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10-10-2016, 11:53 AM   #1
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Pentax 645D auto bracketing ISO

Hi, is there a way to autobracket the ISO with the Pentax 645D?

I know I can bracket manually, but it's not convenient. I'm trying to do a portrait HDR, and since I'm using flash, I don't want to change either the shutter speed nor the Fstop, so that leaves ISO.

Anyone knows if this can be done?

Thanks in advanced.

10-10-2016, 12:37 PM   #2
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I don't think that you can do this and TBH even if you could a little thought may suggest that it would seem to be a pointless exercise at least that is my thinking on this.

With normal HDR imaging you are changing the exposure by adjusting s/s or f/stop that is you are modifying the quantity of light entering the system to be collected by the photosites.

On the other hand adjusting ISO only changes the way the signal is handled (it does not allow more light to be collected) i.e. the higher the ISO the more the camera electronics amplify it leading eventually to the point where noise becomes objectionable due to poorer signal to noise ratio.

I would suggest that you would be much better off making a single exposure and spawning a series of under / overexposed to be combined later to give a HDR 'look', with the added advantage of only having a single image with no additional subject movement
10-10-2016, 01:55 PM   #3
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QuoteOriginally posted by TonyW Quote
I don't think that you can do this and TBH even if you could a little thought may suggest that it would seem to be a pointless exercise at least that is my thinking on this.

With normal HDR imaging you are changing the exposure by adjusting s/s or f/stop that is you are modifying the quantity of light entering the system to be collected by the photosites.

On the other hand adjusting ISO only changes the way the signal is handled (it does not allow more light to be collected) i.e. the higher the ISO the more the camera electronics amplify it leading eventually to the point where noise becomes objectionable due to poorer signal to noise ratio.

I would suggest that you would be much better off making a single exposure and spawning a series of under / overexposed to be combined later to give a HDR 'look', with the added advantage of only having a single image with no additional subject movement
Thanks.

I don't know if it will be the same thing doing it in post, for one, if anything is clipped, you can't recover it, if it's done when you take the picture, you'll have detail, bacuse it applies the underexposure while taking the picture rather than after. The same goes for shadow detail.

And I can't use the shutter, since that will only affect ambient light and not flash.

I can do it with Canon or Nikon using Camranger, but that doesn't work with the Pentax. So I was wondering if there is something similar for Pentax. And my Fuji X100 does it automatically, it has ISO bracketing.
10-11-2016, 05:05 AM - 1 Like   #4
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QuoteOriginally posted by Pablo Villegas Quote
..I don't know if it will be the same thing doing it in post, for one, if anything is clipped, you can't recover it, if it's done when you take the picture, you'll have detail, bacuse it applies the underexposure while taking the picture rather than after. The same goes for shadow detail.
I should say that I have not tried bracketing using ISO so there may be something it brings to the table, but I must say that from what I understand and seeing other comments it does sound like 'Snake Oil' to me.

FWIW:
1. We are talking about raw image acquisition here aren't we (not JPEG as that may throw a different light on this) ?

2. If anything is truly clipped (i.e. in the capture not what your editor may be showing) you will not be able to recover it regardless of setting ISO, s/s or aperture.

3. ISO settings do not influence the amount of light captured by the sensor (there are only two things that do control that shutter and aperture). Your cameras base ISO (lets say 100) is used for all capture and all for ISO changes you make the cameras electronic circuitry amplifies the base ISO signal to give the effect of increased speed and allowing different s/s and f/stops to be used from base ISO settings. In amplifying the signal inherent noise is also increased eroding the Signal to Noise ratio until such time as the noise becomes unacceptable.

4. If you do change ISO settings then you are going to be getting a different noise signature for each ISO that may be a problem when combined as a faux hdr image.

QuoteQuote:
I can do it with Canon or Nikon using Camranger, but that doesn't work with the Pentax. So I was wondering if there is something similar for Pentax. And my Fuji X100 does it automatically, it has ISO bracketing.
It would be interesting to see a comparison using Camranger for ISO only changes vs changing shutter speed to get a real increase in the amount of light hitting the sensor.
I do not know the Fuji but I believe that ISO bracketing is carried out on JPEG images and is limited to +/- 1 EV.

You mentioned you are looking to do portrait HDR therefore my assumption is that you are looking at producing a 'funky/grungy' aesthetic as it is unlikely that your flash portraits are going to have a wider scene dynamic range than your sensor ?

As I do not think it possible that ISO bracketing is applicable (other than manual) then I would suggest giving a try to single image faux HDR - it may be what your are looking for. An example below from a single flash shot (checking the sync between Yongnuou units so no artistic merit ). As can be seen three images from the same single raw capture processed =/- 2 EV in ACR from straight out of camera shot.

In doing it this way it will be very similar (although possibly not exactly the same as three separate exposures) to increasing/decreasing camera ISO. Just make sure that you are giving the maximum exposure to still retain highlight detail and your shadows can be pulled up in post.

Just an example which could be more subtle or really in your face depending on taste



10-12-2016, 02:42 AM   #5
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Can you bracket by keeping the camera settings the same but changing the flash output?
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