Lenses is it worth waiting?

[Chris Law]

I've currently got my NEX-VG20 with a SEL1855 lens attached, for a better shallow depth of field I was going to get the new SEL1850 but I was wondering would it be worth hanging on for a bit longer to see if any more new lens are coming out.

Would the f1.8 come any near to the shallow dof on the camcorder at the start of the video, 0:00 to 0:15
Sony NEX-VG20 (Sony Promotional Video) - YouTube

[Chris Barcellos]

Depth of field is a function of lens aperture, focal length of lens and size of imager.

The lower the aperture, the shallower the depth of field will be for any specific focal length. The higher the focal length, the shallower the depth of field will be at any given aperature setting.

Finally the larger the imager, the shallower the depth of field will be at any given angle of view. So, for instance, a 35mm lens on my VG20 will have asimilar angle of view as my 50mm on my Canon 5d. Even though the angle of view is the same, at a given aperture, the Canon would exhibit a shallower depth of field.

[Chris Law]

Thanks for the reply, so I gather there are many factors effecting shallow dof then although despite that wouldn't the new SEL1850 would still have the best 'shallow dof' because of that wide aperture. Im just very enhustiastic about having great looking video when it comes to close up shots.

I guess I haven't explained my question well enough, my first question is which SEL lens is the best at present for 'shallow dof' as you've seen above im assuming its the new SEL1850 lens.

My second question: is it likely Sony or any third party companys make any E mount lenses with autofocus and a aperture lower than f1.8 or would it be hard for the autofocus to work under those conditions.

My third question: would I just be better using the LA-EA1 and an A mount lens for the best 'shallow dof' since in most situations the shot would be static and wouldn't need the stabilisation and I guess manual focus is the way to go for some scenes.

Finally I would like to finish off with the fact that theirs a new E lens that I don't think has being mentioned on this forums so heres the link: Tamron 18-200mm VC Di III Lens for Sony NEX - See it first at Jessops! - Jessops - Lenses

[Chris Barcellos]

Best I can answer is that if you have two lenses, one an Emount 55mm that opens to 1.8, and one an old Nikon 55 mm that opens to f 1.8, the depth of field should be the same.

Second, a zoom lens in the 28 to 55 mm range, and if it had f 1.8 aperature available should also have the same depth of field at that setting.

Where you would likely see a difference is in the bokeh exhibited in the out of focus areas, and of course the color and resolving power of the lenses.

Check out this on line Depth of Field calculator.

http://www.dofmaster.com/dofjs.html