DSLR Cameras for Astrophotography

Be sure to check out dpreview.com, robgalbraith.com, or imaging-resource.com. All have excellent reports (though tested for daytime shooting) on all these cameras, and much more.
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DSLR Choices (as of November 2009)

Here are our choices for recommended DSLR cameras, updating advice in Chapter 13.

A year after we wrapped up the Third Edition of The Backyard Astronomer’s Guide, the DSLR market has changed, with the main trends being higher pixel density and the addition of HD movie recording. The cameras we recommend in the book still represent good choices and may be still available from some suppliers. But both Canon and Nikon, the two industry leaders, have advanced the state of the art by degrees, by upping the megapixel count while controlling noise. NOTE: All the cameras suggested here sport “live focus,” (aka Live View) a feature absolutely essential for astrophotography. Don’t buy a camera without it! So here’s a rundown on our currently recommended models.

Recommended — The Canon EOS 50D
Canon announced the 50D in August 2008, just a year after it introduced the 40D, the model we suggest in our book as the best choice for an astrophoto camera. The 50D is our new “best choice,” but with provisos.

The 50D offers 15 megapixels on an APS-sized chip (22.3 x 14.9 mm), the same size chip as its predecessor 40D (with 10 megapixels) and older 30D/20D models (8 megapixels). That’s a whopping 4752 x 3168 pixels, for about $1300.

As we explain in Chapter 13, cramming more pixels onto a chip means making those pixels smaller. Smaller pixels means less light gets collected, which means less signal gets generated — ergo, a worse signal-to-noise ratio. Images look noisy. That’s what kills pocket point-and-shoot cameras, despite their 8- to 12-megapixel chips.

The pixels of the 50D are just 4.7 microns (μm) across, compared to 5.7 μm in the 40D and 6.4 μm in the trend-setting 20D. While smaller pixels yield images capable of resolving finer detail, they can also introduce more noise in long exposures.

Several clever innovations in the 50D allowed Canon USA to suggest it would offer a 1- to 1.5-stop improvement in noise over earlier models, despite the smaller pixels. Now that one of us (TD) has used a Hutech-modified 50D for some months, we can say that noise in the 50D is not lower than in previous models. If anything, in RAW images at least, the 50D exhibits slightly more noise than the 40D, conversant with its smaller pixels. Improved internal noise reduction in the 50D does mean that its JPGs look a little smoother than the 40D’s. Even so, noise in RAW files is well controlled and we’ve been very pleased with the images taken with it to date. The Canon 50D is certainly our current top choice for anyone considering a DSLR. To save some money, the older Canon 40D may still be available from some suppliers. New or used, it still represents an excellent buy.

Even More Megapixels — The Canon EOS 7D

In August 2009 Canon announced a new “prosumer” camera, the EOS 7D. Staying with the same size sensor as the 50D, the 7D packs even more pixels onto the chip, for 18 megapixel images. The individual photosites are 4.3 μm across, the smallest yet for a DSLR. HD Movie mode is standard (every new DSLR has it). Price is about $1,700 US for a stock camera, placing it above the 50D in the price ladder (a movie-capable 60D can’t be far away).

For the 7D, Canon promises low noise levels, stating in its press release: DIGIC 4 removes the highly noticeable colour noise as well as reducing luminance noise without loss in detail, allowing for very clean high ISO images. Even at ISO 6400 noise levels are similar to those of ISO 1600 from DIGIC III.

However, one of us (AD) has tested a 7D and found that in long exposures, unprocessed RAW images from the 7D showed fine-grained noise that was about two stops higher than those taken at the same time with the standard-setting Canon 20Da (with its 6.4-micron pixels). In other words, RAW images taken with the 7D at ISO 400 looked similar, in terms of background noise, to images taken with the 20Da at ISO 1600. Again, these are in RAW images to show what really comes from the sensor.

With JPGs, where Canon applies internal noise reduction through its DIGIC IV processor, the difference isn’t quite so severe. But 7D test images still looked noisier by at least one stop than images taken with the bigger pixel 20Da and 5DMkII cameras.

That all sounds worse than it is. For one, the 7D shows no artifacts such as amplifier glow or uneven banding. The background is very smooth and uniform. And ... even basic noise reduction will remove most of the coloured chrominance noise component, leaving a very fine-grained luminance noise that can also be reduced, though not eliminated, without sacrificing detail. As the review of the 7D at dpreview.com shows, Canon has managed to make 7D less noisy than the 50D, even in RAW images. This tell us that if the 50D works fine in practice (as we’ve proven to ourselves) the 7D should be even better.

The upside is that with its small pixels the Canon 7D is very sharp, and clearly resolves (in lunar close-ups for example) more detail than do the bigger-pixel cameras. The 7D is a great landscape/nightscape camera, superb for lunar and solar imaging, and good for piggyback shooting. Its advantage for deep-sky shooting is that it can extract excellent resolution from shorter focal length optics, if those optics are sharp. But, as with the Canon 50D, images from the 7D will require careful processing to smooth out noise without blurring detail. Scroll down for test images taken with the classic 20Da, and the current 5DMkII and 7D.

Bargain Megapixels — The Canon Rebel T1i/500D

Released in May 2009 the new 500D, or T1i, is the latest camera in Canon’s entry-level “Rebel” series (as it is called in North America), with 15 megapixels, just like the 50D. With the same DIGIC IV processor we might expect similar noise performance as the 50D, but for much lower cost ($800 for a stock camera body, $1200 for a filtered-modified T1i/500D from Hutech).

However, we have yet to test a Rebel T1i/500D to see if it does perform as well as the 50D for long exposures. But it does have one feature that might prove enticing — the ability to record 720p and 1080p HD movies with audio (mono sound only). This can be handy for some astrophotography, and attractive for anyone buying a DSLR for vacations and family albums.

Should I Buy a 50D or a Rebel/T1i?

The Rebel series cameras (the new 500D and earlier 450D and 1000D models) have several characteristics worth noting:

They do not have a top-mounted screen for readout of cameras settings, unlike the 50D/40D models. All settings are made by looking at the rear LCD screen (above), awkward to see when mounted on many telescopes. And it can be blinding at night.

They do not accept the wonderful Canon accessory, the TC-80N3 interval timer, at least not without modifying the timer so it can plug into the little mini-phono-style jack the Rebels use for their remote release accessory. (Hutech sells a plug-modified TC-80N3 or a third-party interval timer for Rebels is available from Phottix). This accessory is essential for deep-sky shooting, negating the need for a computer just to control exposure sequences. We don’t know how many times people have asked us about the TC-80N3 — get it! It makes time lapse shooting possible. But to use one on a Rebel you have to snip off the connector and wire on a new plug to fit the Rebels.

The Rebels use SD cards and a unique battery — perhaps important if you have an older 20D/30D model and want to keep using the same style of battery and charger you already own, and wish to stay with CF cards. (The 40D and 50D are both compatible with older 20D and 30D for style of battery and memory cards, as well as in the style of remote release connector, the “N3” jack used by the TC-80N3).

For these reasons alone, we usually recommend people to the 40D/50D series. Plus, past Rebels have usually had slightly worse noise than similar xxD-series Canons. But for someone buying their first DSLR, a camera in the Canon Rebel series is a great buy. But upgrade later from a Rebel and you’ll need to buy new remotes, batteries, chargers and memory cards.

The Best Astrophoto DSLR? — The Full-Frame Canon EOS 5D Mark II

For a couple of years both of us used a Canon 5D and loved it. But we eagerly awaited its replacement, with more pixels and live focus. In September 2008, it was announced — the 5D MkII, offering 21 megapixels vs. 13 of the old 5D, in a full-frame chip as large as a 35mm film frame. That translates into 5616 x 3744 pixels, each 6.4 μm across, the same size pixels as in the original Canon 20D and 30D cameras. The pixels are larger than in the 50D which, in theory, should yield lower noise, on par with or better than earlier cameras with similar sized pixels. Tests by websites such as dpreview.com seemed to show better noise reduction than the original Canon 5D, which was pretty low. So the 5D MkII promised to be a fabulous astrocamera — and now we can say without question that it is!

One of us (AD) has used a Hutech filter-modified 5D MkII since July 2009 and can now proclaim that this may be the best DSLR on the market for shooting the sky. Noise is very low even at high ISO speeds on warm nights, comparable to other 6.4-μm pixel cameras, which are becoming scarce as companies cram more pixels onto chips. There are no artifacts from amplifier glows, the background is smooth and uniform, and the red sensitivity of the filter-modified model is outstanding.

Price is about $2,700 US ($3,000 for a modified camera), clearly making this a camera for the serious shooter of the sky, or any subject matter.

The 5D MkII also offers HD movie recording capability, with true 1080p (1920x1080 pixels at full 30 fps video frame rate and stereo sound). Dyer used a 5D MkII to shoot the July 2009 total solar eclipse in HD. It worked great! Compared to conventional HD movie cameras, the 5D MkII allows use of all lenses from 8mm fish-eye to telescopes and, as cinematographers have delighted in, offers much lower noise than normal movie cameras for low-light video shooting. That opens up some interesting astrophoto opportunities.

However ... what we say in our book about any full frame DSLR will be even more true of the 21 megapixel 5D MkII — it will tax the optical quality of any optics attached to it, ruthlessly revealing off-axis aberrations. For deep-sky shooting through a telescope, you’ll need optics with field flatteners designed to fill large chip cameras. The Takahashi FSQs, Tele Vue “is”, and Borg astrographs would be good examples in the refractor league. For piggyback shooting, you’ll need top-class glass — like the Canon L-series lenses. A full-frame DSLR is a serious commitment. For most users, the smaller-chip Canon 50D or 500D will be just fine, thank you.

What About Nikon?

Like Canon, Nikon has been busy introducing new models. In the last year Nikon has made great inroads at producing cameras with low-noise for use in low-light situations where high ISO speeds are required. Tests published on the web and done under normal daytime conditions seem to show that new Nikon models perform as well as, if not better than, competitive Canon DSLRs for low-noise performance, at least for short exposures.

That said, however, we have not tested any of the models listed below, so we cannot vouch for how well they work during the long (> 5 minute) exposures required for deep-sky imaging. In 2007 we tested a then-current Nikon, the D80, against a competitive Canon, the Rebel XTi/400D, and the Canon won. Download a copy of the SkyNews magazine review here: SLRcameras.pdf While the older Nikon D80 (the D90 now replaces it) had low noise, image quality fell apart in long exposures:
images turned green after 5 minutes of exposure
amplifier glow added hot spots at the edges of the frame, even after subtracting an internal dark frame
stars did not de-Bayer well, leading to multi-colored specks instead of white stars.
Based on that experience, and the fact we have seen few published long-exposure (> 5 minute) images, or tests of Nikons from other astrophotographers, we are reluctant to recommend Nikon DSLRs.

• If you’d like a second opinion, check Jerry Lodriguss’ comments at his excellent website, Catching the Light. Jerry also offers a detailed camera comparison chart well worth inspecting.
• Or check Christian Buil’s meticulous measurements of DLSR performance at his website, Spectroscopy, CCD & Astronomy.

Nevertheless, here are the main models Nikon offers as of September 2009 (all have Live View or Live Focus):