Pictures: 28mm f/1.4 Nikkor-D on IR a7

I don’t know if you’re tired of looking at pictures of bookcases and test charts, but I’m tired of making them. So, for a little break, here are some IR pictures with the LifePixel-modified Sony a7 and the 28mm f/1.4 Nikkor-D. The camera has LifePixel’s “Super COlor” filter, which passes some visible light in addition to the IR. For some of these images, I used a 830 nm lowpass filter over the lens, resulting in IR-only images. For others, I used the whole spectral  range of the modified sensor.

I was lucky to encounter what Fred Picker used to call “squall light”, which occurs when the sky is cloudy, the sun low, and there’s a break in the clouds right where the sun is. It only lasted about 15 minutes, so I had to work fast.

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Sony a7II IBIS with a 16mm lens

A reader asked if I’d test the in-body image stabilization (IBIS) on the Sony alpha 7II with a really short lens, to add to  the testing I’ve done previously with a 180mm Apo-Telyt and the Zony 55mm FE and the Leica 28mm f/2.8 Elmarit-R. I selected the Leica 16/18/21mm f/4 Tri-Elmar, aka the WATE. Sony calls IBIS SteadyShot.

I employed the following protocol:

  • The camera: the Sony a7II.
  • The lens: the Leica WATE, with a Novaflex M to E adapter, set to 16mm.
  • The target: Imatest slanted edge with Siemans star for focusing.
  • No filter.
  • The lighting: a single Fotodiox LED-200WA-56 daylight balanced variable-output flood.
  • ISO set to 400, f/8, to minimize the effect of manual focusing errors.
  • Focusing manually at f/4, using the magnifier. The focus point as a Siemens star on the target.
  • Drive set to single
  • EFCS on
  • Manual exposure mode.
  • Hold the camera in the “Pete Souza” grip: left palm under base, left fingers bracing the underside of the front part of the lens, elbows against chest. With the WATE, you have to be careful to keep your fingertips out of the picture.
  • Exposure protocol: LED light to full, shutter to 1/60 second, make 16 exposures, turn the light down a stop, make 16 exposures… until you get to 1/8 of a second.
  • Develop in Lightroom 5.7.1 with standard settings.
  • Crop, export as TIFFs, analyze for horizontal edge and vertical edge MTF50 in Imatest.
  • Export the results to Excel, crunch the stats, and graph.

First, with IBIS off, looking at the horizontal edges:

WATE MTF IBIS offb

Then with it on.

WATE NTF IBIS ona

Finally, with both of the results sets on the same plot:

WATE MTF IBIS botha

It’s clear that IBIS helps a lot. As with the 28mm lens, 1/(half the focal length in mm) is eminently usable, and better than 1/(twice the focal length in mm) without IBIS.

However, at 1/4 second, IBIS isn’t much help at all. Is is possible that it runs out of travel at that shutter duration and my body motion. It’s also possible that translation, which it can’t correct for in lenses that don’t tell it the subject distance, becomes too big a factor at that shutter speed.

It’s a small effect, but we saw it in the case of the 28mm lens, and we see it here: at high shutter speeds, IBIS might actually hurt a little. I wouldn’t worry about it.

Sony a7II 12-bit mode’s effect on shadows

When you change shutter modes on the Sony alpha 7II, you may affect the bit depth. Because of the raw compression algorithm on this and all the other alpha 7 cameras, which is not defeatable, I need to go into a little detail about just what bit depth I’m talking about.

The raw compression scheme is to take the linear output of the analog to digital converters (ADC), which is either 12 or 13 bits, apply a nonlinear digital tone curve (kind of like gamma encoding) and resample the now-nonlinear signal at 11 bits. The camera then uses a delta modulation scheme to reduce the data necessary to encode the raw file to an average of 8 bits per pixel.

When the shutter is not set to bulb, and the shutter mode is set to continuous drive, speed-continuous drive, continuous bracketing, A7s’s silent shutter, and any possible combination of these, the linear, pre-tone-curve, bit depth of the camera is 12 bits. With all other settings, including single bracketing, the linear bit depth is 13 bits.

The loss of precision associated with the affected shutter modes causes an increase in the read noise by about one stop, a decrease in the dynamic range by about a stop, and more shadow noise, as can be seen in this photon transfer curve of the a7II’s performance in the two modes:

a7ii PTC SS CS

The above curve is for ISO 100, where the effects are the greatest, since there is little analog read noise to dither the ADC.

Does this change in the photon transfer curve cause visible effects in images? I set out to learn about that.

I put a Leica 28mm f/2.8 Elmarit-R on the camera with a Novoflex adapter, mounted the camera to the RRS generic plate (the L-bracket isn’t yet available), the bracket to an Arca-Swiss C1 head, the head to a RRS tripod, aimed the camera at the bookcase I usually use for this test, set the f-stop to f/8, the shutter to 1/50 second, the ISO to 3200, the shutter to single shot, and made an exposure. Varying nothing but the ISO setting, I made five more exposures at ISO 1600, 800, 400, 200, and 100.

Then I put the shutter in continuous slow mode and did the same thing.

I developed the images in Lightroom 5.7.1 with default settings except for turning off sharpening and noise reduction. Then I set the Exposure control on the ISO 100 image to an extra +5, the Exposure control on the ISO 200 image to an extra +4, the Exposure control on the ISO 400 image to an extra +3, the Exposure control on the ISO 800 image to an extra +2, the Exposure control on the ISO 1600 image to an extra +1, and didn’t adjust the Exposure of the ISO 3200 image.

I cropped the images and magnified them by a factor of twp.

The results:

ISO 100 Continuous

ISO 100 Continuous

ISO 100 Single Shot

ISO 100 Single Shot

There is quite a bit more noise in the continuous case.

 

ISO 200 Continuous

ISO 200 Continuous

ISO 200 Single Shot

ISO 200 Single Shot

The single shot is better, but not by much. The extra noise is providing useful dither.

ISO 400 Continuous

ISO 400 Continuous

ISO 400 Single Shot

ISO 400 Single Shot

I don’t see much difference at all.

The ISO 800 and 1600 exposures continue the trend. Here are the ISO 3200 exposures:

ISO 3200 Continuous

ISO 3200 Continuous

ISO 3200 Single Shot

ISO 3200 Single Shot

No difference.  By the way, don’t read too much into the color balance differences in the above images. I left the WB in Lr set to “As shot”. My bad.

OK, what if we do the same series, but this time start at ISO 12800 and go to ISO 400, with the shutter set to 1/200. This time I’ll make the WB the same.

Here are the five stop pushed images:

ISO 400 Continuous

ISO 400 Continuous

ISO 400 Single Shot

ISO 400 Single Shot

There’s not as much difference as in a five stop push at lower ISO, but the single shot image is still a bit better.

28mm f/1.4 Nikkor-D on Nikon D3x in deep IR

A couple of days ago, I tested the MTF vs f-stop of the 28mm f/1.4 Nikkor-D mounted on a IR-modified Sony alpha 7. At the time, there was some discussion as to why the lens delivered the best IR-only results at f/2.8. Jack Hogan speculated that it might be something with the adapter. I checked and found that the lens uses internal floating elements, which could be flummoxed by a too-short adapter, which left me agreeing with Jack.

I couldn’t just leave it there. I had to test my assumption.

Here’s the protocol:

  • Nikon D3x, modified by LifePixel with the “Deep IR” filter
  • 28mm f/1.4 Nikkor D
  • RRS L-plate
  • Landscape orientation
  • Arca Swiss C1 head
  • RRS TVC-44 legs.
  • Imatest SFRPlus target
  •  I focused the lens using live view at the taking aperture for one series and focused at f/1.4 for the other one.
  • Paul Buff Einstein strobe set to 10 watt-seconds, for the f/2.8 shots, 20 ws for the f/4 ones, 40 ws for the f/5.6 ones, following that progression until I got to f/16.
  • Mirror up mode, remote release
  • Images developed in Lightroom 5.7.1 with default settings, exported as TIFFs
  • measured on-axis MTF50 for horizontal edges.

The results:

D3x deep IR MTFa

There doesn’t seem to be any focus shift. Focusing wide open works as well at small apertures, and better at the widest ones.

F/2.8 still offers the best performance

I don’t think we can blame the adapter for the earlier data.

If I put a 830 nm lowpass filter on the lens and put it on the a7, we can get something to campare against the D3x results:

a7 D3x deepIR MTFa

 

The D3x has higher resolution. That’s because its AA filter is weaker.

Here’s the D3x:

F14f028-1_YB10_01_cpp

And here’s the a7:

R72F028-6_YA10_01_cpp

Note the zero in the a7 image at 0,6 cy/px. That’s what AA filters typically do.

 

Sony a7II IBIS with 28mm lens

A reader asked if I’d test the in-body image stabilization (IBIS) on the Sony alpha 7II with a shortish lens, to bookend the testing I’ve done previously with a 180mm Apo-Telyt and the Zony 55mm FE. I picked the Leica 28mm f/2.8 Elmarit-R, which has shown strong sharpness in previous testing. You won’t find the acronym IBIS in and Sony literature; they call the feature SteadyShot.

I employed the following protocol:

  • The camera: the Sony a7II.
  • The lens: the Leica 28mm f/2.8 Elmarit-R, with a Novaflex R to E adapter.
  • The target: Imatest slanted edge with Siemans star for focusing.
  • No filter.
  • The lighting: a single Fotodiox LED-200WA-56 daylight balanced variable-output flood.
  • ISO set to 400, f-stop set to 8, to minimize the effect of manual focusing errors.
  • Focusing manually at f/2.8, using the magnifier with IBIS on (even at 28mm, this makes a difference). The focus point as a Siemens star on the target.
  • Drive set to single
  • EFCS on
  • Manual exposure mode.
  • Hold the camera in the “Pete Souza” grip: left palm under base, left fingers bracing the underside of the front part of the lens, elbows against chest.
  • Exposure protocol: LED light to full, shutter to 1/125 second, make 16 exposures, turn the light down a stop, make 16 exposures… until you get to 1/8 of a second.
  • Develop in Lightroom 5.7.1 with standard settings.
  • Crop, export as TIFFs, analyze for horizontal edge and vertical edge MTF50 in Imatest.
  • Export the results to Excel, crunch the stats, and graph.

First, with IBIS off, looking at the horizontal edges:

a7ii28IBIS offa

Then, with IBIS on (note the vertical axis is different):

a7ii28IBIS ona

And, finally, with both of the results on the same graph:

a7ii28IBIS botha

In the graph with both sets of curves on it, the blue lines are with IBIS off, and the orange ones are with it on. The thick lines are the average ofthe MTF50s for each set of 16 images, and the thin lines are the average plus and minus one standard deviation. My take is that IBIS is at least as effective for short lenses than for long ones.

A few specifics:

  • As with the longer lenses, the most confidence-inspiring thing about IBIS is not how much it helps the average image, but the huge improvement in the spread of the results.
  • The average image is improved by about two stops.
  • The average minus one sigma image is improved by about two and a half stops.
  • With IBIS on, the tightness of the standard deviation is almost as good at 1/15 second as it is at 1/125.
  • There is no statistically significant difference in the performance with and without IBIS at 1/125 second.
  • Although the average sharpness at 1/60 second is the same with IBIS on or off, the variance is much less with it on.
  • 1/half the focal length appears to work well with the 28mm with IBIS on.

Color me impressed.

 

Nikon 28mm f/1.4 D on Sony a7 in infrared and mixed light

I tested the 28mm f/1.4 Nikkor-D on the Lifepixel-modified Sony alpha 7. The Lifepixel filter I chose was the Super Color one, which passes some visible light. That makes the job of focusing more difficult for the lens, since it needs to simultaneously bring visible and infrared light to the same focus point. The Coastal Optical 60mm f/4 that I tested earlier is designed specifically to do just that. The Nikon 28 that I’m testing now make no such pretensions. It has a little dot on the barrel indicating the infinity focus point for IR; it appears to be about where the f/8 depth of field marker would be if there were one. You could conclude that stopping down the lens to f/8 or so would allow enough depth of field to simultaneously focus IR and visible light. Of course, the zone of sharpness would still be different for the two parts of the spectrum, so that wouldn’t be a complete solution.

I made two series of tests to see what I could find out about this. I made the first one with no filter over the lens, and another with a visible-light-blocking R72 filter.

I mounted a RRS L-plate to the a7, clipped it in landscape orientation into an Arca Swiss C1 head which was attached to a set of RRS TVC-44 legs. When focusing, I lit an Imatest SFRPlus target with a Fotodiox LED flood, which, like the strobe I used for the photographs, is balanced for 5500K. However, I don’t know the relative mix of IR to visible light for the two sources. If there’s less IR in the LED source, my focusing will be more weighted towards getting visible light sharp. If there’s more IR in the LED source, the situation will be reversed.

There are a few unknowns. Ignoring them for the time being, I blithely pressed on.

I focused the lens at the taking aperture for series without the filter, but the light was too dim to do that when the filter was on the lens, so I focused at f/2.8 for that series. For the exposures, I turned off the LED source, and lit the target with a Paul Buff Einstein strobe set to 2.5 watt-seconds, for the f/2.8 shots, 5 ws for the f/4 ones, 10 ws for the f/5.6 ones, following that progression until I got to f/16. At least that’s what I did for the pictures without the r72 filter. For the ones with the filter, I turned up the strobe power by two stops, I set the ISO to 100, the shutter speed to 1/125 second, the shutter mode to 3-second delay and electronic first curtain shutter (EFCS). I made both series with the target centered.

I developed the images in Lightroom 5.7.1 with default settings, exported them as TIFFs, and measured on-axis MTF50 for horizontal edges.

The results:

a7ir 28,, Nikkor R72 and not

The blue lines are for the exposures through the R72 filter, and the orange lines are for the images made with no filter. It looks like f/8 is indeed the aperture needed to allow the depth of focus to smear over the difference between the visible and infrared light focus planes, Past that point, the greater diffraction of infrared light versus visible light makes the case with the R72 filter slightly, but not materially, sharper. I’m thinking that, for lansscapes with some depth to thm, that f/11 is probably the sweet spot for the no-filter case, and f/8 with the R72 filter.

Focusing strategies for the 28mm f/1.4 Nikkor D on a Sony a7II

Jack Hogan suggested that some of the unusual results for the Nikon 28mm f/1.4, and possibly the Leice 28mm Elmarit-R, might be due to focus shift, since I did all my focusing at f/2.8.

Here’s a test with the Nikon lens. I did one 96-shot series (16 shots each at 6 f-stops) focusing as before. I changed the orientation of the edge that I’m using from horizontal to vertical just to get another look.

Then I did another series, focusing once at the taking aperture. I thought I would have to focus each image independently, but I was able to obtain accurate focus on the Siemens star on the target by using a bright focusing light (turned off for the actual exposures so that it wouldn’t contribute to the exposure). I had been focusing using the modeling light on the strobe, but that just wasn’t repeatable at small apertures. I used different amounts of focus peaking at different apertures, and could see just from that that f/2.8 was the sharpest aperture, but not by much.

By the way, the vertical elements of the SIemens star lit up like a Christmas tree while he horizontal elements remained dark. But we know that the AA filter on the a7II is anisotropic the other way. That leads me to believe that the focus peaking in the camera is strongly tuned to be sensitive to vertical lines, and is relatively insensitive to horizontal ones.

The results:

Nikon 28 2 focusing strategies

The blue curves are for focusing at the taking aperture, and the orage ones are for focusing at f/2.8. The remarkable alignment of the f/2.8 results is not because I dry-labbed them and used the same data; each is the result of its own set of 16 exposures. The thin lines are at the mean pous and minus three standard deviations.

It looks like there is focus shift at f/4 through f/8. It’s not bad, but it’s there. This is not a happy development for me, since I can’t reliably focus at the taking aperture in the field under most circumstances. I guess I could carry around a focusing target. Hmmm…

For reference, here are the curves from the previous post:

nikon 28mm mtf

The shape of the orange curve on the graph immediately above should be the same of the blue curve on the top graph. It isn’t.

I went back and did the calculations for the same horizontal edges:

Nikon 28 2 focusing strategies. H

 

That doesn’t explain it. It looks like there’s some difficulty achieving the same setup, even though the three-sigma lines indicate tight repeatability. Of course, they only apply within a given setup.

The big surprise of the first round of testin was the f/2.8 was the best aperture for the lens. That held up, but barely, and f/4 is in a virtual dead heat. Actually, from f/2.8 though f/11, there’s not enough difference to matter in the field. Even f/16 is eminently usable.

3 28mm lenses on the Sony a7II

The Coastal Optical 60mm is a great lens for infrared, but it’s too long for a lot of landscape use. I’m shooting handheld around the house, and I don’t like to do double-row stitches that way. So I’m looking for something wider.

28mm is a nice focal length for landscape. It’s probably the most versatile wide angle lens for me. Why not the 35? I don’t have anything against that focal length; I just don’t consider it a wide angle lens. The diagonal of the 35mm format is 43mm, so 35 is a wide normal lens, and 50 is a long normal lens, the way I look at it.

I set out to test three candidates. I will eventually get around to testing them in the infrared, but I’m waiting for some filters to arrive. I figure if they’re bad in visible light, they won’t be any good in IR, and if they’re good in visible light, they might be good in IR.

The first lens is the Leica 28mm f/2.8 Elmarit-M ASPH. This is truly a long shot, since it’s had bad corner smear on every alpha 7 camera I’ve tested it with.  The next is its R-series brother, the Leica 28mm f/2.8 Elmarit-R. The M-series lens is of 2013 vintage, with all the fancy stuff that modern optical engineers can do. The R-series lens is from the 1980s. The third lens is also an older one: the Nikon 28mm f/1.4 D. This lens has a great reputation, and, after Nikon discontinued it, sold on eBay for way more than its original sale price.

The test protocol:

I mounted a RRS L-plate to the a7II, clipped it in landscape orientation into an Arca Swiss C1 head which was attached to a set of RRS TVC-44 legs. I focused all the lenses at f/2.8. I lit an Imatest SFRPlus target with a Paul Buff Einstein strobe set to 2.5 watt-seconds, for the f/2.8 shots, 5 ws for the f/4 ones, 10 ws for the f/5.6 ones, following that progression until I got to f/16. the narrowest opening shared by all three lenses. I set the ISO to 100, the shutter speed to 1/125 second, the shutter mode to 3-second delay and electronic first curtain shutter (EFCS). I made a series with the target in the center, and one with the target in the upper right corner, focusing on it in each location.

I developed the images in Lightroom 5.7.1 with default settings, exported them as TIFFs, and measured on-axis MTF50 in both the vertical direction — horizontal edges.

The M-series Elmarit:

LeicaM28mm

The center is pretty good, but the corners are awful at wide apertures, becoming acceptable at f/11, where the center is beginning to roll off. If I were to use this lens on this camera for landscapes I’d be stuck with f/11 all the time.

The R-series Elmarit:

LeicaR28mm

A little better in the center, and a lot better in the corner. Looks like a winner in visible light.

The Nikon:

nikon 28mm mtf

The center performance at f/2.8 is incredible. The corner, not so much. It looks about the same as the Leica R lens at the other apertures.

So far, I have two winners. I think for most uses, the Elmarit-R is the better lens — smaller, lighter. The Series VII front thread is a pain, though.

Nikon D810 EFCS with 135mm f/2 Apo Sonnar

A week or so ago, a reader asked if I could try to find out if there’s any vibration difference between a heavy carbon fiber tripod with the skinny legs extended first, or the fat legs extended first. I was doubtful that there would be any difference, and first tried to find out if there was measurable vibration with the skinny-leg-first regime.

I mounted the Zeiss 135mm f/2 Apo-Sonnar to a Nikon D810. I mounted a RRS L-plate, clipped it in landscape orientation into an Arca Swiss C1 head which was attached to a set of RRS TVC-44 legs. There are four leg sections in this tripod; three nested in the one that’s attached to the top plate. I extended the two skinniest legs.

I lit an Imatest SFRPlus target with a Paul Buff Einstein strobe set to 2.5 watt-seconds, which gives a 1/13000 second strobe duration. I set the ISO to 100, the shutter speed to 1/250 second, the shutter mode to 3-second delay and electronic first curtain shutter (EFCS), set the mode to mirror up, focused wide open, and set the aperture to f/5.6. I double tapped the shutter release 16 times. That gave me a set of baseline images with no — or at least minimal — vibration-induced blur.

Then I lit the target with a Fotodiox variable-output 5500K LED light. I set the power to max, and made 16 exposures at 1/125 second. I dialed the light down a stop, and made 16 exposures at 1/69 second. I kept doung that until I got through the 1/15 second sequence. I developed the images in Lightroom 5.7.1 with sharpening and noise reduction turned off, exported them as TIFFs, and measured on-axis MTF50 in both the vertical and horizontal direction.

The results:

D810-135VMTF D810-135HMTF

The top graph is for horizontal lines, and the second is for vertical ones. The thick lines are the mean values, and the thin ones are three standard deviations higher and lower. You can see that the higher shutter speeds are more problematical than the lower ones, though the differences are small. That’s because the time the second curtain is moving is a larger portion of the time the shutter is open when the shutter speeds are shorter.

You can also see that, since the shutter moves up and down, it affects the horizontal lines a bit more than the vertical ones.

You can also see that the effects are very small. One day, we’ll have global shutters, and the curves will be virtually flat.

But back to the issue at hand. It looks like there’s maybe a statistically significant worsening in the spread in the horizontal sharpness of the 1/125 second exposure over the strobe-lit one, even if the mean is about the same. The mean values for the two slower shutter speeds, both vertically and horizontally, are actually fractionally better than the strobe-lit case.

I dunno. I’m thinking that there will be too much variation introduced by taking the camera off the tripod, adjusting the legs, putting it back on the tripod in as close to the same place as the first time, refocusing, and making a new sequence to answer the original question. And anyway, from the tiny differences between the strobe-lit and continuously lit cases, if there is any difference, it’s unimportant in this case.

By the way, 1700 cycles/picture height is 0.344 cycles per pixel. That’s a very sharp lens!

15-6_YB10_01_cpp

Note the over and undershoot from the Lr default sharpening, which makes the MTF50 higher than it would be if there were no sharpening.

 

COASTAL OPTICAL 60MM F/4 light falloff

I think this is my last test on the Coastal Optical 60mm f/4 UV-VIS-IR Apo Macro lens. It’s a simple visual demonstration of light falloff. The camera is a Sony a7 modified for IR by LifePixel, using the Super Color sensor stack filter. I put an Expodisc on the lens and aimed it at a Fotodiox LED 5500K light source. I made exposures at f/4 through f/22.

Here they are:

f/4

f/4

f/5.6

f/5.6

f/8

f/8

f/11

f/11

f/16

f/16

f/22

f/22

There’s some noticeable falloff at f/4 and f/5.6, but I don’t consider any of it a problem.

 

Photography meets digital computer technology. Photography wins — most of the time.

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