We are living in the golden age of backyard astrophotography and while the internet is drowning in millions of beautiful nightscapes, every astrophotographer always struggles to find new techniques and tips to stand out from the others... Astro-modification is a technique that is becoming more and more popular amongst amateur and professional photographers. But what does specifically lie behind this weird word, and should you consider transitioning towards it? Here is all you need to know!
Nowadays most digital cameras are built with a CMOS sensor (Complementary Metal-Oxide Semiconductor) that is made of different layers. Among these layers is a special filter that blocks Infra-red (IR) radiations and the most energetic Ultra-violet (UV) emissions (some UV still pass through, explaining why you sometimes need to attach an extra UV filter to get rid of haze and flares in a bright sunny day). If this IR-cutting filter wasn't present, your pictures would appear red and pink, because your camera would be able to pick up the IR radiations.
As these radiations are arguably useless for photography (unless you want to adopt a certain photographic style, which can be pretty cool, look up full-spectrum modification!), CMOS sensors are equipped with these filters, rebalancing the temperature of your pictures. However to make sure that no IR would pass, the filter blocks 50% of EMR (electro-magnetic radiations) at a wavelength of 650 nm (visible red light) and blocks 100% at 700nm (beyond 700nm: Infra-Red). It seems to work really well for day photography, but not so much for astrophotography. See, your camera is cheating you without you knowing it. It is blocking about 10% of the visible spectrum (all the red)! This a problem, because a lot of deep-sky objects emit red radiations, especially at 656.28nm called H-alpha radiations that reveal the presence of hydrogen electrons de-exciting. Long story short, with a CMOS sensor, you can only see about 22% of these emissions, which are very faint on a single picture. You would have to expose for a very long time to get 100% of the emissions. Even then, you won't get Hubble-style results!
Now, if you feel like you are being swindled by the digital camera industry, you're probably right. However you are only part of a small fraction of the market who is astrophotographer that need more band response to show beautiful nebulae. In other words, it hasn't been profitable for any big company to offer out-of-the-box digital cameras without IR-cutting filter. Yet, at least... We might see the emergence of a new market in the near future as amateur astrophotography is skyrocketing. Until then you will have to have an astro-modification done to your camera! To astro-modify (it should enter the dictionary) your camera simply means to remove the native IR-cutting filter from your sensor to take advantage of the whole spectrum of the visible light, taking-in the red emissions as well. From this point on, you have several options.
-Leave the sensor the way it is. Your camera is now called full-spectrum modified and can also pick up IR's and some UV's. Now it is cool if you want to see the world in Infra-Red and create artistic compositions (google IR photography). However your sensor has now less thickness, implying a change in focal point and focus (which is corrected by a simple piece of glass added as replacement).
-Replace the IR-cutting filter by a specialized filter that blocks IR from 700nm but still lets a lot of emission under 700nm (see on the graph above). Your camera is now called astro-modified and can pick up the 10% of visible light that were missing in your previous astrophotos. The advantage of the new filter is that it just replaces the old one, meaning that you won't have any change in the focal point (if the filter is of the same thickness as the previous one of course!).
WHERE TO ASTRO-MODIFY YOUR CAMERA?
There are plenty of specialists and firms that offer an astro-modification at various prices. Count between $200 and $500 to get yours fixed. You can also do it yourself if you know what you are doing. There are some videos and guides out there to show you the step-by-step procedure. However I would not recommend doing so, because removing sensor seals also means annulling the warrantee on your camera, plus the hassle and risk of losing teeny tiny screws (or putting them back in the wrong order), or getting grain/dust onto the sensor, which would forever ruin your photos. If you do not possess the necessary professional gear to perform a modification, don't go down that road!
Links to guides and videos:
Links to sellers:
-http://www.baader-planetarium.com/en/filters/dslr-astro-conversion.html (For modification within the EU, in Germany)
-http://www.spencerscamera.com/store/store_sub.cfm?Category_ID=1 (US, NASA)
Google for more!
ADVANTAGES AND DRAWBACKS...
Yes, all things have an upside or a downside! By astro-modifying your camera, you will still be able to take day-time photographs, but expect a shift in the white balance (even at night!). All colors are shifted to the red and your pictures will look pink, like on the RAW image below, taken straight out of my Baader modified Canon 6D. This is no biggie though, as it is easily corrected by a add-on lens filter, or in post-processing. So technically you can still use your camera for everyday purpose photography, you will just see your life in pink! One drawback that you might also encounter, as I did, is a nasty flare in the middle of your picture if you are shooting with your LCD screen on (not using the view finder mode) with DSLRs. That is not a problem for day photography, as most photographers prefer (as you should probably too...) using the view finder, but I prefer using the LCD mode to focus at night. As the mirror is stowed in an upright position in LCD mode, it somehow reflects the light entering from the view finder onto the back of the sensor, which produces and annoying flare. I am not sure if it was specific to my modification or camera (Canon EOS 6D), but I simply need to switch back to view finder mode to take my pictures at night.
On the other hand, the advantages are worth the money spent! Your astrophotos will reveal the true hidden beauty of the night sky. You will now be able to see deep-sky objects that were too faint before, especially those with emitting radiations H-alpha. My biggest surprise was the California nebula (NGC 1499), Barnard's loop and Orion nebula region (Sh2-264), Rosette and Cone nebula region, the Cygnus region and Cederblad 214... And this is just the beginning, as I only shot the winter milky way! See the difference on two panoramas of the Orion region I took this winter, one without and one with astro-modification (both are a stacked-picture pano to enhance contrast)