Verito Question

[Peter De Smidt]

I took a still life picture with my 18" Verito for the first time in decades today. The neg is drying as I type. As most know, the lens is at it's softest wide open, and it get's sharper as it's stopped down. For this shot, though, I had to add 1.5 stops of exposure to account for bellows extension. In effect this means that the effective aperture is 1.5 stops smaller than the set aperture. Thus the f/6 aperture set on the lens became effectively f/8.5 for the purposes of exposure. Does a smaller effective aperture affect sharpness?

[8x10 user]

The level of softness is controlled via the set aperture and is not altered by the effect of bellows extension on the effective aperture.

[Peter De Smidt]

Good to know. Thanks!

[cowanw]

Perhaps the effective speed is 1 1/2 stops faster than the set speed.

[Tin Can]

I'm not convinced bellows extension does not change angle of view and by correlation change effect of aperture diameter especially on softness in SF lenses.

Seems every lens becomes sharper with smaller diameter actual holes.

[8x10 user]

Yes the effective aperture changes like every lens, however when we are talking about soft focus we are talking about a lens that has a different focal length on the outer edges of the glass then the inner (spherical aberration, chromatic might also be present). The amount of this different FL glass that is exposed / unblocked by aperture remains constant independent of bellows factor. The total amount of light is of course affected so exposure must be compensated with like other lenses.

There are other factors that we could dive into... Like what the effective aperture the inner cone of sharpness has and how this inner core could be affected by DOF and diffraction. However in terms of % of light that is used in the glow versus the inner core the %'s stay the same independent of bellows factor.

I hope I am making sense here.


I'm not convinced bellows extension does not change angle of view and by correlation change effect of aperture diameter especially on softness in SF lenses.

Seems every lens becomes sharper with smaller diameter actual holes.

[8x10 user]

Maybe someone can post a picture that demonstrates spherical aberration in an optical system?

[Tin Can]

Yes the effective aperture changes like every lens, however when we are talking about soft focus we are talking about a lens that has a different focal length on the outer edges of the glass then the inner (spherical aberration, chromatic might also be present). The amount of this different FL glass that is exposed / unblocked by aperture remains constant independent of bellows factor. The total amount of light is of course affected so exposure must be compensated with like other lenses.

There are other factors that we could dive into... Like what the effective aperture the inner cone of sharpness has and how this inner core could be affected by DOF and diffraction. However in terms of % of light that is used in the glow versus the inner core the %'s stay the same independent of bellows factor.

I hope I am making sense here.

Yes, that makes sense and of course introduces 'other factors'...

Thanks for clearing that up.

[cowanw]

I wrote what I wrote in post 4 because the question of bellows extension is a exposure question relative to the film. Physically, the shutter speed and the lens don't change. The physics of the lens and shutter doesn't know where or what you put behind it.

[Peter De Smidt]

As magnification goes up, the effective aperture becomes smaller, and diffraction increasing limits the maximum obtainable resolution.

[8x10 user]

Yes, and so a lens like the bergheim that sharpens at smaller aperture (maybe f/16) might be more ideal for landscape use while something like the bi quality or PS945 (sharp at F/8) might be more adapt to ratios closer to 1:1 (i.e. portraiture and still life).. At least in terms of the obtainable detail available to the inner core (the parts that form the sharp image).