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Soft edges on C330 shots



 
 
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  #11  
Old February 3rd 09, 10:47 PM posted to rec.photo.equipment.medium-format
Alan Browne
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Default Soft edges on C330 shots

Peter Chant wrote:
Alan Browne wrote:

Do you think it is lens softness wide open or solely focus? I don't
think I'd expect enough softness to be seen on a lowish res scan with a
MF lens. Am I thinking along the right lines?

Could be softness from being wide open.

Tripod? Shutter speed? Release cable? Bad scan?


Can't be the tripod, wasn't using one...

Shutter speed, probaly 1/60th, may have been chancing it at 1/30th...
Actually amazed that with the 55mm lens I have gotten away with 1/15th
on occation.

Release cable, bit silly if you are hand held...


Duh, but I didn't know it was hand held.

I know - I'm going to get the tripod lecture - I really must take it out on
a tripod and see what happens some day!


That's it - beat yourself up before I get a chance. The 'rule-of-thumb'
speed is only good for smallish prints, IMO. Present that photo screen
size and it starts to look a bit soft.

I'd put most of the softness to being handheld.

I'm wondering about the scan. Would explain why the bottom left of the
building is unsharp when the top is.


Plane of focus?

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  #12  
Old February 3rd 09, 11:15 PM posted to rec.photo.equipment.medium-format
Peter Chant[_2_]
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Default Soft edges on C330 shots

Alan Browne wrote:

I'm wondering about the scan. Would explain why the bottom left of the
building is unsharp when the top is.


Plane of focus?


I doubt it. Even at f2.8 the differences in slant distance between the
bottom and top of the building would not be that large.

Pete

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  #13  
Old February 7th 09, 06:38 PM posted to rec.photo.equipment.medium-format
Alan Browne
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Default Soft edges on C330 shots

Peter Chant wrote:
Alan Browne wrote:

I'm wondering about the scan. Would explain why the bottom left of the
building is unsharp when the top is.

Plane of focus?


I doubt it. Even at f2.8 the differences in slant distance between the
bottom and top of the building would not be that large.


So what is it:

lens? -esp. near wide open.

lack of tripod?

I'd tend to think the tripod...


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  #14  
Old February 8th 09, 11:26 AM posted to rec.photo.equipment.medium-format
Peter Chant[_2_]
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Default Soft edges on C330 shots

RolandRB wrote:

Peter said he was probably using 1/60th sec and possibly 1/30th so
assuming 1/60th sec then the picture should have looked sharp at the
size he was showing it and at 1/30th should not have looked as soft.
So at full aperture my suspicion is the focus is out between the
viewing lens and the taking lens and if you know these cameras then
this should be no surprise.



Something for me to re-check. I originally checked it with my 135mm, the
lens that is used least. I'll have to dig out the calculations but depth
of focus (ie at the film) does not depend on lens focal length. IIRC it is
something simple like 2*fstop*circle of confusion, but I need to check
that.

Pete

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  #15  
Old February 10th 09, 12:07 AM posted to rec.photo.equipment.medium-format
Peter Chant[_2_]
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Default Soft edges on C330 shots

RolandRB wrote:

You need to tape a broken piece of ground glass to the back rails of
the taking lens and using a lupe, adjust the focus to infinity while
looking at a distant scene. If your broken piece of ground glass is
from an old camera and it has a split prism then so much the better.
Then make the ground glass in the camera at the top be in focus with
this scene by using spacers or adjusting screws to adjust the ground
glass distance from the viewing lens. If you have one of these old TLR
Mamiyas then there is no point in using it unless you know the
adjustment for this is correct. It is often wrong for any camera you
might buy on ebay.


I've done it once. I found a maintenance manual for the 220 on line. The
220 uses shims but the 330 is much easier as it has three little adjustment
screws. I used a couple of sheets of newspaper taped flat to a cardboard
box at about six feet distance - this seemed to replicate the set up in the
maintenance manual. Not having a loupe I used a 50mm lens of a 35mm
camera. Question is, has it drifted since then or perhaps the 135mm lens,
my least used, was a bad one to adjust the screen with. I should have used
the 55mm or 80mm which I use most.

Any reason for picking infinity rather than a closer target?

For the ground glass screen I used a piece of glass and an oil stone. A
tedious job!

Pete


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  #16  
Old February 10th 09, 09:44 PM posted to rec.photo.equipment.medium-format
Peter Chant[_2_]
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Posts: 203
Default Soft edges on C330 shots

RolandRB wrote:


No, you can pick a closer target so long as it stays in the same
place. The 135mm lens would be a good choice as it would amplify any
incorrect focussing. Using a 50mm or a 35mm lens from a 35mm camera as
a loupe should be adequate. It would be worth using the same setup
again to check that the focussing coincides.


Pulled out my sums:

Depth of focus = 2 x circle of confusion x aperture

From this, with a 0.06mm circle of confusion we get:

f D o Focus (mm)
2.8 0.34
3.5 0.42
4.0 0.48
5.6 0.67
8.0 0.96
11.0 1.32
16 1.92
22 2.64
32 3.84

Depth of focus does not, surprisingly to me, depend on lens focal length.


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  #17  
Old February 11th 09, 08:31 PM posted to rec.photo.equipment.medium-format
Peter Chant[_2_]
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Posts: 203
Default Soft edges on C330 shots

RolandRB wrote:


So at full aperture of f2.8 the film distance has to be accurate to
within a third of a millimeter. That would take some very careful
adjustment on your part. If you have adjusting screws then once you
"get it right" and then tighten the screws (if that is what you have
to do) then the very act of tightening them might shift the distance
by that amount and throw it out again.


When I last did it I adjusted the three screws a quarter of a turn at a
time, being careful that all were turned the same amount and checking that
I had focus over the whole screen.

There is no locking mechanism on the adjusting screws. They are reasonably
stiff to turn and with the new foam in the screen holder there is a fair
bit of pressure on them so, as I don't change screens, little reason to
suspect that they rotate.

The more I write the more urgent I feel the need is to check them for piece
of mind with the more usual lenses. Also ought to go out with a tripod and
see what I get at f22.

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  #18  
Old April 4th 09, 10:33 AM posted to rec.photo.equipment.medium-format
Rob B[_2_]
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Posts: 8
Default Soft edges on C330 shots

RolandRB wrote:
On 11 Feb., 20:31, Peter Chant
wrote:
RolandRB wrote:
So at full aperture of f2.8 the film distance has to be accurate to
within a third of a millimeter. That would take some very careful
adjustment on your part. If you have adjusting screws then once you
"get it right" and then tighten the screws (if that is what you have
to do) then the very act of tightening them might shift the distance
by that amount and throw it out again.

When I last did it I adjusted the three screws a quarter of a turn at a
time, being careful that all were turned the same amount and checking that
I had focus over the whole screen.

There is no locking mechanism on the adjusting screws. They are reasonably
stiff to turn and with the new foam in the screen holder there is a fair
bit of pressure on them so, as I don't change screens, little reason to
suspect that they rotate.

The more I write the more urgent I feel the need is to check them for piece
of mind with the more usual lenses. Also ought to go out with a tripod and
see what I get at f22.

--http://www.petezilla.co.uk


I don't suppose there is any chance that somebody has been handling
the camera and dropped it?


I would look to ensuring the negative/transparency is flat when you
scan, is it soft at the edges when viewed directly (perhaps on a light
box)? Given the odd pattern of softness you describe I would doubt the
film plane is off,
 




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