Lens speed relations to medium format

Jessestr · Apr 29, 2014

As I've just bought the Mamiya RB67 I was thinking about the relation between lens speeds and larger formats on film.

At 645 you can find f1.9 on a Mamiya, f2 on a Contax 645 .. but when you go up, it suddenly goes to f2.8 .. then f3.5 and large format is even smaller apertures.
Is it because the depth of field that would be too tiny to actually have something in focus or is it's just harder to have such an amount light coming for a larger format?

I got the 90mm f3.8 .. In relation of depth of field, how much f stops would the f3.8 be on a 35mm camera?

Thanks

AgX · Apr 29, 2014

No, it's much simpler: lenses would otherwise get too big (and expensive) to handle.

cliveh · Apr 29, 2014

I would imagine the cost would have a lot to do with this.

AgX · Apr 29, 2014

But DOF also is of interest. One may hint at the ability to swing plane of focus with many MF and LF cameras. But this rarely would be of use in situations where wide-aperture lenses would be chosen to reduce exposure time.

MattKing · Apr 29, 2014

In addition, with respect to the RB67, Mamiya had to fit a shutter into the lens barrel.

It is easier to build fast lenses if they don't have shutters in them.

And of course, it is more difficult and expensive to build a lens to cover the larger film area of 6cm x 7cm then it is to build a lens to cover the smaller film area of 6cm x 4.5cm. By comparison, building a lens to cover just 24mm x 36mm is a walk in the park!

AgX · Apr 29, 2014

The larger the lens the more difficult it is to yield high resolution when designing for a larger aperture.

Thus we got issues with

-) size

-) DOF

-) image quality

film_man · Apr 29, 2014

The bigger the format the bigger and longer the lens has to be. Also, the faster the lens the bigger it has to be. And bigger in lens = more expensive and heavier. So they would get impractically heavy and very expensive very quickly.

In relation to DOF, I think 6x7 to 35mm is 2 stops. So 90/3.8 is 45/1.8 or thereabouts.

Jessestr · Apr 29, 2014

Thanks for the info guys ! Such a good place to ask questions, immediate response!

RalphLambrecht · Apr 29, 2014

Jessestr said:
A In relation of depth of field, how much f stops would the f3.8 be on a 35mm camera?

Thanks

the same as the two formats CoCsratio,given the same subject to lens distance.

Slixtiesix · Apr 30, 2014

There is also a 110/2 available for Hasselblad and Rollei. I think apart from costs, the shutter is the main hindrance in designing a fast MF or LF lens. It is no coincidence that Hasselblad 500, Rollei and Mamiya RB/RZ lenses are rather slow, while Hasselblad 200, Kiev, Pentacon Six and Pentax 67 lenses are comparably fast. The former feature an in-lens shutter while the latter do not.

Pioneer · Apr 30, 2014

I know I should leave well enough alone but I just have to ask.

So far, all the examples posted here have been interchangeable lenses. I have a very nice 6x6 Rolleiflex equipped with 2.8 lenses. Also, there are some very nice 6x9 folding camera with 3.5 lenses. These are not huge lenses in the general scheme of things. So, I have to wonder whether "size" is really that much of a limiting factor. Perhaps it really is more about usable depth of field and resolution?

Xmas · Apr 30, 2014

Pioneer said:
I know I should leave well enough alone but I just have to ask.

So far, all the examples posted here have been interchangeable lenses. I have a very nice 6x6 Rolleiflex equipped with 2.8 lenses. Also, there are some very nice 6x9 folding camera with 3.5 lenses. These are not huge lenses in the general scheme of things. So, I have to wonder whether "size" is really that much of a limiting factor. Perhaps it really is more about usable depth of field and resolution?

You Rolli /2.8 is a five or six element double Gaussian design a 5cm for 35mm with the same design and glass catalogue could be /1.8 or /2, they are.

The optical abberations increase with the focal length the size and weight as well.

A f/2 80mm covering 6x6 would be larger and heavier than a 80mm /2 tele for a 35mm and need more elements or higher refractive index glass or aspherics.

The /2.8 on 120 is marginal on film flatness as well.

Jesper · Apr 30, 2014

Apart from all things already mentioned in this thread there is also the increasing probability that the camera will be used on a tripod with increasing negative size. A shallow depth of field is also not a problem since you use longer lenses for the same angle of view (at 5m you will have about the same DoF with a 50mm at f1.4 and a 300 (normal lens for an 8x10) at f45).
Practical reasons are however the main reason as mentioned before but remember that the reasons for using fast lenses not apply to the same extent when you move up in negative size.

AgX · Apr 30, 2014

The /2.8 on 120 is marginal on film flatness as well.

A further aspect on the DOF issue.

Xmas · Apr 30, 2014

AgX said:
A further aspect on the DOF issue.

correct but it does not apply to all the TLRs or all the film backs or all film cameras to the same extent.

eg the autcords, & c22-c330 don't pre kink film, a rolli at /2.8 needs to avoid the 2nd frame in the cold, blads and RB67 in warm studios shooting a fast series on multiple backs more practical.

dorff · Apr 30, 2014

film_man said:
So they would get impractically heavy and very expensive very quickly.

As if in their heyday MF lenses weren't expensive already! The reason is of course that the image circle is larger, while the nominal quality expectation is not lower than for 35 mm film.

film_man said:
In relation to DOF, I think 6x7 to 35mm is 2 stops. So 90/3.8 is 45/1.8 or thereabouts.

There are few absolutely equivalent examples, based on actually available lenses. A Pentax 105/2.4 equates to more or less a 52/1.2. Likewise, a 200/4 equates to roughly 100/2. And a 165/2.8 equates roughly to 80/1.4, which should make it a very fine portrait lens. The one thing that does not scale in unison is minimum focus distance. My Pentax 6x7 and Mamiya 645 lenses don't focus as close as their 35 mm field-of-view counterparts, and I often have to use extension tubes to get close portraits etc. It has frustrated me to the point where I simply use a 120 Macro on the Mamiya for everything that is reasonably close, portraits included.

Dan Fromm · Apr 30, 2014

Pioneer said:
So far, all the examples posted here have been interchangeable lenses. I have a very nice 6x6 Rolleiflex equipped with 2.8 lenses. Also, there are some very nice 6x9 folding camera with 3.5 lenses. These are not huge lenses in the general scheme of things. So, I have to wonder whether "size" is really that much of a limiting factor. Perhaps it really is more about usable depth of field and resolution?

Hmm. I have a 4"/2.0 TTH Anastigmat (2 1/4" x 2 1/4") (so engraved) in barrel that I use on a 2x3 Speed Graphic. The lens was made for Vinten F.95 and AGI F.134 and F.139 aerial cameras. Both have focal plane shutters and interchangeable lenses. I haven't measured it for ages but it is not tiny. Long fast lenses have to be large and heavy.

I once bought a 6"/1.9 Dallmeyer Super Six to use on my little Speed. I wanted to take it on a Graflex/Graphic club excursion, never did, never had it adapted to my little Speed, and eventually sold it. Gross monstrosity. I got it for a joke.

And last year I sold a 200/2.0 S.F.O.M. lens that had flown on an OMERA aerial camera. It covered 4x5. Gross monstrosity is an understatement. More than 15 pounds. Oh, yeah, OMERA cameras have rotating slat type focal plane shutters and lenses for them are interchangable.

Fast leaf shutters for large lenses don't exist. Slow leaf shutters (Packard) do. Without a fast shutter, using a fast lens wide open is often impossible.

paul ron · Apr 30, 2014

Doesn't it have more to do with circles of confussion?

AgX · Apr 30, 2014

Both, DOF and resolution at focus have to do with circle of confusion.

paul ron · May 1, 2014

I thought coc was the limiting factor relation of format vs lens.

Dan Fromm · May 1, 2014

paul ron said:
I thought coc was the limiting factor relation of format vs lens.

Nah, the Circle of Confusion (not to be confused with people, trolls excepted, who post questions on bulletin boards) is a user-selected way of expressing how much it will be reasonable to enlarge the negative. "reasonable" is also user-selected.

CoC has nothing to do with format or lens. It is a way of expressing how much detail has to be resolved in the negative for it to appear sharp in a print of the desired size. Sharpness is user-specific, as is print size.

Alan Klein · May 1, 2014

Another issue is shutter speed. Because the maximum shutter speed for RB67 lenses is 1/400, shooting at wider apertures would be limited to very slow film and/or darker situations. You just won't be able to shoot faster in brighter situations so the wider apertures would have little use. For example, in normal daylight shooting with 100 ASA film, you would shoot at 1/125 at let's say f11 or 1/250 at f/8 or 1/500 at f5.6 or 1/1000 at f4, etc. Since the maximum shutter speed is 1/400, you'd be limited to f/8 even though the lens can stop down to f/3.8 for a 90mm . So smaller apertures could not be used even of you had them available.

paul ron · May 1, 2014

Dan Fromm said:
Nah, the Circle of Confusion (not to be confused with people, trolls excepted, who post questions on bulletin boards) is a user-selected way of expressing how much it will be reasonable to enlarge the negative. "reasonable" is also user-selected.

CoC has nothing to do with format or lens. It is a way of expressing how much detail has to be resolved in the negative for it to appear sharp in a print of the desired size. Sharpness is user-specific, as is print size.

Its a bit more complicated than that n has everything to do with format n lens. Read about it here......

http://www.normankoren.com/Tutorials/MTF6.html

Dan Fromm · May 1, 2014

paul ron said:
Its a bit more complicated than that n has everything to do with format n lens. Read about it here......

http://www.normankoren.com/Tutorials/MTF6.html

Stuff and nonsense. You're confusing a convention based on acceptable perceived sharpness in an 8x10 contact print with the sharpness required in the negative to obtain a print of the desired size with acceptable perceived sharpness.

The less enlargement, the larger the CoC. This has nothing to do with format and everything to do with how much the negative is to be enlarged.

AgX · May 1, 2014

There is CoC and tolerated CoC.

Lens speed relations to medium format

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