talkFestool  

Go Back   talkFestool > Social Club (Off Topic) > Photography and Video

Photography and Video Helping you take better photos and videos

Reply
 
LinkBack Thread Tools Display Modes
  #11 (permalink)  
Old 03-31-2013, 12:13 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default WHY THE APERTURE NUMBERS ARE WHAT THEY ARE (1.4, 2.8 etc)

Ever wondered? It's not too difficult really, so I'm going to indulge in a wee bit of tech talk which will hopefully give some understanding.

The aperture numbers that many will be familiar with are:
f1.4 which lets in double the light of
f2 which lets in double the light of
f2.8 which lets in double the light of
f4 which lets in double the light of
f5.6
f8
f11
f16
f22


So, each time we close the aperture down to the next number (or "stop") we are letting in half the light. To compare two different surface areas, where one is twice the area of the other one:
one of the circles (aperture) is 1 square unit (and what the unit is doesn't matter), and it has a radius of 0.564 units
and the other circle is 2 sq.units, and it has a radius of 0.79 units

We want to compare these two radii, as a ratio:
0.79 divided by 0.564 = 1.4 and this is our magic number. This tells us that if we want to double the surface area of a circle, then we multiply the radius by 1.4

1.4 x 1 = 1.4
1.4 x 1.4 = 2
1.4 x 2 = 2.8
1.4 x 2.8 = 4
1.4 x 4 = 5.6
and so on.

"Hang on" I can hear you saying, "if f1.4 is twice as bright as f2, why do the numbers increase with diminishing brightness, instead of the other way around????"

And quite right too. I'll defer to any better explanation that anybody else can give, but as near as I can tell this is just a convention to make the number comparisons more human friendly. After all, who wants to work with apertures (in diminishing brightness) of:
f1, f0.7, f0.5, f0.36, f0.26 etc
which is what they logically should be. So they decided that to express the numbers in a friendly way they would multiply by 1.4 rather than divide by 1.4. After all, it's only a reference comparison.



__________________
Please sign my Petition to get decent Saw Files made...it takes a few seconds - help us get a result!
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #12 (permalink)  
Old 03-31-2013, 12:16 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default DEPTH OF FIELD (how much of the subject is in focus relative to the distance from the

....the last word in the title is "camera"

There are four things that affect DOF:

  1. The focal length of the lens (shorter focal length gives larger DOF)
  2. The aperture used (smaller aperture, or bigger number gives larger DOF)
  3. The distance of the field from the camera – the greater the distance away the greater the DOF)
  4. The size of the format (i.e. how big the sensor is) – and this relates back to the focal length

Given that it’s only immature technology/production cost that keeps digital sensors small, I’m not going to discuss the last of those four points. One day in the not too distant future all/most camera will have a proper 35mm sized sensor. Suffice to say that in film cameras the same focal length and aperture combination will give a very different result from one format size to another.

The notes that I have put after each point above are really all that you need to know about each of them. I did read in the other thread that someone was saying that there is a sweet spot of aperture for the best performance of any given lens, and that’s true. It’s usually around three stops smaller than the maximum aperture of the lens, but specialist lenses can be exceptions to this. For example, the Canon 85mm f1.2L Portrait lens has been designed to be used at f1.2 so that the DOF is miniscule, and focuses our attention on the all important eyes, where a macro lens is better at the narrower apertures because DOF is already restricted by the closeness of the subject to the camera and so smaller apertures are required to get any DOF. Even then there is an exception to this – the Canon 200mm Macro lens has magnificent out-of-focus characteristics where the background is just a smear of colour, and this is particularly useful shooting wildflowers et al where there a sticks and other nasties in the background that just get obliterated by these characteristics.

However, to say that you’ll get a poorer result from stopping right down or opening right up is not necessarily correct, especially with a good quality lens. You will still get a slightly better result from using a middle aperture, but I’d have to say that I don’t think I’ve ever really seen a noticeable difference from any of my Canon or Mamiya lenses.

Remember – everything in photography is a trade off – if you gain one characteristic then you will have lost something else, without fail.



Very helpful post by a reader:
I use a great little App to occasionally work out the DOF.
It's called DOFMaster.

For example; on that shot, with the 400D, 39 mm focal length lens, f5 (all obtained from the EXIF data), assuming a half metre away from subject, DOFMaster says that about a depth of 4.6 cm will be in focus.

Doubling the f number will ~ double the DOF, so f10 will make a depth focus about 9.2 cm, f16 will make a DOF of ~ 15 cm which should cover the full width of the plane.

The App also determines the hyperfocal distance (minimum focusing distance for which everything beyond that to infinity will be in focus).
At f16 for that setup above it's 3.2m. The final DOF would be 1.6m to infinity.






__________________
Please sign my Petition to get decent Saw Files made...it takes a few seconds - help us get a result!

Last edited by FenceFurniture; 03-31-2013 at 12:18 AM.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #13 (permalink)  
Old 03-31-2013, 12:30 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default DEPTH OF FIELD COMPARISON

Here we have two pics taken with the widest aperture my camera has (f3.5) and the narrowest (f8).
The focusing point has not changed (the little timber stop on the rule)
The camera position has not changed
The zoom lens is set for the same focal length


The pic on the left is at f8, and has a reasonably good (large in this case) DOF, whereas the pic on the left is a much shallower DOF. On the left you can quite easily read the 200 mm mark (although it's not properly sharp), but on the right the 200 mm is just a blur (smear).

However, at the top they are both reasonably similar, even though the right is a little more out of focus(and bear with me on the sharpness - forum restrictions on pic size have diminished that).



In this next picture, the aperture is still wide open at f3.5 (like on the right, above), but I have gone to a wide angle zoom position (and that is the ONLY thing that has changed)
The focusing point has not changed (the little timber stop on the rule)
The camera position has not changed

But unlike the picture on the right (at the same wide aperture) everything in the whole room is in pretty good focus (not critically sharp)




What to do if you cant get enough Depth of Field?
This is where the miracle of Digital photography comes to the fore, and Im going to talk mainly from a perspective of posting pictures on the forum (where the maximum width is 800 pixels).

If you are already at minimum aperture, and cant get the DOF that you want, there is a very nice little work around move the camera back (still using the same focal length) and crop the pic later, but BEFORE you resize it for posting. To do this you need to shoot at a higher resolution than 800 pixels wide, of course. This works an absolute treat because of the third point above the greater the distance away the greater the DOF (with the same focal length).

In other words, because you are restricted to 800 pixels wide, you can shoot at (say) 1600 pixels wide, and crop the extraneous part(s) of the pic off and still get the required resolution.

Its true that you can achieve a greater DOF by moving in closer to the subject with a shorter focal length (but its a trade off), but the biggest problem with this is ending up with a wide angled perspective where the subject will get narrower as it recedes from the camera, so that your box with its nice parallel sides will look quite ridiculous.

This technique is actually the equivalent of using a smaller sensor (Point 4) which gives a greater DOF.



__________________
Please sign my Petition to get decent Saw Files made...it takes a few seconds - help us get a result!
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #14 (permalink)  
Old 04-01-2013, 12:06 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default POLARISING FILTERS

These are the single most useful accessory in photography. They eliminate (or at least reduce) distracting light reflections, and show the real colour that is in the subject. They will not reduce reflections from metals to do that the light source has to be polarised as well as using a PF on the lens. They will NOT reduce the reflections from on-camera flash, and work best on reflections that are at about 45 degrees. This means that on a curved surface you may not reduce all of the reflection, but its all these subtle little things that make a good pic into a great pic.

A good PL will set you back around $100 or so, and you need to be careful about the type required. Many camera light meters are fooled by Linear PLs, and need a Circular PL. They both have the same effect on the reflections, so if you are shooting in manual exposure then its no matter.

Be very wary of cheap PL filters as they too often have a cold colour bias (cyan/blue). Nothing will suck the life out of a pic more than this. I used to have a very expensive B+W brand PL for my medium format camera, and it was superb. It was about $600 in the early 90s as much as a lens.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #15 (permalink)  
Old 04-01-2013, 12:37 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default SUNLIGHT - THE REAL DEAL, and what a POLARISING FILTER WILL DO FOR YOU

This pic was purpose-shot (i.e. another application beyond the forum) and it was always envisaged that the background would be removed, hence not a great deal of effort went into that. I had to shoot it at f8 because that is the limit of my camera, but with a big boy's camera I would have used f16. Focal length is short tele (maybe 100-120mm).

The first pic is with a polarising filter. The second is without, and you can see the effect in the left hand face of the box (the shadowed part), and the corresponding face of the insert tray. The filter has removed the reflection of the yellow base, and appears to give it more contrast (and therefore more 3D form) as a result. Single light source, no fill flash, no reflectors.

I must say that I can see the difference in the quality of the sunlight up here (1007 metres), and minus the pollution and humidity of Sydney. This was taken around 3.00, so not late afternoon light in the least - just good clean mountain light.
No, I didn't make the box.

With PL filter



No filter



And with the background removed (different choice of pic, but you get the idea)





FIN


.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #16 (permalink)  
Old 04-01-2013, 12:43 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default VARIOUS COMMENTS POSTED BY READERS

Ok, that's the end of the pre-prepared material.

These are just a few comments made by previous readers.

Originally Posted by a reader:
I still have never used any of my cameras to full potential.
My response:
I don't think anyone ever does Ray, for two reasons: they can be very complex, and nobody needs all the features (i.e. some need this or that, others need something different)

Originally Posted by a reader:
..and often have to re-read manuals for specific function settings
My response:
So glad you brought this up. Read it, use it, and re-read it. A few months later, read it again. Keep on reading it until there is nothing new before your eyes. Then read it every 12 months, to refresh. APPLY THIS PRINCIPLE TO ALL TOOLS etc.

Originally Posted by a reader:
..just try getting into menus when the shot will be gone in a flash pardon the pun.
My response:
ARRGGH! Don't start me
Ok, you started me. Having spent 10 years as a COBOL programmer, I was trained in the flow of logic, and I can't for the life of me remember where many of the things are in the menus because they are so illogical. Different buttons bring up different menus, but the half of the contents of one should be in the menus from the other button, because they are of a similar nature. It drives me crackers! As does not being able to grab the camera without a button being pressed (then you have to work out which button it was to reverse the error)


Comment Posted by a reader:
I am first a woodworker, and far from a photographer. I'm a P&S kinda guy, BUT have since have explored the camera's functions and didn't even know it had macro (+ other functions) it is only a $120 samsung ES75,

Excellent comment by a reader: I am a master of the art of what not to do. If you need any help with this aspect, please let me know. I have been perfecting my skills in what not to do in photography for 50 years. In fact, I gave up on what not to do in photography when digital came along, and am now working hard on what not to do in woodwork. I expect to master that in due course.
Regards, Mike.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #17 (permalink)  
Old 04-02-2013, 11:33 PM
Member
 
Join Date: Oct 2010
Location: Melbourne, Australia
Posts: 13
Default Re: Photographing your Woodwork pieces doing it properly

Nice outline,
So I need to go out and buy one of every L lens with the red stripe, get the latest and greatest mark III or the like ...learn when to use primes...
And then you want me to learn about seeing the composition, understand depth of field, Ev's and the resultant range of correct sutter speed/ aperture combinations
My oh my you don't want much...
Next you'll want me to have tasteful subject matter that is publishable in a G rated forum.

Honestly

It's a great summary.
Thanks for sharing.
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #18 (permalink)  
Old 04-02-2013, 11:40 PM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default Re: Photographing your Woodwork pieces doing it properly

Cheers Kev.

I think you should definitely spend that dough on more planes.

Where I'm talking about some of the higher cost gear it's really only to highlight that it is worthwhile, if someone is so inclined. I'd rather see people improve on their pics (again, if they feel inclined) with what they've got at hand, and putting a bit more thought into what happens beyond the camera.

Cheers
Brett
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #19 (permalink)  
Old 04-02-2013, 11:54 PM
Member
 
Join Date: Oct 2010
Location: Melbourne, Australia
Posts: 13
Default Re: Photographing your Woodwork pieces doing it properly

Hi Brett,
Now you tell me...
I guess I'll just have to return all the red ringed stuff and the Zeiss lenses seem useless anyway...I'll have to work on my sharpening technique.
More common ground it seems.
Take care
Kev
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
  #20 (permalink)  
Old 04-03-2013, 04:58 AM
FenceFurniture's Avatar
Member
 
Join Date: Sep 2012
Location: Close as dammit to Sydney, Oz
Posts: 137
Default Re: Photographing your Woodwork pieces doing it properly

Yesterday my partner finished the deep etch on the main picture. I felt that the previous green background was a little too bright, and competed with the box for attention, so we went for a more olive colour.




The original photograph has the same spec:
  • Single light source (Old Sol)
  • No reflectors/fill cards
  • No fill flash
  • Polarising filter
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump


All times are GMT +1. The time now is 06:49 PM.