Challenge I - Aperture and Depth of Field

[Becstarr]

Let's try again,

[Robjess]

chelle - yep thats it, the head is the same distance from the camera so its all focused. The tail is further back from the camera, so its not in focus.

[Robjess]

Good examples Bacstarr

[J.davis]

Two Macro shots I have taken today that realy show 'Depth of field' - Comments?
F5 @1/125 90mm

F57 @1.3 90mm

[ricktas]

So John, what did you learn about aperture? and when would you use each in a real life situation?

[J.davis]

I cant hold still long enough to take a photo in macro longer than f22 allows.

[MrJorge]

I cant hold still long enough to take a photo in macro longer than f22 allows.

Lol!!

[Paper_Mache_Man]

Ok Rick I do have one question.

It was said to me a long time ago that the smaller the aperture (higher the f stop) the sharper the image. This is incorrect is it not? I mean, they were basically referring to DOF but calling it sharpness instead.

So what aperture setting is sharpest and what setting will provide a "crisp" image? Does it vary from lens to lens or is there a general rule of thumb shared by most lenses? Can you surmise where the sweet spot may be depending on the lens construction? Or, does the aperture setting bear no relationship to the final image sharpness.

My own take on it was that somewhere around f12 should be the best as it's the midpoint for a lot of lenses and so shouldn't represent a compromise of any sorts.

What are your thoughts on this?

[Kym]

Ok Rick I do have one question.

It was said to me a long time ago that the smaller the aperture (higher the f stop) the sharper the image. This is incorrect is it not? I mean, they were basically referring to DOF but calling it sharpness instead.

So what aperture setting is sharpest and what setting will provide a "crisp" image? Does it vary from lens to lens or is there a general rule of thumb shared by most lenses? Can you surmise where the sweet spot may be depending on the lens construction? Or, does the aperture setting bear no relationship to the final image sharpness.

My own take on it was that somewhere around f12 should be the best as it's the midpoint for a lot of lenses and so shouldn't represent a compromise of any sorts.

What are your thoughts on this?

Sharpness and DoF are not the same.

Lenses have a sweet spot (re: sharpness) that is usually around f/8 to f/16 and somewhere in the middle to 2/3 of their zoom range if a zoom lens. In part this has to do with a technical issue called the Circle of Confusion (CoC) - which is a fancy way of saying what the human eye can discern at a set distance. CoC is important in lens design.

High f/stops also have an issue with another technical term - limit of diffraction. And this relates directly to the pixel density of the sensor. This is why very high f/stops are often not as sharp as lower f/stops.

Google "Circle of Confusion" and "limit of diffraction" for the gory technical details.

Ok, what does this mean?

CoC defines what the DoF is. Technically only one distance is truly in focus. The DoF is the range of distance to which the human eye cannot discern out of focus (OOF).

The sharpest part of the image is the items at (or practically very close) to the focal distance (the distance where things are 'exactly' in focus).

Hope this helps - it is a bit beyond the scope of NTP.

Edit: Other factors affecting sharpness include : lens quality, focus accuracy and pixel density.l

[MrJorge]

Ultimately it depends on the lens. Most lenses have a "sweet" spot at where they are "sharpest".

But they're not talking about DOF here they are talking about how sharp the detail (that is within the DOF) captured is @ that particular aperture.

General rule of thumb I've seen is a lens is never at its sharpest when @ wide open (smallest f number). Generally if you step down one stop (one stop bigger f number so 2.8->4.0, 4.0->5.6 etc) it will be sharper than wide open.

But where it is "sharpest" will depend on the lens. A lot of the kit lenses are probably best about f8-f11 or so from what I've seen/heard. But better quality lenses are better generally.

Read up on reviews on your lenses at sites like dpreview.com and see if they have any test results you can get a feel for and then go and play yourself and see if you can find it if you're interested.

[jeelan]

hi guys..

just thouht i'd join in the challenges and learn as well..

here's my two pics..

both were taken on a 50mm f1.8D lens

This one's at at f1.8



This one's at f22



i took these at 0.5m distance from the camera, i'll try and take another couple of something involving larger distances at the local park or similar...

cheers
Jeelan

[ricktas]

So Jeelan, what did that teach you about aperture, that will help out in future with your photography

[jeelan]

hey rick..

the smaller aperture (higher f no.) gives you a greater depth of field vs a larger aperture (lower f no.) which gives you a shallower depth of field...

interestingly, the depth of field itself increases quite a bit when i'm standing further away from my subject....

in the above pics, i was only about 0.5m away from the pins and they were only about 20cm apart from each other..

i've just taken another two pics with greater distances and the changes to depth of field are a lot more ...."subtle" than this....

is there a mathametical relationship between distance from subject to DOF? meaning can you calculate it?

cheers
Jeelan

[ricktas]

Yeah there is, do a google on Depth of Field calculator, the further the subject is away from the lens, the greater the DOF.

So at say using your lens (50 mm) at f1.8

at a distance of 1 metre your depth of field is from 0.99m - 1.01m
at a distance of 5 metres your depth of field is from 4.66m - 5.39m

So even though nothing changed except the distance to subject, the depth of field (area in focus) increased from 2cm at 1 metre to over 60 centimetres at 5 metres.

[happy.grl]

I had a chance to take some shots on the weekend and thought that I would also post my results.

The first shot which was taken at f/8 and 1/50



The second shot which was taken at f/4 and 1/200



The only thing that I have edited with the shots is to crop them so they are basically the same shot with different settings. Both shots were taken using the AV mode on my camera

What did I learn.... I've read a lot about using aperture to blur the backgrounds to make the subject stand out - in the small space that we had the effect was quite subtle. I'm guessing that that is because my aperture has a max (or is that min) of f/8 and the background was not far enough away? I've learned that using DOF to affect foreground can be very effective as well - to me the first photo is really boring, like a shot that went wrong (just composition - ignoring the fact that the cat is not looking at the camera). The second shot interests me a lot more - it kind of feels like I'm observing some action and my attention is not drawn away from the cat

I've also learned that trying to take photos of cats can be really hard when they are not asleep, especially when they decide to come sniff the strange black thing that some crazy girl keeps pointing at them.

Wow. I really didn't mean for this post to be so long

[MrJorge]

Great stuff HG, looks like you've learnt a few things and had a play which is fantastic. The differences are subtle in your shots due to the relatively small difference between f4 & f8 but as you say even that can help concentrate interest a bit more and not be distracted by foreground or background elements.

May I ask what you used to shoot these with?

[happy.grl]

Thanks MrJorge
I used a Canon Powershot sx100 is - which is basically a point and shoot, but with optional manual controls.

[MrJorge]

I bought my fiancee the sx110IS last year. Great little camera. And as you say plenty of manual controls (why I bought it) to help you learn. Good luck with it and look forward to seeing how you go with the other challenges and learnings.

[Kym]

Thanks MrJorge
I used a Canon Powershot sx100 is - which is basically a point and shoot, but with optional manual controls.

If you have manual control a P&S will do what 80% of people do with a DSLR. So well done!!

[stylo]

Rick, can I ask a question re. the DOF Depth of Field preview button ?

I think it somehow relates to this thread.

Have googled it before but don't quite get the gist of it.