Welcome to this quick tutorial on laser triggering with Pluto trigger.
Today I was playing around with freeze motion photography, and thought it would be cool to share with you what I tried to get this type of shot.
It’s my first time doing this shot this way, and I certainly would improve the process next time.
I shot this using a Pluto trigger (link in description), but you could do it with an assistant, but it would be a bit more unpredictable.
I was shooting things like cherry tomatoes and rubber balls dropped into a wine glass, with regular water or with food colouring in water.
Let’s walk through the setup.
With the Pluto trigger there is a laser. I had this set up on a light stand pointing at the pluto trigger, which acts as a receiver.
The Pluto trigger is connected to my camera to trigger the shutter when the laser beam is disturbed.
My camera has a Godox X1T Nikon trigger. It is triggering an AD 200 flash. You don’t need this set up – I did it because I have one and it is able to do high speed images. Many external flashes and strobes are limited to slow speeds (e.g. 1/125 sec) due to the nature of the SLR’s shutter. I won’t go into this, but if you want to understand this, check out this article on high speed sync…
On the flash is a Magmod grid, to make the light shine only on the glass, and limit light spill on the background and camera.
Between the two lasers is a string using dental floss, so i can properly aim through the laser. It’s a lot harder to aim than it looks, so this helps.
So I would drop the tomato cherry, it would break the laser, triggering my camera and the light all at once.
I used the LensBaby Composer Pro II with Sweet 35 lens, because it was a good focal length for the distance I was shooting, and added a bit of creativity, even if I was shooting mostly at the smallest aperture (which gives the least amount of blur effect).
Not shown is my phone, which is required to control the Pluto trigger.
In the end, I processed the photos in Lightroom (initial RAW develop) + Photoshop (layers and masking) + Luminar 2018 (detail enhancement).
Here are some samples of the results:
Some things worth noting:
It took me a while to realize the laser of the Pluto had to be pointed to the small sensor to the left of the big sensor. See the following image:
You need to tune the laser sensitivity so it’s just on the sweet spot between being triggered. You don’t want the setting too high or too low, or it will not trigger or trigger too often.
You may want to go into Pluto settings and give it a trigger reset value (see image below), so you aren’t inadvertently triggering the flash when you are recovering the dropped objects. E.g. I set the retry to 2 seconds, but you may want even as high as 10 seconds if you aren’t dropping things more rapidly than that.
I added a delay of 7ms since the objects were hitting the dental floss on the way down, and slowing down a bit. I could have tuned this number a bit more to get the optimum “splash”, but I am impatient.
Areas of improvement
I think next time I would create a tube that objects would roll through (probably held by light stand and “magic arm”), and hit the laser and glass 100% of the time. Before I set up the dental floss (halfway through the shoot), I was missing the laser and glass often. I lost a few grape tomatoes this way.
Even with the dental floss, I wasn’t always triggering the laser, and the dental floss was impacting the quality of the “splash”.
Next time I will try to drop from a higher altitude, to get a bigger splash. I will probably try a bigger object too.
Even with the grid on the light, there was quite a bit of light spill. I’ll be more careful, and use a snoot or cinefoil to control the light more.
Some of the photos I took you’ll see hairs in the glass. This is from the tomato or cherry rolling on the floor previously when I missed the glass, and collecting cat hair :/
This experiment was fun, albeit a bit messy. I’ll certainly take some of my lessons learned and do it again, and try to improve on it.
The setup was just how I did it – you don’t need any of the tools I used, except a camera and a flash. The tools make it easier (e.g. the Pluto Trigger, high speed flash) and more consistent, but not necessary.
However if you are looking to spend money on new gadgets, the Pluto trigger does have many creative features that in my opinion are worth the investment. I’ll certainly post some more of the features of the Pluto trigger in future blog posts (e.g. star trails, water droplet, lightning, fireworks, time lapse).
Thanks for checking out my instructional blog post!
Today I tried it with water balloons and a bust. Here are the results…
Lens manufacturers tend to play with this definition, as you may sometimes see macro lenses that are 1:2, which means they are only half as big as real life when projected onto the negative or sensor. We will be using a macro lens that is true 1:1, which means the image size on sensor is same as in real life.
There are several ways to take macro photos. Check the above Wikipedia article for a more thorough list of tools and tricks, but in summary you can achieve macro photography using:
Using macro lenses. This is a common method with great optical quality (using great lenses), but can get expensive. I shoot with Nikon, and the go-to macro lens is the 105mm 2.8 macro lens, which is priced at US$900 – not cheap. There are cheaper Nikon alternatives (with smaller focal length), but I have not tried them. Other manufacturers, such as Canon, have similar macro lenses and prices (equivalent Canon lens is 100mm at US$750). Macro lenses have special construction optically to be able to focus on very close objects. Normal lenses require the object to be some distance from the lens to be able to focus, and thus will appear smaller.
Extension tubes are basically optically neutral tubes that get a normal lens closer to the subject, therefore making it look bigger. The extension tubes get installed between the camera and the lens, thereby moving the lens further away from the camera. There is typically nothing in the tubes (no glass or other optical elements) – just air. To get an idea of how this works, hold a pair of glasses further away from your eyes to see things appear bigger. That’s essentially what you are doing with the lens. The advantage to extension tubes is price. The model I will be testing can be found on eBay for around US$50. In conjunction with a 50mm prime lens, which goes for about US$200, the total for this outfit is around $250, which is considerably cheaper than the $900 macro lens.
Here is a link to the extension tubes I will be testing purchased from Amazon.
(If the link doesn’t work, just search for “Neewer Extension Tubes” and your camera manufacturer).
Extension tubes are often sold with multiple lengths, thereby giving you different options and combinations for your focal length. You can put all three tubes together for the closest zoom. We will be testing multiple combinations of extension lengths.
You can get more expensive extension tubes, such as those manufactured by the camera manufacturer. You can also get cheaper ones than what I tested, but they may not have the electrical contacts to allow auto-focus to work. I chose the slightly more expensive ones so I can use auto-focus, if needed. I will be focusing manually during these tests, however.
I will be using a Nikon D750 camera, mounted on a mini tripod from Amazon (with Manfrotto ball head), shooting into a Foldio2 light table, and using the closest focus distance for each shot. I will be using a consistent focal length of 5.6 to keep the depth of field reasonably consistent. The camera is set to A (aperture priority), with ISO 200. There may be minor differences in sharpness between the lenses at f5.6, but those should be negligible. I will be using a quarter as the test subject. The distance from subject and angle may change slightly in order to keep the closest focus distance.
Some more notes before we get to the images:
To show how big and small the images appear on the sensor, there is no cropping, so some images may seem like a lot of “negative space” intentionally.
The photos were mostly taken tethered to my PC (I’ll do another blog post on Tethering). The only processing done was “auto tone” so the lighting and white balance appears somewhat consistent between shots.
I wanted to be able to let you zoom into the photos by clicking on them, but I haven’t figured out how to do that in WordPress. When I do, I’ll update the article so you can look closer, but hopefully images are big enough so you get an idea of sharpness and depth of field.
The lighting may appear different since different angles and camera height was needed for the different lens combinations.
This experiment is not a review or recommendation, just the raw data from an experiment. I will let you zoom into the pics and decide what you think is sharper and more aesthetically pleasing.
Macro Lens Only (105mm at f5.6)
Our first photo is that using the Nikon 105mm macro at f5.6. Note how large the coin looks in terms of the whole image (no cropping). Even at 5.6, the depth of field is pretty narrow due to the distance from the subject.
Due to the distance needed to the subject, I needed to prop the mini tripod onto a book.
Ok this is not a macro shot, but just for baseline and reference, here’s a shot of the quarter with only the 50mm lens shot at f5.6. The image may not be sharp as I had to hand-hold the camera it was so far away (the closest I could with this lens get and have the quarter in focus).
50mm lens with 12mm extension tube
This shot was also taken at f5.6, with the 12mm extension tube between the 50mm lens and the camera. Notice how much close I can get to the quarter than with no extension tube. The lens is about 14cm from the quarter (the closest I can get). The quarter is mostly in focus from top to bottom.
50mm lens with 20mm extension tube
This shot was also taken at f5.6, with the 20mm extension tube between the 50mm lens and the camera. The lens is about 11cm from the quarter (the closest I can get). The quarter is even closer than with the 12mm tube, as expected. The quarter is still pretty sharp and in focus.
50mm lens with 36mm extension tube
This shot was also taken at f5.6, with the 36mm extension tube between the 50mm lens and the camera. The quarter is even closer than with the previous tubes, as expected. I have to get the lens pretty close to the quarter (approx 9cm). The quarter is still pretty sharp and in focus. The quarter looks much different with the lighting because the camera is almost completely overhead from the quarter, as opposed to at an angle from it.
Here’s what the 50mm looks like with the 36mm extension tube attached (and how close we can get):
50mm lens with all extension tubes
Here we have the 50mm with 12mm+20mm+36mm. If my math is correct, that’s 68mm equivalent extension tube. The quarter appears closer than 1:1, and is fairly quite in focus with a decent depth of field.
Here’s what the 50mm looks like with all tubes connected (and how close we can get):
105mm macro with all extension tubes
Now the real reason I bought the extension tubes was to use with the macro lens. (I bought the macro lens much earlier than the tubes). So here’s what that looks like at f5.6. It’s definitely closer than 1:1, but with a very narrow depth of field. Depending on what you are trying to achieve with your photo, this narrow DoF could be good or bad.
Now that we covered what we set out to do, let’s look at some photos outside the parameters we have set out for this experiment.
Since the 105mm with all extensions is super narrow depth of field, I wanted to try with different aperture settings. The 105mm macro is able to stop down to a whopping f57 (many lenses only stop down to about f22, for example).
Here are some of the various other aperture settings. The aperture setting is captioned in the photo.
At f11 the depth of field is quite a bit larger than at f5.6, as more of the quarter is now in focus.
At f22, even more of the quarter is in focus (wider depth of field), and the image is still pretty sharp. But even at f22, only about half the quarter is in focus.
At f57, the smallest aperture the macro lens will go to, the quarter is mostly in focus, and still reasonably sharp. Even at this setting, you’ll see the bottom of the quarter is out of focus. And at this aperture setting, you will definitely see any dirt on your sensor or lens!
I know I said this wasn’t a review, but here are some thoughts. Using macro lenses or using normal lenses with extension tubes are both means to get decent macro photographs. The Nikon macro 105mm lens is relatively expensive, but a phenomenal lens not only for macro photography, but also great for things like portrait photography, with it’s sharp and fast f2.8, with VR (vibration reduction). I have no experience with other macro lenses, but the Canon macro lens also seems to be a great lens. (See comparison at DXOMARK)
Non-macro prime lenses, in particular the Nikon 50mm f1.8 (or Canon’s f1.8), are quite inexpensive, are very sharp, and good alternative for macro shooting when using extension tubes (and even with combined cost, will cost you less than a top end macro lens). You can also use other lenses, such as your camera’s kit lens, but the results probably won’t be as sharp. The f1.4 (or Canon f1.2) are even sharper, but they are at least double the price of the f1.8, so I would not recommend those if price is a concern.
If you just want to play with macro photography without a huge commitment – I would recommend you start with extension tubes. It’s fun, and the results can be quite good.
If you are looking to do macro photography more professionally, looking to get wider control of depth of field, or you are looking to also get a good portrait lens, I would recommend investing in the 105mm macro lens (or 100 if you are shooting Canon). Or even invest in both macro and extension tubes – the additional cost is negligible at that point!
Note, I have not tested the other macro lenses available for Nikon, since I don’t own them. My decision to buy the 105mm was as stated above – it is well reviewed and a great portrait lens. The reviews for the other macro lenses, such as the 40mm and 60mm, note that they aren’t true 1:1, so they don’t get the same level of close-up as the 105mm. For a good overview of the various macro lenses, visit Ken Rockwell’s article here.
And somewhat related thoughts…
Related discussion topics that we haven’t discussed yet are tethering (hooking up your camera to a computer or tablet) and focus stacking. I started doing these tests tethering my camera to my computer using Adobe Lightroom 6, but it was having difficulty finding my camera between lens configurations, so I tried out another app called “ControlMyNikon”. It’s my first time using it (trying the trial), but so far I love it. Unlike Lightroom, you can do live preview, which helps you focus better, and allows you to do other advanced things like focus stacking (I’ll do a future blog post on this), HDR photos, etc.
All that to say, look for future blog posts on tethering and on focus stacking.
Let’s face it, photography equipment is expensive. A beauty dish, which is just a reflector that wraps around your studio strobe, can cost you up to $1000. Take a look at some of the prices here.
A beauty dish casts a harsh(er), direct light onto the subject. But since the light is reflected outwards, it makes a larger light source. And since there is a go-between that blocks the light from coming directly from the bulb, the light is not as harsh as a bare strobe or a strobe with a reflector.
Short definition: basically a beauty dish is harsher than a softbox, but softer than a bare light.
So if you want to experiment with different light modifiers, but don’t want to mortgage your house, why not build your own?
Now professional beauty dishes are typically bigger, and they are engineered to evenly distribute the light from the small reflector into the larger dish, but we’re just playing around here – this is good enough for us to play with, unless you are shooting for a high end glamor magazine (IMHO).
I purchased the metal bowls at Wal-mart, in a box of 5 mixing bowls for under CDN$13. A great bargain!
Note I am building this for my cheapy Cowboy Studio strobe. I wouldn’t recommend jamming this DIY beauty dish on an Elinchrom or Prophoto strobe – it does scuff it up a bit.
34cm metal bowl
16cm metal bowl
3.5 inch, 1/4 machine screws x 3
1/4 hex nuts x9
Black spray paint (optional)
Dremel tool for cutting and cleaning
Take your 34 cm metal bowl, place your studio strobe on the bowl. Center the strobe.
Using your marker, draw where you need to cut the bowl to fit the studio strobe through.
Use your Dremel tool with a cut-off disk to make a triangular incision in the middle of the bowl.
Use your metal cutters to work out from the incision, to cut around the circle you drew for the diameter of your strobe.
Use the cleaning tool and/or sanding tool to smooth out the inside cut in the bowl. You don’t want any sharp bits that could cut you.
You now have a bowl with a nice clean circle in the center. Congratulations! You won’t be mixing any salad in this bowl anymore.
Test fit the bowl around your studio strobe. You may have to widen the hole a bit if you cut too conservatively.
Hopefully you didn’t make it too loose. (You can use a speedring from a softbox if you made it too loose, but let’s hope it doesn’t come to that).
Hold the small bowl in front of the light so you can see what the end result will look like.
You can move the bowl forward and backward to see the optimum position of the small bowl for the most even light distribution.
Mark where you will be drilling to place the machine screws on the big bowl.
Put the holes at equal distance near the center – but don’t put it too close
to the center where you might break the edge.
Do the same to the small bowl – but again – not too close to the edge.
Drill your holes. Make sure you are wearing your saftety goggles! Metal will fly everywhere.
Note I didn’t really drill on the ground, this is just for demonstration purposes.
Drill your holes on the small bowl too. Use a workbench, not the ground!
Step 10 (optional):
Spray paint the outside of the small bowl to make it look professional-like. Make sure none of the paint goes on the concave part of the
bowl, because that side needs to reflect. (You can use the Dremel polisher if some paint does get on the reflective side).
I used Tremclad glossy black spray paint.
Step 11 (optional):
Use masking tape to cover the big and small holes on the big bowl, and spray paint the rear of this bowl too.
Feed the 3 machine screws through the small bowl.
Put two hex nuts on each screw. One hex goes on the opposite
side to the machine screw head (against the small bowl) to keep it from sliding. The other hex will be pressed against the
large bowl to prevent sliding.
Feed the machine screws into the large bowl. This might require some “persuasion”- i.e. brute force.
Secure the machine screws with hex nuts on the outside of the large bowl, then tighten the “inside” hex nuts against each
bowl to properly position and secure the small bowl. Again, refer to figure for Step 13 for this.
Attach your dish to your strobe head – hopefully it should just slide on with a snug fit.
Turn on your modeling light and bask in your success.
Some sample pictures taken with the beauty dish will be forthcoming.
If you’re shopping for a lens, you may want to consider vibration reduction (on Nikons) or image stabilization (on Canons). These are marketed as “VR” and “IS” on the lens model name. Other brands have this technology too, and may have different marketing terms.
Image stabilization is a technology that stabilizes the lens even if your hand is shaking (your hand shakes – trust me). This allows you to shoot at slower shutter speeds and still get sharper images.
As a rule of thumb, you should shoot at 1/ (without using image stabilization). So if you are shooting with a 50mm lens, you shouldn’t shoot any slower than 1/50 of a second. If you are shooting with a 200mm lens, you shouldn’t shoot any slower than 1/200 of a second.
This is a rule of thumb, but you may be able to hold your camera more sturdier than the average person, and may be able to operate at slower shutter speeds.
Without image stabilization, if you are shooting at slower speeds than you can hold and keep the camera stable, then you will need to lower your f-stop (increase the aperture size), or boost your ISO.
Lowering the f-stop is a good option, as this will allow you to use a faster shutter speed. But if you are at your widest aperture (in this example, I’m at f2.8, which is as wide as this lens goes), then you are stuck.
Boosting the ISO is an option; this will also allow you to use a faster shutter speed while keeping the same f-stop. Boosting the ISO however introduces noise into the picture, and this may be undesirable. The more you have to boost your ISO to get the optimal shutter speed, the more noise you get. If it’s very low light, you may get a lot of noise due to a high ISO.
Vibration reduction/image stabilization introduces a new option – you can shoot at a slower shutter speed while keeping your f-stop the same and without having to increase your ISO as much (or not have to increase it at all).
In the example provided, I shot the freezer at f2.8, 70mm at 1/3 of a second, at ISO 200. Using my rule of thumb, I would need to quicken my shutter to 1/70s to get a sharp picture. Since I’m at the lowest f-stop number (2.8) that my lens will allow, I would have to increase my ISO to get 1/70, and the picture would get noisier (if I didn’t have VR).
In the second image, I have VR enabled. Note that even though I am shooting much slower than I should be able to steadily hold, the picture still looks reasonably sharp.
This is the great value from VR.
(Note: anther option in addition to boosting the ISO or lowering the f-stop is to mount your camera on a tripod. This is sometimes a good option, but a tripod is not always convenient, and sometimes not allowed.)
It’s been a while since we’ve posted a blog, so let’s talk about something important that many people ask me.
“Steve, what camera should I buy?”
Unfortunately there is no right answer for everyone, but there might be a right answer for you.
Decide what lenses you’d like to have in the next 5-10 years. Price them out and read the reviews. It’s a lot of work, I know, but a camera purchase can be a big decision.
What kind of lenses do you eventually want? If you want to do landscapes, you want a nice wide lens, like a 10-15 mm. If you want to do Wedding Photography, you want a fast zoom lens, like a 70-200mm 2.8. If you want to shoot insects and flowers, you’ll want a macro lens. If you’re indecisive on what you want to shoot, a zoom lens that spans the gamut might be a wise idea, such as a 20-200mm.
Choosing a DSLR should be a long-term investment. If you become serious about photography, over your photography life, you will invest in many (and some expensive) lenses. Once you’ve made these commitments, it will be hard to switch to a different manufacturer.
Do you have any old lenses already? Do your friends have dSLRs, and will you be able to borrow their lenses? Do you intend to buy used lenses? These questions should navigate you towards a brand to purchase.
For example, (as far as I know) a Pentax dSLR camera can use any old Pentax lens. There are quite a few old, rock-solid Pentax lenses out in the used market to choose from, at reasonable prices.
Sony Alpha cameras can use Minolta lenses dating back to 1985. There are quite a few used Minolta lenses on the market.
Olympus dSLRs have some backwards compatibility with older lenses, but they need a special adapter.
Canon EOS dSLR cameras can use EF labeled lenses that were first manufactured in the 80s.
Nikon dSLRs can use just about any Nikon 35mm lens, so long as you purchase a mid to high-end dSLR (D80 or better). The entry level dSLRs are only compatible with DX type lenses.
Even if a lens is not compatible, you may be able to mount it on your camera, but use it in Manual focus mode. Just do some Google-ing for compatibility before you try to mount a mystery lens.
Third party vendors
The biggest dSLR manufacturers are hands-down Nikon and Canon. So if you are a third party manufacturer, you will at least make components for these brands, but perhaps not for the smaller brands. That is the reason why there are more third party products available for these two brands. If you are looking for more selection from companies other than the original equipment manufacturer (OEM), you may want to stick with Canon or Nikon.
Examples of third party components are batteries, flashes, grips, wireless triggers for flashes, remote triggers, flash accessories (like softboxes), etc.
As far as the quality of the images from dSLR manufacturers, you can’t go wrong. Any of the big dSLR manufacturers can produce great pictures. The differences are more in the lenses available and the lens quality, rather than the camera body itself.
Every camera manufacturer and model markets different features. You need to decide what features are important to you. For example, video, ISO capabilities (how well does your camera shoot in low light), live view (being able to see what you are shooting on the LCD – on most dSLRs you need to use the viewfinder).
There are many companies that will rent cameras and lenses. If you plan to buy an expensive camera, rent it first. e.g. Try out the interface for a Canon and a Nikon, and see which one you find more intuitive. dSLRs are more similar than different, but their interfaces can be significantly different.
There are companies, like LensRentals.com, that specialize in renting. And some camera stores, such as Henry’s (Headshots) and Vistek in Canada, have renting services.
What I use and why
I shoot Nikon. I have both a Nikon D40x and a Nikon D90.
I originally bought the D40x because I had some old lenses, and sticking with Nikon would give me a wider lens selection in my arsenal.
I then purchased the D90 for the following reasons. The D90 has support for older lenses in which the D40x (etc) does not. Being able to use auto-focus with prime lenses like the 50mm was important for me. The D90 has great low light capabilities. Nikon is the only major manufacturer that allows for wireless flash triggering without any additional hardware to be purchased. (You can do wireless flashes on a Canon using their add-on wireless triggers, or with any manufacturer using Pocket Wizards, but that is a significant additional cost). Having HD video was a nice to have, but not a necessity. The higher-end Canon cameras have better video capabilities than the Nikons, and can produce 1080 video versus 720 video (not an issue for me, but it might be for you). And the price for this unit was quite reasonable.
On the negative side of my purchase, Canons are more prominent than Nikon. It seems that the prices for Canon lenses are slightly lower (but close), however the Nikons do boast a wider selection of used lenses compatible with the D90 (etc).
Basically there will be good reasons and bad reasons to buy any camera. Each manufacturer has its strengths and weaknesses, as well as its marketing focus.
Choose from one of the major manufacturers if you want some long-term commitment that they’ll still be in the dSLR business a few years from now.
Start with an entry level dSLR if you are unsure how committed you will be to photography. The prices are very reasonable these days, and an entry level camera’s quality of pictures is practically as good as a high-end camera’s. A higher end camera will have more bells and whistles, and will be designed to be easier to use for a professional (but probably harder to use if you are just starting out). Once you’ve mastered the low-end camera, you can decide to invest in a better one, and still keep the lenses you’ve acquired!
The good news is you really can’t go wrong.
(Footnote: Since I am a Nikon shooter, my information on other manufacturers is strictly hearsay and based on knowledge from the internet, fellow photographers, and casual observation. If I’m wrong about something pertaining to another manufacturer, please let me know).
Battery grips’ primary purpose is obviously to be a battery and a grip. Obviously.
But battery grips are worth more discussion than that.
So let’s explore the first function: battery. Battery grips typically allow you to insert more than one proprietary battery at a time, doubling battery capacity. But here’s the great thing: many battery grips, such as the Nikon’s MD-80 and Canon’s BG-E5, also accept AA batteries. Although the AA batteries don’t last as long as the proprietary batteries, well, they are cheap and can get you out of a jam, such as a week-long camping expedition.
The next best reason to use a battery grip is if you are a portrait photographer, turning your camera in portrait orientation (ie. sideways) is easier, as you now have a side grip and an extra shutter release button on the battery grip.
For some cameras, such as the Nikon D300 and D700, using the AA batteries actually increase the frames per second. (e.g. 5frames/sec to 8frames/sec). You eat up batteries much faster, but this is great for action shots such as in sports photography.
The last reason I can think of – it makes your camera look more professional. With the trend for DSLRs getting smaller and smaller, the grip makes it look more serious and easier to manage.
I will let you in on a little secret. One of my secret weapons when I shoot is this: kneepads. Technically I usually only wear one kneepad, on my dominant knee.
Kneepads let me drop to one knee quickly when doing portraiture and modeling shots. They also let you quickly change your point of view when shooting anything (like nature photography). If you are less likely to get lower because it’s uncomfortable, or you are concerned you will wear out your knee over time, a kneepad is a quick remedy. Taking pictures from your normal standing position is boring – it’s good to change things up to make photos more interesting. Getting lower is a must in portraiture (e.g. full body shots).
If you say you don’t need kneepads, that’s fine – but if you find yourself not bothering to get low, then ask yourself why not.
Today’s DSLR cameras have magnificent light metering technology. There are still situations where you will want to use a separate light meter. The main situation is where you are using studio flash lighting. If you set your camera to anything other than Manual mode, the camera will meter the lighting before the flashes fire, and that will result in an overexposed image.
When I first got my light meter, I didn’t understand why my light meter let you dial in the shutter speed I was going to use (which would then give you the aperture f-stop number after taking a light reading), but it wouldn’t let you input the f-stop and give you a shutter speed setting. After buying my studio lighting I then understood: when measuring studio lighting, you always know what shutter speed you are using based on the speed of your flashes. If your flashes fire at 1/200 of a second, you are going to set your camera to 1/200 of a second, and thus you need the light meter to tell you what f-stop to use. If you set your camera to a faster shutter speed, you may be too fast for the flash sync to occur. If you set it to a longer exposure, well, your studio flash (for example) is only firing at 1/200 of a second, so any longer won’t contribute to your exposure.
Having said all that, a light meter will give you a suggestion of f-stop based on what shutter speed (and ISO) you tell it you are going to use. It will give you that reading to provide you with an average (like the 18% gray) image. If you don’t want 18% gray, then you are going to tweak the numbers.
I find that trial and error with the camera is often faster than taking a light reading, and then tweaking (trial and error) to get the right lighting for the shot. Modern DSLRs have histograms, allowing you quickly see how much light is in your shot, and allowing you to quickly adjust if it’s too much or too little.
Since light meters can cost as much as an entry-level DSLR, my advice is not to bother with a light meter, or try to find a used one to see if you like it. You may find that the trial and error method is just as effective, and much cheaper!
(If you didn’t understand this post, don’t worry. Go back and read my post on Aperture and Shutter Speed. Then come back and re-read this).