Nikkor SW 90mm not so much light?

[norly]

Hi.
Ive been thinking about something and was wondering what you experts think. When Im using my 90mm Nikkor sw lens I feel that the view glass is significant darker then with my lets say 210 or 135 Rodenstocks. Its not really a problem unless I shoot indoors with low light situations, but its a bit strange. I cant remember noticing any differents on the negatives, but I haven't spent that much time looking either.

Should not the width of the lens let more light in and therefore be brighter? Since its a 4.5 and the rodenstock (if I remember right) is 5.6 that should also help.

thanks for any thoughts.

[Armin Seeholzer]

No a longer lens is always brighter because of the angle of the light hitting the groundglas more straigt at longer lenses!

Cheers Armin

[Daniel Stone]

the light has to be "bent" when being put through the small aperture hole of the lens(even a 4.5).

Having a wider field of view means that the light has to be bent more(well, squeezed might be a better word) than a longer F.L. lens, where it tends to "pass through" easier.

hence why faster(like your 4.5 90mm) are popular.

you might also want to look at getting a brighter ground glass. There's a few manufacturers still out there making them on a "commercial" scale. They sure help a lot with dim lenses!

-Dan

[Łukasz Owsianka]

When you got 4x5in format the 90mm lens is at center f5,6 but in corners you have got EV0,3 less light. In 150mm lens is at center is f5,6 in corners you have EV0,1 less light. The difference can be EV2,3 for Super-Symmar 5,6/210 XL at 11x14in format. Sorry for my poor english...

[Nathan Potter]

People have mentioned two effects that are relevant. As Lukasz says there is a light falloff from center to edge that is due to the optical design constraints for wide angle lenses. The shorter the focal length the greater the radial light falloff.

The second effect mentioned is the additional falloff from differential scattering from the ground glass. When rays strike the ground glass orthogonally (on the optical axis) and are viewed on axis (at the center of the ground glass) there is maximum transmission (brightness to the viewer). As the viewer moves toward the edge of the ground glass there is substantially less light transmitted through the glass due to increasingly off axis rays being less efficiently scatted by the GG. The functional form of the falloff varies with type of grind on the glass. The use of a tilting loupe used collinearly to the exiting rays from the lens can help greatly to alleviate the scattering loss phenomena. For global improvement in brightness a Fresnel lens (Google is your friend) of focal length matched to the lens will greatly improve the brightness.

Nate Potter, Austin TX.

[Michael Kadillak]

Yes, there is obvious less than optimal illumination. So what?

f22 at a 15 ft focal point your depth of field is from 6.67 ft to infinity. Innovate.

Drop a small mini mag with the cap unscrewed at the optimal point in your scene so it can be focused as a point light source. Stop down and let her rip. You could do that with two beers under your belt worse case scenario.

[Leigh]

The Nikkor SW 120 is an f/8 lens.

The others you mentioned are f/5.6. Try stopping them down to f/8 while viewing and see how similar the brightness is to the 120.

- Leigh

[engl]

Yes, there is obvious less than optimal illumination. So what?

The OP is asking what this depends on, not complaining.

f22 at a 15 ft focal point your depth of field is from 6.67 ft to infinity. Innovate.

Only with a 0.1mm CoC sharpness criterion, which would be good for making a sharp postcard-sized print.

[norly]

No a longer lens is always brighter because of the angle of the light hitting the groundglas more straigt at longer lenses

The shorter the focal length the greater the radial light falloff.

Makes sense. Thanks for the many replies. I think I got my answer. Thanks for taking time to sort this out.

[rfesk]

A fresnel screen or Maxwell screen of the proper focal length design is designed to brighten up the corners.