Background blur with ND's

[DamianBlades]

Hi is it possible to get background blurring using ND's? I have just brought a set of Cokin ND's 2,4,4 (was meant to be 8 but turned up 4) If so how do I do it?



I want to recreate the background bokeh but without having to use pshop.

[andy-xr]

Get further away and use a longer lens would be one option

[DamianBlades]

andy-xr said:

Get further away and use a longer lens would be one option

Currently only have the 18-105mm, unless of course you want to give me a longer lens

[SamHH]

Neutral density filters won't make any difference; their purpose is to cut out some of the light. Use as long a focal length and as wide an aperture as you can to give you the narrowest depth of field.

[DamianBlades]

SamHH said:

Neutral density filters won't make any difference; their purpose is to cut out some of the light. Use as long a focal length and as wide an aperture as you can to give you the narrowest depth of field.

I swear someone told me that because they reduce light you can have a wider ap and longer exposure to create blur?? Oh well will just have to get a new lens . Going to get a 50mm on the 31st then thinking a 10-20 sigma for Christmas?

[andy-xr]

Have a read of this

http://en.wikipedia.org/wiki/Depth_of_field

[Simpo Two]

DamianBlades said:

I swear someone told me that because they reduce light you can have a wider ap and longer exposure to create blur??

You may be confusing 'motion blur' with 'out of focus'. An ND filter can certainly allow you to use a larger aperture, which will give a shallower DOF, but if your lens isn't physically able to deliever it (either for reasons of maximum aperture, focal length or magnification) then nothing much will happen.

[Gemm]

The way you can blur the background using a ND filter is....for example, if you are trying to use certain shutter speed, e.g. 1/125s in a bright light for certain effect, i.e. blur etc, and your setup only gives you f11 at lowest ISO, then you could use ND filter to make the aperture to f2.8 (4 stops).

Edited by Gemm on Saturday 17th October 21:20

[flat-planedCrank]

DamianBlades said:

SamHH said:

Neutral density filters won't make any difference; their purpose is to cut out some of the light. Use as long a focal length and as wide an aperture as you can to give you the narrowest depth of field.

I swear someone told me that because they reduce light you can have a wider ap and longer exposure to create blur?? Oh well will just have to get a new lens . Going to get a 50mm on the 31st then thinking a 10-20 sigma for Christmas?

ND filters don't effect depth-of-field, they just reduce amount of light entering your camera.

For short depth-of-field - use a wide aperture, on as long a lens is possible, focused as near as you can.

ND filters will allow you to use a wide aperture on very sunny days when normally your camera will not be able to set a fast enough shutter to compensate. They do not directly effect depth-of-field though


Cheers.

[AndWhyNot]

Bear in mind that at a long focal length and a wide aperture you may not have sufficient DoF to retain the whole car sharp and in focus. And if it's focus-based (as opposed to motion-based) blur that you're after, forget the Sigma 10-20; even at f/4 if your focus point is more than about 4ft away everything will be sharp (read up on hyperfocal distance).

[GetCarter]

DamianBlades said:

I swear someone told me that because they reduce light you can have a wider ap and longer exposure to create blur???

we were talking about moving water at the time

[Simpo Two]

GetCarter said:

DamianBlades said:

I swear someone told me that because they reduce light you can have a wider ap and longer exposure to create blur???

we were talking about moving water at the time

Hence:

Simpo Two said:

You may be confusing 'motion blur' with 'out of focus'.

This is why it's important to use correct terminology, otherwise you just get in a mess