Picked up my first medium format camera - equiv. f stop?

rayonline_nz · Apr 14, 2016

Hi all

I was probably going to ge the 500CM being more compact but the Mamiya RB67 (non pro) was just so cheap it was at least worth a play around and maybe later off load it if I not like it. $150US with a back, WLF and a 90mm F3.8 (C or not not sure).

What is the equiv. f stop between 135 format and this 6x7? For my own curiosity I will shoot the same roll off my Nikon and this thing and compare them. Do I just add an extra stop? Ie F8 on the Nikon is F11 on the Mamiya?

Cheers.

MattKing · Apr 14, 2016

If you are talking about exposure, f/8 = f/8, irrespective of format.

What does vary is the focal length to achieve the same angle of view, as well as the depth of field obtained with a particular f/stop.

A 45mm lens on 135 format will give you a somewhat similar field of view as a 90mm lens on the RB67 (using a 6x7 back).

rayonline_nz · Apr 14, 2016

Yeah I was talking about depth of field. What is like a F8 on Nikon on the Mamiya?

BrianShaw · Apr 14, 2016

... Or you could play with this and see the differences.

http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

MattKing · Apr 14, 2016

Here is a link to an instruction manual for RB lenses: http://www.cameramanuals.org/mamiya_pdf/mamiya_rb_lenses.pdf

As with anything on Mike Butkus' site, I suggest that if you get benefits from one of his downloads you should honour his request for a donation.

The manual includes depth of field tables for several lenses.

You will need to find something similar for the Nikon lens in order to make a comparison.

Offhand, I would guess there is at least a two stop difference.

The lenses allow you to stop down to view depth of field.

MattKing · Apr 14, 2016

BrianShaw said:
... Or you could play with this and see the differences.

http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

Good suggestion!

BrianShaw · Apr 14, 2016

APUGuser19 said:
I clicked on that site. Pretty neat. But they've made a couple errors. They're calling 4x5 and 8x10 the wrong way. I've looked everywhere and film isn't made in 10x8, as it doesn't fit in an 8x10 holder. And the next larger size is 11x14, and that's too big.

I'm a bit dyslexic so it looked correct to me!

Soeren · Apr 14, 2016

LOL

You are joking, right?

piu58 · Apr 14, 2016

YOu have to add roughly 2 stops to get the same DOF. That means f/4 in 135 means around f/8 in 6x7. The lens should cover the same angle of course.

Soeren · Apr 14, 2016

But there another thing to it. Rendering of the oof areas and "softening" of those which is dependent of the larger pupil size (of the longer focal lenght). Right? Wrong?
I think the oof areas are just as interesting as whats in focus.

Kawaiithulhu · Apr 14, 2016

APUGuser19 said:
calling 4x5 and 8x10 the wrong way.

This is European, you'll get used to it.
(a UK example: http://www.ag-photographic.co.uk/kodak-ektar-5x4-10-sheets-1550-p.asp )

RalphLambrecht · Apr 14, 2016

rayonline_nz said:
Hi all

I was probably going to ge the 500CM being more compact but the Mamiya RB67 (non pro) was just so cheap it was at least worth a play around and maybe later off load it if I not like it. $150US with a back, WLF and a 90mm F3.8 (C or not not sure).

What is the equiv. f stop between 135 format and this 6x7? For my own curiosity I will shoot the same roll off my Nikon and this thing and compare them. Do I just add an extra stop? Ie F8 on the Nikon is F11 on the Mamiya?

Cheers.

I don't understand the question either.Why would there be a difference in f/stop between formats?

Kirks518 · Apr 14, 2016

RalphLambrecht said:
I don't understand the question either.Why would there be a difference in f/stop between formats?

When I first got into MF, I also wondered the same as what the OP was wondering. Reason being, is that if the FOV/AOV between the formats is different, would the f/ be different as well. I originally thought that f/2.8 on MF would be (roughly) the same as f/1.4 on 35mm format. It comes with over-thinking.

baachitraka · Apr 14, 2016

https://en.wikipedia.org/wiki/F-number

The diameter of the entrance pupil for 50mm @f/4 = 12.5mm and that result in Dof A. And if you want to have same 'Dof A' for a 35mm lens you may need to stop at f/2.8. Only change is Field of view.

CropDusterMan · Apr 14, 2016

He's questioning about DOF...as he stated. F5.6 on a Nikon 35mm (for instance) will have much greater DOF than F5.6
on a Mamiya 6x7...In order to achieve the same DOF of the Nikon with the 6x7, you'd have to stop down considerably
and some lenses are lens sharp at each end of their apertures. It's been years since I used an RB...doesn't it have
a DOF preview?

wiltw · Apr 14, 2016

rayonline_nz said:
Yeah I was talking about depth of field. What is like a F8 on Nikon on the Mamiya?

DOF, using lenses suited to the format size for comparable FOV, are merely scaled proportional to FL.

24mm tall 135 format with 48mm f/2 lens would have same FOV as 56mm tall 6x7 format with 112mm FL, so equivalent DOF is obtained on the 6x7 camera with 112mm f/4.5 (2.33EV aperture difference for 112:48 ratio (2.33:1)

So assuming your FL is truly proportional -- that is, NOT using the diagonal as the equivalence measure, due to the overly long aspect ratio of 135 (1.5:1) vs. 6x7 (1.25:1)--, f/8 on 135 format is like f/12.6 on 6x7

Digital shooters might be more aware of the 'proportional' relationship, for equivant DOF for FF vs. APS-C sensors, which both have same aspect ratio and everyone is aware of the 1.6:1 FL proportional multiplier for FL, and 'same DOF' is 1.6x smaller aperture for FF than for APS-C.

As for the issue of out-of-focus blur intensity,

48mm f/2 = 24mm aperture diameter
112mm f/4.5 = 24.88mm aperture diameter

so the far field background blur will be very close in magnitude, but the 6x7 will be slightly more blurred, as evidenced by this chart

Kyle M. · Apr 14, 2016

CropDusterMan said:
He's questioning about DOF...as he stated. F5.6 on a Nikon 35mm (for instance) will have much greater DOF than F5.6
on a Mamiya 6x7...In order to achieve the same DOF of the Nikon with the 6x7, you'd have to stop down considerably
and some lenses are lens sharp at each end of their apertures. It's been years since I used an RB...doesn't it have
a DOF preview?

Yes the RB67 lenses have a DOF preview lever on the low right side of the lens when the camera is pointed away from you.

wiltw · Apr 14, 2016

APUGuser19 said:
I clicked on that site. Pretty neat. But they've made a couple errors. They're calling 4x5 and 8x10 the wrong way. I've looked everywhere and film isn't made in 10x8, as it doesn't fit in an 8x10 holder. And the next larger size is 11x14, and that's too big.

I suggest a bit of flexibility will allay your issue. When I want a Portrait orientation shot, I grab my 5x4 holder and insert 5x4 film. When I want Landscape orientation, I grab my 4x5 holder and insert 4x5 film. Fortunately both film holders can fit my view camera without me turning the camera on its side, as the designers of the camera had the foresight to permit the groundglass back to fit in the rear standard in either direction. Good thing they did, as the ballhead tends to slip if I try to lay my 14lb. Horseman monorail on its side because of the added weight of the lens, and the bubble levels become useless in that orientation.

I find that the selection of emulsion is today a larger issue than sourcing 4x5 film in the USA and getting 5x4 film from a store in the UK, because I am forced to use colour film rather than my preferred color film. I will admit that I seem to mix up my 5x4 holders with my 4x5 holders quite often, but a dab of paint on the corner of one keeps them sorted out, although this fails to work in the dark, which accounts for the mix up and the frustration of trying to put 5x4 film in the 4x5 holders and vice versa. But I adapt...bringing us back to simply having a bit of flexibility in our choices.

CropDusterMan · Apr 14, 2016

Use the DOF preview to get your desired DOF and take the picture...or you can pull out a slide ruler and stare at DOF
calculation charts all day.

Alan Gales · Apr 14, 2016

CropDusterMan said:
Use the DOF preview to get your desired DOF and take the picture...or you can pull out a slide ruler and stare at DOF
calculation charts all day.

Do people still use those? When I was in High School my Trig teacher showed us how to use a slide rule because we were curious. Calculators had replaced them by that time. It was 1978.

Soeren · Apr 14, 2016

wiltw said:
I suggest a bit of flexibility will allay your issue. When I want a Portrait orientation shot, I grab my 5x4 holder and insert 5x4 film. When I want Landscape orientation, I grab my 4x5 holder and insert 4x5 film. Fortunately both film holders can fit my view camera without me turning the camera on its side, as the designers of the camera had the foresight to permit the groundglass back to fit in the rear standard in either direction. Good thing they did, as the ballhead tends to slip if I try to lay my 14lb. Horseman monorail on its side because of the added weight of the lens, and the bubble levels become useless in that orientation.

I find that the selection of emulsion is today a larger issue than sourcing 4x5 film in the USA and getting 5x4 film from a store in the UK, because I am forced to use colour film rather than my preferred color film. I will admit that I seem to mix up my 5x4 holders with my 4x5 holders quite often, but a dab of paint on the corner of one keeps them sorted out, although this fails to work in the dark, which accounts for the mix up and the frustration of trying to put 5x4 film in the 4x5 holders and vice versa. But I adapt...bringing us back to simply having a bit of flexibility in our choices.

Argenticien · Apr 14, 2016

I have tended to use this site instead: http://www.dofmaster.com/dofjs.html
But it is the same idea. And as said above it depends greatly on which lenses you're talking about on both formats. For example, DOFMaster tells us a 105 mm lens at f/2.4 on 6x7 format, focused at 5 m, has DoF 0.64 m. That's a slightly long-normal lens (a popular one for the Pentax 6x7). A 58 mm lens at f/1.4 on 35 mm format, also focused at 5m, yields about the same (0.63 m) DoF. That's my favorite slightly long-normal on my Minolta SRTs.

If instead you could have a 45 mm lens on the 6x7, also focused at 5 m, also at f/2.4 (to isolate variables; yes I know a 45 is likely to actually be f/4), it would have far greater DoF ... about 4 m. This illustrates how the comparison becomes more about lenses than simply about film format.

--Dave

RobC · Apr 14, 2016

DoF will be dependant on subject distance which would be different with different lens focal lengths and film formats. So unless the OP starts quoting some actual figures for subject distance and focal lengths then I have no idea how anyone can answer the question.

CropDusterMan · Apr 14, 2016

Alan Gales said:
Do people still use those? When I was in High School my Trig teacher showed us how to use a slide rule because we were curious. Calculators had replaced them by that time. It was 1978.

Lol. I actually have a pretty valuable collection of slide rules I've collected over the years...some of
them are works of art...beautifully made with Bamboo...as smooth today as 60 years ago. By the
mid-1970's, the electronic calculator had all but replaced them, but when I was in high school, my math
teacher said "Any good man worth his salt should know how to use a slide rule", and he forbid the
use of electronic calculators, so we were all pretty awesome with them.

They even have an iPhone app. The one picture above is a Faber Castell 2/83N...goes for big bucks...
the Leica of Slide rules.

HiHoSilver · Apr 14, 2016

APUGuser19 said:
Well I got it right. Lysdexia doesn't run in our family.

'Good chuckle, 19.

the agnostic dyslexic insomnia lies awake nights, wondering if there really is a Dog.

The rule of thumb on DOF I was told & it has worked more or less is an extra 2 stops - on an 80mm cz on a 500cm. 'Was good to read others seem to think this is a fair estimate.

In 135, I try to shoot 5.6 when possible - being the sharp spot for alot of those lens. In the MF, I'm always trying for F11/16 for the same reason. I'm a bourgoise that Bresson mocked. Sharper *is* better. Most of the time.

Picked up my first medium format camera - equiv. f stop?

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