explain like I'm 5......... 90mm lenses

[Dan Fromm]

Benno, do you know who Ring Lardner was? If you don't, look him up and look up his book You Know Me, Al. There's a great classic line in the book. "Shut up, he explained."

So, shut up and accept that f/a @ shutter speed b will have the same effect on film for all focal lengths, subject to the lenses used having the same transmission. Not all lenses transmit the same fraction of the light that strikes their front elements.

More seriously, Emmanuel Bigler posted a thorough explanation of the math behind the assertion somewhere on this site. Your next assignment is to find it.

[Drew Wiley]

I used a Nikor 90/4.5 SW for architectural use. Huge coverage and the extra brightness was highly welcome if doing dim interiors or focus with a center filter in place. Big.
I once ice axed my way up a steep 13,000 ft ridge with a big 120 SA as well as a full Sinar kit and a week's worth of backcountry gear. Tied myself onto a tiny ledge for sake of a sunrise shot, and found a block of stone barely large enough for the tripod. Reprinted that neg recently. Very sharp image, even with both a CF and 29 red filter involved. The 90 Nikkor is even sharper. But at my age, if I need a wide angle in my 4x5 backpacking kit, it's going to be a tiny Fuji 125W instead. Paid my dues long ago.

[Doremus Scudder]

Wait now I'm further confused lol.

f/8 for any two different focal lengths is the same light input total. Isn't it kinda like slow, wide river or fast, narrow river?
A 3000000mm f/8 is picking up light from like .0005 degrees, so to get a balanced exposure it needs to pick up a HECK ton of light/degree.
A 30mm f/8 is picking up light from like a jillion degrees, so it's a much lower level of light/degree.

Benno,

You're confusing the actual size of the aperture with the f-number. Just remember, f/8 means: focal length ÷ 8, which means the actual size of the aperture at f/8 is dependent on the focal length of the lens. The f-number is a ratio, not a fixed size.

Your imaginary 3,000,000mm lens at f/8 is going to have an aperture of 375,000mm, or 375 meters, if you prefer. So, yes, it will pick up "a HECK ton of light."

The impracticality of making long focal-length lenses with wide apertures becomes apparent when one realizes that the size of the aperture at a given f-number increases with focal length. A 500mm lens at f/8 has an aperture of 62.5mm; a 50mm f/8 lens has an aperture of 6.25mm. The 500mm lens has to be ten times bigger to have the same maximum aperture.

If you have a totally dark room with one light bulb in it, metering a 'correct' exposure at f/8 will yield two different shutter speeds for two different focal lengths. Right?

No, not right; the exposure will be the same at f/8 for all focal lengths. The longer lenses will have larger apertures to pick up more light, but the ratio of f-number to focal length remains the same: f/8 or focal length ÷ 8.

The wider lens needs a longer shutter speed because it's viewing more darkness, so the light bulb takes up a lower percentage of the exposure.
The tighter lens can have a faster shutter speed because it's just looking at a light bulb...

The wider lens projects the light bulb smaller on the film. The exposure of the bulb on a smaller area is just right. The darkness is spread over the rest of the film. The longer lens has a bigger light bulb on the film and less darkness.

Think of a light meter. It gives you ONE exposure for a given light measurement (yes this can be divided up into different aperture and shutter speed combinations, but it's the SAME exposure. f/8 at 1/60 sec. = f/5.6 at 1/125 sec. and f/11 at 1/30 sec. and so on.)

If different focal lengths required different exposures at a give f-number, then there would be focal lengths on the meter. There aren't; f/8 is f/8 for all focal lengths.

Hope that's clear,

Doremus

[swmcl]

I will say that as one gets long in the tooth ... the more light you have when focusing is a good thing. I cannot understand how the weight difference between a f4.5 lens and a f8 lens makes much difference in the field. Then again, I live in a flat land in comparison to others and I hate any gradient when walking !!

My Nikkor 90mm f4.5 is a dream come true. I just love it.

[Salmo22]

I used a Nikor 90/4.5 SW for architectural use. Huge coverage and the extra brightness was highly welcome if doing dim interiors or focus with a center filter in place. Big.
I once ice axed my way up a steep 13,000 ft ridge with a big 120 SA as well as a full Sinar kit and a week's worth of backcountry gear. Tied myself onto a tiny ledge for sake of a sunrise shot, and found a block of stone barely large enough for the tripod. Reprinted that neg recently. Very sharp image, even with both a CF and 29 red filter involved. The 90 Nikkor is even sharper. But at my age, if I need a wide angle in my 4x5 backpacking kit, it's going to be a tiny Fuji 125W instead. Paid my dues long ago.

Drew:

I recently acquired a Nikkor SW 90/4.5. I've been wondering about getting a center filter. What brand/type do you prefer?

Thank you;

Jeff

[Dan Fromm]

Jeff, PMFJI. There's a link to my article on center filters in post #39 above. Until someone writes a better one it is definitive. Read it.

To answer your question, they're all functionally equivalent. What matters is diameter -- the filter has to fit -- and central density.

[BennoLF]

Benno,

You're confusing the actual size of the aperture with the f-number. Just remember, f/8 means: focal length ÷ 8, which means the actual size of the aperture at f/8 is dependent on the focal length of the lens. The f-number is a ratio, not a fixed size.

Your imaginary 3,000,000mm lens at f/8 is going to have an aperture of 375,000mm, or 375 meters, if you prefer. So, yes, it will pick up "a HECK ton of light."

oh duh duh I was forgetting that I'm so smart haha

slightly different question (I think different?):
Do lightmeters measure total amount of light or light density? A softbox with, let's say, 3 sq. ft of area that given out light at, lets say, 50 cd./sq. ft would be 150 total candlepower, correct?
but a softbox of twice the size would give out 300 candlepower? (I may be botching the terminology here)

Think of a light meter. It gives you ONE exposure for a given light measurement (yes this can be divided up into different aperture and shutter speed combinations, but it's the SAME exposure. f/8 at 1/60 sec. = f/5.6 at 1/125 sec. and f/11 at 1/30 sec. and so on.)

If different focal lengths required different exposures at a give f-number, then there would be focal lengths on the meter. There aren't; f/8 is f/8 for all focal lengths.
Doremus

^^ the lightmeter is always reading the same angle. Will a meter is covering 30 deg will read a different exposure than an 80 deg meter unless the scene is of identical luminous density across 80 degrees?

I feel even crazier now. Sorry to keep on keeping on but the more I think about this the more I'm confused lol.

Also I can't find Emmanuel Bigler's math post. Could someone kindly link it?

[Oren Grad]

oh duh duh I was forgetting that I'm so smart haha

slightly different question (I think different?):
Do lightmeters measure total amount of light or light density? A softbox with, let's say, 3 sq. ft of area that given out light at, lets say, 50 cd./sq. ft would be 150 total candlepower, correct?
but a softbox of twice the size would give out 300 candlepower? (I may be botching the terminology here)



^^ the lightmeter is always reading the same angle. When a meter is covering 30 deg it will read a different exposure than an 80 deg meter unless the scene is of identical luminous density across 80 degrees.
I feel even crazier now. Sorry to keep on keeping on but the more I think about this the more I'm confused lol.

Also I can't find Emmanuel Bigler's math post. Could someone kindly link it?

Benno -

If you have questions about lighting and metering, please start new threads for those questions in the appropriate subforums rather than tangling together many different topics in the "Lenses" subforum.

Thanks!

[Doremus Scudder]

... Will a meter is covering 30 deg will read a different exposure than an 80 deg meter unless the scene is of identical luminous density across 80 degrees? ...

At the risk of tangling topics, here's the short answer:

A meter averages the light from the angle of view it sees. Meters with different angles of view will indeed give different readings. Think of a spot meter pointed at a shadow; it'll give a low-light reading. If you point a 30° meter at the same shadow, it's going to see the sky and the sunlit areas too, so the reading will be different.

If you want more info, start a new thread in the appropriate category or we'll get into trouble with Owen

Doremus

[Bernice Loui]

From the point of view of one who spent decades burning LOTS of color transparency film between the early 1980's to late 1990's...

Higher contrast, Sharpest lens is NOT always desirable. It completely depends on the goal of the image. Back then color transparencies were the primary mean to color printing. Color prints from color transparencies were much secondary. Difficulty with color prints made using color transparencies becomes limited contrast range or excessively high contrast producing a "Cartoon" effect on these color prints (Cibachrome, later Ilfordchrome and Fuji had their variant of this color print paper). The high contrast problem could be controlled by contrast masking (Drew W, lots of experience with this and willing to share, discussed on LFF numerous times) or starting out with a lower contrast color transparency using a modest contrast lens (Tessar, Kodak Commercial Ektar, Schneider Xenar, etc) combined with modest contrast color transparency film like Fuji Astia, Agfa chrome RS100 or similar, this combined with contrast masking worked good to extend the contrast range of a print made using a color transparency.

High contrast is often perceived as "sharper" when under broader and closer examination higher contrast is much the same regarding "sharper".

After using every brand of modern lens from the big four (Schneider, Nikon, Rodenstock, Fujinon) the preference for wide angle is Rodenstock's Grandagon due to their contrast & color rendition, Schneider's XL for pushing image circle requirements with Nikon higher contrast compared to the European brands, Fujion mixed in between. I've got the Fujinon 105mm f8 & 125mm f8 wide wide angle lenses, they are not preferred. In that focal length default is the 115mm f6.8 Grandagon. All of which means ZERO to another image maker-artist-photographer, this is more a point of view and preference base on experience and visual expectations. Overall speaking, I'm not a fan of high contrast, perceived sharpness prints as overall tonal rendition and visual perceived contrast range in the print is IMO, FAR more important. All this said, any of the modern wide angle lenses from Fujinon, Schneider, Nikon, Rodenstock are again, FAR more similar than different.

~Pick one and make images.. Don't get too caught up in the belief-idea a given lens alone can produce exceptional results.. This will NOT happen.~

Soft focus lenses are a completely different kettle of film-prints...

Vintage lenses work good for color transparencies, Really depends on what is considered "Vintage" which can mean a lens from 1900's or post WW-II or ?

Having been around, used, owned lenses from the early 1900's to late 1990's they All have their place dependent on the needs of the image maker with a print goal in mind. I'm no longer convinced or accept the f64 school if LF image making is the proper orthodoxy, as there are many, many, many ways the view camera and all it's possibilities can be utilized as a very powerful creative tool for print and image making.



Bernice

I'm currently only doing black and white ( 4x5 TMax 100 and 5x7 Delta 100) on LF and then scanning for digital post-processing and printing.

Chromes are certainly more susceptible to vignetting and more difficult to correct. I cannot comment about shooting LF chromes as I lack personal experience there.

That said, while some may take a different and possibly idiosyncratic view, IMHO sharpness and contrast are very important optical criteria, although certainly not the only ones, because higher sharpness and crisp contrast usually record the image more faithfully and thus provide more "information" and more accurate information, than lenses that are not as sharp nor exhibiting crisp contrast.

You'll of course find differing opinions - think 1930s Pictorialists vs. the f/64 revolution by Edward Weston, Ansel Adams, et al. It all depends upon what you want to do and whether you want to achieve a particular result and do so in-camera via a particular lens.

If you want a softer image, that's possible after the fact IF you start out with enough information in the original image capture, but you can't go the other way and try to extract more information from an image where the underlying information was never captured when the shutter was clicked.

Older lenses would likely be less suitable for chromes than more modern lenses from Nikon, Schneider, Rodenstock, and Fujinon, all of whose more recent products have excellent reputations.