Reply to 40D with 50mm 1.8

ishootblue posted a reply:

Pavel is correct in his explanation of the use of 50mm on an aps-c sized sensor. The lens will produce the same size image circle regardless of the size of the sensor. Full frame will cut out an image in this circle which goes nearly to the outer edge of this circle (hence why some lenses vignet on FF bodies), cropped sensors will cut out a smaller picture which will have an equivalent viewing angle to a large focal length. e.g. 50mm on 1.6 sensor will have the same viewing angle as an 80mm on a FF sensor.



with regards to the depth of field, this will be different between a cropped and FF sensor. again to stick to the 50mm analogy as this is the lens we are talking about. For a practical example if you take a 50mm, at a distance of 1 meter and an aperture of f5.6 then the DOF will be as follows:

50mm on FF (e.g 5D): 13cm

50mm on APS-C (e.g. 40D): 8cm

So the statement that the depth of field stays the same is not a valid one as the DOF is actually nearly half. For reference the depth of field of an 80mm lens on FF (e.g 5D) would only be 5cm. DOFs can be easily calulated with some of the online calculators.



I think that the whole discussion on focal lengths between sensor sizes is one where there is a hell of a load of misunderstanding and pseudo science rather than hard facts. The confusion is part created by marketing blurb and part by ignorance from people using their camera and not really understanding the workings of their camera. I never remember seeing discussions on this when comparing 35mm film to 120mm roll, because in essence that is what this is.



This topic has now gone way off topic :) to get back to the original posters request:



I have got a 40D 50mm 1.8 combo and it is a nice set up. it all depends on what kind of pictures you take. If you are into landscape photography then no this lens is not good for your needs. if you want a cheap prime for portrait photography or need it in low light situations then yes it is a good lens. As a first lens ... I wouldn't recommend it (even though it was my first). I would stick with the 18-55mm kit lens as your first lens. it is very cheap and gives very good results. It is often dismissed as cheap plastic, but mainly by people with lens envy. Try it and you may be surprised.



with regards to the noise of the flash popping up, I'm afraid you can't change that. You can prevent the flash from popping up automatically by shooting in the creative modes rather than in the automatic mode. if you need the flash, you can just press the button and muffle the sound with your hand.