5x7 to 4x5 Reducing back - design questions...

[Scott --]

Hi, all -

Well, my quest for a 5x7 wooden field camera came to an end with a Seneca Competitor 5x7 (http://flickr.com/photos/scott--/sets/72157600202201845/) (thanks Kevin!). I've started in on the repair work, and I'm setting my sights on the reducing back I want to make for this puppy.

Here's the existing back, after cleaning it up and adding a grid to the ground glass:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1819.jpg

Question on this back: Two of the screws in the folded brass springs have been moved over:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1820.jpg

Can someone suggest a reason to this noob why that'd be done? I feel like I should move them back to where they were, as it looks goofy this way. But that's really thte only reason I have to do it.

Now, for a reducing back: I'm guessing that I size the base of the new bed identically to the existing bed to fit the camera. Then, size the inner dimensions of the rails on the back to match the outer dimensions of a standard 4x5 holder. Center the ends between the ends of the larger base, and make the thickness of the glass holder such that the glass and the film will be held at the same distance from the bottom surface of the base.

This right? I'm thinking that the metal work will be in thin brass stock and should be pretty straight forward.

Let me hear your thoughts and suggestions.

Thanks!
Scott

[Nick_3536]

The screw holes stripped and instead of fixing them the "right" way they moved them?

I've no idea what you are say about the back-) Buy a scrap 4x5 back. Remove the hardware. Mount it on a board [whatever] that is the right outer diameter for the camera with a 4x5 opening.

All done.

[Scott --]

C'mon, Nick -- where's the fun in that? :D

[Nick_3536]

You say that now-) Wimping out and canabalizing a scrap back is an time tested method.

[Scott --]

You know, I've already got the hunk of 12/4 mahogany ready to be pulled from the board.

Actually, the base frame itself is pretty straight-forward, if I follow the existing manufacturing. Through mortise-and-tenons, the sides of the holder part are applied, and the frame for the glass is another M&T frame. One router table setup and all the joints are done. What's going to be challenging are all the curves and recesses. But applying the back parts (as opposed to routing them from a thicker piece) is going to simplify all that.

I'm in design phase on a 4x5 camera, too. Making the back from scratch is an exercise in ironing out design kinks, anyway.

[wfwhitaker]

The screws may have been moved to allow the back to open further to accommodate a thicker holder. Who knows.... If it works, leave it well enough alone and go take pictures.

Making a 4x5 reducing back is relatively easy, especially if you adapt an old back as suggested. Graflex backs show up periodically on Ebay and are a good start. If you adapt it directly, you may not be able to get your fingers under the holder to remove it because of the surrounding frame. You'll probably need to set it out from the camera a bit to allow finger relief.

[Gene McCluney]

The screws may have been moved to give more tension on the inserted filmholder, to compensate for age-weakness in the brass springs. However the correct way to do this is to take the springs off and bend them slightly, thus restoring the tension.

[Rafael Garcia]

I respect the ambition to build the reducing back from scratch. Best of luck! For mine I followed the "buy the scrapped back and just build the lid" method and I'm happy. As for the moved screws, looks like an attempt to gain more width for thicker holders.

[Paul Fitzgerald]

Scott -- ,

If you make your adapter back flat you will have a bear of a time inserting and removing holders and darkslides. Look at commercial reducer backs, they all have a stand-off built in, a place for your fingers to be.

just a thought.

[Flexnib]

Hello,
I have an Improved Seneca View and the 2 holes you are looking at used to hold a metal bar that went from the top to the bottom of the holder. You turned the metal bar at the top and it opened the back up for easier insertion of the film holder. It was also missing on mine but I am purchasing a beat up one for parts and this bar is on this one. The 5x7 back that is missing the bar has had the 2 holes filled with old paper.
I can send a picture next week of the mechanism if you are interested.
Arthur

[Scott --]

Scott -- ,

If you make your adapter back flat you will have a bear of a time inserting and removing holders and darkslides. Look at commercial reducer backs, they all have a stand-off built in, a place for your fingers to be.

just a thought.

Ok, I admit to being daft here. I can't picture what you guys are talking about. The edge of the existing ground glass frame has a relief on the bottom edge to grab the frame by:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1824.jpg

Is that what you mean?


Hello,
I have an Improved Seneca View and the 2 holes you are looking at used to hold a metal bar that went from the top to the bottom of the holder. You turned the metal bar at the top and it opened the back up for easier insertion of the film holder. It was also missing on mine but I am purchasing a beat up one for parts and this bar is on this one. The 5x7 back that is missing the bar has had the 2 holes filled with old paper.
I can send a picture next week of the mechanism if you are interested.
Arthur

Yeah, Arthur, I'd be very interested in seeing that. Thanks for the offer. And if you have any spare parts left over from that beater, PM me. ;)

Incidentally, here's the mahogany I'm using, before I started milling on it:
http://i80.photobucket.com/albums/j185/bliorg/IMG_1822.jpg

It's beautiful stuff.

Thanks for alll the help.
Scott

[Nick_3536]

Why are you using 3" thick wood to make a back?

[Scott --]

I'm resawing the stock off the 12/4. The 12/4 has been sitting in the shop for 3 years, so it's stable. Plus, it's paid for. ;) Anyway, I get complete color and grain matching doing it this way, and will have enough material from this one 12" piece (there's about 6' of board left) to do the back, plus a few lensboards, too.

[Robert A. Zeichner]

The back is the most critical part of any view camera. Your bellows can be gunked up with duct tape, your lensboard can be made out of cardboard and everything else can be clamped together with a pretty ungainly collection of hardware, but if the ground glass/film plane coincidence is out of whack, you'll never get really sharp negatives. The ANSI spec for film holder depth for 4x5 is 0.197" =/- .007". That's the depth from the septum to the bearing surface of the holder. You have to take into account the thickness of the film you will be using and subtract that. Make the finished depth as close to +/- 0.0" as you can as the film holders will vary and the tolerance is provided to take that into account. This is why a lot of folks just adapt an old Graflok back. That and so you'll be able to use roll film holders should you desire to do so.

[Scott --]

Alright, alright - I'm throwing my hands up. Even though I think the spring back is doable, and would be purty, I'm going to lower my sights and try to find a Graflok back. The allure of speed, ease, and rollfilm backs is too strong... :rolleyes:

[Robert A. Zeichner]

Scott, you'll still have plenty of opportunity to put your cabinetmaking skills to use in that you'll have to make something to which to attach the Graflok as well as maybe routing out some relief along the edge where the film holders get inserted. You see this on Deardorff reduction backs and this is handy for getting your fingers behind the holder and also to make it a bit easier to fit things like Polaroid backs and such. It's probably a good idea to chamfer the window on the inside of the back so light rays don't glance off that surface and potentially cause some non-image forming light to strike the film. If you're really ambitious, how about a revolving panel? I've always wanted one of these as I find it inconvenient to remove and reattach the back and always worry I'll miss the pins someday and the darn thing will hit the ground and ruin my day. Good luck with this project and be sure to post your handy work when it's complete.

[Jack Fisher]

Scott,
In your shop picture, do I see a guitar mold? I built a classical guitar in 1970. I used Honduras, ribbon-stripe book-matched Mahogany for the body, and Alaskan Spruce for the sound board; along with a lot of other woods (Rosewood fretboard, etc. ...over 80 pieces in all). It is a fine instrument, and plays very well.
Nice shop - and I bet the envy of many.

Jack

[Scott --]

You know, you're the second person to ask that. It's actually a pair of Windsor chair seats that have been waiting to be legged up for too long.

The shop is/was a mess, but I spent a few hours cleaning this past weekend. Looking much better now. Might actually be able to build something at the bench this summer. ;)

[Jan Pedersen]

Scott, remember to save some of that Mahogany for lens boards to my new 2D;)