Originally posted by pschlute Keeping a constant aperture
size while zooming would involve me using my calculator to work out the f-stop and I suspect the subject would get bored and move away
I am not discussing the different variants of how one can approach making different photos or "zooming".
Think of comparing a 50/1.4 lens versus a 200/5.6 lens wide open for a portrait on a corn field.
Originally posted by stevebrot This is where I say...show me.
Anyone can compare any situations he wants here:
DOF simulator - Camera depth of field calculator with visual background blur and bokeh simulation.
Use Framing: Lock field of view for a constant portrait framing.
On the upper right corner you see the background blur, e.g. 1.880 mm for both.
On the lower end you see the DoF; 12.4cm vs. 3.1 cm
So you get the same subject separation, but the DoF is 4x bigger on the 4x longer FL.
1)
Essentially this means that if you want good subject separation but still want nose tip and ears sharp and have enough space and the background is far away, you'll want to use 200mm F5.6 and not 50mm F1.4. Large aperture size is your friend in this scenario.
The sharpness drop off due to DoF is much more aggressive for a lens with smaller F-number and same aperture size.
2)
On the other practical side end, if you shoot in a small space and nasty background is very near to the subject, your best friend is sheer F-number. You'll want to use a F1.2 lens.