Checking Zeiss Sonnar 1.5 optimization with Fuji Xpro2?

[Thealexxx]

Hello everyone,

Ive recently bought a Zeiss Sonnar 1.5.
I know that this lens could either be optimized for f1.5 and would back focus from f2-5.6, or optimized for f2.8 and would front focus from f1.5-f2.

I wanted to do a quick test to see which aperture the lens was optimized for

I'm primarily using it for my film leica, but I wanted to know if it was possible to use my Fujifilm Xpro2 to check the sonnar's optimization for focus shift?

Would I still be able to set it on a tripod at 45 degrees, minimum focus distance of 0.9m and focus on a test chart with no problems despite the cropped sensor?

Or should I use a roll of film to do this test.

Thank you for your time,
Alex

 

[retinax]

You can certainly do a series of pictures with the same focus setting and vary the aperture. That should show if there is any focus shift. But you still won't know how that relates to the rangefinder. At least if there isn't any, you can stop worrying. If there is, you may still want to test on the film camera. Supposedly film is more tolerant of focus shift.

 

[Thealexxx]

Will do, thank you retinax

 

[LukasB]

I don't see why not. Focus distance does not change with use of a different Camera - it would be localized within the Lens. However, as pointed out, calibration in relation to the Rangefinder of your Camera is also necessary.

- L

 

[jonmanjiro]

I wanted to know if it was possible to use my Fujifilm Xpro2 to check the sonnar's optimization for focus shift?

You would focus the Sonnar 50/1.5 on the Xpro2 by live view right? In which case you're gonna see correct focus for whatever aperture the lens is set to when you focus. Optimization concerns how the focus shift of the lens relates to the focus cam of the lens that pushes against the rangefinder cam on the camera, so testing by live view is no use at all for checking how the lens is optimized on a film Leica.

Do the test with your film Leica instead. Problem solved.

 

[brbo]

On your X-Pro you can't determine what aperture your Sonnar is "optimised" for. You'll need your rangefinder camera for that. Just focus on a target and take pictures with apertures from f1.5 to f4. Develop the film and establish at which aperture the actual focus is as intended.

When you know at what aperture your Sonnar is perfectly mated to your film rangefinder camera, you can then use your X-Pro to simulate the effect the focus shifting will have on your pictures taken with your rangefinder camera, learn in which situations you'll want to avoid certain apertures and/or correct for focus shifting (deliberately placing focus closer/further that your rangefinder would suggest)...

 

[Thealexxx]

Thank you everyone for your responses, I'll shoot a test roll

 

[Sarcophilus Harrisii]

I don't see why not. Focus distance does not change with use of a different Camera - it would be localized within the Lens. However, as pointed out, calibration in relation to the Rangefinder of your Camera is also necessary.

- L

In theory this may be true. In reality, unless the dimensions of the lens mount to film plane of the film camera, and those of the lens mount to sensor plane of the digital camera plus those of whatever adaptor is needed to fit the lens to the digital camera, are all identical, variances could occur. Even then differences in the way a lens focuses onto a piece of film versus a digital sensor might account for some smaller inconsistencies.

Whilst observation of the shift in focus characteristics of the lens using the digital may inform how to try and compensate for focus changes at different apertures, when the lens is used on the film camera—the only easy way to establish exactly where the lens focuses on the film camera, is to test it on the film camera. It will eliminate any of the aforementioned variables between the two cameras which might compromise the conclusions drawn, thus, it is the safest and most conclusive methodology.

None of the above necessarily means testing the lens on the digital camera and then adjusting the film camera to suit wouldn't work, in practice—but the point is that the dimensions that could make the results vary are difficult for most people without the appropriate measuring equipment to quantify. Rather than trying to ascertain these unknowns, and compensating for them, testing the lens on the film camera involved is ultimately safer, simply because it eliminates them.
Cheers,
Brett