Stars with foreground element?

Let's say I'm shooting the starry night sky, with a prominent object in the foreground that I want to have as the lead-in part of the composition (e.g. a tree or a structure).

 

I've been told that, for pinpoint stars, I should always be using manual focus against the brightest star in the sky.

 

My question is this: Is that always the case, even if you have a prominent object in the foreground? Or, in those cases, should you be manually focusing on that foreground object?

 

What would the best focus point to get the sharpest focus, from beginning to end, in cases where stars are the end?

 

Any help would be appreciated!

 

(If it matters, I'm using a Tokina 11-16, F2.8)

Your 11-16mm/2.8 will give you a very deep DoF. I'll assume you're using an APS-C body. With that lens, and it's best aperture of f/8 at 15mm, you have a hyperfocal distance of just under 5 feet. From a practical standpoint, if you set up 5 feet from your foreground subject, and focus on it, both that object and the sky will be in "reasonable" focus. The focus characteristics get better the further you are from your foreground subject. Keep in mind that anything beyond about 6 feet will be at infinity focus, so that keeps things easy. If you can keep your foreground object a reasonable distance away (more than 6-8 feet), and focus there, then your stars should be OK. I recommend you get familiar with hyperfocal distance and how it relates to your lens + body combination. If you do this, then you'll be able to make very informed decisions about these issues. I use a phone app, Hyperfocal Pro, to help me make good decisions in these instances. Let me know if this helps. If you're still confused I'll try to give some examples. I have that exact lens and should be able to provide some useful data.

For example: This image was shot on a D5100 APS-C body using a kit 18-105mm/3.5-5.6 lens, 18mm/3.5, ISO 3200, 40 second exposure. At these settings, the hyperfocal distance is about 15 feet, but the rock formation is well beyond that. The rock was intermittently lit up by the headlights of passing cars. I timed the exposure to coincide with a car's passing. Now, this image is limited by the D5100's high ISO performance and the cheap lens, but illustrates the principle well. The rock formation (Balanced Rock in Arches National Park) was well beyond the hyperfocal distance, and I focused on the rock (as best I could), rather than the stars. Lack of sharpness in the stars is due more to the character of the lens and the noise of the camera, rather than a lack of focus. You might could get them in slightly better focus, but only at the risk of losing (some) definition in the foreground subject.

An extension of David's technique, that doesn't rely on passing vehicles, is to use 'painting with light'.

 

This entails using a powerful handheld torch (flashlight), and playing its beam over whatever you want illuminated during an extended exposure.

 

You obviously need to stand out of frame while doing this, and keep the torch out of shot as well.

 

If you do a Google search for 'painting with light', you'll probably get a few Youtube videos showing how to do it.

Not an answer to the question, just a comment. If it was me, I'd take two exposures (one focused on - and exposed for - the foreground, one focused on/for the background). and combine them in PP.

Mike

An extension of David's technique, that doesn't rely on passing vehicles, is to use 'painting with light'.

I actually tried this, but there was another group there who yelled at me for messing up their pictures, so I fell back on the headlight option. I'm not sure what a midnight rumble between photographer gangs might look like, but I wasn't up for it.:p

I'm not sure what a midnight rumble between photographer gangs might look like

It might look like an Internet forum titled Film vs. Digital. ;)

Thanks for all that info--it's really helpful!

 

@DavidTriplett I am currently using a Nikon D7500. Your point about F8 is a really good reminder for me. I have been using PhotoPills to give me the maximum shutter speed before stars would become blurry. But, because I'm on DX and am trying to keep my ISO low, I have been almost exclusively shooting in F2.8 to let in maximum light. In that case, I suppose I'm also running the risk of getting star bokeh if I'm focusing on the foreground tree or tree bokeh if I'm focusing on the stars. It hasn't been an issue so far, but I will definitely start paying more attention to hyperfocal from the outset and also experiment with F8 using my setup. Thanks again!

I'm not suggesting my sample image is laudatory, only that it illustrates the issue in question. The D7500 certainly will have better high ISO performance than the D5100 used here. Me experience with the Tokina 11-16 is that it is not at its sharpest wide open, and you'll want to be at something like f/5.6-8 for reliably sharp results. However, there's a lot of sample variation, so experiment with your particular lens to see what it likes best. Watch out for sagital coma, particularly away from lens centerline. Keep in mind, also, that the closer you are to Polaris the shorter the star trails on longer exposures. The further away from Polaris the more territory the stars cover in a set time, so the streaks get longer sooner.

Stars are essentially points of light at the distance we see them, where

the foreground object is not.

 

On the other hand, there is diffraction, which gives stars the size as we see them.

 

In any case, out of focus stars will be more noticeable than out of focus

foreground, unless the foreground has a lot of fine detail.

 

Reminds me, in the early years of telescope astronomy, diffraction wasn't

understood and stars were thought to have a visible size, and so be much

closer than they actually are.

 

Not an answer to the question, just a comment. If it was me, I'd take two exposures (one focused on - and exposed for - the foreground, one focused on/for the background). and combine them in PP.

Mike

Expanding on Mike's comment - what I like to do is set up a nightscape composition in twilight with the camera on a sturdy tripod, then photograph the foreground before complete darkness. Without moving the camera, I then wait for complete darkness to expose for the sky. In post-processing, I use a foreground layer and a background layer in Photoshop and blend the two (or more) images. I typically set focus at infinity and adjust aperture and ISO settings for the foreground, with a small enough aperture to insure that the foreground is in focus. While waiting for darkness, I reset aperture and ISO. Of course, I can only use this method once per night before reverting to more conventional approaches.

Edited January 16, 2020 by Glenn McCreery

 

(snip)

I typically set focus at infinity and adjust aperture and ISO settings for the foreground,

 

Do note that some lenses, especially longer focal length, will focus past infinity.

This is necessary in some cases to allow for thermal expansion.

The exact point of infinity focus isn't always so obvious.

 

(snip)

 

Of course, I can only use this method once per night before reverting to more conventional methods.

 

Only once per camera (and tripod). Bring along more of each, and you can do more!

Glen said, "

Do note that some lenses, especially longer focal length, will focus past infinity.

This is necessary in some cases to allow for thermal expansion.

The exact point of infinity focus isn't always so obvious."

 

Right. When I was using a Rokinon 24mm f:1.4 lens, the infinity focus position was well past the fiducial mark. I made a fine pencil mark on the barrel to indicate the actual position, which fortunately did not change noticeably with aperture or temperature. Now I use a Sigma Art 24mm f:1.4 lens, on which the infinity mark is spot-on. I use f:1.4 for star images and, just to make sure, check focus at f:1.4 using 10x magnification on my Canon 5D IV well before complete darkness.

 

 

Glen said, "Only once per camera (and tripod). Bring along more of each, and you can do more!"

 

The whole process is complicated enough with only one camera, but I suppose that I could try using two, although I would be using two different camera brands with two different lenses and focal lengths, different remote shutter releases, tripods, settings, etc. But, you have me thinking.........