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 on: Today at 07:22:28 AM 
Started by stamper - Last post by stamper
Not far from home. Bowling harbour, on the river Clyde, Scotland.

 on: Today at 07:21:53 AM 
Started by keith_cooper - Last post by artobest
The best way of assuring this on the V750, though not essential once you have the frame properly adjusted, is to use the glass mount assembly and film cleaner to hold the film to the glass. The 850 is said to come with a special mount adapter.

This is the best way of achieving perfect focus on the Epson V750, used in conjunction with either T-locks or ANR glass, depending on the springiness or sagginess of the film. I love curled film strips, because I can use the T-locks to obtain perfect flatness, without extra glass and all the associated dust and problems.

From pictures I've seen, it appears Epson have upped the number of height adjustments on the film holders from 3 to 5. Is that right, Keith?

 on: Today at 07:21:14 AM 
Started by Kevin Gallagher - Last post by michael
Agreed. Adult discourse seems as elusive on this topic as on just about any other on this forum.

Thread closed.


 on: Today at 07:15:04 AM 
Started by Arlen - Last post by stamper
Nothing to forgive and a lot to like. Smiley

 on: Today at 07:13:46 AM 
Started by seamus finn - Last post by stamper
There is definitely a story here of hope and good fortune for the future. A "true" street scene. Well done!

 on: Today at 07:05:44 AM 
Started by Phil Corley - Last post by Dave (Isle of Skye)
Thanks Dave.  Hopefully your weather will improve as I am up there tomorrow for the week :-)

Well I know you wanted some active weather during your visit to Skye Phil and that is exactly what is being forecast right through until at least this coming Sunday, with high winds and horizontal rain due to the after effects of hurricane Gonzalo and the ongoing cyclonic weather formations barrelling into us from across the Atlantic, that Gonzalo seems to have set in motion.  Sad

So in this case and I do hope I am wrong, but for the coming few days I think Bill might be right and you will definitely be needing your "Photoshop Scottish Blue Sky plug-in"  Wink

I'm happy just enjoying such a lovely photo without having to worry about weather or midges.

The midges finished really early this year due to a cold snap we had in late August, so we have been midge free for months already, which is nice  Wink


 on: Today at 06:30:16 AM 
Started by seamus finn - Last post by petermfiore
A nice one.. Somehow I feel unsettled with their world and yet hopeful.


 on: Today at 06:22:33 AM 
Started by seamus finn - Last post by seamus finn

 on: Today at 05:45:26 AM 
Started by Here to stay - Last post by BartvanderWolf
I am I correct to assume that the maximum resolution( I really should be calling it contrast) that a lens and sensor can resolve is at the point  a lens projects an Airy Disk size at which the sensorís pixels pitch can accurately measure the size, brightness and location of that disk in an image?


That's hard to answer for several reasons, one of which is that the diffraction pattern is not of limited/fixed size. We usually refer to its diameter as the diameter of the first zero (ring) of the Airy disk pattern, which represents something like 83.8% of the total intensity of the pattern, and is not uniform across its diameter (so alignment with the sensel grid also plays a role).

What we do know is at which spatial frequency the diffraction pattern of a perfect circular aperture will reduce image contrast (MTF) to zero amplitude, for 555nm wavelength:
cy/mm = 1 / (wavelength x aperture) , e.g. 1 / (0.000555 x 8) = 225.2 cy/mm
and it takes (more than) one full cycle to allow reconstruction of the original waveform (225.2 / 2 =112.6 mm, or 1/0.00888mm, or 8.88 micron feature size).

We also know that the sensor array has a limiting resolution of maximum:
Nyquist frequency in cycles/mm = 0.5 / senselpitch, e.g. 0.5  / 0.00488 = 102.5 cy/mm

We can therefore calculate the Aperture at which resolution will be totally eliminated by diffraction, and will prevent all aliasing, by reducing contrast to 0% at the Nyquist frequency:
Aperture = senselpitch / wavelength, e.g. 0.00488 / 0.000555 = f/8.8

However, that is only taking diffraction (of a single wavelength) into account. Diffraction, will in practice be combined with the MTFs of residual lens aberrations, a less than perfectly round aperture, defocus (anything not in the thin perfect focus plane), a filterstack with or without AA-filters and a sensor coverglass, and a Bayer CFA pattern that needs to be demosaiced. The diffraction pattern size also changes with focus distance, so the above formula is based on infinity focusing.

So resolution will be totally limited at wider apertures than that for diffraction alone. It is also not simple to calculate, because there are positive and negative wave contributions that will cause interference patterns that may or may not align locally with the sensel grid.

The only thing we do know for certain, is that the absolute diffraction limit to resolution will not be exceeded (if even reached). Instead, the overall image will already deteriorate before that limit is reached by stopping down. It is only high contrast detail that will even theoretically reach that limit, lower contrast features will have lost significant modulation long before that. That's why limiting resolution is often set at lower spatial frequencies, e.g. MTF10 or Nyquist whichever is reached first. It also explains why even lower spatial frequencies, MTF50 are often used to give an overall impression of average performance for comparisons between different systems.


P.S. Using smaller sampling pitches than can be resolved from a diffraction limited image, still brings a benefit, because the diffraction pattern is not uniform. So smaller sensels allow to more accurately sample the diffraction patterns that are larger than single pixel, and thus allow more accurate deconvolution restoration of the original signal.

 on: Today at 05:44:35 AM 
Started by Bob_B - Last post by k bennett
I'm not clear on whether you already have the speedlights.

If not, the new 600EX-RT speedlights are pretty awesome. They use built-in radio instead of infrared for TTL and manual settings. The little transmitter sits on top of the camera. It's not a cheap kit, but it's less expensive than a Canon speedlight + a Pocket Wizard.

There are some restrictions on using them with older cameras, though.

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