AboutScott Valentine Expertise Most anything about digital post processing (Photoshop, etc), effects, and image restoration, some technical information about digital imaging systems, light and electron microscopy, optical physics and image analysis. I can help with shooting basics, lighting setups, and getting the most out of your digital camera. I am also an 'expert' here for Photoshop (Computers/Technology > Software > Graphics Software > Photoshop).
I am currently writing a book for Adobe Press on composite artwork using Photoshop CS4.
Experience I've been an image analyst and advanced amateur photographer for over 6 years. I run an Adobe user group, focusing on digital media, and have lectured on digital image capture systems. Currently, I am an administrator for a rather large instructional Photoshop forum
Organizations Adobe User Groups, National Association of Photoshop Professionals, Advanced Imaging Specialists
Education/Credentials Bachelor of Physics, University of California, San Diego
Awards and Honors Winner: Best in Show and several category first place awards - Imaging Professionals of the Southwest Print Competition (multiple years)
Expert: Scott Valentine Date: 4/7/2007 Subject: group photography
Question Hi, Scott. I have a recurring problem with photographing groups of around twenty or more. Even though I zoom in on the camera, and everything appears to be fine, when I start enlarging the shot many of the features don't seem to be ultra-crisp. I use a Canon Rebel 8 mp XT, and I've tried using manual focus, auto focus, a-dep...I'm not really sure what I'm doing wrong. Is it my lens? Tripod or lack of? Can you advise? Thanks.
L
Answer Hi Lori,
Without seeing exactly how you are shooting, and under what conditions, I can not give you an accurate diagnosis. What I can do for you is give you a few common problems and solutions. Try any/all of them!
First, I need to clarify the difference between lack of resolution, lens blur, and motion blur. Your image could be suffering from any one or combination of these things. Motion blur is pretty obvious, and you should be able to identify it by distinct motion 'streaks' or wobble in the image. Lens blur can either be intentional, as when controlling depth of field, or an artifact of a low quality lens. If the lens is good, you will have areas that are very sharp and in focus when using something like f/8 (or whatever the optimal speed is for your lens). But poor quality will be evident in differing patches of blur, or images in which nothing is ever sharp. Finally, low resolution results in blur when details are too small when compared to the size of the pixels on a sensor - there is a finite limit to how small a feature can be in the image plane and still be distinct.
How are these issues solved? Let's start with motion blur.
Whenever you are shooting, you will be more stable with a tripod. If you are using a small aperture, you are getting less light per unit time to the sensor. That means you have to leave the shutter open for longer periods which can lead to blur or shake. You have a nice camera; invest in a good tripod. And beg your subjects to stand perfectly still ;)
Lens blur due to aperture settings may be awkward to deal with at first. There is an optimal range for most adjustable lenses which will be combination of zoom and aperture. A good camera store, or someone with specific knowledge of your lens can help identify this range. Find it, set up some focus targets at different distances, and take your picture. See if the target you intended is actually sharp. If not, you may be focusing incorrectly; check your user guide to see if you can change the diopter setting for your eyepiece, and check some online forums to see if there's a problem with your lens not being properly calibrated. While unlikely, it is possible. Try the diopter adjustment first, as this is much more probable.
Finally, resolution. This can be a royal pain. As you get more people in the shot, you are necessarily reducing the number of pixels committed to any one face. It may just be that you are trying to ask too much from your sensor when blowing up the image. There is some math you can do to relate pixel size to feature resolution (the Rayleigh criterion), but I doubt it would do much good, because it doesn't account for sharpness in an obvious way. A better test is to take a few shots of some resolution targets - even a ruler can work for this.
Basically, you will need to take a shot of the ruler at various distances with your lens of choice. Since it's a zoom, start by placing the ruler so that your lens' maximum zoom allows the ruler to fill the frame along the horizontal direction. Repeat the shot at several f-stops from high to low, and keep track of the information. Do the same test at a few different distances, using the same aperture settings. Be sure to hit the max, min and mid-point zoom at the very least... others are optional, but can only help you find the sweet spot for resolution and lens performance.
After you have your images, compare the aperture settings in a given zoom range against eachother. There should be one that is at least a little sharper than the others. Do this for each zoom and see if there's a pattern (there should be).
The next step is to shoot the same ruler, but end-on. Set it up so you can see all the numbers, with zero closest to the camera. You are essentially shooting a ramp, so angle the ruler in such a way that you can see all the lines, but the last few should be very close when seen through the camera. Shoot this at various zooms using the smallest aperture, and again with the 'sweet spot' aperture you found above.
You will be looking to see if you can distinguish the last few lines on the ruler when you view the image, and at what point they become blurred or indistinct. This will help you identify what size of feature you can still make out with your sensor. That should give you an idea of just how much detail you can expect when shooting large crowds, and how many is 'too many' to keep good features.
I've seen some wedding photographers who only use medium format cameras for large groups, but do everything else digitally. Your other option may be to split the crowds into smaller groups. That's not always a good option, but keep it in your bag of tricks.
If you'd like more clarification, or have more information on what kind of image problems you are having (e.g., posting a link to an example), I'll be happy to follow up with you.
