150mm f5.6 Symmar-S Image Circle

[Tom Nirider]

This lens shows image circle at 220mm @ f/22. On my 5x8 camera (yes, you read that correctly, it's 5x8)... there is what seems to be even illumination in the corners even at f/5.6. The diagonal for this format is 238mm. I thought I understood that an image circle is usually larger at higher f-numbers. What am I missing? How is this lens covering my format?

[BrianShaw]

Is it even illumination to they eye, or on film also?

Eyes can be subjective and film is quite a bit more objective.

[Dan Fromm]

Tom, posters on this forum use two different coverage definitions. Circle illuminated, which is what you see on your camera's GG. Circle of good enough definition, which can be discerned clearly only on film. This is what lens makers use.

[Oren Grad]

Are you focused at infinity, or closer?

[Tom Nirider]

Is it even illumination to they eye, or on film also?

Eyes can be subjective and film is quite a bit more objective.

Well, it is clearly illuminated to the edges on the ground glass. If I can see even illumination then it should appear even on film also? Again, trying to understand what I'm missing. And I fully realize I may have to just do a test with film to see...

[Tom Nirider]

closer than infinity.

[Tom Nirider]

Now this is very confusing. It's either illuminated or not... When I look through the cut corners I can clearly see light from the lens at all apertures. Again, just trying to figure out if I have coverage before I use up film...

[Oren Grad]

closer than infinity.

Keep in mind that the image circle expands as you extend the bellows to focus closer. Imagine projecting a cone of light on to a flat screen, and then think about what happens to the illuminated circle as you move the screen away from the light source.

[Bob Salomon]

Now this is very confusing. It's either illuminated or not... When I look through the cut corners I can clearly see light from the lens at all apertures. Again, just trying to figure out if I have coverage before I use up film...

No, you have illumination but it’s outside the area the lens critically covers. It’s just light outside the rated coverage. Shoot a couple of sheets of film at infinity and check sharpness at the edges and corners. Make sure you have something there like a brick wall or fine tree branches or telephone wires, etc.

[ic-racer]

I used a Symmar-S 210mm (IC 294) on 8x10 for a few years. There are some tricks like back tilt that relax a format's coverage criteria. Other times, there was nothing to resolve in the upper right or left corner (sky).
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[Kevin Crisp]

The Schneider Symar 150's were all described by the factory as 4X5 lenses until the APO version, which they called a 5X7 lens. I don't know if a 150-S (single coated or multi) will cover at infinity. Since they cost next to nothing, get a 150 g claron and you will have plenty of coverage and room for movements. There a number of historic threads on here that indicate the g claron 150 barely covers 5X7. My experience with multiple samples is that it does much more than that.