Why use slow lenses?

JayC

JayC

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The answer may be buried somewhere in the forums - don't know.

I read of users saying "if the light is low, I will take out my 1.4 lens, but if I am out shooting street stuff or landscapes, I will take the 2.5 lens" or variations of this.
My question is, why not use the fast lens for everything? I mean, it does have the other apertures available to use.....

Besides "footprint" which I have difficulty seeing with my untrained eye, what is the point of having a slower, (usually) less expensive lens, when your faster one that is the bomb, can cover all the f stops the other lens can?

I am asking because I am looking to build up/thin out what I currently use.

Jay
 
Probably a lot of different answers.
One factor is that the faster lenses tend to be larger. Some folks like to put a tiny (slower) lens on the camera, making it more lightweight and pocketable than it would be otherwise.
 
For 35mm and longer, from f2 and up you are right. Most of the f2 M or LTM mount lenses are high quality even wide open, some of them setting resolution benchmarks for all other lenses out there (like the Summicrons, the Hexanon, the Planar, etc).

Going faster than f2 usually means making design compromises. Diffraction and other effects make it harder to design a lens that is fast and high resolution closed down, at the same time. There are some exceptions like the 50/1.5 CV Nokton or the 50/1.4 ASPH Summilux.

Bottom line is: you can get highest resolution pictures with f2 lenses. If you want to go faster, choose very carefully and be clear to yourself what purpose you need the lens for (portrait, available light street or city scapes, etc).

Best,

Roland.
 
Fast lenses weigh a lot more and have large front elements that may be more susceptible to flare. Also, the faster lens is typically much more valuable and it may be that people would rather carry their 'ordinary' lens for the day-to-day stuff and use their special glass only when conditions really warrant it.

Matthew

EDIT: Wow, 3 replies saying similar things while I was typing that.
 
Weighs less, costs less, provides a different image. The design constraints for a 1.4 and a 2.5 are very different.
The high-speed cult grew in the '50s and '60s when films weren't nearly as good as they have become in the past 10 years.
 
Well....I think just because a lens is fast does not make it good. I have a very expensive 1.4 lens that tends to flare in both low and daylight. I've been in denial about it for a while. Now I'm thinking of selling it becuse it seems to have almost doubled in price (don't you love Leica?). But, often times, the slower lens is easier to use because it's smaller and lighter in weight. It tends to be sharper at the mid apertures as well.
 
I'm not very trained, but - my versions is: fast glass is more flare prone (how about modern multicoated lenses, they should be more resistant than old ones) , they might be focal lenghts you just don't have so fast (f1.4 45mm vs f2.8/f3.5 135mm or f2.8 28mm), and finally, big piece of glass weights more. Another reason - loosing cheap body w/ slower lens in field on street isn't so scary as expensive f1.2 lens, which could be stopped down most of time.
If there would be f1 12-500 very compact and reasonably priced lens, it would change shooting habits of many :)
 
I don't want to be spreading some old wives' tale but I recall reading somewhere during my early photography days that generally the sweet spot for a lens is 3 stops from max aperture so for an f/1.4 lens it would be at f/4 and for an f/2.8 lens it would be at f/8. So if you are shooting landscapes then use a slow lens and portraits with a fast lens since you would want max dof for the former and less for the latter. I generally use my large format Schneider 90/8 at f/32.
 
Every lens is a compromise. Fast lenses are bigger, heavier and are not necessarily suited for all types of photography. Slower lenses are smaller, lighter, and better for general use. Ferraris are for motorways, Land Rovers are for fields. You can drive either on a B-road, but horses are generally suited for courses. I have a number of 50mm lenses for just this reason.

Regards,

Bill

EDIT: Metaphors mangled while you wait.
 
Fast lenses are hugely over-rated here on RFF (and in general) imho. Rangefinders are perfect for small light f2.8 or slower lenses, since your viewfinder stays just as bright no matter what lens you put on.
 
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The CV 28mm f/3.5 Skopar is a great example of a superb performer that isn't terribly fast. I love its small size, and I don't really need the extra stops ... at least in 28mm. It's about half the size of the 28mm Ultron.
 
I think that most of this concept of slow lenses being sharper than faster types comes from the dark age of photography when a fast lens was allways (and it still is) a compromise of sharpness, aberrationas and other pests. It also had to do (IMO) with lens cost. Then, a cheap slow lens was a better performer than a heavy, expensive and not perfectly corrected fast lens.
However, there are many examples of fast lenses performing as good or better than slower types of the same era, namely Sonnars or others.
At some time, it was said that the Sonnar 1.5 was (I never checked it by myself) far better than the "Leitz" (Schneider designed) Xenon of 1937, proving that some lens perform better than others and that sharpness isn´t depending on aperture rather than lens design and materials used.

Cheers

Ernesto
 
Some lens designs are inherently "slow", take the original Voigtlander Heliar for example. This is what is said about it:

"A 5 elements/ 3 groups Triplet derivated lens, similar to the Zeiss Tessar but with a splitted front-element. Invented 1900 by Dr. Hans Harting, later executive board member at ZEISS, even at age 78 recalled to VEB Carl Zeiss Jena to help with postwar reconstruction and appointed Honorary member of Academy of Sciences in Berlin (DDR). The design was slightly altered during its production time, at last after WWII with coating to the "Color-Heliar" from Voigtlander R&D team headed by Dr. A.W. Tronnier 1952. A simple and harmonical construction (slightly curved lines) but this wasn't able to produce a fast lens and therfore to some extend outdated by the market in the middle 1950's. The Medium format (MF) lens was f/3.5 105mm.Very sharp but some soft contrast wide open. One of the very best lenses ever for landscape and portraiture."

Taken from this website: http://www.taunusreiter.de/Cameras/Bessa_RF_histo.html

So are modern SLR macro lenses, they are slow to provide that biting sharpness necessary for extreme closeups.
 
Most common question asked on RFF is which lens is best? Having more than one lens of the same focal length with differing speeds is just a courtesy of most long term forum members to offer their personal comparative insight to new members seeking their first lens. ;)

PS Those here that own 5 to 8 50mm lenses for example, they are just really really courteous LOL
 
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I find 50mm/2 lenses to be the best for my needs, but there are times when a 50/1.2 or 50/1.4 can offer more. I may choose a 35mm/2.8 for a travel kit to keep weight down.
 
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I have a Rokkor 28mm/2.8 that used to be my only 28mm lens for many years. Its max aperture is fast enough for most situations that I will encounter, but one day I spotted a cute little Canon 28mm/3.5 from a Japanese seller, and then I had two 28mm lenses. They differ. The Rokkor is like a Leica lens in many aspects. The Canon is a very small chrome lens that has a classic charm for a vintage lens. Once I used both lenses side by side, and some people viewed the Canon images as being sharper. Sometimes, the slower lenses are sharper but in other cases, a faster lens can be sharper than its slower cousin.

So why in the world would I buy another 28mm lens?! A Kobalux 28mm/3.5 came across my way [here], and I could not refuse a partial trade with David Murphy. I bought the Kobalux because some people claim that it is super sharp.

This is my story [so far].
 
I tend to use the faster lenses F1.4- F2 more often, even outdoors in bright light. At F4, they are all very sharp- better than the Tessar 50/2.8 or Elmar 50/3.5 stopped down to F4.

The "super-Speed" F0.95 is big and heavy, but quite sharp stopped down to F2 through F8. It's the only lens that gets left at home just because of the weight.
 
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