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Tech cameras and IQ.

jlm

Workshop Member
what all this points to is a shortcoming of the helical focus mounts. who makes these, and why can't they change the thread pitch to something more like 3-4mm? these new lenses have been mounted on pre-digital helicoids with a way too coarse pitch
 

Jack

Sr. Administrator
Staff member
what all this points to is a shortcoming of the helical focus mounts. who makes these, and why can't they change the thread pitch to something more like 3-4mm? these new lenses have been mounted on pre-digital helicoids with a way too coarse pitch
That's exactly what Arca did with the RM3D John -- the helical has a 2.5mm thread pitch and minimal thread clearance -- and it's why it's on the body and not the lenses...

The more I use this camera, the more I love it. Heck, my entire Phase DF kit may be up for sale soon :ROTFL:
 

Jack

Sr. Administrator
Staff member
:ROTFL: You mean I would have the last laugh. You will never give me that pleasure.
Well I would if I did, but I seriously doubt it will ever come to that reality. But I do understand the sentiment! :ROTFL:
 

Guy Mancuso

Administrator, Instructor
Well I would if I did, but I seriously doubt it will ever come to that reality. But I do understand the sentiment! :ROTFL:
3 months and you are over it. Trust me you'll find your art slide. Its not really your style. I just know you too well. I know slowing me down would kill my art
 

jlm

Workshop Member
so all that cambo/alpa have to do is make a new design finer picth helical mount and offer that on their lenses. I wonder who makes those for them?
 

Jack

Sr. Administrator
Staff member
so all that cambo/alpa have to do is make a new design finer picth helical mount and offer that on their lenses. I wonder who makes those for them?
Perhaps Milich Machining should offer a proposal? :D
 

Thierry

New member
Dear Jim,

Alpa do not have to re-design a finer pitch helical mount: they are as precise as Arca's, despite what is told here and there, even more precise in some situations. It simply needs to have both cameras side-by-side and do a field testing.

The theory presented here makes abstraction of some important facts:

Read here what has been said from a Arca user, Post #63 and myself, Post #64 & #65

http://www.luminous-landscape.com/forum/index.php?topic=49894.0

Best regards,
Thierry

so all that cambo/alpa have to do is make a new design finer picth helical mount and offer that on their lenses. I wonder who makes those for them?
 

jlm

Workshop Member
with all due respect, how can the focus resolution of the alpa, if full range of rotation is less than one revolution, match the arca, which has several rotations for the same lens travel?
 

Christopher

Active member
It can't. And yes I had both cameras side by side. And to say that it could be even more precise is just wrong. While the Alpa is a great camera, it has the same limitations and benefits from the normal heli mount.
 

Thierry

New member
Jim,

No harm at all.

Please read what the member says in Post 63, have a look at the tables provided by both, and moreover test it practically, that's what is relevant, not some theoretical values.

Best regards
Thierry

with all due respect, how can the focus resolution of the alpa, if full range of rotation is less than one revolution, match the arca, which has several rotations for the same lens travel?
 

Thierry

New member
Dear Christopher,

One often forgets to mention that the Arca helical ring DOES NOT turn 5 rotations for all lenses, in fact much less with shorter lenses. And in this situation, with these lenses, look at the focus tables provided.

Best regards
Thierry

And to say that it could be even more precise is just wrong.
 

Jack

Sr. Administrator
Staff member
with all due respect, how can the focus resolution of the alpa, if full range of rotation is less than one revolution, match the arca, which has several rotations for the same lens travel?
It can't. And yes I had both cameras side by side. And to say that it could be even more precise is just wrong. While the Alpa is a great camera, it has the same limitations and benefits from the normal heli mount.
Correct, it cannot -- and very well stated on all points. All good systems, but the heli-mount has limitations.

Jim,

No harm at all.

Please read what the member says in Post 63,
Thierry,

Just so you know, it is j l m for John L Milich in small letters, not "j *i* m" :) The next thing you should know is John is a precision machinist that also fully understands the physics of optics.

Re post 63: While it is correct that not all lenses use all 4 rotations for normal use on the Arca, the fact remains the helical itself is of very high quality with a finer thread pitch and larger barrel diameter than the typical (including Alpa's) helical. Both of those aspects create a much finer vernier on the dial, and the finer the vernier, the higher the precision. It really is as simple as that. Now we can debate practicality of having that in use for typical tech cam photography, but as somebody who has used both, I'll take the finer vernier over a faster one 8-days a week -- though I respect other's opinions may vary.

PS: John, I can edit your name to caps or anything else you want without losing your post integrity.
 

jlm

Workshop Member
the fineness of focus adjustment is a simple matter of the thread pitch; the finer the pitch (smaller number), the finer the focus. the arca pitch seems to be the smallest at 2.5mm/revolution.
alpa and cambo are not that fine


jack: i kind of like the ambiguity all those verticals give in my name. ;)
 
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Thierry

New member
John,

My apologies for having misread your name: it must be my eyes, getting older, it definitively is. But with time passing I will certainly become aquainted with all these name particularities.

:)

As for what is written concerning the helical focus ring:

with the risk of being "attacked" from some and the argument going on, this is all theoretical and does not hold in the field. I stand by my point of view, but respect others if they believe so.

But could Andreas Gursky, Walter Niedermayr, Mark Dubovoy, Candida Hoefer, Raymond Depardon, Ardon Bar Hama, Raymond Meier, among many other top-photographers all be that wrong when they choose Alpa because it gave them the most precision in focusing and fine-tuning among all cameras available?

With all due respect for anyone here, and theoretical precision and literature put aside, it's the practical use and the resulting images which speak for themselves, nothing else. All the rest is only endless discussions or arguments making no sense in the field and when it comes to the point, showing an image.

This is not to speak bad in any way about Arca or those working with this camera. To each one his respected choice. But pretending like it is done in this thread and some others that all of a sudden Arca is the non-plus-ultra in focus precision is going a little too far and not the truth. There still is a difference between the theory and the practice.

More about it, with some relevant information, tomorrow. Going to have a sleep now.

Best regards
Thierry

jack: i kind of like the ambiguity all those verticals give in my name. ;)
 

Jack

Sr. Administrator
Staff member
But could Andreas Gursky, Walter Niedermayr, Mark Dubovoy, Candida Hoefer, Raymond Depardon, Ardon Bar Hama, Raymond Meier, among many other top-photographers all be that wrong when they choose Alpa because it gave them the most precision in focusing and fine-tuning among all cameras available?
Did they test for precision directly against Arca? If so, I'd like to hear from them exactly how they found Alpa "superior." Or is more accurate that they just found that the Alpa was "sufficient" for their needs? In this case, I have no argument. I know Mark Dubovoy was not happy at all until he shimmed.

With all due respect for anyone here, and theoretical precision and literature put aside, it's the practical use and the resulting images which speak for themselves, nothing else.
Agreed in that whatever works best for an individual is what they should choose.

But pretending like it is done in this thread and some others that all of a sudden Arca is the non-plus-ultra in focus precision is going a little too far and not the truth.
Please then define what you mean by "precision" for us Thierry. The Arca by any *mechanical definition* is more precise, period. You may have a different definition which I'd like to hear. Finally, you keep saying it is irrelevant in use, and that may be true for some folks, but that is a different discussion and does not change that fact that by a true mechanical definition, the Arca helical is more precise than the Alpa's. Just trying to keep the facts correct here :).
 

Thierry

New member
Dear Jack,

Shimming is another issue which needs to be explained as well: I shall come back to this later, tomorrow or another day with some input on this particular point.

As for the rest, I shall as well come back to it, but not today, ways too late here, and I need to go and visit my bed.

But I agree with you, words on paper and "mechanical definition" are facts, but unfortunately not all variables are taken in account in it.

More later. Good evening
Thierry

I know Mark Dubovoy was not happy at all until he shimmed.
Please then define what you mean by "precision" for us Thierry. The Arca by any *mechanical definition* is more precise, period. You may have a different definition which I'd like to hear. Finally, you keep saying it is irrelevant in use, and that may be true for some folks, but that is a different discussion and does not change that fact that by a true mechanical definition, the Arca helical is more precise than the Alpa's. Just trying to keep the facts correct here :).
 

gazwas

Active member
Without sounding rude, this thread is starting to turn into an Alpa sales pitch.

As for dropping in the photographers names into the mix I'm sure if we had a direct representative from Arca on this forum they could list established photographers who have pledged their reputation on Arca's precision.

Alpa or Arca, both are great camera manufacturers that offer precision equipment.
 

stephengilbert

Active member
Wow. Thierry didn't make it through a week....

I guess Doug Peterson's high post/negative comment ratio is really admirable.
 
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