bronica RF645 lenses not sharp! (diffraction test)

[gameone]

Allright, maybe a bit provocative title, but this is the case:

I use a bronica rf645 with a 60mm. I use it for shooting (urbanised) landscapes almost solely. I want a large depth of field, so use small apertures, f16 90% of the time. And a tripod.
I did quite some shooting the past months, and recently started scanning my slides. I used a Imacon for scanning, and very soon I found out that my slides were absolutely not what I'd expected in terms of sharpness.
A strange sort of fuzziness was there all over the frame. Since I found all obvious causes for unsharpness unlikely, I started thinking about diffraction. So a did a TEST.

I set up my tripod and shot 4 photo's of a scene, stopping down from f8 to f22. I did this with four scenes. (4x4=one roll of film)

And each time, f8 was tack sharp, f11 was way fuzzier (and I mean really significantly)
and f16 and f22 fuzzy too)

This is weird right?

I own a 45mm lens too and did the same, one scene 4 photo's f8 - f22, and again. f8 very sharp. f11 upwards fuzzy.

Is this diffraction, and is it that big a factor?
RF645 lenses have a killer reputation, one would think the lens would be sharper at more apertures...

I am puzzled. Anyone with a suggestion, thought, solution, knowledge, please help me out here..

Many thanks, best S.

[Matus]

Well, diffraction is there at ANY aperture, but it usually becomes visible (on film with good lenses) only at f/11 - f/16. Still it should not be that strong at around f16.

If you say that f11 is significantly less sharp than f8 I can only imagine that the lens performs outrageously well and delivers very high resolution - and so you see the diffraction effects sonner.

Still - at f11 the slides should be perfectly sharp. I guess your scans are 4000 spi as that is the maximum for Imacon for 645.

[gameone]

Hey thanks for the quick reply.
Well, I made 100mb scans, so plenty of resolution to perfectly judge sharpness.
At f8 the camera delivers what I'd expected from it. Very nice and very sharp. f11 upwards really SIGNIFICANTLY fuzzier. But one would not expect that big a difference between f8 and upwards... right?
Maybe any rf645 users recognize something here?

[Turtle]

I did not notice this with mine when I had it, but maybe I am less demanding (I mean this literally and not as a judgment). Once I did shoot at f22 and f32 and I would not have used those shots for anything bigger than postcards.

My Mamiya 7 lenses are amazing at f16 but drop precipitously at f22.

[ColSebastianMoran]

At f/16, the Airy disk is 20 microns. At f/8 it's 10 microns.

At 4000ppi in your scan, the spacing between points is 6.35 microns. Yes, I think the scanner would be able to see the diffraction difference between f/8 and f/16.

A more general comment: Raw scans of film are always disappointing when pixel peeping. A scan might look crummy looking at actual pixels, but after some noise reduction and sharpening, could still make a great, sharp print. I suspect your image at f/11 will make a great print.

[Michiel Fokkema]

Did you use a very sturdy tripod. Closing down you aperture will results in longer shutterspeeds. are you sure it in camera movement that caused the fuzzynes?

Cheers,
Michiel Fokkema

[gameone]

That comment about the mamiya dropping in quality after f16 I find interesting. apparently the rf645 shows this behaviour after f8. Is this common knowledge? Are there lens curves somewhere confirming this behaviour?

Originally Posted by Michiel Fokkema

Did you use a very sturdy tripod. Closing down you aperture will results in longer shutterspeeds. are you sure it in camera movement that caused the fuzzynes?

Well, I used a very sturdy Foba tripod, the same I use for 8x10", so that shouldn't be the problem. Plus the Bronica is a very quit camera, plus motion blur looks different. I'm 200% certain it's no motion blur.

[Turtle]

I have seen lens tests which show the Mamiya dropping off a little from F11 to f16, but more sharply at f22 and it concurs with my practical experience. I dont shoot at f22 unless I have to. The problem with the Mamiya 7 is the negs are so insanely sharp at middle apertures that you do notice the reduced performance at f22. At f16 it is still so good as not to matter, but with the right scenery and slow film it is evident that at f8-11 is where things are best technically

[eia41]

I wonder what you would find if you were to project your slides...

[gameone]

Originally Posted by eia41

I wonder what you would find if you were to project your slides...

Why? Imacon is perfectly for judging this kind of stuff, besides, a loupe shows the same

[rogerzilla]

My Bronica SLR lenses weren't all sharp. The 75mm was impeccable, the 135mm and the 40mm were OK. The 60mm was bad. Not Leica quality at all.

[Steve M.]

Assuming that the tests were done at a high enough shutter speed to eliminate camera shake, or assuming that it wasn't necessary because you had the camera on a tripod (stopping the lens down means your shutter is running slower and slower), that does sound odd. Diffraction is real, and some lenses are worse than others, but I wouldn't expect to see what you saw.

Could be that the metering wasn't right when you stopped the lens down further, or that the difference you're seeing on scans won't show on a print. The only thing left seems to be that your lens is particularly inclined to refraction.

[f16sunshine]

Diffraction is related to the physical size of the iris regardless of focal length or f-factor relationship. So a longer fl will have less diffraction at the same f -stop when compared to a shorter FL.

[rogerzilla]

Originally Posted by f16sunshine

Diffraction is related to the physical size of the iris regardless of focal length or f-factor relationship. So a longer fl will have less diffraction at the same f -stop when compared to a shorter FL.

But the longer focal length has its rear nodal point further from the film (i.e. the diffraction is magnified), so it works out roughly the same.