Lens Image Circle

[david_gardner2]

If I want to measure a lens' image circle, can I simply support it at

its focal length above some bright flat object (like, say, a piece of

white mat board), shine a light through it in a darkened room and

measure the diameter of the resulting light cone? Sounds like it

should work, but I want to make sure that there's no flaw in my plan.

 

As always, thanks in advance.

 

David

[steve_levine]

The trouble would be that you don't know where the lens' optical center is. Focal length, is the distance from the optical center to the film plane, when the lens is focused at infinity.

Try looking at a site like this:

http://www.graflex.org/lenses/lens-spec.html

 

There is a chart with various lenses and their basic information(covering power included).

[ronald_moravec1]

The iluminated circle may be larger than the area of useable sharpness.

 

Put the lens on a camera, raise it one or two inches, focus on a brick wall and a place where ther is detail in the corners, stop to f22 or you favorite stop, and make a neg.

 

If it is still sharp in the top corners, raise it 2 inches and repeat. You will find the point where you have to stop.

 

If two inch rise cuts off 1/2 inch, you know you can go 1.5 inch and no more.

[35mmdelux]

Why don't you just procure the lens test reports and save yourself the time? Could your test match the labs? don't think so. Regards, Paul

google google

[peter_black1]

Far easier to just go <A HREF="http://www.largeformatphotography.info/lenses/LF4x5in.html"> here </A> unless it is a particularly unusual lens.

[kelly_flanigan1]

Re <i>The iluminated circle may be larger than the area of useable sharpness.</i><BR><BR>This good comment needs to be tattoed on folks arms; etched in their brains. <BR><BR>Older lens literature often gave two sets of numbers; one for illumination; and a smaller set for "good sharpness". <BR><BR>Here I have a 210mm f4.5 Russian Industar which has still good illumination; when the off axis imagery tanks.

[david_gardner2]

Thanks again to all the responders.

 

Let me rephrase and elaborate a little. I have a lens that I suspect is a medium format lens. In any event, I can't find it listed on any large format lens info spec sheets. (FWIW, in case anyone knows anything about it, it's a Schneider 5cm.) So what I'm really after, before I start to worry about a zone of sharpness (which I agree is an important consideration) is "Does it even have an image circle capable of covering a 4x5 negative?"

 

Given that, is my test sufficient? Realizing that there will be issues with where I place my penlight in terms of angle and distance, this should still give me a good rough notion, no?

[dan_fromm2]

David, why did you ask the wrong question? Why did you ask how to measure when you should have asked "what is this lens and what can it do?"

 

"it's a Schneider 5cm." Not much info, but at even odds it is for 35 mm still, barely covers a 43 mm circle. NOT a medium formal lens, not a lens for LF except at magnifications well above 1:1. What were you thinking? Were you thinking at all?

[david_gardner2]

I'm going to assume that Dan's just trying to be funny.

 

I've read accounts of 50mm ultra-wide lenses used on large format cameras, so I know that they exist. A friend came across this lens and gave it to me, thinking it to be one of those. I don't think it is, but I want to verify what it is and isn't before I decide what to do with it.

[c4-contemporary-art]

Well - I'd be suspicious. It SOUNDS like the lens dates back to the 40s or

before - Schneider's origins as a budget low-quality lens maker would not

be terribly supportive of the argument for a 50mm LF. Doubt they would

have had the wherewithall. At any rate, one EASY way of determining

image circle - is to simply cut out a piece of cardboard, preferably large-ish

in size. Cut a circle out of the centre that would allow you to mount the lens

on the card (or TAPE it down - if you HAVE to). Next hold it up to a window

during daylight in a darkened room with a piece of white paper where the

neg would be. You should be able to eyeball the image circle well enough

to determine this. I'll BET it's for a 35mm camera.... but hey... you never

know. The hologon is one of the only lenses I know of that might have been

made in something like a 50mm range 4x5 lens...

[dan_fromm1]

David, I wasn't joking. I was serious.

 

Schneider made millions of lenses engraved, variously 5 CM and 50 mm, for 35 mm folding cameras. Millions. Schneider's archive and current product slate list no, as in none, not any, zero, 50 mm lenses for LF. 47 mm, yes. 53 mm, yes. 50 mm, no.

 

Further, those 5 cm lenses for Kodak Retinas and the like are tiny little things. No modern wide angle lens for formats larger than 35 mm is tiny. Have you looked at the thing? Is it tiny? Shorter than its focal length?

 

I'm intimately familiar with the fantasy of finding buried treasure. As, for example, an inexpensive and very good lens. It rarely happens. In my limited experience, there are NO cheap wide angle lenses for formats larger than 6x6. I wish there were.

 

Good luck, have fun, keep on digging,

[paul_e._cassidy]

Hey Dan, I know this is an aside, but I have a question please? I know you like macro photography so my question is "Would some of these short focal lenghts work in a macro situation, or is it best to use a "flat field" lens like an enlarger lens of the same focal length? My only macro knowledge is using a Nikon F with micro-nikkor lenses but since we last chatted I have had some questions arising? Thank You in advance Dan. If you prefer I can start a new thread regarding macro work in general but would you be willing to share some of your experience please?

Thanks Paul

[dan_fromm1]

Hi, Paul. Short answer, yeah, sure, why not. But remember that a normal lens for a 35 mm camera has to cover only 43 mm at infinity. MOst just barely do that. So, all being well, one will justcover 86 mm at 1:1. Above around 4:1 it will cover 4x5, but should be reversed if used above 1:1.

 

Another point to consider is that lenses for general photographic use are optimised for a long front conjugate and a short rear one, i.e., for infinity or nearly infinity. Lenses intended for use closeup are usually optimised for a shorter front conjugate and a longer rear one. In fact, based on my experience, most of them give best results over a fairly narrow range of magnifications.

 

If you're going to shoot close up, i.e., in the range 1:1 to 1:5, a good enlarging lens that will cover your format at the magnification should give good results. In this range, f/22 is a reasonable aperture to use, and stopped down that far most lenses are roughly equivalent. But it helps to have a lens designed to work in that range.

 

Cheers,

 

Dan

[paul_e._cassidy]

Hello Dan,

Thanks Always, I want to do about a 3:1 on a 4x5 negative. Let me ask you this, since I have a fairly extensive array of lenses for 35 to 8x10 both camera and enlarger. . ."Is there a particular lens design and size you would recommend?"

The subject is a 3d object, an unusual water lily with unique petials that I wish to zoom in on for detail. I think some transparencies may be called for, to capture the coloration. You tutoring is very much appreciated. Paul

[dan_fromm2]

Paul, if you can manage the extension (600 mm for 3:1) any old 150 mm process lens will do just fine. Otherwise, if you can borrow or buy a 100 Luminar or 100 Neupolar or 90 Microtar or 80 or 120 Summar (post-WWII coated), any one of them should do. Come to think of it, a 105 Tominon should do well enough too.

 

I don't believe it will quite cover 4x5 at that 3:1, but if you have a 50-60 mm macro lens for 35 mm, try it reversed. My 55/2.8 MicroNikkor AIS works very well that way, but on 2x3, at the magnification you need.

 

Another alternative that you should consider seriously if you can find some KM is to shoot on 35 mm with a good macro lens at a magnification that will fill the frame with the details you're interested in. Film is limiting, and KM is, IMO, less limiting than anything you can get in 4x5.

 

Good luck, have fun,

[paul_e._cassidy]

Thanks Dan,

 

I was sure you could help me. I think I can do the 600mm with my view camera or my 2D and I can match a couple of the options you have given me. I also plan on having my Nikon F at my side with the micro Nikkor at the ready.

 

It's a scorcing day today in north Florida so I'll sort through my gear and maybe do a practice setup on the shade porch before going to the back pond. Tempted to jump in but don't want to scare the pan fish and snakes!!!

 

Thanks Always Dan, Paul

[dan_fromm2]

North Florida, eh? Where, approximately? I ask because I plan to go to FL late in August. Yeah, I know, not the best time. Will visit an old friend in Stuart, try to collect some snails between, roughly, Tallahassee and Spring Hill.

 

Cheers,

[paul_e._cassidy]

Dan I live in Gainesville, Home of the Gators. . . been on the farm since I came here as a student in the mid-70's . . .after graduation I couldn't think of anyplace I wanted to go, so we have homestead ever since. . . if you think you'll be in the Gainesville area we can switch to email and I'll send you my phone number etc??? In any event bring your camera and carry your film in a cooler bag. And please make sure you consume 8 glasses of water daily while here during dog days! It is so easy to dehydrate in the 105 heat indexes that are the norm lately.

Please travel safely and enjoy the beauty of Florida, Paul

[bob_salomon]

<p>"Far easier to just go <a rel="nofollow" href="http://www.largeformatphotography.info/lenses/LF4x5in.html" target="_blank">here </a>unless it is a particularly unusual lens."<br>

Except there are some errors. For instance, the 55mm Apo Grandagon covers a 163mm circle at f11. It is in diffraction at f22. some lenses are at optimal performance before f22. But the chart just clumps them all at f22.</p>