Could it be the glass?

[ccplim]

I believed I have encounter this previously but did not really take note of it.

I was setting up my photo tank today and both side of the glass was clean. While shooting, I noticed that I sometimes have problem trying to focus. Initally, I thought it might be the auto focusing.

I tried switching to manual focus, focus the subject by using the focusing ring and adjusting my distance between the subject and myself but no matter how I try, I just couldn't get a sharp focus.

Anyone here encounter the same problem before? What could have causes that? [smilie=huh.gif]

[Charizzi]

I'm not 100% sure, but you might be right about the glass throwing your focus off... I'd imagine it (the glass) to be like putting another lens on top of your lens. One time I accidently put two contact lenses in my eye and it was all blurry [smilie=oops2.gif]. I could be wrong though... I hope I somewhat helped! [smilie=biggrin.gif]

[gulf18]

Hi,

focusing manually should not be a problem on it's own. The glass can't fool a manual focus. However, you might be having problems just because when focusing manually, along with the large aperture, a moving subject can soon be out of the area that appears in acceptable focus. A large aperture= shallow depth of field (sure you already know that). Either you'll have to be quick when re-focusing(depending on subject movement), prefocus on a spot ahead of time, add more light to allow for a smaller aperture, or press your lens right up against the glass. Hope this helps.

Chris

[ccplim]

Hi,

focusing manually should not be a problem on it's own. The glass can't fool a manual focus. However, you might be having problems just because when focusing manually, along with the large aperture, a moving subject can soon be out of the area that appears in acceptable focus. A large aperture= shallow depth of field (sure you already know that). Either you'll have to be quick when re-focusing(depending on subject movement), prefocus on a spot ahead of time, add more light to allow for a smaller aperture, or press your lens right up against the glass. Hope this helps.

Chris

I did tried on fishes which are stationary but I still got the same result. That is why I feel puzzled [smilie=huh.gif]

[benny]

This happens when you have exceeded the minimum focusing distance allowed by the lens. Move back and the problem will be solved.

Cheers,

[ccplim]

This happens when you have exceeded the minimum focusing distance allowed by the lens. Move back and the problem will be solved.

Cheers,

But I don't get this everytime leh. Sometimes I get till very close but I can still get a sharp focus.

[benny]

This happens when you have exceeded the minimum focusing distance allowed by the lens. Move back and the problem will be solved.

Cheers,

But I don't get this everytime leh. Sometimes I get till very close but I can still get a sharp focus.

I can only guess that the fish was further back in the tank and the total distance is still within your minimum focusing distance of the lens. Once the fish swim forward, it will be the same problem again.

Adding extension tubes or close up filters will decrease you minimum focusing distance.

Cheers,

[Pyrowolf]

I've experienced the same problem, but normally with plastic tanks. Even with manual focus, and tons of pictures taken in succession with slight adjustments to the focusing ring, none of them really were sharp and in-focus.

[ccplim]

This happens when you have exceeded the minimum focusing distance allowed by the lens. Move back and the problem will be solved.

Cheers,

But I don't get this everytime leh. Sometimes I get till very close but I can still get a sharp focus.

I can only guess that the fish was further back in the tank and the total distance is still within your minimum focusing distance of the lens. Once the fish swim forward, it will be the same problem again.

Adding extension tubes or close up filters will decrease you minimum focusing distance.

Cheers,

Hey benny, it seems like I get this problem more often if I were to shoot at an angle.

[benny]

If that's the case, then the thickness of the glass is causing distortion to the images. The camera does not understand this and tries to hunt for the precise point to get the image sharp, obviously to no avail. This is especially the case with thick glass.

Use Manual Focus if you are not shooting directly perpendicular to the front glass pane.

Cheers,

[ccplim]

If that's the case, then the thickness of the glass is causing distortion to the images. The camera does not understand this and tries to hunt for the precise point to get the image sharp, obviously to no avail. This is especially the case with thick glass.

Use Manual Focus if you are not shooting directly perpendicular to the front glass pane.

Cheers,

But then, like what I mentioned in my first post, I can't even get a sharp focus when I use manual. How should I retified that? [smilie=huh.gif]