the ISO the more "noise" is generated in your images (noticable as small dots of the wrong colour). One reason to learn how to control this yourself is because the sensitivity also dictates which aperture and shutter speeds you can use and these are the basic settings to control the look of the image. ISO, aperture and shutterspeed are like 3 corners of a triangle, you can't change one without at least one of the others also changing,Do you want a short depth of focus or do you need a deeper? Do you want maximum sharpness or would you prefer a fuzzier feel? Do you need a fast shutter speed to stop motion or can you sacrifice speed to close down the aperture for better optical sharpness? The camera has no idea what you want so it just tries to maximise the image quality on the basis of the "mode" you have chosen which might or might not be what you have in mind and I find it's unnecessarily generous with ISO so that it can produce a reasonably sharp image under all circumstances.

Thank you everyone! ) I'm getting cleverer P