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smr

So I don't need a modded DSLR?...

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Referring to this article:

 

http://www.clarkvision.com/articles/do_you_need_a_modified_camera_for_astrophotography/

horsehead+m42_300mm_c11.21.2014.0J6A1631-1750-SigAv.h-pan1-b6x6s.jpg

These photos were taken with a stock 7D Mark 2 Camera. I have a similar Camera with even more recent sensor technology insofar as the Canon 80D, therefore do I need it modifying in terms of Ha sensitivity ? I'd like your opinions please as I may be missing something from Roger's take on it.

"Modifying digital cameras is not necessary to obtain great astrophotos. Many stock cameras have good hydrogen-alpha response, e.g. recent Canon DSLRs. More important than a modified cameras is proper post processing methods that will bring out and not suppress hydrogen alpha emission, and cameras with good sensitivity and very low thermal dark current. The best digital camera for deep sky astrophotography that I have evaluated has good sensitivity, including hydrogen-alpha, and amazingly low dark current is the Canon 7D Mark II 20-megapixel digital camera. A great full frame digital camera for astrophotography is the Canon 6D 20-megapixel digital camera.

The advantage of a stock digital camera in astrophotography is that the color balance is close to that of the human eye, and shows compositional differences better. Modified digital cameras are too sensitive to hydrogen alpha emission, making scenes containing hydrogen too red, swamping colors from other compositions. Often this shows in amateur astrophotos as dominantly red. The choice of course is personal. I prefer images with more colors to show more processes and chemistry. I believe such images are more interesting, so I only use stack digitalcameras for my astrophotography."

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Much depends on the target, and personal taste. I find the above colours a bit garish, and personally prefer subtler handling. I have a modded 550D which works well, and gives good results in my book.

M42USM3expcropsat2curves.thumb.jpg.13932e16535b78ba0a86f3bc04665276.jpgM45-21625.0scrop-curves.jpg.ee7f5d5014cf53e9ed4e4819b64692ea.thumb.jpg.98f94fe68613e7ea708b2e6e8e20931d.jpgOrion07012018LPremBGcal.jpg.0f1b9829700289fe109af187079703ef.thumb.jpg.c08d69922bacb218fa12d3aa0af58e48.jpg

 

Not sure this is way too red, and anyway, to the human eye the scene is all grey because at night the cones in the retina don't work that well. You can always push back the red signal in postprocessing. I might give my non-modded 80D a shot one of these days, but I would expect I need far longer exposures to get the same S/N on H-alpha rich targets

 

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Hmmm, not sure there is such a thing as 'too sensitive to Ha'. You can always change the balance in post processing, while if you haven't captured enough of it in the first place, you can never make up for it properly. Sure, great astrophotos can be achieved with unmodified cameras, but I would never present greater Ha sensitivity as a disadvantage. 

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Very nice images. I like your PP on them, and I too prefer the more subtle editing. I agree that the colours in Roger's photo look a tad over done, I'd pull them back slightly if my own, but that's not to take away from what fantastic images they are as is. I was astounded more than anything at what a stock DSLR from the 7D2 era onwards can achieve though more than anything.

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I personally wouldn't modify my Canon 80D (I think I would rather have hot needles through my eyeballs), the Ha response is plenty with the newer cameras and modification can introduce lots of negatives like bloated stars/no AF/loss of auto sensor clean etc.

Alan

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10 minutes ago, Alien 13 said:

I personally wouldn't modify my Canon 80D (I think I would rather have hot needles through my eyeballs), the Ha response is plenty with the newer cameras and modification can introduce lots of negatives like bloated stars/no AF/loss of auto sensor clean etc.

Alan

I'd never modify my 80D either, I was wondering if it's worth getting a cheaper DSLR just for astrophotography and modifying that though.

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1 minute ago, smr said:

I'd never modify my 80D either, I was wondering if it's worth getting a cheaper DSLR just for astrophotography and modifying that though.

That is a better option I think..

Alan

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Have tried the 6D and 7DMK2 both are very good as is.

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I can only afford one DSLR - it has to do for all purposes and so I leave it as it was purchased- unmodded!  At the moment it is taking photos that are giving me personal satisfaction and is plenty good enough for learning to do this night sky business.

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42 minutes ago, smr said:

I'd never modify my 80D either, I was wondering if it's worth getting a cheaper DSLR just for astrophotography and modifying that though.

That is more-or-less what I did: I got a modded 550D with fewer than 9000 clicks for around 200 euro, to replace my old (modded) 450D. The 80D is used for daytime imaging. It is however absolutely brilliant under low light conditions, showing very little noise even at ISO 6400, so I might give it a spin on targets like Markarian's chain.

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I'm afraid that I'm not keen either on his arguments or his images. If his aim is to create images with a full range of natural colours then I don't think he has succeeded. The heavy handed processing has produced strange by-products such as the cyan shell around M42/Running Man, which I think is spurious, and the curious green/blue streak around and above (in this orientation) the Trapezium. In imaging this target in assorted filters I've never found any trace of this, but maybe I missed it. I find the colours garish and unconvincing, but that can be said of any over-saturated image however captured. 

As thomasv says above, you don't have to retain the overly red colour balance captured by modded DSLRs but you have the signal in the bag. Once you have it you can process it as you wish.

In Roger Clark's Heart Nebula and NAN we do indeed see what these objects would look like to a more sensitive human eye and, with their very low Ha component (low compared with what is possible) they have a certain natural charm. If that's the objective, fine. For other imagers, though, it isn't the objective. They are looking to find structure and detail not apparent without specialist filtration.

The mono camera's advantage is not its sensitivity to Ha but its ability to make efficient use of an Ha filter to isolate the Ha, and so isolate those structures emitting in that wavelength. These structures add information and interest to an image. A modded camera can still be tolerably efficient through an Ha filter but I don't know how well an unmodded one would work. The important aspect of a narrowband filter is not so much what it passes as what it blocks. I think it is this point which the author misses. You don't have to exploit an Ha layer in order to find lots more red, you can use it to find lots more structure.

Olly

 

 

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Posted (edited)

I have used a Canon 60Da (i.e. factory Ha modded) since I started in AP about three years ago, and I thought that camera would have a great advantage over a standard 60D. Due to the few nights with clear skies, I have now first doubled and then tripled my effort in collecting data when the sky occasionally clears by adding a 300mm and 135mm telephoto lens side by side of my 5" refractor, and since the 60Da is still rediculously expensive (used) compared to the standard 60D, I felt I could only afford to buy two 60D for the other lenses. To my surprise, I have not found much difference between the 60Da and 60D although I have not felt I could use precious imaging time to make a direct comparison with the same lens and exposure times. Here is the California Nebula with a 60D and my Canon 300 mm f/4 and I feel it is red enough (76 x 3 min at ISO1600). A few days ago I even tried Ha imaging of the Soul Nebula with a 60D under a full moon and snow covered grounds, and I think it also worked out quite well (Canon 300 mm f/4, Astronomik 12 nm Ha clip filter, 38 x 8 min at ISO1600).

So my conclusion is that unmodded is good enough - Ha imaging can be done but you will need more exposures to get the same number of photons. I assume you had a look at the link that Clark gives, showing Ha transmission with different DSLRs:

http://kolarivision.com/articles/internal-cut-filter-transmission/

Apparently it is about 25% for the 60D, but some cameras are close to zero - so check that carefully before you buy a DSLR.

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Edited by gorann

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Flicking through the first part of the answers there's a of conflicting bad advice...you can't process ha signal if you haven't got it..and seeing it as a red colour on over sensitive modded cameras! Ha signal captures all the details and combined with a narrow filter ,smaller stars.. you can expose for longer without the light polluion affecting the image..capture more details with smaller stars..awesome...the only thing it won't give you is star colour..thats the only downfall I can see..the rest is a positive..

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