dullesguy
Posts: 243
Joined: Thu Jul 06, 2000 12:12 am

Long Lense

Wed Aug 23, 2000 6:41 am

Hello, is it normal for a longer lense to not focuss as well as the shorter lenses. For example, I have a 70-190mm and a 70-300mm lense. The 70-190mm focusses well no matter how far away, but the 300mm focuss is real crappy when the subject is a good distance away, but when close to the subject it takes some nice pics. Aslo can you get camrea shake with a 300mm lense when using its full zoom and with a shutter of say 1/250th? Because my pics have been coming out real blurry when using the 300mm at full zoom and with the subject being a good distance away. Is there a trick to use with long lenses such as 300mm? If so please tell me! =)



Stephen
"..the joy of the Lord is your strength" Nehemiah 8:10
 
ckw
Posts: 4586
Joined: Fri Aug 27, 2010 12:26 am

RE: Long Lense

Wed Aug 23, 2000 6:14 pm

You don't say whether you're using manual or autofocus - if the latter, there could be a mechanical/electrical fault, get it checked.

If this is a manual focus, here are some things to note:

1) the tendency is to rack the barrell round to "infinity" when shooting distant objects. In fact, many long lenses don't actually focus at infinity - they focus beyond infinity - this is a design feature to allow for thermal expansion of various lens components. The focus point (esp. at wide apertures) is very critical with long lenses - the smallest movement of the focus ring makes a huge difference. As part of your technique, try turning the focus ring either side of the correct position quite rapidly - at the correct focus point the image should appear to "snap" into focus.

2) shutter speed - while the rule of thumb says "use the shutter speed closest to the focal length" this is just a guide - if you're cold or tired, if its windy, if the lens is heavy or doesn't balance well can all significantly affect your ability to steady the lens. You will need to eliminate camera shake as the possible cause - take some tests shots with the camera securely mounted on a tripod.

3) the lens - the sad fact is that the design of (most) zooms is such that their poorest performance will typically occur at maximum zoom. You don't say which make yours is, but I've learned the hard way that cheap 3rd party zooms are a false economy. However, the most serious problems are normally only apparent when the lens is wide open - if you can stop down to, say, f8, you might find a significant improvement.

Ok - so you've got to maybe shoot at a faster shutter speed AND stop down as well - probably means faster film ... but a bit of grain is better than out-of focus!

Cheers,

Colin
Colin K. Work, Pixstel

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