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Which is the fastest lens?


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Stuart, I'm not saying my answer is a solid rule, it's just discussion regarding the considerations. Remember we don't all have access to every lens set ever developed... You've kind if forced my hand in that I just need to ask: So if low light was causing you to shoot wide open for exposure and the resultant DOF was too low because of that your solution is to go to a faster lens so you can open it up more??? Maybe a wider lens and/or a FOV change could work yes?

 

But going wider-angle and moving in closer to get back the same subject size just reduces depth of field again, so it's not really much of a DOF solution.

 

I think this discussion is just mixing up too many separate issues. A T/1.4 lens is faster than a T/2.0 lens, period, don't confuse things by bringing in focal length. If you need more exposure from the lens, then you need more exposure from the lens. There is no scenario where the T/2.0 lens can be faster than the T/1.4 lens if both are shot wide-open.

 

But if you had to use a single lens in Super-16, a 16mm focal length would probably be more practical than a 50mm focal length, simpler because a 16mm lens has a medium-to-wide view and a 50mm lens has a telephoto view in Super-16.

 

But being a shorter focal length doesn't solve your exposure problems if you need a T/1.4 exposure. But if you're not sure whether you absolutely need the T/1.4 speed, I'd get the 16mm over the 50mm because I can probably find a way of adding another stop of exposure to get to T/2.0 and the 16mm focal length is just going to be a lot more practical. Though I'm not sure why I'd put myself in a situation of only taking a single focal length with me to shoot something...

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What I'm saying is go with a FOV change - either with a wider lens, or by moving the camera (what I meant by 'FOV change')...

 

I understand an MCU might be called for but what good is an underexposed MCU and or one without the DOF you need ?

 

So you 'consider' it...

 

Its all I've said

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the MCU on a 16mm and a 50mm will have the same DoF @ the same stop on the same format....

 

Let's keep this simpler; take a 25mm lens. Find out the DoF @ 4Ft and T2.

Now do the same for a 50mm @ 8ft and T2.

 

the 25mm @ 4ft T2 is 3' 8" to 4'5" according to my CineCalc spredsheet (from panavision) (9 INCHES DOF)

 

now a 50mm @ 8ft (2x the focal length, so we back up accordingly) @t2 is 7" 8" to 8"5" (9 inches!)

 

Same Dof.

 

Now whether you can move the 50mm away 8ft is another story.

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What I'm saying is go with a FOV change - either with a wider lens, or by moving the camera (what I meant by 'FOV change')...

 

I understand an MCU might be called for but what good is an underexposed MCU and or one without the DOF you need ?

 

 

If the shot is underexposed with the camera at 10ft away, it will still be underexposed at 5ft away. Moving the camera does not change your exposure, and changing your lens won't either, unless it is a faster lens.

 

I also can't see why DOF would be so important that you would be willing to commit to a frame that you don't want in order to achieve it.

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This is all confusing the issue. It's simple, the lens with that goes to T/1.4 is faster than the lens that goes to T/2.0. If you need T/1.4 to get the exposure, then playing around with the focal length or shot distance of a T/2.0 lens isn't going to help you get a T/1.4 exposure. I don't know why we are complicating this thread with DOF issues and I still don't even understand what Chris Millar is trying to say, what his point is regarding whether to get a 16mm T/2.0 lens versus a 50mm T/1.4 lens.

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I don't understand why DOF got brought into this discussion either, so I'll just reiterate what has been said in just about every post in this thread - the t1.4 lens is faster than the t2 lens.

 

I believe that answers the original question.

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I don't understand why DOF got brought into this discussion either, so I'll just reiterate what has been said in just about every post in this thread - the t1.4 lens is faster than the t2 lens.

 

I believe that answers the original question.

 

It's almost a stop more light. The focal length doesn't matter.

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Ok, many things going on here...

 

I can't follow them all up without just adding more confusion and more misunderstanding of what I'm failing to communicate.

 

I know what you're talking about, I didn't know once, but I did a week ago and continue to do so today - I can see how you think I don't and I can also see how you might think I still have it wrong ;)

 

You gotta choose your battles...

 

wrong.jpg

Edited by Chris Millar
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In any professional realm, correct terminology is vital. The 'speed' of a lens is specifically referring to the amount of light transmitted at the widest aperture.

 

The quality of the image is a separate issue. Sometimes a lens design will sacrifice certain aspects of quality to obtain a faster maximum aperture. So while lens "a" may open to T1.4, even stopped down to T2 it won't perform as well as lens "b" at T2, which is at its maximum.

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  • 2 weeks later...

To the original poster...would you consider using a faster film stock so that you can use the slightly slower 16mm lens? That will also get you more depth of field - (if you want more DOF.) If you're shooting in a confined space and you can't back away enough to use the faster 50mm, then it seems like the 16mm would be a good choice, provided you use fast film or alternatively 'push' the film. By the way, what sort of low light environment will you be shooting in?

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To the original poster...would you consider using a faster film stock so that you can use the slightly slower 16mm lens? That will also get you more depth of field - (if you want more DOF.)

 

No, it won't, for all the reasons that have been quite comprehensively explained above.

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No, it won't, for all the reasons that have been quite comprehensively explained above.

 

Seems you've got replying to this thread on a hairline trigger so I'd just be taking the bait in trying to explain what I mean/meant which might (only might) be the same thing this other poster is thinking of.

 

Here goes:

 

 

Maybe there are more options involved, each has a trade off - some people for either the sake of ease, experience, fitting in with 'the ways its done round here', personal choice and so on might neglect to consider some of these options and therefore 'get the damn job done' - but don't let this mindset cloud possibilities that others might bring up, like dare I mention it, a change of the FOV (via a wider lens) to get more apparent DOF (keeping the film/sensor size the same and the image magnification on playback also the same (no zoom in)), this is all in the case that there is enough light at the fully open speed of the slower and wider lens, but in the case of instead using the longer and faster lens at the same aperture as the fully open wider lens you don't get enough DOF. So light has not just a bearing on exposure, but also a bearing on the DOF, via the aperture setting...

 

YES, you get a FOV change, YES, you can pull focus - either of which might be completely unsuitable, either of which MIGHT NOT BE - especially if your lens and crewing choices are restricted, which is what this thread was partly about. We don't all have a big ol' lens set that we never touch as we've got a crew walking around in puffer jackets with cans of compressed fart and assorted of sticky tapes.

 

Maybe yet again I haven't clarified every element involved, put in the correct emphasis on certain words or spoken in the correct filmy speak so again rolleyes.gif there will be some way to prove me stupid...

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Chris, I understand perfectly well what you are saying. What I don't understand is why you think that essentially shooting everything wide is a useful option. You may well get a shot, but unless it's the shot you need, what's the point? When the Editor says 'did you get a CU on his reaction?' it's not really much help to say 'no, but we've got it in a wide'.

 

I also don't think it's very helpful to try to characterize this discussion as being "them and us". It's not snobbery that leads me to disagree with you - the science of DoF is easily provable. Neither is anyone willfully misunderstanding you because you haven't 'spoken in the correct filmy speak'. You've made your point quite clear, it's just that I, and I would assume, others don't regard what you are suggesting as being a viable solution.

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Chris, I understand perfectly well what you are saying. What I don't understand is why you think that essentially shooting everything wide is a useful option. You may well get a shot, but unless it's the shot you need, what's the point? When the Editor says 'did you get a CU on his reaction?' it's not really much help to say 'no, but we've got it in a wide'.

 

I also don't think it's very helpful to try to characterize this discussion as being "them and us". It's not snobbery that leads me to disagree with you - the science of DoF is easily provable. Neither is anyone willfully misunderstanding you because you haven't 'spoken in the correct filmy speak'. You've made your point quite clear, it's just that I, and I would assume, others don't regard what you are suggesting as being a viable solution.

 

Some of the things you've said here show me that you haven't carefully read what I've said (and maybe I'm at fault of the same with you). I wont do that endless quoting of myself and you trick that you see here occasionally and just deal with one particular example, I never once say that shooting everything wide is a useful option, I think I'm fairly balanced about it, to paraphrase myself I suggest its a consideration (among others), and that it would give you a FOV change and that it might be "completely unsuitable".

 

Perhaps ask yourself why you: "don't understand why Chris thinks that shooting wide is a useful option" - you'll note among contextual editing I've removed the 'everything' from my quote.

 

Hopefully we're on the same page ?? I'd like to able to stop with all the underlining, caps and italics wink.gif

 

 

The them and us thing was me trying to illustrate that there might be a mindset amongst professionals that would lead to certain ideas about workarounds that are completely unsuitable for lower-budget filmmaking - the reverse is probably even more pertinent as they dont even have the advantage of memory of how it used to be when they started out... But remember sometimes a directors hand is forced by the limitations of the equipment at hand, so you try to make the best of it, and there aint no better way to prepare yourself for these situations than having a near as can get complete understanding of what you're dealing with. This forum is visited not only by the bleeding edges of both ends of the spectrum but also everyone else between, I was trying to provide some balance - and yes, it true sometimes I'm unclear, its a hard thing to describe and I was at fault to think that people would fill in the gaps of missing technicality with the same understanding.

Edited by Chris Millar
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Perhaps ask yourself why you: "don't understand why Chris thinks that shooting wide is a useful option" - you'll note among contextual editing I've removed the 'everything' from my quote.

 

Perhaps I should have said 'shooting everything wide with that lens' which is what you would have to do if you want extra DoF. As we've already agreed, the moment you move closer to your subject to shoot tighter coverage, you start to have the same DoF problems that you had on the tighter lens. So by definition, you must be shooting wide.

 

Maybe we should properly define the problem, before we decide whether this is a solution. If your problem is that you need to shoot a CU, but you don't have the DoF you want, then slinging on a 16mm and shooting a MED is not the solution, because you still don't have the shot you need. You have all the rest of your coverage, but you don't have the CU that tells the story. In all the time I've been shooting, I have never met a director who has said 'the DoF in the CU is too shallow, give me a medium instead'. It just never happens. In this context, composition trumps DoF every time.

 

Now, If your problem is merely that you have to get a shot, any shot then yes, this is one alternative, but it's not a situation I have ever found myself in.

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No, it won't, for all the reasons that have been quite comprehensively explained above.

 

Using a faster film allows the use of a smaller aperture. That's just logic...there's no deying it. If you use a film stock that's one stop faster compared to another film that you were using in a previous scene, you would close down the aperture one stop more than what you used in the previous scene. If you use a film that's two stops faster, you would close down the aperture two stops. With a faster film stock loaded in the camera, it is no longer necessary to use an exceptionally fast lens. Point out where it has been comprehensively explained that this is not so?

 

If you were 4 feet from a subject, shooting a 25mm lens at f8 (enabled by the use of faster film or 'pushing' the film), this will give you more depth of field than using f4 on the same lens at the same shooting distance. Therefore, depth of field would be increased...not by a substantial amount of course. DOF is always compromised with short shooting distances. And by the way, I'm not insinuating that depth of field is of the highest preference here. Personally, I would prefer to have the correct framing of the shot and just be content with whatever depth of field I have available.

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sorry Chris, but Focal length has no bearing whatsoever on low light shooting. You don't suddenly switch to wider lenses because it's getting dark,

 

This reminds me of something quite amusing that Ive seen in a number of movies. One of the characters is doing a bit of spy work / espionage, photographing from some hidden vantage point at night. Typically, they are using a big telephoto lens (whose maximum aperture would not be all that generous in size), shooting with barely any light + hand held. And the resulting photographs turn out perfectly crisp, well exposed and grain free!

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Using a faster film allows the use of a smaller aperture. That's just logic...there's no deying it. If you use a film stock that's one stop faster compared to another film that you were using in a previous scene, you would close down the aperture one stop more than what you used in the previous scene. If you use a film that's two stops faster, you would close down the aperture two stops. With a faster film stock loaded in the camera, it is no longer necessary to use an exceptionally fast lens.

 

If you were 4 feet from a subject, shooting a 25mm lens at f8 (enabled by the use of faster film or 'pushing' the film), this will give you more depth of field than using f4 on the same lens at the same shooting distance.

 

I assumed that that you meant using both lenses wide open, where the difference in DoF between f1.4 and f.2 would be minimal. Obviously if you were to use a much faster film and/or push process it, you could shoot at a much deeper stop. Whether or not it would be advisable to do this within a single scene is different question...

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Yea, sorry I wasn't clear enough in my first post and that I mixed a few issues up. To be honest, I really wanted to leave the depth of field issue out of the discussion but found myself getting caught up in it!

Edited by Patrick Cooper
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the MCU on a 16mm and a 50mm will have the same DoF @ the same stop on the same format....

 

Let's keep this simpler; take a 25mm lens. Find out the DoF @ 4Ft and T2.

Now do the same for a 50mm @ 8ft and T2.

 

the 25mm @ 4ft T2 is 3' 8" to 4'5" according to my CineCalc spredsheet (from panavision) (9 INCHES DOF)

 

now a 50mm @ 8ft (2x the focal length, so we back up accordingly) @t2 is 7" 8" to 8"5" (9 inches!)

 

Same Dof.

 

Now whether you can move the 50mm away 8ft is another story.

 

 

While this looks to be true, this is misleading to what you are trying to answer. In regards to depth of field and how the bokeh effect would be resolved by going with a wider lens and maintain the same frame/composition.

While you have proven that the DOF/area in focus may be about the same at the compensate distances whar you haven't proved is that the background/bokeh hasn't change.

 

If the back ground is a flat plane at the same distance behind the actor/talent/object in focus the resulting image/bokeh would be less out of focus on the 25mm than the 50mm.

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If the back ground is a flat plane at the same distance behind the actor/talent/object in focus the resulting image/bokeh would be less out of focus on the 25mm than the 50mm.

 

You'll have some foreshortening effect, so the soft background elements will appear larger in the frame with the longer focal length, however the DOF will be similar.

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You'll have some foreshortening effect, so the soft background elements will appear larger in the frame with the longer focal length, however the DOF will be similar.

 

Exactly, what I refer to as less out of focus may be attributed to the fact the the background will appear larger or smaller depending on the focal length/FOV. Making things more or less discernible. Because the bokeh of lens can't necessarily be quantifiable, only in relation to itself in focus compared to the size of the frame. Make sense?

But even if the DOF is somewhat similar, numerically they show the DOF of a wider lens will always result in a background image/bokeh that appears to be more in focus even if it's only fractions of inches. :)

Edited by darrin p nim
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