PDA

View Full Version : The Basics - Sensitivity/Shutter Speed/F stop



Puffer Fish
11-21-2007, 06:55
In the old days of 35mm, everyone knew that you controlled your film speed by what film you bought, the F stops were on the outside of the lens, and the shutter speed was set on the camera. Today, they are all mixed together, usually in some combination that comes out of the "AUTO" setting.

Over this holiday weekend, will see if I can go thru each of these, show their effect and provide some basic recommendations.

Aquagirl - this one is for you...

I'm doing this, because many of today's camera's default to setting that produce less than great results. A great example of this is the new Fuji F50... great camera, with resolution better than many DSLR's being used, but if you turn it on auto, you will get grainy, poor quality images. And if you go to the other settings, you need to know what they do.

I'll start with ISO and it's effect on picture quality... then the effect of shutter speed adjustment and finally F stop setting. To save server space, will do two images to show the difference for each one.

It would surprize most people, but a perfectly exposed G9 or F50 image, can have better image quality than a D80 or D200..but your chances of getting that image are around 1 in 200 with the point and shoot, and 85% or so with the DSLR's. Would like to see those odds go to at least 50/50.

Silverlode
11-21-2007, 07:07
It would surprize most people, but a perfectly exposed G9 or F50 image, can have better image quality than a D80 or D200..but your chances of getting that image are around 1 in 200 with the point and shoot, and 85% or so with the DSLR's. Would like to see those odds go to at least 50/50.
The 1 in 200 point and shoot, is that on manual setting or the 'awful' (I agree with you actually) Auto setting.
Has the 'lag' in point and shoot improve? As in I'd used a G5 and it drove me nuts with the lag between each shot. The DSLR's a bliss in this area. I'd tried the Ixus recently and there's still a lag time between each shot, but I am not sure if the technology has improved but Canon may not have applied it to their lower model camera. What about the F50? Does it have this 'problem'?

Puffer Fish
11-21-2007, 07:17
It would surprize most people, but a perfectly exposed G9 or F50 image, can have better image quality than a D80 or D200..but your chances of getting that image are around 1 in 200 with the point and shoot, and 85% or so with the DSLR's. Would like to see those odds go to at least 50/50.
The 1 in 200 point and shoot, is that on manual setting or the 'awful' (I agree with you actually) Auto setting.
Has the 'lag' in point and shoot improve? As in I'd used a G5 and it drove me nuts with the lag between each shot. The DSLR's a bliss in this area. I'd tried the Ixus recently and there's still a lag time between each shot, but I am not sure if the technology has improved but Canon may not have applied it to their lower model camera. What about the F50? Does it have this 'problem'?


I am being nice, if you use "auto", then it will be zero.

Lag is less, but still a bit of an issue, but timing and such are latter subjects.

frankc420
11-21-2007, 09:37
I'm awaiting your posts... :)

Puffer Fish
11-21-2007, 09:54
I'm awaiting your posts... :)
Sorry, but will not be until tonight... have to take pictures to show things.

gibson1525
11-21-2007, 09:56
me too, let's get this started

Puffer Fish
11-21-2007, 10:27
me too, let's get this started
I would like to keep this simple, but also show what is really going on, so people can judge for themselves. Tonight I will do:

1. ISO's effect on image quality (real world).

2. F Stop effect on how thing look (there are two aspects to this)

3. Shutter speed - what is too slow, and how to know from an image.

I will also see if I can under and over expose images and show what "adjustments" due to the image (not good, by the way).

Cheddarchick
11-21-2007, 12:26
Yippee!!! Thank you Puffer!!!!

quasimoto
11-21-2007, 21:34
Oh man, just when I am thinking about buying a camera for some UW photos you go and do this. I know my head is going to start to spin.

Puffer Fish
11-21-2007, 23:12
Ok.. I have taken two images, from roughly the same distance, enlarged roughly the same (If you check, I actually made the 1600 ISO a bit better, so there was no issue)

Keep in mind that this is an enlargement of a section of a picture... the original is very large.

ISO 100 -

http://i78.photobucket.com/albums/j98/garinj/ISO100.jpg


I took this, at the edge of resolution, so it would be easy to compare.

Now the same image, in ISO 1600 -

http://i78.photobucket.com/albums/j98/garinj/ISO1600.jpg


I hope everyone can see the difference.. and in auto, this camera might actually choose 1600.

Notice the blotchy appearance in the second image... it is "Noise".

I cleaned up the images a bit, and while there is no major difference, one gets this:

http://i78.photobucket.com/albums/j98/garinj/ISO100A.jpg

http://i78.photobucket.com/albums/j98/garinj/ISO1600A.jpg

Obviously, between 100 and 1600, the image varies in quality.

So, if you want the best pictures, shoot in the lowest practical ISO...

Puffer Fish
11-21-2007, 23:13
Next up... F stops.

gibson1525
11-22-2007, 09:16
thanks for posting that. can't wait for the next one.

ReefHound
11-22-2007, 10:04
Can you explain exactly what ISO is and how to select what is "practical"?

frankc420
11-22-2007, 10:23
Can you explain exactly what ISO is and how to select what is "practical"?

I would have to agree with RH here, what conditions would you use 100 and what conditions would you bump it up?

Silverlode
11-22-2007, 15:48
When one is using film in the 'old' days before digital camera, ISO is the measurement of the film's sensitivity to light.
Generaly, most film speed people used then were/are ISO 100, for daytime photography. If you use ISO 50-200 at night or in a room, the flash would go off (if there's auto flash). I used to use ISO 200 film because it allows me to take photo at lower light without firing off the flash as often. There are also ISO400 film, which can be used at lower light without flash.
So if one has a high ISO, long shutter speed (Puffer will cover this), and if you have steady hands (pr tripod), and steady subject, it is possible to take a nightshot without using the flash.
However, one down side of high ISO is that the photo can get very grainy. The higher the ISO the grainier it gets, and it's especially obvious if it's enlarged.
In the digital camera age, the same thing applies in term of grain, though I can testify that the better camera, as in DSLR, can take higher ISO with less grain effects. When I used my G5, I never shoot past ISO 200, because anything beyond that gets very grainy. However, with my Nikon DSLR, my ISO is normally set at 400, and I have pushed it up to 1600 with acceptable (to me) grains. (low light, indoor condition with no flash or night shot with no flash)

Edit: Each digital camera is different, the sensor size, resolution, manufacturer's measurement and quality means that each camera reacts different to different ISO. Canon point and shoot starts at ISO 50, and other manufacturer's starts at ISO 100.
But they may end up with similar sensitivty to light. It would pay to play around with the different ISO settings on your camera, take some photos (like what Puffer did), and zoom in on when you look at it on the computer and see at which ISO setting is the photo unacceptable to you. Generally, higher ISO is used to take 'action' photo without flash or in lower light condition without flash.

Puffer Fish
11-22-2007, 15:57
Can you explain exactly what ISO is and how to select what is "practical"?


Here is a very complete definition:

Film speed - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Film_speed)

But keep this in mind... It is the combination of ISO/F-stop/shutter speed, along with the light present, that defines how much light gets to the sensor (what used to be film).

When should you use it? Whenever possible.. we will get more detailed as I go thru the other settings, but keep this in mind - If you could.. you would use the best of each setting, but that is almost never possible, so you are going to have to compromise...the trick is to know which to compromise first (will get in much more detail shortly)

Puffer Fish
11-22-2007, 16:19
Ok, next up, F-stops. The camera I have has a range of 2.8 to 8. The range varies a lot, depending on the camera. The number actually means the size of the lense(opening) versus the focal length. Each number, in the old days, used to be halving or doubling the amount of light that gets to the film... modern ones will have lots of partial stops, by the way.

For those that want to know:

f-number - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/F-number#Standard_full-stop_f-number_scale)

The important things to know are:

1. The smaller the number, the more light it lets in.

2. The bigger the number, the more will be in focus.

So my camera has four standard stops - 2.8 - 4 - 5/6 - 8 These are steps like the units of ISO 800 - 400 - 200 - 100, and shutter speeds (in portions of a second) of 1/60 - 1/120 - 1/240 - 1/500 (really 1/480, but there is a lot of rounding).. So.... 1/120/F 5.6/ISO 200 is the exact same exposure as 1/240/F 2.8/ISO 100, but they will not look the same. Mostly because of the change in F value.

This test takes a very accurate setup, so I used a tripod, set the paper 10 inches away, focused on the grey line in the middle and took images. I used the widest angle, which make this look the best, but it is the one that is mostly used underwater.

The image looked like this:

Note: This image is compresses, made smaller and I am showing it just so you can see the size of the original.

http://i78.photobucket.com/albums/j98/garinj/F28test2.jpg


Here is the bottom of that image, taken with F 2.8...

http://i78.photobucket.com/albums/j98/garinj/F28test.jpg

Here it is with F 8....

http://i78.photobucket.com/albums/j98/garinj/F8test.jpg

So, so far, one should use the lowest ISO number and the biggest F number... but there are still two issues left.... the shutter speed and the amount of light left to begin with.

Puffer Fish
11-22-2007, 16:22
Due to the really small actual focal length of the lense, the F8 image above is truly amazing... no normal SLR or large sensor DSLR can do that, as their focal lengths are typically much bigger, and this effect is both focal length and f-stop, with the focal length being the most important (small is better here)

bversteegh
11-23-2007, 13:25
Can you explain exactly what ISO is and how to select what is "practical"?

I would have to agree with RH here, what conditions would you use 100 and what conditions would you bump it up?


What ISO to use depends on the ambient light, and whether you have a strobe. If you are using a strobe, use a low ISO (like 100); as the lower ISO speeds have less noise.

If you have limited ambient light and no strobe - that is when you use higher ISO's. As Puffer Fish showed, you add noise as ISO increases. You really need to test your camera to see what ISO levels are acceptable to you - most non-DSLR cameras start showing noticable noise increase above 400 ISO.

You use a higher ISO to give you sensitivity in low light, so you can use an acceptable shutter speed (anything lower than 1/60 sec is likely to blur unless you have a really short focal length lens). Another place higher ISO's can be used are places that prohibit flash (museums for example). Shooting a higher ISO here can allow you a little more flexibility in shutter speed.

Puffer Fish
11-24-2007, 15:27
So, what about shutter speed?

Well, shutter speed effects the exposure, the same as F-stops, with faster letting in less light, and slower letting in more.

I took a large picture of a map, and then just cut out the center portion, so that you could see what it is doing.

All images were hand held, at wide angle, using macro.

At anything faster than 1/125th of a second, it is easy to get a sharp image... if you jerk the camera, you can still mess it up, but in general, it works really well. This is a 1/256 shot:

http://i78.photobucket.com/albums/j98/garinj/256thsecond.jpg

Remember, this is a very small section of a picture.

Hold the camera steady.. and you can go lower... this is a 1/106 image:

http://i78.photobucket.com/albums/j98/garinj/104thsecond.jpg


Going slower:

A 1/64th Picture:

http://i78.photobucket.com/albums/j98/garinj/64thsecond.jpg

Here is a 1/30th:

http://i78.photobucket.com/albums/j98/garinj/30thseond.jpg


Look carefully and it is starting to blur.

Here is a 1/26th of a second:

http://i78.photobucket.com/albums/j98/garinj/26thsecond.jpg

The camera I am using has anti-shake.. and it attempts to adjust for that movement, and I can, but only about one stop...

A 1/39th and a 1/26th with the shake control on:

http://i78.photobucket.com/albums/j98/garinj/39thsecondshake.jpg

http://i78.photobucket.com/albums/j98/garinj/26thsecondshake.jpg

So, there are the first three big ones.... if you could, you would use the lowest ISO... the smallest lense opening (bigger number) and a shutter speed of at least 125th or maybe 1/60 (if you have anti-shake).

How likely is this to happen? If it is a nice sunny day, and you are in clear water, 30 ft or less... all the time. If you have the correct strobe (more on that later), all the time. In 70ft of water, with 50 ft of vis..never.

So, what should you adjust?

First should be f-stop (particularly in wide angle), most camera's actually have slightly better resolution in the middle of the range... so go to F4 or f5.6. Then, adjust the ISO, but beware of going over 400.

So, if 1/125 shutter, F5.6 and ISO 400 does not work... then consider what you are taking a snap shot.. in don't worry about it.

Puffer Fish
11-24-2007, 15:28
Next thread... the JPEG issue.. how does it effect your picture? And is RAW always better than JPEG?

ReefHound
11-24-2007, 16:57
Interesting. I wish my camera's "auto" modes showed me the parameters it decided to use.

Puffer Fish
11-24-2007, 17:30
Interesting. I wish my camera's "auto" modes showed me the parameters it decided to use.


Even if you cannot see it, it is stored with the image, so you can always see what it was using. Ok, after the fact, but at least you will know.

Some compact camera's also show the histogram... which is one valuable piece of information... wish the F50 did, but that is the only thing it does not.

dbh
11-24-2007, 18:18
Would like to see those odds go to at least 50/50.

Not probable due the difference in quality of glass.

Dave

dbh
11-24-2007, 18:35
In a nutshell, your aperture controls the part of your picture lit by your strobes (foreground) and shutter speed controls the background.

On wide angle, If you want blue background, use a slower shutter speed....if you want black....speed it up.

If you are shooting macro, changing your shutter speed isn't going to affect your outcome (unless you use way too slow and get blur as Puffer illustrated above).

As to JPEG vs RAW, nothing is better ALL of the time. RAW is better MOST of the time (and all accomplished u/w photographers that I know shoot in RAW). With JPEG, your camera is doing the "correcting" for you (and remember, MOST cameras are made for topside shooting).

Dave

Puffer Fish
11-24-2007, 19:09
In a nutshell, your aperture controls the part of your picture lit by your strobes (foreground) and shutter speed controls the background.

On wide angle, If you want blue background, use a slower shutter speed....if you want black....speed it up.

If you are shooting macro, changing your shutter speed isn't going to affect your outcome (unless you use way too slow and get blur as Puffer illustrated above).

As to JPEG vs RAW, nothing is better ALL of the time. RAW is better MOST of the time (and all accomplished u/w photographers that I know shoot in RAW). With JPEG, your camera is doing the "correcting" for you (and remember, MOST cameras are made for topside shooting).

Dave


Dave, as you shall see shortly, the issue is not JPEG, and not all camera's have an issue...If most people believe in RAW is the only way to go... then most people will be wrong... it is very, very camera specific...

Puffer Fish
11-24-2007, 19:12
Would like to see those odds go to at least 50/50.

Not probable due the difference in quality of glass.

Dave

You need to go back and look at resolution charts... a D200 does not have better glass, regardless of the lens, it has lots of other stuff (and good stuff it is) but it has no quality advantage over a F50....hard as that is to believe. The quality differences, in most shots are due to settings and several other issue, that one can control. Just that most do not know how to.

Soonerwink
11-24-2007, 19:19
This is a great thread for those of us that are new to underwater photography. I have only shot in auto becauase I knew no better. Thanks for the education. I will have to save this thread though, because I will forget before next Spring.

pav
01-10-2008, 07:58
Appreciate all of the information. I am trying to learn all I can to take some good u/w photos while I am on vacation in a few weeks. This thread was very helpful.

Puffer Fish
01-10-2008, 12:57
Appreciate all of the information. I am trying to learn all I can to take some good u/w photos while I am on vacation in a few weeks. This thread was very helpful.
I think, or at least hope, that most people just want to be able to take pictures they are proud of, to remember where they have been, to show friends, to just look at and thing - "I took that".

If you can afford it, don't mind all the details and time it takes, then shooting with two strobes and a DSLR is a wonderful thing. If you just want the best pictures possible, after spending what you believe is the right amount for you, then all you need to do is address each issues, set it the best, most forgiving place and move on until you have a comfortable system for you to use.

Along the way, I hope you will stop and ask if you don't know the answer.

cutter77
01-12-2008, 01:21
With JPEG, your camera is doing the "correcting" for you (and remember, MOST cameras are made for topside shooting)."
______________________
Very helpful tip....thanks.

Puffer Fish
01-12-2008, 11:31
Argg... sometimes that is true, but not in every case, and it does not need to be the case.... here is a quote, from DPreview, comparing the JPEG and two different raw processers..

"As you can see Fujifilm's RAW conversion engine is delivering no more (or less) resolution than the camera itself, though to be fair I think this is more a measure of how good the in-camera JPEG conversion is than anything else. What's interesting is that ACR 4.1 seems unable to pull any of the resolution advantage offered by Super CCD from the files, producing a result that simply looks like a 6MP file upsized to 12MP. ACR also produced some pretty strong moiré on all diagonals. I've also stuck a crop from the S5 Pro output at 6MP to show that there is a tiny resolution advantage to shooting at full resolution."

Please read the whole article, but what they are saying is that adobe raw actually produces a poorer quality image when compared to the incamera JPEG....

It is and always will be, that a bad JPEG is the result of bad image processing. I dearly love most of the Nikon DSLR's, but their JPEGs suck, you have to use their raw. But to assume that has to be that way is wrong.

If you don't believe me or DPreview, just download the actual images and look for yourself.

Also, a lot of camera's allow you to control a lot of the JPEG setting, just as you would out of the camera.


With JPEG, your camera is doing the "correcting" for you (and remember, MOST cameras are made for topside shooting)."
______________________
Very helpful tip....thanks.

Reg
01-21-2008, 04:32
Can we add 'White Balance' to the 101 Curriculum?

Puffer Fish
01-21-2008, 10:05
Can we add 'White Balance' to the 101 Curriculum?

Can do, how technical do you want it?

To explain it in semi-technical terms - white balance is the adjustment of the RGB values for each pixel.

Every pixel is made up of a set of values. You can "adjust" these values as the picture is taken in "white balance" or adjust them later. But there is a catch to doing it later.

The reason why sometimes it is important to use white balance in the camera is the issue of "clipping". This almost always in UW images is an issue with the red value. Without a flash, there is less and less red light available, the deeper you go, so at say 60 ft (and this varies a lot), the value for the red will, at best be in single digits (on a scale of 0 - 255). It the white balance calculation adjusts down this value even more... you may have "0", or a number so small, that you can no longer adjust it back up. In that case, there is no correction possible.

Actually, the white balance could be set to increase the sensitivity to red, which can at least make the situation better, rather than worse.

Note: If there actually is no red, then it does not matter. This only works for if there is very little red.

People working in raw have all the data the sensor got, so they don't have to worry about the issue. People working with strobes don't want excessive red sensitivity, but anyone using JPEG's, and nature light, should be very concerned.

There is also a subject regarding RAW adjustments, where you need a reference white image, to adjust for accurate color. This is actually a valuable tool for any camera, just that the methods differ greatly.

Even with strobe images, without a reference, know how the light changed going thru the water and back to the camera is an unknown... shooting a white target can allow that adjustment to be made accurately.

I think sometimes the two issue listed above are mixed together, but they are very different issues.