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Tech cameras and IQ.

RodK

Active member
Question

IF we agree that precise shimming of a Tech Camera setup within 1/100 can make a big difference
in terms of IQ, why shouldn't we use this precision at any distance?

quote: Jim post 94

brain wandered while i was running a machine...came up with this comparison to jack's findings. I am using Cambo lenses on I assume, Cambo helical focusing mounts

43mm lens: closest focus is 400mm with lens-to sensor calculating to 48.17mm. focus barrel rotates about 110 degrees. that works out to .047 mm (47 microns) per degree of rotation

70mm lens: closest focus is 800mm with lens-to sensor calculating to 76.7mm. focus barrel rotates about 270 degrees. that works out to .025 mm (25 microns) per degree of rotation

120mm lens: closest focus is 2,600mm with lens-to sensor calculating to 125.8mm. focus barrel rotates about 250 degrees. that works out to .023 mm (23 microns) per degree of rotation

Looking at what jack posted, he was getting 170 ticks per full revolution, so each tick is about 2.11 degrees. His result of 14 microns per tick is then 7 microns per degree

So the Arca is 7 microns per degree for all lenses
the Cambos (and probably the Alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation...
Rod
 

gazwas

Active member
Still wondering however, if the Arca R series focusing device is better than my rail (without motor).
Darr, not sure about the RM3d as there is very little info around about anything Arca but if things work like the Alpa site suggest you could test the sort of image magnification with you ML2.

The details of the Schneider 120M Digitar lens are:

Shutter: Copal 0
Aperture: f 5.6 - f 45
Image circle at full aperture: 110 mm (1:1)
Image circle at f 11: 110 mm (1:1)
Max. angle: 48 °
Distance settings: 1.1 m - infinity
Helical mount: special helical mount with 17 mm travel

So if the minimum focus distance is 1.1m, that doesn't sound that close/macro to me.

If you camera suffers view camera slop, imagine hanging that (pic attached below) thing off the front of an Alpa at full stretch....... You'd get pancake droop I'd imagine. :p

Sorry if I'm breaking any rules posting an Alpa image? :confused:
 
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Hi Darr ...
"but when does it matter if you focus with the front or the back if the plane of focus is stationary?"

The problem with Macro is that by changing the focus (therefore the distance between the lens and the film), you actually change the size of the image projected to the film. The more magnification of the subject the more you will see this effect. So stitching becomes potentially more error prone. If you use a macro rail to actually move the whole camera you'll be better off, but you are limited to how much of the subject the macro rail can accommodate.

By focusing with the back it is less of a problem but it's still there.

The big problem with focus stacking is the stuff that is wider than can be accommodated with your focus rail but still close enough that changing the focus changes it's size.

With regards to tilts. I am still working through the math and until I actually get an Alpa tilt adapter, will not really know if what I am seeing is true ... basically as you tilt, you loose DoF and need smaller apertures. It seems more and more that tilt will be quite limited on the new backs.

Paul
 

darr

Well-known member
Question

IF we agree that precise shimming of a Tech Camera setup within 1/100 can make a big difference
in terms of IQ, why shouldn't we use this precision at any distance?

quote: Jim post 94

brain wandered while i was running a machine...came up with this comparison to jack's findings. I am using Cambo lenses on I assume, Cambo helical focusing mounts

43mm lens: closest focus is 400mm with lens-to sensor calculating to 48.17mm. focus barrel rotates about 110 degrees. that works out to .047 mm (47 microns) per degree of rotation

70mm lens: closest focus is 800mm with lens-to sensor calculating to 76.7mm. focus barrel rotates about 270 degrees. that works out to .025 mm (25 microns) per degree of rotation

120mm lens: closest focus is 2,600mm with lens-to sensor calculating to 125.8mm. focus barrel rotates about 250 degrees. that works out to .023 mm (23 microns) per degree of rotation

Looking at what jack posted, he was getting 170 ticks per full revolution, so each tick is about 2.11 degrees. His result of 14 microns per tick is then 7 microns per degree

So the Arca is 7 microns per degree for all lenses
the Cambos (and probably the Alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation...
Rod
So Rod, can I give up my rail for more accurate focus stepping?
 

Jack

Sr. Administrator
Staff member
So Rod, can I give up my rail for more accurate focus stepping?
Darr,

If I shot a lot of studio product and/or macro, I would own an Arca M-line 2 rail camera AND the RM3D. You can get the R lens-mount for the M-line 2 and use all your existing tech lenses in the R mounts, best of all worlds in tech land :)

Edit: For whatever weird reason, Rod's post above was not visible when I posted this comment -- Sorry Rod!
 

darr

Well-known member
Darr, not sure about the RM3d as there is very little info around about anything Arca but if things work like the Alpa site suggest you could test the sort of image magnification with you ML2.

The details of the Schneider 120M Digitar lens are:

Shutter: Copal 0
Aperture: f 5.6 - f 45
Image circle at full aperture: 110 mm (1:1)
Image circle at f 11: 110 mm (1:1)
Max. angle: 48 °
Distance settings: 1.1 m - infinity
Helical mount: special helical mount with 17 mm travel

So if the minimum focus distance is 1.1m, that doesn't sound that close/macro to me.

If you camera suffers view camera slop, imagine hanging that (pic attached below) thing off the front of an Alpa at full stretch....... You'd get pancake droop I'd imagine. :p

Sorry if I'm breaking any rules posting an Alpa image? :confused:
I looked at getting the Schneider 120 macro for my Max for about 15 seconds. I realized I would need to buy some very expensive extension plates, plus, as you stated, the front weight distribution would appear awkward . :( The advantages of using the M2 always comes back into play when I look at the cost of lenses, accessories and bellows extension.

I think I am looking for a 'magic bullet' in helical focusing. :deadhorse:
 
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You can add the macro tubes to the lens and/or back side to balance it :) Also I think the 120 has a special extended helical that means you might not need as much extension via tubes
 

darr

Well-known member
Darr,

If I shot a lot of studio product and/or macro, I would own an Arca M-line 2 rail camera AND the RM3D. You can get the R lens-mount for the M-line 2 and use all your existing tech lenses in the R mounts, best of all worlds in tech land :)
That Jack is one of the reasons I am trying to make it to New Hampshire this Fall. Other reasons are the scenery and people, but I want to try the R series and pick the heads of all the photogs there. I will know in a few days if I can swing it.
 

darr

Well-known member
Hi Darr ...
"but when does it matter if you focus with the front or the back if the plane of focus is stationary?"

The problem with Macro is that by changing the focus (therefore the distance between the lens and the film), you actually change the size of the image projected to the film. The more magnification of the subject the more you will see this effect. So stitching becomes potentially more error prone. If you use a macro rail to actually move the whole camera you'll be better off, but you are limited to how much of the subject the macro rail can accommodate.

By focusing with the back it is less of a problem but it's still there.

The big problem with focus stacking is the stuff that is wider than can be accommodated with your focus rail but still close enough that changing the focus changes it's size.

With regards to tilts. I am still working through the math and until I actually get an Alpa tilt adapter, will not really know if what I am seeing is true ... basically as you tilt, you loose DoF and need smaller apertures. It seems more and more that tilt will be quite limited on the new backs.

Paul
Thanks for this Paul.
 
Ah no, the special helical is so that you can buy lots of extension tubes and switch between them and have all magnification ratios down to 4:1 with no gaps between the tube heights.
 

Jack

Sr. Administrator
Staff member
That Jack is one of the reasons I am trying to make it to New Hampshire this Fall. Other reasons are the scenery and people, but I want to try the R series and pick the heads of all the photogs there. I will know in a few days if I can swing it.
Great, hope you can make it -- should be an awesome workshop!
 

Guy Mancuso

Administrator, Instructor
That Jack is one of the reasons I am trying to make it to New Hampshire this Fall. Other reasons are the scenery and people, but I want to try the R series and pick the heads of all the photogs there. I will know in a few days if I can swing it.
Love for you to be there Darr. Hope you can swing it
 

jlm

Workshop Member
to address Rod's question:
"IF we agree that precise shimming of a Tech Camera setup within 1/100 can make a big difference
in terms of IQ, why shouldn't we use this precision at any distance?

let's say we do require that precision at any intermediate distance: if you calculate what the effect is in object distance by moving the sensor .001mm, it is going to be small, obviously affected by the focal length and the magnitude of the distance. i would venture, so small that it would not create a measurable change in object distance.
just did a quick calculation:
70mm lens: lens-to sensor is 75.000mm = object distance 1,050mm
so adding a .001 shim: lens to sensor is 75.01mm = object distance is 1,048mm
.01 shim would change the object distance by 2mm at around 1 meter
all my arithmetic subject to error, of course ;)

more numbers, just to give this some scale, again, the 70mm lens: not sure how meaningful in reality, but by the formula:
lens to sensor: 70.01mm = 490 meters
lens to sensor: 70.02mm = 245 meters (here a .01mm shim makes a 245 meter difference!)
lens to sensor: 70.05mm = 98 meters
lens to sensor: 70.10mm = 49 meters
lens to sensor: 71.0mm = 4.9 meters
lens to sensor: 72.0mm = 2.5 meters
lens to sensor: 75.mm = 1.0 meters



Infinity is another bag, though, and if you cannot get the lens close enough, because the shims are too thick, inf will not come into focus. if the shims are not thick enough, you can reach focus at inf, just not at the inf stop on the ring. My guess is that the arca can "focus" beyond infinity and so you use the table, making shims irrelevant
 
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Thierry

New member
Gareth,

There is obviously a reason to this design.

Alpa didn't want to overlap the 2 shift planes one over the other, but to have 2 completely separate H and V shifts with in-between a fix "carrier" plane.

The reason is obvious: getting a much stabler and more long-term-suited design responding to professional needs.
That's also the reason why all Alpa carriages are designed with roller bearings: best possible stability and precision with long-term use.

Best regards
Thierry

Why have Alpa designed the Max with movements that are usually done together on the back or lens rather than seperate on the Max?

Is is just a design decision or is there a specific reason/movement I'm not seeing.
 
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