2 stop/ 4 stop filters vs 2 stop 4 stop adjustment. are they the same

[oldhippy]

Been working on sweet spot on lenses. and quite often I see that stopping down 2 or 4 stops improves picture sharpness.
Can you achieve the same with a filter. if not what are the primary differences.
If you can do this by adjusting your aperture, why bother with filters.
Would love to here some replies. Thanks Ed

 

[Juga]

Introduction to Aperture - Digital Photography School

Aperture is the opening in the lens that will allow more or less light in the lens. So the larger the number the smaller the opening allowing less light in vice the smaller number which is more wide open allow more light in.

Using a filter is not the same. Because aperture is internal to the lens it effects DOF and overall sharpness. A filter does not effect DOF or sharpness, to my knowledge, rather it allows one to achieve a desired effect during a lighting situation where normally one would not be able to...such as slow shutter speeds a lot during bright lighting situations.

I still consider myself a noob so maybe someone would be willing to either correct me or validate what I just said.

 

[oldhippy]

Introduction to Aperture - Digital Photography School

Aperture is the opening in the lens that will allow more or less light in the lens. So the larger the number the smaller the opening allowing less light in vice the smaller number which is more wide open allow more light in.

Thanks Joe. I know what aperture is. my question is. What is the difference between, stopping down two stops with a filter, or manually stopping down. And if there is a difference how does it affect picture quality. ie sharpness. Dof ect

 

[pgriz]

Reducing the aperture by 2 stops is the same as using a 2ND filter as far as the amount of light is concerned, but... reducing the aperture also changes how much lens is used to transmit the light, and generally cuts off the rays that pass through the outside portions. The lensmaker's problem is that the wider the lens, the harder it is to arrange all the curves so that all the rays end up on the same plane, so reducing the aperture allows better image quality because the rays at the perimeter are cut off, and the ones at the center are relatively easy to focus on the plane. However, once you get past the "sweet spot", further reducing the aperture further starts making the diffraction effects more and more prominent. This is why most lenses have sweet spots. Complicating things a bit more, zoom lenses have different profiles at different focal lengths, so the sweet spot may move around based on the focal length.

 

[Juga]

Introduction to Aperture - Digital Photography School

Aperture is the opening in the lens that will allow more or less light in the lens. So the larger the number the smaller the opening allowing less light in vice the smaller number which is more wide open allow more light in.

Thanks Joe. I know what aperture is. my question is. What is the difference between, stopping down two stops with a filter, or manually stopping down. And if there is a difference how does it affect picture quality. ie sharpness. Dof ect

Sorry Ed...I had to edit my response a bit more. I was very vague at first...my apologies.

 

[pgriz]

As for the question of why use ND filters, consider that you have an aperture (say f/1.8) which gives you the thin depth of field that you want, AND you want a relatively slow shutter speed which allows you to show some motion blurring, but the amount of light will require you to use a fast shutter - then you use the ND filter to cut down on the light and allow you to shoot with the aperture and shutter speed you want.

 

[maxwellmcauley778]

So what yous are saying is that pretty much at any focal length there is a sweet spot

Sent from my Galaxy Nexus using Tapatalk

 

[pgriz]

The "sweet spot" usually refers to the range of apertures over which the lens is sharpest. The best (and most expensive) lenses have very wide ranges, whereas the cheap ones have very narrow ranges. In zooms, the arrangement of the individual elements changes, and this can affect the range of apertures at which the lens is sharpest. Looking at some of the lens review sites, it can be noted that the lenses with the widest ranges of "sharp" are also the ones with the highest $$$.