Photographing artwork focus issue

[kenneth_bruno]

<p>Greetings,<br>

Recently I attempted to photograph a flat piece of artwork with my 4x5 Busch Pressman (b+w film). All the negatives were in sharp focus EXCEPT for one corner, and not the same corner either. In some cases one edge was out of focus half way down. Figuring the Busch was out of whack I used my old plate camera with a 4x5 back and Symmar-S 210 lens. The same situation; one or two corners out of focus (as seen through the ground glass). I would refocus on the corner to only find the center out of focus. I didn't bother wasting any film. What gives? Any ideas? <br>

The artwork is of very fine black lines and requires the sharpest focus possible.. <br>

The wall is level (at least vertically).<br>

The camera appears to be perpendicular with lens and back aligned (maybe not?)<br>

The camera is quite close so I realize depth of field is limited. Could there be next to zero depth of field? Might shooting at f/32 do the trick?<br>

Any help would be greatly appreciated.<br>

My best,<br>

Ken</p>

[tim_ludwig2]

<p>The simplest guess would be that you are not in proper alignment between the camera and the artwork. Go the the hardware store and where they sell levels, you should be able to find an angle finder. It is a simple device that when held against the artwork, will establish the actual angle at which it hangs. Once that is complete, set up your camera for the magnification you want and then align the film back to the exact same angle as the piece your are photographing. Next, do it again on the lens standard so that all three are at exact parallel to one another. That should make it just about perfect as far as eliminating variables. You need to do this on both the horizontal and vertical axis to be certain of perfect alignment and to center the camera and lens to the center of the artwork.</p>

<p>I would not use an f stop above f11-f16 to avoid diffraction of the light off of the edge of the iris blades which degrades sharpness and possibly contrast. I would also select a fairly long focal length lens to flatten the field, a copy or process lens if you have access to one, is designed for flat field work.</p>

<p>Some lenses do have a focus fall off from center to edge. A test for this would be to tape a full sheet page from a newspaper to the wall. Light it evenly, crop to the whole page, focus on the center, and then follow the above methods with the angle finder to set the camera and photograph the page at several f stops (label each with a post it with the shooting f stop written on it). After processing the film, use a strong loupe to examine the sharpness of the type at both center and edge on each exposure. That should give you answers to both the lens sharpness and to the question of which f stop produces the best center to edge sharpness.</p>

<p>If you still experience focus problems, that might indicate some odd problem with the lens itself.</p>

[garypeck]

<p>Perhaps a more efficient method to achieve alignment would be to simply place a mirror on top of the artwork in the center and on exact same plane as the art and view it through the camera. When you can see an accurate image of the groundglass in your loupe you'll know your in alignment and parallel to the art. Turn on a very bright light and check the corners at shooting aperture and your done. </p>

[kenneth_bruno]

<p>Thank you for the replies.<br>

I am leaning more towards an alignment issue rather than a fall-off issue. My guess is that if it were fall-off, each edge and corner would be out of focus similarly, rather than just one or another. However, I think it a great idea to photograph a piece of newsprint (after checking the alignment) to determine if there is fall-off and to find the best aperture.<br>

A process lens is also a great idea though spending the money on a lens I might never use again seems a waste (unless I find it to be the only option).<br>

The mirror 'trick' is interesting too, though it might prove difficult to mount it on the artwork since it is hung vertically. If I could position the artwork on the floor or table, I could simply rest the mirror on top. Such is not the case. I will keep this in mind though. Clever!<br>

I never thought photographing a flat subject would be such a challenge.<br>

Again I thank you for your input. <br>

Let the games begin!<br>

Ken</p>

 

[garypeck]

<p>The mirror "TRICK" is considered a standard alignment technique by such companies as Hasselblad. Sorry to waste your time with it. If the painting is hanging vertically so will the mirror.</p>

[kenneth_bruno]

<p>Gary,<br>

No waste of time at all. In fact, I found a way to hang a small mirror and will do just that.<br>

A genius idea that I don't recall ever hearing before.<br>

My best,<br>

Ken</p>

[oyvind_d]

<p>I have noticed this also on a 210mm symmar-S, as well as 210mm Nikkor-W, 180mm Fujinon-W, but not 120mm Nikkor-SW.<br>

Corners have different focus from center, and if you do not have them parallell, one or more corner will be different from the others.<br>

You could also have a problem with centering.<br>

And you have the wrong type of lens, try an Apo-Ronar 240mm, and you will be surpriced at the increase in sharpness at this kind of work.<br>

If you must do it with this lens, use the mirrors and stop down to 22 or 27 as minimum.<br>

I have seen suggestion of using a shim to place the front further way out to get the corner at the same focus, not more than 1mm (1 turn or so)<br>

<br />Øyvind:D</p>

[bob_salomon]

<p>You are also using a lens that is not corrected for what you are doing. A process or a macro lens will give far better results.</p>

[sgust]

<p>You need a flat field lens for this application. The field of focus on most lenses is a curved section of a sphere. Hence your problems with trying to get a flat image in focus all the way across. As Bob stated, a macro or copy lens will likely work because most are of a flat field design. This will allow you to get everything in focus while setting the aperture for maximum sharpness. You could also try to use a longer focal length, as the radius of the curved field of focus increases with the distance of the subject in focus to the lens. If the the radius is sufficiently large the curved field starts to resemble a flat one.</p>

[mukul_dube]

<p>The field of the lens is not flat. Best to focus on a point half way between the centre and the edge and then stop down.</p>

[bob_salomon]

<p>You can do whatever you like but this lens was never designed for copy work if optimal performance is the requirement.<br>

That is the realm of the process lens and the macro lens. If your time and materials have no value to you you can keep on trying. But renting, borrowing or buying the proper lens for the job will be the best and quickest solution. Assuming the lighting is correct as well as exposure and the camera is properly position to the subject and you shoot within the optimal magnification range of the lens and at within the optimal aperture range.<br>

How much time and film and chemistry have you already used up?</p>

[kparratt]

<p>As Bob states, wrong lens for the job was my thought too. For the same application, I fit my G-Claron 240mm the Linhof Technika. It has no shutter, so I'm using either ND filters plus colour correction if necessary (for tungsten light) to enable exposures of 1+ seconds, lens cap off & on, or with studio lamps, dim the room lights way down, off the cap and pop the flash, cap back on. (I have two of the 240mm G-Clarons. I'm going to get one fitted with shutter)</p>

 

[kenneth_bruno]

<p>As most, if not all of you have suggested, I could keep fiddling around with the alignment or just get the proper lens for the job. Perhaps worth the piece of mind alone. <br>

Is a process lens the right choice though? I thought these lenses best for shooting actual size, not for images needing enlargement. Not the sharpest for this application. Maybe I'm wrong? <br>

A macro lens the better choice?<br>

I am using tungsten hot lights not strobes. Either way, I might be able to use a packard shutter for a barrel lens.<br>

Not much in the way of film and chemicals. More frustrating than costly at this point.<br>

My best,</p>

[tim_ludwig2]

<p>Kenneth, Regarding your either-or statement regarding the alignment OR choice of lens.....you will NEVER get away from the need to come very close to nailing the alignment. Even with a perfect macro or process lens, you will still need to have the artwork, film plane and lens alignment work together to keep all points of the work to be copied, within true sharpness tolerances. </p>

<p>The use of a flat field type of lens will unquestionably improve the flatness of the projection of the image, but not for one minute will it eliminate the need for technical accuracy to achieve the finest sharpness results.</p>

[kparratt]

<p>Yes of course, do both: Combine the advice of both Tim L and Bob S, and you can not do better than that.</p>

[charles_wood]

<p>I concur with Kevin's use of the G-Clron 240mm. I owned it when I was shooting large format and I understand that it was originally a reprographic design for precisely the type of work you want to do.</p>

[bob_salomon]

<p>There are several lenses that you could use including the Apo Ronar 150 or 240mm process lens. </p>

[kenneth_bruno]

<p>Apo-Ronar, G-Claron....240mm<br>

Any other suggestions?<br>

Again, I will be enlarging 4x5 to 16x20 if this makes a difference.<br>

I GREATLY appreciate the expert advice you all have given. Thank you.<br>

Regards,<br>

Ken</p>