Aperture speed - a practical question

[northlondon43]

Hi everyone

I was intending to take two lenses tomorrow to my b in law's birthday dinner at a pub (going via train so no intention of bringing a tripod); a 18-55mm min f stop 3.5, for some focal length flexibility and a 16mm prime, min f stop 2.4, for dinner table shots and because it's indoors, for low light. Here's the thing...theory tells me that the prime will let x2 more light in, but so what in practical terms? I've just taken a couple of practice shots with both lenses, at the same ISO at max aperture at home, in low light conditions and the only difference I can see is that the shutter speed goes from 1/5th for the 18-55mm to 1/10th for the prime. In practical terms, i.e. being able to hand hold the camera rather than tripod, there's no real difference.

The reason I'm posting this is because, as a relative newcomer, I keep reading about how 'fast' lenses are 'wow' for low light situations etc. My question is, given the above, why???

Cheers

Adrian

[Geoff F]

If you are comparing F2.4 against F5.6 lenses there is a considerable difference.

But the other consideration is if you don't want to shoot wide open so you get a bit more focus depth.

However, for the type of photos you intend to shoot I would be thinking about a shutter speed of 1/60 or a little faster to cope with potential subject movement as well as camera shake problems.

This means, if possible, using flash. Alternatively, try to find some slightly better lit areas for the main shots.

[northlondon43]

Thank you. I understand what, in practical terms ,I need to do vis a vis shutter specifically speeds...I gave context just to illustrate my specific question: apart from the minute difference on dof what's the big deal about faster lens when shooting in low light?

[Scott Stephen]

Yes. Both 1/5 and 1/10th are too slow a shutter just for simple camera shake, much less for any subject movement at all. Flash would be highly useful. I don't suppose this pub has white ceilings? Bounce flash looks a lot better than direct flash.

What was your ISO set on? Was the camera controlling it for you, or did you set it? You can jack the ISO up, but you pay the price in bad image noise.

What kind of camera do you have?

[northlondon43]

Gosh, I don't seem to have explained myself very well. I'm not asking how to remedy the situation (I know I can alter ISO, use flash etc), I'm asking a question about why people are so passionate about faster lenses when, given the scenario I gave, I can't see any real advantage bar a slightly faster shutter speed and a slightly larger depth of field. In the scenario I have described, taking pictures in low light of my family, I see no advantage.

[Mark von Kanel]

Adrian its not that you are not explaining your self very well at all, people are passionate about fast lenses not only because of the extra light gathering capabilities, that are as you say negligible but the additional shallow depth of field that you can obtain with them.

The extra stop can ok, help with exposure in some situations but this is not important to the soft back ground and bokher that a fast lens can give. so in answer to you question, theres more to be gained than additional light.

Also lens's dont tend to be at there sharpest when fully open, so a faster lens when stopped down slightly can be sharper than a lens fully open but at the same aperture, it all depends on the lens and its characteristics.

[northlondon43]

Thanks Mark. In my case a one stop difference in aperture between the lenses is of no significance....I guess two or three might. Cheers

[Mark von Kanel]

Your quite right, in your case not a lot of good but imagine if you wanted to shoot some action at 1/500 instead of 1/250, all of a sudden the extra stop helps, and not to mention as you have such a shallow DOF that only the essential action will be in focus, so nothing will distract from you images central point of interest

have i convinced you to buy one yet ?

[northlondon43]

Hee hee only if Samsung produce an affordable low stop lens....the new 45mm is f1.8 but given the lenses i already have it may not be worth it :-)

[Glenn NK]

My personal experience is that a lens with a good (VR, IS, OS) is more valuable than a lens that's two stops faster without (VR, IS, OS). Typically the newest generation of (VR, IS, OS) is worth three stops. And of course greater DOF comes along with this (not all images call for shallow DOF - at a birthday party for example, I want deep DOF).

I've handheld both the Canon 24-105 and 70-200 at 1/15 second with good results. Without IS, this is difficult to say the least.

Glenn

[northlondon43]

Good point Glen....even more convinced that for amateur photographers such as myself the nuances that professionals care about simply don't apply...you can end up getting really anal about theory and forgetting about just enjoying yourself. Big lesson to be learnt for me. Thanks :-)

[Colin Southern]

I can't see any real advantage bar a slightly faster shutter speed and a slightly larger depth of field. In the scenario I have described, taking pictures in low light of my family, I see no advantage.

Hi Adrian,

Slightly faster shutter speed? It DOUBLED your shutterspeed! It won't give you a slightly larger DoF though -- it'll give you LESS DoF.

In reality - if you're not using flash - then in that situation you'll probably find you need to max out the ISO & Aperture to get your shutterspeed in the range where you won't get camera shake. If it were me, I'd start by maxing out the ISO - see what kind of shutterspeed I got - then stop-down the aperture until the shutterspeed was at a minimum I could hand-hold - and then "reassess" the compromise from there (eg stop down more for better DoF - ISO down for less noise - shutterspeed up for better motion freezing etc).

To answer the question though, fast primes are specialty lenses, but the downside of wide apertures can be insuffienct DoF. Here's a case in point ... an image I took recently. The Camera was at ISO 3200 (the max for that camera) - the aperture was at F1.2 (the max for that lens) - and the shutterspeed was STILL only 1/20th of a second to try and freeze an aeroplane doing about 180km/hr (100 mph).



If I'd had a lens that could only open up to - say - F3.5 then the shutterspeed would have been around a ridiculous 1/4 to 1/2 a second (I'll let someone else to the exact maths -- too hard for me!).

[northlondon43]

Thanks for correcting my error ref dof Colin but as already stated that's not really what I'm on about.
By the way doubling the shutter speed might theoretically sound great but as I explained, practically it's of no use

[isdennys]

I think,
between F2.4 and F5.6 so much influence in poor light conditions. it all depends on the breadth of point shooting.
I think more dug try again or more tries with limited equipment, light etc. so that we can more leverage in the technique and its use can also increase the knowledge we have, as long as we know the theory as a guide


best wishes

[Colin Southern]

My personal experience is that a lens with a good (VR, IS, OS) is more valuable than a lens that's two stops faster without (VR, IS, OS). Typically the newest generation of (VR, IS, OS) is worth three stops. And of course greater DOF comes along with this (not all images call for shallow DOF - at a birthday party for example, I want deep DOF).

I've handheld both the Canon 24-105 and 70-200 at 1/15 second with good results. Without IS, this is difficult to say the least.

Glenn

We're up to 4 stops now (and I've even seen 5 mentioned). I'm not disagreeing with you, but unfortunately, VR / IS only helps with camera shake -- it doesn't do anything to arrest subject motion that a fast lens would address. If you're shooting people with an IS / VR lens that's still only around 1/15th then your keeper rate will probably start to go right down.

[northlondon43]

I think I'm starting to lose the plot with this thread..................

[Colin Southern]

Thanks for correcting my error ref dof Colin but as already stated that's not really what I'm on about.
By the way doubling the shutter speed might theoretically sound great but as I explained, practically it's of no use

You're welcome, but I don't understand why you say "doubling the shutterspeed is of no use".

Sometimes it won't be any use what-so-ever (eg if you were shooting a static scene with a tripod), but at other times it might be EXACTLY what's required for a particular effect. Case in point, if you were to look at the original of my shot of the plane landing you'd see that although I panned the camera, there's still a degree of motion blur; if I'd been forced to shoot that at only 1/10th then the blur would have made the entire shot marginal.

In your case - if you're forced to shoot at around 1/15th you'll probably get not only camera shake but also motion blur -- if you can shoot at 1/30th then both of those will be reduced by 1/2 which visually will make quite a significant difference. I appreciate that you know that you can increase the ISO to compensate, but in situations like you're describing where the light is usually quite bad, you'll probably find that you have your ISO already maxed out and the only thing that makes a difference between an acceptable shutter speed and one that is too low is the max aperture.

[William W]

I think I'm starting to lose the plot with this thread..................

Hang on and hang in there.
Just a little re-cap:

Firstly you are asking a GENERAL question (“Why do people get passionate about fast lenses for Low Light Work?”) – yet you want to apply that generality to your ONE SPECIFIC situation.

Secondly you want to debate against the generalization using only that one specific situation.

Thirdly – F/2.8 is NOT “a fast lens” - sure it is fast for a 16mm lens – but it is NOT a “fast lens”.

Fourthly – (and we are now into minutia and only partially relevant trivia) – F/3.5 to F/2.8 is not a stop but it is close to a stop

Fifthly – F/2.8 is a major increase in lens speed over the GENERAL SPEED of the kit lens.


Most importantly (just addressing your specific situation) you can (almost) double the shutter speed moving from F/3.5 to F/2.8 – and that MIGHT (i.e. not always but “MIGHT”) make a difference between the shot being possible or impossible – and THAT is what the passion for faster lenses, is all about.

A Fast Lens for Low Light Work Portrait work is F/1.0 to F/2 ish – hence the (traditional) range of fast 24mm; 28mm; 35mm; 50mm; 58mm and 85mm Prime Lenses.
Obviously, there are fewer possibilities for fast and wide, if one is using and APS-C sensor.

WW

[William W]

By the way doubling the shutter speed might theoretically sound great but as I explained, practically it's of no use

“No amount of experimentation can ever prove me right; a single experiment can prove me wrong.” - Albert Einstein

***


As merely one example, which is at hand, because I use it often in workshops, to show this exact point which you have posed in your OP.

Around April 2006:

I was happily shooting this swimming meet at around F/4.5 @ 1/1250s @ ISO1600 with the EF 70 to 200/2.8 and a circuit breaker tripped the floodlights knocking out about 5 to 6 stops of light .

I needed a shot of the Swimmer in Lane 6 at a Backstroke Start. I was being paid for these shots.

I used my 85mm and crept as close as I could under and near one of the Judges.


1/800s is close to the absolute limit for a Backstroke Start.

This shot was still about two stops underexposed, but my 70 to 200 F/2.8L was useless in this situation - for to use it would have meant the shot would have been 3 or more stops underexposed – and thus “impossible”:



Tech: F/1.8 @ 1/800s @ ISO3200.


***


As luck would have it she qualified into the final and I made a better shot of her, under a full lighting bank:



I have more examples of how a fast lens, (by even one stop faster) can make a shot “possible” which otherwise, might not be. . . and 'possible' means "of very, very much use".


***


Perhaps it is important to mention that the “passion” about lens speed is (usually) for a need to address Subject Motion, than Camera Shake: Subject Motion is NOT addressed by VR, IS or OS.


WW

[groovesection]

If I'd had a lens that could only open up to - say - F3.5 then the shutterspeed would have been around a ridiculous 1/4 to 1/2 a second (I'll let someone else to the exact maths -- too hard for me!).

Assuming i understand correctly, your math is way off ;p
That would be 1/25
f/1.4 - f/2 - f/2.8 - f4 = 1/200 - 1/100 - 1/50 - 1/25