Re: Takumar Pentax 6x7 tests RE: [ap-gto] [ap-ug] A colorful Southern Sky Beauty


Richard Crisp
 

SNR can be increased by taking more and longer exposures as long as the exposure doesn’t saturate

You continue to win using longer exposures if your dark signal from the longer exposure has less shot noise than the single exposure’s read noise: once the dark shot noise exceeds the read noise, longer exposures will reduce the SNR. Cooling controls this.

Multiple images stacked imposes no limit to how low you can drive the noise in the stack, thereby increasing the SNR up to the point of zero noise (unachievable)

Sorry but that’s how it works


“Corrected” by my iPhone

On May 1, 2021, at 1:18 AM, ayiomamitis <anthony@...> wrote:



Rolando,

I am not sure I agree here. We both know that an easy and effective method to increase S/N is to stack multiple images. As for aperture impacting light flux, I would agree here for objects with a low surface brightness but, again, we have many targets where aperture (and absolute light flux) is not necessarily the only solution.

Anthony.

On 01-May-21 02:23, Roland Christen via groups.io wrote:
F-ratio means nothing. Aperture is the deciding parameter that determines light flux arriving at the detector. More light = more signal to noise.

Rolando



-----Original Message-----
From: ayiomamitis <anthony@...>
To: main@ap-ug.groups.io
Sent: Fri, Apr 30, 2021 5:05 pm
Subject: Re: Takumar Pentax 6x7 tests RE: [ap-gto] [ap-ug] A colorful Southern Sky Beauty

Rolando,
Why shoot wide open (say f2.8) when our astrographs are f4 or slightly slower? I would rather see results at such f-ratios (ex f4 to f6.3) so that results can be that much more comparable.
Anthony.
On 01-May-21 00:48, Roland Christen via groups.io wrote:
Try shooting stars wide open with a color digital chip. You will see the limitations. I wish I had kept the result of my 90mm F2.8 Pentax lens - you would not believe how bad it is wide open.

Rolando

-----Original Message-----
From: Richard Crisp <rdcrisp@...>
To: main@ap-ug.groups.io; robert-wynne@...
Sent: Fri, Apr 30, 2021 3:28 pm
Subject: Takumar Pentax 6x7 tests RE: [ap-gto] [ap-ug] A colorful Southern Sky Beauty

Some years back I did some tests of a handful of Pentax6x7 lenses I had picked up on the cheap
 
Even though they aren’t very well corrected over an electronic imager’s broad spectral responsivity, it seemed if you stopped them down, used a single wavelength filter with a mono sensor, you could get pretty decent results
 
You might find the slide deck useful that I made
 
 
I was using an FLI ML4022 camera (KAI series sensor w/7.4 micron interline pixels).

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