K5 - Exposure bracketing with contant aperture...again


WaypointCharlie

Link Posted 04/06/2013 - 10:48
With better software (SNS) and a bit more experience behind me I've started to look again at multi shot HDR. However, I've hit the same problem as before...how to keep the aperture constant when using camera exposure bracketing mode.

The only way I've found of ensuring the aperture remains constant between shots is to use Av mode and, in some cases, P mode. This doesn't seem to be possible in M mode. Or is it? Is there no way of using camera exposure bracketing at constant aperture without relying on camera metering?

johnriley

Link Posted 04/06/2013 - 11:25
Av you set the aperture and the camera varies the shutter speed when you use exposure compensation. That does the trick and it's what I use. Quick and effective.

In manual set the aperture and find the shutter speed that gives normal exposure. Then just change the shutter speed manually to give a spread of shots.

I do seven shots from -3 to +3 stops exposure, in 1 stop steps.
Best regards, John

WaypointCharlie

Link Posted 04/06/2013 - 11:54
Thanks John. I'm trying to avoid touching the camera between shots as this causes movement with my flimsy tripod. When I finally upgrade the tripod I'll test if fiddling with the speed dial moves the camera.

I suppose I could do it via PK-Tether but I think I'd prefer to lug a robust tripod with me than a delicate laptop!

johnriley

Link Posted 04/06/2013 - 12:21
I'd suggest ditch the flimsy tripod and use a wall or other support instead. There's auto bracketing in the camera as well, that might help.

Don't forget also that using the 2 second delay flips up the mirror before exposure, so that reduces any chance of shake. Any tripod vibration might have also died down by using this method.

Photomatix will auto align images if asked to, so any slight variation can be covered in software.
Best regards, John

WaypointCharlie

Link Posted 04/06/2013 - 13:09
Sorry John, perhaps I didn't make it clear. It was the camera auto bracketing I was originally on about.

Using Av mode is fine for auto bracketing, as long as you don't want more than 5 exposures and as long as you don't mind relying on the camera metering to set the base exposure.

In manual mode the camera perfoms auto bracketing by varying aperture and time, not just time. (The reason I'd prefer manual control of the base exposure is because I'm proposing to stitch together two HDR shots and this would be easier if they had identical exposures).

johnriley

Link Posted 04/06/2013 - 13:22
No problem. I'd see the answer as ditching auto bracketing and looking instead at replacing the tripod. Perhaps a second hand tripod from eBay?
Best regards, John

johnha

Link Posted 04/06/2013 - 13:45
Have you tried combining auto-bracketing with exposure compensation? When you set the auto-bracketing up you get the numberline with the positions under/middle/over on. You can them move these as a group with exposure compensation away from the cameras metered exposure.

Doing this in Av might achieve what you want as long as your 'difference' from the camera metered exposure is predicatble or can be determined by a test shot.

This worked well on my Z-1 and from memory the K-5 works the same way (I don't have mine to hand at the moment).

John.
PPG Flickr

WaypointCharlie

Link Posted 04/06/2013 - 14:16
Thanks John & John!

Yes, I already combine auto-bracketing with exposure compensation. I think I'll stick with Av mode, auto-bracketing. I'll make a note of the exposure the camera sets for the first stitch position then use exposure compensation to ensure the second stitch position gets the same. It's not quite as simple as being able to use M mode but probably quicker and safer than fiddling with the dial on every bracket shot.

As for the tripod, my difficulty is deciding what I want/need and if I'm prepared to lug it with me for several hours. (e.g. something like the the Red Snapper 283/284 may not always be tall enough without the column extended, the 324 a bit heavy, especially with an RSH-12 head). I can see I may end up buying two!

McGregNi

Link Posted 04/06/2013 - 14:17
Thats the way to go - after deciding which way you will bias your exposures (eg plus 1 stop, or 1.5 etc) and after setting the spacing in stops between frames, press and hold the EC (+/-) button and turn the rear dial in the direction you want. You will see all the exposure points move in parallel in that direction but keeping the spacing you have set.

It depends on the scene of course, but as there is not an even spread of data recorded by the sensors throughout the range (most of it is at the mid to upper end) it makes sense to push these brackets for HDR upwards in brightness to ensure capturing the best detail in the shadows.

Too many dark exposures, and certainly where the histogram is off the left edge, will throw away good quality image data that the HDR program will need.
My Guides to the Pentax Digital Camera Flash Lighting System : Download here from the PentaxForums Homepage Article .... link
Pentax K7 with BG-4 Grip / Samyang 14mm f2.8 ED AS IF UMC / DA18-55mm f3.5-5.6 AL WR / SMC A28mm f2.8 / D FA 28-105mm / SMC F35-70 f3.5-4.5 / SMC A50mm f1.7 / Tamron AF70-300mm f4-5.6 Di LD macro / SMC M75-150mm f4.0 / Tamron Adaptall (CT-135) 135mm f2.8 / Asahi Takumar-A 2X tele-converter / Pentax AF-540FGZ (I & II) Flashes / Cactus RF60/X Flashes & V6/V6II Transceiver

WaypointCharlie

Link Posted 04/06/2013 - 18:01
I agree that you want to have a good exposure for the shadows. My interest in using multiple shots is when there is a very large dynamic range to capture. In these case I find the default camera metering overexposes the highlights. Therefore I'm after quite a lot of negative compensation to ensure the lowest exposure bracket caputres the highlights without clipping. Mind you, I've very little experience with HDR to date. What I do know is I don't like HDR that immediately shouts HDR to the man on the Clapham omnibus!

Here's a three bracket process which I think worked out reasonably well (it wasn't taken with the intention of using an HDR merge)

American Air Museum

Here's a five bracket process from the other day. Unfortunately I was rushed and I didn't spot that -2.6 EV wasn't low enough to capture the window without clipping highlights (not that it's that obvious at this size).

Debden Church

For reference, this is the in camera JPEG at 0 EV


Last Edited by WaypointCharlie on 04/06/2013 - 18:12

McGregNi

Link Posted 04/06/2013 - 21:12
I think you've put you theory into practice very well - these don't shout 'HDR' to me.

The air museum shows a nicely expanded visible DR - the detailing on the surfaces looks natural I think.

Your camera JPEG of the church has a muddy green cast which has been balanced in the HDR version, although maybe the magenta is a bit too strong. Again, looking out the rear window, the white highlights are pulled nicely back (although this type of clipping is normally easy to correct conventionally with 'recovery' type sliders).

There's a natural balance of shadows across the back too - maybe these 'lows' need a touch more depth, perhaps 'black point' pulled down a bit?
My Guides to the Pentax Digital Camera Flash Lighting System : Download here from the PentaxForums Homepage Article .... link
Pentax K7 with BG-4 Grip / Samyang 14mm f2.8 ED AS IF UMC / DA18-55mm f3.5-5.6 AL WR / SMC A28mm f2.8 / D FA 28-105mm / SMC F35-70 f3.5-4.5 / SMC A50mm f1.7 / Tamron AF70-300mm f4-5.6 Di LD macro / SMC M75-150mm f4.0 / Tamron Adaptall (CT-135) 135mm f2.8 / Asahi Takumar-A 2X tele-converter / Pentax AF-540FGZ (I & II) Flashes / Cactus RF60/X Flashes & V6/V6II Transceiver

WaypointCharlie

Link Posted 04/06/2013 - 21:51
I'm not too fussed about getting the JPEG colour balance right as I always process from Raw. Although I did grey card on the altar I agree I've ended up a bit too far in the other direction, particularly in the mid tones.

There's no way I can recover the blown highlights in the window from the 0EV shot. The window is overexposed by about 4EV, so not even recoverable cleanly from the shot at -2.6EV.

When you suggest moving the black point down a bit to me that means lifting the shadow levels. Is this what you mean?

I took the Air Museum at -3.3EV, -1.3EV and +0.7EV. If I'd intended to HDR I might have done it differently, but again I was very pushed for time as a security man was trying to chuck me out! Here's the -1.3EV camera JPEG




I find the HDR version over processed for my liking, but that's perhaps because I know where it's come from!

McGregNi

Link Posted 05/06/2013 - 09:17
I was thinking about the slider options in Photomatix Pro - to deepen the blacks I think you've got a 'Black Point' slider : moving it right pulls the darkest tones down even more and would add contrast to the shadow areas. This would be similar I think as using PS levels and moving the blacks slider right also, but I think the Photmatix one targets a more limited range at the very darkest end.
My Guides to the Pentax Digital Camera Flash Lighting System : Download here from the PentaxForums Homepage Article .... link
Pentax K7 with BG-4 Grip / Samyang 14mm f2.8 ED AS IF UMC / DA18-55mm f3.5-5.6 AL WR / SMC A28mm f2.8 / D FA 28-105mm / SMC F35-70 f3.5-4.5 / SMC A50mm f1.7 / Tamron AF70-300mm f4-5.6 Di LD macro / SMC M75-150mm f4.0 / Tamron Adaptall (CT-135) 135mm f2.8 / Asahi Takumar-A 2X tele-converter / Pentax AF-540FGZ (I & II) Flashes / Cactus RF60/X Flashes & V6/V6II Transceiver
Last Edited by McGregNi on 05/06/2013 - 09:17

WaypointCharlie

Link Posted 05/06/2013 - 12:43
Thanks.

I don't have Photomatrix but merge exposures using SNS at a fairly neutral setting, then process manually in CS5 in 16-bit mode. However, I suspect the black point slider in Photomatrix works much the same and does much what it says on the tin, i.e. moving to the right increases the point at which data are clipped to black. Unless the left hand side of the histogram is empty I'm not usually brave enough to do this as I hate throwing anything away!

Sorry, we seem to have moved a long way from my original question about auto bracketing. I take it that there isn't a way of using auto bracketing in M mode with a constant aperture?

McGregNi

Link Posted 05/06/2013 - 14:26
I think this is counter-intuitive. M mode holds a constant aperture and shutter speed. ISO would normally remain fixed as well in M. Obviously the exposures could be bracketed then by the iso changing, but I haven't tried it to see if this is what happens.

But clearly, quality - wise, the only variable it makes sense to adjust during exposure bracketing for HDR is shutter speed - so Av mode is the clear choice. As I think John has said, M mode would be for when you want to pause between brackets and change the shutter speed yourself. But then that's not 'auto bracketing!'.

I always try and take the auto route - I want the shots fired off as fast as possible to reduce the possibility of anything moving significantly during the process.

Regarding the blacks - I made the suggestion because I thought the shadow areas in the church looked a little 'hazy', a sign of low contrast. Raising the black point should add some base to the shadow range generally and firm up the contrast, which should give better definition throughout those areas of the shot.

I wouldn't worry about throwing away a bit at the very blackest black parts - its not like clipped highs which look bad on digital, clipped blacks in small doses should still look natural, and its in a good cause if it gives you that base and firmer contrast I was on about. You've gathered the data from the brackets firstly - now you have the latitude to throw a bit away!

And finally, about the clipped highlights. If you end up with a single shot that needs substantial 'recovery', give Pentax Digital Camera Utility 4.0 a go - its Highlight Adjustment' tab provides great power and sophistication to this brightest zone, you might be surprised at how good the results can be even with so many stops over. I've given some more details on its use the guide I wrote some time ago... link
My Guides to the Pentax Digital Camera Flash Lighting System : Download here from the PentaxForums Homepage Article .... link
Pentax K7 with BG-4 Grip / Samyang 14mm f2.8 ED AS IF UMC / DA18-55mm f3.5-5.6 AL WR / SMC A28mm f2.8 / D FA 28-105mm / SMC F35-70 f3.5-4.5 / SMC A50mm f1.7 / Tamron AF70-300mm f4-5.6 Di LD macro / SMC M75-150mm f4.0 / Tamron Adaptall (CT-135) 135mm f2.8 / Asahi Takumar-A 2X tele-converter / Pentax AF-540FGZ (I & II) Flashes / Cactus RF60/X Flashes & V6/V6II Transceiver
Last Edited by McGregNi on 05/06/2013 - 14:26
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