Confused ? f value ?

jackdaw

Now im confused ... I thought that the lower the f value
the sharper the image ?

now i find out that its actually softer ?

OK i know the lower the F value (1.8 for eg.) the faster the shutter speed
can be, but i thought it also made it sharper, hence the image quality being very sharp on the Tamron 17-55 at f2.8.

So if I wanna shoot landscapes in wide mode, is it better to use a higher f value with a slower shutter speed (using a tripod to avoid blur) to get sharper images ?
or is there an ideal "in between"

ShakeyBlakey

jackdaw wrote: »

Now im confused ... I thought that the lower the f value
the sharper the image ?

now i find out that its actually softer ?

OK i know the lower the F value (1.8 for eg.) the faster the shutter speed
can be, but i thought it also made it sharper, hence the image quality being very sharp on the Tamron 17-55 at f2.8.

So if I wanna shoot landscapes in wide mode, is it better to use a higher f value with a slower shutter speed (using a tripod to avoid blur) to get sharper images ?
or is there an ideal "in between"

Landscapes .......f22, tripod, its the only way mate, and lowest iso,
Cheers
Mark

SOL

Actually f22 is not the best idea unless you want to catch something that is very close as well as a far object, if you check out the lense reviews you can see that as you go past f8-11 on a wide angle lense you start approaching diffraction limits and the sharpness will decrease.

So to answer your question, usually at wide open you are pushing the limits of the glass engineering but if you stop down from wide open so from f2.8 down to maybe f8 you may notice a good increase in sharpness however beyond you will not. The actually mid point for this depends on the focal length of the lens but for all intenets and purposes either f8 or f11 or in between should be your best bet

leohoju

ShakeyBlakey wrote: »

Landscapes .......f22, tripod, its the only way mate, and lowest iso,
Cheers
Mark

F/22 might be a little too much though as most lenses have their "sweet-spot" between f/8 and f/16 if you're after the sharpest and clearest pictures possible.

<edit> Beaten to it by SOL! </edit>

jackdaw

OK
to summarise

Wide apertures (f1.8,f2) very fast shutter speeds - image not so sharp

'narrower' apertures (f8-11) slower shutter speeds (still fast enough id imagine- in good light) but sharper images


f22 -32 image may be blurry due to long exposure times ?

SOL

One word, DIFFRACTION

amcinroy

No no no, there's a bit of confusion here.

Ignore shutter speed completely. This has no effect on image sharpness at all (at least at an optical level). This blur seen when handholding longer exposures is nothing to do with aperture or the lens and is actually to do with your physical movement during the exposure. To evaluate the sharpness effects of aperture you really need to do some tests on a tripod.

Now, all lenses have a sweet spot for sharpness (of the focal plane!) which can be anywhere between f2.8 and f11 depending on the lens. You also have to take into account the depth of field which will affect the rate of sharpness rolloff at points in front of (or behind) the focal plane.

At smaller apertures, diffraction can become a limiting factor to image sharpness but then again if you need huge depth of field then there is no alternative to using small apertures. It's a seesaw of tradeoffs.

Now consider the example of taking a distant landscape. There is no point using f22 in this case because there is no foreground and you should therefore be working at you lens sweet spot (f8 is usually a good general place to be). But in the example of a deep landscape shot where you are low to the ground with huge foreground then f22 (and on a tripod) is a better bet.

Andy

Dades

jackdaw wrote: »

Now im confused ... I thought that the lower the f value
the sharper the image ?

The lower the f value the shallower the depth of field - i.e. a softer focus on objects that are not the main focus of the shot. The subject of the shot will appear sharper - but only in comparison to anything at a different depth within the frame. The higher the f value the more in focus everything in the frame will appear.

At least thats my understanding!

Mellor

Dades wrote: »

The lower the f value the shallower the depth of field - i.e. a softer focus on objects that are not the main focus of the shot. The subject of the shot will appear sharper - but only in comparison to anything at a different depth within the frame. The higher the f value the more in focus everything in the frame will appear.

At least thats my understanding!

I think thats what the OP was refering to, depth of field and focus,
not the sweet spot.

OP, check out depth of field on google

amcinroy

Dades wrote: »

The higher the f value the more in focus everything in the frame will appear.

This depends on what distance everything in the frame is from you. If everything is reasonably far away then this is incorrect. There's no point in having a huge depth of field for a landscape that is essentially at infinity. In this case, using a mid aperture will actually give a sharper image.

Andy

Thirdfox

Also diffraction occurs at really high f values (high is a confusing term and should really say smaller aperture).

f/8-11 is normally the sharpest and by f/16 you the image starts dropping in quality (although more of the image will generally be in focus) and f22 gives you the sharpness as f3.5 but with the benefit that practically everything is in focus.

amcinroy

Thirdfox wrote: »

by f/16 you the image starts dropping in quality (although more of the image will generally be in focus)

Remember, the only thing that is actually in focus is the focal plane.

The rest of the image is out of focus, although by different degrees. Depending on the size of the enlargement made, this may or may not be perceptible. Depth of field is an optical illusion and should not be confused with the term "in focus".

Andy

Dades

amcinroy wrote: »

This depends on what distance everything in the frame is from you. If everything is reasonably far away then this is incorrect. There's no point in having a huge depth of field for a landscape that is essentially at infinity. In this case, using a mid aperture will actually give a sharper image.

Undoubtedly good advice.
I gave the simple version I understood as I figured that's what the OP was looking for!
*Hey there's editing going on*

Thirdfox

amcinroy wrote: »

Remember, the only thing that is actually in focus is the focal plane.

The rest of the image is out of focus, although by different degrees. Depending on the size of the enlargement made, this may or may not be perceptible. Depth of field is an optical illusion and should not be confused with the term "in focus".

Andy

Rightio and that's why people pay massive amounts of money for the TS lens right? For the hobbyist though I don't think the differences are that substantial.

mathias

I didnt help that much on the other thread by getting my fractions back to front , but I will say the best thing Ive read on this particular topic was in the old favourite ,

Understanding Exposure , by Brian Peterson ,

http://www.amazon.co.uk/Understanding-Exposure-Photographs-Digital-Camera/dp/0817463003/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1204652988&sr=8-1

And the section on " Story telling apertures" , it has an exercise you can do so that you can get to grips with the topic by trying it out with your camera.

jackdaw

OK guys that really helps thanks !!

jackdaw

Scott Kelby says you should use the highest F value ??

surely f 36 is too high ??

f 22 should be sufficient yeah ?

if i shoot a blue sky for example on f36 i can see dust specks

nilhg

jackdaw wrote: »

Scott Kelby says you should use the highest F value ??

(

In what context?

Once you get into high f values with most DSLRs diffraction can have an effect so you need a good reason to use them.

Paulw

I think if you ask many landscape photographers, they will use around f/16 for images since that is probably best for a large area in focus combined with the lens/camera sweeter area.

I'm just back from holidays, mostly taking landscapes, and most were shot around f/16, and I'm very happy with the DOF and clarity. Images on my FlickR if anyone wants to check the images and their settings.