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Thread: Stupid Q on shimming and focusing...

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    Stupid Q on shimming and focusing...

    The Alpa prides itself on being able to shim the back to precisely match the camera.

    How important is that if you are using hyperfocal distance or guesstimating your focusing? (rather than say using the IQ in liveview, or a laser rangefinder and the high precision focus ring)?

    Thanks.

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    Re: Stupid Q on shimming and focusing...

    IMO, the main value is to ensure your lens can actually reach focus at infinity, preferably when on the inf stop

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: Stupid Q on shimming and focusing...

    It also helps ensure that when you select intermediate distances that you really are at those intermediate distances. Infinity is the reference point that should set all the other marked distances (subject to you actually accurately selecting them of course). If you use HPF rings then this is more important.

    If you are just using hyperfocal distance or guestimation then you could reasonably assume that the shimming won't make that much difference, assuming of course that your back isn't wildly out of alignment.
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    Re: Stupid Q on shimming and focusing...

    Richardman,

    John is right, that's the first thing to make sure that the lens can reach focus at infinity.

    Then, no laser rangefinder and no HPF ring can be of help, if your OWN back is not calibrated itself with the camera used. There are samples variations, with each DB, in terms of position of the sensor, despite what one may expect from a DB costing that much. And those tolerances are not little, a few 1/100th to the 1/10th of mm, which has huge consequences on the real position of the focus when measured with a laser or set with an HPF ring, backwards or in the front.

    This becomes even more important, when focusing in a close range or in macro setups.

    That can be corrected by a shimming, and it must be corrected, otherwise it doesn't make any sense to have the most precise and resolving back, lens and camera, when one link is broken in the chain. Even more so with the latest generation of DBs with their small pixel pitch.

    It is not especially a pride, of having a camera allowing to do that, it is a must, IMO.

    Best regards
    Thierry

    Quote Originally Posted by richardman View Post
    The Alpa prides itself on being able to shim the back to precisely match the camera.

    How important is that if you are using hyperfocal distance or guesstimating your focusing? (rather than say using the IQ in liveview, or a laser rangefinder and the high precision focus ring)?

    Thanks.
    Thierry Hagenauer
    [email protected]

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    Re: Stupid Q on shimming and focusing...

    "There are samples variations, with each DB, in terms of position of the sensor, despite what one may expect from a DB costing that much. "

    i still can't understand why phase one, leaf, hassy don't incorporate a shimming system inside the back itself !
    They all know that issue for a long time...

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: Stupid Q on shimming and focusing...

    That would certainly be a desirable option. However, I think you really need shims for both the body AND each camera if you want to have uniform performance. Shimming the body would allow you to accurately set the body for a particular camera but what if you have multiple systems - each with their own slight variances? I agree though that it would very useful to setup a DF & back perfectly together and not just a technical camera.

    I suspect it's not as simple as assuming that the alignment issue is purely with the plane of the sensor on the back. Each camera also has some manufacturing tolerance built in and even Alpa, shock, has to have slight variability between bodies/adapters/lenses.

    I'm sure that the back manufacturers would have heart palpitations at the thought of the support costs from handling users in the field adjusting their backs like this. I'd rather that the DSLR manufacturers provide the AF fine adjust that is now common in high end 35mm digital gear. Obviously this doesn't help much with manual focus lenses though.
    Remember: adventure before dementia!

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    Re: Stupid Q on shimming and focusing...

    Scientific cameras have had "back focus adjustment" for decades. It moves the CCD package fore and aft. Simple and elegant with large pixel cameras. Not sure how it would work given the tolerances required with tiny perfect pixels.

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    Re: Stupid Q on shimming and focusing...

    It is really not that critical for your applications if Alpa QC is good. The backs can't show that much variation as they are also used on other cameras such as Mamiya, Hasselblad, Contax, Horseman, etc,. I don't believe any of those cameras allow or require shimming.

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