How much is IC affected when moving up in Format Size?

[audioexcels]

4X5:

Schneider Super-Angulon XL 72 f/5.6 f/45 226

Excess Coverage=72.3
Excess%=31.99



8X10:

Nikon Nikkor SW 150 f/8 f/64 400

Excess Coverage=87.5
Excess%=21.88


A 72mm lens on 4X5 sheet film with less IC than the 150mm lens on 8X10 film gives 50% more excess coverage%...


What puzzles me is that users of the Nikkor 150SW have felt no need for a center filter (color or b/w) since it has plenty of coverage and provides excellent movements.

Why is this the case when the majority of 75mm F4.5-F5.6 lenses that have a similar or greater percentage of coverage than the Nikkor 150SW on 810 sheet film need a center filter? Rather, that most would say anything below a 90 on 45 sheet will need a CF especially shooting color film.

[Ron Marshall]

4X5:

Schneider Super-Angulon XL 72 f/5.6 f/45 226

Excess Coverage=72.3
Excess%=31.99



8X10:

Nikon Nikkor SW 150 f/8 f/64 400

Excess Coverage=87.5
Excess%=21.88


A 72mm lens on 4X5 sheet film with less IC than the 150mm lens on 8X10 film gives 50% more excess coverage%...


What puzzles me is that users of the Nikkor 150SW have felt no need for a center filter (color or b/w) since it has plenty of coverage and provides excellent movements.

Why is this the case when the majority of 75mm F4.5-F5.6 lenses that have a similar or greater percentage of coverage than the Nikkor 150SW on 810 sheet film need a center filter? Rather, that most would say anything below a 90 on 45 sheet will need a CF especially shooting color film.

My 75mm has an image circle of 195mm, so I can't make large movements. If I am shooting neg with the 75mm I often don't bother with a CF. But with the 72mm and large movements I would use a CF. But, it's obviously a personal decision as to how much falloff is acceptable.

[Bob Salomon]

4X5:What puzzles me is that users of the Nikkor 150SW have felt no need for a center filter (color or b/w) since it has plenty of coverage and provides excellent movements.

Why is this the case when the majority of 75mm F4.5-F5.6 lenses that have a similar or greater percentage of coverage than the Nikkor 150SW on 810 sheet film need a center filter? Rather, that most would say anything below a 90 on 45 sheet will need a CF especially shooting color film.

Because the SW series needs a center filter just as much as Schneider, Rodenstock and Fuji do. If one does not see the need for it on the Nikon they won't on the others as well.

One of the main reasons was that Nikon never offered a CF in their program so many people assumed that one was not needed. Not so.

The need for the filter will depend on what you shoot, how you shoot and what you want to do with what you shoot just as much as the lens itself.

[audioexcels]

I have read numerous threads from users of both Nikkor 150SW and Schneider Symmar 150XL lenses, and the 150XL absolutely needed a CF when the Nikkor did not. In other words, the same shot required a CF with the Schneider but not with the Nikkor. The Schneider CF will fit the Nikkor and Heliopan possibly marketed one for it also.

[Ron Marshall]

I have read numerous threads from users of both Nikkor 150SW and Schneider Symmar 150XL lenses, and the 150XL absolutely needed a CF when the Nikkor did not. In other words, the same shot required a CF with the Schneider but not with the Nikkor. The Schneider CF will fit the Nikkor and Heliopan possibly marketed one for it also.

They may or may not be required!

On 4x5, using neg film and without large movements neither requires a CF. On 8x10 with large movements and positive film most people would probably use a CF.

[Really Big Cameras]

Yes, precisely. Say we are using even 40mm's of rise on both the 4X5 and 8X10 format, using a wide, normal, etc. Will both still only need 40mm's or will one need more than the 40mm's...

No, if we assume film dimensions that are twice as big and the focal length of the lens is twice as long, you'll need twice as much rise to get a comparable composition on the larger format. It's all just a function of simple linear proportions.

For simplicity sake, lets assume a 4x5 image is exactly 4" x 5" and an 8x10 image is actually 8" x 10" (they aren't in real life due to nominal film sizes and film holder margins, but they're close enough for a simple approximation). So, the 8x10 image is exactly twice as tall and twice as wide as the 4x5 image. Now, let's take a 75mm lens with a 200mm image circle on the 4x5 format and a 150mm lens with a 400mm image circle on 8x10. Again, everything scales by 2x - both focal length and image circle. Now, if you apply 20mm of front rise using the 75mm on 4x5, you'll need to apply exactly twice as much front rise (40mm) when using the 150mm lens on 8x10 to get the same composition.

Another way to look at it is that the 75mm lens with a 200mm image circle gives you approximately 30mm of usable front rise (in landscape orientation) on 4x5 and the 150mm on 8x10 gives you twice as much excess coverage - approximately 60mm. However, you need twice as much rise to get the same affect.

Kerry Thalmann
Really Big Cameras

[Really Big Cameras]

I have read numerous threads from users of both Nikkor 150SW and Schneider Symmar 150XL lenses, and the 150XL absolutely needed a CF when the Nikkor did not. In other words, the same shot required a CF with the Schneider but not with the Nikkor.

The lenses are different designs, therefore, their illumination fall-off characteristics are different. Modern wide angle lenses like the Nikkor SW, the Schneider Super Angulon, the Fujinon SW and the Rodenstock Grandagon employ a tilting entrance pupil to reduce illumination fall-off compared to lenses of standard design. The Super Symmar XL series do not employ tilting entrance pupils and therefore have greater illumination fall-off than other recent wide angle designs that do.

The theoretical best-case illumination fall-off for lenses with a tilting entrance pupil follows the function cosθ^3 (cosine theta to the 3rd power). Theoretical illumination fall-off for lenses without a tilting entrance pupil follows the function cosθ^4 (cosine theta to the 4th power). If you look at the illumination charts for modern lenses you will see that they come very close to achieving these theoretical best-case illumination characteristics.

So, if we assume an image diagonal of 312mm (which is an actual measurement on one of my 8x10 negatives) for 8x10, a lens like the 150mm Nikkor SW with a tilting entrance pupil will have an illumination fall-off of approximately 1.59 from the center to the far corners of the film (assuming the lens is centered). For a 150mm lens without a tilting entrance pupil, like the 150mm Super Symmar X, the fall-off in the far corners increase to 2.12 stops. Both lenses have fall-off, but the 150mm SS XL has more and that would explain why some users would claim it needs a center filter on 8x10, while users of the 150mm Nikkor SW swear no center filter is needed.

Whether or not a center filter is needed/desirable is ultimately a personal choice. It depends on the film you are using, your printing methods, and more than anything else, your personal sensitivity to illumination fall-off in your images.

Kerry Thalmann
Really Big Cameras

[audioexcels]

Thanks a lot Kerry. Very simply put and coherent. I appreciate it.