DoF vs. Format

Bennp2000

Bennp2000

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So I've been lent a Mamiya 645 with an 80mm f/1.9 on it and I'd like to firstly say I've enjoyed the whole experience and learnt quite a lot.

However, I was having a discussion with the owner and I pointed out that I thought I could get the equivalently shallow DoF through using a 50mm 1.2 on my full frame body. This would cost less in total than buying a MF film camera.

He was adamant that although my DoF would be the same, the falloff and quality of the OOF areas was dependant on format size not format size relative to aperture (and certainly not just lens design). Is he correct here?
 
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Taking the differences between format and relative aperture into account, then I'd have thought the only variable was the lens design, and that's what would affect the look of the OOF area.

Just a thought :shrug:
 
Bennp2000 said:
So I've been lent a Mamiya 645 with an 80mm f/1.9 on it and I'd like to firstly say I've enjoyed the whole experience and learnt quite a lot.

However, I was having a discussion with the owner and I pointed out that I thought I could get the equivalently shallow DoF through using a 50mm 1.2 on my full frame body. This would cost less in total than buying a MF film camera.

He was adamant that although my DoF would be the same, the falloff and quality of the OOF areas was dependant on format size not format size relative to aperture (and certainly not just lens design). Is he correct here?
Click to expand...

There's a DoF Equivalent Calculator half way down this page.
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm
This assumes the same perspective is required.

Closest I could get was 645, f1.8, 80mm
which equates to Full Frame 35mm, f1.0, 46mm
So your friend may have a point...
 
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645
80mm
1.9
5m
=0.734228554602276

35
50
1.2
5m
=0.7164401164549856

From here.
http://www.bobatkins.com/photography/technical/dofcalc.html

If we accept the minor differences in FOV as I can't buy a 46mm F/1 then they're pretty close and that wasn't the real focus of the discussion. It was more that he believed that the DOF falloff from the mamiya would somehow be better due to being on a larger format, not lens design or aperture.
 
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Not sure on this but would the larger format longer lens give a flatter/more compressed perspective than the wider lens? I know comparing my 178mm f2.5 on large format 4x5 to a 50mm f1.4 on full frame, the dof isn't miles apart but does look different.
 
puggie said:
Not sure on this but would the larger format longer lens give a flatter/more compressed perspective than the wider lens? I know comparing my 178mm f2.5 on large format 4x5 to a 50mm f1.4 on full frame, the dof isn't miles apart but does look different.
Click to expand...

Perspective is almost identical; so that's not the problem.

Response to the OP - Ah - I see!
And thinking about it, the figures I posted were probably not significantly different.
Sounds like this is going into the world of bokeh; so it's all going to be a relatively subjective assessment and I think is more to do with the lens construction than the sensor format.
 
Bennp2000 said:
I thought I could get the equivalently shallow DoF through using a 50mm 1.2 on my full frame body. This would cost less in total than buying a MF film camera.
Click to expand...

Depends on what M645 body you're using (I have an M645 1000s) but can you tell me where you can get a Canon EF 50mm f/1.2 for under £350 (which is about what a 1000S + 80mm f/1.9 have been going for recently on eBay)? :)

edit: I suppose you could use something like an Olympus OM 50mm f/1.2, which you can pick up for under £400 if you look carefully.
 
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Pro Tl with Prism (£500 with the standard 80mm?), Winder etc. which quickly nudges into used 50mm 1.2 territory (especially when you factor in scanning etc.).
 
I suspect this is about the smoother rendering of MF's much larger recording area rather than the quality or appeal of the bokeh.
You could liken it to the visibility of grain in 35mm vs MF.:)
 
I'm comparing 35mm film with 645 film, though the principle is probably the same, in fact its probably the same for crop v ff digital, in that the larger recording area aids smoother more graduated rendering.
I wouldn't like to comment on bokeh beauty between a 1.2- 50 35mm frame and a 1.8- 80 645 frame but, the larger capture area holds all the cards when displaying what has been recorded.

Anyway, no matter what you do, there ain't no way a 50mm 1.2 on a digital camera will produce 645 slide you can hold in your hand, I'm certain there will be doors in your house that need holding open though, so all is not lost..

:)
 
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