Bulb Ramping ("Bramping") is a method by which the exposure length of your images is changed as your timelapse progresses. This is useful in situations with gradually changing light levels, like a sunset or sunrise. The Bulb Ramping Video Tutorial for Michron is very similar to bulb ramping with Radian.
Please note that Bulb Ramping on Radian's running the R1 Software only works with cameras with a built-in PC Sync port, such as the Canon 5D and 6D series. As of October 2014 were have an R2 software update available that allows you to Bulb Ramp without a PC Sync Cable.
- Camera capable of operating in "Bulb Mode". Please note that unless you have a Radian with R2 Software, Bulb Ramping does not work with cameras that do not have a built-in PC Sync port.
- If you are using a PC Sync Cable - 3.5mm stereo jack to PC Sync Cable, like this one.
- 2.5mm Shutter Release Cable, specific to your camera
- a Radian!
You can access the Bulb Ramping Settings Page via the "Advanced" button on Page 2 of the Radian App.
This will depend on the duration of the sunset in your region (it varies by latitude and season). In the continental United States, 45 minutes is a good reference point, but even then you will need to vary it based on the time of year.
This setting will depend on your camera, but you will want this to be as small as possible, to minimize the length of your maximum exposure. Keeping the exposure duration as short as possible will also reduce sensor noise, which increases over time. If you are reducing your exposure over time, you will need to ensure that your final exposure is not too short for your camera.
EXPOSURE CHANGE :
This will also depend on your latitude and season, but in the continental US, 1.9 f-stops/10 minutes is a good starting place. The App will give you feedback on what results to expect based on your input settings; in general you want to get your minimum exposure time as close to the speed limit of your camera as possible.
Radian sends an electrical signal through the trigger port of your camera. This signal is based on standard protocols that were established long ago, and the signal is essentially the equivalent of holding your finger on the shutter button of your camera. This means that Radian cannot alter your ISO, aperture, or any other camera settings beyond the length of time that the shutter is open.
When you put your camera into Bulb Mode, the length of time that the shutter is held open by the camera is equal to the length of time that your camera receives the signal from Radian (or from your finger being on the shutter button). If the signal coming form Radian lasts for 1 second, then your camera's shutter will stay open for 1 second.
All cameras have some delay between the time that Radian sends the pulse, and the time that the action (shutter open or shutter closed) takes effect. This delay is camera-dependant, and is not consistent even within the same camera. This delay is generally fairly small (usually about 1/30 of a second) but if you are shooting with a short exposure time, you may notice "flicker" whereby some frames in your time-lapse are much darker or brighter than adjacent frames. This is why we recommend using 1/10 of a second as your minimum exposure time when Bramping, though some cameras you may need to use an even longer minimum exposure time.
To figure out the minimum exposure time of your camera, the simplest way is to perform a few tests using the Hold Functionality in the "Advanced" menu. As you do this, please keep in mind that many cameras do not accurately indicate the exposure time when in bulb mode. Because of this, do not worry about what your camera's display says the exposure length was, just check for consistency between photos, and a change in exposure between different hold settings. In addition, please note that there is an error in Radian where the first image will not always be the correct hold length, so it is important that you disregard the first image taken when performing this test.
Set up the tests as follows :
Set all of your camera's settings to Manual (this includes ISO, Aperture, WB, etc) and set up your camera so that the first frame will be properly exposed. You will need to set your exposure equal to the starting exposure you have set in the app, and then adjust your ISO and Aperture settings so that your images are properly exposed. Once this is complete, put your camera into Bulb Mode, and connect Radian to your camera to begin capturing your Bramp.
For Radian to control your camera's exposure time, you will need to place your camera into Bulb Mode. The way that this is done varies based on your camera, and not all cameras have a Bulb Mode. Please reference your camera's manual, or do some searching online to find how to place your camera into Bulb Mode.
Whew, that was a lot of information! While it's helpful, and sometimes necessary to understand the nitty-gritty of Bramping, here is a quick cheat sheet to get you up and running for your first sunset Bramp (try this at home first!) :
You can use Radian with a PC Sync to 3.5mm cable in conjunction with the regular shutter release cable to achieve faster flicker-free shutter speeds. This is done because PC Sync cable tells the Radian when the camera has actually opened it's shutter (there is an inconsistent delay between the command sent by Radian and the actual shutter opening) ensuring that the exposure time set is actually the exposure time used for the image. In our testing we found that without a PC sync cable the resulting image has large amounts of "flicker" due to inconsistencies in exposure time between photos that should have otherwise identical exposure times. Because of this, a PC Sync cable used to be absolutely necessary for Radian to operate, but as of the newest Software update, we have relaxed that requirement.