Astrophotography with a DSLR Tom Nicolaides Carriere, MS

1. Astrophotography with a DSLRTom Nicolaides Carriere, MS

2. Astrophotography with a DSLRTom Nicolaides Carriere, MS List of acronyms and obscure terms DSLR: Digital Single Lens Reflex CCD: Charge Coupled Device T adapter: A coupling ring that allows standard accessories (such as nosepieces, field flatteners and coma correctors) to be attached to a DSLR camera RA: Right Ascension Dec: Declination Light Frame: A single image of some object Dark Frame: A single image of dark (with the scope cover on), used to compensate for noise and Amp Glow Flat Frame: A single image of an evenly illuminated field, used to compensate for an unevenly illuminated light frame Amp Glow: The appearance of a glow in or along one side of any frame caused by the heating effects of the sensor�s amplifier

3. Astrophotography with a DSLRTom Nicolaides Carriere, MS DSLR vs CCD camera The DSLR can be used for other things besides Astronomy In general a DSLR has a much larger imaging area than a dedicated CCD A DSLR costs a LOT less DSLR has much higher noise than a cooled CCD camera DSLR has more limited color range than a CCD camera (in general), and less dynamic range (14 bit for the typical DSLR and 16 bit for a CCD camera) What�s needed for DSLR Astrophotography? A telescope, of course � to start, keep the FL relatively short � say 400 to 1000mm � The Orion ED80 is one of the most popular. Meade�s Schmidt Newtonians are popular A good mount � LXD75, Vixen GP class at a minimum. The Losmandy G11 seems to be one of the main workhorses of astrophotography. The Orion Atlas is coming on strong. Focusing aid DSLRFocus Stiletto �Through the viewfinder� Not recommended Hartman Mask Methods to control the shutter Timed Remote DSLRFocus DSLRShutter A manual release and stopwatch

4. Astrophotography with a DSLRTom Nicolaides Carriere, MS What else is needed? Software for processing � At least one of the following, with many considering Photoshop an essential addition. ImagesPlus IRIS (free) PixInsight (free) MaximDL Photoshop Eventually you will want to guide. This will take a 2nd camera � a webcam, DSI, Guiding software such as PHD. Reason? Even the best mounts can�t stay on target much more than 2 or 3 minutes. However, excellent photos can be taken unguided if you keep the exposures short (less than 60s) and take care to get a good polar alignment Now, you don�t REALLY need a computer and separate imager to guide. You can do it manually with a guidescope and reticule eyepiece. Place a guidestar in the crosshairs and make small adjustments to RA and Dec to keep it centered.

5. Astrophotography with a DSLRTom Nicolaides Carriere, MS So how do you do it? Mounting the camera to the focuser is accomplished using a T adapter and nosepiece (usually 2 inches) Try focusing through the viewfinder on a distant object during daylight. This will get you in the right ballpark Now it�s nighttime and time to focus for real. If an aid such as the Stiletto is used, the method is fairly foolproof. Attach the Stiletto to the camera adapter (The stiletto is made for specific cameras). Point to a bright star. Adjust your focuser until the diffraction lines disappear. Lock down your focuser. Remove the Stiletto. Re-mount your camera. You�re done. If you use something like DSLRFocus, use it to take a sample image. Select a star. Adjust focus until DSLRFocus tells you it�s right. This takes some back and forth between the computer and focuser. It�s taken me as long as 15 or 20 minutes to get it right in this way. One can also achieve focus using a Hartman mask. This is done by making a front cover to the telescope with 2 or more holes in it. Point the scope at a bright star and adjust focus until the star images converge. Time to start acquiring images

6. Astrophotography with a DSLRTom Nicolaides Carriere, MS Acquiring images (sub-frames, light frames, darks, flats) Always set your camera to RAW mode. This prevents the camera from messing with your picture � no stretching, etc. Try to get at least 30 light frames regardless of your exposure time. This will make processing and noise reduction easier. And in general you�ll get a better final product Acquire at least 5 dark frames at the same setting as your light frame. The dark frame will help in subtracting out camera noise from your light frames. Don�t forget to put your scope cover on or it won�t be dark! Acquire several flat frames. This is a photo of an evenly illuminated, featureless object. It is used to correct for an unevenly illuminated field of view. Virtually all scopes/camera combinations have vignetting. A flat frame will correct for this and other things like dust motes in your optical path. A flat may be taken at daytime by pointing the scope to an area of blue sky A flat may be taken at night by covering the scope front with a white T shirt and illuminating it with a flashlight. Some take a dark frame to apply to their flat. This would be taken at the same ISO and shutter speed. I generally don�t do this as a flat exposure is usually so short that noise isn�t a problem. You now have your data set. Time for processing!

7. Astrophotography with a DSLRTom Nicolaides Carriere, MS Here�s a typical single light frame, unstretched. Nothing spectacular.

8. Astrophotography with a DSLRTom Nicolaides Carriere, MS You�ll need software to convert your RAW files into something your processing software can work with. I use ImagesPlus for this and most other processing things. There are many others, some of which are free � most notable are IRIS, PixInsight, DeepSky Stacker and Gimp. Here are the processing steps I go through: I convert the entire data set (lights, darks and flats) into lossless, compressed FITS format. I make a master dark by averaging and combining my dark frames I make a master flat by averaging, combining and de-saturating the color Next step is calibration of the light frames. This is where the master dark and master flat are applied. With ImagesPlus, one tells the software the name of the master dark and flat. It then applies the masters to each light frame and makes a calibrated set of light frames. Next is alignment. Select the same star in each calibrated light frame. Tell your software to align. It makes a new set of calibrated, aligned light frames Next is combining. There are several methods for combining frames � Simple average, sigma-clipped average, addition and others. The method used depends often on the quality of your subframes At this point you�ll have a partially complete photo. It won�t look like much. Some additional things need be done.

9. Astrophotography with a DSLRTom Nicolaides Carriere, MS After your have your combined image, you�ll need to do some things to it that your camera in RAW mode doesn�t do. Using ImagesPlus, I apply �Digital Development.� This feature examines the levels of the photo and adjusts them such that intensity range spans the range of the photograph. The left is the combined image (sigma clipped average) of IC443 (43 subframes, 240s each) the right is after Digital Development.

10. Astrophotography with a DSLRTom Nicolaides Carriere, MS After this I go to Photoshop. I adjust levels again and use Curves to expand the photo. Sometimes I use an Unsharp Mask to bring out details. Here�s the final result of the supernova remnant IC443

11. Astrophotography with a DSLRTom Nicolaides Carriere, MS Where to start I suggest selecting a fairly large, bright object, such as M42 or M8. Other good first attempts are open clusters such as M35, 36, 37 and 38 Use a relatively short exposures � 30 to 60 seconds. Experiment with speed (ISO setting), but ISO800 should get good initial results Try to get between 30 and 60 light frames Make sure to take a set of darks and flats Process as described here and don�t be afraid to experiment!

12. Astrophotography with a DSLRTom Nicolaides Carriere, MS Other considerations The standard Canon DSLRs, and the Nikons too, do not have much sensitivity to the Hydrogen Alpha spectral signature (deep red). However, this is not a limitation of the sensor, but an artifact created by the introduction of an aggressive IR filter. It is possible to modify a DSLR to take out and/or replace this filter with one more friendly to the light of emission nebulae. There are companies or people who will do this for you, most notably Hutech. My new camera is a Canon 350D (the Digital Rebel XT) modified by Hutech. To see the difference, look at the two following photos.

13. Astrophotography with a DSLRTom Nicolaides Carriere, MS

14. Astrophotography with a DSLRTom Nicolaides Carriere, MS What else can be done? Here�s an image of M1, the crab nebula taken by Mike Broussard of Louisiana and the same image of M1 taken by Hubble.

15. Astrophotography with a DSLRTom Nicolaides Carriere, MS Additional Resources The Cloudy Nights DSLR Forum http://www.cloudynights.com/ubbthreads/postlist.php/Cat/0/Board/DSLR My own humble web site http://www.first-light.org The Astromart forums http://www.astromart.com Hutech http://sciencecenter.net/hutech/index.htm Mike Unsold�s ImagesPlus http://www.mlunsold.com/ DSLRFocus http://www.dslrfocus.com/ Hap Griffin�s cables and connectors http://www.hapg.org/astrocables.htm Shoestring Astronomy http://www.store.shoestringastronomy.com/ A Guide to Astrophotography with DSLR Cameras http://www.astropix.com/GADC/HELP.HTM