Esprit 100ED or RASA 8"

[andrew s]

15 minutes ago, vlaiv said:

Ah, that is where I disagree. Speed is not determined by aperture alone. You showed in the rest of the post that achieved SNR depends on photon / pixel "concentration".

That one is governed by relative pixel size, which can be "changed" in a few different ways for given aperture.

1. Change of physical pixel size - use camera with larger pixels

2. Shortening of focal length for same pixel size - use of reducer

3. Use of binning - which is in some respect the same as 1. but a bit different in terms of things we decided to neglect for this discussion.

So, having a patch of target with uniform brightness - system with reducer in place (having same aperture and same pixel size) - will reach target SNR in less time. It will be faster. That is not the only way you can go about that - you can bin and result will hit target SNR in less time, or you can exchange camera for one with larger pixels (otherwise equal) - and it will also reach SNR in less time.

All three trade sampling rate for speed, each one being slightly different in details we've choose to neglect here

Your right. I should have added the qualification "at a given resolution"  the speed is governed only by aperture.

Regards Andrew 

[newbie alert]

On 07/04/2019 at 20:24, Datalord said:

As such, comparing an f/10 to an f/2 at same aperture is complete nonsense

If this was aimed in my direction then i was pointing ou the relevence of fl on f ratio..if I'd changed the aperture and  kept the fl then that would be even more nonsense ..

[Datalord]

2 hours ago, newbie alert said:

If this was aimed in my direction

Not at all, it was in the context of the quote right above the sentence from @ollypenrice

[ollypenrice]

2 hours ago, newbie alert said:

If this was aimed in my direction then i was pointing ou the relevence of fl on f ratio..if I'd changed the aperture and  kept the fl then that would be even more nonsense ..

To clarify my own position (since I'm mentioned in the conversation?) if you change the aperture and keep the focal length you can meaningfully compare the results because they will be results on the same target. Within reason there will be a real world gain in both speed and resolution with more aperture. Does 'within reason' describe all ultra-fast optical systems on the market? In my view, no, but nobody is obliged to concur!

Olly