20x16" Camera lens advice?

Hi there,

I am currently building a (very basic) 20x16 inch camera as I have just bought some Harman Direct Positive Paper that size and was after a bit of advice about what lens to use if anyone could please help...

I have a Schneider - Kreuznach APO - Symmar 5.6/210mm Multicoating lens that I use on my 5x4 camera, I'm aware that this won't cover the 20x16 area but I read somewhere that someone used a -2 diopter on a 240mm lens that did so I was hoping I might get away with it, but I'm not sure exactly what is meant by a -2 diopter or where I could get one that would fit my lens. If it will work!

I'm on a budget so can't really afford to spend lots on a lens (I could stretch to £100-300 at this stage and will be saving for something better in the future if i get good results) so just looking for ways I can get started and get some images as I work on the design of the camera, getting money together etc.. I know I can use a pinhole but have experiment with this a lot in the past so now looking for a bit more control. (The inspiration for this project came from here and I am following a similar design http://petapixel.com/2013/02/12/buil...amera-by-hand/ . This will be Mark I, Mark II will be better I hope!).

Any advice on what I could use (and where to get it) or any tricks, tips or solutions would be really appreciated. Also can anyone suggest an 'ideal' lens I should be saving up for, mostly for portraits.
Many thanks,
Brendan

Diopter is the power of a lens, equal to the inverse of the focal length, in meters. So a -2 diopter is focal length of -0.5m. The power of your 240mm is 1/0.24m = 4.166 diopter.

If you put “thin” lenses one in front of the other, their powers add. So if you put a -2 diopter lens with your 4.166 diopter lens, you get 2.166 diopter, or effective focal length 0.462m = 462mm.

HTH

Ed

Sorry, the power of your 210mm is 1/0.21m = 4.762 diopter. Combined with -2 diopter gives 362mm EFL. -3 diopter would give you 568mm EFL. The stronger the diopter value of your add-on lens, the worse your image quality.

You can find diopter singlets from various sources, but they are just that, and won't be corrected for color, spherical aberration, field curvature, etc.

Ed

Since you'll probably have some pretty long exposures, you don't need a shutter. A long barrel les would be ideal. There was a 19" Nikkor in the classifieds recently for very little money.

There's also a 19" red dot Artar in barrel for sale on ebay right now for $400.

20 x 16 and "budget" are mutually exclusive......you should be able to get a 19" Artar in Ilex if you take your time for under $400. L

355mm f9 Schneider G-Claron in barrel might be a possibility.

There are tables on the forum that list large format lens by coverage circle here http://www.largeformatphotography.info/lenses/

the standard lens for 16x20 is approximately 25.5 inches focal length, which is 635mm. This also approximately the size of the image circle (coverage circle) required from the lens. Looking through the list by Michael Gudzinowicz the largest image circle (coverage circle) listed is about 500mm, this is significantly less than the 635mm required, the result will be dark corners, also known as vignetting.

While I am not an expert on large format lenses I know enough to know that a format such as 16x20 requires a special lens. There is a forum at APUG for ultra large format photography, that might be a good place to seek advice about suitable lenses.

PS of course, there is an ULF forum here also which I should have mentioned.

The requirement for a large coverage circle can be turned into an advantage by the use of a lens having shorter focal length that gives a circular image in the center of the 16x20 format, the surrounding unexposed area being black. With an appropriate choice of subject this can be visually interesting and avoids the problem of how to find the coverage circle required for full coverage of the 16x20 format.

My advice for a first lens for 16X20 would be a 450mm Nikkor-M. It will be much sharper on the corners than a 19" Artar, with better coverage than any other 19"process type lens. A 24" Artar would also work, as would 24" process lenses by other makers. In this format you can do a lot of work without a shutter if necessary since you really need to stop down the lens a lot to get adequate depth of field.

When doing research on lenses for ULF seek out advice from people who have actually used ULF formats such as 12X20, 16X20 and 20X24. Tables on lens coverage on this forum and in other sites can be useful, but they don't include much empirical data that is know by those who have used these formats.

Sandy

All my LF lenses are somewhat simple and cheap.

I'd suggest a large magnifying glass, I've got a few that measure at around 350mm focal length.

Or get an over head projector lens, they are usually around 300mm.

Or get some cheap reading glasses, +1 is 1000mm focal length, +2 is 500mm focal length.

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