A question about lenses and image focus

xMissyx · Apr 22, 2012

Example: I'm shooting with a 50mm 1.8. I love this lens but I find even being completely still with a sleeping subject, focusing on the eyes and my focus points are selected....import photo and the face is out of focus..Now i don't mean BADLY ...it's really just slight and only other photographers may notice but my question is if I upgrade lens will that help or should I check to see if I have a case of shaky hands?

I had this problem today ...settings were 1/60 f stop 8 ISO 800 =/

murklemark · Apr 22, 2012

The 50mm 1.8 Canon or Nikon is a nice sharp lens. You'll never get a perfectly sharp picture while using it handheld as there will always be minute movements.

How out of focus is it? And are you shooting DX or FX?

TheBiles · Apr 22, 2012

Sounds like motion-blur. You want to be at 1/80 or faster at a minimum on your body.

Sent from my Galaxy Nexus

pgriz · Apr 22, 2012

Here's an experiment you can try to determine YOUR handheld limit...

Set up your target with lots of fine detail (a newspaper will do) at your "normal" target distance, say 10 ft.

To get your comparison shots, put your camera on a tripod, and shoot a sequence of shots in Av mode, starting with the lens wide open, and progressively closing the lens by one stop for the next shot, until you've gone through the range of apertures. It is important that in this sequence, your focus is set manually and with the most precision possible (if you have magnified life-view, use that to get the correct focus). This then gives you a sequence of shots where your focus is perfect (as good as it is going to get with your equipment), and camera shake is not an issue (unless you have a really bad tripod).

Next, take the camera off the tripod, and go through the exact same sequence, but now handholding the camera and using the usual AF method you use. Shoot from exactly the same point as you had with the camera on a tripod, aim at exactly the same point on your target. You should now have a sequence that looks like this (shutter speed is arbitrary since it is used for illustrative purposes...): f/2.0 at 1/1000, f/4 at 1/500, f/5.6 at 1/250, f/8 at 1/125, f/11 at 1/60, f/16 at 1/30, f/22 at 1/15.

Now compare the tripod/handheld shots at each setting. Hopefully, the focus will be on exactly the same point in both sets. Magnify each pair of images and see at what setting the detail starts getting blurred. Now you know the shutter speed which becomes your limit for hand-held shooting.

Note that the minimum shutter speed depends also on the focal length of the lens. The usual guide for 35mm cameras is that the minimum shutter speed is the reciprocal of the focal length, so for a 50mm lens on a 35 mm camera, that would be 1/50 sec. Since the crop bodies "magnify" the image made at any focal length, the guide here is the reciprocal of the focal length x crop factor. So if you have a crop camera (1.5x say), the same 50mm lens will have a minimum shutter speed of 1/75 sec, which would be 1/90 sec on the dial.

KmH · Apr 22, 2012

Canon's 50 mm f/1.8 lens has some image and build quality issues, but focus should be sharp at f/8.

Sharp lens focus can be degraded by using to slow a shutter speed. A slew shutter speed allows camera shake to be recorded which softens what was a shot made with a lens sharply focused.

The rule-of-thumb is that the shutter speed needs to be at least 1/the focal length of the lens. With a 50 mm lens, that would be 1/50 for the shutter speed.

If your camera holdng technique is less than good, even 1/50 may be to slow a shutter speed.

As a rule, I use 1/100 as the slowest shutter speed I will use with a normal or short focal length lens, and my camera holding technique is a fair bit better than average.

Which brings up why supplimental lighting (flash) is so often needed inside. The added light allows using a lower ISO setting than 1/800.

If you had had 2 stops more light you could have used ISO 400 and a shutter speed of 1/120. One stop more light allows the one stop reduction of the ISO from ISO 800 to ISO 400 (less image noise too). The second stop of light allows a one stop faster shutter speed, 1/120.

A second benefit of using strobed light is the flash of light has a short duration and can assume the motion/camera shake stopping duty from the shutter speed.

A third benefit of using strobed light is that with a single shutter release, you can control the ambient light exposure separately from the strobed light exposure.