Author Topic: Photography technical advice, questions, tips and techniques.  (Read 16918 times)

Tank

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This thread is intended to be about technical questions eg What'd the difference between a RAW file and a jpg file? etc.

To post pictures of interest and for comment critique use the thread Photography, photos you took, photos you are in, photos you like, the lot!

I got my first serious camera in 1977, it was one of the first things I bought when I got a job. I have written some very simple novice level descriptions of the terms you will come across in photography if you want to do anything more than 'point and shoot'. In most of the subject headings I have added a link to the Wiki page for the subject if you wish to look at a subject in more detail.

If you have a question ask it. There is no such thing as a stupid question if it's an honest question.

Basic terms


What is the focal length of a lens?

Imagine a simple magnifying glass. Hold it up with a piece of paper behind it. Focus an image on the paper. The distance between the centre of the lens and the paper is the focal length of the lens.

The longer the focal length of the lens the narrower its angle of view. The shorter the focal length the wider its angle of view.

What is a telephoto lens? (Trick question)

It is any lens where its physical length is less than its focal length. In this case 'tele' stands for 'telescoped'. It is a term that has become synonymous with lenses with long focal lengths.

What is a telephoto lens? (Not a trick question)

It is a lens that appears to bring the subject closed to you than you would normally perceive it.

What is a 'standard' lens?

Well this has changed over the decades. Before zoom lenses (lenses that can change their focal length and remain in focus) a standard lens had a focal length of between 45 and 55mm (usually 50mm) on a 35mm film body. That focal length approximates the perceived central angle of view of the human eye. I say perceived as the actual angle of view of the human eyes are about 180°.

With zoom lenses now the norm a standard lens is in the order of 18mm to 55mm. (28 to 83mm in old 35mm terms)

What do the aperture numbers mean?

If a lens has a focal length of 100mm and the front lens is 37mm in diameter the lens has a maximum aperture of 100/37 = 2.8 or f2.8 in tog (photographer) speak.

This ratio is important as if you double 2.8 you get 5.6, then 11 (approximately) then 22, numbers that are often printed on lenses. So what? Well the area of the aperture halves with each successive step ('stop' in tog speak). This matters because halving the area halves the light transmitted through the lens as the numbers get larger the aperture physically gets smaller. So going from small numbers to larger numbers is called 'Stopping down' the lens.

What is the shutter speed?

This is probably the simplest thing to understand in photography. The shutter is a mechanism (there are different types) that opens for a set time to let light coming in the lens get to the film (or digital sensor) to capture an image.

The shutter speeds go in steps (like aperture know as stops) that cut the mount of light in half e.g. 1/250th of a second lets in half the light of 1/125th of a second.

Film sensitivity or 'speed' and digital sensor sensitivity

In the pre-digital era the sensitivity of film was rated as 'ASA' or 'ISO' and started as low as 25, and went in a sequence approximating 25, 64, 100, 200, 400, 800 etc. and each step vaguely approximated a 'stop' like shutter speed and aperture size.

There was a distinct trade off between speed and picture quality. The higher the speed the lower the quality. There were two distinct process types, slides (projected) and negatives (printed). And within slides there were two distinct processes Kodak's 'Kodachrome' and the 'E6' for the rest.

Digital photography has inherited the terminology but as it has improved it has expanded the sensitivity range out of all recognition to the film era. While there are still issues with quality vs sensitivity I.E. the higher the sensitivity the poorer the quality you can now use sensitivities of 3200 with relative impunity and as technology improves the usability of higher sensitivities is bound to improve.

Another benefit of digital technology is that one can change sensitivity between frames and not wait till you had to finish a whole roll of film!

Secondary effect of the aperture, depth of field control.

The primary effect of the aperture is exposure control. However it has a creative secondary effect. It can be used to control which part of the image is in focus in front of the lens in relation to the position on the lens. This zone of focus is known as the 'depth of field'. It is sometimes called the 'depth of focus' but that is something else that goes on behind the lens.

The aperture you use is dependent on the effect you want in your final image. If you want everything to be in focus from as close as possible to the horizon then you use a smaller aperture (f16, f22). If you want your subject to appear against an out of focus background you use a larger aperture (f1.4, f2, f2.8)

To get the correct exposure you will have to adjust the shutter speed and/or ISO 'speed'.


More advanced subjects


Hyperfocal distance.

For any given aperture and lens combination there is what is known as a hyperfocal distance. This is the distance from the front of the lens that you focus on, respective of where the subject actually is. The farthest point of the depth of field will be at infinity (the horizon) and the nearest could be be a couple of meters in front of the lens while the lens is actually focused say 25m away. And everything from the horizon to 2m in front of you is in focus. This is how cheap little film cameras get away with not having a focusing mechanism. They have a wide angle lens with a small (f8) aperture lens with a focus set at the hyperfocal distance.

You can use the hyperfocal distance to good effect where you have moving subjects like a football match. Set the lenses focus so the distant part of the depth of field is the far side of the football pitch and then you don't have to touch the focus for the whole game.


File size vs file types.

The most basic file is a Bit Map. It's pretty much what it says. Each pixel has a red, green and blue (RGB for short) byte associated with it. So a 100 x 100 pixel image will have 10,000 pixels each with 3 bytes of storage so it'll make a file of 30k bytes. If the image were 6,000 x 4,000 pixels the file would be 6,000 x 4,000 x 3 = 72 mega bytes! Well you couldn't view porn via a dial up modem with those file sizes so something had to be done!

The result was a jpg or jpeg file. A jpg file is a compressed file. The compression works because the human eye is imperfect and can't distinguish the subtleties of colour that can be reproduced on a screen. Essentially it takes adjacent pixels and if they are close enough in colour it makes an average colour for those pixels and records that. So if you have a blue sky it compresses very well indeed. A highly detailed photo of a peacock feather does not compress anything like as well. This is why images of a constant size (6k x 4k) have different size .jpg files.

A jpeg is what is known as a 'lossy compression' you can't get the original data back as it will have been 'averaged'. The TIF file type, often used in printing, is a non-lossy compression in that if adjacent pixels are identical the encoding loses no information by making an 'average' value.

A RAW file, given different names by different camera makers, is like a TIF file in that it is a non-lossy compression but is often a propitiatory encoding so you have to use a specialist image viewer to see it. Or the image viewer you use has a specific decoder built in for it.

Some image types such as .gif or .png can have layers and those layers can be transparent allowing an image to be dropped onto a coloured background and not having a white rectangle around it.
« Last Edit: August 09, 2018, 03:55:22 PM by Tank »
If religions were TV channels atheism is turning the TV off.
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Remember, your inability to grasp science is not a valid argument against it.

Dave

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Re: Photography technical questions.
« Reply #1 on: July 30, 2018, 11:38:58 AM »
This thread is intended to be about technical questions eg What'd the difference between a RAW file and a jpg file? etc.

To post pictures of interest and for comment critique use the thread Photography, photos you took, photos you are in, photos you like, the lot!

Good move, Tank.
Tomorrow is precious, don't ruin it by fouling up today.
Passed Monday 10th Dec 2018 age 74

Tank

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Re: Photography technical questions.
« Reply #2 on: July 30, 2018, 12:55:06 PM »
Thanks Dave
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

jumbojak

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Re: Photography technical questions.
« Reply #3 on: July 30, 2018, 01:11:58 PM »
This is a great idea. Expect lots of questions from me...
 

"Amazing what chimney sweeping can teach us, no? Keep your fire hot and
your flue clean."  - Ecurb Noselrub
" Please hold your high school or college math books in higher esteem than
your copy of the KJV. " - Icarus

Tank

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Re: Photography technical questions.
« Reply #4 on: July 30, 2018, 01:15:24 PM »
File size vs file types.

The most basic file is a Bit Map. It's pretty much what it says. Each pixel has a red, green and blue (RGB for short) byte associated with it. So a 100 x 100 pixel image will have 10,000 pixels each with 3 bytes of storage so it'll make a file of 30k bytes. If the image were 6,000 x 4,000 pixels the file would be 6,000 x 4,000 x 3 = 72 mega bytes! Well you couldn't view porn via a dial up modem with those file sizes so something had to be done!

The result was a jpg or jpeg file. A jpg file is a compressed file. The compression works because the human eye is imperfect and can't distinguish the subtleties of colour that can be reproduced on a screen. Essentially it takes adjacent pixels and if they are close enough in colour it makes an average colour for those pixels and records that. So if you have a blue sky it compresses very well indeed. A highly detailed photo of a peacock feather does not compress anything like as well. This is why images of a constant size (6k x 4k) have different size .jpg files.

A jpeg is what is known as a 'lossy compression' you can't get the original data back as it will have been 'averaged'. The TIF file type, often used in printing, is a non-lossy compression in that if adjacent pixels are identical the encoding loses no information by making an 'average' value.

A RAW file, given different names by different camera makers, is like a TIF file in that it is a non-lossy compression but is often a propitiatory encoding so you have to use a specialist image viewer to see it. Or the image viewer you use has a specific decoder built in for it.

Some image types such as .gif or .png can have layers and those layers can be transparent allowing an image to be dropped onto a coloured background and not having a white rectangle around it.   
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Tank

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Re: Photography technical questions.
« Reply #5 on: July 30, 2018, 01:20:57 PM »
This is a great idea. Expect lots of questions from me...

That's exactly why I started the thread and it could become a useful archive for others.
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

hermes2015

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Re: Photography technical questions.
« Reply #6 on: July 30, 2018, 02:01:50 PM »
This thread is intended to be about technical questions eg What'd the difference between a RAW file and a jpg file? etc.

To post pictures of interest and for comment critique use the thread Photography, photos you took, photos you are in, photos you like, the lot!

I like your idea. Hope to learn lots here! I have taught myself some tricks over the years, but one can always learn new ones.
“Who is to say that pleasure is useless?”
― Charles Eames

hermes2015

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Re: Photography technical questions.
« Reply #7 on: July 30, 2018, 02:06:07 PM »
A RAW file, given different names by different camera makers, is like a TIF file in that it is a non-lossy compression but is often a propitiatory encoding so you have to use a specialist image viewer to see it. Or the image viewer you use has a specific decoder built in for it.

And it usually looks pretty disappointing and needs some post-processing similar to what we used to do in the darkroom.
“Who is to say that pleasure is useless?”
― Charles Eames

Tank

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Re: Photography technical questions.
« Reply #8 on: July 30, 2018, 02:11:58 PM »
This thread is intended to be about technical questions eg What'd the difference between a RAW file and a jpg file? etc.

To post pictures of interest and for comment critique use the thread Photography, photos you took, photos you are in, photos you like, the lot!

I like your idea. Hope to learn lots here! I have taught myself some tricks over the years, but one can always learn new ones.

I hope to learn a lot from you too!
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Dave

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Re: Photography technical questions.
« Reply #9 on: July 30, 2018, 02:12:09 PM »
You just beat me to it, Tank!

 :grin:
Tomorrow is precious, don't ruin it by fouling up today.
Passed Monday 10th Dec 2018 age 74

jumbojak

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Re: Photography technical questions.
« Reply #10 on: July 30, 2018, 02:31:08 PM »
What should I look for in a wide angle lens? I'm trying to document some of the swampland around home and the neither my telephoto nor the lens that came with the camera do a satisfactory job.
 

"Amazing what chimney sweeping can teach us, no? Keep your fire hot and
your flue clean."  - Ecurb Noselrub
" Please hold your high school or college math books in higher esteem than
your copy of the KJV. " - Icarus

Tank

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Re: Photography technical questions.
« Reply #11 on: July 30, 2018, 02:32:02 PM »
What should I look for in a wide angle lens? I'm trying to document some of the swampland around home and the neither my telephoto nor the lens that came with the camera do a satisfactory job.

What lens came with your camera?
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Tank

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Re: Photography technical questions.
« Reply #12 on: July 30, 2018, 02:39:47 PM »
What is the focal length of a lens?

Imagine a simple magnifying glass. Hold it up with a piece of paper behind it. Focus an image on the paper. The distance between the centre of the lens and the paper is the focal length of the lens.

The longer the focal length of the lens the narrower its angle of view. The shorter the focal length the wider its angle of view.

If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Tank

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Re: Photography technical questions.
« Reply #13 on: July 30, 2018, 02:42:34 PM »
What is a telephoto lens? (Trick question)

It is any lens where its physical length is less than its focal length. In this case 'tele' stands for 'telescoped'. It is a term that has become synonymous with lenses with long focal lengths.
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Tank

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Re: Photography technical questions.
« Reply #14 on: July 30, 2018, 02:45:15 PM »
What is a telephoto lens? (Not a trick question)

It is a lens that appears to bring the subject closed to you than you would normally perceive it.
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.