R2a/35mm Ultron Focus problems..

[jamxo]

Hello there, I would like a little bit of a help if that's possible.
Had my R2a and 35mm 1.7 ultron for a couple of weeks now (well actually the first body developed a fault so I'm about to recieve a replacement) and although im very happy with the combination, I'm noticing ever more often a focusing problem.

I've tried to show it in the attached image, but basically, If I focus on someones face, and I'm spot on in focusing in camera with the rangefinder patch, when I've scanned my negs on, the actual focus is in front of their face, and the part on which I originally focused on is blurry. I'm getting this throughout alot of the apertures so it's not some obvious mistake with my depth of field. Hopefully it's illustrated in the attached picture where the girl who I foucused on is blurry and unsharp, but the part of the table to the left of her which is forward is sharp and in focus.

I keep on seeing questions about rangefinder alignment and back/front focus and whilst I think its one of these, I would be extremely grateful if someone could explain the terms and pin down which one I have, and how it's remedied (if its a problem with the body then great - hopefully the new replacement body wont have it - but I still have the same lens if its a problem with that!)

Thanks very much in advance!

 

[ferider]

This is a tough one. I am guessing your camera and lens are OK but your scanner defocuses the center of the image. How does the negative look under a loupe ?

Roland.

PS: reason why I am saying this is that you have enough DOF, and the table on the left is in the same plane as the girl's face.

 

[jamxo]

I'm not entirely convinced its the scanner as I have other scans from other cameras/lenses which are fine, but i shall flatten the same neg and see if it makes a difference (and check it under a loupe.)

Could someone please explain or link me to a description of backfocus or frontfocus? I see it mentioned but can't pin down what exactly it is..
Thanks!

P.S, perhaps this image illustrates the problem better: the entire group which i focused on is blurry yet the pavement a the bottom of the neg is tack sharp?!

 

[mfunnell]

Following on from Ronald's suggestion that it may be a scanning problem, a quick way of checking would be to put a quick roll of C-41 process film through it, shot at wide aperture to maximise the visibility of focusing errors (including, for example, regulation test shots of a ruler) then have it developed and printed commercially. If the commercial prints look good, but your scans from those negatives look fuzzy, then the scanning is the component that's "off".

To eliminate the possibility that the lens is at fault, you could perhaps try to borrow a lens (even if just briefly in a camera shop) and go through a similar exercise with your lens on some of the frames and the borrowed one on the rest. If both end up with focus errors then its likely the RF on your camera is out of alignment (unfortunately, I think that's the most likely circumstance).

For that I guess you can have it serviced by the manufacturer (esp. if still in warranty) or some other serviceman or ask one of the many knowledgable people around here about how to go about realigning the finder on your camera.

...Mike

 

[ferider]

Back/Front focus:
----------------------
It happens when RF and lens are misaligned. Typically the plane of focus is a
little off when a fast lens is used close-up and wide open. For example, with
a good Leica/lens combo, the RF will be within 1 inch of the true focal
plane of the lens, at close distance (1m or so). When the RF error is larger
one speaks of back- or front-focus, front-focus when the lens focuses closer
to the camera than the object targeted with the RF, back-focus when the lens focal plane is
farther away than the object.

With the Ultron wide open, at 1m distance, you have minimum depth of field
of about 8cm. This is the maximum accuracy your system has to work with.

In your example, I am guessing you shot at f2.8-4 or so (?) and you are around 2m away (?).
You will have plenty of DOF to hide any RF in-accuracies, unless they are severe.

Roland.

EDIT/ADD: For a pictorial explanation, Jorge showed some test pictures recently taken with some
Leitz lenses and his M8 that showed back and/or front focus. Couldn't find the thread
but you might search for it.

One more: in case you observe front/back-focus, it is very rarely the lenses fault, if you
use a modern, non-Russian lens. It is typically the sensitive RF mechanism of the camera
that is off.

 

[jamxo]

Thank you very much for the detailed replies!
So I will do some tests with the scanner to see if thats the cause of the problem (it could be something to do with curling negs..), and tomorrow a new bessa body is arriving, so Ill try a test roll with the ultron and a jupiter 8 to see if its all sorted!

 

[ferider]

I'm not entirely convinced its the scanner as I have other scans from other cameras/lenses which are fine, but i shall flatten the same neg and see if it makes a difference (and check it under a loupe.)

Could someone please explain or link me to a description of backfocus or frontfocus? I see it mentioned but can't pin down what exactly it is..
Thanks!

P.S, perhaps this image illustrates the problem better: the entire group which i focused on is blurry yet the pavement a the bottom of the neg is tack sharp?!

Jamxo, it seems to me that in this example both the foreground (the bottom)
and the background (the middle column behind the group) is sharper
than the people's faces.

Best,

Roland.

 

[jamxo]

Well I left the negatives under a large stack of books overnight to flatten them and it has indeed fixed the problem! I guess when the neg is too curved the middle of the image is too close to the scanning surface, making it blurry!
Re-scanned this image and now the entire subject is sharp!:

Thank you all very much! Very relieved that its nothing to do with the camera!
So i supposed my next question is what's the best way to flatten negs?

 

[wintoid]

I like the photograph very much 😀

 

[Avotius]

something you might try that worked very well for me is to kind of redo your scanner plate, what I did is cut the little guide tabs off the plastic holder and then bought two very cheap chinese off brand UV filters, then cut the glass in them to fit into the film slot so I could squeeze the film flat while scanning, if cheap uv filters are not available for cutting up you might try just some very thin and very clean glass, just practice with a glass cutter before you do

 

[Krosya]

something you might try that worked very well for me is to kind of redo your scanner plate, what I did is cut the little guide tabs off the plastic holder and then bought two very cheap chinese off brand UV filters, then cut the glass in them to fit into the film slot so I could squeeze the film flat while scanning, if cheap uv filters are not available for cutting up you might try just some very thin and very clean glass, just practice with a glass cutter before you do

Wouldn't that create effect known as "Newton rings" ? I think scanner has to be designed to use a glass holder or it will cause this. - reason many scanners don't have glass holders. Just a thought.

 

[RF-Addict]

I like that picture too!

What scanner are you using? Most flatbed scanner have very crappy film holders and that might just be your problem. If you only shoot 35mm, then you could pick up one of the older Minolta scanners, they go very cheap and are known to be of high quality - just a thought.

 

[ferider]

Great Jamxo. That is a great photograph, BTW, and a pretty girl ...

Roland.

 

[jamxo]

Thanks alot guys! definately was the scanner, flattened the rest of the negatives (thousands of tonnes of history of art textbooks finally come in use!) and the shots are scanning in sharp as hell now! I'm using a epson v700, perfect for what I need.

Thanks for the comments on the photo, the rest are over at http://flickr.com/photos/jsphotography/
ta!