Hi,
Just joined here and having browsed through various posts I came across a few on lens calibration.
A little knowledge can be a dangerous thing and I am not sure if there is anything wrong but maybe someone out there can help.
I have a Canon 400d and a 70-200mm f4 L lens. I have taken several shots and have to say pleased with results but when viewing at 100% they all seem slightly out of focus. Does that mean they are out of focus photos or just because they are blown up on screen? (I thought at 100% this meant actual size?!)
Enjoy the useful forum and looking at photos...there are some lovely shots.
How are you processing them? Subject to the settings for sharpness on the camera - and most would not apply sharpening there - DSLR files will normally require sharpening due to the softening effect of the AA filter in front of the sensor. If they are sharp after editing you are OK.
At 100% you are viewing the image at its natural size.
I import them from the camera to my mac via the EOS utility and then view them in imagebrowser or lightroom. I havent changed the majority of them though and then only played with exposure on a very few, they are as is from the camera. The setting on the camera is faithfull.
When viewing at 100% in Lightroom or any other image software I have, preview, iphoto seashore etc not one picture is sharp as I say (100% being actual size ) Whats going on? This is worrying and annoying!
Phil, you need to give us more facts, and maybe a sample image for good help. Focus problems can be one of many things.
1. If you shot hand held and had a slow shutter speed, you could be seeing simple camera shake, not bad focus. What is your shutter speed?
2. If you had a large aperture (f4) and large zoom (200mm), and short distance to the subject, then the depth of field is very small. Very little of your image will appear in focus. What apertuer, zoom, and distance did you use?
3. The 70-200 lens is excellent glass. I have one. But it is a little soft at the 70 to 90 range. Still much better than most other lenses, but the "sweet spot" for this lens is 100 to 200.
4. I don't remember if your lens has image stabilization. I think not. But if it does, and it is "On" when you don't need it, then it can actually blur the image a little.
5. You could actually have a bad autofocus. It's rare, but it happens. It's a problem in the camera, not the lens. The camera reads the focus and sends a signal to the lens. If the camera is out of calibration, the signal focuses the lens up to 3 millimeters off the actual focus point.
I recommend you do a simple test. Get a newspaper, or cereal box, or anything with large crisp text. Place it at a 45 degree angle to the camera and shoot some images at different focal lengths. Use a tripod if you have one. If not, prop the camera on some solid object and use the self timer for the shots. Or shoot in very bright sun so your shutter speeds are greater than 1/300 second. Look at the images to see if any part is in focus.
If there are sharp areas, but they are behind or in front of the spot you focused on, then you have problem 5. That's bad news. You have to send your camera to Canon for calibration. If there are no sharp areas at all, I'd still suspect blur from camera shake, not focus problems.
I doubt you jpeg settings (faithful) have anything to do with the problem. Some settings may sharpen more than others, and post processing in Photoshop can make an image sharper, but the original still should be reasonably sharp.
Many Thanks Paul that is helpful. Out of interest what did you use to sharpen and process the shot?
DOF was limited because of the aperture f5.6, shutter 1/100, ISO 400 and 176mm but I expected it to be tack sharp at least in places. There are other shots with f11, 1/125, ISO 100 that arent as sharp as I would like but I will do the test as redcrown describes.
Thanks again.
Finally got round to testing as redcrown suggested and did several test shots. Pleased to say lens focused fine, I did use a tripod at 100 ISO in Av mode (Aperture Priority) so I could vary the aperture and allow the camera to calculate the shutter speed, but also did some handheld shots at 200 ISO in the same mode which were sharp too. As I increased the aperture to increase DOF obviously the shutter speed dropped, and I found that the focusing was a tad softer than the shorter DOF, low aperture high shutter speed shots. Is that normal?
At the end of the day with telephoto lenses you obviously need to use as fast a shutter speed as you can to overcome camera shake whilst hand holding and generally a step up to 200 ISO (any further or faster and be aware of noise on the 400d) will allow you that or lots more light! Basic/simple stuff you might be thinking but playing with time and light is what we all enjoy!
Most lenses have a "sweet post", usually between f4 and f8, where their focus is best.
You last post indicates you might be seeing the effect of "mirror slap" vibration. This usually occurs at shutter speeds between 1/2 second and 1/60 second. Using a tripod does not help with mirror slap vibration.
Some cameras are better at dampening mirror slap than others. I have the high end Canon 1Ds, and with the 70-200 IS lens, mirror slap is very bad. And it is much worse when the camera is mounted using the lens ring than when mounted using the camera body. The solution is to use mirror lock-up and shutter delay. A delay of 2 seconds or more is needed between mirror lock-up and firing the shutter.
This is an interesting test too. Mount your camera on a tripod, use maximum focal length and a shutter speeds between 1/10 and 1/30 second. Shoot some images with mirror lock-up and some without and see the difference.
