Custom White balance for modded DSLR + CLS Filter?

[Vega]

Hi

I have a modded Canon 1000D and have just finished imaging M3... what can I say.. very red! I believe I used the daytime white balance setting at capture and selected at capture WB when processing. This got me wondering about maybe doing a custom white balance and what is the best method for my configuration.

I'm thinking of using a grey card on a sunny day to take the CWB image to store in the camera. Should I have the CLS filter in while taking this image? would this have a detrimental effect to the modification of the camera for AP?

Regards

[wxsatuser]

Grey card at noon on a sunny day is a good method and put the CLS in as well.

[Guest]

Hi,

I have that same camera modded also, and use the CLS filter, that filter is designed for use in modded cameras as it restores the white balance almost perfectly, but on an unmodded camera it will give a green tinge to all images.

I don't use anything but daylight WB as with that filter the colour balance is almost perfect.

Try taking a picture in the daylight with your camera and the CLS filter in place, and you will see the picture will be almost normal.

So my answer is no CWB just youse daylight and the images will be pretty much as the human eye would see them.

I did try doing a CWB once with a grey card at noon with the CLS filter in place, and it came out almost exactly the same as taking it with an unmodded normal camera without any filter, so what is the point, I know this because I have two 1000D camera one for daytime photography which is obviously unmodded and one modded for astro use so wanted to see the difference after I had it modded.

Hope that helps

MM

[IanL]

I don't worry about white balance at all when taking my images through by Hutech which definitely introduces a colour cast.  You need to shoot in RAW mode since any white balance data is applied by software after the event,which enables you to ignore it completely if the balance is wrong.  (Don't shoot JPG as it throws away a lot of useful data before you ever see it and permanently applies the white balance to the image before you can get your hands on it).

Just calibrate your RAW images (bias, darks, flats as you see best), debayer and stack them and then sort out the colour balance of the resulting image as part of the processing.

There are lots of ways of doing it ranging from simple to complicated, but ideally you want to remain in control of the process rather than relying on white balance correction in whatever software you are using:

- The simplest way is to adjust the three colour channels so the histogram peaks line up - that will usually get you pretty close to the correct balance from the get go, and then you can tweak by eye.  The peaks correspond to the background sky and by lining them up you are making the background 'dark grey' which usually kills off any colour cast from the filter (though if you have LP that isn't being blocked, it might need a bit of tweaking by eye).  You can do that in pretty much any package, including DSS and Photoshop.

- Using something like PixInsight you can simply use the automatic screen transfer function (with the channels unlocked) to have the software do much the same as above.  You can then use the histogram transformation to permanently apply the STF settings.

- PI also has other processes that can balance the colour by using references selected from part of the background and either a whole bunch of stars (which should average out to 'white') or a galaxy core (again should average out to 'white' as it's a whole bunch of stars!)

- If you want to get really advanced you could use something like Excalibrator (free - google it) which will find and measure the RGB components of reference stars in your image, compare them to known values from spectroscopic data in catalogues and then give you correction factors to apply to the three channels to balance them (it is quite complex to do, but guarantees your image will match reality if that is what you are seeking to do).

- Most astro processing packages will have the necessary functions to perform these processes, not just PI.

Obviously you would want a custom white balance if you are using a modded camera for daylight imaging, since you wouldn't have a reliable reference in the image itself (unlike astro-images where you do).

[Vega]

Thanks for the replies peeps. You've confirmed what I was thinking as I never used to get colouring issues with this setup. I will put it down to M3 being lowish on the horizon during my imaging session and it also containing several reddish stars. (Its the first time I've tried imaging M3)

Cheers

[jgs001]

I use a CLS, and don't bother changing the WB settings on my unmodded dSLR from auto... Then I let DSS create a custom white balance in processing.  That sorts out the CLS blue colour cast quite nicely. 

MM there are two flavours of CLS filter... one with an IR cut, and one without. I believe the one with the IR cut filter is flagged as CLS CCD and is designed for use with a modded dSLR or a camera that does not have a built in IR cut filter. I've no idea which version my CLS clip filter is, as it doesn't matter as my dSLR is unmodded. 

[Guest]

I use a CLS, and don't bother changing the WB settings on my unmodded dSLR from auto... Then I let DSS create a custom white balance in processing.  That sorts out the CLS blue colour cast quite nicely. 

MM there are two flavours of CLS filter... one with an IR cut, and one without. I believe the one with the IR cut filter is flagged as CLS CCD and is designed for use with a modded dSLR or a camera that does not have a built in IR cut filter. I've no idea which version my CLS clip filter is, as it doesn't matter as my dSLR is unmodded.

When you have a newer canon camera modded there are two filters in the camera, one is left in as it has very good IR cut, but does not cut out Ha, and the other is removed because it cuts a lot of the Ha signal, aswell as IR, so you only need the cheaper non IR cut CLS filter, but if you have a full spectrum mod they will remove both filters, then you would need the one with the IR cut for imaging. As there would not be one left in the camera

Hope that helps

MM

[cathouse42]

I would prefer camera sensors just have no filters at all and then make them optional in the after market. Most people buy a UV/IR cut filter anyway with most cameras under the pretence of protecting their DSLR lenses or better contrast (usually by a sales pitch in the camera store). Having them on-sensor is just stupid for DSLR's, fine for point and shoot but not DSLR's. I even have them and I wouldn't mind having a Ha cut filter if need be during daytime at the front of the objective.

[Psychobilly]

I would prefer camera sensors just have no filters at all and then make them optional in the after market. Most people buy a UV/IR cut filter anyway with most cameras under the pretence of protecting their DSLR lenses or better contrast (usually by a sales pitch in the camera store). Having them on-sensor is just stupid for DSLR's, fine for point and shoot but not DSLR's. I even have them and I wouldn't mind having a Ha cut filter if need be during daytime at the front of the objective.

I wonder what percentage of all the DSLR's produced are used for  photography where anything other than the visual spectrum is "relevant"....   It's great  to see the manufactures producing models for these "niche" markets  but for thier "run of the mill" products then the filtering is in the right place...  Surely it makes more sense for the manufacturers  for the minority to remove filters than the majority having to add them...

Just my opinion which is different from yours...

Peter...