Image Circle

[Terry Hull]

How does one determine whether a given lens will cover film size once the image circle is known? For example there is currently a Calumet 210 f6.8 lens for sale ebay. The Gudzinowicz LF table suggests the image circle ( if it is the same lens) has a cover circle of 230, which seems suspect as to covering the 5X7 format I am working with. Is there some math I can use to determine coverage? I am looking for a smaller lens to fit linhof boards, that is F6.8 or faster, hopefully filter thread of 58mm or less. I know of the Fujinons, but are there other lens, which might be more readily available that are smaller at F6.8 or faster for 5X7?

Thanks

[ic-racer]

The image circle should be greater than the diagonal of your film image.

[Roger Thoms]

Use the Pythagorean theorem to calculate the diagonal. This link explains it much better than I ever could.

http://upload.wikimedia.org/math/1/4/5/1455314a78f39a594485adbaf74d63f9.png

Roger

[rdenney]

How does one determine whether a given lens will cover film size once the image circle is known? For example there is currently a Calumet 210 f6.8 lens for sale ebay. The Gudzinowicz LF table suggests the image circle ( if it is the same lens) has a cover circle of 230, which seems suspect as to covering the 5X7 format I am working with. Is there some math I can use to determine coverage? I am looking for a smaller lens to fit linhof boards, that is F6.8 or faster, hopefully filter thread of 58mm or less. I know of the Fujinons, but are there other lens, which might be more readily available that are smaller at F6.8 or faster for 5X7?

A 5x7 camera needs a lens with an image circle at least 215 mm. A lens with a 230mm circle will cover fine. Most 210mm lenses are intended as normal lenses on 5x7, which is why that focal length appears so much. A tessar design like the Calumet might not allow for a lot of movement, but it will cover. Also, most image circle specifications are conservative because what is report is not what is illuminated, but what is illuminated at the design standard of sharpness of the lens.

Rick "the hypotenuse of a right triangle equals the square root of the sum of the squares of the sides" Denney

[Terry Hull]

I'm square guys-thanks!

[ic-racer]

Use the Pythagorean theorem to calculate the diagonal. This link explains it much better than I ever could.

http://upload.wikimedia.org/math/1/4/5/1455314a78f39a594485adbaf74d63f9.png

Roger

Since you are measuring the two distances off the negative, you could just as easily measure the diagonal directly with a single measurement and not have to do any math;) .

[SergeiR]

Since you are measuring the two distances off the negative, you could just as easily measure the diagonal directly with a single measurement and not have to do any math;) .

Riiight.. how hard it is to do sqrt(5x5 + 7x7) ;)

[Brian Ellis]

Riiight.. how hard it is to do sqrt(5x5 + 7x7) ;)

Harder than holding a ruler next to two corners of a negative. : - )

[JJeffrey]

Why don't we put this thread between yellow and black covers and call it "Lens Coverage for Dummies"!!! ;)

[SergeiR]

Harder than holding a ruler next to two corners of a negative. : - )

I dont have ruler.. *ashamed*

[Kerry L. Thalmann]

The actual film diagonal of an exposed sheet of 5x7 film varies depending on the film holder being used, but is generally in the 210mm range. The actual exposed film area is smaller than the nominal film size due to the margins around the edges created by the film holder, which varies slightly by brand of holder.

In my experience, for most film holders, an 1/8" margin on all four sides is pretty close. So, in the case of 5x7, the exposed film diagonal, in millimeters, would be about:

SQRT(4.75^2 + 6.75^2) * 25.4 = 210mm

for 4x5:

SQRT(3.75^2 + 4.75^2) * 25.4 = 154mm

Both of those calculated results are within 1mm of the actual measured image diagonals for the film holders I use.

However, keep in mind that is the minimum diameter of the image circle required to hit the corners of the format with the lens centered and absolutely no camera movements. Of course, camera movements are one of the biggest reasons to shoot large format. How much extra coverage you need depends on what you shoot (subject matter) and how you shoot it. Architectural photography will, in general, require more extensive movements than landscapes.

For 4x5 landscapes, I always liked to have an image circle arouund 195mm to 200mm minimum. I did occasionally settle for less when selecting compact lenses for backpacking, but I knew the limits of my lenses and used them accordingly.

For 5x7 landscapes, I liked at least 250mm to 260mm, a little more would be better. For example, I found the 150mm APO Sironar W (252mm image circle) and 150mm Super Symmar HM (254mm image circle) MUCH more usable on 5x7 than the 150mm APO Sironar-S (231mm image circle).

Of course the first two are much larger and heavier than the latter, but you don't always have to sacrifice size for coverage. One of my favorite 150mm lenses for 5x7 is the 150mm f9 Grahic-Kowa or it's twin the 150mm f9 Computar. These two have image circles of 290mm, but are very compact and lightweight. You can see what one looks like in the photo in this post (http://www.largeformatphotography.info/forum/showpost.php?p=413207&postcount=15) - it's the lens on the left (the one on the right is a 210mm Graphic-Kowa that covers 8x10 with plenty of room for movements).

Two other possiblities in compact wide angle lenses that cover 5x7 are the 150mm f9 G Claron and the 150mm f9 Germinar W. Scheider only rates the G Claron coverage at 64 degrees (189mm image circle), but stopped down to f22 or below, it covers 80 degrees (for an image circle of about 252mm). It is single coated, but fits in a Copal 0 or Compur 0 shutter and takes tiny 35.5mm filters (I recommend using a 35.5mm - 52mm step-up ring to avoid mechanical vignetting). The 150mm Germinar-W is similar in size and coverage, but multi-coated. Unfortunately, it's rather rare and hard to find. If you can happen to find either of these lenses in a late, all-black Compur 0 shutter, you will have a 150mm lens that covers 5x7 with moderate movements that only weighs about 130 - 132g (4.65 - 4.7 oz.)

Kerry

[Terry Hull]

Kerry-Thanks to you and others for taking the time to help explain this. Of course I am looking for a reasonably fast lens(perhaps f6.8 or faster) in the 200-250mm range for the 5X7 I just bought, (smaller linhof lens boards). I made the initial post in that context, but find the info on some of the older lenses, particularly image circle data hard to find. At this point the Fujinon 250MM F6.7 seems the best, but with a 67mm filter size I had hoped to find a lens a little bit smaller. Maybe they don't exist?

[rdenney]

Kerry-Thanks to you and others for taking the time to help explain this. Of course I am looking for a reasonably fast lens(perhaps f6.8 or faster) in the 200-250mm range for the 5X7 I just bought, (smaller linhof lens boards). I made the initial post in that context, but find the info on some of the older lenses, particularly image circle data hard to find. At this point the Fujinon 250MM F6.7 seems the best, but with a 67mm filter size I had hoped to find a lens a little bit smaller. Maybe they don't exist?

I'm not sure which lens you are describing. I looked on ebay and I saw Calumet 210's from several manufacturers. There was a 210 f/6.3 that was mounted in a Sinar DB mount--that would be unusable for you. I didn't see one, but you might have been looking at a Caltar II-E, which is a Rodenstock Geronar. That's a triplet, which isn't bad but it needs to be stopped down to at least f/22. They had a Caltar Type S, which is a Rodenstock Sironar, and an S-II, which is a Schneider Symmar if I'm remembering correctly. Both are f/5.6 plasmats with image circles in the 300 range. And they had a Caltar Pro f/6.1 which is a Komura. The Caltar II-E (Geronar) has an image circle of 240mm.

One interesting option is the Calumet Caltar Type Y, which is a 240mm f/6.8 tessar-type lens, and probably the longest such that is mounted in a No. 1 shutter (if one ignores the f/9 process lenses as not meeting your requirements). It provides abundant coverage for 5x7. Under the label, it's really a Rodenstock Ysarex, and it was probably made in the middle 70's. They are not common but they are often well-priced when they do pop up. Unusually, there is one on ebay right now, but the price is quite a bit more than I paid KEH for the same lens.

Speaking of KEH, they have what seems like a dozen 210's from all the classic makers, all likely to be excellent, with a number of good ones in the coupla-hundred range. All of them would work fine on 5x7 and would fit in a Technika board.

Rick "210's are thick on the ground" Denney

[Kerry L. Thalmann]

Kerry-Thanks to you and others for taking the time to help explain this. Of course I am looking for a reasonably fast lens(perhaps f6.8 or faster) in the 200-250mm range for the 5X7 I just bought, (smaller linhof lens boards). I made the initial post in that context, but find the info on some of the older lenses, particularly image circle data hard to find. At this point the Fujinon 250MM F6.7 seems the best, but with a 67mm filter size I had hoped to find a lens a little bit smaller. Maybe they don't exist?

With that criteria in mind, there are actually several other options to consider in smaller, reasonably fast lenses in the 210mm - 254mm (10") range.

There is another thread going on right now that may also interest you. That thread is titled: Is a SCHNEIDER XENAR 210MM F:6.1 MC a good Portriat lens for a 4x5 (http://www.largeformatphotography.info/forum/showthread.php?t=76176). And, while the OP of that thread specifically asked about lenses for 4x5, many of the recommendations will also work for 5x7 - including the 210mm f6.1 Xenar in the thread title.

The Schneider Xenar is a derivative of the classic Zeiss Tessar. At one time, pretty much every large format manufacturer offered a line of Tessar derivatives for sale. That includes classic lenses, like the Kodak Commercial Ektars up through modern, multicoated lenses like the Nikkor M series. Coverage and max. aperture varies from brand to brand, but in general they all perform well and have coverage in the 60-64 degree range (some published specs are a little lower, some a little higher). In general, the 210mm Tessar types, will cover 5x7 with modest to moderate movements and the 250mm/10" lenses will offer plentiful movements on 5x7.

I had an article on large format Tessar and Tessar derivative lenses published in the May/June 2004 issue of View Camera magazine. The title of that article was: "Tessar Lenses: The Legend and the Legacy". If you can find a copy of that issue, the article is chock full of photos and specs for many of these lenses. During my research for that article, I amassed quite a collection of these lenses. Given your requirements, here's a few you may find of interest.

210mm f4.5 Schneider Xenar
Shutter: Compound 3
Angle of Coverage: 62 degrees
Image Circle: 253mm
Weight: 550g
Filter Size: 58mm
Coating: Single

210mm f5.6 Fujinon L
Shutter: Copal 1
Angle of Coverage: 59 degrees
Image Circle: 240mm
Weight: 320g
Filter Size: 49mm
Coating: Single

210mm f6.1 Schneider Xenar - also sold as 210mm f6.1 Caltar Pro
Shutter: Copal 1
Angle of Coverage: 60 degrees
Image Circle: 249mm
Weight: 375g
Filter Size: 46mm
Coating: Single

210mm f6.3 Zeiss Jena Tessar T
Shutter: Compur 1
Angle of Coverage: 70 degrees
Image Circle: 294mm
Weight: 195g
Filter Size: 40.5mm
Coating: Single

8.5" (215mm) f6.3 Kodak Commercial Ektar
Shutter: Ilex 3
Angle of Coverage: 64 degrees
Image Circle: 270mm
Weight: 330g
Filter Size: Series 7
Coating: Single

8.5" (215mm) f6.3 Ilex-Caltar
Shutter: Ilex 3
Angle of Coverage: 64 degrees
Image Circle: 270mm
Weight: ??? - probably around 320 - 330g, give or take
Filter Size: Series 7
Coating: Single

240mm f4.5 Schneider Xenar
Shutter: Compound 4
Angle of Coverage: 62 degrees
Image Circle: 282mm
Weight: 780g
Filter Size: 67mm
Coating: Single

10"" (254mm) f6.3 Kodak Commercial Ektar
Shutter: Ilex 4
Angle of Coverage: 64 degrees
Image Circle: 317mm
Weight: 505g
Filter Size: Series 8
Coating: Single

10" (215mm) f6.3 Ilex-Caltar
Shutter: Ilex 3
Angle of Coverage: 64 degrees
Image Circle: 317mm
Weight: 355g
Filter Size: Series 8
Coating: Single

Another lens in this range, that is reasonably light and compact is the 9.5" (241mm) f6.8 Goerz Dagor. This is not a Tessar type and offers more coverage (68 degrees at f22 and up to 86 degrees stopped down to f45). Needless to say, coverage won't be a problem on 5x7. I no longer have one to weigh, but most came in Ilex 3 shutters and are similar in size and weight to the 8.5" Commercial Ektar. Dagors were made for over 80 years. I personally prefer post-WWII coated samples with serial numbers of 770xxx or higher. As mentioned, most of these came in Ilex 3 shutters, but some of the very last ones made came in smaller, lighter, more modern Compur shutters. Those are usually the "Gold Dot" variety and command premium prices. A slightly older, dotless sample in an Ilex 3 will likely perform just as well, for a fraction of the price of the Gold Dot version.

Hope that helps,
Kerry

[Kerry L. Thalmann]

And they had a Caltar Pro f/6.1 which is a Komura.

Actually, the 210mm f6.1 Caltar Pro (1982 - 1986) was a rebadged Schneider Xenar. The one I used to own was clearly engraved "Made in West Germany".

Komura (made in Japan) did offer a 210mm f6.3 Commercial Komura, that was briefly (1980) sold as a Caltar Pro, but it's not nearly as common as the f6.1 Xenar version.

Kerry

[rdenney]

Actually, the 210mm f6.1 Caltar Pro (1982 - 1986) was a rebadged Schneider Xenar. The one I used to own was clearly engraved "Made in West Germany".

Komura (made in Japan) did offer a 210mm f6.3 Commercial Komura, that was briefly (1980) sold as a Caltar Pro, but it's not nearly as common as the f6.1 Xenar version

The example I saw did not show the engraving. And the seller had it wrong, but there's nothing new about that.

By the way, your list shows a 10" Ilex-Caltar with (215mm) in the description. I'm assuming you meant 254mm.

There were other tessars in this focal range. I have an 8-1/2" Ilex Paragon, but at f/4.5 it's large and heavy, being mounted in an Ilex No. 4 shutter. It's about the same size as my 12" f/6.3 Ilex-Calumet Caltar, which is also in a No. 4 shutter. The 240mm Caltar Type Y that I mentioned is considerably more compact.

Rick "noting that longer lenses must be bigger to maintain the same maximum aperture" Denney

[Leigh]

Since you are measuring the two distances off the negative, you could just as easily measure the diagonal directly with a single measurement and not have to do any math;) .
Invalid assumption...

If I'm talking about a lens to cover a specific film size I don't necessarily have a physical piece of film that size in front of me.

Easier to just calculate the diagonal based on the nominal film size, which is a bit larger than the image size.

Just one man's opinion. Worth what you paid for it. :p

- Leigh

[PolarBear1973]

If you were to use a lens that had too small of an image circle for a particular format, would the corners be blurry, darker, or black? (or a combination)

[Leigh]

The light falls off over a narrow band, not instantly like a sharp edge, but rapidly.

- Leigh

[Jack Dahlgren]

If you were to use a lens that had too small of an image circle for a particular format, would the corners be blurry, darker, or black? (or a combination)

First thing to go would be sharpness - it falls off as you go out from the center, then it would get darker until it is black.

[ic-racer]

would the corners be blurry, darker, or black?

Yes! :)

[Kerry L. Thalmann]

If you were to use a lens that had too small of an image circle for a particular format, would the corners be blurry, darker, or black? (or a combination)

It really depends on the design of the lens, both optically and mechanically. Most modern lenses employ field stops to mechanically limit coverage once the optical performance of the lens reaches what the manufacturer considers a minimum acceptable. The field stops will cause the corners to go black, not a sharp line, but rather abruptly, once the coverage is exceeded. This is mechanical vignetting.

Many older lenses do not have field stops Classic examples are the Dagors and Angulons. There coverage gradually tapers of due to decreasing sharpness as you move of axis. The actual usable coverage depends on both the particular lens and the user's own quality criteria, but increases as you stop down.

In general, Dagors cover about 68 degrees at f16, but "usable" coverage increases to about 87 degrees at f45. These are just approximate values. Dagors were made for about 90 years by several different manufacturers. Coverage varies by vintage and focal length.

Scheider Angulons, which are a variation of the Goerz Dagor and often called a revers Dagor. They generally cover about 80 degrees at f22 and about 90 degrees at f45. Again, these lenses were made over a long time period (from 1929 until the early 1970s, with the exception of a rare production run of 165mm Angulons that were made in 1979) and coverage and performance varies with age.

And, the performance of some lenses drops off very rapidly, due to poor resolution and usable coverage cannot be appreciably increased by stopping down. It really depends on the design of the lens. For example, the coverage of the Goerz Artars doesn't really increase much, but stopping down below the f9 maximum aperture. However, Goerz was very conservative in their coverage specs (46 degrees) for the Artars. For general purpose photography, their usable coverage is a bit more than that (typically in the 50 - 55 degree range, especially for contact printing), but that is due to conservative specs, not stopping down.

Hope that helps.

Kerry

[rdenney]

If you were to use a lens that had too small of an image circle for a particular format, would the corners be blurry, darker, or black? (or a combination)

It depends on the lens. I the old days, lenses were allowed to illuminate the picture beyond where they could do so sharply. They expected the photographer to evaluate his own sharpness boundary. Newer lenses seem to design the barrels to prevent illumination outside a coverage that achieves a minimum image-making standard.

Rick "noting that sharpness to the edges does not fit all aesthetics" Denney

Edit: Should have read Kerry's post before writing my own. Oh, well...