Disappointing results with my Crown Graphic

[tim48v]

As a formally trained engineer (not a former train engineer), I appreciate the math and physics that make all this work.

Anyway, as has been said: "In theory, there is no difference between theory and practice. However, in practice, theory isn't worth the paper you derived it on."

With that in mind, I don't think the problem with the photos I've posted (and most of the others I've taken) can be traced down to the thickness of the film or some other 0.006" error. If so, then people would have stopped using these cameras decades ago. I think there's a bigger issue. Surely, this group has taken thousands of similar photos, probably with the same setup, how sharp are your photos?

Some have asked about my focusing technique. Fair question. They've even suggested, politely, that I try new glasses. To be honest, I do wear bifocals and have two different pair: one for normal living and one for my life in front of a computer. I've tried both and found no difference in the end result. Probably because I'm using both a 8x and 20x magnifier for focusing.

To complicate things, (I am, after all, an engineer), I set up my m4/3 digital with extension tubes and a manual lens. Since we're getting carried away, we might as well do it right. Here's a shot of the focus screen I took just before taking one of the test photos:

The thick line just below the inverted "18" is a mark on the glass. My technique: blur the image from the Crown's lens until it can't even be seen, then focus the digital on the grooves of the Fresnel. Then focus the Crown. I don't think focus is the issue.

My best guess after reviewing all the input: I need a new tripod. I hope to pick one up this afternoon (via craigslist) and take some more test shots. (Note that all the DOF shots of the ruler were taken using a tripod with the center post retracted and with the self timer. The shots of the Barn were take with the post extended and me tripping the shutter release on the lens.)

I really do appreciate and enjoy on the feedback. I'm going to review the CoC and depth of focus equations for my own entertainment.

Hopefully, I'll have some new data tonight.

 

[RobC]

cable release is a must have. And a longer one which is not stiff like some of them. That way you tend not to transmit hand movement down it when you press the the release.

 

[RobC]

i agree with you to a point but ... ...

circle of confusion charts
and information about depth of focus for min/max circle of confusion
down to the 1/1000mm or 1/10000mm is interesting .. but a bit excessive.

its like someone having trouble with their car and someone talking about
the minutia regarding throddle bodies or the precise measurement of carbureted mist sprayed into
the piston heads ... when the answer is much simpler (dirty spark plug)..

unfortunately, complex answers to simple problems
seems to be the way of the internet

Without understanding how critical depth of focus is you can't understand why film flatness and repeatable film position are. And to understand the limits you must understand that the CoC which is effectively the Rayleigh limit is often smaller than what is acceptable, hence theoretical min and target min since theoretical min is never likely to be achieved.

It's easy if you already know about it. It isn't if you don't but would like to know. You should remember that instead of saying do what I tell you but I'm not going to explain why.

 

[RobC]

I'm going to review the CoC and depth of focus equations for my own entertainment.

get yourself this piece of software which does all the calcs for you and will save you a lot of time (you didn't think I did it with a calculator did you?)

http://www.winlens.de/index.php?id=70

suggested starting settings. And note you can overide CoC which should be twice diffraction limit radius or bigger. Rounding means you may need to add one to smallest place or it goes red. And a bug in program requires you to maxmise program window otherwise depth of focus tab shows contents of systems tab.

 

[removed account4]

Without understanding how critical depth of focus is you can't understand why film flatness and repeatable film position are. And to understand the limits you must understand that the CoC which is effectively the Rayleigh limit is often smaller than what is acceptable, hence theoretical min and target min since theoretical min is never likely to be achieved.

It's easy if you already know about it. It isn't if you don't but would like to know. You should remember that instead of saying do what I tell you but I'm not going to explain why.

i suppose it is useful ... if you want to know optics theory or something...

in my experience ( close to 30 years with a LF camera and about 45 with other cameras )
i have never heard of the rayleigh limit, or needed to know critical unachievable theoretical limits
for anything i own ( used or new ) or even thought about circles of confusion ( even when images weren't "sharp" ).

the thing that is important to know when images are unfocused or blurry with a LF camera is
the T distance, and the fact that lenses and cameras bought USED can sometimes have issues because
everyone who reads the internet thinks they are a lens or camera repairman and wants to save a few dollars
so they take things apart and have no idea what they are doing, so when they re-assemble things
they are screwed up ... they are embarrassed about their flawed repair so they sell the dis-repaired camera/lenses
and don't tell the future owner they did anything so the new owners have problems from the start ... so it is a good thing
to bring any camera or lens for a CLA when bought used ...

i also know that film holders are not all the same depth, and film is not all the same thickness.
super xx, bergger, forte films were known to be extremely THICK base and aero film is so thin it curls .. people use all 4 .. no problems.
one can use a film holder in a PLATE camera from the last centuries without a problem too.
sure, the film distance is a few mm off ( probably 2 since plates are +/- 2mm ) but shooting at f11 or 16 takes up the slack and things are sharp.
if someone puts a piece of 1 ply mat board in a falling plate septum, and put photo paper in there, the image is sharp as well.
my uneducated guess is the few plate holder conversion septums i have lying around for 2 or 3 different formats and plate holders
will all have different distances because the manufacturers know critical distances really might have a little wiggle room ...
especially if one stops down to f11 or 16 or 22 or it is a fixed stop box camera ... no need for unachievable limits or circles of confusion.

but different strokes for different folks as they say ...

and of course take everything posted on the internet with a HUGE grain of salt, and ... YMMV

 

[BrianShaw]

That level of engineering is important when developing a camera or lens design, but not generally used by photographers or camera repair people. Camera repair manuals tend to focus on the use of OEM parts to ensure that the as-designed specs are maintained. I applaud the engineers who want to reverse-engineer to either understand or modified a well-established design. That is a culture and approach that I am quite familiar. But it is sometimes a long way to go to make a camera work. When faced with similar situation I opted to take the quicker approach so I could be more quickly a photographer instead of an engineer.

 

[tim48v]

I've taken some more test photos, using a much more solid tripod and the self timer. The results are better but still not as good as I've had with my Century Graphic.

I've got a replacement Ground Glass coming. We'll see if that helps.

 

[Ken Nadvornick]

Surely, this group has taken thousands of similar photos, probably with the same setup, how sharp are your photos?

Posted by me previously, but worth a reprise to help answer your question with an example:

B-25J Mitchell medium bomber, Flying Heritage Collection, Everett, Washington
Pacemaker Crown Graphic 4x5 w/135mm f/4.7 Wollensak Optar
1/200 sec at f/16 at ~25-feet on HP5+, handheld using a single on-camera Press 25 flashbulb
Plane of focus on furthest tip of propeller using calibrated top-mounted rangefinder

Apologies for the hotspot...



Ken

 

[tim48v]

Ken,
Cool. My son got to go for a ride in one of these (The Pacific Prowler) when he was about 12. He had three complaints:
1. The ride was too short.
2. They wouldn't let him fly it.
3. No ammo for the machine guns.

Probably the same complaints we'd all have.

Could you email me a hires copy of that shot? Timothy@stearmanpress.com.

Tim

 

[tim48v]

I've posted some more test shots on our website: www.stearmapress.com.

These were taken with a Brightscreen in place of the Fresnel/GG. The Brightscreen combines the Fresnel and ground glass into one piece of plastic. I didn't believe it would work until I realized that the Fresnel in the Crown is being used as a collimator; thus the distance between it and the ground glass doesn't matter.

I find the image to be a bit "courser" than the original ground glass but it seems to "snap" into focus for me. Overall, I like it and plan to try it on my Century Graphic.

I think the images are sharper; whether due to some physical difference between the GG vs Brightscreen or my focusing technique, I don't yet know.