Does changing aperture move the focus point

[tenniss_balls]

Hello,

If I focus the camera at a brighter aperture so that I can see the object on the ground glass, and then change the aperture does that move the focus point or just change the depth of field?

I have never made an exposure and about to make my first attempt.

I have purchased a fresnel screen yesterday does anyone have tips for focusing when it's dark?

[Peter De Smidt]

Ok. Well, use some ingenuity. Place a flashlight at a normal subject distance pointed at the camera. Focus (with a good loupe) wide open. Stop down. Check focus. A Fresnel will not help with this at all.

[Bernice Loui]

GOOD suggestions here, based on real world view camera experience.


Bernice

Ok. Well, use some ingenuity. Place a flashlight at a normal subject distance pointed at the camera. Focus (with a good loupe) wide open. Stop down. Check focus. A Fresnel will not help with this at all.

[tenniss_balls]

OK thanks for the replies. It was difficult to see the wood grain because the angle of the light was not reflecting back to the lens where I wanted to focus. I moved the light and checked wide open and stopped down. It doesn't look much different. Sharper and more contrasty.

Thanks for the flashlight suggestion.

I have to say working and thinking about every aspect of your imagery is very theraputic! And i'm amazed by the image on the ground glass. I'ts surprising what details you can see through the loupe.

The loupe I have is a Silvestri. Not too sure of it's quality.

Is there a particularly good quality loupe which is recommended?

[Mark Sawyer]

Berenice was quite right in post #5.

I'll add that focus shift is the result of spherical aberration, which is also the driving force behind the soft focus effect. The outer area of the lens is focusing on a slightly different plane than the center. As you shut down the aperture, outer areas of the lens are blocked, and the dominant focus shifts to the center of the lens.

Early Dagors still had a bit of spherical aberration, hence the famous "Dagor Glow". By the time Dagors were coated, the spherical aberration had been corrected and the glow and focus shift were gone.

If your lens doesn't have spherical aberration, it won't have focus shift. And any sharp modern lens will be well-corrected for spherical aberration.

[BrianShaw]

It might be worth exploring the question using a depth of field calculator and the parameters of the shot you are planning. With the exception of Imagon, I would think that under “normal conditions” dof accounts for any minuscule focus shift that may occur.

[afotandolaciudad]

Another point: focus shift while stop down happens with convertible lenses when using converted. So seems to be related with alterations in the iris position or configuration. This barely occur with smaller formats.

[tgtaylor]

Well I have the Nikkor 135mm AF DC f2 lens and the Nikon instruction manual says to focus after setting the DC (defocus image control) ring or the subject will be out of focus. The purpose of the DC ring is to control the focus of the foreground or background. So I would focus at the shooting aperture.

Thomas

[BrianShaw]

Well I have the Nikkor 135mm AF DC f2 lens and the Nikon instruction manual says to focus after setting the DC (defocus image control) ring or the subject will be out of focus. The purpose of the DC ring is to control the focus of the foreground or background. So I would focus at the shooting aperture.

Thomas

It’s not likely for that lens to be used on a large format camera!

Even in its intended application... is “unique”.

[Drew Bedo]

Maybe testing the lens described in the OP would help. However, shooting LF film today can be costly and takes time. A slightly inclined ruler or yard stick/meter stick under strong flood lights would allow a visual check of focus shift as it is stopped down.