On documentaries long focal length lens will be eye focused and this can also be the case on dramas, depending on the subject matter. The 1st AC may also get their focus marks by doing this, because it's not practical to use other methods.

Oh okay, I thought I could use the same camera and lenses for every project, as long as I had versatile equipment...
There’s a considerable difference between videography and cinematography when it comes to gear and staffing.

The biggest difference in workflow is that in cinematography you (or someone) is in control of the set. Blow a shot? Do it again. Relight. Discuss blocking and characterization. Emotional context and subtext. Whatever.

In videography you are not in control of the set. There will be no retakes. There will be no AC. You just have to nail every shot, usually working alone.

The OP’s wildlife shoot is different than the indie-style features and shorts projects described in previous posts. The latest greatest AF is really going to help for wildlife - that’s going to be on a fly-by-wire focus controlled lens. Use of super-telephoto lenses is a common need for wildlife - it’s a basic tool for such work.

So, no, although one may find oneself using a common set of tools for a particular kind of work, no one set does equally well at all of it. And, the gap between videography and cinematography is particularly wide, even wider for wildlife work.

Rentals! In the professional world you make your gear purchase decisions primarily on the basis of whether you will make money or lose money on it. And, sound, grip and lighting tends to age better than cameras, where technology is changing so quickly.

Yeah I would rather just do directing since it's what I am use to, with a collaboration of others, rather than nail everything myself.

As for lenses though, I was told by a cinematographer recently that the reason you hardly see any microbudget indie features use telephoto lenses, compared to Hollywood, is that lower priced DSLR telephoto lenses, are just not sharp enough to be acceptable.

Do you think that's true though, and there is no way to get a softer look in telephoto to be acceptable?

Compared to Hollywood? Can you get Hollywood sharpness from budget kit? Of course not, but you can get big improvements with sensible increases in bottom end budget. Good glass, for professionals or amateurs has never been cheap. Look at a sports event. The canon grey sports lenses. Why are they using them? The answer is pretty obvious.

Sharpness isn't just about using a test chart. It changes. Sharpness at the centre, sharpness at the edges, or somewhere in between, and then sharpness at certain focal lengths and then sharpness at different apertures. Cheap lenses might if you are lucky, do a few well.

Years ago, we had people experimenting with x2 adaptors for stills, and some being happy, while others found the sharpness drop off unacceptable. Another choice for you personally, Ryan. Does it pass your test? I suspect most people have a quality standard that is based on a mix of gut reaction alongside what their eyes tell them.

I wonder when you ask opinion from knowledgeable folk, you forget to ask the important supplementary question. WHY? Their answers will be very useful when it starts with 'because'.

If you've got a limited lens budget, you are better spending the money on a used higher quality lens, rather than buying a low priced new lens.

A few years ago I saw my old Zeiss Contax f 4 300mm (fitted with an Aaton film camera mount) being sold online for a lot less than I paid for it new. It was still more than you paid for your current lens, but I gather they go for $300 (Contax mount). Downside it's a big heavy lens, with a 300 degree focus (as loved by 1st ACs, but not photographers) . However, you may need to factor in lens adapters when using lenses with older mounts.

Contax Carl Zeiss Tele-Tessar 300mm f 4 - YouTube

Good glass isn't going to be cheap and unless there's either an obsessive cinematographer with deep pockets or a revenue stream for the gear on paying projects, it's unlikely to be around on freebie projects.

Oh okay. He also said that Nikkor lenses were better and I should check out those, but he has doubts they would be sharp enough at 300.

What about this one:

https://en.nikon.ca/nikon-products/product/camera-lenses/af-s-dx-nikkor-18-300mm-f%252f3.5-6.3g-ed-vr.html

Or I could invest in an even older, more high quality lens perhaps, just worried they may be damaged since they are used, and there is no warranty on them or anything.

the reason you hardly see any microbudget indie features use telephoto lenses, compared to Hollywood, is that lower priced DSLR telephoto lenses, are just not sharp enough to be acceptable.

I think the real reason telephoto lenses aren't used much in micro-budget indie features is that most scripts simply don't call for them.

In feature filmmaking, no matter what the budget is, the shots that require a telephoto lens are nowhere near as common as the shots that require a wide or medium focal length. Think about it.

If the shooting script calls for a long focal length, you rent that lens for a day or two. Done.

just worried they may be damaged since they are used, and there is no warranty on them or anything.

This is yet another reason why rental is always the best way to go.

Most pro cinema houses require insurance, and therefore they build that cost into the quote so that you have nothing to worry about from the moment you pick it up until you return it.

Some photo houses offer insurance as an add-on, not already built into the cost. You always take it though, especially since it's only a few extra dollars. Well worth it to be completely covered.

You can always get your own gear insured, but it's expensive. Your homeowner's policy most likely will not cover you in the event that you were "out shooting a movie with some folks."

The film and TV industry standards are the Canon telephoto lenses. Telephoto lenses tend towards contrast for best results, and the Canon L series primes are designed for full frame 35 mm film resolution, which is pretty similar to what you're using for video. These are the white coloured lenses that Paul mentioned earlier seen at every sporting event.

You buy Nikkor lenses if you want, however, you can't make a general statement about one make being better, because there will be variations across each lens in the range. Also, each brand will have a characteristic "look" that may be desired, so be wary of people saying one manufacturer is better than another without going into details. What matters is the lenses giving you the images you want..

The prime lenses will usually be better image quality than zooms.

The build quality on these lenses is a lot higher than the new low cost lenses you can afford. Test the lens before you buy them, or have a return arrangement if you buy of eBay etc if they goods aren't as described.

You need to test the lenses yourself, or at least look through the in depth reviews that give you a chance to sort things out initially. In the end testing, is the only way to make a final decision, if only by looking at film you know has been shot by a particular lens, Don't take anyone's word at face value.

The standard workhorse zoom lenses are in the 18 to 100mm range, the main prime lenses are also in the same range. You can shoot a feature film mostly using just one focal length, some directors are well known for it. One film I worked on was shot with a 16mm lens on Super 16.

What about this one: https://en.nikon.ca/nikon-products/product/camera-lenses/af-s-dx-nikkor-18-300mm-f%252f3.5-6.3g-ed-vr.html

Looks like this lens has very good reviews from still photographers.

Just be sure to do some deeper research regarding its use for video, though:

Focus Breathing -- of interest mostly to cinematographers focusing back and forth between two subjects, the image from the Nikon 18-300mm f/3.5-6.3 VR gets smaller as it's focused more closely.

Source: Kens Rockwell (at https://www.kenrockwell.com/nikon/18-300mm-vr.htm)

The B&H link for this lens is https://www.bhphotovideo.com/c/product/1045736-REG/nikon_2216_af_s_dx_18_300mm_f_3_5_5_6g.html//BI/2855/KBID/3801 (https://www.bhphotovideo.com/c/product/1045736-REG/nikon_2216_af_s_dx_18_300mm_f_3_5_5_6g.html//BI/2855/KBID/3801/BI/2855/KBID/3801/BI/2855/KBID/3801/BI/2855/KBID/3801/BI/2855/KBID/3801)

If you choose to go this route, you'll need to purchase either a Nikkor-to-EF mount adapter, or a Nikon DX series DSLR.

You'd need to check if the focus ring moves continuously, that the Nikkor doesn't seem to have a focus scale doesn't sound positive in this regard. It's probably a varifocal lens, so don't plan to use it for zoom shots.

Okay thanks. Perhaps I can do without the zoom as long as it is good in other quality.

I think the real reason telephoto lenses aren't used much in micro-budget indie features is that most scripts simply don't call for them.

In feature filmmaking, no matter what the budget is, the shots that require a telephoto lens are nowhere near as common as the shots that require a wide or medium focal length. Think about it.

If the shooting script calls for a long focal length, you rent that lens for a day or two. Done.

The price it costs to rent a lens and have it shipped, I figure I could just by a lens that zooms up to 300mm and I can have it for any shoot date I want, rather than the rental store's availability schedule I figured.

The feature film I am budgeting is a horror thriller script, so I thought that a lens that zooms up to 300mm would be good for quite a few of the shots, because during the running chase scenes, I can pan with the actors for probably 3 seconds or more before they start to go further away, thereby making the chase more exciting. Kind of like the running scenes in a movie like The Good, The Bad, and The Ugly, or Seven Samurai, or something like that.

Or with a lens that long, I could have shots with lots of compression in such as a character pointing a gun towards the camera, but the pistol is small compared to the face, in a face close up. You don't get that with wider lenses.

Or I could do OTS shots which makes two actors look like they are sitting really close to each other when it calls for such a shot.

Shots like those are what I wanted a telephoto zoom lens for.

In my opinion 300mm is too short for a wildlife lens. Your mileage may vary.

An excellent stills lens for video that covers telephoto shots like you describe is the Canon EF 70-200mm f2.8 IS mk 2.

Please excuse my contrarian opinions. I don't care what people say. I say test-test-test and see what works for you. "A filmmaker I talked to said..." carries no weight with me. Did your 300mm with the spot on it actually get the shot you wanted?

Ryan, with all respect to the many pros on this forum who have contributed their decades of experience in this and other threads, you are now swimming in a sea of opinions and others' experiences. What I call "internet truths". They're not like the truths you can discover through shooting. They're not like the learning you get through experience.

Fly-by-wire lenses all bad? No, in my experience. Will ACs and DPs whine about your lenses? Yes, whether they're fly-by-wire or not.

If you have a prime the DP will want a zoom. If you have a zoom the DP will want a prime. That's part of working with people.

Would you do better with Nikon still lenses? Older nikons can be great, but so are a lot of the classic lenses. Contax. Pentax. Rokkor. Get some, polish them up, get them cleaned-lubricated-adjusted and declick the apertures while you're at it. Then the next DP you work with will say "Nikon, huh? Well, those aren't bad, but, I just worked on a project with these amazing vintage Contax lenses, you should get those! Want me to call and see if we can get them?"

You've dismissed rentals as difficult to schedule and expensive to ship. There are many working pros who differ, but if you want to own more lenses you should buy them!

What do you like? What shots speak to you? Ask that question of the contributors here and you'll get hundreds of answers, including: Vintage Nikon primes, primes not zooms, zooms not primes, must be PL mount, can't work without a mattebox, never use one, it goes on and on. And we haven't even gotten to cameras and lighting yet!

Yeah for wildlife it's too short, but this wildlife project is just a one time thing I think I still want a lens for future projects, and thought at least 300mm would be good.

I wanted one for a feature film project as well, and it's a horror thriller, where I wanted to do some chase scenes on foot, and use it for that. What focal length is this lens in this clip:

telephoto lens shot example - YouTube

It looks to me to be at least a 300mm and I want shots like that for the chase scenes, if my current lens is not up to snuff for that.

Ryan, you are going over old ground again that shot was covered in another thread, this was probably shot at 250mm using a 25mm to 250mm zoom lens, a pretty standard piece of kit on a feature film of the period.

If you're concerned about warranty, specialist dealers often sell older lenses with a short warranty e,g. 3 months. I checked such one site and there are quite a few very good and excellent 300mm lenses in your price range. There are also 400mm, plus 600mm but these are more expensive. With some dealers you can go and test the lens before purchasing it.

Buying a cheap lens instead of renting a high quality. professional grade lens is a false economy, which can effect the quality of your film.

With these long focal length lenses you also need a good head and tripod. However, that's something worth having regardless of this.

Sorry, yes you're right, we did.

As for the possibility of zooming during the shot, I was advised before that if the lens is varifocal, to pull focus during the zoom. What if I got a lens that also has an aperture ring. Then I could have someone pull focus, but also have another person turn the aperture ring while zooming, so the aperture remains constant. Would that work?

No, the lens will probably go out of focus because it's a varifocal lens.

Stopping the lens down will avoid avoid aperture ramping, it usually occurs when the lens is wide open and usually disappears when stopped down one or two stops.

If you're tallying about the 18 to 300 mm Nikkor, it's a still lens, personally I wouldn't even consider it as a video lens unless I was really stuck for a lens and there wasn't any other options availble on the day. I wouldn't zoom with it, but regard it as a variable prime lens, so no zooms in shot.

Then I could have someone pull focus, but also have another person turn the aperture ring while zooming, so the aperture remains constant. Would that work?

Good heavens. No. That would *not* work. Think about it for a minute. Can you see how that isn't possible?

Instead, as Brian mentions above, the way you handle a variable aperture lens is to simply adjust it for constant aperture.

Do this by setting the camera's aperture to match the maximum aperture value at the telephoto end. As a result, your variable aperture zoom is now constant aperture.

For example, let's say your zoom lens is f/3.5-5.6 -- set your camera aperture to f/5.6 and now the lens will not ramp aperture during the zoom.

Okay thanks, but I already tried that, where the aperture is on the same setting from the beginning of the zoom till the end of the zoom, but you can still see it changing. Here is a test I did at f8, and it was on f8 the entire time:

aperture zoom test - YouTube

As you can see the aperture changes during the zoom, even if it's on the same setting. Something about the zooming is still changing the exposure, isn't?

Sure it's the lens and not your camera in some auto exposure mode that is messing it up? If it is the lens, then you're stuck. The test on this would be a simple one. set the focal length and move in closer, not zooming and see if the highlights changing in the background trigger the same response.

It doesn't look like aperture ramping, that gets darker as you zoom in, it doesn't get lighter and you don't have variations. As Paul suggests, it's probably the auto exposure system on the camera.

Oh okay, but what auto exposure system would that be, or is there a way to turn that off perhaps? I know it's not the ISO cause I had it locked on 800. Is there a way to turn off that system?

What camera is this again? Are we talking about the Canon EOS Rebel T2i?

Sorry, yes that one. It appeared to have the same problem on the sony a7s II though.

Check your auto exposure settings on both cameras, go through the menu settings to ensure that the exposure is totally on manual. You may need to go through the camera manuals to find the required menus.

Yep its totally on manual. I dont have the sony now but the t2i is. What now though if its on all manual yet it still does that when zooming?

Don't create a problem that may not exist, that's the purpose of the test to prove, If the camera is totally on manual exposure the characteristics of the lens can be seen, rather than the inputs from the camera's exposure system.

The exposure variations match the exposure system making adjustments, either that or the lighting is changing during your shot.

Don't zoom, move the camera. Something is clearly causing it. The lens is changing the iris aperture or the gain of the camera is doing it. Has to be one or the other. You need to find out which it is.

This lens does seem to be a very unfriendly and uncontrolled beastie - all things considered, you need to get something better.

Okay thanks. Well I know it's the lens changing the exposure, cause I just borrowed the Sony A7s II to try it, with a couple of adapters. One of the adapters communicates with the lens, and the other is not electronic and does not.

The one that doesn't communicate the lens with the camera, the aperture is constant throughout the zoom and doesn't change. But with the adapter that does communicate with the camera, the aperture changes, even though it's on the same f stop setting throughout the zoom. So the lens being powered by the camera is causing the exposure changes, cause if you cut off the power between camera and lens, then the aperture is constant.

That sounds a good reason why you should use dumb lenses for drama or other video work where you want total control of the exposure. Cine lenses don't have such auto exposure features (with a couple exceptions for use on the Arri 16 SR film camera - the mechanical control pins could get jammed if you changed the lens mount. It happened to me on a new Zeiss zoom lens, so they were removed by the dealer) .

The alternative is to get a dumb lens adapter, so that the lens doesn't communicate with the camera.

Okay thanks. But the problem with a dumb lens adapter is that you cannot control the aperture, if you want to change it, since the lens does not have an aperture ring.

Are there any adapters, where the power can be switched on and off, so that I or a DP can switch the aperture with the lens, but then turn off the power to the lens after?

That's one reason why people were telling you to buy manual lenses for video work, otherwise you have to fool your camera's auto exposure system to get the stop you want.

ND or neutral density filters are the standard tools for getting the stop you want, since they don't change the shutter speed or the sensitivity in the process.

Indeed, and any lens you cannot control manually is a real limitation. Real video lenses have a manual or auto switch for a very good reason.

Come on Ryan - time to retire that lens and buy something that can do what you need.

Okay sure but i thought it was the camera changing the exposure since the lens does not change it when not attached. Shouldnt i get a new camera tgat doesn't change the lens's exposure as you zoom?

Many people on a budget buy used lenses, some of them prefer the older glass because of the look. Plus you can get lenses with an aperture ring.

Buying from an established dealer reduces the risks and, as I mentioned, will usually have a short warranty.

We were discussing aperture ramping, which is different to what the camera auto exposure does. If you wish to buy a camera that's designed/useful for digital cinema, you'll need lenses with aperture rings.

Oh okay but i thought the camera was telling tge lens to ramp up tge aperture, and therefore, its the camera thats doing it, not the lens.

In your test video the camera's auto exposure system was controlling the aperture. That's nothing to do with what happens with a max aperture f3.5 to f 5.6 zoom lens and avoiding this change called aperture ramping, which was the subject of the discussion.

You should reread the earlier posts which explains it.

Lens with no aperture ring are designed for the camera to control the iris in the lens. This is fine with stills cameras where you can also use the shutter for the exposure etc and each still photograph is complete in it's own right.

With higher end video work you don't want this, you need manual control of the iris so you can set the aperture. If you've lit a scene, you don't want the camera going off and automatically doing it's own thing and hunting the exposure during a shot.

Oh ok i see. But since my t2i is so old and not the greatest camera, i was thinking of upgrading the camera though. So what about getting a camera that does not have an auto exposure system and is all manual control? Would that be good, since i was going to get a new camera anyway?

I suspect you won't be able to get a DSLR without an auto exposure system., however, you may be able to override it in manual mode. How practical it will be for shooting video is another matter, the requirements for stills photography and video, especially high end work like drama are different.

You can get digital cinema cameras without the feature, but you'll need to use lenses which have an aperture ring in order to set the stop. This is a lot faster than setting the aperture using the viewing screen on the back of a DSLR in manual mode, while keeping the same shutter speed.

Alternately, you could use a dumb mount adapter (if required) and fit one of these lenses on your current camera .

Your current camera and changing it was discussed in an earlier message, if you wish to use it for shooting video that's worth considering..

Okay thanks. Well I was going to get another camera soon anyway. The T2i is full manual control, accept for during zooms it seems. Is there a camera out there that has full manual control during the zooms?

I thought about the Panasonic GH5 based on some other recommendations, and I was told it was invented for video in mind as well as stills, and not just primarily stills, if that's true.

But does the GH5 have full manual control when it comes to zooming, even with an adapter that is not 'dumb'?

It's just if I get an old vintage telephoto lens with an aperture ring, I am worried that the look of it, will not match my other lenses, if older lenses have a different look to them. So if I get an older lens, with a ring, does that mean it won't match my other lenses?

The aperture controls are the same for prime and zoom lenses, there's no difference.

Don't get confused with the aperture ramping that you get with many zoom lenses when they're wide open

This is a compromise used by designers to keep the physical size down. As mentioned earlier, this is the outside diameter of the lens acting like a stop aperture at longer focal lengths. F stops are calculated using a formula that has focal length over the diameter so "A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A 200 mm focal length f/4 lens has an entrance pupil diameter of 50 mm",

If the physical outside diameter of your lens at 200mm is less that 50mm, you wont be at f4, it might be f5.00 for example, so that will affect your exposure, even if the aperture iris is set at f4 and is correct for shorter focal lengths.

However, if you set the lens aperture at f5.00 in this case, the aperture will remain the same throughout the zoom range because the effective diameter is now the same for all focal lengths.

Here's an example of a cine zoom lens that has no ramping: https://www.angenieux.com/collections/optimo-style-spherical-lens-line/long-lens-zoom-optimo-style-25-250/

This is nothing to do with your automatic exposure system changing the exposure as you zoom into lighter or darker areas of the wider shot. That's what these systems will do if you physically changed the lens to a longer focal length instead of zooming in.This won't happen with a manually set exposure.

If you buy the same make of lens it should match pretty well with the newer ones, so if you've currently got Canon lenses buy those..Don't buy a Zeiss lens and use it with a Tamron, the Zeiss lenses have a look of their own. It's better if you can compare the lenses when you buy them. The high quality older lenses will produce better quality than your current 300mm lens.

If your lenses change the light passing through in the same way they look the same, some lenses do add things like colour shifts, but of course they shouldn't. In professional quality lenses, you should be able to mix and match for optical reasons, not age ones! This is why people protect their glass investments because a nice lens that works well and is friendly in how it interacts is worth hanging on to when you change cameras. In broadcast, working with different brands and types of lens is everyday stuff and your concerns would be considered a little strange? It is not only old lenses that have real mechanical control. Vintage glass or modern glass can have proper iris controls. The problem is when the servo control is poorly designed.

Canon 300mm lenses have been pretty standard in the industry for many years and they've been mixed with other makes and age of lenses on a wide range of productions. A used 300mm f4 Canon should do the job without getting into the thousands for a used 300mm F2.8 Canon.

However, if you set the lens aperture at f5.00 in this case, the aperture will remain the same throughout the zoom range because the effective diameter is now the same for all focal lengths.



Okay thanks, but I'm confused. What do you mean exactly by this? If you are saying that the aperture should remain the same throughout the zoom at a certain fstop, then why is the camera changing the aperture during the zoom it seems, even though it says the aperture is the same throughout?

If the lens is doing aperture ramping cause of how the lens is built to keep the size down, then why does it do the aperture ramping only when attached to the camera, but not if there is an adapter between the lens and the body? Sorry, there is just something in the concept that I am not understanding, and trying to pinpoint what that is.

If I get a zoom lens with an aperture ring for example, will it be a constant aperture throughout, or does the lens have to be a certain size then? Is it about the ring that keeps the aperture constant, or the size, or both?

Sorry, there is just something in the concept that I am not understanding, and trying to pinpoint what that is.

Yes indeed. We need to figure out what it is that you're not understanding. I think it would be helpful for you to go back and review the progression of this entire discussion thread. Plus some of your earlier discussion threads as well. It seems to me that you tend to circle back to cover a lot of the same ground over and over again, just as if the previous input didn't even exist, even though it's very plainly documented and very easy to go back and review. You really should consider taking the time to go back through the entire discussions that have been laid down not only here but several other threads as well (specifically the ones that you yourself have started). I think this would be a big help to you.

If I get a zoom lens with an aperture ring for example, will it be a constant aperture throughout...?

Not always, no. Some cine zooms that have manual zoom rings are variable aperture, and some are constant aperture. For example, take a look at this: https://www.dvinfo.net/article/buyers_guides/buyers-guide-canon-cinema-eos-lenses.html#cinezoom

The one on the left, which is a wide zoom at 14.5mm to 60mm, is constant aperture.

The one on the right, which is a telephoto zoom at 30mm to 300mm, is variable aperture. Both have manual aperture control rings.

Is it about the ring that keeps the aperture constant, or the size, or both?

It's the size. The 30-300mm mentioned above is variable aperture, very big, very heavy, and very expensive at $45,000. If it were constant aperture, it would be even more expensive, and prohibitively larger and heavier, too much so for practical cinema work. Therefore it is variable aperture. Does that make sense?

The other advantage of that particular telephoto zoom is that its front diameter matches its counterpart on the left (the wide zoom). Those two lenses are often rented (or bought) in pairs, and the same matte box can be used with either one because they both have the same front diameter. The benefit here is a faster set-up time during lens changes.

It’s amazing this thread started 6 pages ago about a spot of dust. You guys should be commended for limitless patience. I’ve recused myself from all things Ryan to preserve my sanity even though it’s taking all my self will to refrain from giving any advice. May your zoom be long, your aperture be constant and your depth of field always be shallow.

Hear hear Pete!

Speaking of lenses. I pulled out an old macro Nikkor lens to take some closeup photos of a garden spider. Turns out the aperture blades are frozen in the wide open position. Lucky I found a Youtube video detailing the disassembly and repair. Looks like I can fix it myself all I need is some time and patience.

Sorry, what i dont understand is, 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?

What's the point of a heavier lens when you can make a variable aperture into constant? Is there a hidden catch or hidden problem to that, that i am missing?

What you're missing is the largest maximum aperture value at full telephoto.

With a constant aperture zoom, you don't have to stop down. That's the advantage.

The trade-offs are size, weight, and cost.

The 30-300 cine zoom that I mentioned earlier has to be variable aperture in order to keep those three factors manageable, because it's *already* big, heavy and expensive.

Your 75-300 is variable for one reason only: to minimize the cost. It is, after all, a very cheap lens.

The Canon 70-200 f/2.8L is constant aperture, and fairly big and heavy for a still-photo lens. If you get it with IS, it's almost $2,200.

The Canon 70-200 f/4L is also constant aperture, but f/4 is as open as it will go. It's also half the size, half the weight, and half the cost of the 70-200 f/2.8L.

The Canon 70-300 f/4-5.6L is a constant f/4 from 70 to 260mm or so and only after that does it stop down to f/5.6.

The Canon 100-400 f/4-5.6L works pretty much the same way as the 70-300 above, but it can be used with extenders (at a cost of one or two stops).

Almost all telephoto zooms above 200mm are variable aperture. It's easier to do constant aperture on wide zooms, such as the Canon 16-35, which can be had two ways, either f/4 with IS, or f/2.8 without IS.

But some wide zooms are variable aperture because they're a lot less expensive that way. Such as the Canon EF-S 10-18, which goes from f/3.5 to f/5.6. But it's a steal for less than $300. I own one and I love it.

All of these lenses though are designed for still photography and were never intended for video production, even though some people use them that way.

It's a lot easier to get larger maximum aperture values (and sometimes constant aperture ranges) on broadcast video lenses since their image circles are smaller than Super 35. For example, the lens in the Canon XF300 is f/1.8 at full wide angle and stops down only to f/2.8 at full telephoto. The equivalent 35mm lens would be 600mm. Canon doesn't even make a 600mm f/2.8 still photo lens. The make a 600mm f/4 and it costs $11,000. The XF 300 has the equivalent of a 600mm f/2.8 and it's half the money of the 600 f/4 still photo lens.

Constant vs. variable aperture zooms are a function of a balance between several factors:

1.) size of image circle (full-frame, Super 35, half-inch, etc.)
2.) maximum focal length: wide zoom vs. telephoto zoom
3.) zoom ratio (widest to longest focal length, could be less than 2x or more than 10x)
4.) application (cinematography, videography or photography)
5.) size and weight
6.) cost

There's no single determiner. Does that help?