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Old 15-05-2019, 11:20 PM
RyanJones
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Camera combination image

Hi all?

I have a question ? I have both a modified and unmodified Canon 350d. I love my modified one for deep space imaging because of its ha sensitivity but the trade off is the lack of color in everything else. My unmodded camera doesnít capture anywhere near the same levels of Ha but does bring out beautiful Oiii blues and yellows etc.

My question is, would there be any benifit to combining subs from both cameras to give my images a better colour range while still capturing the Ha . Effectively like you go about NB combinations. And if so, what would be the best way to combine them ? Will putting into DSS sort it out or will that just average everything out and give me neither ?

And I guess while Iím here Iíll ask ? Is the lack of blues etc simply because the Ha overwhelms the rest ? So theoretically if I took more subs then the blues etc. would start to come through to balance out ?

Thank you for your responses in advance
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Old 16-05-2019, 09:28 AM
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Hmm. I wonder, I'm no expert but your modded camera will still be getting the same B/G as the unmodded. Is it just a matter of processing to pull those colors out?
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Old 16-05-2019, 10:03 AM
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Originally Posted by ChrisV View Post
Hmm. I wonder, I'm no expert but your modded camera will still be getting the same B/G as the unmodded. Is it just a matter of processing to pull those colors out?

Not really.. The absence of IR cut filter not only allows more IR to Red channel.. As G and B filters are not perfect, they will pass excess if IR as well, so the whole colour balance will be affected.
If you want to use modified camera for terestrial photography, you must use external IR cut filter.
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Old 16-05-2019, 10:11 AM
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Well this is what I thought Chris but it seems like the Ha is so much greater that it tints my blues and yellows into browns and magentaís. I was just thinking if I could overlay the low Ha data that I could create a better colour range. I do notice that when people are imaging NB, their exposure times are different between the different filters. I assume ( but certainly donít KNOW ) that they do this because the O3 and S2 are more feint than the Ha ? Happy to be told Iím wrong and why though.
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Old 16-05-2019, 10:30 AM
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Ryan did you do a custom white balance after your camera mod?
I did it using a 13% grey card under the sun and am also using a LP filter when I used my modified DSLR and it works great, no problem showing the blue in M20.
I have the cards, message me if you want to borrow them.
cheers
Bo

Last edited by traveller; 16-05-2019 at 10:44 AM.
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Old 16-05-2019, 10:57 AM
RyanJones
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Hi Bo,

Thank you for that great suggestion. I did try doing a custom white balance just with a white piece of paper in daylight but at the time I was using a non CCD filter ( armature mistake ) so it didnít have the I/R cut that Bojan alluded to. Do at that time I was swapping filters in and out and havenít returned back to it.
Iím happy to buy the grey card if you can give me the details of what Iíd need to buy ? Is it just a ď standard ď 13% grey card ? Do you take the shot through the scope with all filters in place ?

It would be great if this works out to be the fix to my excess red issues. Thank you
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Old 16-05-2019, 11:24 AM
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Sent you a message Ryan.
I am happy to lend you my cards. Don't buy more plastic
Bo
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Old 16-05-2019, 11:25 AM
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Thank you so much Bo. I really appreciate it
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Old 17-05-2019, 10:50 AM
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I don't use 1 shot colour cameras, but maybe the answer is to use the non-Ha sensitive camera to give your basic colour and then create a synthetic luminance from the colour to which you add a SMALL amount of the Ha data (which will primarily be only in the R channel of the Ha sensitive camera). You also want to add a SMALL amount of Ha to the other red channel and then regenerate the RGB. There are tutorials all over the place describing this type of processing. My favorite way of doing this is described by Adam Block using Photoshop. For sure, too much Ha will overwhelm all the other data as you have already observed. In my opinion, Ha data is data that gives very interesting detail...but too much and the reds will blow out everything. Really, I think you just want the detail.


Peter


EDIT: " Modified cameras with enhanced hydrogen alpha sensitivity result in hydrogen alpha dominating the images of nebulae, hiding the multiple colors and processes present. An unmodified camera shows these colors and their varying intensities better so you can discern chemical and physical processes and composition."


Interesting read: http://www.clarkvision.com/articles/...rstellar.dust/

Last edited by PRejto; 17-05-2019 at 04:34 PM.
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Old 18-05-2019, 11:29 PM
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Thank you Peter,

Thatís exactly what I was hoping to do and youíve described it perfectly. Added bonus is that I use Photoshop already for processing so Adam Blocks techniques should make sense to me. Thank you for your help. Itís really appreciated.
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Old 20-05-2019, 01:23 PM
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Very interesting discussion, it explains a lot.

I had a DSI III Colour camera and its output were LRGB files. In ImagesPlus the best results came from tweaking the L file before using Combine LRGB. Maybe you could try the modded camera output as Luminance and tweak it fully before combining with the stock camera RGB files.

GlennB
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Old 20-05-2019, 02:45 PM
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Hi Ryan,


This technique is described very well in Adam's tutorial on processing M1. It's worth every dollar in my view!


Peter
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Old 20-05-2019, 08:24 PM
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Definitely an interesting question.

As long as you're not clipping digital signal at any point in the spectrum I'd argue that you should only use the modded-camera. It will contain the spectrum you'd obtain from the stock camera plus great red/Ha.

Almost any astrophotography needs colour balancing these days and you can control colour balance as you wish within software (as long as no data was clipped during collection phase).

You won't/shouldn't increase your signal to noise in any way combining stock and modded (over just using the modded for the longer total period) and certainly won't gain in resolution.
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Old 20-05-2019, 08:50 PM
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I seem to have opened an interesting topic ? And thank you all for your input .

I’d imagine there wouldn’t be a huge amount of people with 2 identical cameras, one modded and one not that would have bothered doing what I’m suggesting.

I agree with the theory that whatever photons hit the sensor, they will be the same in either camera in the shorter wavelengths and only greater in the shorter and so good processing should be able to extract the colours. I guess it’s how unevenly balanced the levels of the photons are that I’m struggling with. On that note, can I ask, why when I see NB images are the intergration times different for each filter ? And does this extrapolate back to what I’m suggesting where the unmodded camera is effectively my O3 filter and the modded is my Ha ? ( I understand that’s not correct in the literal sense )

Thoughts ?
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Old 28-05-2019, 09:14 AM
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Originally Posted by RyanJones View Post
And does this extrapolate back to what Iím suggesting where the unmodded camera is effectively my O3 filter and the modded is my Ha ? ( I understand thatís not correct in the literal sense )

I wouldn't expect so unless you can measure the spectra thats filtered by what was removed in the modded camera. (just because its called an IR filter doesn't mean to me anything in terms of transmission at various wavelengths. I don't know if it's viable to say use an SA100 filter and a street light or star to work out what the spectra range of each camera is and then how to proceed to be able to combine both meanigfully. I suspect it wont be worth the bother and you may need to add filters to get a reasonably linear spectra.

Still no reason you can't play with splitting up data to channels and mixing them up to recombine as if they were properly filtered mono captures. Signal is signal after all. There will be overlap and likely some signal will push to overexposure, but then again no two pieces of equipment produce the exact same characteristics, its all about things falling in a range so that the device can be sold has having certain specs. Shoot a large nebula with each camera then split into RGB channels and compare R to R, G to G and B to B, pick the best of each to recombine (register etc of course). Even if not ideal I would think you could combine each pair of same channel to produce an L channel that you can use for a mask when stretching since it'll be masking the actually structure thats there. Explore and play
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Old 28-05-2019, 12:25 PM
gb44 (Glenn)
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Notwithstanding the great opinions already given, maybe someone on the old yahoo group " digital astro" can add to the ideas for Ryan to try.

GlennB
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Old 28-05-2019, 09:21 PM
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Ok. So I have a result . Iím not going to say itís a good one but it was successful. After stacking an equal integration time from each camera on Carina, I managed to regain a lot of the colors that were lost when the red of the modded camera took over. I did however also retain the detail in the Ha regions that the modified is good for. The challenge I have now is working out a better combining method. The proof of concept has been achieved though.

Thank you all for your comments and following the progress of my idea.
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Old 30-05-2019, 10:06 PM
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Interesting to read, but in the end you really should set a custom white balance. Much easier to get the other non-red colours to show up in your images. Astrophotographer Jerry Lodriguss article link ... http://www.astropix.com/html/i_astrop/customwb.html

Note especially from that aticle ... shoot images for no filter, as well as every filter you are going to use with it as they all cast a different colour hue over the image. Even your unmodded camera you should shoot a CWB for it with every filter you are going to use with that cam.

BTW, while I've got a digital grey card, before I had that I set my CWB by shooting straight down at noon at a bitumen road surface. I shoot one which is fully illuminated bitumen and one fully in shade. I actually found the one in the shade (so a much darker, almost black surface) yielded better images at night on the scope. But you may find otherwise? Try both. Very simple and easy to do. Do not put on a lens as you want it totally out of focus. Pointless putting on a lens and focusing on the bitumen as all the slight blemishes and reflections off the surface will create a speckled CWB. Totally out of focus means the sensor see's just a flat grey edge to edge. So you can go try it out right now. Cheers
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Old 31-05-2019, 11:22 PM
RyanJones
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Thank you for your input Bo. A fellow IIS member (Bo) is lending me his greycard so a custom white balance is next on the cards ( pun intended ).
Iíve read a bit of Jerryís stuff and it makes for some interesting reading.
I might give that bitumen idea a go too and see what results I get also.

Cheers
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