Blurry Jpegs with B+W Red Filter attached on lens

[Olivier76]

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Hello

I just received couple of filters I wanted to try on my M8.2 / Voigtlander 28mmF2 Ultron for B&W photogrphy.

Yesterday I went on the beach setting the M8.2 in Jpeg Fine. Did couple of photos with and without filter. When back home, all pictures taken with the Red Filter (B+W) where not sharp at all, when the photos without had no issue. 

Today, I made sure the filter was clean, set up the camera in DNG+JPEG Fine with the red filter. The DNG files have no issue, perfectly sharp but the Jpeg are blurry... 

Do you think the M8.2 is somehow downgrading sharpness to compensate the red color ?

Is there somebody who have this Issue.

Just curious as I shoot in DNG 99% of the time.

Cheers

[a.noctilux]

Hello Olivier,

Red filter (deep red) was mainly used in film day with false color IR film.

Two things to be aware of : focus point of red is not the same as other colors, compensation of the "focus distance on lens" can be learned.

The discrepencies depend on lens construction, so trying out with your M8+28mm+red filter can be easy.

First in far set the aperture to f/5.6 or f/8, then set the focus ring "infinity mark" in front of the f/5.6 marking, then try if the sharpness is better.

Then closer with same set up : rangefinder to say 2m, then set the 2m marking in front of the f/5.6 to see if the sharpness is better.

Experimentation with digital M is the best way to well know the gear.

 

As side note, the LCD of my M8 has difficulty to show "sharpness" when I zoom in.

With computer screen, the less sharp pictures (seen on the M8 LCD) can be "better view" 😉.

 

Arnaud

Edited November 1, 2020 by a.noctilux

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[jaapv]

+1 - We  should make this a FAQ. It is  worth to note that the focus shift is lens-dependent. The Ultron has quite a bit of chromatic aberration, so it is quite susceptible. The best solution is to focus-bracket.

[BrianS]

The IR absorbing cover glass of the M8 has a 5% leakage. Using a Red filter on the M8 leaves the Blue and Green channel sensitive to IR only. The difference in focus point of the IR portion of the spectrum is large even compared with that of the Red channel. You are getting a soft IR overlay on top of the image.

To test this with your lens, use the Red filter and an IR blocking filter both on the lens.

 

My experiments with the M8 and color filters-

https://cameraderie.org/threads/experiments-in-leica-m8-and-m9-conversions.38737/

 

From my test, 3 images from that thread.

Visible image;

Red Filter;

Processed image using my own code. Blue and Green are equalized to the red channel, meaning the IR is boosted.

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Edited November 1, 2020 by BrianS

[farnz]

Adding a red filter might reduce your shutter speed if shooting on auto so the lack of sharpness could be caused by a low shutter speed and camera movement.

Pete.

[jaapv]

On the M8, the leakage is more like 20-30 %. 

[tommonego@gmail.com]

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If you were using f2 or f2.8 the red shift could make the bluriness with all that has been said before. It would help to show us the DNG and jpegs of the image. 

[Jeff S]

As a secondary point, I never saw the benefit of color filters on any digital M other than the Monochrom(s). And even then, red is too extreme for my needs and tastes. I realize this doesn’t answer the OP’s question (guessing it’s red focus shift), but I am curious about the OP’s use case.

Jeff

[BrianS]

The leakage is 5% up to 1uM, 10% last that- but the KAF-10500 is not very sensitive in that range. The cover glass for the M8 is about the same as the cover used for the meter.

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[farnz]

18 minutes ago, BrianS said:

The leakage is 5% up to 1uM, 10% last that- but the KAF-10500 is not very sensitive in that range. The cover glass for the M8 is about the same as the cover used for the meter.

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Interesting.  The filter's character is more Butterworth filter (approaching flat in the passband) than Chebychev filter (steep roll-off).  

There's good steep roll-off between the visible blue and ultraviolet spectra but much gentler roll-off between visible red and infrared bands.  Since the roll-off starts at around 520 nm quite a lot of the usable visible red spectrum is attenuated (suppressed) - the bit above the line between, say, 600 and 700 nm and up to 1 - which is quite a large chunk.   The combination of the suppressed visible red and the bleed-through of infrared (above 720 nm) is likely to be the cause of the infrared contamination that lead to needing to use UV/IR filters to suppress magenta in black fabrics etc.

I don't believe the characteristic curve of the cover glass of the Kodak KAF-10500 sensor shown above (no disrespect aimed at you, Brian) because it shows 0% Transmission above about 800 nm but I have been happily taking pictures with my M8 for more than 10 years with an infrared pass filter that blocks all wavelengths below 850 nm.  If the cover glass response was as shown and 'flat' at 0% above 800 nm then I wouldn't be able to do what I have already done.

Pete.

[pippy]

I posted some results of using a red filter a few weeks back. The quick answer is that with a deep red filter the 'correct' focus is reached when the actual lens distance is lined up almost exactly where an Infra-Red index mark would be...

Philip.

EDIT : Here's the thread. My examples are in post #8. Please not that the crops are at 150% (not 100%) which is why they are a bit pixelated.

https://www.l-camera-forum.com/topic/313352-monochrom-type-i-and-color-filters/

 

Edited November 2, 2020 by pippy

[adan]

On 11/1/2020 at 2:01 AM, Olivier76 said:

The DNG files have no issue, perfectly sharp but the Jpeg are blurry... 

Just a point - the OP wants to know why his .jpgs are fuzzy - but his .DNG files are sharp.

Doesn't that rule out all the comments regarding red wavelengths and IR compensation?

[BrianS]

4 hours ago, farnz said:

Interesting.  The filter's character is more Butterworth filter (approaching flat in the passband) than Chebychev filter (steep roll-off).  

There's good steep roll-off between the visible blue and ultraviolet spectra but much gentler roll-off between visible red and infrared bands.  Since the roll-off starts at around 520 nm quite a lot of the usable visible red spectrum is attenuated (suppressed) - the bit above the line between, say, 600 and 700 nm and up to 1 - which is quite a large chunk.   The combination of the suppressed visible red and the bleed-through of infrared (above 720 nm) is likely to be the cause of the infrared contamination that lead to needing to use UV/IR filters to suppress magenta in black fabrics etc.

I don't believe the characteristic curve of the cover glass of the Kodak KAF-10500 sensor shown above (no disrespect aimed at you, Brian) because it shows 0% Transmission above about 800 nm but I have been happily taking pictures with my M8 for more than 10 years with an infrared pass filter that blocks all wavelengths below 850 nm.  If the cover glass response was as shown and 'flat' at 0% above 800 nm then I wouldn't be able to do what I have already done.

Pete.

Pete- this chart is from the Kodak Data Sheet for the KAF-10500. Saved from the PDF file. The numbers shown for transmission show almost 10% for the longer portion of the spectrum. The curve shown- does not agree with the numbers, perhaps the light source used for the measurement.

 

The cover glass for the KAF-10500 does not corrode, the chemistry is much different from that used in the M9. But- the glass does not have a sharp cutoff for IR,

[BrianS]

The DNG files record raw numbers, JPEG most likely attempts to balance the color channels. Perhaps it is boosting the Blue and Green channels, which mostly have Infrared in them. The IR is out of focus compared to visible. Having a 100% crop of the JPEG image and the post-processed DNG file would help determine the issue. Also knowing what processing was applied to the DNG file to view it would be helpful.

The White Balance sensor will measure the entire spectrum without regard for the Red filter. 

Edited November 3, 2020 by BrianS

[Pintpot]

This one is a single shot IR with deep red filter, M8 + 28mm Elmarit reprocessed as HDR 

 

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Edited November 24, 2020 by Pintpot
More information

[Stephen.s1]

try a smaller aperture opening...

I seem to recall something about a focus difference with IR.

[Stephen.s1]

oops.. didn't notice all the other responses..  Delete the above. 

 

 

[BrianS]

Your IR image is a good example of how much leakage comes through with the M8.

[Olivier76]

Thank you for all your answers. Indeed I was speaking of exact same pictures DNG and Jpeg. When seeing the difference, no edit were done. Interesting observation BrianS

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