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Rodenstock's Hard Stop Vignette

dchew

Well-known member
I have actually emailed Rodenstock this very question, and even asked if there were any world in which the hard stop on the image circle could be removed. I’d gladly have the data, albeit deteriorated quality at the far edges of the frame, over those hard black stops. They said nope, and further that they’d not be making anything like an 18mm to satisfy the need further.
The above quote is from @JamesJetel in the "Current State of Phase One" thread. I have been curious about this hard-stop topic. For most of my technical camera history I had the Alpa STC, so the largest image circle I could experiment with was 98mm (18mm shift horizontally on a 54x40 sensor). Over the years I've used the 40, 70, 90, 100s, and now the 138f Rodenstocks. I never saw a hard stop, even on the 100s, which technically only has a 70mm image circle. But I couldn't shift that much. I did have to mount the Alpa adapters on the back of the camera to avoid camera body vignetting on my longer lenses like the 100s (and the sk 150).

I currently have the Alpa 12+, which can combine for a 123mm image circle if I shift simultaneously in both dimensions, but the only Rodi lens I currently own is the 138f. It officially has a 110mm image circle, yet I see no hard stop out to my current image circle limit of 123mm. That got me wondering: is this hard stop thing we've been talking about really from the lens, or is it from the camera body? As far as I know, Arca only has lens extensions on the front side of the camera. There is no option to space the back away from the camera to avoid camera vignetting like you can with Alpa. [Please note I'm not trying to throw stones. I'm just trying to figure out the real story here.] I asked Steve Hendrix to do a test with the 70hr on an Alpa with the spacer in the back, and he sent me a 4-image stitch from the Alpa Pano (35mm horizontal each way plus 10mm up/down). That's an insane 137mm image circle. There is no hard stop on that image. It gets dark in the very corners, but not until beyond >130mm image circle. Yet the 70hr has always had an official image circle of 100mm. See below.

So my question: Is it possible this "hard disk" we've been talking about that limits Rodenstock lenses to their "official" image circle is really just the camera body vignetting? Has anyone done a real test to see the source of the vignette? Someone who can put the adapters / spacers on the back of the camera to see if there is a difference? Maybe there is a hard disk in there, but from what I can tell it is well beyond the official image circle.

Dave

70hr 35mm shift L/R plus 10mm rise/fall:
7hr_imagecircle.jpg
 

dchew

Well-known member
This is how camera body vignetting is reduced by moving the adapters behind the camera:
adapter_position.jpg
 

Paul2660

Well-known member
I believe it’s dependent on the lens. Rodenstock places it dependent on the IC of the lens. The 32mm is 90mm and you hit the indicator at around 12mm of shift the 23 is IC of 70mm and you hit it at 5mm.
Other reason I believe it’s in the lens is that with Schneider lenses you can shift out as far as you want and you will not hit a hard corner vignette within reason. Just a darker edge the more you shift.
Paul
 

buildbot

Active member
Would one way to the test image circles be to project light through the lens in a dark room and measure the resulting circle? Not sure how the physics would work out here.
 

dchew

Well-known member
I believe it’s dependent on the lens. Rodenstock places it dependent on the IC of the lens. The 32mm is 90mm and you hit the indicator at around 12mm of shift the 23 is IC of 70mm and you hit it at 5mm.
Other reason I believe it’s in the lens is that with Schneider lenses you can shift out as far as you want and you will not hit a hard corner vignette within reason. Just a darker edge the more you shift.
Paul
Hi Paul,
The thing is, exit pupils of Schneider lenses are much closer to the sensor. I would expect their lens not to vignette as much against the body because the angle is wider. Do we really know? Has anyone with an Alpa and those wider SB lenses ever tested those limits you quote with the adapter mounted on the back? There is no limiting disk on the 70, 100s, and 180s. If it is lens-specific, it would be really nice to know which lenses have the disk and where: 23, 32, 40 and 50mm??

Edit: BTW, the 40mm has the same quoted image circle as the 32, and I don't remember a hard edge out to 98mm, which is 10mm further than what Paul reports above for the 32mm lens. Note I had an image posted here, but I need to check to verify how much shift there really was. I don't have those old raw files with me.

Dave
 
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ThdeDude

Active member
I once had the Digaron-SW 90mm on my Linhof Technikardan (easy, since same lens board as the Linhof Techno) and it did cover 4x5" including the corners. Sharpness to the eye looked OK. (Shame I can't find the photograph I took of the ground glass.)

4x5" has roughly a 162mm diagonal.
Digaron-SW 90mm image circle is stated by Rodenstock to be 120mm.

P.S. Not unexpectedly, the Digaron-SW 90mm did not cover 4x5".
 
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Steve Hendrix

Well-known member
On Cambo WRS 1600, Rodenstock 40HR begins hard corner vignette in horizontal orientation shifted right to 20mm + 4mm-5mm vertical. Without the vertical shift, you don't see it.

On Alpa Pano, Rodenstock 50HR begins hard corner vignette horizontal orientation shifted right to 21mm-22mm (with no vertical shift). Unfortunately, the only 50HR in house at the moment at CI is a Long Barrel. Presumably, the Short Barrel would yield more shift before the hard corner cutoff (depending upon what we think creates the hard corner cutoff), particularly if you mounted the 34mm spacer for the 50HR on the rear of the camera.


Steve Hendrix/CI
 

Attachments

alajuela

Member
Hi
The Arca uses back spacers on all lens from the 90mm SW and above - same as Cambo does. Don't know about the Alpa. My experience has been; the hard stop is in the lens.
As far as distance to the capture plane, my understanding is the Rodenstocks are retrofocus up until (and including) the 40mm not sure about the 50mm, and Schneiders are not. Above 40mm I would expect the distance to capture plane to be the same between Rodenstock and Schneider.
That was why there was an issue on the Scheinders with smearing and color shift on the sides of the frame on the 100 MP sensors until the BSI sensor of the 150 MP
Thanks
Phil
 

Paul Spinnler

Active member
On Cambo WRS 1600, Rodenstock 40HR begins hard corner vignette in horizontal orientation shifted right to 20mm + 4mm-5mm vertical. Without the vertical shift, you don't see it.

On Alpa Pano, Rodenstock 50HR begins hard corner vignette horizontal orientation shifted right to 21mm-22mm (with no vertical shift). Unfortunately, the only 50HR in house at the moment at CI is a Long Barrel. Presumably, the Short Barrel would yield more shift before the hard corner cutoff (depending upon what we think creates the hard corner cutoff), particularly if you mounted the 34mm spacer for the 50HR on the rear of the camera.


Steve Hendrix/CI
I can check later the vignetting has I have all my lenses in SB and an XY - let me get back on this. The IC is improved in my memory. I think it is one of the cooler features of the Alpa system as the SB allows you not only to get bigger ICs, but flexbility on tilt swing and theoreically a longer focal flange distance meaning you could adapt the lens to a view camera ... no other manufacturer has the SB concept to me knowledge, but you can order the Cambo 138 now also in SB with an extension tube.
 

Steve Hendrix

Well-known member
Hi
The Arca uses back spacers on all lens from the 90mm SW and above - same as Cambo does. Don't know about the Alpa. My experience has been; the hard stop is in the lens.
As far as distance to the capture plane, my understanding is the Rodenstocks are retrofocus up until (and including) the 40mm not sure about the 50mm, and Schneiders are not. Above 40mm I would expect the distance to capture plane to be the same between Rodenstock and Schneider.
That was why there was an issue on the Scheinders with smearing and color shift on the sides of the frame on the 100 MP sensors until the BSI sensor of the 150 MP
Thanks
Phil

Some lenses require a spacer with any of the tech cameras (typically longer lengths, ie; 90mm +, etc.). Alpa is unique in that they offer short barrel mounts up and down the lens range, which provide the opportunity for a tilt or standard separate spacer that can optionally be mounted to the rear of the camera. This opens up some possibilities.


Steve Hendrix/CI
 
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