[maw]

You are correct.

A "full-frame" lens on an APS-C camera will bring in spurious light from outside the APS-C field-of-view and may cause flare, ghosting, or contrast loss. For APS-C cameras, DA lenses probably have better real-world flare properties than "full-frames" lenses although I really hate to to say this is a rule because a full-frame lenses with great coatings might beat a cheap DA lens.

The general problem is that all light gathered by the lens (with its full image circle and intended format size) end up inside the camera. Although a camera mirror box may have "black" walls, limitations in materials mean that even "black" surfaces reflect a fraction of the light that hits them. That reflection then hits the sensor and creates ghosting. The worst-cases of this happen when the sun or other really bright object or area is just outside the frame so it's not visible in the viewfinder but it is visible to the lens.

Basically we affirm the same concept, in particular when you talk about "great coating", you are referring to the SMC Super multi multicoating treatment that was introduced by Pentax around the sixties (67/70)?

If I remember correctly, then improved in 96/97 ? With the first target, which happened to be the famous 43mm, to eliminate or better decrease the Gosthless effect, then there was a progressive improvement
(technology is pressing).

But obviously we know that the light is very bizarre and assumes multiple aspects depending on the materials that stand in the way. So could this be a cause of the halo (alien) that manifested itself in the photo?

I would like to see other shots from other angles because not least it could also be that particular type of light ''wavelength'' that influences the images of barondla.

Ciao Mario

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Last edited by maw; 09-22-2020 at 07:26 PM. Reason: rectification

[maw]

Yes, Pentax supplied hood was on the lens. No spots or foggy areas on lens elements.

Long exposures sometimes are marred by a sort of flare. I took 30 sec exposure pictures inside a Basilica and the interior lights created strange patterns ressembling flare. Maybe the sensor misinterprets those incident lightrays and renders them as flare or ghosts. Try to up your ISO and take shorter exposure pictures to check.

The general problem is that all light gathered by the lens (with its full image circle and intended format size) end up inside the camera. Although a camera mirror box may have "black" walls, limitations in materials mean that even "black" surfaces reflect a fraction of the light that hits them. That reflection then hits the sensor and creates ghosting. The worst-cases of this happen when the sun or other really bright object or area is just outside the frame so it's not visible in the viewfinder but it is visible to the lens.

Hi all,

Despite the coatings I was surprised what is stated in this article, that is the percentage of light dispersion is around 64% and only 36% reaches the film or sensor.

About Super-Multi Coating (SMC)

Incredible!

[kaseki]

...
The solutions are: 1) adding a smaller petal hood optimized for the smaller format; 2) ...

...

Don't suppose Pentax makes "crop" lenshoods for this situation? .

That would be a longer petal hood, I would think.

I understand that the 645 25mm DFA hood is shorter than the 645 25mm DA hood.

[Ed Hurst]

I understand that the 645 25mm DFA hood is shorter than the 645 25mm DA hood.

That is so. Contrary to what is often said, that is not the only difference between the 25mm DFA and the 25mm DA.

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Last edited by Ed Hurst; 09-22-2020 at 11:21 PM.

[Papa_Joe]

Hi all,

Despite the coatings I was surprised what is stated in this article, that is the percentage of light dispersion is around 64% and only 36% reaches the film or sensor.

About Super-Multi Coating (SMC)

Incredible!

This would be the case for a lens with 10 elements without a coating. The second pargaraph makes it clear, that SMC reduces the overall loss for such a lens to 4%. Good result, isn't it?

[climbmountainway]

It looks like the light fixture shown in the approximate roof rafter leading lines roof scene center is switched on, or is reflecting another light source (sun, general daylight from another source outside the scene, or a source of other light coming to its presenting center glass-like cover for its reflection or projection of light into the camera lens of choice glass surfaces and on to the camera sensor). All the other in scene subject illuminance looks fairly even from available light, except that center bright slightly off axis whiteish illuminated imperfect circle's ghosted light seemingly bleeding onto its nearby area. So the exposure value of that light as an illuminance source itself and as a part of the scene coming to the lens differs from exposure value of all else presenting in this scene (without any such similar illuminance by projection or of a brighter source reflection). The rest of the scene acts as a kind of darker background to the imperfect center circle bled-cast light of a brighter illuminance, in addition to it being its own larger part of the scene. A light source seems to be reflected as smeared and diffused on to the roof surrounding background and/or on the capture lens glass element(s) surface as well.

All else we see evenly presents similar illuminance values, and embraces the lens attributes achieving its capture for an adequate rendering, whereas the light source of contrast smears its presence into the otherwise geometric roof scene one way or another. Is this then excessive flare due to format size 'lenses', as the poster wants to know?

I have a quantity of 645 Medium format MC Mamiya lenses, and Pentax and other multicoated lenses for full format and APSC format. They are not flare prone in everyday conditions. They become so when a light source of notable reflection or projection is part of a scene with a higher area illuminance value than in the rest of the scene. When showing up as more about a direct light source itself than a scene in itself, flare can appear in a scene challenging a lens to reckon its associated light controlling attributes as acceptable for the photograph's intention (where its presence is not presented out of sorts with the rest of the scene). The challenge of how to deal with such flare happens with focal length lens choice, use, and photographer placement of his system's light capturing tools juxtaposed with finesse to the axis of a scene's in scene light source.

This is not about a format size available system lenses, but often can be about a specific lens engineered design, as is made for its angle of acceptance, contrast handling of a light source appearing in a scene going above the scene illuminance values charted potential for a comfortable result, a lens component internal light controlling parts being off axis to the scene's direct light illuminance source(s), and glass elements surfaces shapes angles inside a very wide angle lens (as differ from those with less curvature of internal elements to achieve more narrow angles of acceptance for other system interchangeable lenses: elements as may be set inside of a lens barrel by its elements or aperture components light handling design).

Off of direct axis to a subject or scene, an unevenness of light coming from a direct in scene high light value source, or being cast onto a scene background, or coming onto a lens element or element group surface within a lens barrel can challenge any lens internal geometry to render an acceptable photograph without flare (as to mastering the issues of any of its abilities employed when using such an optic). This one involves a light source disrupting a simple appreciation of the scene rendered. And, for the 645 format, it is shot by an extreme wide angle lens. A 35mm 645 lens has a bulb-like highly rounded element or elements group near the very front of the lens. It must be accounted and compensated for as to how the camera is positioned regarding its lens axis to the subject angle and the presenting problem light source in the scene, as well as the focal length used for capture. The presenting bleed cast, I believe, is falling on the very front side of the bulb like element or group of the lens, and then falls off for a literal distance from its top side presenting the light source onto the element(s) group, and smears evenness of light capture by the element shape front toward back of the lens employed in reference to the whole scene's otherwise even illumination presentation. The element could be a hybrid element, made of different material than other elements in the barrel, and is presenting to the scene with its own contributing characteristics of handling rendition and reflection off its own internal to the lens extreme shaped bulb-like internal group. This is not about the format size, but the challenges to designing and handling this kind of lens, and its composition framing of scene by a photographer's very careful placement regarding the light source to camera location in the scene capture environment.

The new Pentax 11-18mm f2.8 APSC ultra wide zoom costs twice as much as its earlier brother, the 12-24mm f4 DA. It has greater aberration control abilities than the earlier DA lens, uses a different engineered optical elements design, offers a slightly different focus mechanism, and certainly more costly elements glass or glass substitute composition in its design. It costs much more too for its extra f-stop for light capture than the earlier unit. It seems to have less flare as well when in such direct light challenged scenes. It masters good edge to edge sharpness. This too is not about its format size, but its own design and engineered composition of elements and aperture control. These two lenses also have frontal bulb-like elements. I have the older one, which has similar flare challenges to the 35mm 645 lens.

Because of the number of elements contained in a camera lens barrel, and the shapes of various elements and element groups of various lens glass compound and complex groups making up the focal length: all and any photographic lenses differ from one another regarding handling flare characteristics. They are placed in alignment, are centered, and shaped for their compound positions which make up a focal length and aberration control and light handling abilities for a lens. Within a lens barrel confines we know not all lenses can do their light gathering, spreading, and focusing exactly the same in all available formats lens systems when placed on any camera.

Photographic lenses are made to achieve a complex optical design for a focal length, for handling, scenic light admission, transfer, evenness of light across the frame, to keep all in a scene in acceptable spatial perspective relationships -- with controlled distortion -- and so to rear project a sharpened color imaged area of a lens focus onto a light sensitive rendering flat surface. All achieved presents challenges to overcome not just flare, but of a scene to the spheres of the various glass surfaces in the barrel held in juxtaposition to a scene (which you presented above with varied light sources, and exposure value differences from the rest of the scene. What we see indeed reflects off a definitive glass surface of an inner element or element group of almost a bulb-like shape which ghosts and smears its own capture of the light source reflection or projection coming into and onto the lens element itself: and so presenting in contrast to the even light of the rest of the scene. Likely as you go longer in focal length, say to a 45, 55, 80, 105, 200 mm 645 format lens, with a less extreme bulb-like shape, the phenomena will lessen or disappear. And, if you shift the axis the photographer controls of the light source to the near center of the lens used and its front bulb-like inner element(s) you should get an acceptable variance on the light smear effect (when it strikes more to the center of that element, and less to one of its bulb-like sides). This issue would not be akin to the format but to the lens type itself; it is not then as conjectured to be about the format's interchangeable lens system.

There is no such animal as a totally flare proof consumer lens: depending on the illuminance light source, the exposure value difference between all else in the scene and that direct light source, the inner lens elements shapes, these elements compositions, and designs, the lens elements coating, the aperture design, and the juxtaposition of the presenting scene light source or reflective source to the axis of the lens both to the sensor plane and subject being photographed. The trade offs to achieve an acceptable photograph using any system's available tools and technology are legion.

As to this photograph, the photo tools being used are not directly below the light source, but are off axis from the lens center: the sensor full plane. where all these center at an angle to the light source. Of course the elements in the UWA lens so disposed will render what presents as was set up pointing toward the light source in this scene. You can move the lens and camera around to show more or less reflection off of the element(s) of the front most behind the first element bulb-like element or element group. What is not presented as perhaps essential to your question is any real comparison to other alike types of UWA lenses in other formats photographing the same scene to then make the hypothesis so that what we see is because of the medium format and its available lenses somehow being more flare prone than other formats. No evidence is presented to prove this.

Your hypothesis is that this is because of the lens to format reality. Likely a 20mm or 24mm on a full frame camera can replicate this rendered result, if set up exactly like the camera and with a similar format to format UWA lens, with its alike on scene camera support, with the same basic angle to the source of illumination as was so positioned to this lens (and likely too with such a bulb-like near the lens front element or element group. You are requiring a flare to format conformity by the principle that your question is correctly or authoritatively framed, when it is not likely just an issue about what you have proposed it is about (format and format lenses flare tendency). When we think through the use of tools to get the shot, and all other factors contributing to the render you show, than simply a lens to format flare factor -- we have to form a different and other formats comparison hypothesis as to what causes and how to lessen such flare.

[BarryE]

The answer is "yes" but it's not a "medium format" lens issue. Instead, it's a general problem with putting any lens made for a larger format camera on any smaller format camera.

In this case, it was a full-size 645 lens on a crop-factor 645 camera. You have a lens designed to cover a 56 mm x 41.5 mm film frame but the sensor is only 44x33. Light from the full-size image is being collected by the lens and entering the camera, mirror box, etc. Light from the extra parts of the scene reflect off surfaces inside the camera and look like flare. But the 645Z viewfinder isn't showing that part of the scene. (If you've removed the petal hood of the 35mm, things wold be even worse!)

Looking at that shot, it seems extremely likely that full outdoor lighting was visible to the lens just below the furthest rafters.

TL;DNR: A lens for a larger format sitting on a camera for a smaller format pulls in a lot of light from parts of the scene that are not visible in the smaller format camera.

The solutions are: 1) adding a smaller petal hood optimized for the smaller format; 2) using only lenses optimized for the format; 3) paying attention to bright elements that lurk just outside the viewfinder but that are visible to the lens.

+1. Not really sure why this is not made more of. FA Limiteds on APSC, for instance ...

Also, if long exposure there may have been a problem if any light was creeping in through the viewfinder. Initially, I thought this issue was over stated. Wrong! It happens frequently ...

[climbmountainway]

PS This may not be flare at all. It may be the lens and shutter speed's ability to capture the nuances of greater light near its bright source overcoming what you would like to be, in the best of all possibilities, an evenly lit roof. In fact opening up the shutter longer may let those light waves do their thing. And be and do light, as well as render a subject struck by light.

[RICHARD L.]

I also think the combination of this lamp in the center of the roof (which I hadn't seen before someone talked about it) and prolonged exposure time (25 sec) contributed to the creation of this ghosting.

Regards

Sunrise or sunset pictures are a good test for flare and ghosting. Recently I photographed the shoals of the St Lawrence at sunset and no flare or veiling was visible, even with the 645 zooms with the lowest scores of all or a 67 zoom with a high score.

645 FA 33-55 mm f/4.5 @ 33 mm

645 FA 55-110 mm f/5.6 @ 55 mm

67 M 55-100 f/4.5 @ 100 mm

[texandrews]

That is so. Contrary to what is often said, that is not the only difference between the 25mm DFA and the 25mm DA.

Ed, what's the other difference(s)?

[kaseki]

Ed, what's the other difference(s)?

OK, I'll bite too. Waiting with bated breath.

[Ed Hurst]

Ed, what's the other difference(s)?

OK, I'll bite too. Waiting with bated breath.

Hello chaps! Take a look at the shots below. These are my 25mm DA and Mike Oria's 25mm DFA side-by-side (sitting in a damn fine café he took me to, by the way!).
At first glance, the hood is the most obvious difference. But take a look at the shot where we are peering down into the front of the lenses - notice how the glass front element is a different size (which could also affect behaviour in some ways, including tendency to flare). Also, when we were there looking inside the lenses, it was apparent that the baffling/masks inside were slightly different. It looks like, when making the DA version, they did a few things to reduce flare by closing in on the 33x44mm crop frame (internally and externally). I expect the actual optical design (internal optical elements) are the same, but the construction of the lens around them has more differences than the hood.

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[barondla]

Hello chaps! Take a look at the shots below. These are my 25mm DA and Mike Oria's 25mm DFA side-by-side (sitting in a damn fine café he took me to, by the way!).
At first glance, the hood is the most obvious difference. But take a look at the shot where we are peering down into the front of the lenses - notice how the glass front element is a different size (which could also affect behaviour in some ways, including tendency to flare). Also, when we were there looking inside the lenses, it was apparent that the baffling/masks inside were slightly different. It looks like, when making the DA version, they did a few things to reduce flare by closing in on the 33x44mm crop frame. I expect the actual optical design (elements inside) are the same, but the construction of the lens around them has more differences than the hood.

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Great information! Interesting to see the differences in the hoods and lenses. Think how rare it is for two 645Z shooting Pentaxians to have lunch while comparing 25mm lenses.

Thanks,
barondla

[torashi]

I suspect this could also be an IR hot spot. Given the long exposure and red-shifted light coming from a setting sun. Also, with these longer exposures one has to cover the viewfinder because IR tends to enter through it and color cast/smear all over the image.
I would keep a small circular cap that fits over the eyecup in case there is a chance that light can enter. People also use gaffer's tape, but I'm not sure how effective it can be against IR.

[kaseki]

Ed:

Thank you very much. Having the DFA, I'll have to pay more attention to possible flare that might not be obvious when setting up a shot.

kas