How To Hook A Camera Up To A Telescope
The principle of taking photographs through your telescope with your DSLR is quite simple: just use the telescope in place of the camera lens, and snap away. Simple! Just as presently every bit you try it, you lot will first to notice the problems.
Attaching the photographic camera
The simplest manner is to utilize a T-adapter. Many modern telescopes have an eyepiece holder with an external thread which is the same as that adopted by Tamron many years ago when designing lenses to fit a wide variety of cameras. It is 42 mm in bore merely has a different thread from the former Pentax 42 mm lens fitting. You can get T-adapters for nigh DSLRs to fit this thread.
If your telescope doesn't take this thread, yous tin can get a 1¼-inch adapter with the thread.
You will need to rebalance the telescope once yous have attached the camera. Meade ETX telescopes in particular cannot be balanced, the simply alternative being to tighten upward the declination clamp rather more than is wise. You can buy additional weights to fix to the ends of Schmidt-Cassegrains to assist balance them. Don't look an axis clamp to exist able to cope with the actress weight of your camera – information technology may work to start with, only yous'll cause boosted wear on both the clamp and, more importantly, the motors, which volition always be straining to move more than weight than they were designed for.
Focusing
This is not as straightforward equally you might wish. DLSRs invariably employ autofocus, and lack the focusing aids of film SLR cameras. Merely your telescope has to be focused manually and judging when a star is in perfect focus tin be catchy. You might fifty-fifty discover that you can't bring a star to focus at all, particularly with the cheaper Newtonians. The popular basic SkyWatcher 130, for example, doesn't focus shut enough to the mirror to reach focus with a photographic camera attached, though there is a version that does have the focusing range for photography.
If yous can't adjust the focus far enough out, you could add together a short extension tube or a star diagonal, or if yous are using a ane¼-inch adapter just don't push button the adapter right in just tighten up the thumbscrew to hold it in place. But if y'all tin't focus far plenty in, all yous can try is to use a Barlow lens in the system equally well. This increases the effective focal length of the system, giving more magnified images, simply information technology oftentimes allows y'all to focus.
If your photographic camera has Live View (which shows the actual paradigm seen through the system), use information technology to help you to focus. On many cameras, such every bit the Canon 40D, the maximum zoom of Live View has some interpolation and never appears every bit abrupt as the final image then y'all nonetheless have to judge the verbal focus point, simply it is more precise than using the basic optical viewfinder.
Credit Robin Scagell/Milky way
All the same, the best solution, if your photographic camera manufacturer provides the software, is to shoot 'tethered' to a estimator. This allows you lot to see the Live View prototype on the computer screen, but without whatsoever interpolation, so you tin can focus critically, but even if you don't have Live View you tin can still take a shot and check the focus. Shooting tethered has other advantages: you fire the photographic camera from the computer, then you won't jog information technology, you may be able to operate the camera from indoors, and you accept the whole storage capacity of the computer rather than just your memory menu. The drawback is that it means nevertheless some other black wire to trip over in the nighttime, and of course you need the figurer near the camera, which more often than not means using a laptop.
Otherwise, utilise a cablevision release to trigger your shots and so every bit not to jog the camera when shooting. Some cameras use a conventional mechanical cablevision release, which is comparatively inexpensive, while others opt for their own electric releases, which cost more than. Alternatively, set the camera's timer then that the shutter goes off either two or ten seconds after you press the shutter release, giving vibrations a take a chance to settle down.
Shooting
Now you are ready to start taking photos. But as yous know, objects move through the field of view quickly unless your telescope is driven. In the case of non-driven telescopes, you volition exist restricted to the Moon and peradventure Jupiter and Venus, which are sufficiently brilliant that yous can give exposure times faster than about i/100 second. But for longer exposures, the telescope must be motor driven, ideally on an equatorial mount. If you accept an altazimuth, you'll notice that later a short fourth dimension stars at the border of the field of view volition start to trail around the heart of the field of view – called field rotation. In this example you may be restricted to exposure times of just a few seconds.
This photo of the Ring Nebula, M57, was taken through a telescope on an altazimuth mount with no periodic error correction. The star trails are zigzags, and the paradigm has rotated effectually the centre. It also shows vignetting – the cutoff of light at the edges of the frame by the camera adapter
Assuming that you accept a driven equatorial mount, you will soon discover its limitations. A drive that keeps Jupiter, say, in the field of view for many minutes at a time for visual observing does not need to be very accurate. Information technology will probably suffer from periodic error, which is a regular variation acquired by errors in the machining and alignment of the worm and wheel drive mechanism. Typically, you will encounter a periodic motion of a few arc seconds every eight minutes or so. The other error is the polar alignment of the equatorial mount. If this is not spot on, stars will trail even in the absenteeism of periodic error.
Periodic error correction (PEC) is provided by many mountings, only you need to follow a star for the duration of the periodic error, using an eyepiece with crosswires which itself is a considerable extra expense, correcting the error equally you go. You may demand to practise this every night yous observe, if the telescope is not left in situ during the day. Polar alignment is time-consuming and requires care, and is too lost unless yous proceed the mount in place. But you can get away without doing PEC every dark, and with but skillful-enough polar alignment, by using an autoguider. Merely using an autoguiding organization is a subject area in itself and will not be covered here.
Other issues
As well as autoguiding, you may now need to tackle the other major bug of astrophotography – getting rid of low-cal pollution on your images, and image processing to bring out the faint particular. These subjects will hopefully be the subject area of further assistance files, not yet written!
Robin Scagell
Source: https://www.popastro.com/main_spa1/imaging-with-a-dslr-through-the-telescope-2/
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