amature F number question

[Igor]

i recently took a landscape photo and it came out pretty poor (ive already posted it on here). i always thought on a landscape i need to have everything in focus. now thats supposed to be a small aperture = large F number. i used F22

after i posted on here i was told not to use any higher than F8. could someone explain to me why that is as i thought i want a small aperture to make everything crisp. as it was a small aperture it needed more light so i had it on a tri-pod and decreased the shutter speed to allow more light

could someone please help me get my head around this :bang:

cheers

 

[strumstrum]

don't get excited I am not about to answer your question

by what I have read f/8 pretty much on any lens is its best sharpest setting, I tend to do landscapes at f/8, unless I want creative bokeh I pretty much start of any shot at f/8 and then adjust if I need to i.e on really sunny days you will need to go f/11-f/16.. the only time I have used really narrow apertures is when doing slow shutter speed light trails at night.

 

[petersmart]

This refers to a phenomenon known as diffraction.

When light hits a sharp edge some of it gets bent very slightly - normally you won't notice this in the ordinary world but when you deal with lenses and sensors it becomes a limiting factor on the F stops you can use.

If you use very small stops then the bending of some of the light causes a slightly unsharp image.

On Digital cameras with very small sensors this normally means that the best stops are no smaller than F8 or F11.

If you have a very good lens then obviously you can use wider apertures when necessary.

 

[Euan]

It could be a number of factors, but at f22 i think (and im no guru!) but your running into diffraction. have a read here, but it could also be haze etc

 

[AliB]

Sure Igor don't let it get to you.

You are quite right in that the larger number means more depth of field and more chance of everything being in focus. There are however, like any "rules" exceptions. Some lenses for instance are not at their best at very wide or very small apertures and tend to deliver their "Optimum" performance at the middle of the range so around f8. Hence that might have been the advice you received.

The other thing to bear in mind especially since I mentioned all that rule breaking is that different lenses on different cameras at different distances give different amounts of depth of field. Now I really don't expect you to memorise this lot but it IS very useful to have a little look at and to get some understanding of where about those really sweet spots are, that way you won't be trying to shoot f22 unless you really need to So.........
http://www.dofmaster.com/dofjs.html

Have a little play with that lot. Put your camera and lens in there and you can play around with distances and read off what would be in focus for you. Lots of good explanations on there too.

Happy bedtime reading

 

[mrtoad]

don't get excited I am not about to answer your question

by what I have read f/8 pretty much on any lens is its best sharpest setting, I tend to do landscapes at f/8, unless I want creative bokeh I pretty much start of any shot at f/8 and then adjust if I need to i.e on really sunny days you will need to go f/11-f/16.. the only time I have used really narrow apertures is when doing slow shutter speed light trails at night.

perfect answer especially with wide angle..28 upwards..in 35mm mode...for good dof with f8
lenses are happiest somewhere near 2/3 there fully closed aperture..iirc
my camera only goes to f8..being a small compact type and i am happy with f4 to f5.6 on most days...since that then gives me fast speeds...i set iso at 64

its where you focus as well...not on infinity but somewhere around 8-30 metres from your standpoint for general landscaping...this gets some decent foreground sharpness with good presentation of far objects...which your eye cant see in focus anyhow...all at the same time
keep the shot looking natural...as you saw it

 

[HoppyUK]

It's diffraction, as mentioned. With crop format cameras like your Sony, good lenses usually peak around f/5.6. On full frame, the same lens will improve until about f/8 due to the larger format. For the same reason, Mr Crow's compact with its tiny sensor won't go higher than f/8 because diffraction just wrecks image quality beyond that.

It's easy enough to see for yourself. Camera on tripod, and shoot a sequence through the aperture range. For diffraction, look only at the centre of the image as the edges are more affected by all sorts of other aberrations.

At lowest f/number, the cenrte will probably be quite sharp and the edges and corners will be less good. As f/number increases the edges especially will get much better but after f/5.6 or so the centre of the image will start to look less sharp. F/11 is usually okay but f/16 is getting iffy and f/22 looks pretty poor IMO. I never shoot at f/22.

 

[mrtoad]

It's diffraction, as mentioned. With crop format cameras like your Sony, good lenses usually peak around f/5.6. On full frame, the same lens will improve until about f/8 due to the larger format. For the same reason, Mr Crow's compact with its tiny sensor won't go higher than f/8[/colour]because diffraction just wrecks image quality beyond that.

i do object..my sensor is all of 1/2.5..

 

[a lex]

Thought I might just add a question at the end here in the hope someone can clear it up for me...

Just took a few photos of a pen (its been sold but thats irrelevant) from my tripod mounted camera. Focal length was around 70mm and shutter time was at about 1/6 second. Anyway, I shot them using f8 and only the centre of the photo is sharp and in focus (which I assume is where the focus points were?) and the further out the picture went from the centre it went out of focus. Am I right in thinking that if I wanted to make the entire picture in focus it would just be a case of increasing the f number? To say f12 ish.


Thanks for the help.

 

[mrtoad]

Thought I might just add a question at the end here in the hope someone can clear it up for me...
Just took a few photos of a pen (its been sold but thats irrelevant) from my tripod mounted camera. Focal length was around 70mm and shutter time was at about 1/6 second. Anyway, I shot them using f8 and only the centre of the photo is sharp and in focus (which I assume is where the focus points were?) and the further out the picture went from the centre it went out of focus. Am I right in thinking that if I wanted to make the entire picture in focus it would just be a case of increasing the f number? To say f12 ish.
Thanks for the help.

other considerations are how far from the object you were
speed wont affect depth of field and since you were 'on 3' you were steady
from f8 the next is f11.then 16 22 32 etc...

i would think you would have needed to go to f16 or 22 if possible
or get closer with a smaller focal length lens...
why did you use 70

 

[HoppyUK]

Thought I might just add a question at the end here in the hope someone can clear it up for me...

Just took a few photos of a pen (its been sold but thats irrelevant) from my tripod mounted camera. Focal length was around 70mm and shutter time was at about 1/6 second. Anyway, I shot them using f8 and only the centre of the photo is sharp and in focus (which I assume is where the focus points were?) and the further out the picture went from the centre it went out of focus. Am I right in thinking that if I wanted to make the entire picture in focus it would just be a case of increasing the f number? To say f12 ish.


Thanks for the help.

You're probably looking at shallow depth of field as a result of shooting at close didstance, in which case using a higher f/number would sort that.

It could also be field curvature, depending on the lens, or maybe other things. Hard to say withot seeing the pic or at least knowing what camera (format) was used and which lens.

 

[a lex]

Yeh I meant f11...! Not sure why I mentioned shutter speed, of course it means nothing! I was in AV mode, just f8 and that was the metered speed. Anyway...

Used 70 for a few reasons, firstly it was awkward with the tripod, didn't have enough room to get right up close. Also, I only had my 17-85 to hand. Getting up close to the object though it just wouldn't AF. I really should think about getting a macro lens for these upclose sort of shots huh.

Thanks for the pointers Geoffrey, will have a go at f22 later.

 

[mrtoad]

Yeh I meant f11...! Not sure why I mentioned shutter speed, of course it means nothing! I was in AV mode, just f8 and that was the metered speed. Anyway...

Used 70 for a few reasons, firstly it was awkward with the tripod, didn't have enough room to get right up close. Also, I only had my 17-85 to hand. Getting up close to the object though it just wouldn't AF. I really should think about getting a macro lens for these upclose sort of shots huh.

Thanks for the pointers Geoffrey, will have a go at f22 later.

well thats the trade off for big lenses...no dof to speak of
you did your best and got a result...you sold the pen!!

my pos has a macro mode on it...but you have to get close for it to work...
macro also has limited dof...unfortunately...
:|

 

[a lex]

You're probably looking at shallow depth of field as a result of shooting at close didstance, in which case using a higher f/number would sort that.

It could also be field curvature, depending on the lens, or maybe other things. Hard to say withot seeing the pic or at least knowing what camera (format) was used and which lens.

Cheers Richard, will try with a higher f number later on.


One more question if you don't mind... now I do not yet have a macro lens... all I have is the 17-85 IS USM, 50mm 1.4 and 18-200 IS all on a 450D... for this sort of picture what sort of set up would you recommend? I mean is it better to have the camera further away and zoom (like 70-200mm in) or is it better to use the 50mm or get even closer with the camera and use say 20mm. Of course the problem I find with getting the camera much closer is it struggles to auto focus.. I assume this is the minimum working distance of the lens or something to that effect...?


Cheers, appreciate the help.

 

[a lex]

well thats the trade off for big lenses...no dof to speak of
you did your best and got a result...you sold the pen!!

my pos has a macro mode on it...but you have to get close for it to work...
macro also has limited dof...unfortunately...
:|

Im still undecided what lens to buy this weekend... either the 70-200 f4 IS for some nice sharp long-ish range shots or the 100mm macro... hmmm.

 

[bomberman]

diffraction is the reason to avoid very high f numbers, but i would say the advice not to go above f/8 is just plain silly. surely for a very large scene (like a landscape) f/8 could still throw some areas out of focus depending on where your focus point is so i would say f/11 - 16 are perfectly OK.

Also i have a lens with 7 aperture blades and on night shots i like to stop down to f/12 and above because this gives me very defined 14 pointed sun-stars that i can't get otherwise.

so i would say f/16 is as far as i would go unless i had a reason.

 

[HoppyUK]

Cheers Richard, will try with a higher f number later on.

One more question if you don't mind... now I do not yet have a macro lens... all I have is the 17-85 IS USM, 50mm 1.4 and 18-200 IS all on a 450D... for this sort of picture what sort of set up would you recommend? I mean is it better to have the camera further away and zoom (like 70-200mm in) or is it better to use the 50mm or get even closer with the camera and use say 20mm. Of course the problem I find with getting the camera much closer is it struggles to auto focus.. I assume this is the minimum working distance of the lens or something to that effect...?

Cheers, appreciate the help.

No reason why your lens would struggle to focus close, unless you are up against the minimum distance. Canon 17-85 doesn't go very close, but you could probably sort that quite well enough to photograph something like a pen with a simple close-up lens for £20 - Hoya +2 diopter should be fine.

Im still undecided what lens to buy this weekend... either the 70-200 f4 IS for some nice sharp long-ish range shots or the 100mm macro... hmmm.

Canon 100mm macro is a serious lens. Fine if you're keen on macro, down to 1:1 magnification, and shoot critical stuff where edge to edge sharpness is necessary. But if it's more like butterflies and flowers (and pens) then you probably don't need to go that far. Try the close-up lens first.

I use a 70-200L 4 IS and a superb lens it is too. I sold my 100 macro and swapped it for this lens and a set of Kenko extension tubes (£120). I get pretty good quality down to 1:1, at a range of shooting distances thanks to the zoom, and IS also helps. There is full auto-exposure and auto-focus retained with the tubes but in practise most people use manual focusing for really close macro - set focus and rock backwards and forwards gently with your body to pick the optimum focus position.

These alternative macro options are well worth considering carfully before splashing out on a pukka macro lens.

diffraction is the reason to avoid very high f numbers, but i would say the advice not to go above f/8 is just plain silly. surely for a very large scene (like a landscape) f/8 could still throw some areas out of focus depending on where your focus point is so i would say f/11 - 16 are perfectly OK.

Also i have a lens with 7 aperture blades and on night shots i like to stop down to f/12 and above because this gives me very defined 14 pointed sun-stars that i can't get otherwise.

so i would say f/16 is as far as i would go unless i had a reason.

I don't think anybody said don't go above f/8 for macro. If you're referring to Mr Crow's camera, that is a compact which simply doesn't go any higher than that as diffraction cuts in much sooner with the tiny sensors on compacts.

I'm very happy to use f/11, and f/16 is usually not a problem either, but after that things do get very noticeably more mushy on crop format DSLRs.