Alive View Focusing

Live View is a video epitome that is output from the sensor to the LCD display on the back of the camera in existent time. Alive View can be a tremendous help in focusing an astrophoto if it is used correctly.

Information technology is very hard to precisely focus a star field through a DSLR viewfinder by eye alone. To cut costs, most manufacturers skimp on the viewfinder, knowing that almost all photographers are going to be using autofocus. But autofocus won't work nearly of the fourth dimension for astrophotos. You will usually have to manually focus your camera lens or telescope on a star.

Live View can make the difference between images that are nigh in focus and ones that are abrupt. When you become closer to focus, information technology is harder to tell if the image is exactly focused. If focus is a little scrap off, information technology can atomic number 82 to blurriness and larger star sizes, and loss of fainter stars. Live View'south power to magnify the image to 10x makes information technology like shooting fish in a barrel to tell when you have accomplished right focus.

Click your mouse cursor in the image to see a comparison between an image that is correctly focused and one that is about focused. Click again to become back to the previous paradigm. This is open cluster M11, the Wild Duck Cluster. It was shot with a Catechism EOS 1000D (Digital Rebel XS) DSLR camera and a Stellarvue SV70ED doublet refractor. It was focused with Alive View.

In my opinion, Live View is the best and easiest way to focus for astrophotography, and believe me, I accept tried all of the other methods of focusing.


Nuts of Live View Focusing

  • Use transmission exposure and manual focus.
  • Use ISO 1600, bulb shutter-speed, and a wide aperture.
  • Employ a brilliant star or planet to focus on.
  • Get shut to focus before you use Live View!
  • Zoom in to 10x to focus.

In that location are a several of import things yous need to know to employ Live View for focusing.

First of all, realize that Alive View is non that sensitive. It's really made for bright scenes encountered in normal daytime photography. You're not going to exist able to see a nebula or galaxy on Alive view, just it definitely can be used for astrophotography past focusing on stars. How faint of a star that you volition be able to focus on will depend on the aperture and focal ratio of the lens, and the photographic camera settings.

Second, note that most mod lenses focus past infinity. You can not simply rack them all the manner to the infinity mark and expect critical focus. Some lenses done' accept any focus calibration on them at all.


Using Live View for Focusing

  1. Turn on Live View focusing. Turn on exposure simulation in Live View if your camera has this option. Read your manual to larn how to do this.
  2. Set the camera to Transmission exposure and the Bulb setting for long exposures. Employ ISO 1600. The brightness of the epitome for focusing is related to the camera settings. College ISOs and longer shutter speeds produce the brightest star images.
  3. Turn off autofocus on the lens. Set it to transmission focus. Y'all tin can endeavour to use autofocus with longer fast lenses, just I like the feedback on actually being able to see the star in focus in Live View. This is coming off the sensor itself, so this is what is going to be recorded in your image. It doesn't become any more accurate than that. So turn autofocus off on the lens and use Live View.
  4. Utilize a bright star. If at that place isn't a bright star in the field you want to shoot, first move the scope to a bright star, focus, and so move dorsum to your deep-sky object. If you have a refractor, or SCT or scope where the epitome comes out the tail finish, it helps to pick a bright star that is not too loftier upwards in the sky so y'all tin come across the Alive View on the LCD screen on the dorsum of the camera in a more convenient position than if information technology was overhead.
  5. Employ your fastest discontinuity if you are using an f/2.8 or slower camera lens. For example, with an 18mm to 55mm f/3.5 to f/v.6 zoom lens, set the lens to f/3.five for focusing if yous want to shoot at 18mm. If y'all desire to shoot at 55mm, gear up it to f/v.half dozen, the fastest aperture bachelor at that focal length.

    Note that most zoom lenses are not parfocal. That means when y'all zoom, you have to refocus. You tin can't focus at 55mm and zoom out to 18mm and shoot. The stars won't be in focus.

    If you are using a fast f/one.4 or f/1.8 lens, stop it down to f/2.8 for focusing to get rid of the worst optical aberrations. You may want to stop it down even more for your actual long-exposure astrophotos to clean upwardly most of the residuum of the aberrations. Merely focus at f/2.eight.

    If you lot are using a telescope, your focal ratio will be stock-still.

  6. YOU Accept TO BE CLOSE TO FOCUS TO Beginning WITH, OR Yous WON'T SEE Annihilation ON THE Live VIEW SCREEN. This is ane of most common mistakes in using live view. Set up the camera to manual focus and put the focus ring to the infinity mark. If you have a lens that doesn't have a focus scale, just eyeball it through the viewfinder and become as close to focus as you can.

    For the rough focusing past eyeball, don't forget to conform the diopter on the photographic camera offset. You do this in the daytime past taking the lens off the photographic camera and focusing the diopter on the little focus squares on the ground glass. This focus will exist different if you employ spectacles, and so if y'all focus the diopter in the daytime with your glasses on, be sure to go along them on at night when you try to focus the scope or camera lens.

  7. Put the star equally close to the center of the field as you can become it. This will assistance when you lot zoom in after to focus.
  8. Turn on Alive View. Read your camera transmission to discover out how. Play around with it in the daytime to familiarize yourself with how it works (you'll accept to utilise a short shutter speed in the daytime however).

    If you start out shut to focus, you lot should be able to see a bright star at 1x. Then zoom in to 10x to critically focus. If the star is non exactly in the middle of the field, you can move the zoom box around with the controls on the back of the camera to centre information technology. You can also move the box once you are zoomed in.

  9. Dial down the exposure - once you lot are close to focus, dial the exposure fashion down. This will allow you to improve meet the "seeing". The seeing volition crusade the star to wobble around and scintillate more when the star is a little scrap on each side of focus. Information technology will be sharpest when information technology is exactly at focus. Note that on nights of bad seeing you will still see some seeing effects even at the point of exact focus, simply it will be worse on either side of focus.
  10. Utilise a magnifier on top of the LCD screen - I have found that using fifty-fifty more magnification than 10x in Alive View helps me to focus better. Mayhap information technology is because I am old and my eyes are non that neat. You tin can find an Inexpensive 5x or 10x loupe that photographers used to use when they shot film and just concord information technology upward to the LCD on the back of the photographic camera. Personally, I employ a pair of high-ability reading glasses.
  11. Focus by going through the point of best focus and back once more several time and then that you know what the point of all-time focus looks like. There may exist some play or wobble in the lens. Get used to it.

    This is a video of the focusing procedure using Live View video way on a Canon 1000D (Digital Rebel XS) to focus on the bright star Vega. Because this video was shot with a 70mm aperture, and considering Vega is and so bright, it is easy to come across the star even when it is out of focus. With a wide-bending lens with a small true discontinuity, you have to be very close to focus to start with, even with a brilliant star, or you won't see annihilation.

  12. Lock the focus down without moving the focus. This is easier said than done! I use a slice of masking tape on the xviii-55mm. Merely you have to be extremely careful you don't move the focus. I scout the star on alive view as I press the record down to make certain it doesn't move.

    In the real earth, inexpensive lenses, especially like Catechism's 18-55mm f/three.v to f/5.6 zoom lens, and Canon's 50mm f/1.8 lens, have extremely sensitive focusing rings. Since these lenses are made out of plastic, they take some play in them too. They are very touchy. One time you lot take them focused you have to be incredibly careful non to motility them. any time you bear on the focus band, the focus has a take a chance to move. So if you tin't tape it down, don't affect it! Don't attempt to attach or remove any lens hoods, filters or anti-dewers in one case y'all have focused either.

  13. Once you have focused, it's a good idea to take a test exposure and examine the paradigm. Zoom in to 100 percent enlargement and check out the stars to make sure they are in focus and that you haven't accidentally moved the focus ring on the camera lens.

Aperture and Alive View

The faintness of a star that you will be able to see on Alive view is a role of the ISO setting, the shutter speed, the aperture and f/end.

You will exist able to focus on fainter stars with a larger discontinuity. But it is with broad-angle lenses where discontinuity really comes into play.

When you get downwardly into broad-angle lens' focal lengths, the truthful aperture gets tiny.

Even if an 18mm lens seems to accept a 2 or 3 inch hunk of glass in the front, that is not actually the size of the discontinuity. An 18mm lens' truthful aperture at f/iii.5 is just about 5mm. That is not very much. That size discontinuity is simply not going to collect a lot of light. The large lens on the forepart is to become y'all a broad angle of view, only it is non the true aperture of the lens like on a telescope.

Yous can easily calculate the true aperture past simply using the formula Aperture = Focal length / focal ratio. Then with our instance of a lens with 18mm of focal length and a focal ration of f/3.v, Discontinuity = 18mm / 3.five. Therefore the true discontinuity = five.1428mm.

The moral of this story is use the brightest object in the sky to focus wide-angle lenses with Live View.

Don't expect to be able to see about anything through the viewfinder visually with an 18mm lens. They are not easy to aim exactly, but y'all tin prefer a blood-red dot finder to the hot shoe and aim information technology at the center of the field you want to shot, and then have test shots to see if you are framed correctly.

If you accept a big discontinuity scope and use a very bright object to focus on, you may get more than accurate results by dialing downwards the shutter speed to reduce the brightness of the object on Live View.


Other Notes

Long fast telephoto lenses, like a 300mm f/ii.8, and telescopes are sensitive to focus changes due to temperature. As the temperature falls, metal in the lenses contracts and the focus shifts. The faster the optical system, the shallower the depth of focus, and the more critical the focus. If the temperature is falling during the night, it is a good idea to re-focus. This is normally not as critical with wide-angle lenses.

Bahtinov Masks - some people employ them, I don't. With Live view at 10x I don't accept any problem seeing the point of exact focus. However, with my old eyes I do demand reading glasses to meet the screen up close. :-)


Summary

Live View makes it piece of cake to focus anything from a wide-angle lens to a gigantic Schmidt Cassegrain if you use the procedures that I've outlined to a higher place.

In this commodity I've tried to be comprehensive, but using Live View for focusing is really pretty simply one time you know these tips and tricks. Recall: Utilise manual focus on a bright star at wide aperture at ISO 1600 with bulb shutter speed and eyeball the focus to get close, and so use Live View and zoom in to 10x magnification to nail the focus.