"Focus" problem that is driving me insane

[wmokrynski]

Hello,

I have a problem that has been occurring for quite a while, which has been driving me crazy, and I believe is getting worse. Yet another shoot down the tube last week has me at at the end of my rope. I'm now questioning everything, my technique, camera, lenses, tripod, shooting environment, sanity. I'm hoping someone here might have a solution. Is the problem something I'm doing, or is it a technical issue?

The problem I'm regularly having is that I'm getting part of the image coming out sharp, always the lower central part of the frame, then falling off to a blur in the upper area of the image. The unsharp part is not a soft out of focus lens blur, rather what looks to me like a motion blur.

All the work is shot at night with long exposures, almost always at f32. The long exposures in itself shouldn't be an issue as I've had dozens of successes under nearly identical setup.

Here's the most recent image. The white line indicates the border between sharp and unsharp.
http://www.wmokrynski.com/temp/London1-full.jpg
A detail of the sharp area:
http://www.wmokrynski.com/temp/London1-sharp.jpg
A sample of the problem:
http://www.wmokrynski.com/temp/London1-blur1.jpg
A closer view:
http://www.wmokrynski.com/temp/London1-Blur2.jpg

As you should be able to see with the closer views of the problem, the blur is more of an overlapped or offset exposure as you'd expect with some sort of motion. However, if there were motion from ground vibration, wind, or from a tripod leg slipping, there shouldn't be a sharp area anywhere in the image. So I've ruled this out. (This image was taken on a still night with almost no traffic).

Admittedly my perspective correction technique is self-taught from books, so this is where I have my largest suspicion. But I have had success with this technique. Here's my technique:
- Set up and level the camera
- ensure the lens is in the center of the vertical rise on the front standard.
- frame the scene, which usually involves tilting the camera angle up (with the tripod head)
- To correct the perspective I tilt the camera back forward till the grid lines on the ground glass line up with the structure
- I then tilt the lens standard so it is perfectly parallel with the camera back.
- Sometimes I then need to tilt the camera angle further up and repeat the standard tilts to get the scene framed correctly.
- After focusing, the frame appears to be in focus throughout.
- I then ensure everything is tightened down (and have been paying particular attention to this lately), and expose

I would have expected that if there was a problem with my tilt adjustments not being perfectly parallel, that it would be compensated for with the stopped down lens (at f32), and any issues would appear as a soft lens blur. Again, I'm no expert in this. The problem I believe has also occurred in images without perspective adjustment. (Though I'm questioning my memory now too)

I'm working with an Ebony 45RW, 135mm Rodenstock lens (used in the image), 90mm Rodenstock lens (which I'm having the same issues with), on an older Manfrotto Art 190 (silver) tripod.

I can gladly post more problem images if needed.

Thanks in advance for any help.
William

[wmokrynski]

I should add that this problem happens randomly. I'm still able to produce perfect night images, but 25-40% of the time now I'm having this problem.

[wmokrynski]

Also, when the problem occurs, most of the time all of the images taken with the setup will have the problem. I always take a second exposure as a safety measure, and check focus in between.

[domaz]

Could be a film holder not loaded correctly or one is not holding the film flat Time to think about labelling your holders and recording which exposure goes to which holder. That way you can narrow down if it's a holder or not.

[Liam:]

Pinhole in the bellows? It certainly looks like motion blur or two images overlapping each other.

Are you able to upload a full size image?

[Eric Biggerstaff]

Film can "pop" during long exposures which can cause this, it sort of bows outward due to tempreture or humidity changes. I was just talking to a very well known photographer who is now doing a night project and he told me this just happened to him. The night was cool and foggy and he did not let the film adjust to the climate prior to exposure so it "popped" a little in the holder. Part of hte neg was sharp but a section of it was soft. Perhaps this is occuring.

[Kevin Crisp]

I was going to guess a film pop too.

[Oren Grad]

Film pop #3. The tell-tale is that the exposure in the affected areas looks doubled-up, indicating that the film was sitting in one position for a while, and then in a different position for a while. I've had this happen to me very occasionally.

Further to what Eric said, try pulling the darkslide and letting the film equilibrate to the prevailing temperature/humidity before you open the lens to make the exposure. You may need to experiment a bit to find out how long you need to wait for the film to "pre-pop".

[Bob Salomon]

At f32 you are in diffraction. What happens at f22 or f16?

[Brian C. Miller]

What is the exposure time? Are you using a cable release?

I can only recommend that when you pull the dark slide, wait a minute for the film to settle down. That amount of time should allow the film to equalize with the air inside the camera. Also, give the holder a tap before putting it in the camera.

Added:
From looking at the areas which show the problem, it is definitely a motion problem. When the exposure starts, the film is in one position, and then it shifts to another position, in a diagonal upper-left to lower-right movement. Look at the upper-right side of the photo. Is the movement in the same direction, or a different direction, as if the film momentarily bowed in the middle?

From the way you describe your procedure, it sounds like the camera does not have enough front rise for your photo. Is this correct? (This happens to me, too, I'm just trying to nail things down.) If there is enough front rise on the front standard, then just use that instead of tilting the camera back and adjusting the standards.

[Gem Singer]

Have you tried mounting your camera on a heavier, more solid tripod?

[rdenney]

I don't see how this problem could be:

1. Diffraction.
2. Unstable tripod.
3. Camera shake.
4. Above, caused by cable release.

All of these would affect the image with a different-looking pattern. A corkscrew motion of the camera might affect one end of the negative more than the other, but I do not see how such vibration could caused the double images. And given that the sharp end of the negative is at the bottom of the picture, which is at the top of the negative in the camera, the tripod-end of the camera would have to be wiggling back and forth with the top remaining still--the center of rotation would have to be near the top of the camera. I can think of no vibration mode that could cause that. And that sort of a shift seems to eliminate the possibility of the camera flopping from one side of the slack caused by a sloppy tripod head to the other.

Diffraction would affect the whole image, and a diffraction pattern leading to a linear double image does challenge the mind somewhat.

As Doyle said in the voice of Sherlock Holmes, when one eliminates the impossible, then what remains, however improbable, must be the truth. Film popping is the only suggestion so far that could cause the effect.

Rick "who has certainly experienced film popping in scanners--and slide projectors" Denney

[Bob Salomon]

You might find this useful.

http://www.luminous-landscape.com/tutorials/understanding-series/u-diffraction.shtml

[lenser]

This looks one heck of a lot like an image that Edward Steichen did of fruit in a bowl where he had the subject under a very dark tent with only a very tiny opening for light to enter. The exposure was made over several hours (days?), and resulted in overlapping layers of sharpness attributed by him as resulting from the expasion and contraction of the lens between day and night temperatures with a resulting change of the point of focus.

I'm voting for temperature changes first, but is there the possibility that you have the lens position raised to some extreme, on all of these images where you've experienced the problem, and that your front standard locks for either the rise or the tilt, might be just slightly slipping (maybe due to bellows tension) in such a way that it only effects the top of the images.

Are you using a standard or bag bellows? Also, does this happen only with one camera and lens combination or does it happen with different body, bellows and lens combinations? Does your camera have center pivots for tilt or base tilts? If base tilts, it is possible that there could be a combination of a fractional top tilt and therefore focus change at the same time which could keep one area sharp and others slightly double exposed in their focus point. Extremely far fetched, but mechanically possible.

[wmokrynski]

Wow, all these replies. This is amazing! Where have you been?

The film pop theory makes a lot of sense. The film holders travel out with me tucked in a warm padded (insulated) case, then are suddenly exposed to a different temperature and humidity, for a 4-14 minute exposure. (yes using a cable release)

Though my problem is not limited to winter temperatures. I can think of 3 or 4 sessions that experienced this problem in July (in northern Europe). I suspect humidity could be a significant factor. I wonder why the lower central part of the image is always unaffected, perhaps gravity plays a part somehow?

Here's a closer look at the very top edge of frame just above the other sample I posted. This area would presumably be secured by one of the film holder edges. Sharp.
http://www.wmokrynski.com/temp/London1_top.jpg

Thinking back through the history of shooting this project (which you're welcome to view at http://www.wmokrynski.com, follow the project link to 'Nylon Chrysalis', (the project is also featured in this issue of Eyemazing Magazine)), I started off exclusively shooting with Fuji Quick Load films. Then my supply ran out, I couldn't get more within Europe, and I switched to conventional holders. Thinking about it now, I had zero (motion blur) pop issues with those early exposures utilizing the quick load film. The film must have been held nice and tight within the package.

Has anyone else experienced film pop? I can't be the only one. Might there be a preferred film holder that would hold it more securely and prevent a pop? How long would you suggest I acclimatize the film within the camera before making an exposure? (just what I need, another step which makes the nocturnal session longer :rolleyes: ) Do you really think tapping the holder will help? The film would have bounced around in the rolling case on the travel to the location.

I'll post another problematic potential pop image or two tomorrow for analysis.
I'm feeling much better about it now, though the big question is how am I assured the film has acclimatized before exposing? ...Or do I scrounge the world for all the remaining Provia Quickload film? (and plead with Fuji to restart production)

Thanks for the help so far,
William

[wmokrynski]

Thanks for the diffraction information. Incredibly, I wasn't aware of it.
Down to f11 I go.

[wmokrynski]

A heavier tripod has been suggested to me before, though I don't think tripod is the problem here. I've had many successes with the same conditions using this tripod. Besides the 190 fits nicely in the bottom of my suitcase. Tell me how one can fly with a bulkier, heavier, tripod and not get dinged with a ludicrous extra baggage charge.

[Filmnut]

I really don't think that a heavier tripod would help. This looks like film "pop" to me also. I've never had this happen to me in a camera, but as a professional printer this was a relatively common problem on big enlargements when everything was printed from negs or trannies. The effect was virtually the same as what you have here.
Keith

[ic-racer]

Based on the picture, my guess is that your not parallel with the building. Getting a 90mm lined up can be difficult. I just spend a good deal of time getting the zero detents on my 4x5 lined up because of some similar issues with a new 90mm. Though my problem was in side-to-side focus. The amount that it was off was so small that I actually wondered why there are not that many threads on zeroing the detents on 4x5 cameras with wide lenses. I can't believe everyones camera is fine from the factory with 90 and shorter lenses.

[Edwin Beckenbach]

From the picture alone I would agree that the film popping is the most likely problem. However, it is curious that the problem would be chronic, consistent and at the top of the image (bottom of the holder) if that is the case. I would not be surprised if there is a combination of issues.

First, as a matter of good practice, control the easy things.
1) Always tap the bottom edge of the holder before inserting it into the camera to be sure the bottom edge of the film is seated and the sheet wont slip down.
2) Always let the film rest for a couple of minutes after pulling the slide. Also, I often take my holder bag out of my camera bag while I'm setting up so they can equilibrate at least partially to ambient temperature.
3) confirm that the lens board and film holder are properly seated in the camera and everything is zeroed before making adjustments.

Regardless of any other issues, failure to do these things will result in occasional failures for long night exposures so just get used to it.

Now I am going to go out on a limb and suggest that you have an alignment problem. This is likely for two reasons. First, you say the in/out of focus areas are consistent over time, even if the problem is intermittent, suggesting a structural problem. Second, the area which is in focus is probably where you were able to focus. You are using a wide lens at night with rise so i'll bet you focused in the bright central area near the street level and probably couldn't have focused at the top of the building very well. This would be much less likely to occur during the day or with a long lens where it is easy to verify focus throughout the entire frame or in situations where you might focus in the center of the frame resulting in a less significant defocusing problem towards the top and bottom edges. IOW, If you have have an alignment problem setting the focus on one edge of the frame will produce twice the error in the other edge as setting it in the center and in the latter case the loss of sharpness may go unnoticed explaining why not all of your images are "bad".

You can check this simply enough with a small bubble level applied to the lens board and the ground glass. put your camera on a tripod, zero everything, position using the level such that you can get the lens board perfectly vertical and verify that the ground glass is also vertical. With such a significant effect at f32 as shown in the image the missalignment should be fairly obvious.

[Edwin Beckenbach]

Also, f32 is a perfectly appropriate aperture for a 90mm lens with a good deal of rise. You could probably get away with f22 but f11 would really be pushing it in terms of aberrations in the corners and much smaller tolerances in the film plane positioning.

Edit: I just reread and see you used 135mm not 90mm. I'd still recommend f22, possibly f16.

[engl]

Thanks for the diffraction information. Incredibly, I wasn't aware of it.
Down to f11 I go.

Keep in mind that shooting at F11 makes the problem even worse. At wider apertures, smaller shifts of the film are enough to result in blur. It also puts stricter requirements on the film being flat and at precisely the right registration distance (not the case with all holders and backs). Apart from this, it is obviously also more difficult to get all critical parts of the shot into perfect focus on the GG, especially if the camera is not rigid and easily adjusted.

F32 will start showing diffraction printed big, and push exposure times to where you might get color shifts due to reciprocal failure during night shooting (reciprocal failure also results in slightly lower dynamic range). With a scene not requiring small apertures to get everything focused (sometimes you just need F45), I'd go with F16-F22, and use the methods described in this thread to avoid "film pop".

[Vaughn]

I get film pop with long exposures under the redwoods (often 10 secs to 30 minutes). And sometimes it is film slippage rather than popping (the film sitting slightly crooked in the holder, than falling into place during the exposure -- this leaves one corner sharp and a double exposure showing more and more as one works to the opposite corner. I give the holder a good tap on the palm of my hand, now, before I load the holder into the camera.

I tried a piece of two-sided tape in the holder, but it just made loading and unloading more difficult and would leave tape residue on the back of the film (interfering with the removal of the anti-halation layer.)

[Arne Croell]

As for your question why the Quickloads were better, remember that the Quickload/Readyload holders employ a pressure plate. That would hold the film at three edges, and the 4th top edge is stabilized by the plastic sheet connected to the film. Regular holders with pressure plates are the Sinar 4x5 Precision film holder (one sheet/holder only), or the older thicker Linhof film and plate holders. The latter used the pressure plate not for stabilizing the film but to allow the use of glass plates in there and grasp the film only on two edges whereas the Sinar holder holds it on all four edges. Both are out of production and were expensive, but can be found used sometimes. Note that a pressure plate is not a guarantee for not popping - if the emulsion side expands, e.g. because of a higher humidity, it could pop out in the center. One would need a larger humidity change for movement with a pressure plate than without, though. The better one of those two for you would be the Sinar Precision holder.
Btw, I think humidity is much more of a point than temperature on its own (of course a temperature change is often associated with a humidity change); imagine the film in the holder being suddenly exposed to a different humidity, the absorption or desorption of water vapor will be much faster in the emusion on the front side than in the anti-curling layer on the back side because the latter is next to the holder wall, leading to a temporary curl or pop.
The best solution would be a vacuum holder like the ones used in aerial cameras or the short-lived Schneider system in the late 1990's, but those would be hard to get.

[BetterSense]

I would imagine a Grafmatic might also help with film popping.

[Joseph O'Neil]

I would go with "film pop" too. Way back in the days when dinosaurs walked the earth, and guys used to still use film for astro-photography, "film-pop- was a common problem for long exposures in cameras, even 35mm at the time.

Solutions back then ranged from drilling and tapping a camera body to run dry nitrogen in during a long exposure (for everything form 35mm to 4x5), make a custom 4x5 film holder that had tiny holes and hooked to a vacuum of some kind to hold the film in place - but that had problems too.

You see, to harsh a vacuum, and it would warp the film too, so believe it or not, a breast pump of all things provided the exact right amount of suction needed to hold the film in place and not warp it. Seriously, if you think it sounds weird, imagine some night watching 50 grand worth of optics, computers and mechanics all working in unison, with a playtex breast pump duct taped to the side of a tripod leg. :)

The other classic answer was plain old fashioned glass plates, but you cannot get those anymore either I believe.

However, I do have a solution that should work, if you can find one. Hunt high and low and buy yourself a used Linhof spring loaded film holder. Not perfect, but pretty darned good, just hard as heck to find them used anymore.

One last thought, for what it is worth, I find if I shoot landscape instead of portrait, film pop is less over long exposures, However that really limits you in some cases.

good luck
joe

[Bob Salomon]

"However, I do have a solution that should work, if you can find one. Hunt high and low and buy yourself a used Linhof spring loaded film holder. Not perfect, but pretty darned good, just hard as heck to find them used anymore. "

Afraid that this would be no better then the regular, and also discontinued, Linhof Double Sheet Film Holders.

What you recommended were the Linhof Glass Plate/Sheet Film Holders. Since these could use either a thick glass plate or a thin sheet of film. To adjust to both they had a spring loaded plate. But this was not a pressure plate and did not hold film any flatter then the Linhof Sheet Film Holders. They would just be thicker and heavier then what would be needed.
Lastly, unlike a roll or 35mm camera, there are no film rails to position the film against in a sheet film holder so the spring adjustment plate in the Linhof Glass Plate Holder has nothing to push the film against to hold it flat. Just like any other sheet film holder without either a vacuum or adhesive the film can still sag forward in the holder.

Film holder for sheet film that do not let film sag were either vacuum holders like the Hoffmann or the short lived Linhof Vacuum Sheet Film Holders or the Linhof 5" Vacuum Roll Back for the Aero Technika and the Technika or adhesive holders like the Sinar and the short lived Schneider holder.

[Brian Ellis]

At f32 you are in diffraction. What happens at f22 or f16?

The effect of diffraction would show up as an overall "softness" of the image, it wouldn't cause only part of the image to be unsharp while other parts are sharp.

Tobasco, your technique sounds fine. I'd check for film "pop" as many others have stated and also a bellows or lens board leak. I had a lens board from which a cable release gizmo had been removed, leaving a small hole in the board. I foolishly didn't think to cover the hole and the resulting photographs looked a lot like what you're posting. So it's probably a long shot but worth checking.

[Arne Croell]

"
Film holder for sheet film that do not let film sag were either vacuum holders like the Hoffmann or the short lived Linhof Vacuum Sheet Film Holders or the Linhof 5" Vacuum Roll Back for the Aero Technika and the Technika or adhesive holders like the Sinar and the short lived Schneider holder.
Only the larger Sinar holders used sticky tape. The 4x5" Sinar Precision holder used a pressure plate and clamped the film on all 4 sides.
And the Schneider holder was a vacuum holder not an adhesive one.

[Doremus Scudder]

I'm voting (strongly) for film pop/slippage as well. Not only does this happen to me on long exposures semi-regularly (irritatingly so) but none of the other possible causes you mention explain the double-image in the blurry area. It's definitely film movement and not diffraction (which would show up over the entire image). If things look equally sharp over the entire ground glass when you are focusing, then it's not bad focus either unless your ground glass is not aligned properly. If you only have this problem with night shots. Bet on the obvious. (But do check to make sure your compressed bellows isn't pushing the lens out of alignment before the shot is taken.)

Some tips to prevent the slip/pop problem: 1: Before inserting the film holder, rap its bottom sharply on the palm of your hand in exactly the orientation it will go into the camera. This will "seat" the film sheet and keep it from slipping down during exposure. 2: Pull the darkslide and wait 30 seconds or so before opening the shutter. This gives the film a chance to adjust to the temperature and humidity inside the camera and pop to a more stable position. This is especially important when you keep you holders in plastic bags at different ambient temps (as most all of us do). 3. Make safety backups of important shots. If you get 30% error like this, then this will increase your chances of a good exposure.

Forget looking elsewhere till you have done the above.

Best and good shooting.


Doremus Scudder

[Bob Salomon]

The effect of diffraction would show up as an overall "softness" of the image, it wouldn't cause only part of the image to be unsharp while other parts are sharp.

Tobasco, your technique sounds fine. I'd check for film "pop" as many others have stated and also a bellows or lens board leak. I had a lens board from which a cable release gizmo had been removed, leaving a small hole in the board. I foolishly didn't think to cover the hole and the resulting photographs looked a lot like what you're posting. So it's probably a long shot but worth checking.

To quote Rodenstock in several of their lens brochures:

"Depending on the reproduction ratio and the depth of the motif (subject), the required depth of field may make further stopping down necessary. In such cases, the sharpness may be reduced due to diffraction - particularly in the center of the image circle."

The above appears in their taking lens brochures.
The following is from their Apo Rodagon-N brochure:

"Sharpness and contrast are at a maximum over the whole image field. While stopping down further will produce a slight increase in sharpness in the extreme corners, the performance in the center is reduced due to the effects of diffraction."

[engl]

But diffraction affects the entire image equally, it sets a limit for the resolution. In practice, the image is sharper in the center, so that is where the limit is reached first. Diffraction never brings center sharpness below corner sharpness.

As Brian Ellis said, diffraction shows up as an overall "softness".

[Steve Gledhill]

Film popping is certainly at play here. Please see this previous post (http://www.largeformatphotography.info/forum/showpost.php?p=546794&postcount=20) from me where I quote some excellent advice from John Sexton.

[Jim Jones]

. . . Diffraction never brings center sharpness below corner sharpness.

As Brian Ellis said, diffraction shows up as an overall "softness".

In practical photography this is true. However, in wide angle pinhole photography with a slightly oversize pinhole, sometimes edge resolution exceeds center resolution.

[icanthackit]

I'm pretty new to the whole large format thing, but I want to either go with this film pop (though I really think it odd that this would happen so much and to such an extent just from my experience with things changing in different temperatures and humidity).

How good is this "135mm Rodenstock lens?" For some reason I'm thinking that is one of the better brands, but how much are you adjusting the camera, like rise I guess it would be. Is it extreme or just a little? Not having much experience with LF, I would guess that you're getting near the edge of the image circle and it's getting wonky? I could be totally off, but that's just my guess.

[Brian C. Miller]

Hi, Andrew! If you take another look at the images, you'll see that the problem is that all of the corners are in focus, while the center starts going "soft" in a movement sort of way, not a focus sort of way. The film itself moved while the exposure was being made.

If you develop film yourself, you'll see it pop back and forth as it dries. A similar thing happens inside the camera when the film's temperature hasn't stabilized.

[tomp1000]

I, too am having this issue with film popping with 8x10. For 4x5 I use a small piece of two-way tape which works for 90% of my long exposures in the damp night air, but it isn't working for 8x10. Maybe there is too much surface area. I am waiting about a minute with the lens closed and the slide pulled for the film to stabilize before I start the exposure. The vacuum holder sounds like an excellent option but making one doesn't.

[Jim Noel]

Ray McSavaney is a master at making long exposure images,often up to an hour.
Hi solution:
1. Film holders are not only light proof, but to an extent air tight. Thus when the film is loaded in one environment and then exposed in another the relative humidity will almost always produce some film pop.
2. Set up the exposure, insert the film holder, cover the camera with the dark cloth and remove the slide.
3. wait 5 minutes and then open the shutter for the exposure.
4. this will take care of the most extreme changes in temperature and humidity. When making an extra long exposure an extra 5 minutes does not matter.

[Steve M Hostetter]

Building movement

It may be a calm night where your standing on the street but go up 30 stories and feel something else

I would imagine the visqueen covered scaffolding has to be moving somewhat

steve