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Focus at Night? Here is a powerful trick

I have addressed the night focus bugaboo before.  It was a singular topic of a post (I can’t focus at night) and it has been a running thread including a sub topic of problems with long exposures.

But I finally broke down and tried a strategy invented by astronomers, specifically a Russian astronomer named Pavel Bahtinov


Here is Jupiter and it’s four moons as seen through a Bahtinov mask in a 2 second exposure.  Notice how the spikes are all radiating from the center. If you look closely, however you’ll see that the horizontal central spike is just slightly below the center. This indicates the focus is slightly off.

How do you get the above spikes? You use a mask that is placed over the end of your lens, lens hood (or if a telescope your dew shield). The mask looks like this:

To use you just snap a photo, zoom in as much as possible on the LCD to check the alignment of the spikes. Tweak the focus and repeat until the spikes are all well aligned. Not hard and doesn’t take very long!

You can read my review of this mask here. The cost, including shipping is about $20.

If you’re bold, you can create a template and cut your own mask. I say bold because there is a LOT of cutting needed.  I gave up after trying to make just a few dozen cuts in some thin black plastic.

If you’re interested in other focusing techniques at night, you can read Jerry Lodigruss’s column on the subject.  It’s geared toward astrophotographers, but don’t let that stop you from applying the principles to terrestrial sources too.

Will it be a little clunky to carry around yet one more thing? You betcha. Especially since you may be able to get autofocus to work just fine on either Jupiter or the Moon. But those bright light sources aren’t always available – and autofocus is not always accurate, either.

The Bahtinov mask should work even if your only source of light is a distant street lamp.

Astrophotography Equipment Recommendations – Beginner to Intermediate

For basic astrophotography I recommend starting with a wide angle lens and a sturdy tripod.  That’s it. Go out there and get some Milky Way or starry sky shots. Take plenty and average stack them (after aligning them). More on this later.

To image things like the moon, planets, galaxies and nebula you’ll want to move up to a decent telephoto lens (200-800 mm effective focal length) and an Equatorial Mount.


To my thinking there are 4 categories of mounts with their approximate prices and assembled total weight (excluding telescope or camera):

  • Light, single drive (e.g. the AstroTrac, $900, 15 lbs, the Polarie or the SkyTracker)
  • Cheap ($189) and probably useless to decent but limited AstroView Equatorial $350, 26 lbs.
  • Mid-range, accurate with features like autoguide ports, and GoTo: Celestron CG-5GT, $690, 42 lbs; Orion Sirius, $1150, 43 lbs; Orion Atlas, $1400, 76 lbs. All are heavy!
  • High end: A hefty hunk of metal with a hefty price point: e.g. Celestron CGE Pro, $4,400, 154 lbs.

In the examples I’ve shown mostly equipment from Orion for three reasons:

  1. I have Orion equipment and they have a local store.
  2. They have a good reputation for being helpful and consumer friendly
  3. Their website makes comparisons easy!

The Portable Solution

The best portable solution is clearly the well made AstroTrac with the power cable, finder scope (upper right) and the drive at the bottom.


To use this you need several other bits and pieces shown here excluding a standard camera tripod.


It’s a well engineered, portable system. All the gear together (including tripod, drive, camera, telephoto lens, batteries, etc) is about 16 pounds – meaning you can carry it with you. The next closest equatorial drive solution is about twice that heavy.

The cost is a minimum of $680 for the drive, polar scope and power cable. But you’ll need some additional head components (about $210), a power supply of some kind ($30) and perhaps a sturdier tripod. The total outlay will be under a thousand making it comparable to the low end of the mid-range mounts.

PROS: The AstroTrac is easy to set up, and relatively easy to align if you use the geared heads and the polar scope. You can pack it in a suitcase or a backpack and take it on an airplane!

CONS: More expensive than a single drive equatorial mount. Only drives one axis (all that is generally needed). Maximum tracking time is about 2 hours. Repointing the camera may misalign the drive. Need to build or buy a 12V battery pack (though this is easy to do). Need to learn your sky to find things.

The Equatorial Mount

Go cheap, go big, go fancy… but you’re not going light.


The AstroView – which I have – requires drive motor(s) for another $130 or so bringing the total outlay to about $380. It’s carry weight is about 35 pounds if you include the camera, and all accessories including counter weights.

PROS: Inexpensive, includes polar scope, lighter of the many mount options, can support modest refractor or small reflector. Tracks well.

CONS: No guide port, limited to about 12 pounds of capacity, no “GoTo” option so you have to learn your skies to use it well. Tripod is thin aluminum. It’s sturdy but may not hold up to extended use.

A step up from the entry level mount would be something like the SkyView Pro ($850) It includes a “GoTo” computerized control which is a great help to the novice and helps you with alignment routines. I’d probably opt for the Orion Sirius ($1150) however as it supports 10 more pounds (30 total) and for that extra $300 bucks you also get a polar scope, the ability to use a decently large telescope and fancier drive options. A highly recommend mount is the Celestron CG-5GT at about $690 add $50 for a polar scope. All of the GoTo mounts will “slew” (move rapidly and accurately) from one object to the next and you can enter the object into a keypad to get there. Save even more money by using your computer instead of the “GoTo” unit.

Attaching A Camera to A Mount

If you opt for a telescope mount, you will want to consider using a ball head for maximum ease of pointing the camera. However you CAN attach the camera directly to the dovetail bar and use it just like a telescope (with limitations on the field orientation). Here I have used a ring collar that couples my telephoto lens to the ball head. This allows me to rotate the camera to change the frame without having to repoint. It’s also better balanced.  There is enough room on the front of the dovetail to put another head and another camera.



I even “cheated” and am using a camera as a counter weight – see it hanging there in front of me?



If you decide to up the ante, here are a few commendable small, light refractors. None are “top of the line”, but I’ve had some pretty good success with the ED80. It’s biggest weakness is that it comes with no mounting bracket, and the focus mechanism is not the “dual speed” (fine focus) option that seems to help fine tune things. I did find that I could mount the ED80 on my scope without mounting rings by attaching it to a Vixen-style dovetail bar and a 1/4″ 20 cap screw. A hex bolt would work fine, too.  I drilled out one of the threaded holes in the dovetail bar.


If you are thinking of going in all at once, various vendors offer bundles that might interest you.  Here are some examples from Orion (www.telescope.com)