Michael
There are maybe not one photographer wich has no problem with very wide lenses like 47mm to75mm.
I for example use always the longest possible lens for a job espescially inside and in low light conditions!
But in my next 3 jobs I know I use only the 47, 55, 75, 90mm combo inside but I will take a very strong light with me for the focussing and framing part of it!
So it can be done, but it isn't easy at all!
Michael P., as I stated above and Armin seconds, even experienced LF photographers can have problems with very wide-angle lenses. This is why I suggested that you resume your focusing experiments with your 210 mm lens. I suggest taking the problems one step at time: figure out whether your system (camera, film holders, etc.) is correctly configured, and if you are focusing correctly, with an easier-to-use lens, then move on to lenses that are more difficult to use.
As the others have answered, on and off-axis refers to the optical axis of the lens -- the line that goes through the center of the lens. Without movements, the optical axis will normally be aimed at the center of the ground glass / film. At this point the light rays fron the lens are mostly going straight back and are easy to view.
The difficulties with using a wide-angle lens that I was referring to arise because the off-axis rays from a short focal length lens strike the ground glass at an oblique angle and thus are harder for the photographer to see. I deal with this by viewing the ground glass at an angle, depending on the spot that I am viewing, so that more of the rays reach my eye. I use a handheld magnifier, perhaps a better way would be to use a tilting loupe.
Yes, you should use your eyeglasses with the loupe. If you vision isn't close to "normal", then loupes will not have sufficient adjustment range to be used without your eyeglasses. You are focusing on the ground surface of the ground glass. Poor vision shouldn't cause a systematic and consistent focus shift -- for example, it won't cause you to consistently and repeatedly to focus on 1.5 m when the object is at 2 m. What you are doing is judging the point that the image formed on the ground surface of the ground glass displays maximum sharpness or detail. (See the second paragraph of Alan's answer above.) Poor vision might cause you to have difficulties judging sharpness and thus to inconsistently make focus errors, so that you might focus at 1.5 m on attempt for an object at 2 m, and then at 2.5 m on a second attempt. This is why I suggested you repeat your focusing experiments several times, in order to try to distinguish between systematic and consistent biases in focusing that might be caused by defective equipment versus random and inconsistent focusing problems from the operator having difficutlies, e.g., for a too dim image or poor eye sight.
Some past answers that might help: Ground glass focusing plane at
http://www.largeformatphotography.info/lfforum/topic/497868.html,
and 4x5 Focusing Screens: THE FINAL WORD at http://www.largeformatphotography.info/lfforum/topic/500118.html#531356
Hi Michael
As you have just said a great deal of information.
May I suggest that Jim’s calculation showing that .3 mm variation of the focused plane could produce similar results to your findings could be a clue to your problem.
Not having the formular I accept Jim’s calcs.
On this basis I did a quick check. 5 inch (127 mm ) engineers small striaght edge laid diagonailly across a Linhof GG, press gently in the center of GG and what do I see a 10 to 12 thou. gap (.25 to .35 mm) or bow between the glass and the striaght edge.
So – how use this information well I would not at all surprised if holding a loupe against the GG whilst “doing ones best “ to get the focus spot on did not cause some form of deflection and .3mm is a very small amount in every day terms. Now while considering this remember the back stand may well all so be deflecting, again not much in everyday terms.
How would I check this :-
First use only one rollback/film holder(and only one sideof the film holder)for all tests.
Borrow or find a hand held magnifing glass ( I would use my clip on lenses which give me about 5-6 inch focal length with my reading glasses, these are ESCHENBACH OPTIK Lupe N ).
Choose any two or three of your test distances and make two runs.
First run using your lupe, defocussing and refocussing the back stand between shots.
Second run using your hand held glass or clip ons, defocussing and refocussing the back stand between shots.
This should indicate whether the GG and or the back stand is springing back after focusing.
Regards Rob Hale
I am very grateful for the suggestions I am getting, and first want to thank everyone for their contributions. I am amazed actually at the responses that you all have put considered effort into. Clearly it's a sensitive issue: exceptionally sharp pictures are what we are after (there are exceptions, I know), which is one of the main draws of large format photography.
One thing I might add about myself: even if I sound like a beginner, I am actually an established architectural photographer where I live, and am able to make an ok living through my work. I guess it's just that I am in the category of a "non-technically oriented" photographer, who has learned on my own from reading, talking with knowledgeable people, and making my own mistakes and discoveries as I go along. I have managed thus far by using small apertures, which works for me 95% of the time. Now, however, I have chosen to check into the problem with the other 5% . . . it's more satisfying knowing you have complete control, always.
Anyway, after digesting everything I have read here, I think I am beginning to understand better how to proceed. If I first test the 210mm, which is the easiest of my lenses to focus, and discover that what I focused on at f/5.6 is also what is sharp on film, then I can right away eliminate that I have an equipment failure somewhere. The film plane would be shown to match the plane of the ground glass, my film holders would be ok, my loupe would be ok, my fresnel/gg setup would be ok, and my focusing with eyeglasses on would be ok. Afterwards, all testing of my wider lenses would only indicate possible errors in my focusing methods, and have nothing to do with failures in my equipment or failures in my eyesight. It will be interesting to see what I discover.
One thing though: during the dark and usually cloudy month of December here in Sweden, a bright sunny day is a rare commodity indeed! I will therefore have to test indoors, blasting a lot of light with my redheads. This should still work, even if less than ideal.
Thanks again!
Hi Michael,
"One thing though: during the dark and usually cloudy month of December here in Sweden, a bright sunny day is a rare commodity indeed! I will therefore have to test indoors, blasting a lot of light with my redheads. This should still work, even if less than ideal."
That would work better for this because tabletop / macro range has no depth of field, it's in focus or it's not. I use a deck of playing cards to do a focus test, just cut 7 slots in foam-core, wooden molding, an egg container, whatever is handy.
Place the ace of spades vertically facing you in the center and the other cards horizontially with the back facing you and slightly staggered. Focus the best you can on the edge of the ace, lens wide open, and take the picture with flash or hot lights. Don't worry about bellows extention or developement, this isn't fine art just a focus test.
If everything is correct you will see fine hairs on the very edge of the ace and be happy. If sharpest focus is closer then the ace your glass is closer than the film and will need to be shimmed. If sharpest focus is farther then the ace the glass is too far back and the view screen face will need to be shaved down. Remember 'I cut it twice and it's still too short' applies, make small changes and re-test.
A little trick for interior work is to use 4 Mini-Mag lights. These are small flash lights, 2 AA size, that can focus. The head turns to turn it on and focus BUT unscrews to become a base to hold the light, an electric candle. The bulb is 2mm and extremely bright, you can focus it at f/90. Just set them up for near, far, left and right extremes of your shot to focus and compose.
Have fun with it and good luck.
Just a thought about why you can't focus the loupe without glasses is not that you need more correction, but perhaps you have a high astigmatism and at no setting your eye will be in focus.
Anyway, definitely verify that the camera system can be focused with longer lenses.
kirk - www.keyesphoto.com
Kirk - www.keyesphoto.com
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