Focal point + sensor cleaning question..

[Bikemansteve]

At the risk of asking a dumb question........I've noticed a few of my shots seem to be focussing a fraction behind the subject with my 300mm zoom lens.
I can centre the focus point in the viewfinder directly at a subject and if there is a small depth of field, I'm finding it has focussed a couple of inches behind which is damn frustrating - but it doesn't happen all the time....Is there any reason for it?

.........Durr in advance.....


Also, does anyone know where I can get the sensor cleaned on my Eos 30D as I'm getting a few spots in my shots.......or is there a thread on here for it so I can do it myself..?

Cheers

 

[voodoochild]

I cant answer your first question, but this may or may not answer the second...

Cleaning sensors can be costly, but a good alternative is to invest in a Giottos rocket air blower. Its a simple device that blows out air but does not suck it back in, therefore avoiding blowing removed dust back onto the sensor. It will cost you less than £10 to get one too. A cheaper alternative would be a balloon pump, but I cant say I have ever tried one. All you need to do is attach your camera to a tripod facing directly down towards the ground and blow like crazy with your balloon pump or rocket air blower. I managed to remove a lot of dust from my sensor, which saved me a fair few bucks in the end. Search for the Giottos rocket air blower on youtube and you will find some tutorials

If you do not know how to lift the mirror to reveal your sensor then you will need to read your camera manual. The youtube videos will probably have advice on this.

 

[Bikemansteve]

I cant answer your first question, but this may or may not answer the second...

Cleaning sensors can be costly, but a good alternative is to invest in a Giottos rocket air blower. Its a simple device that blows out air but does not suck it back in, therefore avoiding blowing removed dust back onto the sensor. It will cost you less than £10 to get one too. A cheaper alternative would be a balloon pump, but I cant say I have ever tried one. All you need to do is attach your camera to a tripod facing directly down towards the ground and blow like crazy with your balloon pump or rocket air blower. I managed to remove a lot of dust from my sensor, which saved me a fair few bucks in the end. Search for the Giottos rocket air blower on youtube and you will find some tutorials

If you do not know how to lift the mirror to reveal your sensor then you will need to read your camera manual. The youtube videos will probably have advice on this.

Thanks for that, I'll have a look

 

[markrichardson]

At the risk of asking a dumb question........I've noticed a few of my shots seem to be focussing a fraction behind the subject with my 300mm zoom lens.
I can centre the focus point in the viewfinder directly at a subject and if there is a small depth of field, I'm finding it has focussed a couple of inches behind which is damn frustrating - but it doesn't happen all the time....Is there any reason for it?

If it doesn't happen all the time, it suggests that the problem isn't with the AF itself. Is it possible that between focussing and taking the shot your camera position is moving slightly? (this happens a lot when people focus and then recompose)