I’ve recently been trying to experiment with sunset portraits but I keep encountering a problem where the sky is lit up exactly how I want it but the subject is under-exposed, with little to no exposure. Is this having to do with metering or will manually exposing the image help? This was shot at f/4 and I’ve heard suggestion on bumping up my exposure compensation meter.
That's a nice silhouette!
You're running into the same problem that anyone runs into when photographing a very backlit subject: a lot of light is coming from the background and creating a drastic difference in ideal exposure between the background and foreground.
Given this, you can handle the situation a number of different ways:
Change the Exposure to Equalize - This is the most ideal in a pinch, but least ideal overall. In your example, you would open up ~2 stops to get the sky on the edge of blowing out. This will create a very underexposed person - but it's better than nothing. You'll need to do quite a bit of post pro work with the RAW file, potentially even exporting a file made ideal for the background and a file made ideal for the subject - and then mask them together. Because the subject will be very underexposed - you can count on a good deal of noise to deal with as well.
Take Two Shots - If you can, take a shot with proper exposure for the background and one for the subject and then merge them together in your post-pro editor of choice. The benefit here is that you will have two great files to start with - so how exactly they map together is really up to you - and overall image quality can remain quite good. Auto-Exposure Bracketing and multi-shot can be used together to string the shots back to back.
Get a Reflector - Shine some light back on your subject! A single reflector can do wonders and it might just be all you need.
Add some flash - On camera flash is nobody's favorite - so if you can, move the flash off camera and into a better location for your lighting.
On exposure compensation...Backlit subjects are some of the hardest for the meter to get right. In these cases, I'd highly recommend shooting in manual so that you can meter the background, meter the foreground, and then use your judgement to pick the best exposure for whichever method you intend to use from the above.
Changing the exposure compensation or using manual exposure can brighten your subject, but it will also make the sky brighter. Too bright to see the effect of the sunset.
You can't change the laws of physics or the physical properties of light. Sunset means darkness and you must provide more light for your foreground subject. This is even more critical because your subject is being back-lit. You might try using a large reflector, but the real solution is artificial light from a flash unit or constant light source.
Another possible solution is High Dynamic Range photography where you take multiple photos with different exposure and combine them with software to make the poorly lit subject brighter. Some cameras now have built-in software to do this automatically.
In short, you can not get both the subject and the sky equally exposed without a flash. Camera sensors do not have that much dynamic range.
If you get that sky at f/4 you have to use a flash in order to illuminate your subject f/4 at the given distance.
In case you still do not want to use a flash you should get a reflector, reflecting sunlight to your subject. But since reflectors do not reflect 1:1 the received light, you will either have to expose for your subject and get an overexposed sky, or expose for the sky and get a slightly underexposed subject. Any of this meaning that you will have to do some post-pro work to get the image you want.
You ask how to do this without a flash, but this is absolutely a situation where you should use flash — at least, if you don't want the silhouette effect you have here.
You could create a composite shot with multiple exposures, but that's somewhat difficult with non-static subjects and hard to get looking right anyway. In some situations, a reflector can be used to create fill light, but that generally works best when you're in shade but there is still lots of natural light. That's not the case in a sunset like this.
Many people are nervous about this because we're used to "flash = bad" due to the awful effect of direct, on-camera flashes (and those terrible things on our phones). But it doesn't have to be like that. These days, off-camera radio-triggered flashes are cheap (you can have a whole system for the cost of a decent lens).
In this case, the difference is not really huge, and if you have the shot in raw, it should be possible to bring up the shadows in postprocessing while not making it look unnatural.
To some extent, it's even possible to do this with the JPEG file you provided here: for this example I used darktable (2 instances of "shadows&highlights" with different settings, and "global tonemap" with a parametric mask). JPEG and quantization artifacts in the shadows become too obvious pretty fast, but if you have the raw file, you can push them even further.
The benefit of using only 1 shot is that you won't have to deal with subject movements (or any movements). It might be extremely hard to correctly merge a pair of photos even if they look similar enough at a first glance.
This method also can be combined with using a reflector.
Here are the exact darktable conversion settings (.xmp) which I used to create this image: jFMHL.jpg.xmp