The fall off follows a cos^4, no need to waste a negative to confirm that IMO. All you need to know is the angular FOV of your lens, diagonally.Originally Posted by Alan Klein
The fall off follows a cos^4, no need to waste a negative to confirm that IMO. All you need to know is the angular FOV of your lens, diagonally.
Someone smart will probably expand or explain this better, but there is a difference between retrofocus wide angles for SLRs and wide angles for view cameras.
On a 4x5 view camera, a 75mm lens sits about 75mm away from the film.
That is so close that light that travels from the lens to the corners of the film has a significantly longer path than light that travels to the center of the film. See the inverse square law, you lose relative illumination really fast as you increase the distance from the light source.
On your Nikon, even if you use a 20mm there is a 46.5mm space between the lens and the sensor. That’s the space needed to fit the mirror assembly. At a distance of 46.5mm to cover a 24x36mm surface, the light paths to the center and the corners are of much closer length.
The maths is easy enough if you know the flange focal length (the distance from the film plane for infinity focus) of the lens you’re considering, and the formula for light fall off (inverse square law).
It is then up to you to decide if that fall off is acceptable or not.
Me personally, I cannot stand the kind of fall off you get with a 75mm and no CF.
Every time this topic comes up I cringe at most of the examples posted by those who find the fall off acceptable.
I don’t understand why one would invest the money, time and effort to use a large format view camera to produce images reminiscent of the toy camera æstetic. Might as well just use a Holga, like Troyce Hoffman.
Last edited by lenicolas; 12-Jan-2021 at 15:21. Reason: Typos
"I am a reflection photographing other reflections within a reflection. To photograph reality is to photograph nothing." Duane Michals
A densitometer with actual film works better for checking, unless one has a film plane probe meter that will get clear to the corners. But what I do first, just to detect for falloff, is overdevelop the film so that if any falloff is present, it will be more obvious. But you'd have to do it relative to different f-stops and applied movements to get the full picture. Any lens that is not longer than "normal" is likely to have an amount of falloff.
It’s all a matter of personal taste and no two photographers have the same aesthetic but at least for landscape and portrait photography there is not a lot of useful information in the corners (generally) and focusing the attention away from the corners is usually quite forgiving. Some even add vignetting when none is present.
So you may cringe and others will not. Even in LF.
Also these filters are usually very costly so it’s not just a question of spending a few dollars. It’s a serious investment! And then there’s the fact that it adds more steps and requires more attention to follow to make the right exposure. Nothing insurmountable of course but just more chances to make a mistake. And if you shoot color slides, every mistake is an expensive mistake.
Lots of folks out there shooting 75mm without filters and I don’t think most people will actually notice the fall off in the prints. Just other photographers, for the most part :-)
Hi,
Of course this was just my personal opinion and taste. I don’t mean to be the police of what others are doing with their cameras, what an exhausting job that would be!!
I just think in all these threads about wise angles and CFs there should be at least one voice saying “Center Filters exist for a reason, and I happen to prefer using them”.
Another thing I’m noticing :
The overwhelming majority of this forum seems to advocate for immense depth of field. Just in this thread OP mentioned that he used front tilt in nearly all his pictures, and someone else declared “does anyone ever shoot wider than f/22?”
So I’m deducting that there is a fraction of this forum that believes all parts of the image should always be in focus, but at the same time don’t fret when the corners of the image are two stops underexposed?
They say being able to hold two opposing ideas in ones mind is a sign of great intelligence... I must be a lesser mind, to me you either care about capturing detail or you don’t. I’d rather create the best negative I can, and add vignette if needed rather than risk discovering on my contacts that a corner with important information is underexposed and muddy.
Last edited by lenicolas; 13-Jan-2021 at 01:31. Reason: Typos
"I am a reflection photographing other reflections within a reflection. To photograph reality is to photograph nothing." Duane Michals
Of course they exist for a reason. And of course one should use them if they are really, really worried about even illumination.
Whilst I often shoot at f/22, or beyond, I also don't mind shooting at f/2.8 if I'm after something else. I also shoot a 47mm XL w/o a center filter - the horror! While my non-usage of a CF on a 47mm is certainly debatable (and once or twice I later realized I probably should have), insisting on the use of a CF on a 75mm lens or even a 90mm is a bit anal IMO, most especially on b&w landscapes where the slight amount of fall-off is almost never particularly noticeable or problematic when printing (I have never in my experience felt the need later on to have used a CF on those types of images).
On the other hand, I have absolutely been unable to make images due to long exposures and slight movement of leaves in the frame, even when shooting 400-speed film and simply not having enough light for fast shutter speeds. Another 1.5 or 2 stops would increase this issue...oh and don't forget about reciprocity in some cases!
Here's a particularly heinous shot with my 47mm XL on Fuji Velvia:
Due to the nature of the shadowed frontal area, I doubt a CF would've done much for me anyway, and I ended up actually burning in the sky and foreground a bit more in the final print IIRC, which was printed very large. I used a GND on this as well, which I would've been unable to do with my equipment if I had used a CF due to the size of the front element and the small IC of the 47mm (A GND in this situation is way more relevant and important than a CF).
Yes (and no, possibly). Some short focal length LF lenses apparently reduced it to ~cos^3 using a pupil distortion/tilting pupil design. Just to add some more minutiae.
You're probably thinking of f/4.5 Biogons. One, the 75/4.5, covers 4x5. Big heavy expensive lens.Yes (and no, possibly). Some short focal length LF lenses apparently reduced it to ~cos^3 using a pupil distortion/tilting pupil design. Just to add some more minutiae.
Dan, don't most modern wide-angles use the tilting pupil design? Glancing at a couple of my lenses, they all seem to have it to an extent (compared to my actual 75mm Biogon).
1) Why don't 35mm lenses have that falloff? Why are their designs different?
2) If it's a simple formula, why do different people say the falloff varies? There seem to be arguments on this point.
3) Why is the falloff more noticeable with chrome film as some people claim?
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