K-3 exposure


BarryE

Link Posted 23/01/2014 - 08:25
I've had my K-3 for a month now and all's well except I'm not totally convinced by the K-3's metering performance, as many shots are underexposed.

There have been arguments about Pentax protecting the highlights etc, and this may well be true. However, I wonder if the reason this is being done so, seemingly, aggressively is because of the increased pixel count from the K-5 variants.

Allowing for improved sensor technologies between the K-5 and the K-3, there is still a finite area for the "lightwells" on a sensor of this size. As the dynamic range correlates with the size of the lightwells, all things being equal, the K-5 would be expected to have a better dynamic range than the K-3. But all things are not equal: the technologies have improved.

The hope that improved technologies would have offset the increased pixel count, thus not affecting the dynamic range, is appearing not to be the case, or this is how I see it.

Am I wrong ? Does the K-5 actually perform better than the K-3 in high dynamic range conditions ? Definition in this case: from this month's experience I can see a "high dynamic" range image as including a mostly medium key image with only a very few tiny high key elements, ie very common.

Overall, the K-3 improvements are significant. The resolution improvement is most welcome; the accuracy of the focusing; the speed, etc., etc, make the K-3 a great camera. But there's extra care needed with the exposure, which may be a problem.

* There's no need to drag out the FF argument here of greater sensor size and thus greater dynamic range. We are where we are ...
Last Edited by BarryE on 23/01/2014 - 08:50

johnriley

Link Posted 23/01/2014 - 09:09
When I had the K-3 for review I didn't notice in practice any difference in metering between that and any of the K-5 models.

I think as they stand images from the Pentax models a whisker light using matrix metering. I always use centre weighted and -0.3EV to give me the exposure I want.

Why not show us examples of correctly exposed and underexposed images so we can see if there's any common denominator, maybe even a fault?
Best regards, John

malcolmk

Link Posted 23/01/2014 - 12:13
That's odd, if I had to think of something a bit negative to say about my K3 it is that it is more inclined to blow a highlight than the K5.

Overall though it is much better, I am now getting the same sort of results (technically) as my cousin does with his FF Canon 5D III, but I am trying to keep ISO no higher than 800 and often much lower.

BarryE

Link Posted 23/01/2014 - 12:37
Malcolm, you say " ... K3 it is that it is more inclined to blow a highlight than the K5" ... I guess this may be my point.

If the photowells have less capacity, because they are smaller, then they are more likely to blow, are they not ? Maybe then the metering software, effectively, "sees" the blown highlights and adjusts the exposure to not blow more, thus the image is underexposed a little.

John, I've looked back at my recent shots compared with the K-5 and the sense is that the K-3 ones tend to be underexposed in comparison. I'll need to get the time to make some more accurate comparisons test shots to see if there's a clear pattern.

One thought, so far, is that the blue channel does seem to influence the exposure more ie a northerly sky - just a thought. This is with/without a UV filter.

JAK

Link Posted 23/01/2014 - 12:43
Which method of metering are you using and on what subjects?
John K

BarryE

Link Posted 23/01/2014 - 12:46
Multi-segment and landscapes eg South Downs

mille19

Link Posted 23/01/2014 - 12:48
I found I was using minus 0.3-0.7 exposure compensation with the K5 to stop the highlights (mainly sky in landscapes) blowing.

I don't need to do this with my K3 I think it does meter to stop highlights blowing at the expense of slight under exposure in the foregrounds.

I recently invested in a 49mm circular grad filter and tried it on my 21mm Ltd on a trip to the Peak District it worked a treat.

malcolmk

Link Posted 23/01/2014 - 13:38
BarryE wrote:
Malcolm, you say " ... K3 it is that it is more inclined to blow a highlight than the K5" ... I guess this may be my point.

If the photowells have less capacity, because they are smaller, then they are more likely to blow, are they not ? Maybe then the metering software, effectively, "sees" the blown highlights and adjusts the exposure to not blow more, thus the image is underexposed a little.

The K5 certainly appeared to work that way and I would quite often find myself lifting the shadows a bit in PS. I think my K3 is attempting the same but to a lesser extent. I suspect nothing but a sample variation and I should dial in a minus exposure.

Most of my work is quickly grabbed street scenes and I use multi-segment metering. I am probably being over-sensitive to it but if for example the sun is caught in a car wing mirror or on a reflective street sign, any detail is completely gone. I don't recall being so aware of that on the K5. Its predecessor, an *istD, would almost black the image if it saw something like that, so the K5 was a huge advance in such situations.

In case there is some confusion over terminology I mean that my K3 produces images which are sometimes just a little too bright, but never enough to wreck things - except my first use of it after the inevitable menu explorations. I had left it on spot metering and forgot all about it. Spoilt a few shots that day but not really looked back since.

I didn't instantly fall in love with the K3 but there's no way I'd go back now. Maybe I had got sloppy with the K5; click and run type shots can encourage that, but taking as much care as time allows, the K3 images have something that was lacking before.

Studio and tripod users may not see those benefits.

JAK

Link Posted 23/01/2014 - 14:32
BarryE wrote:
Multi-segment and landscapes eg South Downs

Can you upload one or two - it should help to see what the issue is. Sometimes the exposure the camera gives is not necessarily the best setting. An obvious example is a snow scene which will be made to look quite grey by an automatic exposure system. In that case the exposure would need increasing to compensate and it could be something similar affecting your landscapes. Similarly a dark subject might be lightened too much by the auto exposure so the exposure would need decreasing to make it better represent the subject. That's not just a Pentax or K-3 issue but affects all cameras using automatic exposure.

The multi-segment takes the brightest and darkest parts of the scene to determine the exposure - just maybe the subject in your photo is not best metered by that method. Some who take landscapes use graduated filers to reduce the overall contrast range.

Given the K-3 gives you an instant review of the photo, it should be possible to retake it if the result you're seeing isn't what you want. Also a tweak in PostProcessing, eg Photoshop Elements may help bring the image to what you expect.
John K
Last Edited by JAK on 23/01/2014 - 14:40

BarryE

Link Posted 23/01/2014 - 17:11
Hi Jak, bearing in mind I've only had limited chance to use this camera, I'll attempt to add 5 images as examples. (First time I've tried this so I'm prepared to get it wrong)

All taken as RAW and converted to med quality jpegs in PS CS5. Multi-segment metering.

Ref the grads, I tend to prefer to use ACR's filter or to bracket and blend in PS (polarisers excepted).

Exposure comments are subjective and most of these are from experiments ...

pf2.jpg (fence post): test shot to check out autofocus fine tuning. Typical of an underexposed image. No highlights to trick meter.
pf3.jpg (green slope) more blue northerly sky - underexposed
pf4.jpg (sheep from above) no sky more accurate exposure
pf5.jpg (cattle) interesting example. There are a few tiny highlights and a good portion of northly blue sky - both seem to excessively influence the end result, I feel. Underexposed a little.
pf6.jpg (mist)it can work ... post processed with exposure lift, cropping and filtering. Worked from an underexposed image, though with the mist around I'll accept the meter might have struggled a little, perhaps.










johnriley

Link Posted 23/01/2014 - 17:29
My feeling is that all these are within workable range, but the third one is too light (the one you think is spot on) and the cows in the field are absolutely spot on. The last shot is very nice indeed, full of atmosphere.

Not sure what you're chasing, but I wouldn't worry. Just dial in exposure compensation to suit the end result you are looking for.
Best regards, John

JAK

Link Posted 23/01/2014 - 17:38
Your uploads have worked just fine.
I agree the colour curves of those look on the low side, albeit they are recoverable. Did you take in camera jpegs as well otherwise it's still hard to say whether it is an issue with the images or the raw processing. I would think it should be possible to produce very acceptable images from your raw files as even from these jpegs the detail is there.
As here:


John K

BarryE

Link Posted 23/01/2014 - 17:43
Hi John, I guess I'm trying to establish if others believe the K-5 tends to underexpose compared to the K-3 and if so, is it because of the higher pixel count. My feeling is that it might be - smaller photowells etc.

I'm seeing about 3/4 to 1 stop underexposure out of the camera often. Oddly the images above do look slightly lighter than the originals. I wonder why that is ?

Happy to dial in some compensation, but just want to understand why I'm seeing a difference between k-5 and k-3.

The mist image was a in a series I took on the only occasion I've been able to get out to take proper photos in the early morning when it was raining or flooded with this new camera. I wish we were having a proper winter. Thanks for your comments.

BarryE

Link Posted 23/01/2014 - 17:51
Hi John K, I only took RAW. Yes the detail is there, but the fact that sensor is underexposing means some data is unnecessarily being lost. My feeling, and it's somewhat subjective, is that the k-5 was slightly better. Maybe it's just a batch issue ...

Looks like I'll have to use compensation a little. Given more time with this new camera and hopefully I'll begin to pick up it's peculiarities.

Thanks for your comments.

MrB

Link Posted 23/01/2014 - 18:43
I don't have an answer but I am just wondering if you have you investigated whether the D-Range Settings (shooting menu 2) affect your exposure problem?

Philip
Add a Comment
You must be registered or logged-in to comment.