Site Sponsors
Results 1 to 16 of 16

Thread: Focus assurance question

  1. #1
    Senior Member
    Join Date
    Aug 2009
    Posts
    422
    Post Thanks / Like

    Focus assurance question

    Noob here -

    I've built a small LF kit around an Ebony RW45 and now am working on technique. A friend who has many years' experience in commercial product photography with LF equipment looked at my first few negs. Among his comments he criticized the lack of sharpness. I fully recognize the largest variable is my own inexperience, but I was thinking that it might be a good idea to confirm the camera itself isn't the issue (the RW45 came to me used).

    How do you measure the lens-to-film plane and the lens-to-ground glass distances and ensure they are within tolerance?

    Or is this obsessive on my part?

    First post - thanks in advance for any advice.

    Mike

  2. #2
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    First off, what magnification is your loupe? If it is anything less than 6x, you are only getting close. 3x or 4x is almost useless for critical focus. Next, the loupe diopter HAS to be set perfectly for your eyes -- if that adjustment is off, your GG focus will always be off.

    Now to checking the GG position: First remove the film back from the camera. If there is a fresnel screen, remove it and reinstall the GG. Then using a steel rule across the flats and a depth gauge, measure the depth to the GG and then insert a filmholder and measure the same depth to the back of the filmholder. The filmholder measurement should be .008" deeper, +/- .004 (so between .004 and .012 deeper), than the one to the GG. If it varies from that, the GG needs to be shimmed or shaved appropriately.

    Note that a fresnel brightens the focus screen, but decreases focus accuracy at the same time, so it is a mixed bag of tradeoffs.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  3. #3
    Senior Member
    Join Date
    Aug 2009
    Posts
    422
    Post Thanks / Like

    Re: Focus assurance question

    Thanks very much, Jack.

    My loupe is 4x and I haven't set the diopter. I will do so. I'll also get a steel rule and gauge to do the measurements.

  4. #4
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    Quote Originally Posted by MCTuomey View Post

    and I haven't set the diopter.
    That is likely your main issue with focus
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  5. #5
    Administrator Bob's Avatar
    Join Date
    Oct 2007
    Location
    Prescott, Arizona
    Posts
    4,492
    Post Thanks / Like
    Images
    367

    Re: Focus assurance question

    Another technique I have used is aerial image focusing.
    Once the ground glass is calibrated to be in the same plane as the film, you might consider marking the ground glass in the center with a sharp pencil (a plus sign for example, then put a tiny drop of Canada balsam at the intersection of the thin pencil lines. Once it has dried, then when focusing, at the small transparent spot, you can use parallax focusing. By moving your head slightly from side to side, any shift of the image relative to the pencil mark indicates that the image is out of focus. This is actually very sensitive and beats a loupe IMO, but you are restricted to judging critical focus to just that one spot.
    -bob

  6. #6
    Senior Member pellicle's Avatar
    Join Date
    May 2009
    Location
    Southport, Australia
    Posts
    1,429
    Post Thanks / Like

    Re: Focus assurance question

    Hi

    Quote Originally Posted by Bob View Post
    ...a tiny drop of Canada balsam at the intersection of the thin pencil lines. Once it has dried, .. you can use parallax focusing. By moving your head slightly from side to side,

    cunning, and the first I've heard of this.

    I've been using a chopped back 'slide viewer' as my ground glass focusing tool for some years, I thought that it had never let me down, but reading the above post makes me wonder ... sometimes with my new 120 roll back I've been getting soft images. I had blamed film sag, but perhaps its something else.

    I'll need to experiment on a roll of 120 this weekend

  7. #7
    Senior Member bensonga's Avatar
    Join Date
    May 2008
    Location
    Alaska
    Posts
    2,416
    Post Thanks / Like
    Images
    819

    Re: Focus assurance question

    Quote Originally Posted by Jack Flesher View Post
    First off, what magnification is your loupe? If it is anything less than 6x, you are only getting close. 3x or 4x is almost useless for critical focus. Next, the loupe diopter HAS to be set perfectly for your eyes -- if that adjustment is off, your GG focus will always be off.
    I've been using the Toyo 3.6x loupe, so thinking I should get a 6x loupe. Any recommendations/favorites?

    Jack -- could you describe the process for adjusting the loupe diopter correctly for use on the GG? I'm a little fuzzy on how this should be done. I've been getting more concerned about achieving critical focus over the past couple years, as my eyesight has worsened.

    Thanks!

    Gary

  8. #8
    aprillove20
    Guest

    Re: Focus assurance question

    Well, 3x or 4x is almost useless for critical focus.

  9. #9
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    Quote Originally Posted by bensonga View Post
    I've been using the Toyo 3.6x loupe, so thinking I should get a 6x loupe. Any recommendations/favorites?

    Jack -- could you describe the process for adjusting the loupe diopter correctly for use on the GG? I'm a little fuzzy on how this should be done. I've been getting more concerned about achieving critical focus over the past couple years, as my eyesight has worsened.

    Thanks!

    Gary
    Hi Gary,

    Sorry it took a year to respond, I just saw this post!

    Anyway, you set the diopter by focusing it on the "grain" or ground surface of the GG. Many GG's are etched with vertical and horizontal lines, so these make excellent reference points to focus your loupe on. If you are using a fresnel, this becomes more problematic, as the actual focus point is the fresnel not the GG over it, so you want to focus on the lines created by the rings in the fresnel.

    Hope this helps,
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  10. #10
    Subscriber Member
    Join Date
    Dec 2007
    Posts
    58
    Post Thanks / Like

    Re: Focus assurance question

    I am using an 8x Loupe for both my Cambo SC and my Zone VI. Currently I am testing my 90mm SW 4.5 Nikon and Schneider Symar 180 5.6 convertible. Tomorrow I should have my Nikon 210 back from service so I will throw that in the mix as well.

    My question is about sharpness between the lenses and brands. Jack have you experienced a difference in Sharpness from the Nikon lenses and Schneider or are they about the same? I am also learning that your scanning technique can also greatly affect the sharpness you see in the end result.
    Jason

  11. #11
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    Hi Jason,

    I tested sharpness using a Betterlight Super 6K scanning back and a USAF resolution target. Bottom line is there was more variability between identical lenses from the same manufacturer than there was between the average performances of modern lenses between manufacturers.

    Stated another way, if all you look at is resolution, any of the modern designs from Schneider, Rodenstock, Nikkor or Fuji are going to be very good. What you will find if you rigorously test all lenses you purchase, is that some stand out as really excellent compared to their identical brother.

    Once again, generally speaking, I did find that the best lenses I tested usually were Linhof or Sinar badged versions of Schneider or Rodenstock lenses. There is a legacy story that back in the day, Sinar and Linhof hand-selected the best lenses off the Schneider and Rodenstock production lines for their name and line of cameras, and my test results would tend to support that story to some degree.

    What you will find different between brands is how they balance contrast and color casts between their lenses. Here you might find that the latest versions of lenses from Nikon tends toward higher contrast and warmer color casts; Schneider towards lower contrast and slightly warm color casts; Rodenstock toward medium contrast and neutral color cast, while Fuji did different things with different series of their lenses.

    So in the end, it's kind of a "shoot what you like" mentality. And as always, how and what you see when recording your vision is more important than the specific optic and capture medium you used
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  12. #12
    Subscriber Member
    Join Date
    Dec 2007
    Posts
    58
    Post Thanks / Like

    Re: Focus assurance question

    Thanks for the answer Jack. That is good information to know. I am in the process of trying to figure out if I have the right lenses for me. I have made some good buys recently, but as you know they are only good buys if they work for you and your shooting style.

    I would also like to pick your brain in regard to how often large format lenses should be serviced?

    Thanks,
    Jason

  13. #13
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    Quote Originally Posted by ComicDom1 View Post

    I would also like to pick your brain in regard to how often large format lenses should be serviced?
    Jack's theory on camera gear: "If it 'aint broke, don't fix it!"

    Seriously, if a lens is performing well, I would not risk having somebody open it up unless there were a good reason. Some typical services for lenses include shutters that get slow and need cleaning, lubricating and adjusting (CLA); haze on internal elements; oil on aperture blades.

    Re shutter speeds, almost all LF shutters are "off" exact speeds to some degree; some run a bit slow, fast or both depending on what end of the scale you're at, and this is especially true as shutters get bigger. Almost any serious LF shooter will own a shutter speed tester and mark their lenses with tape for accuracy; I marked mine if they were over 1/3rd stop off.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

  14. #14
    Member
    Join Date
    Mar 2010
    Posts
    29
    Post Thanks / Like

    Re: Focus assurance question

    Quote Originally Posted by Jack Flesher View Post
    Jack's theory on camera gear: "If it 'aint broke, don't fix it!"

    Seriously, if a lens is performing well, I would not risk having somebody open it up unless there were a good reason. Some typical services for lenses include shutters that get slow and need cleaning, lubricating and adjusting (CLA); haze on internal elements; oil on aperture blades.
    I'd agree, my experience has been years and years of service from a shutter, and problems only seem to crop up immediately after a CLA. I've narrowed my tech list down to a very few that can return a shutter in proper operating condition out of the box.(Primarily Paul Ebel and Carol Miller at Flutot's) Unlike a hobbyist, it's more than just inconvenient to have to send a shutter back and forth mulitple times, it cost real money.

    Since I only use shuttered lenses in the field (my Sinar shutter is used in the studio), I often go weeks or months without using a shuttered lens, it's comforting to know that it will work when I need it to without any drama.

    With regard to accuracy, the only shutter I have found to be consistently spot on is the Compur Electronics, and I'd recommend not buying one, as service is non-existant anymore, the are essentially a throwaway when they fail.

  15. #15
    Subscriber Member
    Join Date
    Dec 2007
    Posts
    58
    Post Thanks / Like

    Re: Focus assurance question

    Where would you suggest the best place would be to find a shutter speed tester and are they expensive?

    Thanks,
    Jason

  16. #16
    Sr. Administrator Jack's Avatar
    Join Date
    Oct 2007
    Location
    Los Altos, CA
    Posts
    10,486
    Post Thanks / Like
    Images
    1031

    Re: Focus assurance question

    Ebay or Calumet (they made one) and not generally, but now they are harder to find so prices are creeping up.

    Here is a current one on eBay, know nothing about the seller: http://cgi.ebay.com/Calumet-Shutter-...#ht_500wt_1154

    If you google "shutter speed tester" you will also find pdf instructions for the above along with several references for building your own inexpensively.
    Jack
    home: www.getdpi.com

    "Perfection is not attainable. But if we chase perfection, we can catch excellence."

Tags for this Thread

Posting Permissions

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