allen_whittier

<p>I agree with Rodeo Joe. The best way is to measure the entrance pupil. When you measure the E-pupil you are measuring the actual diameter of the circle of light that's entering the camera. Then divide bellows draw (Focal length) by the E-pupil size for f stop.</p>

<p>Here is a photo of the back of the helical mount with the rear element of the 65mm removed. The two brackets that stick into the helical assembly are clearly seen here. They are connected to the body with two allen screws. The rear element of the 65mm Super Angulon misses these by just a few thousandths of an inch. The space between them is 1.668 inches and the diameter of the rear element is 1.650. The ring that these guides extend into has a diameter of 1.662 inches. It made getting the face plate centering somewhat critical. You can also see the aluminum face-plate I made.</p><div></div>

<p>You can work off the data sheet or put the lens in a LF camera and measure it. If you work off the data sheet be sure to design the ability to shim the lens in or out. Lenses vary in manufacturing. It's easy to make shims by cutting out thin washers with an Exacto knife mounted in a protractor. Most hobby shops have shim material in various thicknesses for model making.</p>

<p>I don't see the advantage of using a helical that is specifically designed for the lens with infinity set up perfectly. You still need to build the correct flange to film distance into your camera, just like the DIY helical, and account for the lens manufacturers variability. The depth of field is specific to the format, not the lens. It's assuming a 1/1500 of the corner to corner dimension for your circle of confusion (COF) when calculating acceptable depth of field (DOF) focus. Depending on how you are using your images you may want to start with a different circle of confusion. For instance I always use 1/1500 the corner to corner of a square format image when working with any aspect ratio of medium format film. I want a 6x7, 6x9 or 6x12 image to have the same DOF characteristics as 6x6 so I set it up for 6x6 for all medium format applications. This makes it very easy to determine the movement of the lens in and out, because it will be the same as any medium format camera. Just measure how much the lens moves in your off-the-shelf camera and match that in your DIY camera to set up your DOF scale.</p>

<p>Another way to get the DOF scale for 6x6 is to look at the 35mm and 120 formats. the corner to corner for 6X6 is 80mm and for 35mm its 40mm. It will take exactly twice the movement of the lens to get the same 1/1500 corner to corner COF with the medium format as it did with the 35mm. So just double the scale on the 35mm lens. If you are using an existing medium format lens helical use the DOF scale from the old lens.</p>

<p>I don’t remember what lens I started with, but I do remember what limited my choice. There is a guide that mounts to the back rim of the lens and sticks up into the inner helical. It keeps the inner helical and subsequently the lens from spinning while focusing. In many lenses this is mounted to the bayonet that must be removed. But in others it’s attached to the lens body and remains in place when the bayonet is removed. That same guide limited the space inside the helical, and the maximum diameter lens that could be mounted. <br /><br />The two parts that need to be manufactured are a ring to mount the helical to the camera and a small round lens board to mount the 65mm Super Angulon to the helical. I machined these parts out of aluminum because I had the tools to do it, but they would have been just as good made out of an easier material to work with. <br /><br />With the abundance of junk lenses out there right now, you won’t have that much invested in multiple attempts in getting it right. You will know if you have something to work with or not as soon as you start taking the old lens apart. <br /><br />Infinity focus adjustment is easy to achieve. Determine the face plate to film distance and build it into the assembly. The other focal distances can be achieved by measuring the face plate to film distance for the desired focus distances and marking a new scale on the focusing knob as you turn it. A depth of field scale can be calculated for your format and marked using the same method. Calculate the movement and turn the helical to the point that achieves it, then mark. I didn’t make new scales because I’m using mine on my Super Graphic 4x5 and use the focusing screen. I too am working on a 6x12 that this face plate will mount onto and I’ll make new scales then.</p>

<p>If you have a few tools you can build a great helical mount out of an old lens off a 35mm camera. You have to chose the lens you start with carefully to make sure you have all the clearances you need for the lens to work properly. I put a 65mm Super Angulon into an old 55mm lens body. I had to find a lens body that still had a rear flange to connect a lens-board to once the old lens was removed, many don't. The rear lens protruded out to the rear opening of the helical mount I picked and had a clear optical path. I measured the lens movement with calipers to work out the new focus scale and f stop to depth of field scale. There are plenty of charts on the web to help you there. If you can find an old medium format lens it would be even better. There would be a lot more room to work with.</p>

<p>Another option is to shorten a closeup bellows for a 35mm camera to become a focusing bellows for your lens. It's less exacting but will work with a focusing screen. You could make it easier to work with with a stop for infinity and a focusing scale like a sinar on the focus knob.</p><div></div>

<p>Joseph and Ivan are both correct. There's also a characteristic of vision that kicks in to amplify the effect.<br>

The eye doesn't take a little picture of an image and throw it into the brain. It looks at three thing (1) Massing of areas and how they relate to each other (2) Angles and shapes and how they relate to each other (3) a grid to place them on to build a picture. It takes all the info from two of these images derived from concave screens and looks for something to turn into a 3D image. Think of all the conflicting data that has to be thrown away for this to work. <br>

You can throw a monkey wrench into the whole process to get different results. A good example is what artists do to convert a 3D image to a 2D image. There are several tricks. Look through an opening the proportions of your paper to pump up the minds spacial relationships and grid. Or, actually look through a grid to do the same thing. The simplest thing is to close one eye to rid the process of two images to work with for 3D. The brain immediately goes looking for something in the image to create a 3D image. What it tends to find are shadows that weren't obvious before to define form coupled with layering created with the change in focus to determine front to back relationships. Both of these tasks tend to be best done with stereo vision, the default-mode so to speak.<br>

Now take your ground glass. What is the brain going to go looking for when you look at this 2D image on the screen. It seems that it should find a single focal plain and switch to things like relative size, shadows, and light values to interpret form and depth. But your stereo vision finds the effect described by Joseph, grabs it and runs with it because it's the default-mode for determining depth. This is why so many visual tasks require "Training the eye." You have to change your default-mode to one that processes images in a useful way for the task at hand.</p>

<p>What's wrong with the Super 23? That's my preferred camera for 6x9. It has great lenses and great accessories. It's a workout hand held, but wonderful on a tripod.</p>

<p>Jim, I'm with you with the washer. I would cut one side of the washer back almost to the hole. It would look like a "D". Then, from the inside of your lens board frame, screw a machine screw through a tight hole that will hold it from turning. It should stick out the front of the frame a half inch or so. Slip the washer onto the screw and secure it with a wing nut or a knurled nut. to remove the lens board loosen the wing nut and spin the washer around to the gap to clear the lens board. Use full sized washers at the bottom and the notched one at the top. The advantage here is the ability to clamp your lens boards tight.</p>

<p>The Fresnel out of an overhead projector has a very short focal length and works well with wide lenses. They can be found for very little, like $10 to free. At 11x11, they're better suited for 5x7 and 8x10, but will probably cut down OK.</p>

<p>Old slide projector lenses make great focusing loops. If you have one around give it a try. Since they are a DIY you can shorten them by cutting off extra tube length and have an off-the-ground glass loop that can be tilted to check corners.</p>

<p>Joseph, thank you you for the wonderful input. It's nice to see someone well grounded in the present century (I'm not) providing up to date input. I will concede on the entrance pupil vs nodal point because I don't remember my sources to be able to challenge it. In the end, what's important is to improve your camera placement if you're making a number of images to stitch by moving your camera around in the scene. Rotating the camera around a somewhat stationary point around the lens will produce a better set of image files to work with than snapping shots using your tripod movements.</p>

<p>Rodeo, I didn't say the nodal pivot point eliminated lens distortion. I recommended eliminating stereo skewing by reducing lens movement while taking several photos to stitch. I also recommended using the center portion of the image where there is less distortion rather than using a wide angle lens. Using a smaller field of view avoids the problems you get when you try to stitch wide angle images together. Try stitching 4 Wide angle images of a square scene together. Then do the same with 25 images and see how much better it turns out. Unless there is something complicated going on in your scene, it will probably turn out without anomalies using the 25 images. Yes there is still distortion from one shot to the next, but the stitching programs do a nice job of working it out if you don't bury them with overlapping wide angle images. There is very little distortion for the program to deal with if you limit yourself to about 20 degrees of image and a 25% overlap on each side by lens selection or cropping. There won't be much to work out between most images, and 25 shots will give you a nice 100 x 100 degree field of view.</p>

<p>There will always be something unnatural about a scene that takes in more than 50 degrees of viewing field. 30 degrees is the sweet viewing field of the human eye. If we want to see past this width we move our eyes to a new sweet spot. Most of this is due to the poor quality of the image on the retina due to it's shape and orientation of the lens. Then, you have competing images from two eyes. Allowing both eyes to take in a 100 degree field of view all at once and getting it to look good is a subject, technique, composition balancing act that is a challenge to any photographer.</p>

<p>This has been a very informative thread.</p>

<p>I also have a bit of experience setting up a cirkut camera. For those of you who have never seen on, it's a camera that runs the film past a narrow slit as the camera turns and takes a panorama. The secret to getting it to work properly is to get the camera rotating around the nodal point of the lens. By doing this you eliminate the image skewing. The skewing occurs as a result of having to add the lens movement into the equation. If the lens is moving at all as objects move from the right side of the field to the left, near and far objects will start experiencing stereo separation. When you're trying to synchronize the moving image to the moving film this stereo skew dramatically impacts focus.</p>

<p>If you’re going to use your digital camera with its own lens, here are some things that’ll make your job easier. Make yourself a camera mount that rotates around the nodal point of your lens. That is, keep the nodal point stationary as the camera moves. They are easy to make. For as accurate as it has to be it can be made out of wood or any other convenient material.</p>

<p>Build a fork like the front standard of a view camera, and mount a cradle in it that places the nodal point of lens directly between the pivot points. By swinging it you will tip the camera up and down while keeping the nodal point stable. Place the tripod mounting hole for this setup directly under the nodal point and you can swing the camera from side to side and maintain nodal location. If you can’t find the nodal point specs for your lens, use the location of the shutter, it’s close enough.</p>

<p>Now that you can create images with no stereo skew, limit the field of view of your images. If your depth of field can handle it, use a long lens rather than a short one. (Don’t use a telephoto lens. The nodal points for front and rear elements are not the same point. Both points are outside the lens, one in front and one behind.) A short lens introduces all those crazy distortions that stitching programs are supposed to remove but don’t. You are placing a number of flat images onto the inside of a round sphere. The more images you use to do this the fewer distortions you will have between images. Imagine covering the inside of a ball with six images. You are stretching a cube into the shape of a ball. With six thousand it will look pretty much like a ball before any corrections. If you can't sacrifice the depth of field with a long lens, use a short lens and take a lot more images so that you can use the sweet spot in the center that is relatively free of distortion. Before you start your stitch, crop your images down to this part of the image and about a fifty percent overlap. You will find that your stitches will come out relatively free of distortions and anomalies.</p>

<p>Cirkut camera manual: http://cgi.ebay.com/Cirkut-No-8-Outfit-Instruction-Manual-/220718702788?pt=LH_DefaultDomain_0&hash=item3363dc20c4</p>

<p>You shift the film plane not the lens. I hope that's just a typo in the image caption. The lens needs to remain stationary because it is casting an image circle on the film plane and you move from spot to spot on that plane to capture what ever part of the image you want.<br>

I also shoot a lot of stereo and a small movement of the lens introduces an entirely different image to the film plane. A couple of inches of movement creates a wonderful stereo pair. If your image is of a flat row of objects across the field of view there won't be much of a problem. But, if it's a layered image with objects at different distances you will start seeing drastic errors with the relationship of near and far objects.<br>

You need to invest in a lens that can give you the image you want on the ground glass, then capture that image with your camera. This will give you full use of the front movement without introducing distortion. Since Sinar tilts the whole front standard to gain tilt, and there is no way to move the lens and remain focused, Moving the rear standard works best here also.<br>

Have you considered making a two axis sliding mount to hold the digital camera. They have been used for over a century to make large sheets of film with multiple images in rows. They move the film around capturing the central image in a small masked hole. They would also move a camera around to capture different parts of the large image. I have one with my 5x7 Berk and James. It was set up for two side by side images. By changing the detent points and removing the mask it would take a nice ordered row of images quite well. Add a couple vertical positions that the camera can slide into and you have a nice batch of images to stitch without the worry of moving the camera. You might consider picking up a 5x7 back to give yourself a bigger area to work out tooling. It will also give you extra stretch in those great architectural moments. A 90mm Super Angulon will work well with the 5x7 if you aren't using the image to the corners. I shoot a Sinar F with a Noma 5x7 back with a 90mm on a regular basis.<br>

It isn't hard work getting the lines all parallel before you make your shot. Just look at your bubbles and set them vertical and level for architecture. Why not start with a file with the lines as close as possible to a row of pixels. You were correct to want to get lines parallel. Why start with a messed up file, even if it is easy to correct.</p>

 

<p>Why not put a 120 back on the Sinar? Then everything will work together. I use mine with a 65mm Super Angulon and a 6x9 back for architectural.</p>

<p>The Galvin is a nice full movement lightweight medium format view camera. I've seen these turned into short focal length cameras by shortening the bellows or replacing them with a homemade bag bellows, and changing the rear standard to a straight rather than jogged design. I have a Galvin and have always appreciated it's simple design and light weight.<br>

http://cgi.ebay.com/Galvin-2x3-View-Camera-Lens-Film-Holders-/260749008160?pt=Film_Cameras&hash=item3cb5da1d20</p>

<p>I noticed another product on eBay and did a Google search. The DAYI 6x17 Roll Film Back.<br>

http://cgi.ebay.com/DAYI-6x17-Roll-Film-Back-Linhof-Wista-TOYO-4x5-Camera-/270695689592?pt=Film_Cameras&hash=item3f06b86d78<br>

http://www.photo.net/large-format-photography-forum/00TJ6r<br>

http://www.largeformatphotography.info/shen-hao-6x17.html<br>

http://www.flickr.com/groups/354354@N23/<br>

It has the advantage of using a 4x5 camera, but takes a camera that can close down pretty short to work with short lenses.</p>

<p>R miller, you are correct on all counts. The tape does elevate the film, but only .001 inch or so. Less than the slop in the 5x7 film guide. This was not a problem due to my depth of focus with wide angle lenses. The big focus challenge is making sure your lens and film are perfectly parallel. I was using a Burk & James field camera at the time, so spent quite a bit of time setting up the shot for good focus. I now have a Sinar F2 with a Norma 5x7 back. If I ever do this again it will be a lot easier.</p>

<p>I have done 6x17 in my 5x7 with a half slide and it works well. The concern about the light seal is a concern, although I didn't damage any. I found there was a chance of a slight light leak in the light trap as the open part of the slide went by. I solved the problem by using the dark cloth to shield the holder while moving the dark slide. You can avoid damaging your light seals by tapering the cut in the dark slide so it slices a little as its installed.<br /> <br /> If you use a field camera that allows the back to be installed to load from the left or right, you can setup a mask inside the camera to expose only half the image, top or bottom, and flip the back over to expose the other half. I've used both methods. I eventually ended up using both methods together to control unwanted light bouncing around inside my camera.<br /> <br /> Another method I've used is to cut strips of 120 film to 7 inch lengths and install them in the 5x7 holder. I did this by tucking one edge in the film rail and securing the other edge with double stick tape that I put down the middle of the holder. I initially resorted to this method because the film I wanted to use was no longer available in 5x7. In the end it was very successful. My film lab even liked it. They mounted the film in 4x5 clips with the film bowed and found that they did fine in their film processor. If I was doing a lot of this I would glue a couple rails in a 5x7 holder that placed the film in the center of the holder. This method would become even more viable if you are processing your own film. I envision a drum processor with a stack of 120 carriers, all holding one piece of film on the outside turn.<br /> I used my 90mm Super Angulon with this setup and got great results. If you are shooting 1:1 you might be able to use one of your medium format lenses. I haven't tried it, but I think the 50mm off my Mamiya Press or my 65mm Super Angulon would work for what you're proposing.</p>

<p>You get two sheets of 5x7 out of each sheet of 8x10. For those of us who shoot 5x7 as a first choice camera this is standard practice.</p>

<p>Hand held 9x10 is quite feasible, but with a wide lens. Here is a link to the best product on the market right now.<br>

http://www.bostick-sullivan.com/cart/product.php?productid=680&cat=237&page=</p>

<p>Rod, .028 is 1/1500 the Diagonal of 35mm film. The problem with using this number for large format is that the LF lenses were never designed to perform with such a small circle of confusion. Besides, to achieve it you would have to assume your depth of field is much less than it really is. You end up stopping down in an attempt to open up your DOF. (calculate how little focusing movement you get with such a small COC and you find your almost at prime focus.) As a result you will have much more DOF than you anticipated. The 35mm camera uses .028mm because it is 1/1500th the corner to corner of that format. If you use 1/1500th the corner to corner dimension with any other format it will give the same results, and that's what the lenses are designed to.</p>

<p>Calculating the COC (Circle Of Confusion) can also take the more generic form used by cameras that have the Depth of Field limits such as you see on all 35mm cameras and some more sophisticated view cameras like the Sinar. They assume a COC that is a diameter 1/150th the measurement from corner to corner of your film as the largest size a point of light can become. For a format that is 300mm corner to corner, the circle is 2mm. For 75mm it is 0.5 mm.<br>

Since the light from the lens is a cone that starts as the diameter of the light coming from the aperture and ending up as a point on the film, you can determine where along the cone this diameter is achieved. If you have a 100 mm lens at f8 the aperture diameter is 100mm/f8 = 12.5mm dia. So now you have a cone of light 100mm long with a large end of 12.5mm.<br>

For a film format that is 75mm from corner to corner, the COC is 0.5 mm. Using the 100mm/f8 lens above the 0.5mm dia along that cone is easy to determine. Take 0.5mm dia/12.5mm dia and multiply it by the length of the cone, or focal length of the lens. This gives you how far the lens moves to reach the max COC for your format. That's (0.5mm COC/12.5mm Aperture) X 100mm Focal Length = 4mm of lens movement. Since the cone of light spreads out the back side of prime focus at the same rate it came into it the distance is the same on both sides of prime focus for a given f stop.<br>

A nice thing to know when building a camera is that for a given format that distance of movement is the same no matter what lens you use. This happens because all the mathematical relationships are linear. In plain English, no matter what focal length is put into the formula for a given film size and aperture the lens movement will be the same. This is why the DOF (Depth of Field) adjustment on a Sinar 4x5 works with any lens. The prime focus distance from the film is all that changes. As a result, you can create a min/max DOF scale for your f stops and it will work with any lens focused at prime focus at the center of the scale. I use a post-it with the f scale on it to stick on the track of my press camera, after it's focused. Don't forget to recalculate your true f stop for close-up work. The scale will still hold true for the recalculated f stop.</p>

<p>I use the Besler color drum that processes four sheets at a time. I've tried most of the drums out there and have found the Besler to be the easiest to use. The Besler drum comes with rails that slip into slots to create stops that hold various sizes of film. If you get a drum make sure these aren't missing. The drums come in several sizes. The largest one I have will accommodate 11x14 film with ease.<br>

Since I always shoot a Left/Right stereo pair, processing the two together helps me spot a shutter that isn't firing at a constant speed. The disadvantage of processing four at a time is the "learning curve" involved in learning to get the back two negs out without scratching them. It's a great way to process film.<br>

http://www.google.com/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&channel=s&hl=en&source=hp&q=Beseler+Print+Developing+Drums&btnG=Google+Search<br>

http://cgi.ebay.com/Beseler-Print-Developing-Drums-/360315664721?pt=LH_DefaultDomain_0&hash=item53e47cb951</p>

<p>Good buy. You will want a shorter lens right away. 135mm is the wide-normal lens and 150 is the tight-normal lens. A 90mm Super Angulon is a good wide angle with movement for a monorail and an90mm Angulon is the lighter version for a field camera, but doesn't have any movement with 4x5.</p>

<p>The same focal length lens for a 4x5 will be a much lighter lens. For instance, I use a 90mm Super Angulon with my 5x7 with no movement. To do the same on my 4x5 I only need an Angulon. Quite a difference in lens size and weight.</p>