Focus/Clarity Issues

TechArtist · Jun 29, 2012

So, I am trying to figure out an issue I'm having with focus issues. I have a Canon SX40 HS.

This is my lens(taken with my iPhone 4S). I am using lens cleaner with a microfiber cloth(I clean in a circular motion from the center out), but it seems like that just leaves these tiny little streaks or circular scratches(its a lens cleaner for glasses though I was told it would be fine on Camera Lens). I can't for the life of me seem to get any of that small dirt pieces on the very edge of the lens off. I am planning on taken this to Wolf Camera to have professionally clean and see about a different lens cleaner and cloth. Also, if there is anything I can put over the lens to protect it when in use.

So can you all tell me if it is the lens, or if it is me not setting my exposure and focus right(the bottom 2 photos were taken in AV mode).

1/200, f/8.0, ISO 200, 4.3 Focal Length

1/400, f/8.0, ISO 400, 4.3 Focal Length

TCampbell · Jun 29, 2012

Lenses are generally pretty tough, but to keep optical glass in top form it's actually best to not clean it unless it's really necessary (dust resting on a lens won't scratch it... a cleaning wipe dragging that same piece of dust around the glass might scratch it.)

I have a hand-powered air blower which usually can blow the dust off the glass and if that doesn't work, I have a few _very_ soft brushes (one actually is an especially soft paint brush that I purchased to use exclusively for cleaning lenses.)

I would never use a liquid cleaner (any liquid cleaner) unless there was actually something stuck on the lens (but that pretty much never happens.)

Dust on a lens usually won't affect focus or clarity -- it might show up as lens flare if you're shooting into the light and the light reflects off of it.

I'm not sure what you're asking about in the bottom two photos.

But since your post is about focus & clarity I assume you're not happy with the focus. Usually you'd have crop in on a section showing some detail and post a "100% crop" enlargement (don't post the whole image at full resolution... that'd be too big).

Zoom lenses usually have "sweet spots" in the focal length range -- certain focal lengths in which the lens can produce a sharper and more detailed resolution than at the other focal lengths. So you might try shooting at focal lengths other than the maximum 4.3mm wide setting and compare. Your shutter speeds are fast enough, you're not getting any motion blur.

The SX40 has a 1/2.3" sensor, so the camera is probably be diffraction limited at f/8 (which limits the resolving power of the camera -- aka it wouldn't be able to achieve a particularly fine detailed level of focus.) Try backing it off to ... say f/5.6 (then speed up the shutter to compensate.) You can see examples of different sensor sizes here: Sensor Sizes: Camera System: Glossary: Learn: Digital Photography Review Physically larger sensors and lenses are capable of resolving finer levels of detail (if you want the finest level of detail possible, get an old view camera where you actually have to slide in the film.) When it comes to clear "sharp" focus... bigger is better.

TechArtist · Jun 29, 2012

Here are a couple crops from the top image at 100%:

Here is a photo both whole and 100% crop from when I 1st got my camera showing much better detail(this was done in manual):

All photos in this thread I have not edited at all(besides the cropping of course).

Lenses are generally pretty tough, but to keep optical glass in top form it's actually best to not clean it unless it's really necessary (dust resting on a lens won't scratch it... a cleaning wipe dragging that same piece of dust around the glass might scratch it.)

Ah. That makes sense actually. So is it possible the lens was scratched from trying to clean it? Would a professional be able to get it looking good again or should I not bother spending the money on that?

Zoom lenses usually have "sweet spots" in the focal length range -- certain focal lengths in which the lens can produce a sharper and more detailed resolution than at the other focal lengths. So you might try shooting at focal lengths other than the maximum 4.3mm wide setting and compare. Your shutter speeds are fast enough, you're not getting any motion blur.

The SX40 has a 1/2.3" sensor, so the camera is probably be diffraction limited at f/8 (which limits the resolving power of the camera -- aka it wouldn't be able to achieve a particularly fine detailed level of focus.) Try backing it off to ... say f/5.6 (then speed up the shutter to compensate.) You can see examples of different sensor sizes here: Sensor Sizes: Camera System: Glossary: Learn: Digital Photography Review Physically larger sensors and lenses are capable of resolving finer levels of detail (if you want the finest level of detail possible, get an old view camera where you actually have to slide in the film.) When it comes to clear "sharp" focus... bigger is better.

So, when I am using the camera, I should be using a mid-range f/stop with a higher shutter speed? I tend to rely on my light meter a lot which I've noticed it tends to underexpose the photo at higher shutter speeds unless I up the ISO a lot. I will definitely check out that article.