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Image circles listed at f11 and 22 but not smaller f-stops

jodad

Member
The Alpa lens technical info booklets list the image circles of lenses at f11 and 22 but not at smaller f-stop numbers. Is there somewhere I can find this info? I’m looking for the SK 38/47/58 Super angulons and the Rodie 35 and 45 grandagons.

Two follow up questions:

1)How much does the image quality degrade at the wider apertures? Is it just a matter of sharpness moving into smaller and smaller circular areas in the middle of the frame and you get some vignetting? Or is it much worse?

2) Do the Rodie grandagons suffer from the same fragility as apparently the Rodie HR lenses requiring more careful handeling and transport? Not casually hang off the shoulder lenses? What about the super angulons?
 

rdeloe

Active member
The size of the image circle is usually reported at specific apertures and focus distances. As you may realize, the image circle gets larger as you approach 1:1. It is smallest at infinity. I have never seen a lens manufacturer report image circle information across the aperture range. Normally it's for the recommended working aperture and infinity (for normal lenses) or 1:1 or the ideal magnification (for repro lenses). Note that the area illuminated does not change with aperture. What changes is the "circle of good definition", in other words, the part of the image circle where image quality is good.

To your specific questions,

1) It really depends on a lot of considerations. Some abberations are reduced by stopping down. Light fall off will be worse wide open than closed down all the time (that's just physics). With some lenses, light falloff is effectively gone by the middle of the aperture range; with others it's a more gradual decline. Lenses are at their best in the centre, and normally decline in quality towards the corners. You can see this clearly in MTF charts. And then there's diffraction, which starts being more important than aberrations as you close down the aperture. The good news is that when using lenses with large image circles, the image quality may be consistently good within the area covered by the sensor, and only start falling off noticeably once you start shifting. You also have field curvature as a concern in some lenses (but much less so in my experience with lenses actually designed for shift). Some lenses were simply not meant to be used wide-open. For example, when I shot 4x5 film, it was normal to compose wide-open but close down to at least f/11, with f/16 often being the working aperture.

2) This I leave to people who have those lenses. For what it's worth, the Apo-Grandagon 55/4.5 I owned briefly was, like my other large format lenses, quite sturdy and didn't have the enormous lens cells of the Rodenstock HR lenses. I treated those lenses with care, but didn't have the concerns that people using the modern Rodenstock HR lenses mention. A good knock is always bad -- for the lens and for the delicate threads of the shutters.

I hope that helps.
 
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Shashin

Well-known member
With view camera lenses, maximum aperture is for focusing. It is assumed that the lens will be stopped down, which is why those number are only published for f/11 and f/22. I used a Rodenstock 55mm Grandagon on a Horseman SW612, which has an image circle, if I remember correctly, of 125mm. If shot wide open, mechanical vignetting is very apparent as it adds significantly to the natural vignetting. Natural vignetting is also noticeable at all apertures, but a center filter takes care of that. The Grandagon is not particularly sharp at the edges of a 6x12 frame wide open.
 

usm

Member
2) Do the Rodie grandagons suffer from the same fragility as apparently the Rodie HR lenses requiring more careful handeling and transport? Not casually hang off the shoulder lenses? What about the super angulons?
Are the HR lenses a no go for taking them for a mountain hike, specially the HR 35? Is it better to get one with a aperture ring instead of a copal 0 version?
 

dchew

Well-known member
Are the HR lenses a no go for taking them for a mountain hike, specially the HR 35? Is it better to get one with a aperture ring instead of a copal 0 version?
I’ve taken the 90hrsw on multi-day backpacking trips into relatively rugged areas like the Wind Rivers in Wyoming with no issues. If you just take normal care in packing and don’t carry the camera around hanging off the tripod you should be ok. There is always the possibility of a lens getting knocked and damaged, but that’s true in the studio too.
The one exception might be the 32hr, but I know several people, like Kinya, who travel around the world with it successfully. I’ve never owned that lens so I can’t comment. I have heard the aperture mount is more robust than the Copal 0 shutters.
Dave
 

jodad

Member
The aperture mount lenses only work with digital backs so i suppose this is not going to work with a film back where you need a shutter...
 

med

Active member
The aperture mount lenses only work with digital backs so i suppose this is not going to work with a film back where you need a shutter...
For this use case, the best method is to upgrade to the sturdy Phase X-Shutter, and then use your IQ4-150 as a shutter controller. This is the Dante-preferred way, of course....
 

TimoK

Member
The size of the image circle is usually reported at specific apertures and focus distances. ... I have never seen a lens manufacturer report image circle information across the aperture range. Normally it's for the recommended working aperture and infinity (for normal lenses) or 1:1 or the ideal magnification (for repro lenses). Note that the area illuminated does not change with aperture. What changes is the "circle of good definition", in other words, the part of the image circle where image quality is good.
At those LF times for LF lenses like Super Angulons or Grandagons both Schneider and Rodenstock recommended using F22 for working aperture.And for all focal lengths from wide to tele.
They only published the Image circles at F22.
The only exception was Nikon (and maybe some other Japanese lens makers) who did publish Image circles at wide open and stopped down. Nikon made it very clever. They gave IC's for SW-Nikkors at F16 and Wide open And for other, longer LF-Nikkors at F22 and wide open. ( btw sw-nikkors were in range of 65 -90 mm, not what You did ask)
Not across the aperture range but two numbers. If I remember Yamasaki gave also two numbers for image circle, not sure.
 

Alkibiades

Active member
not really: Rodenstock lhave different lenses, so the working aperture on Apo Siroanr - S is ap 16, on the Apo Sironar-N App 22.
the same situation at the wide lenses: Apo Grandagon and Grandagon-N 4,5 have the working aperture 16, only the Grandagon-N 6,8 have 22.
Schneider handle their infos very consevative, but all super angulon 5,6 and xl have allready they working aperture at 16 ( maybe 47 xl only has 22 becouse of the extrem 120°).
the slower super angulon 8 should be used at 22 for full imege circle and best sharpness overall.
The image circle of the apo grandagon 55 is 166 mm at the app 22 and maybe also at 16. It allows some little movements on 4x5 inch.
the image circle for digital work- 125 mm is already achieved at 8/11.
 

jodad

Member
The size of the image circle is usually reported at specific apertures and focus distances. As you may realize, the image circle gets larger as you approach 1:1. It is smallest at infinity. I have never seen a lens manufacturer report image circle information across the aperture range. Normally it's for the recommended working aperture and infinity (for normal lenses) or 1:1 or the ideal magnification (for repro lenses). Note that the area illuminated does not change with aperture. What changes is the "circle of good definition", in other words, the part of the image circle where image quality is good.

To your specific questions,

1) It really depends on a lot of considerations. Some abberations are reduced by stopping down. Light fall off will be worse wide open than closed down all the time (that's just physics). With some lenses, light falloff is effectively gone by the middle of the aperture range; with others it's a more gradual decline. Lenses are at their best in the centre, and normally decline in quality towards the corners. You can see this clearly in MTF charts. And then there's diffraction, which starts being more important than aberrations as you close down the aperture. The good news is that when using lenses with large image circles, the image quality may be consistently good within the area covered by the sensor, and only start falling off noticeably once you start shifting. You also have field curvature as a concern in some lenses (but much less so in my experience with lenses actually designed for shift). Some lenses were simply not meant to be used wide-open. For example, when I shot 4x5 film, it was normal to compose wide-open but close down to at least f/11, with f/16 often being the working aperture.

2) This I leave to people who have those lenses. For what it's worth, the Apo-Grandagon 55/4.5 I owned briefly was, like my other large format lenses, quite sturdy and didn't have the enormous lens cells of the Rodenstock HR lenses. I treated those lenses with care, but didn't have the concerns that people using the modern Rodenstock HR lenses mention. A good knock is always bad -- for the lens and for the delicate threads of the shutters.

I hope that helps.
very helpful indeed, thank you Rob
 

jodad

Member
The size of the image circle is usually reported at specific apertures and focus distances. As you may realize, the image circle gets larger as you approach 1:1. It is smallest at infinity. I have never seen a lens manufacturer report image circle information across the aperture range. Normally it's for the recommended working aperture and infinity (for normal lenses) or 1:1 or the ideal magnification (for repro lenses). Note that the area illuminated does not change with aperture. What changes is the "circle of good definition", in other words, the part of the image circle where image quality is good.
Just a follow up on this. I will be using one of the abovementioned lenses more at close focus distances like 6ft - 14ft, infinity focus much less often. As such, when you write about approaching 1:1, is my understanding correct that the closer you focus the larger the image circle gets and so the larger the "circle of good definition" becomes, covering a larger amount of the frame of film format being used (in better "quality"/definition)?

And, WRT aperture, the smaller the aperture (larger F stops: F11-16 etc. compared to f4.5-5.6) the larger the image circle gets and so the larger the "circle of good definition" becomes?
 

rdeloe

Active member
As I understand it*, it works like this:

The "circle of illumination" is the disk of light the lens projects. It's a property of the lens. It does not change with aperture. It does change with focus distance. It is smallest at infinity, and increases in size as magnification increases. This is why in large format photography you'll see people using lenses designed for 4x5 film, for example, on 8x10 film. How is this possible? It's all a function of magnification: they're only able to do it at high magnification. It's also why lenses designed for macro will sometimes report a huge image circle, but that circle only is valid at 1:1 (for example). People who buy such a lens thinking the image circle is that size at infinity are in for a nasty surprise.

Within that circle of illumination, image quality is best in the centre at every aperture (again, a property of lenses), and generally declines as we go to the edge of the circle of illumination. Sometimes the decline is rapid, sometimes it's slow. And, importantly, the size of the circle of good definition tends to be closely tied to aperture. With most lenses, as you stop down, the size of the circle of good definition increases. The caveat is that as you stop down, you reach a point where any benefits from stopping down are lost to diffraction. Note that I said "generally" and "tends to" here because I've seen data for lenses where image quality across the frame was best wide-open and actually declines as you stop down; those are not common.

MTF charts are a great way to understand what this looks like for any given lens. Here's an example for the 150mm f/4.5 lens for the Mamiya 7 series. Without getting into the details of how MTF charts work, just look at the lowest solid line (which represents 40 lp/mm for the sagittal direction). The left-hand side of the chart is the centre, while the right-hand side is a corner. The numbers on the bottom axis of the chart are distance from centre (0mm at left, 44.5mm at right); this is the radius of the 90mm image circle of this lens, which is what's needed to cover 6x7 film.

MTF for Mamiya 7 150mm lens.jpg

Importantly, what this pair of charts is telling us is that the lens is very decent wide-open at f/4.5, and amazingly good at f/8. Notice how the lines are flat almost to the very corner at f/8. I have this lens in its Mamiya G (for the Mamiya 6) variant. The optics are almost the same. It really is this good on my GFX 50R. I can shift with a lens like this because the radius of the image circle needed to cover the GFX 50R sensor is 27.5mm, so if I were to mount this Mamiya 7 150/4.5 lens on my camera, the part of the image circle I use without shift is marked with the red line. The part of the image circle available to me for shift is everything to the right of the red line. This tells me that I should use at least f/8 if I'm planning to shift the at least 17mm available to me with this lens. (I said "at least" because Mamiya isn't saying there's no usable image circle beyond r=44.5mm -- see below!)

So the take-away here is that the circle of illumination does not change with aperture, but the "circle of good definition" does "grow". That's just another way of saying that as we stop the lens down, the size of the circle within the illuminated area that is good quality gets bigger. Even if you've never heard the phrase "circle of good definition", you know exactly what I'm talking about: we all have used lenses that are crappy wide-open, but get better as we close down. A nice example is my S-K Makro-Symmar 120/5.9. At infinity, the "circle of good definition" at infinity is quite small because it's a macro lens. However, at f/11, it's transformed into a killer lens at infinity with a big "circle of good definition" for shifting and stitching.

Now, here's where it gets trickier: the lens designer, Mamiya in this case, is only reporting MTF data for an image circle of 90mm (what's needed to cover 6x7 film). The circle of illumination at infinity is bigger than 90mm; I know this because I can shift my sensor 70mm on my camera, so I can see empirically where the edge of the circle is for any lens. Furthermore, I can see the circle of illumination growing as I focus on a closer and closer subject. BUT that doesn't mean that the image quality is necessarily any good in the expanded area of the circle. It might be, and it might not be -- you have to test to find out. Back to my S-K Makro-Symmar 120/5.9: at its design distances (under 2m), it's already excellent wide-open across the frame. As magnification decreases, you have to stop down more and more to get that image quality.

My final point in response to your question: image circle size at 6' to 14' will be more like infinity than it will be at 1:1. There are formulas you can use to calculate exactly how big it will be as a function of magnification, focal length, image circle at infinity. However, as a rough rule of thumb don't expect a big difference. If the lens is designed for "normal" (non-macro) work, then you likely won't see a huge difference in image quality as a function of aperture and magnification when used at your distances.

Rob

* I've learned it's always a good idea to use little caveats like that on a photo forum that has lots of more knowledgeable people than me... ;)
 
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