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10-15-2018, 03:00 AM   #12616
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QuoteOriginally posted by BostonUKshooter Quote
Cool image....did you do any FE correction in post?....the FE effect is minimal even on the towers on the rhs….
No corrections were applied, it was taken direct from the DNG (obviously keeping the horizon close to the middle and not having straight lines near the corners helped). I was trying the red filter out (newly acquired used lens) but it seems to have had a significant impact on IQ - I'll try and post a comparison without.


Last edited by johnha; 10-15-2018 at 03:00 AM. Reason: Typo
10-15-2018, 05:44 AM   #12617
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QuoteOriginally posted by johnha Quote
I was trying the red filter out (newly acquired used lens) but it seems to have had a significant impact on IQ
You might have more control using a channel mixer in post (present in PhotoShop and G.I.M.P., not sure about others).
10-15-2018, 06:15 AM   #12618
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QuoteOriginally posted by dsmithhfx Quote
You might have more control using a channel mixer in post (present in PhotoShop and G.I.M.P., not sure about others).
Yes, I've realised that (more likely to do so as part of raw development - possibly in-camera), I was testing the lens and curious as to how well the filter might work on my P6x7.

Below is a comparison with a similar shot taken with the 35mm FE a few minutes earlier from a slightly different position. Straight from the DNG without the red filter (see inset 100% crops from the DNG - no processing):



This is also without processing directly from the DNG which shows FE distortion towards the corners:

10-15-2018, 07:03 AM   #12619
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It's definitely sharper without the filter. Filtering a fisheye is tricky--the rear filters used with the Arsat 30mm lens are part of the formula, so a clear filter is required if no filtration is wanted. I've never used filters on my P67 fisheye, but in theory they should help a bit with the lateral color that lens suffers from. Lateral color is easy to fix in software, but not necessarily for fisheye lenses.

But a red filter will change the focus point slightly, too. Not a problem with film, but everything is visible when viewed at 100% on a monitor.

By the way, a red filter with that scene will darken everything down without much real tonal benefit--everything is blue on an overcast day. I realize you were just testing.

Rick "buildings and trees are tough subjects with a fisheye" Denney

10-15-2018, 09:31 AM   #12620
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A strong red (or blue) filter kills the resolution of any Bayer filter digital camera. It turns the 40 MpIx RGB sensor of the 645D into a 10 MPix monochrome sensor. (Green filters only kill about half the pixels)
10-15-2018, 01:22 PM   #12621
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QuoteOriginally posted by photoptimist Quote
A strong red (or blue) filter kills the resolution of any Bayer filter digital camera. It turns the 40 MpIx RGB sensor of the 645D into a 10 MPix monochrome sensor. (Green filters only kill about half the pixels)
Thanks photoptimist, makes sense after thinking about it.
10-15-2018, 01:48 PM   #12622
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QuoteOriginally posted by photoptimist Quote
A strong red (or blue) filter kills the resolution of any Bayer filter digital camera. It turns the 40 MpIx RGB sensor of the 645D into a 10 MPix monochrome sensor. (Green filters only kill about half the pixels)

The channel mixer has the same effect, I suppose, except that one doesn’t have to go all the way as with a saturated filter.

But I had indeed forgotten about the sensor array.

Rick “who sometimes uses saturated filters with vintage lenses and monochrome film” Denney
10-16-2018, 06:42 AM - 1 Like   #12623
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QuoteOriginally posted by photoptimist Quote
A strong red (or blue) filter kills the resolution of any Bayer filter digital camera. It turns the 40 MpIx RGB sensor of the 645D into a 10 MPix monochrome sensor. (Green filters only kill about half the pixels)
Wouldn't taking the digital picture in color and then using just the luminance data provide the desired B&W image, perhaps preceded by color channel tweaks to change the relative contrasts of different objects?

10-16-2018, 07:40 AM - 1 Like   #12624
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QuoteOriginally posted by kaseki Quote
Wouldn't taking the digital picture in color and then using just the luminance data provide the desired B&W image, perhaps preceded by color channel tweaks to change the relative contrasts of different objects?
Absolutely! A well-designed demosaicing algorithm will estimate the full-resolution luminance pattern implied by pixel-to-pixel variations in all three color bands to fill-in the missing patterns in each color band.

But if the photo is taken with a strong red filter on the lens, then there will be very little signal and detail in the green and blue pixel channels and little ability to estimate the red-channel details that fell on green and blue pixels.

Thus, it's probably better to shoot in full color with no filter and then post-process with the channel mixer to convert the RGB image into a color-filtered monochrome. The only exception is that channel mixing cannot exactly replicate all the spectral effects of a color filter on the lens. For example, a picture taken through an orange filter might be subtly different from a unfiltered color image mixed in post to simulate an orange filter. A true orange glass filter might provide stronger green versus yellow contrast than the unfiltered+post-processing can version offers.

Post-processing of the unfiltered RGB image might be good enough to create the desired effect. Yet some photographers might seek a truer color filtration that only a color filter can provide.

Note: for those who have (and can use) pixelshift, the results with a color filter will be at full resolution.
10-16-2018, 11:44 AM - 4 Likes   #12625
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10-16-2018, 12:36 PM   #12626
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The tonalities of this remind me so much why I loved using my Fuji 6x9. FYI, it's a weird fall here as well, with mostly everything still green, but some trees that dropped their leaves never turned colors. I saw this driving home from Cleveland through PA to Baltimore, and my sister in Wyoming has said the same thing.
10-16-2018, 02:36 PM   #12627
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QuoteOriginally posted by texandrews Quote
The tonalities of this remind me so much why I loved using my Fuji 6x9.
Do you still have your Fuji?
10-16-2018, 07:15 PM   #12628
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QuoteOriginally posted by photoptimist Quote
Absolutely! A well-designed demosaicing algorithm will estimate the full-resolution luminance pattern implied by pixel-to-pixel variations in all three color bands to fill-in the missing patterns in each color band.

But if the photo is taken with a strong red filter on the lens, then there will be very little signal and detail in the green and blue pixel channels and little ability to estimate the red-channel details that fell on green and blue pixels.

Thus, it's probably better to shoot in full color with no filter and then post-process with the channel mixer to convert the RGB image into a color-filtered monochrome. The only exception is that channel mixing cannot exactly replicate all the spectral effects of a color filter on the lens. For example, a picture taken through an orange filter might be subtly different from a unfiltered color image mixed in post to simulate an orange filter. A true orange glass filter might provide stronger green versus yellow contrast than the unfiltered+post-processing can version offers.

Post-processing of the unfiltered RGB image might be good enough to create the desired effect. Yet some photographers might seek a truer color filtration that only a color filter can provide.

Note: for those who have (and can use) pixelshift, the results with a color filter will be at full resolution.
I think I agree for what I consider to be the general case given some assumptions about the spectral responses of the pixels.

Gedanken experiment: If there were no overlap between green and red pixel spectral responses, a pure orange source emitting in the spectral gap wouldn't be detected, with or without an orange filter. An orange laser (Raman shifted green, say) illuminating a board in front of a luminous white background would appear in the image data as a black area against a white background, both in color and B&W. This indicates that some pixel spectral overlap is needed for reasonable raw performance.

Because a computer monitor having red, green, and blue pixels can emit an RGB combination that would look as orange as one might want, recreation of the orange board would depends on the photographer using his memory of the board's illumination color to recover it in PP by filling in the black area. The luminance data of the result should then represent a valid B&W representation (which could have positive or negative board contrast, depending on laser power).

A PP synthetic orange filter (if the physical filter's spectral response is known) could be imposed on the PP color image and the filtered luminance data that resulted could represent a valid expression of an orange filtered B&W scene. I suspect that this process could be very monitor dependent, even with calibration.
10-16-2018, 11:29 PM - 5 Likes   #12629
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That heron looking bird must have been familar with people for letting me get this close. I only got one shot before it flew off.

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10-17-2018, 04:35 AM   #12630
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QuoteOriginally posted by tuco Quote
Do you still have your Fuji?
No, I had to trade it in to get my 645Z (along with other beloved things...). But there was method to my madness: after years and years of holding its value, values had started to decline to the point where I knew I could pick one up again for not too much if I wanted. Values have gone up again a bit, but not too much. Also, in 2014 it was looking more dicey for the film I liked best. That has also now stabilized.


So, if I get into a position where I can more easily process my film, I'll maybe get another.
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