f/1.8 vs f/2.8

I've searched Google but I guess I'm getting the keywords wrong.

How much more shallow DOF can I achieve with f/1.8 vs f/2.8? Could someone post some pictures at the same focal length (esp. 50mm)? I'm trying to decide if I want to get a nifty-fifty or not to go with my Tamron 17-50mm f/2.8. Initially, I was going to wait till I received my Tamron and take some portraits at 50mm f/2.8 but I'm getting a good deal on a nifty-fifty and want to get it if the difference is really noticeable. Please help!

nepali wrote in post #11352844
I've searched Google but I guess I'm getting the keywords wrong.

How much more shallow DOF can I achieve with f/1.8 vs f/2.8? Could someone post some pictures at the same focal length (esp. 50mm)? I'm trying to decide if I want to get a nifty-fifty or not to go with my Tamron 17-50mm f/2.8. Initially, I was going to wait till I received my Tamron and take some portraits at 50mm f/2.8 but I'm getting a good deal on a nifty-fifty and want to get it if the difference is really noticeable. Please help!

do an advanced search on www.flickr.com - you can see plenty of photo examples using a variety of different lens with different apertures (look at the EXIF)
But here's a hint - for portraits don't start out with f1.8 or f2.8 !

http://www.tawbaware.c​om/maxlyons/calc.htm

Plug in some numbers and "see" the difference in DOF.

watt100 wrote in post #11352860
But here's a hint - for portraits don't start out with f1.8 or f2.8 !

Why not? Don't people strive for the bokeh in portraits? Or are you saying that 1.8 is too shallow and you end up with half an eye in focus and the rest blurry?

watt100 wrote in post #11352860
But here's a hint - for portraits don't start out with f1.8 or f2.8 !

Yup as f1.4 might work better.

Cokeman wrote in post #11353368
Why not? Don't people strive for the bokeh in portraits? Or are you saying that 1.8 is too shallow and you end up with half an eye in focus and the rest blurry?

That can happen but the distance to your subject also affects DOF.

http://www.dofmaster.c​om/dofjs.html

Remember also that most lenses are not at their sharpest when wide open.

Cokeman wrote in post #11353368
Why not? Don't people strive for the bokeh in portraits? Or are you saying that 1.8 is too shallow and you end up with half an eye in focus and the rest blurry?

yeah, that what I'm saying (basically)
there's more to it but go to a portrait group look at the EXIF data
see what you see -

here's a few million portraits to contemplate:

http://www.flickr.com/​groups/people
http://www.flickr.com/​groups/portraitaward
http://www.flickr.com/​groups/strobist

XSi (450D) and Tamron lens - (but not at f2.8 or f1.8 or f1.4 ! )

for portraits you should probably get at least a 50 1.4 (sigma or canon) or an 85 1.8. the 50 1.8 is a decent lens, for the price, but it's hardly a long term keeper

The difference of over 1-stop of light and DOF can be dramatic... as others have said DEPENDING ON DISCTANCE TO SUBJECT. That said, the 50 f/1.8 is a cheap way to learn about faster glass, even if its not as fast as it could be. I agree with others that although the quick and cheap gratification of the $100 toy can be good, you won't be sated long. You'll quickly begin to wonder about the benefits of a 50/1.4 or 50/1.2. I've never owned the EF 50/1.8 but I have an FD 50/1.8 (and Yashica 50/1.9) and can honestly say that the difference between that and a f/1.4 is dramatic enough let alone an f/1.2. But everyone has to start somewhere... and at $100 you can't go wrong.

nepali wrote in post #11352844
I've searched Google but I guess I'm getting the keywords wrong.

How much more shallow DOF can I achieve with f/1.8 vs f/2.8? Could someone post some pictures at the same focal length (esp. 50mm)? I'm trying to decide if I want to get a nifty-fifty or not to go with my Tamron 17-50mm f/2.8. Initially, I was going to wait till I received my Tamron and take some portraits at 50mm f/2.8 but I'm getting a good deal on a nifty-fifty and want to get it if the difference is really noticeable. Please help!

If you were shooting a portrait with a 50mm lens on APS-C body from a distance of 10' from the subject, f/1.8 has DOF zone of 8" while f/2.8 has DOF zone of 12.7"