TheCircleOfConfusion
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Reged: 01/03/2006
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As part of a college project (no I'm not asking you to do my homework!) I need to emulate some shots taken on a 10x8" camera. The shots in question were taken "wide open". It has occurred to me that lens tend to get a little slower as the format increases, e.g. my Bronica lenses are a stop or two slower that the equivalents from my Pentax 35mm kit.
So the question is this, what is the typical widest aperture on a LF lens? Something of equivalent FOV to a 50mm and/or 28mm on a 35mm SLR.
Thanks
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www.thecircleofconfusion.com
"They're just photos after all"
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beejaybee
Marvin
Reged: 18/07/2007
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Quote:
what is the typical widest aperture on a LF lens?
Probably f/6.3 to f/8 would be typical for 10x8 format. However the depth of field would be a great deal less than that you would get from a 35mm format lens at the same aperture, or indeed at f/1.4!
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AlexMonro
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Reged: 05/06/2006
Posts: 702
Loc: Exeter, Devon (and Somerset so...
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A little playing around with the DoF calculator at Cambridge in Colour seems to show that a 10x8 large format camera with a 300mm (standard) lens at f/8 has similar DoF to a 35mm camera with a 50mm lens at f/2.
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Woolliscroft
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Reged: 23/08/2005
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Regardless of the DOF issue, you really can't emulate the look of 8 x 10 format images, with their stunning, totally grainless tonality, on a miniature or medium format photo. You can take the same picture from the same angle, under the same lighting, and give it the same DOF and perspective (assuming no lens/film plane movements were used for the large format image), but you still won't get it to look the same. Let's face it who would bother to use such bulky kit if you could? Worse still, if camera movements were used for the original, forget it. Not even a shift lens can compete. You can do a certain amount. Medium format, or a smaller large format, obviously gives you a good start. You can use slower, finer grained film (although that will have a different look) and keep enlargement to a minimum, but even so...
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David.
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beejaybee
Marvin
Reged: 18/07/2007
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Well it does of course depend on what value you take for circle of confusion.
Taking 0.1mm as the value (I don't think it's reasonable to take less) then the hyperfocal distance for a 300mm f/8 lens is 112.8 metres. Taking 0.03mm as the usual value for 35mm the hyperfocal distance of a 50mm f/1.4 lens is 60 metres. To get the hyperfocal distance for the LF lens down to 60 metres we have to increase the circle of confusion to 0.188mm, i.e. 6.25 times the value for the 35mm format lens. Now it so happens that a 6.25 times enlargement is about what it takes to make the long side of a 35mm format frame just fit 10x8 paper....
But a contact print from a 10x8 format camera should (and usually does) look sharper than a 6.25x enlargement from a 35mm format negative (grain is no problem for one thing). Which is why I feel 0.1mm is a sensible value for the circle of confusion.
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huwevans
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Reged: 05/08/2000
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Loc: Dorset, UK
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Quote:
Quote:
what is the typical widest aperture on a LF lens?
Probably f/6.3 to f/8 would be typical for 10x8 format.
Yes, although for so-called 'normal' lenses - the typical plasmat designs that are used for mid-range focal lengths on most formats - f/5.6 is more common. For example, the strict 'standard' is about 300mm (as mentioned elsewhere, and the available normals in that length are generally f/5.6. I don't use 300mm, but I do have a 240mm plasmat that adequetly covers 10x8 (and is the rough equivalent of a 30mm wide angle in 35mm terms) and that is likewise an f/5.6.
However, once you get above 300mm the plasmats tend to get slower - my 360mm is an f/6.8. Similarly the wides are slower, and longer lenses are invariably even slower still - sheer size and weight considerations see to that, even if nothing else. I have a 450mm Fujinon which is a comfortable portrait length on 10x8, and that's just f/12.5. So there's quite a lot of variation, depending on the type of lens we're talking about.
But faster lenses do exist - I have (though I've never actually used it) a rather ancient f/5 12 3/4" Ilex portrait lens which easily covers 10x8, although in theory it's only intended for whole plate, which is a little smaller.
It's decidedly unusual for lenses like this to actually be used wide open though - they're generally stopped down quite a bit, and may not even cover their intended formats unless they are. Large apertures in these lenses are generally just there for easier viewing, though clearly some people do like to make use of the wafer-thin DoF and dreamy effects that are possible if you open them up.
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Huw Evans.
  
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beejaybee
Marvin
Reged: 18/07/2007
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Quote:
Similarly the wides are slower, and longer lenses are invariably even slower still - sheer size and weight considerations see to that, even if nothing else.
I once nearly bought a 36 inch (900mm) focal length f/4 Ross Xpres lens which was designed to cover whole plate. I think these were used in high-altitude photo-reconnaisance in WWII. I had an idea of using it as a specialised telescope for comet finding.... the weight of the thing put me off!
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TheCircleOfConfusion
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Reged: 01/03/2006
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Loc: The People's Republic of Geord...
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Thanks for the info chaps. I was trying to get my head around the apparent contradiction of long exposure and lens wide open but it makes more sense if the aperture is somewhere around f5.6 ish
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www.thecircleofconfusion.com
"They're just photos after all"
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LargeFormat
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Reged: 24/10/2006
Posts: 1056
Loc: Buckinghamshire and Cumbria
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It's pretty difficult to use a large format camera with the lens "wide open". You are focusing on the screen and can go either side of the correct focus, even at infinity. You are highly dependent on stopping down to get any sort of depth of field and any decent level of focus.
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zx9
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Reged: 22/06/2007
Posts: 891
Loc: London
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Quote:
It's pretty difficult to use a large format camera with the lens "wide open". You are focusing on the screen and can go either side of the correct focus, even at infinity. You are highly dependent on stopping down to get any sort of depth of field and any decent level of focus.
That is why you hide under a cape, use a loupe to help you focus and the movements to control where the plane of sharp focus is positioned. All good fun, I think I can just about remember those days.......
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ZX9 (Keith)  
My Flickr Pictures
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DaveS
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Reged: 22/06/2007
Posts: 196
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Well my 240 mm Symmar is f/5.6, my 12" Perfac is f/6.3, and my 480 mm Apo-Ronar is f/9. But hey, I thought everything on 10x8 was shot at f/64 
Dave
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