Why Medium Format lenses are not as fast as 35mm?

[markbarendt]

I don't think that they are the same, f1.4 in 35mm will be f1.4 in medium format, it's the same amount of light that the lens will allow to reach the film

Actually it's not that simple, yes it's the same amount of light projected per square inch at the film plane. but Medium format lenses are normally longer in order to get the same angle on view at the film so they actually have to let more total light through to give equal film exposure.

Helps to do the math in real numbers to understand the f number.

If the lens focal length is 50mm (~2") then the entrance pupil (entrance to the lens) needs to be 36mm (1.4" assuming there isn't anything else restricting the light path): 50/36=1.4 so f1.4.

If the lens focal length is 100mm (~4") and the entrance pupil remains 36mm (1.4"): 100/36=3.8 so f3.8. Since the pupil remained the same the total light stays the same but the focused projection now covers 4 times the area. A lot dimmer per square inch of film, hence the f3.8.

If the lens focal length remains 100mm (~4") then we need to increase the entrance pupil to 72mm (2.8"): 100/72=1.4 to get back to f1.4.

 

[Dan Fromm]

http://www.ebay.com/itm/271978722534?rmvSB=true

18 Kilograms and a quarter million pounds! Sign me up ...

From the listing:

The "Buy It Now" price is set at 10x net market value.

And it isn't a photographic objective.

FWIW, several years ago I sold a 200/2.0 S.F.O.M. lens that covered 4x5. 7kg or so, not what you'd want to carry very far.

 

[apoglass]

The Hasselblad 6x6 Carl Zeiss Planar 110mm f/2 T* F or FE is a wonderful lens (the later FE version has electrical contacts that tell the camera the aperture setting for metering purposes). There isn't room for an in lens leaf shutter, so only the 200 series Hasselblad V cameras with focal plane shutters can be used with this lens. A fabulous very sharp portrait lens. Believe this is the fastest and don't know of any other f/2 Hasselblad V lenses.

 

[Sirius Glass]

The Hasselblad 6x6 Carl Zeiss Planar 110mm f/2 T* F or FE is a wonderful lens (the later FE version has electrical contacts that tell the camera the aperture setting for metering purposes). There isn't room for an in lens leaf shutter, so only the 200 series Hasselblad V cameras with focal plane shutters can be used with this lens. A fabulous very sharp portrait lens. Believe this is the fastest and don't know of any other f/2 Hasselblad V lenses.

Welcome to APUG. Another Hasselblad owner is always welcome.

 

[amellice]

From the listing:



And it isn't a photographic objective.

FWIW, several years ago I sold a 200/2.0 S.F.O.M. lens that covered 4x5. 7kg or so, not what you'd want to carry very far.

+1

 

[Dr Croubie]

http://www.ebay.com/itm/271978722534?rmvSB=true

18 Kilograms and a quarter million pounds! Sign me up ...

On a slightly d**l tangent...
I'm doing my Masters in Electronic Engineering at the moment, my project is in Image Processing / Recognition (in short, "can I tell a Feral Cat from a Kangaroo using a Raspberry Pi?")
Picked up myself one of Dead Link Removed thermal imaging cameras. It's only 60x80 pixels and 3fps, but it's the cheapest thermal camera I could find by a factor of ten.
Tried to mount it in a box with a filter in front of it to keep the weather off it. Simple enough, right?
Turns out that everything in the world (or at least my house & lab) is opaque to thermal wavelengths (8-14 microns). My best B+W filters, IR720s, clear ABS, perspex, window glass, plastic takeaway containers, even freaking cling wrap (yes, I tried them all).
I got a quote for a small (like ~10mm) germanium filter to place in front of it that would pass thermal/far IR. Alone, it well exceeded the budget of the entire project.

So if they reckon that thing's worth only 25,000 squid for something that huge, even comparing to the new prices for some of Jenoptik / Coastal Optics lenses that are a lot slower, I'd call that a relative bargain...



ps, there's also the Jupiter 13 125/1.5 that almost covers 4x5, and is 1.5kg as LF mount (ie, no focussing). But I've never even seen one for sale, or much else besides catalogues and that LFPF post...

 

[Sirius Glass]

DrC, you need a silicon filter designed for infrared transmission.

 

[paul ron]

because we work slower?

 

[Nodda Duma]

Consider that in the design world--i.e. in the design software-- it is easy to scale up a lens to a larger format. Double the radii, thicknesses, diameters, airgaps etc is easy to do. The aberrations also scale: the ray fans, spot diagram, MTF all look the same....but the size of the aberrations scale as well.

So a 50um blur spot for a 50mm f/1.4 lens becomes a 100um blur spot for a scaled-up 100mm f/1.4 lens. Or put another way, 50% contrast at 50lp/mm for a 50mm f/1.4 becomes 50% contrast at 25 lp/mm when the prescription is scaled up to 100mm f/1.4. Note you're also scaling the image size as well, so the focal length-to-image size ratio remains the same.

So you lost resolution essentially. And the weight/size have increased substantially. How to get back the resolution (and/or meet some size and weight requirement)? The easiest lever to pull is reduce the f/#. Or put another way, to achieve that 50% contrast at 50 lp/mm in a larger format lens you have no choice but to stop the lens down.


Edit to add: From a design requirements standpoint, DOF is usually not a driving requirement. I have never seen it specified. What does get specified is f/# and focal length. DOF falls out of that.

So when I start on a new lens the first thing I do is go to my database, pull a suitable design, and scale the focal length. These starting point database designs are usually all presented at 100mm focal length (except for the lenses I've designed in the past).

 

[Nodda Duma]

DrC, you need a silicon filter designed for infrared transmission.

He's talking about the FLIR Lepton, which is a microbolometer imager operating at ~8-12 um. Silicon has significant absorption in the 8-12um band. He needs Germanium. Or ZnS / ZnSe will work also.

 

[amellice]

From the listing:



And it isn't a photographic objective.

FWIW, several years ago I sold a 200/2.0 S.F.O.M. lens that covered 4x5. 7kg or so, not what you'd want to carry very far.

+1

Consider that in the design world--i.e. in the design software-- it is easy to scale up a lens to a larger format. Double the radii, thicknesses, diameters, airgaps etc is easy to do. The aberrations also scale: the ray fans, spot diagram, MTF all look the same....but the size of the aberrations scale as well.

So a 50um blur spot for a 50mm f/1.4 lens becomes a 100um blur spot for a scaled-up 100mm f/1.4 lens. Or put another way, 50% contrast at 50lp/mm for a 50mm f/1.4 becomes 50% contrast at 25 lp/mm when the prescription is scaled up to 100mm f/1.4. Note you're also scaling the image size as well, so the focal length-to-image size ratio remains the same.

So you lost resolution essentially. And the weight/size have increased substantially. How to get back the resolution (and/or meet some size and weight requirement)? The easiest lever to pull is reduce the f/#. Or put another way, to achieve that 50% contrast at 50 lp/mm in a larger format lens you have no choice but to stop the lens down.


Edit to add: From a design requirements standpoint, DOF is usually not a driving requirement. I have never seen it specified. What does get specified is f/# and focal length. DOF falls out of that.

So when I start on a new lens the first thing I do is go to my database, pull a suitable design, and scale the focal length. These starting point database designs are usually all presented at 100mm focal length (except for the lenses I've designed in the past).

+1 thanks for the explanation

 

[alanrockwood]

One thing to consider is that large pieces of optical glass tend to difficult to make, hence expensive and/or difficult to obtain.

 

[SLVR]

I've covered this in this thread.

(there was a url link here which no longer exists)

 

[DREW WILEY]

Another relevant equation involves the increase of gravity as a function of time. My camera pack seems to weigh more than it did twenty years ago!

 

[Sirius Glass]

Another relevant equation involves the increase of gravity as a function of time. My camera pack seems to weigh more than it did twenty years ago!

Cameras, lenses and tripods also gain mass as the length of the walk/hike grows.

 

[Neil Poulsen]

Consider the normal 50mm lens on a 35mm camera. To obtain the same angle of view, this lens corresponds to about a 110mm lens on a 6x9, medium format camera, say a Mamiya Universal Press camera. So as film format size increases, so does the focal length of corresponding lenses on a larger format.

The larger the focal length, the further away from the negative must be the lens for it to focus at infinity. For the longer (110mm) lens to be equally "fast", the image must fall on the negative with the same brightness as that of the smaller film format. Since the longer (110mm) lens is further away from the film, image brightness will necessarily be less, UNLESS the longer (110mm) lens is made to let in proportionately more light to maintain the same brightness on the film. So in comparison to the f1.8 50mm lens on a 35mm camera, an f1.8 110mm lens on the 6x9 camera must be quite a bit larger.

As a design issue, it's more difficult, and a lot more expensive, to make f1.8mm, 110mm lenses on a 6x9 camera that would maintain the same image brightness on the film as the f1.8, 50mm lens on the 35mm camera. It's just not practical. This is certainly the case financially. But, it's also impractical from a composition point of view. Shooting at f1.8 using a 110mm on a medium format 6x9 camera, the depth of field will also be a LOT less.

In a funny sort of way, mother nature is working to our advantage. We like faster lenses, so that we can hand-hold cameras and shoot at the same, or at a faster shutter speed. From the discussion above, we can obtain faster lenses by moving to smaller formats, and these smaller cameras are indeed that much lighter, and thereby that much easier to hand-hold. Moreover, as the camera size becomes smaller, the depth of field increases, and that also makes the smaller camera that much easier to hand-hold, since we can be a little more careless in how we focus.

 

[Sirius Glass]

A comparison of 35mm focal lengths to Hasselblad focal lengths
35mm Camera.......Hasselblad
23.75mm................38mm [SWC]
25mm.....................40mm
31.25mm.................50mm
50mm.....................80mm [Normal]
62.5mm.................100mm
93.75mm...............150mm
156.25mm.............250mm
218.75mm.............350mm
312.5mm...............500mm

 

[lexdiamond20]

Cmon, have you seen what the Mamiya 80MM 1.9 and Pentax 105MM 2.4 can do wide open. Closet Ive seen from a 35MM perspective is the 50MM 1.2 and 85MM 1.2.

 

[Gombrich]

Cmon, have you seen what the Mamiya 80MM 1.9 and Pentax 105MM 2.4 can do wide open. Closet Ive seen from a 35MM perspective is the 50MM 1.2 and 85MM 1.2.

The Noctilux?

 

[Nige]

Hasselblad's approach was to have the CF and later lenses for the most part use the B60 filters. There are advantages to having one set of filters for all the lenses,

I have the Mamiya 80/1.9 but have hardly used it for this very reason. For excursions I carry 80/2.8, 55/2.8, 150/4 (actually a 150/3.5 now) as they all take the same filter size. I might have the 45/2.8 in the bag as well but have no filters for it. The 80/1.9 and 150/2.8 stay home.

 

[jochen]

Hello,
because nobody would pay the price (besides the military) and nobody could carry them and because nobody could produce them in series production.

 

[benjiboy]

You just have to accept that medium format is a different ball game to 35mm, and that very fast lenses aren't necessary.

 

[wiltw]

Another relevant equation involves the increase of gravity as a function of time. My camera pack seems to weigh more than it did twenty years ago!

Seems maybe the Einstein theory needs some modification, to explain the fact that "As you gain Mass, you seem to have less Energy!"

 

[benjiboy]

Seems maybe the Einstein theory needs some modification, to explain the fact that "As you gain Mass, you seem to have less Energy!"

The constant factor in the equation is the passage of time

 

[RattyMouse]

You just have to accept that medium format is a different ball game to 35mm, and that very fast lenses aren't necessary.

So True. The f/3.5 aperture on my 80mm lens has very little DOF wild open. I would not open it up much more if it were able to as the DOF would be almost nothing!