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Stupid beginners question - Exposure
Hi,.

I just got my first dSLR camera today and i've been out in the garden getting to grips with it and learning how it works..

One thing I found though was that the range of light to dark areas in the garden was quite large and often I'd end up with blown highlights. Not too difficult to fix in itself, I just played with the exposure compensation or put the camera into manual and adjusted the exposure using the shutter speed from the A mode as a starting point till I got an image that didn't have blown highlights (but of course other areas were now underexposed)..

What I wanted to be able to do though and couldnt work out how (and I tried playing with the different metering modes) was to point the camera in one spot and have it work out the exposure settings from there (using spot metering say) and then recompose the shot and take the picture... but I wanted to use Autofocus as well.... (Camera in Av mode for example)..

Firstly is this even possible?? If so how do I do it?.

Secondly, I guess this is possible if I manually focus by simply depressing the shutter halfway, reframing the shot, focusing and then taking the picture?.

I'm using a Canon 450D and a 17-55mm f2.8 lens..

Thanks for the advice...

Comments (19)

Canon EOS 450D handbook page 88.

(* AE Lock)..

Comment #1

Perfect! thats exactly what I was looking for. I thought there was a way to do it, I just couldnt remember how..

Thankyou...

Comment #2

Well, I don't know what's on that page but try using spot metering to get a reading for the darkest important point of the scene and then repeat for the brightest important part. Then average the two or aim for near the average and set it for that in manual mode..

It's a lot easier with a hand held meter..

Regards, David..

Comment #3

Wouldnt that have the same effect as just using the evaluative metering mode on the camera?.

I wasn't really looking for an average of two points in any case. I wanted to be able to set the exposure based on a particular point in my composition but that point is not in the center. Answer (page 88 referenced above) is to use a feature called AE Lock. In combination with spot metering this does what I need as it effectively locks the exposure at one point letting you recompose the shot before taking the picture. This way I can make sure that important part of the picture is correctly exposed...

Comment #4

Hamza wrote:.

This way I can make sure that important part of thepicture is correctly exposed..

Hmmm... I don't want you to get the wrong idea.....

Whether or not you get the correct exposure from the subject will depend on how effectively it reflects light. Naturally that varies from one subject to another, but your exposure should nevertheless remain the SAME for ALL lightnesses and darknesses of subject. Not many people realise this at first, because it is counter-intuitive, so please be aware that.......

Spot metering, like any reflected light metering, is only accurate when it is aimed at an ideal metering target.... and that means one that is neither too light nor too dark..

Such an ideal metering target is.....

An 18% reflectance Grey Card in the same light as the subject/scene. something of equivalent 18% grey tone within the subject/scene itself. two or three subject tones, which, when metered together, are 18% equiv..

Please note that a spot meter does not have to be used for this. A normal full-area meter can be completely filled with a grey card, or grey card equivelant....

If you frame in tightly by zooming the lens. just walk closer!!.

You can also manage without the grey altogether. Try spot-metering from.....

The subject's lightest tone, and use 2 stops PLUS Exposure Compensation the subject's darkest tone, and use 2 stops MINUS Exposure Compensation.

(The precise exposure compensation values will vary. Experiment to gain you own experience with your own camera.).

The main point is.....

Whatever you do, DON'T ASSUME that metering the subject will "automatically" (and without further intervention) produce the correct exposure for that subject's lightness or darkness of tone. On the contrary, be aware that...

1) It will do so ONLY if the subject is very close to the 18% level in reflectance of incident light..

2) If the subject is lighter toned, then the metering will tend to render it too dark, and if it is darker toned then the metering will tend to render it too light..

In situation 2) above you MUST step in, one way or another, to restore the camera settings to what they WOULD have been, if 1) above was the case.....

.... In short, you are always trying to return the camera to those exposure settings that result from metering an ideal (18% grey) target..

In the posting above I have I listed some ways you can do that. There are lots of other ways, but these will do for starters..

Good luck! Regards,Baz..

Comment #5

Hi,.

Difficult to add to what Baz has written but as you asked "wouldnt that have the same effect as just using the evaluative metering mode on the camera?" and so I'll say yes and no..

The point is that cameras are just dumb machines. They don't think, worry or create, which is left to you to do. So get to know the camera and what it was designed or programmed to do and then you'll know when to jump in and over-ride it..

So I suggested deciding what was dark and light and important, then juggling with the exposures suggested to get what you want. It doesn't have to be averaged out just decided based on the two extremes suggested..

Or as Baz has said a grey card or, as I'll add, an incident light reading. BTW, there's lots of perfectly good exposure meters on ebay and elsewhere. You can pick them up for a fiver and get them checked easily by comparing with you camera. And a lot of them don't need batteries but might be a bit old and tired. Others need batteries but might need the mercury cells, meaning an adapter and re-cailbration. Or spend a lot of money on a recent one or even a new one.



Regards, David..

Comment #6

Getting a good Skylight filter or a UV filter that will handle the bright ambient light for you will also help. It'll also give you the added benefit of lens insurance. I can't tell you many times I have thrashed a 1A filter and saved my camera lens. It's well worth the $20 or so, believe me..

James DeRuvoDigital Camera HQhttp://www.digitalcamera-hq.com..

Comment #7

Excellent advice from Baz..

If you're looking for a tutorial that expands on these concepts, you might try this one: http://community.spiritofphotography.com/index.php?page=23.

Keithhttp://community.spiritofphotography.com..

Comment #8

James DeRuvo DHQ wrote:.

Getting a good Skylight filter or a UV filter that will handle thebright ambient light for you will also help. It'll also give you theadded benefit of lens insurance. I can't tell you many times I havethrashed a 1A filter and saved my camera lens. It's well worth the$20 or so, believe me..

James DeRuvoDigital Camera HQhttp://www.digitalcamera-hq.com.

I think protective filters are a great idea. Canon engineers were just not too smart. They designed that 17-55 lens with 19 elements, 12 groups including three aspherical elements and two of UD glass with associated glass to air sections. I just can't figure out why they did that when we all know that it should be 20 elements in 13 groups with that extra air to glass section. Stupid them and smart us to add the filter. We have to correct their optical formula mistake.

The more expensive the lens, the better it is to fix them. I put an extra nice $30 filter on my 85 f1.4..

Some of those flying missiles have diamond tips, and the lens has such great depth of field that it can actually see a scratch. I know that a paper thin filter will protect my front element from that spear shaped missile. That Uber glass they use in filters are that strong and front elements are so soft..

So, what a great way to protect while improving the optical formula! I'm in..

I especially like Skylight filters and UV filters because they have such a positive effect on the image. Digital cameras are very susceptible to UV light and Skylight filters do absorb that nasty ambient light. I also prefer the nice $20 ones that aren't coated for my $1100 glass..

Pass the salt..

Cheers, Craig..

Comment #9

The first question I would ask is are the blown highlights important parts of the picture, lik a light building, rocks, etc. If so expose on a neutral color, like grass and take the shot, making sure the shadows aren't blocked. If the highlights are not important just ignore the loss of detail in a part that isn't of importance..

If the blown highlights are importanit I would then consider if the shadows are all that important. In other words is there a compromise here? If not there is the use of HDR or if you can get Color Efex Pro from Nik Software. The software contains Graduated Neutral Density adjustments, just as if you used a glass filter..

I don't sell or work for NIK. This is my opinion...

Comment #10

Firstly thanks to all for those informative responses. I remember reading about metering on 18% gray card or something close to it but I had actually forgotten about it when I was out playing with my camera so thanks for the reminder and the quick tutorial! I'll try some of those tips out tomorrow if I get a chance to go out and play again..

I actually had already ordered some filters (Just the Canon Protect ones, I assume these are good enough? or should I get some UV filters instead?) I'm just waiting for them to turn up in the post so I can stick them on my lenses..

Lastly in the case yesterday, no the blown highlights really weren't important at all and normally I wouldnt really care but as I'm new to this I was just using it as an opportunity to practice and learn so that when I encounter the situation in a photo I really do want to take it's not the first time I'm having to deal with it and so hopefully will handle it better...

Comment #11

Hamza wrote:.

I actually had already ordered some filters (Just the Canon Protectones, I assume these are good enough? or should I get some UV filtersinstead?) I'm just waiting for them to turn up in the post so I canstick them on my lenses..

Do yourself a favour and leave OFF any "protection" filters, unless.....

You are shooting in an adverse environment, like windblown salt spray or sand..

You are a naturally accident prone person, and regularly drop your cell-phone in the john...(mobile down the loo)..

Seriously. .

Instead, make sure you always use the lens-hood, which offers a good measure of impact protection, and also does a positive job of improving image quality, unlike a clear filter which can potentially cause flare and loss of contrast..

Oh....and by the way.....

Digital cameras are not sensitive to UV light, so you don't need to filter it out.Regards,Baz..

Comment #12

Barrie Davis wrote:.

Do yourself a favour and leave OFF any "protection" filters, unless.....

Oh....and by the way.....

Digital cameras are not sensitive to UV light, so you don't need tofilter it out.Regards,Baz.

Darn, you mean I should remove those $20 filters? What about all that bright, ambient and UV light they'll filter? .

Cheers, Craig..

Comment #13

Guidenet wrote:.

Barrie Davis wrote:.

Do yourself a favour and leave OFF any "protection" filters, unless.....

Oh....and by the way.....

Digital cameras are not sensitive to UV light, so you don't need tofilter it out..

Darn, you mean I should remove those $20 filters? What about all thatbright, ambient and UV light they'll filter? .

Gosh! Darnit! Yes! You may be right!.

Shall we get stuck into a 150 post thread to sort the matter out, once and for all?[Or maybe not, eh?].

Be careful out there.. Regards,Baz..

Comment #14

Hamza wrote: >.

I wanted to be able to set the exposure based on a particular point in.

My composition but that point is not in the center. Answer (page 88referenced above) is to use a feature called AE Lock. In combinationwith spot metering this does what I need as it effectively locks theexposure at one point letting you recompose the shot before takingthe picture..

This would be step one..

This way I can make sure that important part of the.

Picture is correctly exposed..

Not without another step..

For step two, you have to decide how much brighter or darker than 18% gray you want your metered spot to be in the capture (i.e., as printed) AND compensate (up or down) using exposure compensation (or, if in manual mode, by manually adjusting the exposure up or down, using the aperture, shutter, or ISO control on your camera)..

The camera, left to it's own devices, will render your spot metered area as mid-gray (in the print). If it isn't actually mid-gray, you have to give it either more exposure (if actually lighter than mid-gray) or less (if darker)..

How much more or how much less is a matter of experience (and know-how, for example a working understanding of the "Zone System" would be a help)..

But, to be specific, if the spot metered area is Caucasian skin (eg sunlit face), you would raise the exposure by one "stop". Same face shaded by the brim of a hat (or shady side of face), would "print OK" as read. And so forth..

Check out "Zone System" on Google..

Try: http://www.normankoren.com/zonesystem.html for starters...

Comment #15

Regarding metering, I'd like to quote from an excellent post (by Vincent Peri) from another forum:.

Quote:.

"With the zone system, you should really use a one degree spotmeter. That will let you zoom in on a part of the scene that is entirely within one zone (green grass in bright sunlight, for example). In this case, grass is pretty much zone V, so you can use the exposure recommended by the meter..

Let's say you are metering caucasian skin (zone VI) for your next photo. The spotmeter thinks it's zone V (neutral gray), so you need to open up one stop to get to zone VI..

For your third photo, a black horse wanders by. Once again, the spotmeter will think the black horse is a zone V neutral gray, but you know better. A very accurate rendition of a black horse (remember, you want visible textures in the horse's fur) can be had by underexposing two stops - going from zone five (as metered) to zone III. If you decide to place the horse in zone II, there will be almost no texture, just black..

Finally, a white horse canters up. Meter it and get an exposure (still zone V). You know that a white horse should be placed in zone VII so you can see texture and detail, which means two stops more exposure. If you put the white horse in zone VIII (3 stops over), I guarantee you'll have one very pale horse..

Of course, this is a crash course in the basic zone system. For much more information, you can read the following good books:.

"Zone VI Workshop" by Fred Picker. This is the zone system reduced to it's basic steps. Easy to understand..

"The Zone System for 35mm Photographers" by Carson Graves. This explains the zone system in greater detail..

"The Print" and "The Negative" by Ansel Adams. Maybe more than you want to know as a beginner...".

Here is a link to the full thread (check it out):.

Http://photo.net/film-and-processing-forum/00Q33F..

Comment #16

Doh!!.

I just re-read those posts and I can't believe I didn't pick up on the sarcasm in them the first time! I blame the fact that I'd just gotten back from a long skate session and it was late at night.....

Ok i'll leave the filters off then  I have lens hoods too for all my lenses so I'll just stick to using those...

Comment #17

Thanks for the examples and references, the examples help clarify the details Baz gave in a practical way..

Will check out the reference later too..

Comment #18

Hamza wrote:.

Ok i'll leave the filters off then  I have lens hoods too for allmy lenses so I'll just stick to using those..

Yes, allthough we shouldn't get dogmatic about it. As already intimated, there are times when a protective see-through type lens cap is a good idea.... (to which hazards you could add sticky fingered kiddies in close up, and slobbery dogs!).....

.... but otherwise, filters are 'mostly' for leaving OFF!  Regards,Baz..

Comment #19

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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