Author Topic: Filming Rocket Testing - settings advice welcome.  (Read 233 times)

Endothermic

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Filming Rocket Testing - settings advice welcome.
« on: October 05, 2021, 07:22:18 AM »
Hi all.

First, thank you for the help on the forum already.

I would like some advice for my use case. I will be filming a rocket nozzle test and want to focus on the nozzle, not necessarily the 'flame' at the end of the nozzle. The nozzles will be between 12 and 36 inches long.

I have a Chronos 1.4
A few mods have been done to it so far:

1. The SSD mod.
2. The remote mod.

For the remote mod, I don't think the 80 meters is going to be enough, so I got a 3.5mm to RCA cable that is 50 feet long. I'm hoping that extra bit will allow the trigger to work where it's needed. (The camera will be ~200 feet away and the trigger will need to go through a few building walls as humans aren't allowed near the test stand.)

I plan on getting a few Estes model rocket nozzles to do some testing with.

I'd love some advice from those with experience on settings that might be good for me to start experimenting with. The gain seems a bit limited as I think negative gain might be necessary?

Any advice for either:
1. Remote trigger from long distance
2. Rocket brightness mitigation

Would be appreciated.

Thank you.

*Unfortunately I won't be able to share the images that I capture from the actual nozzle testing. Sorry!
« Last Edit: October 05, 2021, 11:02:57 AM by Endothermic »

mklinger

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Re: Filming Rocket Testing - settings advice welcome.
« Reply #1 on: October 05, 2021, 08:02:44 AM »
According to the spec sheet, the Chronos 1.4 can record with a shutter speed of up to 1/1000000s.  That is very different from the frame rate.  You would set the desired resolution and frame rate, then adjust the shutter angle to achieve these super fast shutter speeds.  The faster the shutter, the less light is available for exposure.

That being said, I really doubt you'll need to worry about adding ND filters to lower the amount of light hitting the sensor.  Although if you really want to go that route, it should be easy to add these kinds of physical ND filters to any kind of lens you are using.  At the very extreme, you could even mount the camera behind something like a welder's shield. 

I would recommend just playing with the shutter angle and that will most likely get a nice exposure even with a very bright source like a rocket.

If you're not familiar with how shutter angle works, 360 deg is "wide open" and that means, say you are shooting at 1000 fps, your shutter speed will be 1/1000s.  General rule of thumb is to try for around 180 deg shutter for a "pleasing" amount of motion blur.  That means at 180 deg, it would mean 1/(360/180) * 1000 fps) or 1/2000s shutter speed.  Crank the angle down to 10 degrees for example and you'd be at 1/(360/10) * 1000 fps) or 1/36000s shutter speed.  A 1 degree shutter would mean 1/360000s shutter speed, etc.


Nikon1

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Re: Filming Rocket Testing - settings advice welcome.
« Reply #2 on: October 05, 2021, 01:24:18 PM »
I dont really know what you mean by remote Trigger Mod, but you can just connect a really long BNC / SDI Cable to the BNC Port on the Camera and Connect an Trigger to the other end, which would give a very easy setup. Longest Standard BNC Cable i was able to find from an very quick search was 100 Meters, which would be something like 328 feet in length if my math is correct.
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 https://www.ebay.de/itm/383383664906?hash=item594372790a:g:6~AAAOSwb0BeKC9V
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 These are still reasonably affordable, but if you still need longer range, there are very inexpensive BNC-Inline Couplers available, which will allow you to Chain up Individual BNC-Cables to for example make two 100m ones into an 200m long one (656 feet).
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 https://www.ebay.de/itm/312062518509?hash=item48a86024ed:g:5-kAAOxySoJTU-zy
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 The Connector is obviously a weak-Point if in rough use or exposed to the Elements, but for casual use without rain and things like that, that would probably be about the Cheapest.
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 If you want longer than 100m Cable length, there are SDI-Cables available (which basically are just BNC Cables that are rated to carry a specific amount of Data for Video Signals), up to 200m (656 Feet) Standard, and you can get even longer Custom made ones, but they cost a bit more. Would be well worth the extra cost if in rough use at least for me, and if i actually needed the Additional Range.  .
 https://www.ebay.de/itm/153083772536?hash=item23a480fe78:g:tJAAAOSwWDRbOgxg
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 I at this point assume you know how to attach a Trigger button to an BNC Cable and said cable to the Camera, and also own some kind of such a trigger. If not, let me know, then i can also give info on where to get one or how to build one.
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 For the Shutter speed / Shutter angle thing mklinger was talking about, i absolutely agree. Set your Framerate and Resolution, then Set aperture on your lens and your shutter angle for whatever exposure / brightness you want.
 the Shortest Exposure of 1s on the Chronos is plenty short and will give a very dark image. at 1s and Shorter you get into territory of Exposure Time where they capture close-Up Footage of Nukes, so i doubt your Rockets would be THAT bright. If you still manage to overexpose on such short Exposure times, close down your Aperture a lot and make sure you use 0dB analog Gain and 0dB Digital Gain. Would be very surprised if you still needed ND Filters on top of that, but if you do, use them.
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 To actually figure out the Correct settings, i would advise you to do at least two tests before shooting anything critical. I dont know how expensive or difficult it is to redo your tests, but for Stuff like Explosions that cant be redone and have no known reference to base settings of off, they usually do some Scaled down tests, like here:
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 https://youtu.be/ThLtMhiak-Q?t=100
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 In that case they already about knew that it would be very bright, set the camera to their best Estimate, did the Small-Scale test, adjusted Exposure (and then still overexposed a bit on the Actual Shot). Very similar like they also did it with the Footage of those First Nukes and things like that.
 In general, especially if you never did anything like this before and are not familiar with how the Camera behaves in situations like that, try to underexpose quite a bit, its most of the times Brighter than you think (also, while recovering Shadows or heavily boosting the Exposure in Editng reduces Image Quality on the Chronos Cameras quite a bit, its still better than overexposing, because at that point all information on the Overexposed areas is just completely gone and pure White. so you would want to rather underexpose than overexpose in that situation) from every time i shot stuff with big Fires / Explosions/ Reflections. Do at least two tests to be sure, if no previous general Brightness level to compare to is known, so you dont waste an important shot (that maybe cant be redone).
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 #EDIT# forgot to put the Link and the Screenshot for the 200m SDI-Cable
« Last Edit: October 05, 2021, 01:26:13 PM by Nikon1 »

Nikon1

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Re: Filming Rocket Testing - settings advice welcome.
« Reply #3 on: October 05, 2021, 01:43:15 PM »
Also found an 300m long one, which should be almost 1000feet, but no idea what this one would cost in USD or EUR or how much shipping would be, if they even ship to US or wherever you are, seems to be from india?
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 https://rujohnmegaconcepts.com/shop/300m-sdi-cable-75-ohms-3g-6g-hd-sdi-cable/

Endothermic

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Re: Filming Rocket Testing - settings advice welcome.
« Reply #4 on: October 11, 2021, 07:18:15 AM »
Nikon1, I got the longest (50 feet) wire I could find. I will search further and see if I can get a much longer one. That should essentially get us to where we need to be. The only piece I don't have insight into is the material of the two buildlings that the signal will need to go through.

I've successfully used the 50 foot extension and the remote trigger through a few concrete walls at my office.

The 'remote trigger mod' I referred to is detailed here on the site:

https://forum.krontech.ca/index.php?topic=4.0

<<To actually figure out the Correct settings, i would advise you to do at least two tests before shooting anything critical. >>

So, next up is to test these various settings in some sort of controlled way. I'm going to create a spreadsheet with different settings and test shoot the model rocket nozzles and see what I come up with.

There is no way to test shoot the actual items during a test as the are 'fire once' types of objects.

My hope was that I could send this camera to the facility with someone who is not familiar with photography but that is out of the question. I'm afraid I may have to travel to shoot these tests myself.

Thanks for the help. I'll post my test shots as soon as I get them.


Nikon1

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Re: Filming Rocket Testing - settings advice welcome.
« Reply #5 on: October 11, 2021, 08:37:15 AM »

My hope was that I could send this camera to the facility with someone who is not familiar with photography but that is out of the question.

 Well, yes. Id call that very optimistic. Shooting Highspeed-Stuff like that can already be challenging for People who actually know what they are doing, so just having a random Person operate the Camera would be a pretty risky bet unless you are very sure about your Exposure Settings being spot on. You still could try, but chances to get good resulting footage with Fire and Rockets involved and also just a single chance at actually getting the shot would be very low by just guessing exposure i assume.  .
 Also the 50 Feet cable seems pretty short. just did the math, and thats like 15 Meters. I casually carry a 5 Meter BNC Cable in my Camera Case at all times in case i ever need it, which is just so it wouldnt be to bulky to carry around. 15 Meters still is not what i would consider a "long" cable, so i was a bit surprised that you have not found a longer one yet, but maybe thats just a thing in Germany or something, but 50 to 100 Meters are still somewhat standard, even longer ones are actually rare, but do exist, as i wrote above.
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 And regards the Tests / Test Shots: I was very aware that your Rockets would probably be single use with only one chance to capture the Action, thats why i recommended to do two tests or more to really get your Exposure correct for that one Shot you want to be sure to capture at best possible settings. If you figure out the Settings for it, you should be able to get very reproducible results, no matter the Environmental Light or Camera Operator, given of course these Rockets are at least somewhat comparable in Brightness and all that.
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 Also depends on just how important it is to get the Shot here. If you shoot an explosion like the First Nukes ( Cost actually expressed in % of GDP and that exact experiment can not be redone ever again) i mentioned earlier or something that is as crazy unique as that, you want to be sure you dont mess up here and get the Shot, thats what i would call highly Critical. If you can redo it with at least somewhat reasonable effort, i wouldnt worry too much about running 100 Test Shots before, and maybe just Try it (testing still never hurts) and adjust exposure as i go on with testing.