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fast/slow lenses - beginner's question
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PostPosted: Fri Feb 01, 2008 3:36 am    Post subject: fast/slow lenses - beginner's question Reply with quote
very much beginners questions, I hope you don't mind.

fast lenses generally seem to be much preferred
there is the obvious reason, them being 'fast'..

I wonder which other characteristics generally may make faster lenses preferred lenses:
a more shallow DOF?
nicer bokeh? ( and is it right that lenses with many blades - only old lenses? - may shine here? )

and I wonder if there are circumstances when a slow lens would be the better choice?

thank you for any answer,
andreas


PostPosted: Fri Feb 01, 2008 4:12 am    Post subject: Re: fast/slow lenses - beginner's question Reply with quote
kuuan wrote:
very much beginners questions, I hope you don't mind.
fast lenses generally seem to be much preferred
there is the obvious reason, them being 'fast'..
I wonder which other characteristics generally may make faster lenses preferred lenses:
a more shallow DOF?
nicer bokeh? ( and is it right that lenses with many blades - only old lenses? - may shine here? )


Here's my answers, which may not be the most popular answers on the subject. Anyway:

- for me, the best advantage in a fast lens is that it's easier to focus with it. Of course this point is pointless for exclusive autofocus users.

- shallower DOF, yes, this is a feature that goes together with speed and also with format - the larger the format, the shallower the DOF. BUT - I'd be most careful with it. There is, today, a large abuse of this feature. If you go through some photo sites like flickr or pbase, etc, you will see that a lot of people thinks that it's enought to photograph an object, ANY object, with the shallowest available DOF, to make an "artsy" photo, or even a work of art. I am growing terribly sick of this misuse. Every time I open such a photo I always think "Oh no, another one". The fact is that like every other style, the shallow DOF should be used only when it makes sense, and when the subject really calls for it. Not on everything, not in any occasion. Else it's not a style anymore, it becomes a stylization.

- nicer bokeh - no, actually, it's the opposite, bokeh is nicer with the lens stopped down because all the optical shortcomings of a lens are reduced, and these can really make a bokeh become unbearable - such as it happens with the Jupiter-9 and the out-of-focus highlights.

- number of blades - yes it is important, of course only with the lens stopped down - and only if there are strong highlights in the background. But surely round OOF highlights at any aperture is a desireable feature. It does not have anything to do, however, with the maximum aperture of a lens. There are lenses such as the Steinheil Culminar 4.5/135 that are very slow and have 20 blades in the iris, there are other lenses that are very fast and have maybe only 5-6 blades in the iris.

Quote:
and I wonder if there are circumstances when a slow lens would be the better choice?


Slower lens usually means smaller and lighter lens, so if you go out with your photo bag to walk a lot, or if you plan to stay out all day, or to travel in train or plane, every space and weight that you can save is important.
Also, it's not uncommon the case when a slower lens has a better optical performance than a faster lens. This is often the case with Leica lenses, where the Elmarit models (f/2.8 ) often deliver better optical performance than their Summicron (f/2) counterparts. But there are cases in practically all lens catalogues of this situation. The reason is obvious, to build a better lens that is slow, is both cheaper and technically easier. To obtajn excellence of performance from a fast lens, this is the hard part.
So to sum up, if you are the type of photographer who likes to have well defined photos, you are likely to shoot most of the times in the range between f/4 and f/8, which is the range of the slow lenses.
So, in this case, there is no much difference from having a fast lens, except of course that -like I said- a fast lens is much easier to manual focus.


PostPosted: Fri Feb 01, 2008 11:16 am    Post subject: Reply with quote
In most manufacturer product line faster lenses are produce better quality and more easier to focusing with them.


PostPosted: Fri Feb 01, 2008 4:04 pm    Post subject: Re: fast/slow lenses - beginner's question Reply with quote
thank you so much for your detailed answer Orio, I am very grateful.
thank you also for your input Attila.

Orio wrote:

- for me, the best advantage in a fast lens is that it's easier to focus with it. Of course this point is pointless for exclusive autofocus users.


wow, I was not even aware of this fact

Orio wrote:
- shallower DOF, yes, this is a feature that goes together with speed and also with format - the larger the format, the shallower the DOF. BUT - I'd be most careful with it. There is, today, a large abuse of this feature. If you go through some photo sites like flickr or pbase, etc, you will see that a lot of people thinks that it's enought to photograph an object, ANY object, with the shallowest available DOF, to make an "artsy" photo, or even a work of art. I am growing terribly sick of this misuse. Every time I open such a photo I always think "Oh no, another one". The fact is that like every other style, the shallow DOF should be used only when it makes sense, and when the subject really calls for it. Not on everything, not in any occasion. Else it's not a style anymore, it becomes a stylization.


I admit that, besides high ISO performance, it is the shallow DOF obtainable with dSLR which makes me want to get one. Funny thing is, that, years ago with my first analog SLR I usually had tried to get the deepest DOF by choosing the smallest aperture shutter speed would allow, never had played with narrow DOF. Thank you for your observation of it's misuse, I shall remember.

Orio wrote:
- nicer bokeh - no, actually, it's the opposite, bokeh is nicer with the lens stopped down because all the optical shortcomings of a lens are reduced, and these can really make a bokeh become unbearable - such as it happens with the Jupiter-9 and the out-of-focus highlights.

- number of blades - yes it is important, of course only with the lens stopped down - and only if there are strong highlights in the background. But surely round OOF highlights at any aperture is a desireable feature. It does not have anything to do, however, with the maximum aperture of a lens. There are lenses such as the Steinheil Culminar 4.5/135 that are very slow and have 20 blades in the iris, there are other lenses that are very fast and have maybe only 5-6 blades in the iris.


I did not think that the max. aperture would influence the bokeh, specially as it should be used stepped down as you explain. Higher number of blades does gives round OOF highlights. Are OOF highlights, in strict definition, not bokeh? or are they part of it? to my limited understanding they could be big part of a good bokeh, which other elements make a good bokeh?

Orio wrote:
Slower lens usually means smaller and lighter lens, so if you go out with your photo bag to walk a lot, or if you plan to stay out all day, or to travel in train or plane, every space and weight that you can save is important.


simple but very valuable point.

Orio wrote:
Also, it's not uncommon the case when a slower lens has a better optical performance than a faster lens. This is often the case with Leica lenses, where the Elmarit models (f/2.8 ) often deliver better optical performance than their Summicron (f/2) counterparts. But there are cases in practically all lens catalogues of this situation. The reason is obvious, to build a better lens that is slow, is both cheaper and technically easier. To obtajn excellence of performance from a fast lens, this is the hard part.
So to sum up, if you are the type of photographer who likes to have well defined photos, you are likely to shoot most of the times in the range between f/4 and f/8, which is the range of the slow lenses.
So, in this case, there is no much difference from having a fast lens, except of course that -like I said- a fast lens is much easier to manual focus.


Your points makes me think that the main advantage of fast lenses simply is their use at little light, and not to forget the easier focussing.
I like street photography which often must do with low light, so my wide to normal lenses rather should be fast.
But how about nature shots at good daylight, or even street photography at day light? Slow lenses for their deeper DOF, lighter weight - and cheaper prize - could be just the better choice.

Thank you very much again, I believe that I slowly get the picture.
and I'd be glad if this questions are of interest also to other members and if there will be more observations coming, but would not be surprised if this is too basic for that to happen.

thank you again,
andreas


PostPosted: Fri Feb 01, 2008 4:14 pm    Post subject: Reply with quote
Quote:
Your points makes me think that the main advantage of fast lenses simply is their use at little light, and not to forget the easier focussing.
I like street photography which often must do with low light, so my wide to normal lenses rather should be fast.
But how about nature shots at good daylight, or even street photography at day light? Slow lenses for their deeper DOF, lighter weight - and cheaper prize - could be just the better choice.


WIth digital cameras, fast aperture is not the only way to obtain speed, there is also ISO control. A good setting is always a balanced one, one that balances the impact of shutter time, aperture, and ISO.

About fast lenses quality, at wide open image quality is problematic even with the best brands (that cost $$$), let alone with average brands.
Unless you buy one of the 4-5 main lens brands, chances are that your superfast lens might have an image quality that is nearly unuseable wide open.
Of course, the advantage of having a brighter view for manual focusing will remain even if the glass is bad.
So even cheap fast lenses have this one good quality.

As for depth of DOF, it's not that slow lenses have a deeper DOF than fast lenses. When the focal lenght is the same, a fast lens stopped down to f/4 will have the identical depth of field as a f/4 lens.

-


PostPosted: Fri Feb 01, 2008 4:17 pm    Post subject: Reply with quote
Don't forget apparant DOF is determined by aperture, but also focal length.

It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.

Determining what's a pleasing bokeh is quite personal - some people like extremely smooth gradations others don't mind a slight swirl effect.


PostPosted: Fri Feb 01, 2008 4:49 pm    Post subject: Reply with quote
Orio wrote:

WIth digital cameras, fast aperture is not the only way to obtain speed, there is also ISO control. A good setting is always a balanced one, one that balances the impact of shutter time, aperture, and ISO.


of course. And itsn't high ISO performance a big advantage of digital cameras and that they allow for low light photos hardly possible with analog cameras.

Orio wrote:
About fast lenses quality, at wide open image quality is problematic even with the best brands (that cost $$$), let alone with average brands.
Unless you buy one of the 4-5 main lens brands, chances are that your superfast lens might have an image quality that is nearly unuseable wide open.
Of course, the advantage of having a brighter view for manual focusing will remain even if the glass is bad.
So even cheap fast lenses have this one good quality.


unless of the 4-5 main brands..but many old german, russian, japanese lenses are good, and one has to buy expensive if one wants similar optical performance from new lenses, right?

Orio wrote:
As for depth of DOF, it's not that slow lenses have a deeper DOF than fast lenses. When the focal lenght is the same, a fast lens stopped down to f/4 will have the identical depth of field as a f/4 lens.


ahh of course, there was my thinking mistake.
so usually slow lenses only advantage is being smaller and cheaper. Some slow lenses may be sharper though as they are easier to build, e.g. I remember that the f3,5 variants of both 35mm and 135mm Takumars are considered sharper, maybe even rendering colors better than their faster counterparts.


PostPosted: Fri Feb 01, 2008 4:54 pm    Post subject: Reply with quote
Richard_D wrote:
Don't forget apparant DOF is determined by aperture, but also focal length.


yes, though I am aware of that I do not understand how DOF is influenced very well though. I do not really grasp the 3rd point the 'basic facts' in this very comprehensive explanation: http://www.wrotniak.net/photo/tech/dof.html

Richard_D wrote:
It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.


this is very interesting, a point where slower lenses could have an advantage.


PostPosted: Fri Feb 01, 2008 4:57 pm    Post subject: Reply with quote
Quote:
unless of the 4-5 main brands..but many old german, russian, japanese lenses are good, and one has to buy expensive if one wants similar optical performance from new lenses, right?


Being of excellence quality at wide open is not of every lens. It is where you usually measure the difference between the expensive lenses and the normal lenses.
Having that said, I would not make a myth of the wide open performance. It is important, but it's not vital. Of my best photos, only very few were taken wide open. Most of them were taken stopped down. And when you stop it down, a Helios-40-2 is every bit as good as a Contax Planar or a Leica Elmarit.


Quote:
so usually slow lenses only advantage is being smaller and cheaper.


Like I said, they are, often, also optically better, because they can be optimized for performance at the most used apertures (from f/ to f/Cool, while fast lenses have to arrange compromises in order to feature glass sizes and schemes to support fast apertures.
Of course this is not a fixed law and there are exceptions, for instance you can find Leica Summilux 1.4/50 that is a better lens than the Summicron 2/50.
But, in general, that is the way it goes.
-


PostPosted: Fri Feb 01, 2008 4:59 pm    Post subject: Reply with quote
kuuan wrote:

Richard_D wrote:
It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.


this is very interesting, a point where slower lenses could have an advantage.


"sharp" and "slow" or "fast" are not related things.


PostPosted: Fri Feb 01, 2008 5:25 pm    Post subject: Reply with quote
Orio wrote:
kuuan wrote:

Richard_D wrote:
It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.


this is very interesting, a point where slower lenses could have an advantage.


"sharp" and "slow" or "fast" are not related things.


You're right I was thinking of my Nikkors where the sharper lens in the same focal lengths are also the faster lens and with a less pleasing bokeh. It's not a rule of physics.


PostPosted: Fri Feb 01, 2008 5:30 pm    Post subject: Reply with quote
Richard_D wrote:
Orio wrote:
kuuan wrote:

Richard_D wrote:
It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.


this is very interesting, a point where slower lenses could have an advantage.


"sharp" and "slow" or "fast" are not related things.


You're right I was thinking of my Nikkors where the sharper lens in the same focal lengths are also the faster lens and with a less pleasing bokeh. It's not a rule of physics.


Richard I was not replying to you I was replying to kuann.
Your statement is correct (sharper lenses have often worse bokeh)
It's kuann who seemed to interpret as slower lenses = less sharp, thus having an advantage.

-


PostPosted: Fri Feb 01, 2008 5:56 pm    Post subject: Reply with quote
Orio wrote:
Richard_D wrote:
Orio wrote:
kuuan wrote:

Richard_D wrote:
It's not a rule as such, but often sharper lenses will have a less pleasing bokeh than slower lenses.


this is very interesting, a point where slower lenses could have an advantage.


"sharp" and "slow" or "fast" are not related things.


You're right I was thinking of my Nikkors where the sharper lens in the same focal lengths are also the faster lens and with a less pleasing bokeh. It's not a rule of physics.


Richard I was not replying to you I was replying to kuann.
Your statement is correct (sharper lenses have often worse bokeh)
It's kuann who seemed to interpret as slower lenses = less sharp, thus having an advantage.

-
Orio I think I'm guilty of creating confusion through poor wording.


PostPosted: Fri Feb 01, 2008 6:51 pm    Post subject: Reply with quote
Orio wrote:


Your statement is correct (sharper lenses have often worse bokeh)
It's kuann who seemed to interpret as slower lenses = less sharp, thus having an advantage.

-


thank you for the clarification.

abt DOF: I am not sure if I understand the following statement, quote:
( taken from http://www.wrotniak.net/photo/tech/dof.html )
'At the same lens aperture and image magnification (i.e., width of the frame, measured in the subject plane), depth of field remains approximately constant for various focal lengths.'

'Image magnification' means the actual shown frame of a scene, yes? Then this statement is surprising to me, I thought wide lenses always would have deeper DOF compared to long lenses.

any thoughts, clarification?
thank you,
andreas


PostPosted: Fri Feb 01, 2008 7:39 pm    Post subject: Reply with quote
Kuann - take two pictures one with wide angle one with longer lens. Enlarge subject area in wide shot so that it's the same as that in the long shot and both would show same approximately same dof.


PostPosted: Fri Feb 01, 2008 7:59 pm    Post subject: Reply with quote
Richard_D wrote:
Kuann - take two pictures one with wide angle one with longer lens. Enlarge subject area in wide shot so that it's the same as that in the long shot and both would show same approximately same dof.


thank's Richard, the fact slowly does sink in, but it had come as a surprise
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