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

[Brian Drysdale]

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.

[Ryan Elder]

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.

[Brian Drysdale]

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.

[Ryan Elder]

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.

[Josh Bass]

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

[Ryan Elder]

Okay thanks. I asked how to switch this off before to people familar with the T2i. They say switch to full manual controls, but it already is on that, unless maybe it's impossible to turn off.

However, if I do buy a new camera where you can turn it off, is it necessary to still get a telephoto lens with an aperture ring then? What's the point of an aperture ring, if you have a camera, where the servo controls can be disengaged?

[Josh Bass]

I dont know that cam at all. I would look through the menus one by one for auto anything, turn off, look in manual index for auto to see what those settings might be, google search, youtube tutorials for setting up t2i (or whichever cam it is) for filmmaking and also videos about those auto settings.

[Brian Drysdale]

In video the advantage of an aperture ring is that you can adjust the stop during the shot, to the exposure you want, rather than where the auto exposure system wants.

The 1st AC or DP can easily reach an aperture ring, compared to trying to do the adjustment on the back screen of the camera while filming.. This can be really handy during complex shots that involves going from dark areas into light ones etc and when the sun keeps going in and out behind the clouds, you can ride the stop.

Please do the test with a blank surface (gray would be ideal) with flat lighting, It's the method you'd use when testing an exposure meter,

[Ryan Elder]

Okay thanks, I already read through the instructions for my camera, as well as googled it but it doesn't say anything about their being additional servo controls to switch off though.

As for having a ring handy to change when lighting changes, I didn't think it would be any more easy than turning the dial on the camera to change the aperture. Plus on the camera you can see what the aperture is on the screen all the time, where as with the ring, you have to look over on the lens to see.

So I thought that a dial on the camera was just as easy to operate than the ring.

But yes, when I did this test at f22 just now, I did it on a blank wall, and it's the same thing, darker, brighter, then repeat.

[Pete Cofrancesco]

There are 3 possibilities:
1. You haven't set the camera into full Manual. I glanced at the T2i manual and it looks like you need to change this in the menu and turn off auto iso.

2. The camera could be changing the exposure based to compensate for a darkening at the edges (vignetting) which might be located in a zoom range. Modern cameras commonly communicate with the lens and can modify the image to correct for aberrations in the lens. It also could be increasing the exposure to compensate for the variable lens aperture. Note these cameras and lenses were designed for still photography not video, so they often don't operate in a way that film makers would like.

3. Either the lens or camera is malfunctioning. Although I find this highly unlikely.

#2 is the most likely and if it's the case you just live with it. It's a very minor issue and you shouldn't be zooming while filming on a flyby wire lens. You said you're getting a new camera and lens.

Lesson to be learned consumer equipment doesn't operate like professional gear, the value of constant aperture lens and finally always understand and test your equipment.

[Ryan Elder]

Originally Posted by Pete Cofrancesco

There are 3 possibilities:
1. You haven't set the camera into full Manual. I glanced at the T2i manual and it looks like you need to change this in the menu and turn off auto iso.

2. The camera could be changing the exposure based to compensate for a darkening at the edges (vignetting) which might be located in a zoom range. Modern cameras commonly communicate with the lens and can modify the image to correct for aberrations in the lens. It also could be increasing the exposure to compensate for the variable lens aperture. Note these cameras and lenses were designed for still photography not video, so they often don't operate in a way that film makers would like.

3. Either the lens or camera is malfunctioning. Although I find this highly unlikely.

#2 is the most likely and if it's the case you just live with it. It's a very minor issue and you shouldn't be zooming while filming on a flyby wire lens. You said you're getting a new camera and lens.

Lesson to be learned consumer equipment doesn't operate like professional gear, the value of constant aperture lens and finally always understand and test your equipment.

Okay thanks, but I never have the auto ISO on. The ISO was at 800 the whole time during that zoom in the video, and during all my tests, I always set the ISO manually first.

The full manual is on.

I think it's most likely #2 as well. Why is there aberrations going on though, if they need to be corrected? What is causing the aberrations? Is it because less light is traveling into the lens, the longer it gets when you zoom in? Is that what's causing it?

This part I don't understand cause it was said before that the lens could become an constant aperture lens, if I stop down enough. But if there are aberrations, can it become a constant aperture lens, or not then?

I just want to know these things, cause when I get a new camera and lens, I don't want to replace all my lenses, such as my 24-35 lens for example. My other lenses, do not have aperture rings. So when I get a new camera, I want a camera where #2 will not be an issue, since my other lenses don't have rings. Are their cameras out there where it will not compensate for aberrations when zooming?

[Paul R Johnson]

Ryan, why do you never do what people suggest, but just bits of it? It's so frustrating to waste time on your questions and then you answer questions with questions.

What do you really want? It feels like you are looking for solutions to avoid changing the lens, avoid changing the camera and for some reason, avoid the lenses that have a manual, conventional iris setting. Why are you fixated on having servo controlled aperture?

Yesterday I was on an airfield shooting parachutist. The most frequent lens adjustment was the iris ring. A real mechanical one, that I do NOT need to look at because I'm interested in the viewfinder, which shows me where it is. They kept moving across white fluffy clouds, at some points the over level zebra was the entire image but he parachute was the constant. Then it would traverse into clear blue sky, then white again. Everything is on manual. Everything stays static, unless I decide to change things.

Unless your system can do this, it is flawed. Find out now if it is the lens or the camera. This is pretty vital. You do have other lenses I think you said. Pretty much the train of thought points to the lens doing its own thing but you must be certain.

What did your film school teach you about zoom's? It seems to be very little. A curious omission. Did your training do everything with prime lenses? Did you have your zoom at that time? I assume you decided to not follow their training and do your own thing. They also seem to have missed things like modules on image stability, grip equipment and movement? I find it difficult to believe they're teaching film with so many critical elements missed or glossed over. What kind of film making are they concentrating on, because it's obvious they totally missed cinema production no. 1 - as in how it was done for the great movies over the past 100 years.

[Brian Drysdale]

What make and model is this zoom lens?

[Paul R Johnson]

It's this one - Canon EF 75-300.

[Brian Drysdale]

This issue may be possibly vignetting at f8, the image seems to darken at that stop as you go to longer focal lengths in this test video on the lens

Canon EF 75-300mm f/4-5.6 III review - worst Canon lens ever? - YouTube

There doesn't seem to be any aperture ramping after f5.6.

The answer is to sell the lens, the test video confirms what has been said here; it's a poor performer at 300mm. The zoom action is poor, so anything less than a fast zoom won;t work, although its near parfocal, so the focus holds pretty well as you zoom.The video also gives a possible reason why dirt could get into the lens.