40D exposure question

[Beth Goffe]

I'm pretty well-versed in Artie's "make sure data is in the histogram's 5th box" technique. However, I've found, particularly in the morning, that even though the histogram looks ok in terms of data in the fifth box and not pegged on the right, my whites end up looking quite hot with my 40D. I also set the camera so that the image sensitivity is at its highest and most likely to show blinkies in overexposed areas. Doesn't seem to help. Suggestions, anyone, about camera settings, etc.? Thanks in advance!

[Maurice Allen]

Take a look at Artie's 40D setup article. Do you have "highlight tone priority" on?

[Robert O'Toole]

I'm pretty well-versed in Artie's "make sure data is in the histogram's 5th box" technique. However, I've found, particularly in the morning, that even though the histogram looks ok in terms of data in the fifth box and not pegged on the right, my whites end up looking quite hot with my 40D. I also set the camera so that the image sensitivity is at its highest and most likely to show blinkies in overexposed areas. Doesn't seem to help. Suggestions, anyone, about camera settings, etc.? Thanks in advance!

Sounds like a RAW conversion process problem, i.e. default ACR settings. This could even be a problem with the RAW converter itself, i.e. Breezebrowser. I would recommend PS ACR with custom defaults set.

Not sure you mean by image sensitivity at its highest, do you mean ISO?

Having the 40D color space set to sRGB will give you a more contrastyand more prone to Blink histogram than aRGB.

Robert

[Joerg Rockenberger]

Are you looking at the brightness histogram or the RGB histogram? The former will not show if you blow only one channel. That can give the appearance of hot pixels. I noticed that once photographing Marbled Godwits in early-morning light with the red channel saturated.

JR

[Robert O'Toole]

Are you looking at the brightness histogram or the RGB histogram? The former will not show if you blow only one channel. That can give the appearance of hot pixels. I noticed that once photographing Marbled Godwits in early-morning light with the red channel saturated.

JR

Good point about using the RGB histogram in general John but usually a blown channel is usually a color saturation problem with a colorful subject and not a problem with whites as the OP is experiencing.

Since we are on the subject all the current cameras histograms are just an approximation really. This is one of the reasons we all can have problems sometimes with actual results. They all use a conversion offset factor for the display usually for the R and B channels to correct for the fact that there are twice as many Green sensor photosites. So what you see on the Histogram isnt what you always get anyway.

Robert

[Joerg Rockenberger]

You're of course right. JR

[Tim Dodd]

If you want an in-camera RGB histogram that more accurately represents the saturation levels of the RGB channels as captured in the raw data you might like to try shooting with a custom white balance setting affectionately known as Uni-WB. This is a feature that Nikon shooters have had access to for a long time, but Canon has provided no support for an equivalent function. Uni-WB is an attempt to set the R and B multipliers to exactly 1 and thus avoid skewing the true saturation levels to match some arbitrary setting of WB.

I first learned of Uni-WB in this rather long and meandering thread over on POTN....

http://photography-on-the.net/forum/...ghlight=uni-wb

I shot a short video to show just how badly different WB settings can affect what you see on the camera's RGB histogram display, which, as I say in the video, is really quite stupid when you are trying to accomplish the perfect raw capture. Here's the video....

http://www.youtube.com/watch?v=FLXoznsvEvI

Here are instructions for quickly and easily creating a custom Uni-WB setting for your white balance..

http://photography-on-the.net/forum/...ghlight=uni-wb

The dark frame technique works very well for the 40D.

Note that using Uni-WB will give a green cast to your images and thus is only suitable for raw shooters who can easily correct WB with no quality loss. If you shoot to JPEG then you do actually want to shoot with the correct WB setting for the conditions, because you do want the histogram to reflect the end result stored in the JPEG, including all the processing within the camera.

As a final "proof" of the power of Uni-WB, and the relative stupidity of JPEG processing, in camera or out, you might want to look at this thread....

http://photography-on-the.net/forum/...ghlight=uni-wb

Have fun :)

[Robert O'Toole]

If you want an in-camera RGB histogram that more accurately represents the saturation levels of the RGB channels as captured in the raw data you might like to try shooting with a custom white balance setting affectionately known as Uni-WB. This is a feature that Nikon shooters have had access to for a long time, but Canon has provided no support for an equivalent function. Uni-WB is an attempt to set the R and B multipliers to exactly 1 and thus avoid skewing the true saturation levels to match some arbitrary setting of WB.

Thanks for the links Tim. I have had this loaded for some time but I dont use it very much.

The Nikon UWB had been out for years and was developed by a third party not Nikon.

Also its worth noting that with UWB in place one side effect is that the LCD review thumbnails look really bad with a ugly color cast.

Robert

[Beth Goffe]

Thanks for all of the information, everyone. I haven't had a lot of time lately to play with the camera but I will take the time to review all of your comments and suggestions. This particular issue has bugged me for a while now.