Sensitivity, Lux and ISO

[romi]

Hi there,

My Q is as follows: How can one compare between the sensitivity of a DSLR camera (such as Canon 600D) and that of a CCTV

video cam (such as Mintron 12V6).

To have a practical situation, assume that the optics is the same (same lens etc.).

Now, let's assume that I take one frame with the DSLR with a 1 sec. exposure. Also assume that the setting was such that the ISO was 1600.

Let's also assume that under those conditions, the faintest star recorded is of (say) +4.

Here is what I am looking for: setting now the CCTV to 1/50, and integrating for 1 sec, what woud be the magnitude of the faintest star that I should expect to detect in the CCTV result.

Is there an analythical expression that can be applied here?

Thanks - at least for reading this up to this point.....

Romi

[shirva]

Intresting question that I don't know answer too....the dslr has a larger sensor to be able to catch more photons where the cctv can capture as if using a 6mm eyepiece. ..one for the tefal heads....lol...Davy

[johnno]

Setting Exposure Time

_______ _____________

x2 0.03 Second

x4 0.06 Second

x6 0.1 Second

x8 0.13 Second

x10 0.17 Second

x12 0.2 Second

x14 0.23 Second

x16 0.27 Second

x24 0.4 Second

x32 0.5 Second

x64 1.1 Second

x128 2.1 Seconds

x256 4.2 Seconds

x512 8.5 Seconds

Hi Romi, I don't know how to work it out but here are the exposure times for a cctv cam,

A 1 second exposure time is about X64 intergration, I think if you had fast optics at X64 it would be possible to capture bright DSO's at this level,

But like Davy said one of the other technical minded members would give you the right answer. I'm just a numpty that can just about switch it on and off...John

[romi]

thanks John and Davy,

Yes, a x64 is considered to revil some details for bright DSOs. No chance for that with DSLR at any ISO for 1 sec. That is

what triggered my curiosity in the first place...

[riklaunim]

Lux isn't much of use. It's specific to some used lens and testing setup. It's not absolute, nor directly comparable between two different cameras/lenses etc.

CCTV use 8-bit image and much higher gain than DSLR would typically use. That also makes it hard to compare DSLR and CCTV. Best way - test it experimentally.

[Macavity]

You might get *some* idea re. video cams from the following:

http://www.prc68.com/I/Mag.shtml

The magnitude example are for the (obsolete) Stellacam EX.

0.005 & 0.00005 lux in planetary / accumulation mode resp?

http://www.optcorp.c...deo-camera.html

So rather typical for similar cameras of the same generation?

According to me my Watec 120N+ is: 0.005 & 0.00002 lux

The latest WAT910HX is 4x better at: 0.001 & 0.000005 lux

(The first one to break the fifth decimal place barrier?)

Manufacturers can be a bit cryptic? Dealers a tad careless with specs?

Never sure about DSLRs. Pukka imaging cams deal in "quantum efficiency" etc.

[Peter Drew]

These lux ratings are usually expressed in terms of maxmum integration at F1.4, anyone using F1.4 optcs?

[shirva]

Think one of my cctv lens does but on a scope mmmm I'd be suprised...Davy..think what it comes down to really is what do you want to capture ...1 sec on the dslr on the 80mm could be minted but on a 200mm completely washed out on say the moon...now Ive only got a Canon 400d with no live view so click bang wallop you take a shot of say the moon and its a oops its a washout so you reset the camera timer/exposure and try again hey its close rest again wehey cracked it and batter off 50 exposure. ..how many can you use in dss,, a fraction. .....now that I'm a av convert camera on , instant live view or near enough, hit record couple of min later..you have tons of images too chose from to stack.....ok no in same league as the big boys toys but only get what you pay for...but and a big but the gear is getting better. ..know what they say rubbish in , rubbish out......