Using zoom lens = light correction?
 

Hi there,

I just wanted to check if this was normal, or not. I have the kit lens (15-85) + one fixed 50mm f1.8 lens with the 7d.

If I use the fixed lens, everything is ok. When I attach the kit zoom lens and set it to Creative Mode and start zooming in or out, I get light "shifts", meaning it automatically compensates for the difference in lighting. However, I think I disabled everything that could enable this shift.

Is it only me? Am I doing something wrong? Is there something I don't know?

If somebody could help me out with this, I'd be a very happy camper :)

-- F

The 15-85 is not a constant aperture lens. It is a variable aperture lens, which means it has different maximum aperture values at each end of the zoom range. For example at the shortest focal length it might be f/3.5 while at the longest focal length it might be f/5.6. As you zoom in and out, this is the change that you are seeing. To avoid it, set the camera to match the smallest maximum aperture value of the lens, such as f/5.6 at full telephoto, and then you won't see a shift when going from from wide to tele. Instead it will hold f/5.6 throughout the entire zoom. The maximum aperture values are printed on the lens barrel, for example 3.5-5.6

Tell us some of your experiences with the 15-85 (is it the new one?)... How do you like it?

Is it sharp at 15 and 85?

What do you see in terms of vignetting and chromatic aberration?

How does it do out on the streets at night (in combination with the 7D's ISO performance...)?




PS I thought the kit lens is the 28-135, as shown on B&H's page...?

The kit lens is 15mm-85mm? Is this the non cropped measurements? I thought it was a 28mm starting point and I was adding the 1.6x magnification to get something in the lower 40mm range as a wide setting, which isn't very wide. If it is indeed a 15mm then with the magnification factor we'd be looking at a 24mm effective focal length. Is this right? I have read quite a bit about the unit and I was leaning away from getting the "kit" lens because it wasn't as wide as my Nikon kit lens that I use most of the time now.

Hi Guys,

Sorry, wasn't online the past two days.

And sorry, I was indeed mistaken, it's the 18-135mm lens. I love the lens, it's supersharp to me (compared to the 50mm I have as well) - but mind it, I'm not a professional photographer (yet ;). So that's why I can't answer all the questions you are asking. I don't see any vignetting at any setting whatsoever btw ...

Chris Hurd, thanks for the tip ... I'm trying to find out now how to set the aperture value on the camera itself.

Greets,
Frank

Chris,

"To avoid it, set the camera to match the smallest maximum aperture value of the lens, such as f/5.6 at full telephoto, and then you won't see a shift when going from from wide to tele."

Can you explain me how I would be able to set that smallest maximum aperture value?

Thanks!

Greets,
Frank

So if the kit lens is 28mm to start, is that it's effective focal range with the 1.6 crop factor figured in? Or is it more like a 43mm?

With the command mode dial set to either Av (aperture priority) or M (full manual) mode, use the dial on the top right of the camera body (directly above the shutter release) to set an aperture speed of f/5.6 or smaller. Hope this helps,

So can the Av mode be used to control the f-values while in video mode? I've been trying to adjust them, but they don't seem to adjust in video mode, just still mode.

Marty, There are two different kit lenses the 7D can be packaged with.. Here in Canada it seems to be mostly packaged with the 28-135mm lens (lens' are always stated in non-cropped lengths). I don't really like the 28-135 as a kit lens for a APS-C camera because as you stated, it isn't very wide with the 1.6 crop factor. Although I believe they are only charging about $200 for this kit lens, which would cost much more if purchased separately.

However, in the US it seems to be available as a kit with the new 18-135mm lens which seems to offer a much better focal range as an all-around walkabout lens..

No. Not in Av mode.

If you have the mode dial set to anything other than M (manual) the 7D is in full auto mode when video mode is activated.

In M (manual) you have full manual control over aperture, shutter, and ISO unless you have ISO set to AUTO in which case the camera tries to automatically adjust ISO to get you proper exposure at whatever you have the aperture and shutter set to.

With the ISO set to AUTO the camera will try to compensate for lighting changes in the scene. Exposure is NOT "locked" with ISO in AUTO.

I often set the aperture and shutter where I want them and the ISO to auto just to see what ISO value the camera wants to use in that scene. Be sure that with the Info button you have the display set to show exposure data at the bottom of the LCD. Then lightly press the shutter release and the ISO value the camera wants to use will show. Press the ISO button and with the dial move the highlight from AUTO to the value you saw. Then you can adjust the ISO up or down a bit to get the exposure effect you want.

This also "locks" exposure.

I like the way this works.

Thanks VERY MUCH Bruce, that was the info I really needed. As a follow up, please excuse the ignorant question, but how exactly do you control the aperture in M mode (video)?

It's super easy still-shot mode with the Q button, but I can't seem to be able to control the f-stop values at all in video mode, even in M mode.

Any insight would be very much appreciated.

With the camera set in M(anual) mode with the large horizontal dial on the top of the camera, the small "command dial" (knurled wheel) by the shutter release will adjust the shutter speed (at will) while the larger "quick control dial" on the rear of the camera to the right of the LCD adjusts the aperture.

Once you try it you'll see how incredibly easy it is, you can literally adjust aperture or shutter "on the fly" (doing so while shooting is not recommended though.

The third parameter, ISO, is adjusted by pressing the ISO button in front of the top LCD (non image LCD). Once pressed the LCD screen on the back of the camera will display the ISO table with the current ISO being highlighted. Turning the small "command dial" will move the highlight "curser" through the ISO values, highlight the one you want.

As you change the ISO, the image on the LCD darkens or lightens, so you can judge exposure "look" by using the image area "outside" of the ISO values table.

Using the LCD for exposure judgement: You need to "educate" your eye by comparing the same image on your LCD and on the computer monitor you use for image making. Copy a still from the card to your computer then put the card back in the camera. Bring up the same image both on the camera LCD and on your monitor.

Study both until you can "relate" how an image on the camera LCD will likely look on the computer monitor. I wouldn't "monkey" with the LCD brightness at this point because you may have to change it on location.

Yesterday I took my T1i (same LCD as the 7D) out to a Veterans Day ceremony at our outdoor Vietnam Memorial (A Huey chopper on a high "pedestal" and an area for these events). I attached a Hoodman loupe 3.0 with elastic band and even with that the image on the LCD was too dim so I had to adjust the LCD to almost full bright (we really had bright sun). Once I could "see" it well enough I was able to "judge" effects and exposure, but I have "educated" my eye to interpret what I see on the LCD in relation to how it will look on my workstation monitor (I did remember to set it back to normal when I got back in the house).

Hope this "information overload" helps you