My lens has a spot on it, is there anything I can do?

[Ryan Elder]

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.

[Brian Drysdale]

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.

[Ryan Elder]

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?

[Brian Drysdale]

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..

[Ryan Elder]

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?

[Brian Drysdale]

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/collection...-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.

[Paul R Johnson]

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.

[Brian Drysdale]

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.

[Ryan Elder]

Originally Posted by Brian Drysdale

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?

[Chris Hurd]

Originally Posted by Ryan Elder

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.

Originally Posted by Ryan Elder

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/buyer....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.

Originally Posted by Ryan Elder

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.

[Pete Cofrancesco]

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.

[Dave Baker]

Hear hear Pete!

[Pete Cofrancesco]

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.

[Ryan Elder]

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?

[Chris Hurd]

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?