Digital Camera World Forum Histogram question

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#1
12-01-10, 05:42 PM
 Cutter Senior Member Join Date: Oct 2009 Location: Cheshire , England Posts: 2,425 Images: 69
Histogram question

Could anyone tell me what makes a good histogram? I have read that we dont want it to be to much to either side, but if you have a dark background and a small light subject in the centre then its going to show its all pushed to the left, or reverse if the other way around. so how will you know its exposure is right by a histogram?
Sorry if I am a bit thick here everyone
#2
12-01-10, 05:48 PM
 Forseti Senior Member Join Date: Jul 2009 Posts: 578
No, not being thick - you are spot on. The histogram is much like any other graph - an x axis on the bottom and a y axis top to bottom. As relates to photography, the x axis goes from 0 - 250 with zero being complete black and 250 being white. Distribution is shown on the y axis.

So yes, the histogram is to be used as a guide - if the subject matter is predominantly dark then the histogram will be more to the left. It's up to you as the photographer to judge the histogram as it relates to the subject matter.

With your never ending thirst for knowledge here's an excellent tutorial site - and yes, histograms (in detail) are explained. Enjoy. http://www.cambridgeincolour.com/tutorials.htm
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Last edited by Forseti; 12-01-10 at 05:58 PM.
#3
12-01-10, 08:36 PM
 Cutter Senior Member Join Date: Oct 2009 Location: Cheshire , England Posts: 2,425 Images: 69
Quote:
 Originally Posted by Forseti No, not being thick - you are spot on. The histogram is much like any other graph - an x axis on the bottom and a y axis top to bottom. As relates to photography, the x axis goes from 0 - 250 with zero being complete black and 250 being white. Distribution is shown on the y axis. So yes, the histogram is to be used as a guide - if the subject matter is predominantly dark then the histogram will be more to the left. It's up to you as the photographer to judge the histogram as it relates to the subject matter. With your never ending thirst for knowledge here's an excellent tutorial site - and yes, histograms (in detail) are explained. Enjoy. http://www.cambridgeincolour.com/tutorials.htm
Thanks Forseti as usual you come up with the goods I will have a read at your link, I just wanted to know i wasnt missing out on anything

Ps will you have a crtique of my robin? am I getting there? it seems that my problem has been more on the focus side, I now use the zoom button to focus more exact but i wonder why my auto focus cant get it bob on.

In your dept as usual: Mark
#4
12-01-10, 11:57 PM
 matt wilson Senior Member Join Date: Oct 2009 Posts: 593
Cutter I looked at the robin.not bad at all.

Knowing your camera though I have a couple of ideas .It could be the focus mode setting .If mr robin is nicely perched then one shot is fine .If moving then use either ai focus or ai servo.Choose the wrong setting and the camera will keep hunting and moving focus until shutter opens .

Also you could try manually selecting the point of focus .I often do that rather than relying on the auto setting .That way you can zoom in and keep the one focus red square on the part of bird you want sharp ideally the eyes .I set centre point mainly.

Try it and show us the results.
#5
13-01-10, 09:52 AM
 Cutter Senior Member Join Date: Oct 2009 Location: Cheshire , England Posts: 2,425 Images: 69
Quote:
 Originally Posted by matt wilson Cutter I looked at the robin.not bad at all. Knowing your camera though I have a couple of ideas .It could be the focus mode setting .If mr robin is nicely perched then one shot is fine .If moving then use either ai focus or ai servo.Choose the wrong setting and the camera will keep hunting and moving focus until shutter opens . Also you could try manually selecting the point of focus .I often do that rather than relying on the auto setting .That way you can zoom in and keep the one focus red square on the part of bird you want sharp ideally the eyes .I set centre point mainly. Try it and show us the results.
Hi Matte thanks for your sugestions although my friend forseti told me I should centre focus manually and keep the red square on his eye, or the contrast between the red and grey on his breast. But the pictures were still not as sharp as they have been, since I manually focusted on a point I know the bird would land with the auto focus turned off.

I think thats a bit of a dissapointment me getting sharper pictures by manual focus rather than auto focus. I will try to take two pictures today one using manual and one auto focus with the same settings and see what you think.

Ps hope the liitle devil turns up for his meal worms
#6
13-01-10, 11:18 AM
 ap4a Moderator Join Date: Jul 2009 Posts: 702
If pre-focussing it'll help to ensure that you have enough depth of field to give acceptably sharp results even when the bird isn't quite where you focused. (The further away from the focal point you are the greater the depth of field will be, and also the narrower the aperture the greater it will be too.)
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#7
13-01-10, 12:14 PM
 Forseti Senior Member Join Date: Jul 2009 Posts: 578
The saga of the Robin continues....

Yes, well then - the EXIF for the little darling in question indicates an ISO of 500, aperture of f/5.6, shutter speed of 1/60 sec and a focal length of 400mm.

Ok, first things first. General rule: shutter speed should be 1/x, where x represents focal length. In your case the chosen shutter speed of 1/60 sec was much too slower even if a tripod was used as there is always movement induced by either the mirror or the tripod itself moving slightly after pressing the shutter button.

The 50D uses a 9-point AF system - all cross-type for lenses of f/5.6 or faster. The centre AF point additionally is sensitive with lenses of f/2.8 or faster. As the 100mm-400mm is rated at f/4.5 - f/5.6 this last point doesn't apply and all your AF points have the same sensitivity. I advised using the centre AF point in combination with the AF-ON button if you remember so that you could quickly focus on a subject using your thumb leaving the shutter button to deal with the exposure setting. For a fixed subject that you anticipate landing on a pole (the Robin) this will quickly allow you to compose, focus and shoot.

It is better not to use either extremes of a zoom lens but instead discover by experimentation the sweet spot of your lens - 400mm certainly isn't it.

I don't think focus is a problem in your image as the post is sharp in the middle, losing focus both front and back so your focus point seems just fine. No, I believe this is more a case of movement - camera, bird or both which your shutter speed setting has only exacerbated.

All that said, your image hasn't turned out too bad and certainly a marked improvement upon the first one you posted a while back. There is however an unacceptable degree of noise in the image as a result of the dark background and chosen ISO. If you look in my gallery I have posted the original as well as an edited version adding just a touch of sharpening and noise reduction. I tried posting them in this thread a little earlier but the editing effects are not noticeable at thread sizes. They need to be viewed at 100% in the gallery to see editing effects.
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#8
13-01-10, 02:45 PM
 Cutter Senior Member Join Date: Oct 2009 Location: Cheshire , England Posts: 2,425 Images: 69
I remember all that you said but in this case I could not acheive a ss of1/400 there was not enough light so I would have had to boost the iso even more which I tried not to do. I was using centre focus and getting the lock on but still not sharp , so I tried manual manual focus,, shot in Live view so the mirror will be locked up ,used a tripod ,shutter release and turned the IS off and its been the first time I have seen more feathers on the bird.
Seems alot to do to get a sharper picture!!! I have shot at faster shutter speeds in the past and to no avail.
So could you tell me if my sweetspot is 325mm will it be better to crop and get a sharper picture or shoot at400 with no crop? ps I can see the dif after your editing did you just use cs4 for noise reduction?
I am putting two robin pics up again one manual and on auto focus give me your opinion please
Ps I promise if the light gets better I will use your rule everytime
#9
13-01-10, 02:55 PM
 Cutter Senior Member Join Date: Oct 2009 Location: Cheshire , England Posts: 2,425 Images: 69
Check out my gallery to see manual and auto focus
#10
13-01-10, 03:22 PM
 matt wilson Senior Member Join Date: Oct 2009 Posts: 593
Cutter I probably wasn't clear enough .I was not saying manually focus .More a case of manually selecting the area the autofocus works on.

It's the button top right on the back of the camera that is used to zoom in when reviewing lcd .it also lets you toggle the red focussing dot around.