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Author Topic: IQ260 Long Exposure LCC?  (Read 3120 times)

Ramirez

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IQ260 Long Exposure LCC?
« on: January 30, 2014, 02:25:15 pm »

I'm planning to buy a back and a tech camera and have a question:
The dark frame at exposure times of several minutes is of course a pain, but there is no way out, right?
What about the LCC? Do I have to make an additional exposure as reference equally long or can I turn the ISO up and save time?
Logically thought the answer is no, because the noise in different ISO levels is different.
So I expose 20 minutes, then darkframe 20 minutes and then a 20 minutes LCC. That's a horror!?!
I hope you understand my question.

Thanks for your help, this forum is very informative!
 :)
« Last Edit: January 30, 2014, 04:20:02 pm by Ramirez »
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Bart_van_der_Wolf

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Re: IQ260 Long Exposure LCC?
« Reply #1 on: January 30, 2014, 02:35:38 pm »

I'm planning to by a back and a tech camera and have a question:
The dark frame at exposure times of several minutes is of course a pain, but there is no way out, right?
What about the LCC? Do I have to make an additional exposure as reference equally long or can I turn the ISO up and save time?

Hi,

For the LCC you can use a diffused short exposure (assuming you have enough light). You need to use the same lens, aperture, focus distance, and shift if applicable. The point is to get the light distribution as seen by the sensor, so you could even do it afterwards. I think that even the color temperature of the lightsource used for the LCC creation is not that important.

It probably helps to make the LCC with an above average exposure level, say 2 stops above what the lightmeter indicates.

Cheers,
Bart
« Last Edit: January 30, 2014, 03:24:06 pm by BartvanderWolf »
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Paul2660

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Re: IQ260 Long Exposure LCC?
« Reply #2 on: January 30, 2014, 02:48:19 pm »

If you did a 1 hour exposure from a tech camera at night the LCC will be a bit less important even if using the moon for illumination.  Color casts won't be as bad due to light you are working with.  You should be able to get by with a LCC taken at late evening or twilight taken before your 1hour exposure.  Trying to get the exposure right at night on a LCC will be tough. 

Long exposures in daylight you may have to take an eqvilant LCC I believe the color cast issue will be a bit more of an issue. 

One reason to have a Phase One DF or similar body around as here all you need is the dark frame at night or long daylight exposures. 

Tech camera long exposures would get tedious since the camera will be taking a dark frame after both the long exposure and LCC.

Paul
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Enda Cavanagh

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Re: IQ260 Long Exposure LCC?
« Reply #3 on: January 30, 2014, 02:59:04 pm »

With color cast corrections you are doing 2 things. You correct the color cast due to the wide angle lens design and also you have the option of applying a "correct" white balance. You wouldn't want a perfect white balance most likely at dawn/dusk anyway and for long exposures running into several minutes you have the option of noting the camera movements. The next day you can replicate the movements and take a color cast calibration shot in a brighter setting. This will save you the hassle of spending time taking the shot is such low light.

Another tip. I wouldn't really mess around with the iso much but what you can do is change the aperture to the widest setting when taking longer calibration shots. I know you will hear advise about keeping the aperture constant but to date I have seen no difference in color cast and vignetting as I change apertures.

foster_jb

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Re: IQ260 Long Exposure LCC?
« Reply #4 on: January 30, 2014, 03:26:30 pm »

It's my understanding that, while it is generally best to create your LCC "in the field," you can also create an LCC later on back at home or in the studio.  You need to note your lens aperture setting, focus setting, and any movements you have used.  Later at home, you can replicate those same settings on your camera and shoot an LCC using a flash with diffuser.  I have to say that I have not yet tried this myself as I rarely shoot early morning or evening, but the information was from a reliable source.

Best,
Foster
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madmanchan

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Re: IQ260 Long Exposure LCC?
« Reply #5 on: January 30, 2014, 04:02:34 pm »

Ideally you want the LCC shot to be the same optical configuration as the one you used to shoot your real photo.  Small deviations from this are usually not a big deal.

Same goes for lighting.  If the illumination conditions for the LCC shot are significantly different (spectrally) compared to the real shot, then asymmetric color casts may not be completely fixed.
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Eric Chan

Enda Cavanagh

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Re: IQ260 Long Exposure LCC?
« Reply #6 on: January 30, 2014, 06:53:45 pm »


Same goes for lighting.  If the illumination conditions for the LCC shot are significantly different (spectrally) compared to the real shot, then asymmetric color casts may not be completely fixed.

Really. That's strange. I never experienced that myself.

Wayne Fox

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Re: IQ260 Long Exposure LCC?
« Reply #7 on: January 30, 2014, 07:17:26 pm »

haven't seen that either, but most of my LCC's are shot shortly before or after the exposure that needs correcting.

But I do have a library that was shot with direct sunlight for cases where I forgot to shoot one. Using these I've never noticed this either at least with capture one.  I thought it made color adjustments sort of like an offset of the difference from the center so the color of the light wouldn't make much difference, but maybe it's just because basically I only shoot outside in the daylight so even in morning or evening light my light source color variation isn't that great.
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JoeKitchen

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Re: IQ260 Long Exposure LCC?
« Reply #8 on: January 30, 2014, 07:42:49 pm »

haven't seen that either, but most of my LCC's are shot shortly before or after the exposure that needs correcting.

But I do have a library that was shot with direct sunlight for cases where I forgot to shoot one. Using these I've never noticed this either at least with capture one.  I thought it made color adjustments sort of like an offset of the difference from the center so the color of the light wouldn't make much difference, but maybe it's just because basically I only shoot outside in the daylight so even in morning or evening light my light source color variation isn't that great.

You could also use a flashlight hitting the LCC mask to make that exposure quicker.  The light source does not matter so long as it is even on the screen. 
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EsbenHR

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Re: IQ260 Long Exposure LCC?
« Reply #9 on: January 31, 2014, 01:02:01 am »

You could also use a flashlight hitting the LCC mask to make that exposure quicker.  The light source does not matter so long as it is even on the screen. 

I will suggest that this is better than changing the lens aperture of the lens. A good LCC implementation needs to be relatively robust wrt. colors. After all it needs to correct, say, a blue sky even though the LCC is white.

However, Eric does have a point, so use a flashlight with a bulb. I would stay away from LEDs, phone displays etc.

Regards,

Esben H-R
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tmh

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Re: IQ260 Long Exposure LCC?
« Reply #10 on: January 31, 2014, 01:22:15 am »

... or can I turn the ISO up and save time?

IIRC both the LCC and the image need to be at the same ISO, otherwise the software wont be able to match them.

I took a series of LCC shots at F11, all my commonly used shifts (20mm L, 20mm R, 20mm V etc etc), and brought them into Capture One to build a library of LCCs.

However I shot the LCC at 50 and my images were normally at ISO25, and Capture One would not apply the LCC to the image.

This was with Leaf MOS files and Capture One 6, it may have changed in V7.


If you have time to make the LCC during the shoot then that's great, I do a lot of stitching so want to move quickly, especially in changing light. My normal process (after composing and metering etc) with a left+right stitch is:

- Shoot left side
- Shift, shoot right side
- Increase 2-3 stops (shutter only - must leave aperture fixed), slide in LCC plate, shoot LCC right side
- shift, shoot LCC left side


It gets a bit more fun with 6 or 9 shots in the stitch, difficult to work out which LCC applies to which image sometimes!


YMMV with night shots and longer exposures, an increase of 2-3 stops for the LCC may leave you waiting a while - but the whole idea I believe is to keep the aperture (and ISO) constant.



Hope that helps

TMH


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gerald.d

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Re: IQ260 Long Exposure LCC?
« Reply #11 on: January 31, 2014, 03:12:48 am »

If you have time to make the LCC during the shoot then that's great, I do a lot of stitching so want to move quickly, especially in changing light. My normal process (after composing and metering etc) with a left+right stitch is:

- Shoot left side
- Shift, shoot right side
- Increase 2-3 stops (shutter only - must leave aperture fixed), slide in LCC plate, shoot LCC right side
- shift, shoot LCC left side


It gets a bit more fun with 6 or 9 shots in the stitch, difficult to work out which LCC applies to which image sometimes!


YMMV with night shots and longer exposures, an increase of 2-3 stops for the LCC may leave you waiting a while - but the whole idea I believe is to keep the aperture (and ISO) constant.



Hope that helps

TMH



I've found that if you're also using the LCC to remove dust spots, this can be a problematic approach because unless you can match the LCC shift precisely to the original one (which is almost impossible), your LCC's won't be aligned accurately enough.
Kind regards,

Gerald.
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JoeKitchen

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Re: IQ260 Long Exposure LCC?
« Reply #12 on: January 31, 2014, 06:22:45 am »

IIRC both the LCC and the image need to be at the same ISO, otherwise the software wont be able to match them.

I took a series of LCC shots at F11, all my commonly used shifts (20mm L, 20mm R, 20mm V etc etc), and brought them into Capture One to build a library of LCCs.

However I shot the LCC at 50 and my images were normally at ISO25, and Capture One would not apply the LCC to the image.

This was with Leaf MOS files and Capture One 6, it may have changed in V7.


If you have time to make the LCC during the shoot then that's great, I do a lot of stitching so want to move quickly, especially in changing light. My normal process (after composing and metering etc) with a left+right stitch is:

- Shoot left side
- Shift, shoot right side
- Increase 2-3 stops (shutter only - must leave aperture fixed), slide in LCC plate, shoot LCC right side
- shift, shoot LCC left side


It gets a bit more fun with 6 or 9 shots in the stitch, difficult to work out which LCC applies to which image sometimes!


YMMV with night shots and longer exposures, an increase of 2-3 stops for the LCC may leave you waiting a while - but the whole idea I believe is to keep the aperture (and ISO) constant.



Hope that helps

TMH




I have on multiple occasions increased the ISO to shoot the LLC.  I have never had a problem; I use C1 v6. 
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Enda Cavanagh

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Re: IQ260 Long Exposure LCC?
« Reply #13 on: January 31, 2014, 07:10:20 am »

I will suggest that this is better than changing the lens aperture of the lens. A good LCC implementation needs to be relatively robust wrt. colors. After all it needs to correct, say, a blue sky even though the LCC is white.


Changing the aperture has no affect on lCC. I often does this in low light to save time.
How does a LCC correction correct a blue sky? I'm not sure what you mean. I have several times taken calibration shots after the event for various reasons. The only important factor is that a uniform light hits the lens. Adjusting the white balance obviously should not be taken from a corrected calibration shot due to the probable different color temperature from when you shot the original scene

Bart_van_der_Wolf

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Re: IQ260 Long Exposure LCC?
« Reply #14 on: January 31, 2014, 07:36:04 am »

Changing the aperture has no affect on lCC.

Sorry Enda, but that is not true. Changing aperture will change the amount of vignetting and light fall-off, and that will need to be compensated for by the LCC. Remember, an LCC not only corrects Color Cast, but also vignetting and light fall-off.

Noise may affect the LCC to a degree, even though the LCC data is blurred before use (to reduce the influence of dustspots and pattern noise). When the noise becomes large enough to be still visible after blur, it will locally affect the LCC correction.

Quote
Adjusting the white balance obviously should not be taken from a corrected calibration shot due to the probable different color temperature from when you shot the original scene

Depending on how the LCC procedure is implemented in CaptureOne Pro, colorbalance may have only a small effect. This is due to the common procedure to convert the LCC info to Luminance only (in particular to avoid colorbalance shifts), before normalization to 1.0 for the brightest pixels, and dividing the actual image by the normalized LCC data. However, it's best to keep the light quality (spectral distribution) close to the original shot, if only to make the process more predictable. After all, we do not know exactly how Phase One have implemented the LCC procedure.

Cheers,
Bart
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torger

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Re: IQ260 Long Exposure LCC?
« Reply #15 on: January 31, 2014, 07:53:25 am »

Changing aperture also affects how the dust spots if any are rendered. Even changing focus distance has a small effect on the cast, so keep all settings the same is best. If the color cast is relatively minor you can get away with a little mismatch for the color cast part, dust spots must line up perfect of course.

A good LCC algorithm should not affect color balance of the original picture. I assume C1's algorithm is good.

What it does is that it identifies the "neutral" color of the LCC shot and only corrects deviations from that, so it does not matter in which light the LCC shot was made, you could make it in an entirely different light than the actual scene if you'd like. Identifying the neutral color can be non-trivial though, especially for tech cameras and sensors with varying sensitivity over the surface. You can't just pick the center spot in the image and assume it's neutral, because the lens may be shifted. I don't know how C1 exactly does this but assume that they do something intelligent and then you should not get any white balance shift due to the correction.
« Last Edit: January 31, 2014, 07:55:16 am by torger »
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