f64 lens ?

RS have you tried that PINHOLE ? can you show photos online ?

I just found that link >> http://www.photo.net/learn/pinhole/pinhole

Use a tilt lens.

<i>A teleconverter reduces the amount of light to the film plane (or sensor plane for some) because of the distance it adds. So if you have a f/2.8 lens and you put a TC on there that cuts (for example) one stop, then you are forced to open up by lengthening the shutter speed or increasing your ISO. The TC doesn't actually change the size of the aperture. </i>

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A teleconver DOES decrease the focal ratio. It DOES turn an f/32 lens into an f/45 or f/64 because it increases the focal length of the lens.

Bob : here it is >>

 

http://heliconfilter.com/pages/index.php?id=509

 

http://www.hadleyweb.pwp.blueyonder.co.uk/CZ5/combinez5.htm

..."A teleconver DOES decrease the focal ratio. It DOES turn an f/32 lens into an f/45 or f/64 because it increases the focal length of the lens."...

 

Very true, but the physical aperture remains the same. For example, the aperture of a 400mm lens at f8 is 400/8 = 50mm. Add a 2x converter to the 400mm lens at f8 and it becomes an 800mm lens at f16.

 

The aperture is given by the formula FL/f stop. 800/16 = 50mm.

In Ansel Adams' book The Camera, he goes into some great detail about diffraction in lenses.. I don't have it in front of me right now but IIRC, he talks about how diffraction is greatly increased with small format camera lenses vs. large format at the same f stop. So, f/32 on an 8x10 camera lens will have considerably less diffraction than f/32 on a 35mm or DSLR lens. When Ansel talks about f/64 being the maximum aperture for maximum sharpness and DOF (that's why he chose "f/64" as the name of the group he started with Edward Weston in 1932, btw), he's talking about a large format lens.

 

Sorry I can't remember the technical details of why this is so, but it made sense to me at the time I was reading it.

The equivalent DoF, f stop and focal length of lens for the same field of view varies with the diagonal of the format. For example, 35mm format has a diagonal 1.6x greater than the format of the 10D, 20D etc.

 

Therefore, a standard lens for a 20D, 28mm at say f2, is equivalent in terms of DoF and Field of View to a 28x1.6=45mm lens on 35mm at an f stop of 2x1.6=3.2 (3.5 being the closest).

 

 

The same principle applies going up from 35mm to 8x10" format. The 8x10 format has a diagonal of approx 13". 35mm has a diagonal of approx 1.8", ie. the diagonal of 8x10 format is approx 7x greater (a bit more). Therefore a standard lens for 8x10 format with the same field of view as a 45mm lens on a 35mm camera is 7x45=315mm (say 320mm), and equivalent DoF is 7x whatever f stop you are using on 35mm. Eg. 45mm at f8 is equivalent to 7x8=f56, close enough to f64.

 

Hope that's all crystal clear.

The maximum resolution any lens can produce in terms of line pairs per mm (lp/mm) is defined by a very simple formula derived from Rayleigh's theories. For green light, roughly in the middle of the spectrum, it's 1500/f stop.

 

For example, any lens at f64, whatever the focal length or format of the camera, can not deliver more than 1500/64 = 22 lp/mm at the focal plane, due to diffraction limitations.

 

22 lp/mm is not spectacular, but it's even worse than it seems. This resolution limit applies only to the lens, not the system, and those 22 line pairs have lost over 90% of their original contrast and are consequently of little relevance on film or sensor for most scenes that people photograph. However, I daresay that such lines of high contrast ratio might be just discernible on Velvia film shooting a test chart with an 8x10 view camera at f64. But I've never tried it.

 

I think it's certain that they would not be recorded by any current digital sensor.

Bob I have a question about your idea for stitching photos together. I know this is thoery craft or maybe I am not understanding this part of optics. But I thought this would not work because magnification and focal length changes slightly with focus?

The stitching program has to make the appropriate adjustments to size. If it doesn't, you get a blurry result. I haven't looked at such programs in a while, but when I did, I found that sometimes the trial software did NOT automatically adjust for size differences and was therefore of limited usefulness in my opinion.

 

Stitching in general is a very time consuming activity requiring a lot of patience and trial and error.

Here's a link to a program designed for macrophotography, microphotography and hyperfocal landscape photography. I haven't got the time to trial it, but if you find it works, let me know.

 

http://heliconfilter.com/pages/index.php?id=509

Ryan,

 

Distortions due occur due to the shifts in focus when combining frames. But if you bracket in small enough shifts in focus the distortion from frame to frame is small enough not to matter excessively. In the end (I have only tried this with macros of a bee and a reversed 50 mm) it is no worse than the perspective distortions of a non-fisheye wide angle lens. With too much shift in focus between frames I suspect it would be a problem. But that just means you need to bracket your focussing more finely. After all, the distortions form a continuous function as focus distance changes so small enough shifts in focus should allow you to get small enough deviations between frames to blend them.

 

Also, with a landscape, will it matter significantly? I do not know. I suspect (but could be wrong) that the deviations will be smaller as the ratio of the lens to subject distance to the lens to focal plane distance will be fairly uniform in comparison to work at macroscopic distances.

 

some thoughts,

 

Sean