registration of MFDB problem

[David Klepacki]

HUH? if you don't know diddly about alpa, why do u insist on making comparisons between the alpa and rm3d and present them as fact? the fact is: once you shim your digital back, you never have to shim it again for each lens! shim once for your digital back and that's it! YIKES! it's hard to take anything you say seriously when you post things like this. i know you like to say a bunch of positive things about the rm3d - that's ok, if u want to be the rm3d spin doctor - but by trying to say negative things about the alpa that are patently not true doesn't strengthen your case, in fact it makes it weaker. and another point: the shim kit that alpa provide allows one to make extremely fine adjustments. AND the idea that you need only shim ONCE is huge. it's nice knowing that one's digital back is optimally aligned with the camera - and one never needs to address it again unless one buys a new digital back.

richard

richard

richard,

You are obviously unaware or delusional about the variation among lenses. There can indeed be variation in lens accuracy, which you will only find out if you test them yourself. If you don't believe me, just ask Joe Holmes who was able to find only two "good" lenses among eleven from Schneider and Rodenstock (and mostly using Alpa cameras). You can read his review here: http://www.josephholmes.com/news-medformatprecision.html

All I am saying is that I find it easier to manipulate any needed fine adjustment, whether it be for a back or a lens, by the Arca-Swiss method of adjusting the body helicoid setting, instead of adjusting shims. You are simply "assuming" that you will never need to do this, but Joe Holmes study indicates otherwise. I always test the lenses I will use and indeed have found need for fine adjustments, especially in cases where I find slight focus shift from one f-stop to another on the same lens.

I do not mean to denigrate the Alpa cameras. They are obviously fine photographic instruments and are serving the photographic community very well. I am merely pointing out my own preferences, so that others may better evaluate their own specific needs and preferences, which may or may not align with my own. You are free to disagree with me and spend your own money any way you wish. I have nothing to gain or lose either way.

 

[photohagen]

richard,

You are obviously unaware or delusional about the variation among lenses. There can indeed be variation in lens accuracy, which you will only find out if you test them yourself. If you don't believe me, just ask Joe Holmes who was able to find only two "good" lenses among eleven from Schneider and Rodenstock (and mostly using Alpa cameras). You can read his review here: http://www.josephholmes.com/news-medformatprecision.html

All I am saying is that I find it easier to manipulate any needed fine adjustment, whether it be for a back or a lens, by the Arca-Swiss method of adjusting the body helicoid setting, instead of adjusting shims. You are simply "assuming" that you will never need to do this, but Joe Holmes study indicates otherwise. I always test the lenses I will use and indeed have found need for fine adjustments, especially in cases where I find slight focus shift from one f-stop to another on the same lens.

I do not mean to denigrate the Alpa cameras. They are obviously fine photographic instruments and are serving the photographic community very well. I am merely pointing out my own preferences, so that others may better evaluate their own specific needs and preferences, which may or may not align with my own. You are free to disagree with me and spend your own money any way you wish. I have nothing to gain or lose either way.

as far as alpa shimming is concerned: shimming is for correction of the digital back. period. alpa shimming is not meant to correct for any lens problems. you said in your original post that one would have to shim every time a different lens was used. this is a ridiculous notion. once your digital back is shimmed it is optimally in registration with your digital back sensor. an optimally shimmed digital back will make more apparent any abnormalities with your lenses. sometimes when lens elements are not seated perfectly - even being off by a fraction of a mm - you can see it. in a case like this, it is advisable to send the lens back to the manufacturer for realignment. the point is: in the alpa world, shimming is for the digital back NOT the lens.

richard

 

[jlm]

to what end are you shimming?

seems to me the standard should be that the DB is shimmed to match the ground glass adapter (or gg adapter shimmed to match the DB), period.

does anyone want to actually rely on lens barrel distance markings, even for infinity?

 

[David Klepacki]

as far as alpa shimming is concerned: shimming is for correction of the digital back. period. alpa shimming is not meant to correct for any lens problems. you said in your original post that one would have to shim every time a different lens was used. this is a ridiculous notion. once your digital back is shimmed it is optimally in registration with your digital back sensor. an optimally shimmed digital back will make more apparent any abnormalities with your lenses. sometimes when lens elements are not seated perfectly - even being off by a fraction of a mm - you can see it. in a case like this, it is advisable to send the lens back to the manufacturer for realignment. the point is: in the alpa world, shimming is for the digital back NOT the lens.

richard

In a world of absolutely perfect lenses you would be right, but such is not the case. Indeed, I agree that shimming is not meant to correct for any lens issues. This is precisely the limitation of shimming that I am pointing out.

With the Arca-Swiss helicoid, you can not only "shim" your digital back for proper registration, but also you can use it to apply any fine adjustments that may be needed to obtain more precise focusing. Even if the lens registration is absolutely perfect, a lens typically has some amount of spherical aberration that causes slight focus shift within its f-stop range. These types of very fine focusing adjustments can be overcome easily and systematically with the Arca-Swiss helicoid. I find their helicoid mechanism to be more versatile in addressing any need for fine focusing adjustment, precisely because it is has this additional capability over shims.

 

[photohagen]

In a world of absolutely perfect lenses you would be right, but such is not the case. Indeed, I agree that shimming is not meant to correct for any lens issues. This is precisely the limitation of shimming that I am pointing out.

With the Arca-Swiss helicoid, you can not only "shim" your digital back for proper registration, but also you can use it to apply any fine adjustments that may be needed to obtain more precise focusing. Even if the lens registration is absolutely perfect, a lens typically has some amount of spherical aberration that causes slight focus shift within its f-stop range. These types of very fine focusing adjustments can be overcome easily and systematically with the Arca-Swiss helicoid. I find their helicoid mechanism to be more versatile in addressing any need for fine focusing adjustment, precisely because it is has this additional capability over shims.

david, i took issue with you when you made a couple alpa references that were totally off the mark. i myself own a few alpas and feel you can't beat the quality and workmanship. i know very little about the arc-swiss helicoid and therefore i can't comment about it. that said, i do find it very unusual that it can simultaneously correct digital back and lens registration issues. hmmmmm, this is something i will have to confirm for myself.

richard

 

[David Klepacki]

david, i took issue with you when you made a couple alpa references that were totally off the mark. i myself own a few alpas and feel you can't beat the quality and workmanship. i know very little about the arc-swiss helicoid and therefore i can't comment about it. that said, i do find it very unusual that it can simultaneously correct digital back and lens registration issues. hmmmmm, this is something i will have to confirm for myself.

richard

For the record, I never mentioned "Alpa" in my original posting here. I only commented about my preference of the Arca-Swiss helicoid in relation to shimming in general. I was drawing upon my own experience with the Sinar system that I had recently owned which uses shims. Unfortunately, most people think of Alpa whenever the topic of shimming comes up, but Alpa is not the only company that offers a shimming solution.