20x24 Paper Negative Camera and Selecting Edmund Scientific Meniscus Lenses

[Mustafa Umut Sarac]

Hello there,

I want to take my mother and sisters portraits with 20x24 Fomabrom Grade 3 Matte Paper Negatives and contact on to the same paper.
There are 10 papers for 70 dollars at Freestyle and I can shoot only 5 frames.
I have no enlarger or timer and will use Edward Weston bulb lamp enlarging and rabbit hat shutter method.
I looked to the Edmund Scientific and there are meniscus lenses , same focal distance , different diameter.
What is the difference between large diameter lens and narrower second , third best.

AND Do I need to buy negative meniscus or positive meniscus lens ?

50mm Dia. x -505mm FL, Negative Meniscus Lens, Grade 2

36.5mm Dia. x 444.4mm FL, Positive Meniscus Lens, Grade 1

76.7mm Dia. x 324mm FL, Positive Meniscus Lens, Grade

58.5mm Dia x 350mm FL, Positive Meniscus Lens, Grade 1

http://www.edmundoptics.com/optics/o...us-lenses/3479

Umut

[Mustafa Umut Sarac]

88mm Dia. x 750mm FL, Positive Meniscus Lens, Grade 2

47mm Dia. x 700mm FL, Positive Meniscus Lens, Grade 1

I think these are the suitable ones for 24 inches , which is better grade 1 or 2 ?

And 40 or 80 mm diameter , what do you advise ?

Are Positive ones the suitable ones ?

Umut

[ic-racer]

Do you already have the 20x24 camera? If so, how much bellows draw is available?

[Mustafa Umut Sarac]

Do you already have the 20x24 camera? If so, how much bellows draw is available?

Hello ic-racer , I can build a box , glass and paper holder. All fixed , all focus would be done to move the box. No bellow , no movement.

Umut

[jp]

You want positive meniscus, One of the longer focal lengths. I'd suggest going for a larger diameter glass and putting a washer stop in front of it.
Chop up one sheet of paper for experimenting / testing exposure, focus, filtration, etc..

[Mustafa Umut Sarac]

Thank you very much jp.

I tried but shipping 35 euros for single element lens , rip off , I need other source.

Umut

[Randy]

Umut, try a lens from an unused set of eye glasses / reading glasses. I just did a crude test on my reading glasses on a light bulb that was about 3 meters from a wall and my glasses cast a sharp image at about 1 meter from the wall - so at about portrait distance, my glasses have a F/L of about 1000mm. My glasses are fairly week - shouldn't be to hard to find some stronger that should have a shorter F/L...I think.

[Tim Meisburger]

+1 has a FL of 1000mm. +2 500mm. +3 250mm.

Check with a local optician and see if they have round lens blanks in the fl you are looking for.

[Fr. Mark]

close-up lenses that screw on like filters are in diopters and I think they are also the focal lengths/markings mentioned in the previous post. I think they're pretty inexpensive, too. Thanks for the reminder about this, actually, I may try it for long lens with my camera(s).

[ic-racer]

Hello ic-racer , I can build a box , glass and paper holder. All fixed , all focus would be done to move the box. No bellow , no movement.

Umut

Ok, so you need to determine, either how far you want to be from your subject (your perspective for the picture) or how big you want the image on the paper negative.

Then you can use the 'thin lens equation' to determine your box size and lens strength.

As mentioned, you can convert your lens measured in 'diopters' to 'millimeter focal length' by knowing 'diopter' is the reciprocal of 'focal length' in meters.

2 diopter = 0.5m focal length etc.

For the sake of simplicity , lets say you want the head to be the same size as real life on your 20x24 paper negative. So in that case your box size will be twice the reciprocal of the diopter strength of your lens. The subject distance will also be the same.

So for full size head image on film with a "+1 Diopter" close-up lens your box needs to be 2000mm long and your subject will be 2000mm in front of the lens. etc.

If 2 meter subject distance produces unpleasing perspective to you, you can change that to, for example , 3 meters.

Then your box only needs to be 1500mm long, and the head will be 1/2 size on the paper negative, etc.

http://www.ebay.com/itm/46mm-Macro-C...item4a9bdb16cd