5x4 focussing question

ifotou

ifotou

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Tom
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this might sound really stupid but shooting with the 5x4 i've found that my focus is off slightly, what i think is spot on tend to be a touch out when i get the shots back.

I use a loupe to check for focus on the ground glass screen and i'm beginning to wonder whether that's effecting the point of focus as at the moment for the portraits it's shallow depth of field (f5.6) that i was using to get lots of background blur, but it seems that the focus is just in front of the person.

am i being stupid?
 
The focus point probably is a bit out, it usually is on these cameras but it shouldn't be a problem because the large depth of focus means that there's a fair bit of lattitude.

I think your problem will be lens sharpness, not focussing - these cameras are normally used at around f/22, the lenses are not designed to be used at f/5.6, that's just for focussing.
 
The ground glass screen should be at exactly the same plane as the film, so as long as you don't change ANYTHING between focusing and exposure, it should be correct. That does depend on the camera, DDS, lens etc all being precision built, which is not always the case! A lot of 5x4 usage is for landscape or architectural photographers who tend to use the lenses stopped right down - I often use f32, f45 etc for my architectural work. At those apertures, and with focusing distances near infinity, a slight error on the focusing or innacuracy in the camera build is much less critical. The way you're using the camera requires precision accuracy of build and use, so any slight error will show up. What equipment are you using?
 
thanks folks

snowy - i was using a cambo sc2 view camera and Rodenstock 210mm lens

also just got a MPP MkViii that i have yet to test out properly.

might just be my eye sight though ;)
 
ifotou said:
thanks folks

snowy - i was using a cambo sc2 view camera and Rodenstock 210mm lens

also just got a MPP MkViii that i have yet to test out properly.

might just be my eye sight though ;)
Click to expand...

Well, that's quality kit, so I'd expect it to be alright. Maybe it is your eyes ;)
 
yeah i reckon it is, you can see the shots on my large format blog - http://largeformat.ifotou.co.uk just that someone commented that they could be sharper .... maybe time for me to move to f8/f11 as i'll still get a shallow DOF but leave me a bit more latitude for my eyes
 
The usual reason for 5x4 cameras giving poor focus is the ground glass being replaced facing the wrong way. Or a Fresnel screen put in the wrong position.
The second is focussing on the aerial image when they need eyesight correction... though this should not happen with a normal ground glass.

Another reason can be that they are using plate holders or film inserts made before they were standardised for use with an international back. There are still a lot around.. the early mpp ones can be quite a way out though Fidelity or japenese one always seem to be correct. If the plate holders use film inserts these them selves can be non standard thickness. ( may have been swapped with the original ones as they are removed for loading.)
 
Terrywoodenpic said:
The usual reason for 5x4 cameras giving poor focus is the ground glass being replaced facing the wrong way. Or a Fresnel screen put in the wrong position.
The second is focussing on the aerial image when they need eyesight correction... though this should not happen with a normal ground glass.

Another reason can be that they are using plate holders or film inserts made before they were standardised for use with an international back. There are still a lot around.. the early mpp ones can be quite a way out though Fidelity or japenese one always seem to be correct. If the plate holders use film inserts these them selves can be non standard thickness. ( may have been swapped with the original ones as they are removed for loading.)
Click to expand...
I agree. But I feel the real problem in this case is the one I identified in my first answer - LF lenses don't produce sharp images at wide apertures.
 
Garry Edwards said:
I agree. But I feel the real problem in this case is the one I identified in my first answer - LF lenses don't produce sharp images at wide apertures.
Click to expand...

That would indeed cause soft images to a degree but it would not shift the focus position which seems to be his problem.
He does not say which lens he is using but the modern lenses like Symmars
and super angulons have a very good wide aperture quality.
even the older lenses can be excellent in the centre one stop down.

The sharpest lens I have ever used on a 5x7 plate was a 1950's 500mm tele tessar. It produced hair, sharp as barbed wire at any stop.
 
lens being used was a brand new Rodenstock 210mm F5.6 lens

it's definately a case of it feeling like the focus has moved... as it's pin sharp just in front of where i was focusing.

I think either my eyesight or the focal plane?
 
If you just have a plain ground glass, it's easy to check:

Remove the lens and place the lensboard back into the camera. Ensure that that the ground side of the glass is towards the lens then use a steel rule to measure the distance from the ground glass to an edge of the lens board.

Then insert a film holder with a scrap piece of film in place and remove the dark slide. Measure the distance from the film emulsion to the same edge of the lens board.

These dimensions should be the same as the emulsion needs to be in the same plane as the ground surface of the glass is when focusing.

If you have a fresnel fitted then this method will not work.


Steve.
 
with that method it is often better not to use the scale on the rule but use something stuck to it that you can mark with a knife scratch. it is more easy to see if they are identical that way.
 
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