Magnifying glass lens on a 4x5

[mabman]

I picked up a beater Speed Graphic w/ focal plane shutter a while back. I've finally gotten around to playing with it.

Because it didn't come with a lens, I bought a dollar-store magnifying glass (approx. 3.25" diameter). With the magnifying glass' handle cut off, the lens takes up most of the lens/lens board area, so I have just taped it in place for now.

The problem is, I can't get it to focus on the Graphic's ground glass, no matter how close I get to an object, or how far away - all I get are blurry blobs of light (with varying degrees of blurriness when I try to focus or move closer or farther away).

The examples I've seen with people using magnifying glasses as lenses have all been 8x10 or larger - is it just that I need a smaller magnifying glass for 4x5?

Otherwise I'm confused, and open to suggestions

[BetterSense]

It should work. I've used a variety of magnifying glasses. What is the focal length of your magnifying glass? You can find that out using the sun. I think you need to find the approximate focal length of your magnifying glass lens and start by setting the front standard that distance away from the film back. That should get your focus at least close.

[Steve Smith]

It is possible that the focal length of the magnifying glass is too small for the speed graphic. Probably around 50mm.

If you find yourself in a shop with a variety of magnifying glasses available, try them out by focusing something bright like the light fittings or the shop window onto the palm of your hand to judge the necessary distance it needs to be away from the film.


Steve.

[Rick A]

Take a magnifying glass and hold it above some text then measure the distance when focused, thats the focal length of that glass. Looking glass with 4-6 inch focus is fun to play with on LF cameras. Pick up a round one and mount it in a length of plastic sewer pipe and use for meniscus lens.

[mabman]

Thanks, all. I did a quick check with a couple of household lamps, and it appears the focal length of this magnifying glass is actually too long - it's about 18 inches (460 cm). The Speed Graphic doesn't go out that far Oh well, it was only $1. Next time I'm near the store I'll have to check to see if they have any others.

Thanks again.

edit: It's been pointed out using a lamp may not be an accurate measurement, and I should use the sun. Unfortunately it's heavily cloudy here today. I tried it 2 ways inside the house:
a) with the magnifying glass held between my hand and and a ceiling light and measuring the distance between my hand and the magnifying glass when the fixture was in focus on my hand, and
b) using the magnifying glass to "project" the image of an incandescent bulb on the opposite wall, and measuring the distance between the bulb and the glass when the filament was in focus on the wall. Both come out to 18 inches, +/- an inch or 2 due to my own imprecise measuring.

In any event, it doesn't work, so I'll have to try another one.

[MattCarey]

A separate question: why?

You can find some old brass lenses (especially in barrel) for <$10 often times.

[mabman]

A separate question: why?

You can find some old brass lenses (especially in barrel) for <$10 often times.

Because no one that I'm aware of locally has any barrel/Petval lenses (I check various antique, photo, and thrift stores periodically, and have never seen one). This means I'd have to buy one from someone online, pay for shipping and possibly duty, etc. Likely more than $1 I spent on this magnifying glass

Also, I intended to use this beater Graphic with a pinhole, and so I really don't have a lens a mind, but I thought for $1 and some time I could play around a bit.

[brian d]

I use a magnifying glass sometimes on one of my 4x5 speed's. The lens I use is about 2" across.
It gives a very nice look

[MattCarey]

Sounds good.

If you would like, I have a 150mm aplanat and a 150mm process lens (ultragon or something). You could have either for the cost of shipping.

[Rick A]

Swell offer, I would grab the aplanat if I were you, I have a soft spot for them.