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 September 2010)

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

Despite our revision of the print version of The Backyard Astronomer’s Guide in early 2010, rapid changes in the DSLR market mean any print advice is soon out of date. The cameras we recommend in the book (the Canon 40D and 50D among them) still represent good choices for anyone looking for a camera on the used market. But both Canon and Nikon, the two industry leaders, continue to advance the state of the art. 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, as of September 2010.

Recommended — The Canon EOS 7D
Available since August 2009, the 7D is Canon’s “prosumer” camera. It uses an APS sensor (23 x 15mm) but packs more pixels onto the chip than earlier models, 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 $1,700 for a stock camera ($2,100 for a modified camera), placing it above the older 50D and new 60D in the price ladder.

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, in our tests we’ve 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 5D MkII cameras.

So why recommend it? 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, in processing with Adobe Camera Raw without sacrificing detail. As the review of the 7D at dpreview.com shows, Canon has managed to make 7D less noisy than the earlier 15 megapixel 50D, even in RAW images. We were always happy with 50D images; we are extremely pleased with the quality of images from the 7D. We both own one and use it a lot. And these days, unless one opts for the Canon 5D MkII, there is little option now but to go for cameras, at least in the Canon line, that use tiny noise-prone 4 to 5 micron pixels.

The upside is that with its small pixels the Canon 7D is very sharp, and clearly resolves more detail than do the bigger-pixel cameras. The 7D is a great landscape/nightscape camera, superb for lunar and solar imaging, and ideal for piggyback shooting. For deep-sky shooting through a telescope the 7D can extract excellent resolution from shorter focal length optics, if those optics are sharp. But images from the 7D will require careful processing to smooth out noise without blurring detail.

Added features of the 7D are its rugged all-metal construction and a large, very bright viewfinder (brighter than lower-cost models) that really aids in framing and focusing. We recommend the 7D as our top mid-priced choice. But it is $1,700.

Great Value — The Canon EOS 60D

If the price, size and weight of the 7D is a bit much, the new Canon 60D announced in August 2010 is probably the best alternative. We say “probably” because we have yet to try one. However, it promises performance the equal of the 7D for less cost (about $1,100 for the body).

The 60D offers 18 megapixels on an APS-sized chip (23 x 15mm) and Canon’s DIGIC IV processor, the same as with the 7D. But the 60D is much smaller and lighter. The reason is that it uses a plastic-on-metal body, rather than the more substantial all-metal and sealed body of the 7D and earlier 50D, 40D, etc. series. With the 60D, the xxD series that set the standard for so long for astrophotographers becomes a “super-Rebel” line for consumers, with the 7D now the base-model aimed at more serious photographers.

As with all cameras now, the 60D offers HD movie recording capability, in 1080 and 720 formats. This can be very useful for some astrophoto applications, let alone home and vacation shooting. It also has both HDMI and AV outputs for video/audio.

In addition to lightness and size, the new 60D offers one unique advantage for astrophotographers — the articulated LCD screen, a first for a Canon DSLR. A tilting screen will make it much easier to live focus and inspect images when the camera is on a telescope aimed up at the sky.

While the 60D doesn’t have the rapid-fire shooting power nor the 23-point auto-focus system of the 7D, those are hardly necessary for astro-imaging.

If you are upgrading from an earlier xxD series Canon, be aware that the 60D does not use Compact Flash cards that earlier xxD cameras used, but instead uses SD cards, like the lower-cost Rebel cameras. It also uses a different battery (and therefore charger) than earlier xxD cameras, but not the same battery as the Rebels use. It is the same battery as in the 7D and 5D MkII, a very good long-life battery. So consider all that if you are adding the 60D to an existing suite of Canon cameras and accessories. If it is your first DSLR, it’s a moot point.

However, the 60D has one glaring shortcoming for any purchaser. In keeping with its Rebel-like design it uses the Rebel’s mini-phone-style jack (the P3) for its remote control accessory. It does not accept the wonderful Canon accessory, the TC-80N3 interval timer, at least not without modifying the timer with a new plug. (Hutech sells a plug-modified TC-80N3 or a third-party interval timer for the 60D/Rebels is available from Phottix). This accessory is absolutely essential for deep-sky shooting, negating the need for a computer just to automate exposure sequences. We don’t know how many times people have asked us about the TC-80N3 — get it! It also makes time lapse shooting possible. But to use one on a 60D or Rebel you have to snip off the connector and wire on a new plug. Or buy a modified or third-party product.

Bargain Megapixels — The Canon Rebel T2i/550D

If your camera budget can’t swing the 60D, consider the Canon Rebel series. The latest model (they change yearly) was released in April 2010 as the 550D, or T2i “Rebel” (as it is called in North America). Amazingly, it offers the same 18 megapixels as the 7D and 60D and with the same DIGIC IV processor. We might expect similar noise performance as the 60D, but for even lower cost ($800 for a stock camera body, $1200 for a filtered-modified T2i/550D from Hutech). However, we have yet to test one to know what the performance is like compared to the more costly models. But the Rebels always represent a great deal.

They do have one annoying deficiency — they do not have a top-mounted screen for readout of cameras settings, unlike the 60D and all other Canon models. All settings are made by looking at the rear LCD screen (left), awkward to see when mounted on many telescopes. And it can be blinding at night. However, the colour can be changed.

Again, keep in mind accessories should you wish to upgrade. The Rebels use a different battery/charger than the 60D/7D line. But they do use SD cards like the 60D. They use the same remote connector as the 60D but different than on all other Canons.

What about older models? As of late 2010 the Canon 50D is still available but any DSLR without movie recording capability is destined to be dropped from the product line. The newer models, despite the increase in pixel count, do seem to have improved on noise, at least compared to the 50D. For this reason, aim for the 60D or Rebel T2i/550D as your best entry-level choice.

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

Having said all that, we have to say that if you really want the best in a DSLR, the Canon 5D MkII is it. Out since September 2008, the 5D MkII offers 21 megapixels vs. 13 of the original 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 all other current Canon DSLRs which, in theory, should yield lower noise, on par with or better than earlier top-performing cameras with similar sized pixels.

In this case theory has proved correct. 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. 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 $2,500 US ($2,900 for a modified camera), clearly making this a camera for the serious shooter of the sky, or any subject matter. However, it is not far off the price of many entry-level 6- or 8-megapixel CCD cameras, like the Kodak 8300-based models, but with a much larger sensor and 2 to 3 times the pixel count.

The 5D MkII pioneered the feature of 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.

The 5D MkII is also equipped with a special buffer memory that allows it to take up 5 long exposures, then internally apply a single dark frame taken at the end of the sequence to all 5 previous “light” frames. This means, for example, that five 8-minute exposures and a dark frame for those exposures takes just 6 x 8 = 48 minutes. With all other Canon cameras, having the camera take and subtract a dark frame internally means taking one for every light frame. A set of five 8-minute exposures with, say, the 7D would take 10 x 8 = 80 minutes to complete, vs 48 minutes for the 5D MkII. This is a superb and seldom noticed feature of only the 5D MkII.

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 60D or 550D will be just fine, thank you.

What About Nikon?

Like Canon, Nikon has been busy introducing new models. In the last two years 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 2010 (all have Live View or Live Focus):