Digital camera, CCD, or Film?

Introduction:   Which medium is "best"....digital camera, CCD, or film?  Actually, there are seasoned astrophotographers who still debate this point.  In truth, each medium has its strengths and weaknesses, and the "best" should be defined as the one that gives you the most pleasure out of this great hobby.  It's also true that these are not mutually exclusive methods, so it's possible for an experienced astrophotographer to use film for some targets, and CCD for others.  Since I've taken astrophotographs using each medium, I thought that it would be helpful for me to share a few thoughts about this issue.  This is not meant to be a comprehensive discussion of the digital versus film debate, but it's a personal viewpoint that will hopefully be helpful to those who need some guidance.  The following comments do not cover the use of webcams, which are great for planetary/lunar work and are constantly being perfected for use in deep sky astrophotography.

Everything is digital:  This may seem obvious to some, but it's worth stating that all roads lead to an analog-to-digital conversion at some point along the path to a great astrophotograph.  Whether this occurs in the conversion of an analog to digital unit (ADU) in a CMOS or CCD chip, or occurs during the scanning of a slide/print by a typical desktop scanner (which is CCD-based), the ultimate goal is to manipulate digital data in an imaging processing program like Photoshop.  So even film can be considered digital, except that the original analog data is captured by a relatively large silver halide grain on a film emulsion, as opposed to a more sensitive, smaller pixel on a CCD chip.  This simple fact limits the amount of light and resolution achievable by film, when compared to CMOS or CCD.  Although film is capable of capturing faint objects, the price to be paid is the requirement for long individual exposures, which demands great attention to precise polar alignment and autoguiding.  Also, because you do not obtain instant feedback with film (compared to digital or CCD), you must very sure that your object is well-framed and in good focus.  Otherwise an entire night of astrophotography could be ruined.....

So why not just go with a consumer digital camera or an astronomical CCD camera?:  Many reasons.  Film astrophotography is a very cost effective and satisfying way to take simple astrophotographs, using a camera on a piggyback mount (on top of a polar aligned scope, for instance).  With the use of a relatively wide angle lens (28-50mm), exposures in the range of 5-15 minutes each can result in very pleasing photos of constellations and the Milky Way, and they are more forgiving of slight inaccuracies in  polar alignment and guiding.  For those who aren't sure that they want to invest a great deal of money and time in astrophotography, but would like to dabble for a while, this is great way to start.  Unfortunately, as of 4/04 there aren't good choices for color negative (print) films that capture the faint reds of Ha emission, but slide films like Kodak E200 are still great for this purpose.  There is no doubt that for those who wish to develop the skills necessary for performing film-based, long exposure astrophotography, the rewards can be great....although so can the frustration.  Because of the long exposures required, there is simply more that can go wrong with film-based work.  Michael Convington's book "Astrophotography for the Amateur," and Jerry Lodriguss' book "Photoshop for Astrophotographers," provide lots of useful information.

How to choose between a consumer digital camera and an astronomical CCD camera:  If you've decided to take the digital plunge, then either a consumer digital camera or astronomical CCD camera is reasonable.  The choice depends upon your expectations of the hobby.  Either of these choices has greater sensitivity (and resolution) compared to film, meaning that it's possible to limit your subexposure durations to 5 minutes or so (with subsequent stacking of multiple subexposures to achieve a final exposure of long duration). This translates into somewhat less stringent requirements for autoguiding and polar alignment compared to long exposure film-based work.  If you want to obtain very pleasing, one-shot color images with a "film-like" field of view, then go with a consumer digital camera like the Canon 10D or 300D (see below for comparison).  This approach will cost you less than half of what would be required for a good quality astronomical CCD camera, and you can use the digital camera for daytime shots as well.  Software is now available for image processing of digital camera astrophotos (like ImagesPlus), and there are internet groups like the Yahoo digital_astro group that provide useful advice.  However, keep in mind that the sensitivity of CMOS-based consumer digital cameras is generally not as good as CCD technology, with Ha sensitivity being especially compromised in the 10D and 300D.   Also, background noise will be higher in consumer digital cameras, which are typically non-cooled, compared to cooled astronomical CCD cameras.  Even though the noise characteristics of the non-cooled 10D or 300D digital cameras are quite acceptable, especially during the wintertime in New England, noise will increase in warmer climates and will limit the exposure duration, ultimately limiting sensitivity for dimmer targets.  Still, it's possible to take very pleasing astrophotographs of brighter targets during the summertime with the 10D or 300D, as long as you keep these restrictions in mind.  If, on the other hand, you want high Ha sensitivity and high resolution images that are not limited by noise, and if you don't mind a more limited field of view (CCD chips are generally smaller than the current CMOS chips in digital cameras), an astronomical CCD camera would be the way to go.  I will not review the many CCD choices here, but would recommend Ron Wodaski's book "New CCD Astronomy" for additional information.   I currently own an SXV-H9 CCD camera by Starlight X-press and have been very impressed with its sensitivity, anti-blooming feature, and low noise characteristics.

Canon 10D or Canon 300D?:  The Canon 10D or 300D are the most popular options for digital camera astrophotography as of 4/04, because of their low noise characteristics and proven track record.  However, the digital camera field is moving at a fast pace, so other contenders like the Nikon D70 could be available soon.  Since CMOS-based consumer digital cameras currently use an IR cut filter to achieve proper color balance for daytime photography, I would anticipate that they will all suffer from poor Ha sensitivity, regardless of brand (unless this filter is removed, which voids the warranty and risks damaging the camera).  Regarding the choice between the 10D and 300D, here are my thoughts.  I own a 10D and love it.  I like the feel of the 10D- it has a more durable exterior (I like to take it on rugged hiking trips), and it feels more balanced when a large lens is attached.  I also like several of the bells and whistles, including the ability to use flash compensation for indoor shots.  Nonetheless, the 300D uses essentially the same CMOS chip and has similar low noise characteristics compared with the 10D, and it costs hundreds of dollars less.   I have now seen several astrophotographs taken by both cameras and am convinced that technically there is no difference, when operator skill is taken into account.  Keep in mind that the optional Canon TC-80N3 remote controller needs to be adapted to the 300D (no modification is necessary if the TC-80N3 is used with the 10D), although this is quite easy to do and is outlined on Mike Unsold's Yahoo ImagesPlus site.  The 300D does not have mirror lock-up, although this does not appear to compromise the effectiveness of the camera for deep sky astrophotography.  However, the lack of mirror lock-up might be a consideration for solar or lunar astrophotography, in view of the faster shutter speeds involved, especially if your mount is not rock-solid (but I have seen several very nice lunar shots taken with the 300D!).  Mirror lock-up would obviously come in handy for daylight, high magnification photography using a macro lens.  Finally, Hutech is selling a modified 300D in which the IR cut filter has been removed, meaning that it has the potential to be more sensitive in the Ha (red) portion of the spectrum.  I do not have personal experience with the Hutech-modified 300D camera and cannot comment on its astrophotography or daytime performance.  Bottom line:  If you want a digital camera for both astrophotography and casual daytime use, and if you are prepared to modify the TC-80N3 remote, get the 300D.  But if you're a certifiable camera nut, if you like to take your camera mountain climbing, if you want the mirror lock up feature for macro work, and if you're really into "serious" daytime photography, it may be easier for you to justify the cost of the 10D.

With so many great options to choose from,
there's no better time to get involved in astrophotography.   Good luck!  


All Images Copyright Steve Cannistra

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