Over / Under Exposure

[ccaballero]

Hello TPF friends, I have a question that could not find a specific or more direct thread for it.
I have a Nikon D3100 with a Nikon 18-200 VR (just as an FYI) and Im confused when it comes to Over / Under exposure, at witch end is the picture unrecoverable? Is it better to Under exposed if unsure or is it better to Over expose and fix in PP?
Im aware this is only pertaining RAW / NEF files.

Thanks in advance

 

[greybeard]

As a general rule it it better to underexpose than to overexpose. Underexposed shots can be recovered (to a point) in post processing but overexposed shots can not. I look at digital much like I did when shooting color slide film. With this I had to expose for the highlights and let the projector take care of the shadows. With digital I expose for the highlights and bring up the shadows in post processing. There are exceptions to these general rules but as a beginner just starting out, expose or the highlights and process for the shadows is a good starting point.

 

[ccaballero]

Thanks, I notice I have been overexposing the majority of my photos and not using my exposure compensation enough

 

[ac12]

Set your back screen to show highlights. Any place that blinks, is unrecoverable highlights.
The tricky part is, unless you zoom in, you won't see the smaller highlights. In something like a large group photo, that blown highlight could be a face.

 

[Ysarex]

Thanks, I notice I have been overexposing the majority of my photos and not using my exposure compensation enough

Your original question begs further questions. You referenced NEF files in your original question: How do you know if they are over, under, or properly exposed?

Joe

 

[ccaballero]

Ysarex thats were I take the noob out for a walk LOL. I have my D3100 set to take both JPEG and RAW (I wrote NEF because that is how it shows in Capture NX-d) I might have this one very wrong. When I say overexposed is because I took a lot of pictures on Saturday on the bay, under a sunny sky at 3pm and the pictures were extremely bright, not all of them I did fiddle some more to get to a place were in my beginner sense were ok. But for some reason my starting point was always bright.
I apologize if Im describing this wrong, or have the wrong idea in regards to exposure.

 

[Braineack]

The D3100 has a hard time recovering in any direction -- but still, I'd rather underexpose than over.

 

[Ysarex]

Ysarex thats were I take the noob out for a walk LOL. I have my D3100 set to take both JPEG and RAW (I wrote NEF because that is how it shows in Capture NX-d) I might have this one very wrong. When I say overexposed is because I took a lot of pictures on Saturday on the bay, under a sunny sky at 3pm and the pictures were extremely bright, not all of them I did fiddle some more to get to a place were in my beginner sense were ok. But for some reason my starting point was always bright.
I apologize if Im describing this wrong, or have the wrong idea in regards to exposure.

Might not be a bad idea to show us a few of the photos that were extremely bright -- possible problem?

An NEF file is a Nikon raw file. You have your camera set to save both -- good. The whole topic of exposure can be a bit of rabbit hole. Thinking about the NEF files which contain the sensor readout converted to digital values and not concerning ourselves at all yet with any image that you can see, data recorded is exposed within the sensor's threshold limits. Any data that we fail to record beyond the sensor's high end threshold is overexposed -- failure to record. Any data unreadable/indistinguishable from noise is underexposed -- failure to record. The data then that is recorded during an exposure ranges in "quality" (noise, detail, color fidelity, etc.) in direct proportion to exposure such that the data exposed the most is best and the data exposed the least is worst.

Failure to record is unredeemable -- my niece would say duuuuh. The two limits (high end/low end) are somewhat different. The high end limit is very hard, crisp and sharp; think edge of a cliff. The low end limit is kind of mushy; maybe like a quicksand bog. I think we can call the low end a noise bog. Typically our camera's sensors record more data than we need to make a good photo. That means there's some breathing room; latitude for error or sloppiness or if you prefer room to hedge a bet.

So if you're not confident about exposing a digital sensor and you decide you want to hedge the bet which way do you lean? You want to risk going over the cliff or find yourself knee deep in the bog? Most folks as was suggested above hedge that bet preferring the bog over the cliff. It's fairly reasoned that if you're knee deep in the bog at least you're not dead yet which we can't say for cliff jumpers.

Joe

 

[ccaballero]

Some examples, I did work around the over exposure I think but there is so many ways to achieve the same thing.
F25 ISO 100, 1/10
DSC_0033_00001 by carlos caballero, on Flickr

F25, ISO 100 , 1/25
DSC_0032_00001 by carlos caballero, on Flickr

F5, ISO 200, 1/1000

DSC_0160 by carlos caballero, on Flickr

These were all from the jpeg not raw

 

[Braineack]

get out of shutter speed mode if youre not going to set the shutter speed appropriately.

 

[Ysarex]

Some examples, I did work around the over exposure I think but there is so many ways to achieve the same thing.
F25 ISO 100, 1/10
DSC_0033_00001 by carlos caballero, on Flickr

F25, ISO 100 , 1/25
DSC_0032_00001 by carlos caballero, on Flickr

F5, ISO 200, 1/1000

DSC_0160 by carlos caballero, on Flickr

These were all from the jpeg not raw

The first photo is certainly badly overexposed. The second photo of the same scene is much better. There's slightly more than a stop difference between the two exposures but more than that in the two images and so we need to look for causes and possible trouble.

The files indicate that you had the camera in an auto exposure mode. What was that mode on the camera?

Right up front I see potential trouble: f/25. Did you set the lens to f/25 deliberately and if not back to the question above -- what exposure mode did you use on the camera?

F/25 may well be the smallest possible aperture that lens is capable of. Trying to set a hardware max limit value could be an issue.

The difference between the two photos is 8 seconds. I don't believe you made any change to the camera settings between the two shots so the exposure difference needs an explanation.

My gut reaction would be to look to the lens aperture. All of our cameras operate using a methodology we call open aperture metering. The aperture stays wide open so you can see the image through the lens and metering is computed for the f/stop that will be set when you take the photo. You trip the shutter and the mirror lifts up out of the way. While the mirror is being lifted the lens aperture closes down to the set f/stop. F/25 would be the farthest mechanically that the aperture would need to close and if it's sticking even a slight bit then it could fail to reach the set f/stop before the shutter opens -- overexposure is the result.

Joe

 

[Ysarex]

get out of shutter speed mode if youre not going to set the shutter speed appropriately.

That would explain it. Shutter priority and the lens can't stop down any further than f/25. I was overthinking it.

Joe

 

[Strodav]

Here's a worth while read from Cambridge in Colour, probably one of the best photography online learning environments out there. Also, do a search on exposure and you will see several very informative tutorials.

Digital Exposure Techniques

My best advice is to use the histogram on your camera after taking a shot, which comes up after hitting the review button, then using the up and down arrows around the multi-selector until the histogram comes up. If the histogram is hanging off the left (under exposed) then add a little light (open the aperture, slow the shutter speed, up the ISO number), if its hanging off the right side (over exposed) then let in less light (close the aperture, faster shutter, lower the ISO number).

An after thought is to shoot in raw mode, not jpg. You can do a lot more recovery in Post Processing in raw mode than with a jpg image.

 

[ccaballero]

Morning, I was shooting in Aperture priority, the thought process was totally oposite of what I wanted, I wAnted to blur the background wich would have required a wider aperture correct. Went back to my shots and apperture was toned down for subsequent shots.

So, if I had such a small apperture it overexposed because the shotter took in too much light correct.
For example: F5.6, 1/320, ISO 100
DSC_0066_00001 by carlos caballero, on Flickr

F4, 1/400, ISO 160
DSC_0046_00001 by carlos caballero, on Flickr

Cambridge added to favorites. Thanks

 

[Ysarex]

Morning, I was shooting in Aperture priority, the thought process was totally oposite of what I wanted, I wAnted to blur the background wich would have required a wider aperture correct.

Correct.

Went back to my shots and apperture was toned down for subsequent shots.

So, if I had such a small apperture it overexposed because the shotter took in too much light correct.

That's wrong. The camera should have and seems to have appropriately set the shutter to match the f/stop. When you had the f/stop set to f/25 the camera adjusted the shutter to 1/10th sec. That should have produced a normal exposure. We're back to not knowing why you got that overexposure. The photos you posted on this response seem fine.

Braineack's guess was the most logical explanation: that you had the camera in shutter priority and set a shutter speed that required an f/stop beyond the lens's physical capacity. But if that's not the case then we're back to looking for an explanation.

Back to my guess, the lens aperture didn't fully shut down to f/25 before the shutter opened. It should have. A number of different causes are possible culprits including slight condensation on the aperture blades, oil and or cigarette tar and or some other foreign substance on the aperture blades and or the engineers just cut it too close in the camera/lens design.

One way to deal with this is to check for any and all other overexposed shots and see if the same condition, namely f/25, is a common factor. Don't use f/25. You have an APS sensor camera and there's no reason to use f/25. I have an APS sensor camera too. I've been using an APS sensor camera now for about 6 years and I have not once set the f/stop smaller than f/16 and almost never used f/16 for that matter. F/25 on your camera/lens is an extreme that is best avoided.

Still leaves us with a mystery but if the problem can be solved......

Joe