Free Shipping on ALL Products
camera reviewsbest cameraslens reviewsphotography tipscamera forumvideo toursphotography bookssupport me
It is currently Mon Apr 21, 2014 12:07 am

All times are UTC




Post new topic Reply to topic  [ 13 posts ] 
Author Message
 Post subject: Histogram Help
PostPosted: Tue Aug 05, 2008 8:26 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Hello all,

I'm a relative noob to photography, but I'm really enjoying it so far and learning loads each day.

I have a baby daughter who I take lots of photos of indoors and in bright sunlight on the nearby beach.

I tend to use 'P' mode most often and 'AV' mode for portraits. I'm finding it difficult to judge the exposure (especially in 'P' mode) when I'm at the beach and cannot see the screen well due to the bright sunlight. I played around with the bracketing for a while, but firing 3 shots with the flash often means I miss a 'moment' or catch it when the bracketed shot was the other end of the correct scale.

I've been told to use the histogram more. Great, except I don't know how!

Any tips (or a video from Gordon, hint hint :-) ) would be very much appreciated.

I have a canon EOS 400D used mostly with a canon efs17-85mm lens and built in flash (saving up for a speedlite...)

Thanks,

SP30


Top
 Profile  
 
 Post subject:
PostPosted: Tue Aug 05, 2008 7:29 pm 
Offline
User avatar

Joined: Thu Sep 13, 2007 6:31 pm
Posts: 1215
Location: London, UK
The histogram can be used for a few different things but judging exposure is probably the most useful when you're out shooting. The graph shows the range of tones (dark to light) in the image. The scale of the graph goes from 0 on the left (completely black) to 255 on the right (pure white). The "ideal" histogram will differ for each image but the first thing to look for under normal lighting conditions is a gradual peak in the centre of the graph. This means that the image doesn't have too many shadows (not many peaks on the left) or highlights (not many peaks on the right.) If the histogram is skewed to the left it means there are lots of shadows in the image and it may be underexposed. If it is skewed to the right the image has lots of highlights and it may be overexposed.

The histogram greatly depends on the situation and just because it doesn't have a nice peak in the middle (it often doesn't) doesn't mean it's incorrectly exposed. For example, of you're taking a correctly exposed night shot the histogram will probably be skewed to the left because it is a dark scene. This is the brightness histogram. There is also one for each red, green and blue channel in the image but the brightness will give an indication of the overall exposure.

I suggest you have a look at Cambridge in Colour's first histogram tutorial for a much better explanation than I can give. After that you may be interested in this one which describes how the histogram can be used to understand other aspects of the image such as luminance and colour.

The best way to understand how a histogram varies with exposure is to deliberately over/under/correctly expose some scenes and see the differences in the histogram.

I hope I have made some sense!! :P

Mark

_________________
Canon EOS 40D / EF-S 17-85mm IS / EF 50mm f/1.8 / My Flickr


Top
 Profile  
 
 Post subject:
PostPosted: Wed Aug 06, 2008 12:27 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Thanks Mark,

Those links are very good indeed.

So what mode should I use if I need to fiddle with the exposure? Say for example I take a portrait shot in AV and the histogram suggests it's underexposed.

Should I adjust the ISO, or switch to TV and control the shutter speed? Currently I've been adjusting the ISO a lot, but I think this is due to lack of knowledge and would rather learn how to improve the shots by other means and keep the ISO low. M-mode is still a distant scary prospect!

Cheers,

SP30


Top
 Profile  
 
 Post subject:
PostPosted: Wed Aug 06, 2008 10:22 am 
Offline
Moderator
User avatar

Joined: Thu Nov 08, 2007 6:30 pm
Posts: 6941
Location: The Netherlands, Ridderkerk
I only recently started working with the histogram more and more, and I must say it's still a little difficult... I'll read those links too, thanks Mark!
There's an interesting and good video tutorial on YouTube to, click here and watch it!

- Bjorn -

_________________
Street and documentary photographer | Google+ | Twitter
Please vote for my photo(s) in a contest


Leica M9-P (my article on Camera Labs) | Leica D-Lux 5 | 50mm Summilux


Top
 Profile  
 
 Post subject:
PostPosted: Wed Aug 06, 2008 11:45 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Thanks Bjorn,

That certainly is a good tutorial. However, the more I jump around YouTube, the more confused I get; I see lots of people using a white card for the custom white balance and lots of others using grey. Which is correct? Does it matter?

I know, I should spend some money on a proper course instead of trying to learn everything for free on YouTube....

Cheers,

SP30


Top
 Profile  
 
 Post subject:
PostPosted: Wed Aug 06, 2008 12:12 pm 
Offline

Joined: Mon Sep 17, 2007 9:17 am
Posts: 3662
Any neutral colour should work for setting the white balance.

I find histograms to be especially useful when shooting in bright sunlight and it becomes even harder to check exposure on the LCD.

_________________
Graham
Flickr


Top
 Profile  
 
 Post subject:
PostPosted: Wed Aug 06, 2008 3:25 pm 
Offline
User avatar

Joined: Thu Sep 13, 2007 6:31 pm
Posts: 1215
Location: London, UK
SP30 wrote:
So what mode should I use if I need to fiddle with the exposure? Say for example I take a portrait shot in AV and the histogram suggests it's underexposed.

Should I adjust the ISO, or switch to TV and control the shutter speed? Currently I've been adjusting the ISO a lot, but I think this is due to lack of knowledge and would rather learn how to improve the shots by other means and keep the ISO low.


If you're taking portraits Av would usually be best because you want to isolate the subject from the background. If you up the ISO in Av mode the camera will compensate for this by using a quicker shutter speed. So if the shot is underexposed before you change the ISO, it will be after you change it because the camera will try to maintain the exposure it thinks is correct. However, humans know best!!! :D So if you want to fine tune the exposure in any of the creative modes (apart from manual) you will need to adjust the exposure compensation (which in Av mode changes the shutter speed).

Mark

_________________
Canon EOS 40D / EF-S 17-85mm IS / EF 50mm f/1.8 / My Flickr


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 1:44 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Hi Mark,

Thanks very much for the advice.

I've tried exposure compensation in AV mode as you suggested and it works a treat. A quick glance at the histogram lets me make a fast adjustment and I'm ready for the next shot with the compensation. Thanks!

However, the exposure compensation doesn't seem to have any effect in 'P' mode with the flash? I use 'P' mode a lot and the exposure compensation works without flash, so I'm wondering if there's a reason for this; probably me doing something wrong!

Cheers,

SP30


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 2:03 am 
Offline
User avatar

Joined: Thu Sep 13, 2007 6:31 pm
Posts: 1215
Location: London, UK
If you're using the flash you need to adjust the flash exposure compensation. I'm not familiar with the 400D but it is probably a button with a lighting +/- symbol next to it. Press this and adjust the scale as you would for the exposure comp. My instructions on how to do it may be completely wrong since I haven't used the camera but a quick look in the manual for flash compensation should do the trick if I'm way off controls-wise.

Good luck.

Mark

_________________
Canon EOS 40D / EF-S 17-85mm IS / EF 50mm f/1.8 / My Flickr


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 2:55 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Thanks for the quick reply Mark.

You are right, the flash compensation works in 'P' mode, but it's buried away in the menus. I think that might lead to a lot of shots with that 'get on with it!' look :-)

Maybe I'll stick to AV mode so I can make quick exposure compensation changes and still use the flash.

Another question if you don't mind, seeing as we mentioned ISO; If I frame the shot in AV with the aperture wide open and notice the shutter speed is longer than 1/60, for example, should I increase the ISO to speed up the shutter, or is there a better way?

I like to keep the ISO as low as possible as I can certainly see a degradation at 1600, so if you have any more tips, that would be great!

Thanks again,

SP30


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 10:26 am 
Offline
User avatar

Joined: Wed May 28, 2008 6:37 pm
Posts: 926
Shutter speed, aperture and ISO are all you've got to influence the amount of light in the camera. So you are basically out of options short of using a faster lens. The only way to prevent upping the ISO would be to zoom out to a level that allows a bigger aperture if possible/acceptable. But that's not ideal either.

Ben
_________________
When in doubt..... Press the shutter.


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 10:29 am 
Offline
User avatar

Joined: Thu Sep 13, 2007 6:31 pm
Posts: 1215
Location: London, UK
^^^^^^^ Yup. You've either got to invest in some faster lenses or bump up the ISO. :(

Mark

_________________
Canon EOS 40D / EF-S 17-85mm IS / EF 50mm f/1.8 / My Flickr


Top
 Profile  
 
 Post subject:
PostPosted: Fri Aug 08, 2008 11:35 am 
Offline

Joined: Wed Mar 12, 2008 12:15 pm
Posts: 16
Location: Hong Kong
Thanks for the help guys.

Guess I'll keep saving for a faster lens. Speedlite might have to wait...

Hopefully Santa will come early this year!


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 13 posts ] 

All times are UTC


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron

All words, images, videos and layout, copyright 2005-2012 Gordon Laing. May not be used without permission.
/ How we test / Best Cameras / Advertising / Camera reviews / Supporting Camera Labs

Webdesign by Alphabase IT
Powered by phpBB® Forum Software © phpBB Group