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Testing my 500cm 80mm planar equipment

fotoart

New Member
Hi,

after buying my first hassy, i did the following test.

I put a newspaper under 45 degrees, in the middle draw a line. I put the camera on a tripod horizontally focussed at the drawn line. camera was balanced, middle of the lens at the height of the line.

I shot a picture with the 80 at 2.8. Distance was +/- 0.95meter. So almost at the most near position of this lens as possible.
I focussed at the line.

The result gave a image where most sharp area was not the line but behind it. The line was at the edge.
I did the same test with the 150mm lens, same result. I checked my eyes, looked through a loup at the groundglass, and al looked fine...

Is it possible that these lenses are not at there best for closeup work at almost the minimum range of 0.9 meter this lens is capable of? Is this by design?
 

ttam

New Member
> Hello Jan,

It appears that you're back focusing. You should also check your lenses AT INFINITE (use a slow speed film, a tripod and WIDE lens opening). Focus visually and see if you can determine that the focusing screen give you a sharp image (with lens at infinity). You'll need to use a high power loupe - remove the finder, BUT leave the screen in place and place the loupe ON the screen. Take a few shots. Do the recalled what you see on the screen with what you see on the developed negatives?

This is a way to assess if your lens flange and film planes are in register and if your focusing screen placement/mirror angle is in accordance with Hassy specs. Instead of using film for this test, I find that the SWC accessory focusing screen to be invaluable for situation like the one you describe. With this screen you get instant visual verification of your lens flange to film plane register and by comparing with what you see on the camera's own focusing screen, you can determine if the two images agree in focus. The SWC screen is a bit expensive but is a useful tool that Hassy owners don't usually invest.

From what you described, it's possible that the following is the cause or a combination of causes - focusing screen is backward (that is the focusing surface is reversed so the lens HAS to be move farther back to yield visual screen focus thus causing the film to see farther behind the focused line (of course, it is assumed that your lens flange and film plane are in proper order - the infinity test will let you know). Remember to focus farther distances, the lens HAS to be racked closer to the film.

Your mirror angle deviates from the correct position (typically for SLRs, it's 45 degrees unless the focusing screen is NOT designed to be positioned at 90 degrees to the film plane), i.e., the angle is GREAT than 45 degree from the focusing screen. A larger angle will cause the imaging rays to travel farther - to compensate, you rack the lens closer to the film and hence, you are back focusing!

Hope I've help.

Happy snaps,

Tsun

>
 

cs_foto

Member
keep me posted
 

fotoart

New Member
So i'm a lot further...

I used a groundglass adapter in stead of the back to see if what i focused through the finder was also visible on the groundglass.
This was ok, to the problem should be in the back.

I used a different back and this cleared the issue..
(don't keep us longer waiting, tell me!)

This worked fine. The focus point was exactly as i had set it.
So the back is causing the problem....

thanks.

Tip:
If you buy new(used) equipment test it.....
 

cs_foto

Member
very intriguing...

how can the back cause that problem? is it bent? or, did you notice any irregularity on the surface?

:s

thx
 
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