Telescope size observing via exposure

[Guest peepshow]

Say one can only just make out a DSO in a 'scope of say diameter D. 

 

I wonder what exposure time and at what ISO setting and f number of a lens would just be able to image the same object?  

Assume that the camera used as a stand alone and not imaging through the 'scope and taking a

single exposure, but tracking.

 

Is there any formula connecting these two? 

 

Kinda like........D = ISO *  x  +  f   +  time in seconds / y

Where x and y are constants of some kind.

[Tweedledee]

Well Richard, I'm going to have a stab at answering this with another question...

How long is a piece of string?

Someone may have a chance of putting a very rough formula together, but I think it would have far more variables, constants and unknowns than you have suggested. This would then give rise to more errors creeping in through the different ways people assess variables like sky conditions etc. I'm sure an imager would confirm that it is very difficult to predict the results in advance.

I would also think that it would be possible for you to do many trial and error exposures noting down every possible factor and building this into a rough formula or rule of thumb that at least works well for you, your equipment and your location.

That's my 2 pence worth

[Guest peepshow]

Well sky conditions will apply to both the visual scope and the camera.  Various types of filters would complicate matters but a simple formula can ignore them....just a a scope and a camera without any complications.

 

Let's take a 14 inch 'scope which can resolve up to about 16 mag I believe. (you will know the exact value, Pete.  )

 

Now, say we set up a tracking camera and took an exposure at ISO 800, which is about the norm.   If the lens were set at f16 and the exposure was 1/100 sec then nothing would be imaged.  But if we set the lens to f4 with a 10 minute exposure then mag16 objects will be there.  So somewhere between these two there is a spot where mag16 is just discernable  both in the 'scope and in the camera image.   That is where a simple formula would kick in as I see it.

[Tweedledee]

Let's take a 14 inch 'scope which can resolve up to about 16 mag I believe. (you will know the exact value, Pete .

Only if I take up Mount Teide in Tenerife

I like formulae, and look forward to seeing what you come up with. Good luck.