Hahaha... at least I know someone out there knows what I was talking about!

Anyway, bokeh is a lot more complex to explain. I was talking in terms of the angle of view and the exposure control (i.e. the same lens will have the same exposure value on an aps-c camera and a FF camera). But in terms of bokeh... hmm... I think of it this way: we would normally leave the bokehness to the side of the photo. So if on aps-c camera, the sensor will only capture the middle part of the image circle, hence you will have less obvious bokeh (which is around the side / edges of the image circle). But this is only a very general view of how bokeh may seem less on aps-c cameras. It doesn't always apply (for instance in situations where you purposely put the subject at the extreme sides of the frame)....

MechaHerc, you'll get a black circle around the corners. If it is a Sony DT lens, the A900 automatically activates APS-C mode, so you will never get the black circle.

Of course, best understood with a hands-on.

achew, the exposure is the same for a F1.4 on FF or APS-C. The angle of view will be different.

The depth of field will be different also because of the size of the sensor. On FF it is more shallow.

For example, to frame a head + shoulder shot using a 50mm lens on FF, you might need to stand about 1 meter away. On APS-C though, the angle is narrower, so you need to stand further away to fit the same subject e.g. 1.5 meters away instead. And as you know from your Tamron 90mm F2.8 Macro, the closer you focus, the shallower the DOF... that happens in the case of the FF also being nearer to the subject.

Of course, since the distance is different, the perspective is different also! Therefore to keep the same perspective you need to stand 1 meter away on APS-C. But it's not wide enough. So a 35mm lens will give almost the same angle of view as the 50mm on FF, while letting you be the same distance from the subject.

I can't remember if you have the A300/A350 but you can see what crop does if you enable 2x Smart Teleconverter; you can see the DOF become much deeper because you need to stand further away.

Millenia3000, I would rate the F58 higher on priority really.

any here taken macro with sigma 28-300? hehe i'm dslr newbie.. wanan try macro but... failed.... sob sob

frustrated with the night glow show .. it was less then 1 minutes or even 15 seconds ... ... damn it ... I never go to night glow again...

Haha. Okayy.
90mm not too much for macro meh?

Oh. Okok.
But SP90 you need to stand quite far right? 

Im sorry, but i dont understand 

you running out of ideas!? i dun think so man!... haha... you get me going jeles of your shots achew everytime... especially with those amazon toy thingy you have...

after some reading and thinking.. i think i'll change my next-to-buy item from 50mm f/1.4 to tammy sp90.. this is because this lens can also do macro.. i've seen some portraiture using sp90, it's good enough for me i think

well, it's just a wishlist.. dunno when can buy

maybe i'll change my mind again after this, who knows?

wats the focal length for CZ 1680 same as 50mm prime lense??
izit 50mm or other focal length??

thts wat i mean....
but i remember someone said the 50mm have to times with some numbers to become the exact focal length in APS-C camera.....