18mm EF-S vs 17mm EF - don't see much of a difference

[Andy Sharp]

So your average mobile phone camera on Auto Focus has to be spot on otherwise it will be soft front to back, but if it is sharp it will be sharp front to back. Maybe that's partly why it takes 'em so long loads of other factors no doubt too.

[Eifion Williams]

If I can add something to the discussion.
When shooting Sport I often turn to my D300 Nikon as it has a cropped sensor. So the 70 - 200mm lens that I used yesterday on the D700 is now a 105-300mm when fitted to the D300 due to the 1.5x crop factor.
Can be confusing. Only the full frame cameras actually give you the focal length which is on the lens. Others are dependant on the size of their sensors.
Canon 1.6x
Nikon 1.5x
Olympus 2x

[Lee Iggulden]

Do you know - I was going to post all this information but I didn't want to show any of you up

Me

[Andy Sharp]

I think it's that way so that the distance you can focus down to is consistent, The cropping only effects the field of view and the increased magnification is down to digital (sensor gain kinda). I can never work it out myself, but my 10-20 focuses on stuff pretty close up, wouldn't think it'd focus on anything closer with a bigger sensor.

[IanOwen]

Andy it will make a difference, the Full Frame sensor will be able to focus closer. Its down to something called Hyperfocal distance. Basically in order to get maximum front to back sharpness in an image you should try to focus for the Hyperfocal distance. This article http://www.photopursue.com/hyperfoca...html#hyp-chart has some useful tables and shows you that the full frame sensor has a nearer focusing distance than crop sensor. I use an app on my iPhone when I'm out shooting landscapes to determine where I want to focus according to the Hyperfocal distance of my kit.

[Andy Sharp]

Thanks Ian, A very interesting link. I think that Keith must be somewhere close by, rubbing his hands (Circle of Confusion ). I have the an app for it too. Got a couple of FD lenses that still have the DOF marks on.

Andy it will make a difference, the Full Frame sensor will be able to focus closer. Its down to something called Hyperfocal distance. Basically in order to get maximum front to back sharpness in an image you should try to focus for the Hyperfocal distance. This article http://www.photopursue.com/hyperfoca...html#hyp-chart has some useful tables and shows you that the full frame sensor has a nearer focusing distance than crop sensor. I use an app on my iPhone when I'm out shooting landscapes to determine where I want to focus according to the Hyperfocal distance of my kit.