why is it that people say that in order for a lens to be constant aperture, that the lens has to be larger and heavier, when you can just turn a variable aperture lens into a constant aperture by closing the aperture down?

Look, both halves of this are true. First:

people say that in order for a lens to be constant aperture, that the lens has to be larger and heavier

This is correct. If you could take your current 75-300 and hold it in one hand, and hold the Canon EF 70-200 f/2.8L in your other hand, the difference in size and weight (and cost) might astonish you. The 70-200 f/2.8 is much larger and much heavier (and much more expensive) precisely because it is constant aperture (well, also, it has much better glass, plus a much better AF mechanism).

And:

you can just turn a variable aperture lens into a constant aperture by closing the aperture down

This is also true. Except... you wouldn't be shooting f/2.8 at 200mm full telephoto. Get it? Some people want that. And they can afford it. And they don't mind the size and weight.

I've been telling you to "just turn a variable aperture lens into a constant aperture by stopping down" because you don't have much of a choice, my friend. There is no such thing as a constant aperture telephoto zoom to 300mm in a Canon EF or EF-S lens mount. The sole exception to this would be the Canon EF 100-400 f/4-5.6L IS, which would give you a constant f/4 from 100mm to 350mm or so. Beyond that it closes down to f/5.6.

I can't speak for Nikon, Sony or anything else in the APS-C / Super 35 image circle size, but I kinda doubt any of them have a constant aperture telephoto zoom that reaches 300mm. Maybe someone else who knows can chime in on that.

There are some 16mm cine zoom lenses, which also display the variable aperture when at maximin aperture, as do ENG zoom lenses and the zooms in video camcorders. The reason is to keep the sizes and weight down..

I saw some constant aperture zooms intended for 2/3" cameras (to be used on dramas) and they were much larger than the usual zooms made by the same manufacturer (with the same focal length) as found on ENG cameras. .

Look, both halves of this are true. First:



This is correct. If you could take your current 75-300 and hold it in one hand, and hold the Canon EF 70-200 f/2.8L in your other hand, the difference in size and weight (and cost) might astonish you. The 70-200 f/2.8 is much larger and much heavier (and much more expensive) precisely because it is constant aperture (well, also, it has much better glass, plus a much better AF mechanism).

And:



This is also true. Except... you wouldn't be shooting f/2.8 at 200mm full telephoto. Get it? Some people want that. And they can afford it. And they don't mind the size and weight.

I've been telling you to "just turn a variable aperture lens into a constant aperture by stopping down" because you don't have much of a choice, my friend. There is no such thing as a constant aperture telephoto zoom to 300mm in a Canon EF or EF-S lens mount. The sole exception to this would be the Canon EF 100-400 f/4-5.6L IS, which would give you a constant f/4 from 100mm to 350mm or so. Beyond that it closes down to f/5.6.

I can't speak for Nikon, Sony or anything else in the APS-C / Super 35 image circle size, but I kinda doubt any of them have a constant aperture telephoto zoom that reaches 300mm. Maybe someone else who knows can chime in on that.

Oh okay that's what I thought. But since being zoomed at 300 mm around has such a shallow deph of field, I didn't think it was possible to shoot an f 2.8 and still have the footage be usable because the depth of field would be way too shallow to fit more than one actor in focus.

so I didn't think I would be using f2.8 anyway therefore, or a wide f-stop at all.

I thought if i shoot under low light I would just get a camera there was good for it like the Sony a7s II or the Panasonic gh5 and then shoot at a deeper depth of field, unless there would be any reason not to?

Well the store was able to replace my lens since it was under warranty and they gave me a new one under store policy. But as far as getting a lens with an aperture ring goes, since I was going to get a new camera anyway, why not just get a camera where I can switch off the servo controls to the lens, rather than by a new lens with an aperture ring?

High end f2.8 300mm lenses have been available since the 1970s and used by sports photographers and film makers ever since.

As for the aperture ring, it really depends on your future plans and if you wish to buy a digital cinema camera, which commonly have an ISO of 800 when shooting RAW and log. If you don't know what these are (and their advantages), please look it up online, since I don't think a thread would be long enough to explain it to you.

If you plan just to shoot with a DSLR and are happy to get a camera that can set the aperture using manual mode (you'll need to check that you can do this with a particular camera) that fine. I don't think this involves switching off the servos controlling the aperture like you can the focus, it involves using the camera menus.

Personally, because it's intended for video rather than stills, I'd buy a f4 Canon 300 with an aperture ring and a range extender, but you seem to make a simple decision complicated.

Oh okay, I've tried shooting at a wide aperture on my lens but feel I need to close it down to around f11 to get a couple of people at least in focus.

What I mean is a camera where you can shut off the auto exposure system, since it was that that was causing the lens to change aperture when zooming, through the servo controls, unless I have that wrong...

I would want a camera where you can have full manual control during the zooming. Or I could get a video camera instead of a DSLR, but I do have projects I want to to do shooting on streets at night, where I can't light the streets, so I would want a good ISO, like the one the Sony A7s II has or something like that, probably.

The aperture setting should be on manual for drama, regardless of if you're zooming. You need to check that the camera can allow you to set that and that also lock the shutter, so that it also won't change.

My argument for the aperture ring is that it's quick to set and you're not fiddling with the camera trying to set the aperture. I lit a video that used a lens with no aperture ring on a GH5 and it involved some playing around and I'm still not sure if everything was under manual control. I wasn't operating the camera, bit there seemed be some compromise going on.

Oh okay, for sure.

On my camera I have full manual controls and have total control on the shutter, aperture, and ISO and it's all locked and won't change. The only thing I don't have manual control over, is the aperture changing while zooming, so I will want a camera where I can lock it while zooming as well.

I've used lenses with the rings while doing projects in a film school course I took. The one dis-advantage of the rings is that the ring was very sensitive to moving and if the lens was bumped or anything, the aperture would move, where as by setting the aperture in camera, it locks, unlike a ring.

But the ring I could probably get more use to. I just figure that since so many zoom lenses out there don't have rings, maybe I should just get the best one, and get a camera where I have manual control of the aperture during zooming, since I was going to get a new camera anyway. If I get a camera that has full manual control during zooming, then I do really need an aperture ring on the lens?

The ring can get know knocked? Well yes, if you are careless, but you just train yourself to do it. I don't think I have ever knocked the iris ring as it's close to the camera - I've done the focus ring lots, because it's at the other end and easier to move when you hold the lens up?

Why are you asking questions, then ignoring the multitude of comments?

You have a lens that is performing poorly from your posts optically, and physically. So when you buy a new one FOR VIDEO - buy one that:
1. Stays in focus when you zoom
2. Stays on exactly the stop you set it to
3. Has sharp focus
4. Is cost effective.

All 4, or nothing - but until you do, don't keep reinventing the problems you currently have.

If you plain just don't wish to hire the right tool, for goodness sake, buy one that will do what you say you need.

You NEED a lens that will allow YOU, or the camera to adjust the iris. It needs to be selectable - give control to the camera or keep it for yourself. Very straightforward.

Loads of lenses have servo control (I just won't use the 'fly by wire' term) and clearly for you these are bad, because it shows they are designed for photography not video. If you want to shoot video, buy video kit. How many photos do you take on your camera? As I have said, nothing would make me shoot video on my DSLR - it's simply awfully designed for moving pictures. Some, I admit can be optimised for this, but so many do video as an 'amateur' add on, and do it pretty poorly - other than maybe picture quality.

Okay thanks. Yes I will get a new lens, just still deciding. As for a new camera, which I also want, since I am not digging the T2i for other reasons anymore, I want a camera like the Sony A 7sII, which is good for shooting on the streets at night, when you can't light a whole street, since it has a high ISO, but I want a camera that a smaller sensor than full frame, like an APS-C sized sensor, cause then the shallow DOF won't be so sensitive, when shooting under low light.

Are there any video cameras, that would have those two features, plus no servo control limitations? :)

Ryan - I know little of the A7, but my colleagues in the Guild of Television Professionals here in the UK have been looking for users with their own recommended setups to solve the camera's noise problem in low light - dealing down to 400 equivalent, and they complain about the screen which is difficult to see in sunlight? No idea if this impacts on you, but thought I'd mention it.

Yeah when I used the Sony A7 s II before, the screen was difficult to see, especially since it has zero contrast in the image. I thought maybe I would use a monitor that I can add a higher contrast lut to, so the screen would be more viewable if that would make sense.

As for noise problems, I thought it did pretty good when I used it before. Here is some test footage I found on youtube, is there a lot of noise at night as long as there is light around?

Now I See: Sony A7S Low Light - YouTube

Here is also a short film project we shot with the A7s II:

Trioxin Commercial second copy - YouTube

The noise is a lot less in the lit street, but once you get to the cemetery, even though we lit the cemetery, there is still plenty of noise. So it seems that a lit cemetery will still have noise, but on the street, with streetlights, it's much better, but what do you think?

For me that is a LOT of noise and it's that unpleasant 'moving' type of noise. If that's what my friends are complaining about I can see their point.

Well I could use a program like Denoiser II to try to reduce it if that is best. I have a project I want to shoot which is undercover cops, surveying suspects, and it would be on streets at night. It's fiction of course.

I was watching a documentary on the making of The French Connection and they too, had to shoot on streets at night that the couldn't light all that much, so they said they shot at a high ASA and embraced it the grain that came with it, but should I do shoot in a French Connection style, and embrace a certain degree of noise then?

Buying a repair app to cure a problem with a camera - which to be fair wouldn't be an issue if you never wanted low light performance, is daft.

if you have a forthcoming project that needs low light capability, hire something or buy something with a good rep for being noise free. I can't believe you want to buy a new product and software to try to fix its issues?

Oh okay well it was suggested to me by others and everyone I know uses denoiser plug ins, so I thought it was fine...

But is there a camera with better quality high ISO than the Sony A7s II then?

Having shot thousands of hours using lenses with aperture rings, knocking it from the correct stop has never occurred. Also, sometimes you may wish to pull the stop during a shot and the aperture ring is the precise method of doing so,

Don;t use de noisier unless you really have to. Shooting with a high ISO should only be done if there's a really good reason to do so, For example, Professor Brian Cox on the BBC talking about the universe under a sky full of stars - the subject matter links in with the shots.

In most dramas the noise will be excessive and DPs want the best dynamic range and one limitation to this is having acceptable noise in the blacks.

"they shot at a high ASA" What be regarded as high ASA during the time of the French Connection would be the 100ASA film stock forced two stops at the most, That would give you 400 ASA, Film grain is aesthetically accepted more than video noise

How many times do you place all your faith in people who have proven time after time to offer very dubious advice. Denoisers, and I have used one myself just once - to repair something vitally important - are repair tools. They cannot make the picture better, they just remove artefacts but like all processing, throw away data.

I cannot recommend a different camera as I don't use DSLRs - but I respect my colleagues opinion and they like the camera apart from low light performance. Would you buy a car with known hard suspension if you have a bad back and buy a cushion to make it tolerable?

Ryan - this time, it's really for you to draw up the list of things you need a new camera to do, in some kind of priority and then use your skills to make the choice. I just find it very strange to pick a camera to do low light shots and because it does them poorly, spend a lot of money trying to fix something? That night time clip on a big screen is pretty horrid - did you really think that is acceptable, considering the tiny issues you are finding with otherwise good footage? I'd suggest you try to get somebody with the software to clean up that clip and see if it works - I have my doubts.

Well is there a camera that has good night vision that you can shoot streets without lighting them then?

For example, in the movie Skyfall, how did they shoot this scene, without lighting the city, and they just used the natural light, and not have any noticeable noise:

Skyfall - Shanghai (1080p) - YouTube

As to whether or not I think the footage is acceptable, I am not sure. I need to see more indie films shot at night that got distribution I guess, to know what is acceptable then.

They shot the film with an Arri Alexa, using RAW, which usually rated at 800 ISO. I gather the aerial shots were shot on a RED Epic, which has a pretty similar ISO. Certainly there's no extreme ISO involved and digital tends to be very good in the blacks, while film is good at the highlights. so nothing surprising.

I've shot on the city streets with very similar rating and a small lighting rig, so you don't need an ISO of 12,000 to shoot at night.

It's a balance, otherwise your highlights start to blowout

Oh okay, so when it comes to shooting city scenes like that with no extra lighting, and just using the street and building lights, what kinds of cameras would be good for that, that would be around a similar price to the Sony A7s II, if any?

If being serious about dramas I'd look at the new Blackmagic Pocket Cinema Cameras. https://www.blackmagicdesign.com/uk/products/blackmagicpocketcinemacamera https://www.provideocoalition.com/review-blackmagic-pocket-6k/

It seems you need Infra Red corrected ND filters on the new camera, but that's not unusual these days with digital cameras and high density ND filters, (although the situation is improving).

I saw a student film shot on the very first camera Blackmagic made, which was shot last year and it looked really good, with a nice sense of style. Made by an 18 year old student, it certainly didn't look televisual and it wasn't in scope either. The new cameras are a lot better,

Oh okay, but even with that camera, if I want to shoot on downtown streets at night, I will probably have to find some way of lighting the streets, even without permission then, no matter on the camera, is that right?

Absolutely not! have you seen how much lighting is required to light large spaces - Inverse square law applies big time! Some cameras perform well in low light - some, er, less so.

Oh okay, so what would be the best approach, budget wise, if the story calls from some night street scenes, but cannot be lit at the expense that a big budget production would go?

I thought about getting creative and maybe a camera like the Sony A7 s II, or something with that high of ISO might do it, but if not, what would be the best approach then?

So we’re moved on to cameras that can film in the dark? That’s easy the Sony A7 series of course it records in compressed 8bit. The black magic pocket cameras are not intended for low light and use a smaller sensor but record in 10 bit raw/Prores allowing for a proper color grading.

Oh okay, but would low light be more important than the bit size though, in low light shooting cases?

Night scenes really depend on how bright the street lighting and other lighting (eg shops). I've rarely gone beyond 1500 ISO with these and I've done with less using high speed lenses.

You should be thinking of using small portable lights - battery powered LEDs would help for the closer shots. Small generators are useful and can be rented. Some of these are pretty quiet, but not for shooting dialogue beside them. Locations where you can access power are useful. BTW All this is possible on an extremely low budget film, you just need to be organised. Depending on local regulations, you may need a permit, but you may get away with just chatting to the local police.

The new Blackmagic 6k has two 2 native ISO settings: 3200 is the highest. You can see a test in the link to Provideocoalition above.

I feel that small lights will be good for close ups, it's just the wide shots that establish geography that might be a problem to light.

I have a scene at night where the police are surveying suspects, and it builds to a stand off and shoot out. But that kind of a scene would need a lot of establishment of geography, and don't think I could have the viewer make sense of it, if it was entirely in closer up shots, because of the lights not being able to light whole large sections at night, if that makes sense?

It depends where your street nights as to how large an area they'll light. You should pick your location carefully. Modern street lighting is surprisingly bright.

Be aware that if you go too high an ISO the lights on the police cars will blow out causing highlight issues and flares, it's a balancing act.

I would go for the largest lights you can get, 2k lights will do a pretty large area at 1500 ISO when combined with location lighting. Small lights involve a lot more rigging and moving around.

Okay thanks. I noticed that the traffic lights are also blown out too, but not sure how much the audience will care about something in the background more so being blown out.

But on topic of the lens though, if I closed down the aperture so I can have a constant aperture while zooming, wouldn't it get darker as I zoom because the longer you make the lens, the slower the light travels into it?

I thought this is the reason why my camera is turning up the aperture when I zoom, because it gets darker the more you zoom, so the camera turns it up more as a result. Wouldn't the lens exposure get darker, the longer you extend it?

The speed of light is a constant.

You should go through the explanations earlier in the thread again and think about the mathematics of how f stops are calculated. Bear in mind that for longer focal lengths you need a bigger diameter than short focal length lenses, so if your iris diameter is correct at the short end when wide open, the front of the lens is not going to be large enough for the long focal length in a compact lens, so the latter going to be effectively stopped down because the diameter of the lens is acting like an aperture for setting stops.

BTW Don't use zoom lenses on your night exteriors, you lose too much light with large sensor stills camera zooms because they're slow lenses. F1.4 to f2 primes is what you should be using.

Okay thanks, I only have two night sequences in the script and can restrict the zoom lenses to the day scenes then if that's better. It's just that is why I thought a camera with good low light vision, would be good, cause then the ISO can be high enough to shoot at say, f8 or something like that, where you can fit more actors into focus, with a deeper DOF.

As for a constant aperture, it's just that when you zoom, the lens becomes longer, so I thought it would take light longer to travel through the lens then.

As long as the aperture remains constant, if I buy a lens with a ring. If I buy a lens with a ring, will their be any hidden surprises that will make it less usable, or any hidden catches with it at all? Or will it perform perfectly with no hidden catches, as long as I am stopped down enough?

Well - if the lens is longer, it does taken light longer to travel down it. If the lens extends 100mm, then it takes an extra .3335 nanoseconds longer to get to the other end - but why does that matter?

I thought that it matters because the longer the lens gets, the slower it will take for light to travel through and hit the sensor. Isn't that why the camera is using the auto exposure as I zoom, cause it is trying to make up for the light slowing down, as I zoom in closer?

No it just gets dimmer, and that is why the camera tries to compensate.

Did you read Brian's excellent explanation up the topic? Explaining why the iris functions oddly when the focal length gets longer. Worth going back and trying to understand it. you can actually see this in action of you hold a proper lens up to your eye and close and open the iris. Because your eye is only looking through the centre rather than the full field like a sensor, you can see the change in brightness as you zoom. This is what the camera tries to compensate for. google lens ramping for more info, but Brian's post explains it quite simply.

Oh okay, I went back and read it, but this is also what I was not understanding before either. If zooming in causes the image to become dimmer, how does stopping down help be a constant aperture then? Wouldn't it still get dimmer as you zoom?

no - the best I can explain is that of the the overall light that gets to the sensor, through the lens has a pretty strange distribution. As you close the iris, you reduce the light getting through at the edges, working to the middle. The trouble is that at the longer focal lengths, there is very little light at the widest part, so if the lens is stopped down from say f22 to it's specified largest aperture f2, it can be that once you get to f3.5 closing further has little effect, because there isn't any light at the edges to iris out! It suddenly becomes ineffective. If the lens is zoomed out, then the level can be reduced between f3.5 and f2. The practical upshot of all this is that when you have the iris closed so you are only using the centre of the glass, you can zoom through the entire range and there is no drop in light level, but when you use the iris wide open, at some point the light starts to drop off as the focal length increases. and there is no light path that the iris can uncover to recover the brightness.

You'll notice that lenses that have a larger diameter are usually 'faster' - the larger diameters of the glass lenses let more light through. They can manage to function properly in a linear fashion. My Sigma lens is a good example of compromise. It looks quite large in diameter but as you zoom in, the front extends and you can see the diameter of that section is quite small - so at full extension the light has gone down quite a bit, and the camera can compensate in stills by adjusting the shutter opening time to recover the light. Doesn't matter in stills but in video the ramping is obvious. I don't think I've done a great job explaining this to be honest but without spending much longer, it's the best I can do for the moment keeping the language and the physics simple. For the people who know lens physics, I apologise for simplifying some of the actual physics, but it's all about tube diameter, and the clusters of lenses inside the package.

Okay thanks. I understand parts of what you are saying, and just trying to process it.

So would a lens that is not constant aperture though, but has the ring and no servo controls, be able to remain constant aperture, or no, if longer focal lengths, means less light is getting in, at the edges?

The long lens needs a larger diameter hole to let the same quantity of light through than the short focal length lens, but if the lens is too small a diameter the amount light coming through is reduced at the long end of a zoom lens compared to the short focal because of this, This is because the front of the lens itself is also acting as a stop aperture, restricting the quantity of light at the long end of the zoom.

As you stop down using the stop aperture a point is reached where the light passing though all the focal lengths becomes the same because the long focal length is no longer being affected by the restriction of the lens' because of its small diameter.

It's just the mathematics of how f stops work (which involves diameters), if you can't follow it, just accept that when you stop down to the smaller stop in the wide open aperture range, the aperture is then constant at all focal lengths. You don't need to know the reason to use the lens.

How the exposure system works doesn't come into it, so ignore that. It can't bring in more light than the lens allows by the nature of its design.

Oh okay, that seems to make sense, thanks.

This is what I thought, but how come if I stop down to f8, like in the video I posted before, the aperture still goes down as I zoom in though? This part I wasn't understanding before.

In your example, the image content was not even, so maybe the small highlights passing through exposure measuring zones triggered it? Try it again on a plain grey background and see what happens.

As Paul says, your exposure system was probably not totally on manual, so it was still making adjustments. If you had set the aperture, it was probably making adjustments to the shutter speed.

These are two separate items, the lens and the camera. Remember DSLRs are primarily designed for stills photographers, so they may not be as convenient for operation as video cameras, especially older ones. Unless you really know the exposure systems you may end up switching from aperture priority to shutter priority (or the reverse) instead of going totally manual. That doesn't include Auto ISO, which is another setting you want off.

Oh okay, but I thought it was the aperture that is changing because if put the lens on a camera that requires an adapter, then it won't get brighter as you zoom in. So therefore, wouldn't it be the aperture that is compensating, and not the shutter speed and ISO?

We don't know how your camera is set up and given the variables you need to ensure that you're following the correct procedures.

DSLR Basics: 8 Easy Steps to Learn Manual Mode for Canon DSLR Cameras - Nature Photography Simplified (http://www.naturephotographysimplified.com/canon-dslr-basics-for-beginners-8-easy-steps-learn-manual-mode/)

The exposure changes that your video displayed wasn't characteristic of a lens issue because the exposure was intermittently changing during the shot. This was either due the lighting changing during the shot or the exposure being adjusted by the camera or the camera operator.

A lens exposure issues would be linear, not intermittent, unless you got some flickering flare from a light hitting the lens and that cause is external to the lens.

Oh okay, well the lens goes from darker to brighter, to darker to brighter every time I've tried it though, which is a lot of times as I've used in my shoots so far.

So if it was the lighting, would lighting in locations do this, this commonly, that happens every time?

You're not giving the the circumstances when this variation from bright to dark etc is occurring, so no one can give a response.

I know some of these schools are not good, but from the questions you're asking you should be requesting your money back from your film school, as well as getting the lens replaced.

Okay how am I suppose to figure out the circumstances though, like what can I do to figure it out? Do you mean the lighting circumstances?

As for the film school, they taught us on cine lenses, but I guess I should have asked what do you do if you don't have a cine lens in the end, and want to adapt a non-cine lens, and try to want to zoom anyway and what can I do therefore. But I didn't think to ask that, at the time of school, since I was use to learning on their cine lenses.

The lighting circumstances would be if there were flickering lights or a transient sweep of a light that would cause a change of lighting levels in parts of the image that could be mistaken for an exposure change during the shot.

It was the lighting question that left me wondering about film schools, not the lens stuff.

You still haven't given the circumstances when this "darker to brighter, to darker to brighter every time I've tried it" is occurring. If it's at f8 and doing the same thing as in your video, you should possibly get the camera checked together with the lens, especially if it's happening against a gray card or a plain wall with even lighting

If it's when the zoom lens is wide open, you'd expect it to get darker when you zoom in and lighter when you zoom out, it's doing what's expected.

Yes I mean when it goes darker to brighter, darker to brighter, every time I zoom, it happens exactly as you see in the video. I haven't done it under flickering lights. I've done tests in different places, and in the video you see, there were no man-made lights, and that test was done under sunlight shining in the windows, but no indoor lights were on.

I just did another test at f22 in under different lights, and even at f22 it still goes darker to brighter, darker to brighter again, just like in the video.

I took the lens off the camera, and looked through it with my eye as I zoom on it. When I do this, the brightness remains the same through the zoom as far as I can tell, looking through it. Same when I put an adapter, in between the the lens and a different camera. Then the exposure is consistent. If I hook it up to my specific camera, without an adapter in between, then it goes from brighter to darker, and repeat, like in the video.

Thennnnnnnnnn it sounds like you have an auto something engaged on your particular cam somewhere deep in a menu. Godspeed.