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05-22-2012, 07:07 AM   #1
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645D Auto Exposure Bracketing

I typically manually bracket my exposures according to shutter speed (not aperture) when shooting so that I can do exposure blending (or HDR) later on without worrying about the DOF changing and not having images line up correctly.

This past week I tried doing some auto exposure bracketing on the 645D and noticed that all of the bracketing was done by the camera using changes to aperture, not shutter speed. I've not used the AEB function on any of my cameras before and am wondering if this is normal? It sure doesn't seem right to me.

I looked in the menus and didn't see any option to change this, nor did I see any obvious way to do so on the top LCD when turning on the AEB and setting the functions for how many exposures and how many stops between them.

The only thing I can think of is that I changed my e-dials around (I think they are called) for shutter speed and aperture from what the camera is set to for default. I'm just used to the aperture being in the front and shutter in the rear. Could this have caused the AEB to bracket with aperture instead of shutter?

I guess I could just switch them back around and 'get used to it' if need be, or just not use AEB as I typically like to bracket manually to make sure I get all the details in the brightest brights and darkest darks. It would be nice to use in cases of fast changing light, like last week when I was shooting clouds moving over Yosemite Valley and their shadows were moving quite quickly (plus I was shooting a three shot pano with my nodal slide at the same time!)

05-22-2012, 06:13 PM   #2
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Hi Ryan,

Don't quote me on this, because I am not sure, but I think the parameter changed by AEB depends on the exposure mode you are in (not whether or not you have changed the functions of dials). Something like this: if you are in Aperture Priority AE mode, AEB changes shutter speed; if in Shutter Priority AE mode, it changes aperture. Don't know what it does in manual (probably changes aperture) and fully automatic modes, or whether there is any way to get it to bracket with ISO changes, or what happens if you are using a lens on which the aperture is not controlled by the camera - e.g. a 6x7 lens on an adaptor (perhaps you can't use non-compatible exposure modes with those lenses anyway). Please treat this response as indicating the principle that it depends on the mode - and don't take the details as cast in stone. Maybe try setting it to a different exposure mode and see if it does what you want - and please let us know your findings!

Good luck!

Ed
05-22-2012, 06:17 PM   #3
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Ed, thanks for your input here. I was using Manual mode on the dial. I guess I could change over to Shutter Priority and try that. I could also try switching my e-dials back to the original settings and see what that does...just thought I'd see if anyone had a quick answer on here first.

I doubt it has a setting for ISO bracketing, but that would be cool if it did.
05-22-2012, 06:21 PM   #4
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I am pretty sure that the setting on your e-dials is not relevant to this - but you never know :-)

I would be prepared to bet that using Aperture Priority would make the AEB vary the shutter speed in the way you want. I just hope there isn't anything your picture moving at a rate where the change in shutter speed would render things noticeably differently (like moving water or swaying trees).

05-22-2012, 06:27 PM   #5
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QuoteOriginally posted by Ed Hurst Quote
I just hope there isn't anything your picture moving at a rate where the change in shutter speed would render things noticeably differently (like moving water or swaying trees).
Ed, I've never had an issue with moving water like a waterfall or river/stream causing problems. I imagine that capturing waves crashing in may cause issues if you use an HDR program. I've manually blended waves without issues.

Of course, a windy day with trees moving would pose some problems!
05-22-2012, 06:31 PM   #6
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Hope this works the way you would like it to Ryan...
05-23-2012, 04:04 PM   #7
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Ryan, Ed's correct use aperture priority. I have no lenses without an aperture ring, so I select the aperture on the lens and use Av mode for auto exposure when bracketing.
05-24-2012, 08:54 PM   #8
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Happy to be corrected here, but based on my experience, bracketing using aperture is the norm' and the usual way it is done.
If you ever see a conversation on bracketing or exposure compensation it's pretty much always about + or - stops, never about + or - fractions of a second.

Try changing shutter speeds in a studio setting where the burst of light from the strobes is much shorter than the shutter speed, changing from 1/60th, to 1/100th, to 1/125th will do nothing where as a change from F3.5 to 5 to 8 will make a huge difference. Not so critical for landscape and outdoors, but sticking to what works in varying the exposure in all situations will be the method of choice for most.

Bracketing using aperture will also capture different DoF, so when putting it all together you'll have more options in that regard too.

Bracketting using aperture is definitely the normal/usual way of doing it and every camera I've owned changes the aperture when it comes to bracketing and/or exposure compensation.

That's not to say you can't/shouldn't use shutter speeds, but I'll hazard a guess that is why the 645D will be the way it is and go straight to changing aperture.

As for making the 645D change shutter speeds .... I'm not so sure on this.
My gut-feeling is even in AV priority the camera will set shutter speed according to the settting you've selected, but then bracket using aperture changes, as I've yet to see where you can stipulate the bracketting in anything other than stops. All the controls for bracketiing are for how many shots either side or the original, and by +/- how much of a stop.

05-24-2012, 09:52 PM   #9
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I think the term 'stops' merely refers to the amount of exposure given, not whether that is achieved by aperture or shutter speed. So I don't think that dictates or indicates an absolute use of apertures for bracketing in all cases .

In my view, whether you bracket using one method or the other depends entirely on the circumstances, subject and intention. If you have a static scene and wish to maintain constant depth of field between the frames, then varying the shutter speed makes sense. If you have a subject in motion (requiring a specific shutter speed to render that motion either sharp or blurred to a desired extent), and don't mind the DoF varying between the frames, then varying the aperture makes sense. Of course if you have a moving subject AND want to keep constant DoF, then it is, as with some many things in photography, a case of compromise and judging what matters most to you. You could bracket with ISO, but that of course varies the noise and dynamic range between shots, so even that involves a choice of what matters to you.

For this reason, cameras in my experience generally let you bracket using different parameters in different modes, so you have control and choice. In Aperture Priority mode, it is the shutter speed that varies (because you have selected the aperture and presumably that is what you care about, so it is kept constant). In Shutter Priority mode, the reverse is the case. This has always been how it works with cameras I have owned that have this function at all. What is done in manual and program modes I cannot recall. And I cannot remember how or if cameras can be made to bracket using ISO, but I think some can in some modes.

As for bracketing with studio lights, I agree that shutter speed would make no difference since the scene is usually too dark for the exposure to meaningfully render ambient light. Apertures would affect the recording of the scene from the lights. But since DoF would vary this way, I think bracketing by changing the light intensity might make more sense. And of course studio conditions usually are set up with enough care and testing that such bracketing is not needed.

As for your point about varying DoF being good as you bracket with apertures, that might be the case. But if you are going to 'DoF bracket' it woudl perhaps be better to do this for each of the different exposures you take so you have complete control and options. Otherwise the shot with the best exposure may have the worst DoF (or vice versa) thus defeating the goal of bracketing, which is to give you at least one optimal frame (or the components of one optimal image taken in different frames). So I am not sure this argument holds much water.

So, in short, I beg to differ that bracketing with aperture only is always best, or indeed what is always done. It varies and I think cameras offer options (in different modes at least) for that reason.

All of this is of course my own view and nothing more than that...

All the best,

Ed
05-25-2012, 01:37 AM   #10
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By the way, all of that advice is based on the assumption that you want the pictures to look the same apart from exposure differences (either because they are to be compared, because you want to achieve a precise visualisation, or because they are to be used together in some sort of HDR or stitching context). If you are happy for the different shots to be only approximations of each other, much of this does not apply (or applies less rigidly).

Ed
05-25-2012, 06:54 AM   #11
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Thank you all for your replies. In my mind, I was assuming that landscape photography with natural light was the only kind of photography, since that's all that I seriously do in terms of photography. When I bracket I almost always do so by changing shutter speed, rarely by ISO, and pretty much never by aperture. That's because I always want the option of blending the exposures, and the change in DOF would make that problematic when it comes to lining things up.
06-01-2012, 07:53 AM - 1 Like   #12
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Hi, I too was a bit surprised (coming from another camera) that the 645D was, by default, changing aperture during M mode bracketing. For landscape exposure blending this was baffling because the camera was changing the depth of field on me (same issue Ryan mentions above), and I certaintly didn't want that. However, these defaults can be changed in the menu settings. Actually, the 645D is very flexible for bracketing, and works very well when combined with mirror lock up and 2s drive delay. So you can take bracketed exposures on a tripod with one press, and not need a remote cable release if 2s delay is good enough for your needs.

Here are my settings:
- Mirror lock-up UP (rotate dial 'M.UP' near right side of lens mount)
- In DRIVE menu, I select Self-Timer 2s. The camera will flip the mirror up, then wait 2s for vibrations to settle, then take the shot(s).
- In MENU page C1, I have "7. One-Push Bracketing" set to "2. On. Pressing shutter release once takes specified number of bracketed shots"
- In MENU page C5, I have "29. Green Button in TAv & M modes" set to "2. Tv Shift. Camera sets shutter speed relative to the selected aperture for proper exposure."

Its the last setting (C5) that switches how bracketing is done. It also changes the behavior of the green button, but in a way that I find more natural, especially when using third-party lens adapters. With those, I set the aperture manually on the lens, then press the green button to have the camera automatically set shutter speed. From here (optional) you can manually bump shutter speed +/- with the finger dial.

I do wish there was a way to have M.UP dial automatically enable/disable 2s delay. That would be one more menu setting (DRIVE menu) I could avoid when switching from hand-held shooting to being on a tripod.
06-15-2012, 01:51 PM   #13
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Great thread!

Thanks for all the helpful feedback. Lots to learn with the 645D.
10-30-2012, 10:25 AM   #14
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Hi Ryan, It has been said already, though some have approached the correct information with doubt. Pentax Auto Bracketing (not only on the 645D) happens through changing appertures when you shoot in M mode, but when shooting in AV mode the camera mainains the apperture value you have choosen and changes exposure times instead. Actually the only way to be able to blend the images perfectly afterwards, since different appertures never give you the exact same outlining of elements within your picture and thus jeopardise sharpness.

p.s. I love your landscapes!
11-06-2012, 03:22 PM   #15
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Just a couple of supplementary points in response to this...

Firstly, if you set the camera to perform auto bracketing in M mode, how it behaves depends on whether or not the lens attached lets the camera adjust the aperture. I use a lot of P67 lenses via an adaptor (which of course is wholly manual); I also use 645 A and FA lenses with the aperture manually set (i.e. not on the A setting). In these situations, the camera seems to 'understand' that it can't perform the bracketing via aperture settings and automatically does it by changing the shutter speed (just as it does in AV mode).

Secondly, I beg to differ slightly on your point about blending images requiring the same aperture to be used in each shot (and so varying the shutter speed). Firstly, modern software (such as Auto Align in PS) does a good job of lining up shots taken at different apertures. Secondly, blending shots taken with different shutter speeds can also be problematic if there are moving elements in the scene (moving clouds, water, swaying leaves, etc.) which of course will be blurred by different amounts in shots taken with different shutter speeds - which also makes blending tricky at times. So I think the question about whether the bracketing should be done with shutter speed, aperture or ISO depends very much on the software available, the scene and your intentions.
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