A sharp eye in the night

As a few know know, then I got this little silly interest for photography in the dark. The silliness ranges from landscape photography to astrophotography. With darkness comes the ability to shape the visual impression even further than one would be able to in daytime. When it comes to night photography then creativity doesn’t do it alone, you do need to adopt some hardcore skills. There is quite a few but perhaps the most important skill to master is the ability to focus. It might sound silly easy, but it is from from being the case, getting a good focus in darkness can be really tricky.

I started out with shooting stars with my Minolta 17-35, in many ways a good lens to start out with, its affordable and easy to come by, but it is really difficult to get a good crisp focus with. Now I am using a Samyang 14mm f/2.8 which is much easier.

This blog post is about getting that much needed crisp focus at night or low light situations, which techniques i am using to adapt to the situation. I would be very pleased if you commented on this blog with your techniques and told about your considerations and why your technique is particularly good for a special scene.

AF why, why not

You might have noticed that Autofocus is not working at night, the camera keeps hunting for a focus spot but fails to find one. This is because the camera fails to find suitable contrast to focus on. Obviously if you are shooting a photo with an object that is isnt too far away, then you could light this with a strong flashlight enabling autofocus to set focus, after which you can switch to manual and shoot the photo without the flashlight, but this obviously will not do when you are shooting stars.

Distance markings method

When it comes to using the Distance Markings then it gets a little hairy. Knowing the distance to your motive and knowing the depth of field (DOF) you are working with is absolutely key. Get it a little wrong, and you are outside the boundaries of your DOF and the motive will stand unacceptable soft.

 

The math going into calculating your DOF is relatively simple, but if you do not care for such things, then there is plenty online sites and apps squeezing the fun out of it.

Lets say you are about to shoot an object that is 30 meters away, you are using your Sony A99V equipped with a 14mm f/2.8.  At this distance we will have a Depth of field Near limit 2.15 m going to a Far limit at Infinity. meaning that everything  from 27.9 meters in front of the object until infinity will be acceptable sharp.

Lets say we was to shoot the same object with a 200mm f/2.8. This will give us a near limit of 28.2 meters and a far limit at 32m. Having the object within the 3.81 meters will render it acceptable sharp. In other words everything 1.78 meters In front of object to 2.02 meters behind the object will appear sharp.

hyperfocal-distance-lens-markings-featured

 

Eye It

Let me start out with saying that this method is not recommended.

There is not much good to be said about trying to focus a camera through the viewfinder with the unaided eye. It does not have a very high percentage of success for the vast majority of people.

 

My first tries with setting focus at night was to just look through the viewfinder of the camera and try to focus. It seemed like the logical way, but it turned out to be very inaccurate and certainly not repeatable in terms of consistency.

 

The bight beacon method

When shooting the night sky or distant landscape you will always be at hyperfocal distance, and you will be setting your focus to as close to infinity as possible. You might think it is as simple as lining the focus ring up to the infinity mark  on your lens, the problem with the is that it is far from always accurate.

I Prefer using live view on my A99V camera and zooming in with the built in focus magnifier feature. I focus manually as close as I can to infinity, and then find the brightest star in the sky and make minor focus adjustments until the star looks sharp. It is wise to repeat the process making sure the stars are sharp. Do note that your lens possibly is more soft at the edges than it is at the center.

Enabling this Focus Magnifier feature of  the Sony A99V is very easy.  Got to [MENU] – Custom Menu 4 (gear icon) – [Smart Telecon. Button] – [Focus Magnifier]. This will allow you to magnify your image up to 11.7x for assistance in focusing. You can also move around the area of magnification using the multi-selector button. You can get more information at pages 103-104 of the SLT-A99V Handbook.

Temperatures and focus

Note that the longer the focal length of the lens, the more prone it will be to focus shift due to temperature changes during the night.

HartMann or Bahinow

I did read about Hartmann and Bahtinov, but i never tried this methods myself. I would love to hear more about these. If you have tried them to post comments on my blog. From what I understand is it this is basically a piece of cardboard or plastic with a certain pattern cut out that will aid during focussing. Using a right angle finder with magnification in combination with a mask for the best results.

 

 

 

 

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