Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Chemical Focus

  1. #1
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522

    Chemical Focus

    EDIT ( 12/5 ): this turned out to be a silly mistake....

    I've only made 3 exposures so far in my new foamcore camera. It's got a B&L rapid rectilinear lens from a 1914 Kodak 3A Autographic. With the front element removed, the focal length is about 10.5 inches.

    Originally I found the focal length at infinity by using a cardboard box with a sliding clipboard inserted. When I built the foamcore box, I made it close... within a quarter inch. If I tilt the filmholder slightly forward, the image goes out of focus. If I hold a paper slightly behind the film plane it also goes out of focus. I can't say for sure but I think the entire film plane is within 1/8th inch of the true focus. ( No ground glass, this is all by viewing the image projected onto a piece of white paper. )

    1st exposure: forgot to remove the front element, everything out of focus. ( It still looks neat... I'll post it )
    Somewhat overexposed but the light was very tricky.

    2nd exposure at the beach and there must have been a lot more UV than I counted on because it was badly overexposed almost black all over. But there was a very faint image and my impression was that the lines were crisp. I tossed that one.

    3rd exposure today: just a test because I was worried about exposure or maybe a leak since the first two were overexposed. I underexposed, but confirmed that my original ISO 12 for this paper is probably about right, also that there are no leaks. But... the horizon looked fuzzy. This was a F/64!

    I don't have any experience with a lensed camera this big, so my questions:

    1) Wouldn't there be a decent depth of focus at F/45 or F/64? Am I wrong to expect 1/8 or 1/4 inch not to matter much?

    2) Is it possible that I need to worry about so-called chemical focus with this lens? I would have thought by 1914 a rapid rectilinear lens would have two achromats and enough correction so that visual and UV focus would be the same? Has anyone here run into needing to adjust for chemical focus with paper negatives?

    I've used several cameras of a similar vintage with paper negatives, and while I often use a yellow filter, I've made enough without that I think I would have noticed if there was a focus difference w and w/o the filter.

    Any thoughts???
    Last edited by Ned.Lewis; 12-05-2013 at 08:39 PM. Reason: clarify
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  2. #2
    Senior Member spiffytumbleweed's Avatar
    Join Date
    Aug 2005
    Location
    Austin, TX
    Posts
    207
    I'm far out of my area of expertise here, but what purpose is served by removing the front lens element? I shoot a Kodak No. 2 Premo of similar vintage mounted in a body cap using a macro bellows for focus and I find it goes from Disneyland wide open to pretty normal when stopped all the way down. Both softness and DOF seem quite responsive to aperture.

  3. #3
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    "Disneyland" I like that!

    The lens covers 8x10 with one element removed. I've been wanting to make some bigger contact prints.

    With both in place it just barely covers 5x7 but it's made for 3.25x5.5 so it would probably be pretty soft at the edges.

    I got this specifically because I'd read somewhere about it covering 8x10 if you remove the front element, and it does quite easily. This camera actually has an 8.5x11 holder, and it covers the whole thing.

    I'm mystified by the apparent fuzziness in today's try... was expecting it to be sharp stopped all the way down like that.
    Maybe there is a simple answer like I somehow moved the camera ... it was sitting on a corner railing on my back porch.

    Hopefully I'll have time tomorrow to try again!
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  4. #4
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    Okay, well this is embarrassing. I made another test today and made the same mistake. It was out of focus because YET AGAIN I forgot to remove the front lens element. Wow. Out of the first 4 tries, I did it 3 times!

    A test with the element correctly removed is drying now, and I'll look at it carefully when it's dry, but at first glance it looks perfectly sharp. I think I have a working camera that is ready to go make some photographs with.

    I think this goes to show how deeply ingrained habits can be.... I'm used to a certain flow and sequence of doing things when I take a picture with a paper negative, mostly thinking about and then double checking the exposure. I'm going to put some kind of note on top of this camera "Check the Lens!!!"
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  5. #5
    This sounds like an interesting project, looking forward to your results, Ned.

    I haven't used this type of lens myself, but your description of what happens with the front lens element in place sounds like the focal length is reduced which, with the same sized aperture, means your focal ratio is also reduced, which reduces depth of focus. It might also shift the focus plane with the front element in place.

    These foamcore box cameras can be fun, especially when you get satisfyingly sharp results.

    ~Joe
    "There was just that moment and now there's this moment and in between there is nothing. Photography, in a way, is the negation of chronology."-Geoff Dyer, "The Ongoing Moment"
    My Writing Blog: Joe Van Cleave's Blog
    My Pinhole Blog: Obscure Camera
    Visit my F295 Gallery

  6. #6
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    Hi Joe, that's exactly right. With the front element in place the camera is focused at a point about 2 feet in front of the lens.
    With the front element removed, it is supposed to be focused at infinity, we'll see! I think it is going to be a lot of fun to try using it both ways.
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  7. #7
    One thing you might want to consider is working out the hyperfocal distance for your lens, and focusing at that distance, rather than infinity. That way, everything from infinity to half the hyperocal distance will be acceptably sharp, which will give you maximum depth of field for most subjects.

  8. #8
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    Quote Originally Posted by PhilHerring View Post
    One thing you might want to consider is working out the hyperfocal distance for your lens, and focusing at that distance, rather than infinity. That way, everything from infinity to half the hyperocal distance will be acceptably sharp, which will give you maximum depth of field for most subjects.
    Hi Phil, yes that's a good idea and I'll definitely consider it. This is a fixed-focus camera, so I'd want to choose HF for the largest aperture I might use. Even though it's fixed focus, it would be easy to extend the lens a little or to shim the filmholder forward a little, so I can adjust the "fixed focus" to set it in a new fixed position.

    So after all that, I examined my test negative with a magnifying glass and it is perfectly sharp. So this post was much ado about nothing! It's raining here today but supposed to clear up over the weekend so I'm hoping to give it another try soon!
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  9. #9
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    Here's a late follow-up to this thread. My wife solved the problem by making me a label that says "take the lens off!".

    Since then I have not made the silly mistake again. I've now made a number of successful paper negatives, all stopped down to f/45 or f/64. I've also made my first 3 calotypes, with the lens opened as far as it will go, about f/11. To use the camera with the lens all the way open, the focus needed to be adjusted again. For this, I cut a hole in the back of the camera, fashioned a rude ground glass by putting scotch tape on a piece of picture frame glass, and putting it into a frame exactly where the paper is when taking a picture. The lens needed to be moved in a tiny amount to achieve focus... maybe 1/16th or 1/32 of an inch. Now it is probably as close to being in focus as it will get. The corners are soft wide-open but it also has an neat dreamy look that I like.

    8x10fc.jpg

    I built this camera specifically to make big paper negatives for contact printing on "homemade POP" paper. But along the way, I've now made some salt prints from these negatives and it's great for that too. Of course one thing led to another and now I've made my first 3 calotypes in it too... I had no idea when I started how fun and satisfying making a calotype would be. So I'm already planning "version 2" which will use a bigger lens and have the ability to focus. I'm heading toward a sliding box camera like the one Joe made a video about, probably with simple paper holders like Ray Heath showed us it is possible to make from simple materials. This hobby has no end in sight!

    The picture above shows the camera making my second attempt at a calotype. The calotype came out fogged, but here is the scanned and inverted image it made:


    Russian River by Ned, at ipernity

    Over at APUG there is a fun activity called the "Monthly Shooting Assignment" and the theme right now is "cheap cameras". I made this picture with that in mind. I'm still hoping to make a better calotype before the "assignment" period ends next month!

    Calotypes are incredibly slow compared to commercial paper negatives. I metered this scene at a bit less than 2 stops below "sunny 16" ( ~EV 13 at ISO 100 ) to pick up details in the shadows. For a normal paper negative, with no pre-flashing and no filters, it would be about 5 seconds at f/64. This exposure was 14 minutes at f/11, and I think it was about right!!

    To make the calotype, I pretty much followed the instructions here:
    http://www.flickr.com/groups/1384661...7631325185688/

    Really the only difference is that I made smaller volumes of the solutions. I didn't have enough KI to make 500ml, and I only made 100ml of silver nitrate sensitizer. Otherwise that link describes exactly what I did. My "Canson Marker" paper needs to be acidified in order to make a calotype without chemical fogging. That was accomplished by a 1 hour soak in white vinegar 1:2 with distilled water, followed by 2 hours washing. I made my first fog-free calotype a couple days ago in this same camera. Not a very artistic photograph, but a successful calotype:


    Burnside Calotype by Ned, at ipernity

    That one was an 8 minute exposure.
    Having lots of fun!
    Last edited by Ned.Lewis; 01-23-2014 at 02:29 PM. Reason: added results...
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  10. #10
    I'm loving this project, you've made great progress. Seeing how slow the calotype emulsion is, I have no reason to complain about Harman DPP.

    I like your wife's idea of the label, sometimes the best solutions are the most obvious.

    ~Joe
    "There was just that moment and now there's this moment and in between there is nothing. Photography, in a way, is the negation of chronology."-Geoff Dyer, "The Ongoing Moment"
    My Writing Blog: Joe Van Cleave's Blog
    My Pinhole Blog: Obscure Camera
    Visit my F295 Gallery

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •