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Author Topic: flex adaptor critical focusing issues  (Read 3205 times)

michaelnotar

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flex adaptor critical focusing issues
« on: August 13, 2008, 12:29:58 am »

is it normal for the flex adapters to be just a hair off in focus... i have disassembled and reassembled it live 5 times in the last 2 days shooting focusing tests and have concluded

even though i shot at f5.6, i found i needed to expose at F8 1/2-11 to get the DOF i saw in the groundglass, does the GG gives the false impression of more DOF...? i was critically checking focus/ DOF with a 8x loupe.

it seemed to front focus slightly, not sure if this is true or just an CoC issue. im using a flex adapter with a capture integration brightscreen and masks, with a  P25 with a rodenstock 105mm digital lens.

thanks for any help/thoughts.
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ixpressraf

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flex adaptor critical focusing issues
« Reply #1 on: August 13, 2008, 03:26:00 am »

Every sliding adapter is capable of making perfect sharp images( a technical camera is mostly used for the most critical jobs ) but sometimes the focussing screen is off exact sharpness. Best thing is to readjust the focussing screen instead of using shims on the back.
On the other side: the groundglass is only a few centimeters wide and you will get the impression of much wider DOF because you simply can't see things going out of focus on that tiny sreen. But examining the image at 100 percent on your computer screen things look completely different.
I use two digital P2 sets in use ( one is for sale at the moment) with the original Sinar digital sliding back and it works absolutely perfect. No focus shift with non of my backs.
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Morgan_Moore

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flex adaptor critical focusing issues
« Reply #2 on: August 13, 2008, 04:33:51 am »

Quote
is it normal for the flex adapters to be just a hair off in focus... i have disassembled and reassembled it live 5 times in the last 2 days shooting focusing tests and have concluded

even though i shot at f5.6, i found i needed to expose at F8 1/2-11 to get the DOF i saw in the groundglass, does the GG gives the false impression of more DOF...? i was critically checking focus/ DOF with a 8x loupe.

it seemed to front focus slightly, not sure if this is true or just an CoC issue. im using a flex adapter with a capture integration brightscreen and masks, with a  P25 with a rodenstock 105mm digital lens.

thanks for any help/thoughts.
[a href=\"index.php?act=findpost&pid=214711\"][{POST_SNAPBACK}][/a]

Using my Flexadapter (with a sinar back on a sinar P2) I know that I need to turn the rear standard focus knob 1/8th of a turn to get spot on focus after composing

I would be interested in anyone who knows how to adjust a flaxadapter to get perfect focus

I dont want to mess with the shimming of my back as it is well aligned with my H1

I think your problem is misalignment not a percived increase in depth of field

S
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Sam Morgan Moore Bristol UK

jing q

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flex adaptor critical focusing issues
« Reply #3 on: August 13, 2008, 05:30:55 am »

Quote
Using my Flexadapter (with a sinar back on a sinar P2) I know that I need to turn the rear standard focus knob 1/8th of a turn to get spot on focus after composing

I would be interested in anyone who knows how to adjust a flaxadapter to get perfect focus

I dont want to mess with the shimming of my back as it is well aligned with my H1

I think your problem is misalignment not a percived increase in depth of field

S
[a href=\"index.php?act=findpost&pid=214726\"][{POST_SNAPBACK}][/a]
my silvestri sliding back was off focus when it first arrived. turns out they had installed a shim just below the groundglass that threw the focus off.
it should be possible to put a shim below the groundglass of your sliding back to ensure that the focus matches the back
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yaya

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flex adaptor critical focusing issues
« Reply #4 on: August 13, 2008, 06:20:55 am »

Quote
my silvestri sliding back was off focus when it first arrived. turns out they had installed a shim just below the groundglass that threw the focus off.
it should be possible to put a shim below the groundglass of your sliding back to ensure that the focus matches the back
[a href=\"index.php?act=findpost&pid=214728\"][{POST_SNAPBACK}][/a]

This is true if your sensor is front focusing...if it's back focusing you'll have to either shim the adapter plate or to have someone machine the GG base.
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michaelnotar

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flex adaptor critical focusing issues
« Reply #5 on: August 13, 2008, 12:54:50 pm »

in my focus tests, i shot a tape measure running from the tip of the tripod leg going away from the lens. i focused at 40 inches and it appears that i had focus from 40-44.5 inches at f5.6 in the GG, but when it captured it had focus from 41-42 inches. closing down to f11 got me the DOF i saw at 5.6 in the GG.
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Morgan_Moore

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flex adaptor critical focusing issues
« Reply #6 on: August 13, 2008, 01:08:05 pm »

Quote
in my focus tests, i shot a tape measure running from the tip of the tripod leg going away from the lens. i focused at 40 inches and it appears that i had focus from 40-44.5 inches at f5.6 in the GG, but when it captured it had focus from 41-42 inches. closing down to f11 got me the DOF i saw at 5.6 in the GG.
[a href=\"index.php?act=findpost&pid=214814\"][{POST_SNAPBACK}][/a]

I think you need to isolate the problem

is the camera back (or front) focussing

OR

is the DOF just 'less' when you look at an englarged digital file


the first requires some sort of shimming or adjustment to the physical kit the second requires a mental adjustment that for a viewing size of say A3 your definition of sharp is different from when you view GG which is smaller than 6cm wide

I can say that I had a big mental adjustment on 'what is sharp' when I started shooting with a DB because before that in comparison nothing had been sharp enough to show minor focus errors

S
« Last Edit: August 13, 2008, 01:08:54 pm by Morgan_Moore »
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Sam Morgan Moore Bristol UK
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