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broadsword

Correct colour using a modded DSLR

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Last night was the first try out for the brand new modified Canon 600d with an Astronomik CLS clip in filter. In my usual untutored way I snapped away at M82 using ISO 1600 120sec exposures. Whilst the amount of image detail and contrast to the background was much better than with my un modded 1000d, I was surprised at the amount of redness in the image - most of the galaxy was red, plus many stars. In addition, the flats came out vivid blue instead of the normal grey.

Is this normal for a modded image set? Should I have changed the camera settings to compensate, or is it all done in post-processing?

Can't post an example yet as I haven't loaded the Canon software yet....

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Its not over after the shutter closes aye? Now the real fun begins one of the first things i do after stacking is remove all green from the CLS filter with HLVG Are you shooting in RAW? You really want to be if your not.Post is a real challenge put up the shot and i can give you my take.

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Its not over after the shutter closes aye? Now the real fun begins one of the first things i do after stacking is remove all green from the CLS filter with HLVG Are you shooting in RAW? You really want to be if your not.Post is a real challenge put up the shot and i can give you my take.

Ooer, are you implying that processing a modded image is more of a challenge than an un modded? Yes, I am using RAW. I can't supply an image yet as I won't be putting the software on the PC for a week or two.

I just didn't want to take too many more images if I'm using the wrong settings, hence the request for advice...

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You can shoot with a custom white balance, something like a 18% grey card in sunlight would be a good place to start. The cwb raw files should be close to balanced but you can always apply your own fine adjustment to set the black point on the RGB channels in post. That's one of the reasons for shooting in raw there are alot of adjustments you can make when converting the raw files.

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This is something I haven't solved yet either. I need to look into colour balance sometime again.

My M82 image turned out like this back then (images are from back in March) I still have the RAW files though.

post-28221-0-69730200-1364582290_thumb.j

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Processing is in itself an art modded or not an example always helps me out like the image above i can see from looking at it that a gradient filter needs to be used. I have my camera's white balance set to neutral and play with it in post after removing the green.

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Separating, and rebalancing the RGB channels will get you as close as you'll get.

The filter effect of the CLS screws up the overall balance and from what I see makes achieving a final colour balance even more difficult.

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So, looking at the responses, there is the suggestion to use custom white balance and the 'grey card' method, and relying on the post processing (or maybe both).

I'm certainly a bit surprised at the added 'degree of difficulty' involved with a modded camera plus the CLS filter - although maybe the latter is the main culprit? I didn't pick this up from the many posts on using these items. In fact, all that most articles on the web talk about is how to use a modded camera for normal daytime photography, rather than how to get the blessed colour right on your astrophotos. A good topic for a tutorial? Or maybe there are some out there?

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This is a great thread. I do find colour problems around stars with the CLS filter so I'll stop using it. By-the-way, what's 'Grey card'?

Alexxx

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You can shoot with a custom white balance, something like a 18% grey card in sunlight would be a good place to start. The cwb raw files should be close to balanced but you can always apply your own fine adjustment to set the black point on the RGB channels in post. That's one of the reasons for shooting in raw there are alot of adjustments you can make when converting the raw files.

Alex, this is the gray card reference, from Kev above. It seems to be a fairly standard DSLR technique, it is certainly covered in my Canon 600d instruction leaflet. See this site as an example:

http://www.diyphotography.net/diy-making-your-own-gray-cards

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Thanks Neil. I assume this would be with a lens? How would that translate into setting the camera white balance for AP at prime focus? Or is that not an issue? If this will require too much hijacking of this thread, I'll start my own!

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Yes, for a camera lens and daytime imaging without a CLS filter!

There really no such thing as "proper" colour balance in AP. Any corrections ( ie G2v etc) are done post exposure.

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Thanks Neil. I assume this would be with a lens? How would that translate into setting the camera white balance for AP at prime focus? Or is that not an issue? If this will require too much hijacking of this thread, I'll start my own!

Just shoot the cwb with a lens on the body and then use the cwb on the body when connected to the scope. It isn't the finished solution as Merlin has pointed out but it will get you reasonably close. Or shoot the cwb on the grey card directly through the scope with filters added, focus isn't important, in fact unfocussed is better.

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Thanks Neil. I assume this would be with a lens? How would that translate into setting the camera white balance for AP at prime focus? Or is that not an issue? If this will require too much hijacking of this thread, I'll start my own!

Alex,

I'm completely in the dark on this one (no pun intended), and hoping for salvation from the great and the good on here......I'm just trying to avoid too much wasted effort on my next AP session!!

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I hope I get somewhere to helping Neil! Kev, what filters?? Remember Neil and I are still quite green here!

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If you shoot in RAW, then you don't have to worry about colour balance as you have got an image right from the sensor without any adjustments applied to the image. The colour balance embedded within a RAW file only tells the RAW converter what the camera setting was when the photo was taken rather than what it is, of course it would be easier if it is as close as possible, but I just don't bother. After stacking and removing gradients (GradientXterminator), I find that the colour balance is already on its way to being correct.

Using a modified Canon 1100D and an Astronomik CLS clip in filter tends to shift everything into the red for me, however after aligning the histogram in PS it isn't too bad. I tend to shift the red down to the green/blue instead of the other way around which sometimes helps to keep noise under control.

Here's a quick method of doing so:

http://www.activeast...ng-rgb-channels

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Stuart, this seems to make a lot of sense to me. I have been doing almost exactly this after stacking in DSS, using the DSS processing stuff, and it helps a lot with my light polluted orange frames. So hopefully it will also work with my new red shifted frames (which look a lot like Amra's shown above). Guess I'll just be doing bigger red and green shifting. I do background extraction and colour calibration in PI also, so hopefully all will go back to normal colour with lots of new H alpha areas!

Alex, are we getting there yet?

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I do background extraction and colour calibration in PI also

Neil, if you are using PI, then performing a DBE (Dynamic Background Extraction) will do a pretty good job of aligning the RGB channels. Failing that, a Histogram Transformation will deal with them by tweaking the individual channels.

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I hope I get somewhere to helping Neil! Kev, what filters?? Remember Neil and I are still quite green here!

I was assuming you had light pollution filters in your optical train?

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You can shoot with a custom white balance, something like a 18% grey card in sunlight would be a good place to start. The cwb raw files should be close to balanced but you can always apply your own fine adjustment to set the black point on the RGB channels in post. That's one of the reasons for shooting in raw there are alot of adjustments you can make when converting the raw files.

I think I'll try the custom white balance method with the grey card, but should I leave the CLS filter in the camera when taking the shots of the card in sunlight? I think I'll have the CLS filter in most of the time when astroimaging.

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Neil,

You only need to consider a white balance correction for family and fun daytime images...remove the CLS filter...

As mentioned for AP the white balance does nothing for you. All the necessary corrections can be applied to your RGB by the processing software.

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You can shoot with a custom white balance, something like a 18% grey card in sunlight would be a good place to start. The cwb raw files should be close to balanced but you can always apply your own fine adjustment to set the black point on the RGB channels in post. That's one of the reasons for shooting in raw there are alot of adjustments you can make when converting the raw files.

I have only read part way through the thread but recently used custom white balance to restore normal colour to my modded dslr, and used a white card - it works fine and even unprocessed images come out untinted by pink. I assumed the card should be white to remind the camera what white is - have I got this wrong?

Part of my light path includes a sw lp-filter but this doesnt seem to affect the white balance issue. I ask because I had just advised someone to rectify their white balance with the white card - should it definitely be grey?

Regards

Aenima

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Aenima,

The 18% Grey card is the "photographic standard" for a white reference.

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Aenima,

The 18% Grey card is the "photographic standard" for a white reference.

So I take it the white card is ok. and only 18% off?

Aenima

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Aenima, I'm far from being an expert, but from a cursory look on the web it seems a white card is good, but the grey card is spot on...

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