Where to find a Helical Lens mount?

Discussion in 'Large Format' started by art_major, Jul 15, 2011.

  1. Hello,
    I was wondering if anyone knows where I can get a Helical Focus mount? Im looking to build a cambo wide like camera. all of the focus mounts that I have seen are expensive from Schneider $340. Fotoman made some at $200 but they are out of business now. does anyone know where I can get one or hack one from another camera? thanks.
     
  2. Relatively small-run items of good quality will naturally have a high price. Rodenstock also make one, but both it's price and quality will be on a par with the Schneider.
    Just keep an eye on the auction sites and be patient, or if it's important, order one from Schneider or Rodenstock. That is why they there. ;-)
    Fotoman were a "bush carpentry" knock up company and catered mostly for the amateur who did not have a photographic business to justify the investment in professional equipment.
     
  3. Not sure that Fotoman could be described as a 'bush carpentry knock up company'? That's quite a harsh comment...I always though Paul Droluk was responsible for a rather nice product.
    There's a guy on Evilbay trading under the name of 'jinfinance'...he sells helical focusing units for around $139 and they are quite OK. Just specify the focal length.
    The guy is 100% trustworthy IMHO.
    Stuff paying $340.
     
  4. A proper focus mount assures exact infinity focus and has the DOF scales for the lens it is designed for. It also has to be made to perform for decades ubder professional use. If you have a Schneider lens buy their helical. If you have a Rodenstock buy their helical. Don't waste a lot of time looking for a used one they rarely show up since their is an extremely small market for helicals in the rear world.
     
  5. I bought a new Rodenstock 55mm with Helix for a 4x5-5x7 Cambowide clone I'm building ( I guess that would make it a Combowide). Also got a short throw and a long throw Helix from Fotoman China. The Fotoman units are not as "Deutch" and perfect as the Rodenstock but they sem to be the best of the Chinese units, some are pretty bleak. Contact me offline and I'll send you the Fotoman China info I got from Paul; I think the contact there with English as a second language skills is Sally.
     
  6. I had a chance to play with a fotoman, and its build quality was fine. I wouldn't want to
    drop it a few feet to to the ground, nor expect it to be in tact, any more than I would my
    Sinar x. I wonder if sk grimes would carry a helicoil mount (skgrimes.com)
     
  7. 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.
    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.
    00Z3UI-380763584.jpg
     
  8. Alan, That's pretty cool!
     
  9. Alan, if you don't mind me asking, what lens was it?
     
  10. There are old macro focusing converters around on Ebay, for example from Vivitar.
    They have an extender lens group inside, and a nice helical focus mount around. Suppose one could buy those for ~ USD 60.
    On have to do some DIY work on that to get the lens away.

    I have one or two at home for my work. If needed I can measure the inner diameter (mail me if I should).
     
  11. There seems to be some confusion here. There are two major types of helical mounts. One type is used for macro photography, it does not focus to infinity and is usually used with enlarging or duplicating lenses. An example of this type is the Rodenstock Modular Focus Mount.
    The other type is made for specific lenses, ususlly in a 0 shutter, and lets that lens focus properly to infinity and is equipped with depth of field scales on the mount just like a lens on a 35mm, DSLR or medium format camera would have. This type of helical is used on cameras where the user wants to be able to shoot with or without ground glass focusing and know that the lens is properly focused. This type of helical is what the lenses on a Linhof 617 or 612 or Tecnar or Aerial Technika would have. An example of this type of mount is the Rodenstock Helical Focus Mounts (note this is plural as each different focal length lens in a 0 shutter would have its own Helical Focus Mount as this type of mount is made based on the flange focal length of the lens it was designed for when that lens is in Copal 0 shutter).
    The Mickey Mouse way that some have described here will work very well for the macro type applications but it will be very inefficient to use these and try to rely on accurate infinity focus, proper intermediate focus distances and proper depth of field scales without wasting a lot of time and effort. ANd after that time and effort it still probably will not be accurate.
     
  12. The Mickey Mouse way that some have described here will work very well for the macro type applications but it will be very inefficient to use these and try to rely on accurate infinity focus, proper intermediate focus distances and proper depth of field scales without wasting a lot of time and effort. ANd after that time and effort it still probably will not be accurate.​
    Nonesense. It is easy to make a new and accurate distance scale. Having said that, mine is used with a 65mm lens on 6x12 format and as such, there is huge depth of field even 'wide open' at f8 (for my SA lens). And Mr Disney's mouse friend didn't help me at all!
     
  13. Thanks for all the suggestions! that 50mm helical focus mount looks great.
     
  14. Fotoman Camera China still produces and sells HFM's, which are calibrated to a specific focal length. They can be reached via email... fotomancamera@yahoo.com.cn (attn: Sally)
     
  15. 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.

    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.

    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.

    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.
     
  16. The 65mm SA lens has an outer diameter of about 42mm on the rear cell. I went through quite a few junk lenses before I found one with a sufficiently wide enough opening for it to fit.
    Something bigger like a broken Bronica ETRS lens would be good. I did look at mine for a while but managed to resist taking it apart!
     
  17. Where can I find information about lenses about the distance from film plane to rear element to get the lens to focus at infinity? thanks.
     
  18. Where can I find information about lenses about the distance from film plane to rear element to get the lens to focus at infinity?
    Which lens? This information is typically on the datasheets provided by the manufacturer. Some of these datasheets are on the web, e.g., Schneider provides them, including for many older lenses. The values can be used for design purposes but there may be manufacturing variations so you shouldn't actually focus the camera this way.
     
  19. A ground glass screen and a ruler will give a reasonably accurate measurement to start with, then you will need to fine tune. Michael is correct...there are variations. You should treat each lens as an individual. You could use any old 4x5 monorail camera as a measuring device, mounting the lens/helical, checking the focus then use the ruler to ascertain the correct distance to the film plane. Be sure to to set the helical at its infinity position.
     
  20. 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.
    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.
    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.
     
  21. The FFL of a Rodenstock lens in a Rodenstock helical is exactly the same as the lens in shutter without the helical. The user has to devise the mount to ensure this FFL. That would be the board design.
     
  22. 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.
    00Z5EF-382629584.jpg
     
  23. My approach to finding a helical mount for this Obsession 612 was to use one from a Mamiya Universal...
    00Z5KS-382735584.jpg
     

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