I ask this question because I am in process of building my rig. If its a stupid question, please forgive me. I slightly know the obvious difference, but would there be any reason to invest in both (on a budget), or just go with a dolly/track? I just recently bought the CobraCrane 1 and am just looking for some tools to enhance my production value so I dont have to make up for it in post-production. Thanks in advance.
I can chime in, but can't really answer your question. It all just depends on what you are trying to shoot, what kind of projects you do, and what kind of camera moves you need to make.
Obviously both tools do the same thing... they make dolly moves. The difference is just how much. It's a little bit like wondering "Do I need a high-hat or a 6-foot tripod?" Or "Do I need a full-size crane, or is a jib enough?" Well, it just depends on what you need to do with the camera.
If you only ever need dolly moves of a couple of feet or so, then a slider might be easier, less expensive, and of course is much easier to set up if you usually work with small crews. But if you're looking for longer tracking, dollying, or arcing shots, then you need a real dolly.
In a perfect world, both would be nice... but I know sometimes we all have to make choices.
I'd take a good hard look at your needs... more so than budgets... because while dollys tend to be more costly than sliders, a very high-end slider can be a fair bit more expensive than even a low-to-mid-rangish dolly.
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I would opine that if you can only get one, the dolly is more of an all-around value, with a wider range of application. In a perfect world, you'd put a short jib (or your slider) on the dolly, and have all the bases covered.