High shutter speed affecting bokeh?

[engl]

I noticed something interesting when trying out a recently obtained Graflex Optar 135/4.7 with Graphex shutter. I was testing the shutter speed accuracy by using a DSLR shooting through the bellows and lens. One shot was taken using B mode on the DSLR and firing the Graphex shutter, the other picture by opening the Graphex and using the DSLR shutter.

At 1/10 both looked very similar, both perfect circles with even illumination, the Graphex shutter seemed to be somewhat slow leading to a brighter image.

Comparing 1/350 on the DSLR shutter versus 1/400 on the Graphex had a drastically different result. Comparing brightness is difficult as the brightness is very uneven on the Graphex, as a result of the way the shutter blades move. See the attached image.

Will not this in effect act as an uneven aperture shape which would influence the appearance of OOF objects, especially highlights?

[Jack Dahlgren]

It may or it may not. How do pictures taken with it look?

[erie patsellis]

Taking a picture of the shutter blades in operation tell you absolutely nothing about how OOF highlights will render at the typical apertures used (between f16 and f32) The placement of the blade in relation to the principal nodes, as well as the apertures location in the optical path assure that the effect you think you see will have no effect on the operation of the lens pictorially.

Also, you should note that the higher speeds on shutters are rarely accurate, and the typical exposure tends to ~1 sec or longer, once filter factors, bellows factors and such are accounted for.

[Jack Dahlgren]

Erie,

I guess I'm not big on filters so I can't recall any daylight shot of mine which was over a second. I guess typical is relative.

[Donald Miller]

Large format shutters are generally recognized as being highly inaccurate at the shutter speed that you mentioned.

[engl]

Erie,

I know that such shutter speeds and apertures are not the typical case, and I did not claim them to be either. Im thinking it might happen for someone shooting portraits, art or using a hand held Crown Graphic (or other shutterless press camera).

Ive not seen the effect in any of my photos, which might be related to the fact that I have only taken 4. I just received my Crown Graphic and Im still getting familiar with it. I like to know the effect of all the choices I make, including those Id make very rarely. Experimenting is a bit costly and time consuming with large format photography (not to mention boring), so I figured Id ask if anyone had heard of this effect.

[Jason Greenberg Motamedi]

I have not seen this before, but it doesn't surprise me. The leafs (leaves?) have a limited speed when moving especially if they are old, and need a cleaning. This will be most noticeable at higher speeds, where they move relatively slower.

Practically speaking I am not sure this matters. I think the fastest I have ever used a LF shutter is 1/60, and that is with studio strobes.

[Struan Gray]

This has come up a few times before. The flower shape shows up more clearly in out-of-focus bright highlights in the background when using the fastest shutter speed at wide apertures. You can see it clearly in the background sparkles in this image:


http://www.largeformatphotography.info/forum/attachment.php?attachmentid=18358&d=1224017497

It is a consequence of the limited 'efficiency' of a leaf shutter at its fastest speed, when the blades only just reach the edge of the aperture opening before turning round and closing. It's the reason the fastest speeds can be 'wrong' for small apertures - by as much as a stop. Technical optics science uses the word 'apodisation' for spatially-varying aperture openings, in this case the aperture is apodised by the time-average of the shutter hole.

[engl]

Thank you for the reply Struan! The example image shows pretty much exactly what I was expecting would happen. Unless Im shooting movement Ill consider using a ND filter and a slower shutter speed if I come across a situation where I want to avoid that effect (which may or may not ever happen).

Ive been interested in apodisation since reading about the Minolta/Sony 135mm f2.8 [T4.50] STF lens, using apodisation to smooth out the bokeh with very good result. I wonder if it would be possible to build an apodisation leaf shutter greatly enhancing the bokeh of any lens? Many, many shutter blades and capability to move them slower to control the apodisation at any speed... reference this post as prior art if someone tries to patent that :)

Edit: By the way Struan, Im in Dalby, 10km from Lund!

[Struan Gray]

We should meet up. I tend to get at least halfway to Dalby a couple of lunchtimes a week in my ongoing search for weeds and undergrowth to photograph. Just now I'm following the pasqueflowers ('backsippor') at Hardeberga. I'll PM/email.

Apodisation usually refers to using a graduated mask to manipulate the diffraction pattern of telescope objectives, but the name applies to non-diffraction limited use too. It's probably easiest to do with older or graphic arts lenses which have slots for Waterhouse stops. I have played with ideas for using colour apodisation to do colour seperations in-lens, but there are problems.

The star-shaped opening is used to make the shutter more efficient at 'normal' speeds and apertures. It would be possible to make a shutter controlled by micro-motors which could be tuned for different effects, but making it rounder for all opening sizes would make it less efficient for regular use - so you would force the apodisation on occasions where it wasn't needed or wanted.

The photo I linked is the only one I have taken in LF or MF (where I used leaf shutter lenses until a couple of years ago) where the effect shows up clearly, and it was an oddball shooting dried grasses and reeds directly into a low sun. I like it in that shot, but I have never needed to worry about it in practice since.