Defining a 'fast' lens

[bobn2]

In another thread mcabato, who seems to have a different view of what speed means,
put forward these three links to back up his case:

http://en.wikipedia.org/wiki/Lens_speed
http://cpn.canon-europe.com/content/education/infobank/lenses/lens_speed.do
http://www.forphotography.com/how-tos/photographyterms.html

it is what it is. nothing less and als nothing more.

All three of them seem very convinced that the notion of 'speed' is relative to focal length:
From Wikipedia:

'A lens may be referred to as "fast" or "slow" depending on its maximum aperture compared to other lenses of similar focal length designed for a similar film format.'
From Canon:

'This refers to the maximum, or widest aperture of the lens, and is relative to the type and focal length.'
From forphotography:

'Determined by the maximum aperture in relation to focal length. Lens speed is relative: a 400 mm lens with a maximum aperture of F/3.5 is considered extremely fast, while a 28mm F/3.5 lens is considered to be quite slow.'

So, to take an example that was being batted around, it seems to me, under those definitions, reasonable to say that a 300/2.8 is the same 'speed' as a 600/5.6, and to extend that idea, if those two lenses were mounted on cameras such that they gave the same angle of view, they could be considered 'equivalent'.
--
Bob

 

[Great Bustard]

I really don't think we need another though maybe that chap in the movie does?

I missed the movie.

Anyhow, good luck with this thread I'm sure it'll max out...maybe you can hand out quizzes afterward or just start another?

Each round, a few more get it, most don't, and a few more new "faces" that never heard about it all before appear on the scene. In other words, "never ending".

The real question is why hasn't Olympus made some f1.4 or faster primes to try to match or get close to Nikon / Canon primes!

The 35-100 was fantastic while I had it but there were times I'd of loved a 40'ish f1.4 or even a 90 f2...

It was because of the telecentricity:

http://forums.dpreview.com/forums/read.asp?forum=1022&message=37225807

 

[mcabato]

where did you bring the angle of view from in?

http://dictionary.reference.com/browse/speed
http://www.brooksphotopedia.com/definitions/fast-lens.shtml
http://www.lensrentals.com/news/2009.08.15/fast-lenses-a-primer

yes, fast is aperture relative to focal length fo rcomparable lenses.

and, in case a 2/100 is fast, and a 5.6/800 is fast, what is a 2.8/12 called then?

you are interpreting more in than it is.

 

[mcabato]

great bustard, i fully agree with this your statement.

if the term fast lens is woldwide used with a certain meaning, then one should not confuse by giving it a new interpretation, but keep the meaning unchanged.

best regards. gusti.

 

[bobn2]

http://dictionary.reference.com/browse/speed
http://www.brooksphotopedia.com/definitions/fast-lens.shtml
http://www.lensrentals.com/news/2009.08.15/fast-lenses-a-primer

yes, fast is aperture relative to focal length fo rcomparable lenses.

and, in case a 2/100 is fast, and a 5.6/800 is fast, what is a 2.8/12 called then?

well, I wouldn't call a lens with a focal length of 2mm and an f-number of 100 fast under any circumstances, nor one of 5.6mm and an f-number of 800. compared with them, one with a FL of 2.8mm and an f-number of 12 is quite fast in comparison, but I doubt whether many would call an f/12 lens 'fast' until it had a FL of a metre or more.

you are interpreting more in than it is.

More than you would like there to be, more like, since everything on lens speed I 'interpreted' is in the references you gave.

where did you bring the angle of view from in?

At the end, did you miss it?

'So, to take an example that was being batted around, it seems to me, under those definitions, reasonable to say that a 300/2.8 is the same 'speed' as a 600/5.6, and to extend that idea, if those two lenses were mounted on cameras such that they gave the same angle of view, they could be considered 'equivalent'.'
--
Bob

 

[mcabato]

so, you are getting jokingly destructive? time for you to give in.

 

[Great Bustard]

so, you are getting jokingly destructive? time for you to give in.

The differences in native tongues may be the issue here. Let me ask you a simple question, is a 100mm f/4 on FF the same "speed" as 50mm f/2 on 4/3? From what I've gathered from your posts, you would say "yes", and, if so, then you and Bob are in agreement.

 

[bobn2]

so, you are getting jokingly destructive? time for you to give in.

Time for me to go to bed, in any case. If you're still playing when I've slept, I'll put you straight again. meanwhile, if you want to argue the toss about precise definitions, expect to have it argued the other way. Standard way of writing lenses is FL/f-number, just as the usual formula f/2.8 - f is the FL, so you just substitute it. Yours was back to front, without identification of which was the f-number and which the FL.
--
Bob

 

[mcabato]

thanks great bustard, but it is not.

100mm, f/4 on ff is equivalent to 50mm, f/4 on FT when it comes to exposure at the same iso setting.

i think we all are in agreement, that in terms of image noise you can use easily a 100mm f/4 at double iso-number on ff to get the same result as a 50mm f 2 on 4/3.

 

[mcabato]

bobn, have a good night.
but be sure i am not playing.

i'd like to avoid confusion and in that respect one neds to use precise expressions.

by the way thank you that you accept my not perfect english.

good night.

 

[Great Bustard]

thanks great bustard, but it is not.

100mm, f/4 on ff is equivalent to 50mm, f/4 on FT when it comes to exposure at the same iso setting.

Yes, that is true. But 100mm f/2 on FF is not equivalent to 50mm f/4 on FT when it comes to DOF and image noise. So, what is the point of your "equivalence"?

i think we all are in agreement, that in terms of image noise you can use easily a 100mm f/4 at double iso-number on ff to get the same result as a 50mm f 2 on 4/3.

And thus "equivalent". I mean, since exposure is meaningless when comparing across formats in terms of the visual properties of the final photo , what is the point of calling settings that result in different photos "equivalent"?

 

[Godfrey]

Indeed. [blah blah blah blah blah]

There is no value in the gobbledygook you pointed to.

The f/number of a lens is all that matters when it comes to referring to a lens as "fast". F/numbers are light transmission settings normalized to focal length, a system of numbers defined to permit exposure values to be used on any lens, any camera, equally to set exposure.

A "fast" lens is called that because it allowed a "fast" shutter speed, or a short exposure time however you want to say it. When the term came into use, most lenses were f/4.5 and smaller at maximum aperture. A fast lens allowed hand-holding the camera in poor light. That's the only criteria that makes any sense at all when saying that a lens is "fast".

What specific f/number you consider to be fast is similarly irrelevant. I choose f/2.8 for my own discriminator because it is a good divider between most of the pro lenses vs most of the consumer lenses. F/2, f/1.4, f/1.2, etc are all ultra high speed lenses ... very specialized optics.
--
Godfrey
http://godfreydigiorgi.posterous.com

 

[Great Bustard]

Indeed. [blah blah blah blah blah]

There is no value in the gobbledygook you pointed to.

Back at ya.

The f/number of a lens is all that matters when it comes to referring to a lens as "fast". F/numbers are light transmission settings normalized to focal length, a system of numbers defined to permit exposure values to be used on any lens, any camera, equally to set exposure.

A "fast" lens is called that because it allowed a "fast" shutter speed, or a short exposure time however you want to say it. When the term came into use, most lenses were f/4.5 and smaller at maximum aperture. A fast lens allowed hand-holding the camera in poor light. That's the only criteria that makes any sense at all when saying that a lens is "fast".

What specific f/number you consider to be fast is similarly irrelevant. I choose f/2.8 for my own discriminator because it is a good divider between most of the pro lenses vs most of the consumer lenses. F/2, f/1.4, f/1.2, etc are all ultra high speed lenses ... very specialized optics.

Already addressed:

http://forums.dpreview.com/forums/read.asp?forum=1022&message=37227128

Who cares? I mean, seriously, what's the point of saying one lens is "faster" than another when it doesn't deliver either more light on the sensor or a more shallow DOF? It would be like saying the finish of one lens is "blacker" than another and somehow trying to make a point about which is "better" on that basis.

 

[Dan]

OK since we talking equivalent in the OLYMPUS SLR forum how about the following problem:

I'm sure you all know the eclipse is coming up this Dec 20 / Dec 21. I've been "practicing" a bit with my D2X and a lens and a refracting telescope.

The lens is Nikon's 300f4 AFS stated at some 2100 LW/PH and the refractor is Televue's pronto which is 480 mm f6.8 and 212 line pairs/mm!

For the life of me I cannot get the Pronto to look as sharp as the 300f4 when stepped down to f8 (though is plenty sharp wide open too) even when I put the 300f4 at 100% size and the Pronto at 50% to get "roughly" the same image size on the screen.

Both systems are mounted on the same tripod and manfrotto geared head and releasing both with mirror lock up.

So...should the Pronto be sharper than the Nikon and I gotta keep working on nailing the focus or yes the Nikon should be sharper and my results make sense?

The Nikon was exposed in 1/250 and the Pronto at 1/500.

If it's expected the Nikon to be sharper should I sell the pronto and put the money into Nikon's 1.7 or 2.0 tele-extender? I know Nikon says the 300f4 won't focus with the EC20 but I see references to birders using the combo in good light!

Anyhow...sorry for the curve ball but I think I can get a good answer here from a couple fellas!

Thanks in advance,

Dan

 

[Great Bustard]

OK since we talking equivalent in the OLYMPUS SLR forum how about the following problem:

I'm sure you all know the eclipse is coming up this Dec 20 / Dec 21. I've been "practicing" a bit with my D2X and a lens and a refracting telescope.

The lens is Nikon's 300f4 AFS stated at some 2100 LW/PH and the refractor is Televue's pronto which is 480 mm f6.8 and 212 line pairs/mm!

Right off the bat, we have a serious "equivalence" problem. "Lens tests" are always "system tests", so the results only apply to the system that was tested. Nowhere is this more obvious than the 50 / 2 macro tested on the E3 and L10:

http://www.dpreview.com/lensreviews/widget/Fullscreen.ashx?reviews=32,33&fullscreen=true&av=3.667,3.667&fl=50,50&vis=VisualiserSharpnessMTF,VisualiserSharpnessMTF&stack=horizontal&lock=&config=/lensreviews/widget/LensReviewConfiguration.xml%3F4

There's the AA filter at work for you.

OK, moving on -- measurements in lp/mm are line pairs per millimeter on the sensor , but if we don't know the size of the sensor, then it means nothing. The meaningful measure is lp/ph (line pairs per picture height, or, alternatively, lw/ph -- line widths per picture height -- is simply twice the lp/ph measure), which we can get from lp/mm if we know the sensor size by multiplying by the sensor height.

However, as the link above shows, unless they were tested on the same sensor, then we still can't really say.

But let's say that the Televue was measured for a 35mm sensor, just like the Nikon. A measured resolution of 212 lp/mm is nothing short of ridiculously amazing -- for an MTF-50.

That is, another variable is the contrast at which the resolution measurement is made. The Nikon likely tested at 2100 lw/ph at 50% contrast, whereas the Televue may have measured as 212 lp/mm at 5% contrast -- big difference, and no way to extrapolate the MTF-50 measurement from it.

For the life of me I cannot get the Pronto to look as sharp as the 300f4 when stepped down to f8 (though is plenty sharp wide open too) even when I put the 300f4 at 100% size and the Pronto at 50% to get "roughly" the same image size on the screen.

Both systems are mounted on the same tripod and manfrotto geared head and releasing both with mirror lock up.

So...should the Pronto be sharper than the Nikon and I gotta keep working on nailing the focus or yes the Nikon should be sharper and my results make sense?

As I said, way too many variables to know what "should be" the case.

The Nikon was exposed in 1/250 and the Pronto at 1/500.

Seems fast enough to avoid mirror slap (I assume they were mounted on a sturdy tripod), but I'm not sure why the shutter speeds were different. They should be the same for the same f-ratio, and wide open, the Nikon should have had the faster shutter speed.

If it's expected the Nikon to be sharper should I sell the pronto and put the money into Nikon's 1.7 or 2.0 tele-extender? I know Nikon says the 300f4 won't focus with the EC20 but I see references to birders using the combo in good light!

Anyhow...sorry for the curve ball but I think I can get a good answer here from a couple fellas!

A focus error should be rather easy to discover. Barring that, just go with the sharper system. The thing is, however, that a TC will reduce the resolution since it magnifies the aberrations just as it magnifies the scene.

 

[sadwitch]

Are there any information on the equivalence between pentax 645D and Caniksony FF?

--
My Galleries
http://picasaweb.google.com.au/sadwitch

 

[Dan]

OK since we talking equivalent in the OLYMPUS SLR forum how about the following problem:

I'm sure you all know the eclipse is coming up this Dec 20 / Dec 21. I've been "practicing" a bit with my D2X and a lens and a refracting telescope.

The lens is Nikon's 300f4 AFS stated at some 2100 LW/PH and the refractor is Televue's pronto which is 480 mm f6.8 and 212 line pairs/mm!

Right off the bat, we have a serious "equivalence" problem. "Lens tests" are always "system tests", so the results only apply to the system that was tested. Nowhere is this more obvious than the 50 / 2 macro tested on the E3 and L10:

http://www.dpreview.com/lensreviews/widget/Fullscreen.ashx?reviews=32,33&fullscreen=true&av=3.667,3.667&fl=50,50&vis=VisualiserSharpnessMTF,VisualiserSharpnessMTF&stack=horizontal&lock=&config=/lensreviews/widget/LensReviewConfiguration.xml%3F4

There's the AA filter at work for you.

OK, moving on -- measurements in lp/mm are line pairs per millimeter on the sensor , but if we don't know the size of the sensor, then it means nothing. The meaningful measure is lp/ph (line pairs per picture height, or, alternatively, lw/ph -- line widths per picture height -- is simply twice the lp/ph measure), which we can get from lp/mm if we know the sensor size by multiplying by the sensor height.

However, as the link above shows, unless they were tested on the same sensor, then we still can't really say.

But let's say that the Televue was measured for a 35mm sensor, just like the Nikon. A measured resolution of 212 lp/mm is nothing short of ridiculously amazing -- for an MTF-50.

OK that's good and what I was thinking and doing the math it would be an incredible number. And why I was expecting the Televue / D2X results to just kick behind.

That is, another variable is the contrast at which the resolution measurement is made. The Nikon likely tested at 2100 lw/ph at 50% contrast, whereas the Televue may have measured as 212 lp/mm at 5% contrast -- big difference, and no way to extrapolate the MTF-50 measurement from it.

For the life of me I cannot get the Pronto to look as sharp as the 300f4 when stepped down to f8 (though is plenty sharp wide open too) even when I put the 300f4 at 100% size and the Pronto at 50% to get "roughly" the same image size on the screen.

Both systems are mounted on the same tripod and manfrotto geared head and releasing both with mirror lock up.

So...should the Pronto be sharper than the Nikon and I gotta keep working on nailing the focus or yes the Nikon should be sharper and my results make sense?

As I said, way too many variables to know what "should be" the case.

The Nikon was exposed in 1/250 and the Pronto at 1/500.

Seems fast enough to avoid mirror slap (I assume they were mounted on a sturdy tripod), but I'm not sure why the shutter speeds were different. They should be the same for the same f-ratio, and wide open, the Nikon should have had the faster shutter speed.

I had stopped the Nikon down to f8 just because it was only the moon and I didn't need any faster shutter speed.

If it's expected the Nikon to be sharper should I sell the pronto and put the money into Nikon's 1.7 or 2.0 tele-extender? I know Nikon says the 300f4 won't focus with the EC20 but I see references to birders using the combo in good light!

Anyhow...sorry for the curve ball but I think I can get a good answer here from a couple fellas!

A focus error should be rather easy to discover. Barring that, just go with the sharper system. The thing is, however, that a TC will reduce the resolution since it magnifies the aberrations just as it magnifies the scene.

I haven't done a lot of imaging with the Pronto and I'm not sure "how flat" it's field of view is in honesty. Yes both devices where on the same tripod/head and both used the D2X to capture the images. I'm really quite surprised by how good the Nikon looks...this astrophotography is quite the can of worms! I feel I might get decent at wide field stuff haha!

Thanks for the reply and still looking for anyone else with similar experiences or anything else I should be doing to get a little better results out of the Pronto.

Dan

 

[Rriley]

is anyone else here as tired of these brand bashing, grandstanding dorks as I am ?

these people have taken over every aspect of this forum

this brand is systematically trashed at every opportunity by people who have never used one of these cameras or lenses. Anyone with the least bit of loyalty to this brand is attacked by a chain of morons, and that doesnt mean me, that means anyone .

on the same page,

• theyve trashed the sensor The lens is not low-res. The "problem" is more the sensor Olympus offers to put behind it.
• theyve trashed the lens system, So, the proposition put forward by you (I think, forgive me if I've lost track of the discussion) that the Olympus lens is optically better than other brands lacks a bit of substance,
• they trashed 'telecentrics' Telecentricity has been promoted from "marketing fluff"
• theyre trashing 'fast' lenses here what is the point in saying "f/2 on 4/3 is faster than f/4 on FF

and by their own volition, they claim they come here for the 'entertainment'. Well folks, do you feel entertained?

at the same time we are besieged by obvious sock puppet trolls such as these
http://www.dpreview.com/members/3163211182
http://www.dpreview.com/members/1344249995

and when theyre finally removed, they will simply use re -use another nick

Simon Joinson, you have a lot to answer for

--
Riley

any similarity to persons living or dead is coincidental and unintended

 

[sadwitch]

I am... but you'll never get rid of them so long olympus or 4/3 exist. Wonder is it as bad in micro4/3 forums?

--
My Galleries
http://picasaweb.google.com.au/sadwitch

 

[Godfrey]

Indeed. [blah blah blah blah blah]

There is no value in the gobbledygook you pointed to.

Back at ya.

The f/number of a lens is all that matters when it comes to referring to a lens as "fast". F/numbers are light transmission settings normalized to focal length, a system of numbers defined to permit exposure values to be used on any lens, any camera, equally to set exposure.

A "fast" lens is called that because it allowed a "fast" shutter speed, or a short exposure time however you want to say it. When the term came into use, most lenses were f/4.5 and smaller at maximum aperture. A fast lens allowed hand-holding the camera in poor light. That's the only criteria that makes any sense at all when saying that a lens is "fast".

What specific f/number you consider to be fast is similarly irrelevant. I choose f/2.8 for my own discriminator because it is a good divider between most of the pro lenses vs most of the consumer lenses. F/2, f/1.4, f/1.2, etc are all ultra high speed lenses ... very specialized optics.

Already addressed:

http://forums.dpreview.com/forums/read.asp?forum=1022&message=37227128

Who cares? I mean, seriously, what's the point of saying one lens is "faster" than another when it doesn't deliver either more light on the sensor or a more shallow DOF? It would be like saying the finish of one lens is "blacker" than another and somehow trying to make a point about which is "better" on that basis.

The statement is stupid and misses the obvious. And if you can't understand that it is not true, then it isn't worth carrying on a discussion with you any further.
--
Godfrey
http://godfreydigiorgi.posterous.com