Let's talk exposure

[ukcatfan]

You guys have got me on the true histogram. My K100D only has the average histogram. I believe the only Pentax with a true one is the K10D. I will add one thing for those like me. Mark, you might be able to explain better as I am sure you will know what I am talking about.

My camera just shows the average histogram, but it also can flash the parts of a shot that are considered blown out. It is not as good as the histogram Mark describes, but you can use it to tell if you over did it so you can re-take the shot. I guess this feature falls in the middle.

Kevin

 

[Master Mason]

Just average with the XT as well

 

[mabas9395]

My rebel XT only has the average histogram, and I know how to adjust my exposure to get my histogram the way I want it. But if I had an RBG histogram and I was shooting a red rose as Mark suggests, and my Red channel was blown out, how would I go about adjusting my exposure? Is there something you can do to make sure the reds aren't blown out while still exposing correctly for the blues and greens? Or do you need to adjust your average exposure so that the hotest channel is exposed correctly and then boost the other channels in post production?

This is good stuff. Might be kind of heavy for a Friday morning though, I need to stop talking about photography and actually get out and take some pictures.

 

[MarkBarbieri]

With a quick check, it looks like the K10D, the Rebel XTi, and the Nikon D80 all have an RGB histogram. The K100D, the D50, the D40, D70, and the Rebel XT appear to only have luminance histograms. Given that it costs almost nothing to add, I hope that competition will force it down the ranks for all the manufacturers.

While not a perfect solution, the luminance histogram is still very useful in this area. You just have to give yourself a bit more margin for error. If nothing in the picture is particularly saturated, you're probably OK. If it is, bracket down 1/2 stop just to be safe.

But if I had an RBG histogram and I was shooting a red rose as Mark suggests, and my Red channel was blown out, how would I go about adjusting my exposure? Is there something you can do to make sure the reds aren't blown out while still exposing correctly for the blues and greens? Or do you need to adjust your average exposure so that the hotest channel is exposed correctly and then boost the other channels in post production?

Your exposure is for all color channels. If you adjusted one, it would throw off your color balance. Your goal is to make sure that no color climbs the right edge. So if you are taking a picture with a really bright saturated red, you have to set your exposure to make sure it doesn't get over exposed.

 

[MarkBarbieri]

While we are on the subject of histogram variances, I have to say that high end Nikon shooters have it the best. They can set blinkies by color channel and they can show their histogram over the full LCD.

 

[DueyDooDah]

Thanks, Mark. Good simple explanation. I'm really glad you touched on the RGB histogram. I have it, but really didn't understand the difference or how to interpret the results. This little tutorial should help me fix those flower and ocean shots I've been missing.

 

[Steve's Girl]

I have been reading quite a bit about exposure lately trying to figure out how to get it right. As Mark stated, I have learned that the histogram is absolutely necessary to achieve correct exposure. Fortunately, my camera has an RBG histogram which is a huge help.

I recently read a rather lengthy, technical article about using the different channels. Honestly, most of the technical stuff went right over my head. But the summation has been quite useful - any red or blue channel blowout typically means you need to reduce exposure. I can't remember why that is other than something to do with the dominance of green, blah, blah, blah. In practice, I am finding this to be a very helpful tool.

 

[jann1033]

ok i am pretty sure i am right about this....since the partial and spot are pretty much the same ( differing in spot size from that recent link) i can use the partial to focus off the sky or grass and use ae lock ...i tried this with the brilliant blue sky and mounds of snow with daylight wb and it seemed to work but just hoping i am not overlooking some important detail... photo is nothing great but the exposure seemed pretty good to me espe. since i didn't use a polarizer

in case anyone else wonders...this is with a polarizer( couldn't shoot the same scene due to sun position) but i would say it made the clouds whiter, didn't change the sky a ton( did do a color cast removal( which made the clouds whiter still, as it gave a more blue cast to the snow, very slight but still more than the other) just as a comparison

 

[tinksdad]

Those look pretty good to me as well. The snow on the first one looks a tad gray (stupid snow). It does work to add a couple of EV points to the exposure to brighten up that snow.

The second looks more white. EXIF says manual white balance, do you recall what you had it set on?

 

[jann1033]

Those look pretty good to me as well. The snow on the first one looks a tad gray (stupid snow). It does work to add a couple of EV points to the exposure to brighten up that snow.

The second looks more white. EXIF says manual white balance, do you recall what you had it set on?

both were on daylight since i stupidly thought the snow was gone for the yr and removed it from my custom wb..i removed the color cast from the second , not sure if it was the polarizer or something else that made it bluer, so it is faker whiter that is part of what i wondered...how the metering off the sky would or would not compensate for such a bright scene....in case it gets to be summer

 

[jann1033]

since that is also the exposure lock button on the rebel xt how do you lock exposure or if you can't lock it what do you do it? i really like the back button focus , it seems more natural to me than the 1/2 shutter depression but that leads to the lack of ae lock as far as i can tell.


Thanks

 

[mabas9395]

I'm pretty sure that the exposure is locked/set when you hit the shutter. I'm not sure what you would do if you want to lock the exposure on one area then reframe the shot.

 

[cpbjgc]

I was reading the threads about the focus lock and I was just looking as the custom function settings on my XTI yesterday (Custom Function #4). When you cycle through the choices it looked like there were 4 settings: AE lock only, AF lock only (AE is set by the half-shutter press), AE and AF Lock (which I think is the default setting) and AF Lock being turned on and off when in AI servo mode. I am guessing it would be the same on the XT.

Have fun experimenting!

 

[jann1033]

just looked again( not sure when i developed a bad habit on only reading 1/2 of what is written) but i have a shutter /ae button custom function and one choice is ae for shutter/ af for button, default being the opposite..so i'll give that a try and see how it goes...thanks!

 

[MarkBarbieri]

So far, I've been mainly using the shutter button for AE lock. I shoot primarily in evaluative metering mode. If I were shooting flash and spot metering, I'd definitely move it to the lock button.

 

[MarkBarbieri]

On second thought, that probably wouldn't work. I'd probably just shoot in spot mode with manual metering with the flash.

 

[gruZ]

I use the back (*) button for focus, and the 1/2 shutter depress to lock exposure. If I need exposure lock, I'll expose on the subject I want, then recompose with shutter 1/2 pressed.

 

[fitzperry]

Just how does exposure compensation work? In other words, how is the "compensation" part accomplished? Does it alter the ISO, aperture or shutter speed? And if so, why not just shoot in manual and change it yourself?

 

[ukcatfan]

Just how does exposure compensation work? In other words, how is the "compensation" part accomplished? Does it alter the ISO, aperture or shutter speed? And if so, why not just shoot in manual and change it yourself?

It depends on the mode you are in to change the exposure. If you are in aperture priority, it will alter the shutter speed for example. I normally shoot in manual, but when you need a faster reaction time, but still know that exposure compensation is needed, it is useful in other modes.

Kevin

 

[jann1033]

maybe this will help
http://www.photoxels.com/tutorial-exposure-compensation.html