Chamonix 45N-1 Testing Procedure

[Jeremy Moore]

Based on this thread (http://www.largeformatphotography.info/forum/showthread.php?t=56287) I'm going to be doing an actual test with film and a Chamonix 45N-1 camera this evening.

I will make 4 photographs. 2 with a 90mm lens and 2 with a 135mm lens.

The camera will be firmly mounted to a Majestic Tripod with 6" bed indoors and focused on a fixed subject 10-15 feet away.

I will make 1 photograph to the best of my ability with a 90mm f/5.6 Super Angulon at f/5.6. I will then remove the fresnel, refocus my camera if need be due to the fresnel being removed, and make another photograph at f/5.6.

I will then repeat this process using a 135mm f/5.6 Symmar-S.

I will light these photographs with flash and use a shutter speed of at least 1/125th of a second to avoid motion blur. I will shoot Ilford FP4+ and develop it in Pyrocat HD using a 2-bath development in a Jobo 3010 with 6 other sheets I need to develop. I will scan the resultant images and post them back to this thread.

Anyone that may have an issue with how this test is conducted and nitpick it later are given the opportunity--RIGHT NOW--to make suggestions on the testing procedure.

[Darin Boville]

Is there a way, without going overboard, to place a secondary subject somewhat closer to the camera in the same shot? It might be nice to see, if the fresnel fails, to see not only the main subject getting blurry but to also see the secondary subject getting sharper.

That would also serve as a check on camera shake issues, etc--if the secondary subject is sharper than it can't be camera shake.

--Darin

[Clement Apffel]

I do not mean to nitpick.
But if you want to be rigorous you have to introduce statistics in this.

Simple: everytime just make 4 sheets instead of one. And make sure you completely and randomly defocus the camera before each sheet.
This way, you can avoid the nitpicking on your ability to focus and on the focusing error probability on a single sheet test procedure.

Also defocus randomly before refocusing without the fresnel. So you won't be influenced by the current position of the standards when you focus the second shot.

Just my 2cents.

Can’t wait to see the results though.
Good initiative.
Thanks for doing / sharing it.
regards,
CA

[Jeremy Moore]

Is there a way, without going overboard, to place a secondary subject somewhat closer to the camera in the same shot? It might be nice to see, if the fresnel fails, to see not only the main subject getting blurry but to also see the secondary subject getting sharper.

That would also serve as a check on camera shake issues, etc--if the secondary subject is sharper than it can't be camera shake.

--Darin

Good idea. I'll incorporate this.

[Clement Apffel]

Is there a way, without going overboard, to place a secondary subject somewhat closer to the camera in the same shot? It might be nice to see, if the fresnel fails, to see not only the main subject getting blurry but to also see the secondary subject getting sharper.

That would also serve as a check on camera shake issues, etc--if the secondary subject is sharper than it can't be camera shake.

--Darin

Yes, some kind of long ruler in the shot. so we can appreciate where exactly the focus is.
easier to say it than to do it though.

[Mark Woods]

Yes Clement. My thought exactly. Run a tape off the lens axis from in front of the subject to behind it. It should show nicely where the focus actually is.

[Jeremy Moore]

Okay, as my ability to focus a camera has been called into question I will go one better than doing a test with my camera at home.

I will do this test with my Chamonix mounted to a Cambo studio stand with a Betterlight Super8K camera back at work using a ZigAlign system to make sure everything is parallel. This will also remove any question about the development/scanning of the film and also remove any inconsistencies due to different film holder depths.

I can also run a ruler at an angle to the plane of focus to see how/where the focus is shifting.

[Mike1234]

Jeremy, do you have a wider lens to test with or can you borrow one or more? Adding a 65 and even a 47 would be great... would add to the validity of the results. Sorry to complicate things.

[Jeremy Moore]

Jeremy, do you have a wider lens to test with or can you borrow one or more? Adding a 65 and even a 47 would be great... would add to the validity of the results.

No, 90mm is the widest lens I own and if there is a focus shift happening with a 90mm then I see no reason to test wider.

[Jeremy Moore]

I am planning on making the tests with the Betterlight tomorrow or Friday and *may* have a 2nd Chamonix 45N-1 from a different batch to use for this test too, but that is still unknown at the moment.

[lilmsmaggie]

This discussion is way, way over my head but I can't resist the question:

I assume these "tests" are meant to confirm focusing error correction with wide angle lenses as a result of Chamonix's recommended placement of the fresnel.

Once the results have been confirmed, is this information then made available to Hugo for discussion with the factory, and shouldn't the factory be conducting similar tests either independently or based on Jeremy's findings?

[Jeremy Moore]

I assume these "tests" are meant to confirm focusing error correction with wide angle lenses as a result of Chamonix's recommended placement of the fresnel.

Once the results have been confirmed, is this information then made available to Hugo for discussion with the factory, and shouldn't the factory be conducting similar tests either independently or based on Jeremy's findings?

This test has absolutely nothing to do with the Chamonix factory or Hugo.

I am making this test for myself as a Chamonix user and for the benefit of the users of the LFForum and Apug.org (I linked over to this thread on a thread there about Chamonix focusing issues).

[Darin Boville]

Well, since you asked for suggestions...

It occurs to em that it would be nice to have a control...if you have access to another brand of field camera you might want to include that. That would give us insight into the "compared to what?" question...

See what you are getting yourself into :)

--Darin

[Mike1234]

See what happens when you offer to help, Jeremy? :D Many good points though.

[Jeremy Moore]

Well, since you asked for suggestions...

It occurs to em that it would be nice to have a control...if you have access to another brand of field camera you might want to include that. That would give us insight into the "compared to what?" question...

See what you are getting yourself into :)

--Darin

There is no need for such a control in this instance. I'm comparing focusing with a fresnel between GG and lens on a Chamonix camera to no fresnel. Adding another 4x5 camera won't make any difference and just confuse the issue. Showing a sharp scan from a Cambo 4x5 in the same location adds nothing to the final results or the validity of the test.

Actually, this is one of the easier things to test because there will only be 1 variable in play as I can lock down every other practical variable in the lab. That variable is whether the fresnel is installed in the camera.

I will focus on a fixed point with the fresnel installed and make a scan--if the scan is sharp then the fresnel is not causing a focus shift under these conditions.

If this scan is not sharp then I can remove the fresnel, refocus using the same technique and focusing point and make another scan. If this scan is sharp, assuming everything else stays constant, then the difference in sharpness is due to the fresnel.

Obviously, the veracity of the test does rest on my ability to focus a camera and use my equipment, but part of my job is art reproduction which is head-and-shoulders above the difficulty level we're talking here and I have graduate scientific experience designing experimental models and tests. Regardless of all of this, someone will still cry "foul!", but then again studies have shown that people will believe something even when shown overwhelming facts denoting the opposite.

[SW Rick]

I think you need to buy a 47XL and an 80XL, plus 5 of the most expensive view cameras available, put all of it on the Space Shuttle, and conduct this under weightless conditions. :).
As a Chamonix owner (who has had no issues with this, nor have the other owners I have checked with, whose response has been basically, "say what?"), I am really touched by the fervor of those who neither own or have used the camera :). If only we could channel some of that into feeding the poor or sheltering the homeless etc-type issues.

Appreciate what YOU are putting into this.

[Jeremy Moore]

I think you need to buy a 47XL and an 80XL, plus 5 of the most expensive view cameras available, put all of it on the Space Shuttle, and conduct this under weightless conditions. :).

Donations accepted :D


As a Chamonix owner (who has had no issues with this, nor have the other owners I have checked with, whose response has been basically, "say what?"), I am really touched by the fervor of those who neither own or have used the camera :). If only we could channel some of that into feeding the poor or sheltering the homeless etc-type issues.

I'm tired of people spouting off opinions supported by hypotheticals without any practical, real-world testing. The fact these opinions come from those who don't even own the camera makes it even worse. So I figured it time to do those tests myself and lay the issue, at least for myself, to rest.



Appreciate what YOU are putting into this.

No problem. I've benefited so much from the practical testing of photographic issues by Sandy King and Clay Harmon and Kerik Kouklis and the like that, since I have the skills and equipment to test this, it was time to give back.

[brian mcweeney]

Thanks for doing this Jeremy.

[Darin Boville]

>>Showing a sharp scan from a Cambo 4x5 in the same location adds nothing to the final results or the validity of the test.<<

Well, that depends on what question you are trig to answer!

:)

The other brand issue can wait for the results of this test...

--Darin

[BradS]

As it is, the proposed test will only answer one question for Exactly one camera - Jeremy's....and is therefore, of little real use to anybody else. We have no idea, for example, what the variation in this critical dimension is from the factory. It would be interesting to select a random sample of production...and measure. In the real world it would just be nice if the sample size were greater than one - forget about the random sample just test more than one item!

I also agree it would be interesting to know how one brand compares to another...but again, it is meaningless to test a sample size of one.

Classic. :rolleyes:

[Darin Boville]

but again, it is meaningless to test a sample size of one.

Classic. :rolleyes:

Not at all. While it may not give you enough data points for statistical analysis there are other ways of learning about the world :)

For example, if Jeremy's camera fails the test then that would cast serious doubt on all the Chaminox users who claim their camera is o.k.--Jeremy seems to be a knowledgeable user and he failed to see it in normal photography uses. So the others might be not seeing it in the same way.

Likewise, if his camera passes then we know that at least one is o.k., suggesting that it might be a QC or changing design issue.

--Darin

[lilmsmaggie]

This test has absolutely nothing to do with the Chamonix factory or Hugo.

I am making this test for myself as a Chamonix user and for the benefit of the users of the LFForum and Apug.org (I linked over to this thread on a thread there about Chamonix focusing issues).




As it is, the proposed test will only answer one question for Exactly one camera - Jeremy's....and is therefore, of little real use to anybody else. We have no idea, for example, what the variation in this critical dimension is from the factory. It would be interesting to select a random sample of production...and measure. In the real world it would just be nice if the sample size were greater than one - forget about the random sample just test more than one item!

I also agree it would be interesting to know how one brand compares to another...but again, it is meaningless to test a sample size of one.

Classic. :rolleyes:


Jeremy,

Please don't take it personally. I understand that your tests have nothing to do with the factory or Hugo; even as a non-Chamonix owner, I still appreciate your effort in settling the issue at least in terms of your particular camera. :cool:

However, it still begs the question: "What purpose will these tests serve even if they are for the benefit of Chamonix owners?"

I would think the outcome should or at least could benefit Chamonix to consider their design methodology. Seems like a lot of effort and time that may be for naught if it can't be used to improve a product that so many LF photographers seem to have embraced. :confused:

[BradS]

Not at all. While it may not give you enough data points for statistical analysis there are other ways of learning about the world :)

For example, if Jeremy's camera fails the test then that would cast serious doubt on all the Chaminox users who claim their camera is o.k.--Jeremy seems to be a knowledgeable user and he failed to see it in normal photography uses. So the others might be not seeing it in the same way.

Likewise, if his camera passes then we know that at least one is o.k., suggesting that it might be a QC or changing design issue.

--Darin

Good point. Thanks. :)

[BarryS]

I look forward to your tests Jeremy. I suppose you can look forward to getting more criticism from non-Chamonix 45N-1 owners with too much time on their hands, but we actual owners are grateful. I hate doing testing and haven't felt compelled as my negatives generally look pretty sharp and I've been selling prints, but I'd still like to see your results.

[Jim Galli]

Jeremy, I can't believe this hasn't been asked before, but, isn't the better light self defeating since most of the supposed error will be in the far corners of the plate and the better light will only 'see' the center 'sweet spot'? Seems to settle the original intent that you would need full sheet 4X5 film so that the area most affected will be there. Although if you only use the center to focus, I guess it won't matter. Best of luck. The original GPS post was so idiotically biased it made me want to buy my 3rd Chamonix. Luvin' the Hexar!

[Jeremy Moore]

As it is, the proposed test will only answer one question for Exactly one camera - Jeremy's....and is therefore, of little real use to anybody else. We have no idea, for example, what the variation in this critical dimension is from the factory. It would be interesting to select a random sample of production...and measure. In the real world it would just be nice if the sample size were greater than one - forget about the random sample just test more than one item!

I've already stated that I *may* which has now been turned into WILL have 2 Chamonix 45N-1 cameras to test on Friday. They were purchased separately at 2 disparate times and come from different batches. I'd test more, but only have access to these 2. I'm doing what I can here.


I also agree it would be interesting to know how one brand compares to another...but again, it is meaningless to test a sample size of one.

In what way do you want to compare one brand to another? I'm just testing Chamonix design with a fresnel installed b/w GG and lens and no fresnel at all. I don't know what testing another brand would do FOR THIS TEST.

[Jeremy Moore]

Jeremy,

Please don't take it personally. I understand that your tests have nothing to do with the factory or Hugo; even as a non-Chamonix owner, I still appreciate your effort in settling the issue at least in terms of your particular camera. :cool:

Not a problem and I didn't, I just wanted it to be clear I don't have any connection to Chamonix other than owning a 45N-1 that I actually purchased 2nd hand.


However, it still begs the question: "What purpose will these tests serve even if they are for the benefit of Chamonix owners?"

The purpose of the test is determine if my Chamonix and the other camera I have available for testing suffer from a focus shift due to the placement of the fresnel. That is the sole purpose of this test.


I would think the outcome should or at least could benefit Chamonix to consider their design methodology. Seems like a lot of effort and time that may be for naught if it can't be used to improve a product that so many LF photographers seem to have embraced. :confused:

That's up to Chamonix to decide. It's worth it for me because I will know beyond the shadow of any doubt how my camera functions with the fresnel. There is no need to "improve" the Chamonix design, imo, just toss out the fresnel. I would have paid the same amount for a camera w/o a fresnel at all.

[Jeremy Moore]

Jeremy, I can't believe this hasn't been asked before, but, isn't the better light self defeating since most of the supposed error will be in the far corners of the plate and the better light will only 'see' the center 'sweet spot'? Seems to settle the original intent that you would need full sheet 4X5 film so that the area most affected will be there. Although if you only use the center to focus, I guess it won't matter. Best of luck. The original GPS post was so idiotically biased it made me want to buy my 3rd Chamonix. Luvin' the Hexar!

The intent for me is to see if there is a focus shift caused by the installation of the fresnel b/w the lens and GG. I can see this in the center of the frame just as well as towards the outer reaches as any shift visible at the center would only be worse at the edges. If I do NOT find any shift in the center then I will test at the edges, but shooting the Betterlight is essentially free and removes some of the other variables mentioned before. I can also test the edges of a 4x5 by focusing in the corner and introducing a slight bit of shift on the camera so this area is properly recorded by the not-4x5-sensor--the ZigAlign will make sure everything stays plumb.

[lilmsmaggie]

Not a problem and I didn't, I just wanted it to be clear I don't have any connection to Chamonix other than owning a 45N-1 that I actually purchased 2nd hand.



The purpose of the test is determine if my Chamonix and the other camera I have available for testing suffer from a focus shift due to the placement of the fresnel. That is the sole purpose of this test.



That's up to Chamonix to decide. It's worth it for me because I will know beyond the shadow of any doubt how my camera functions with the fresnel. There is no need to "improve" the Chamonix design, imo, just toss out the fresnel. I would have paid the same amount for a camera w/o a fresnel at all.



Understood and Good Luck with the tests :D

[Jeremy Moore]

I hate doing testing and haven't felt compelled as my negatives generally look pretty sharp and I've been selling prints, but I'd still like to see your results.

Barry, same thing here (though I haven't sold anything), but I haven't noticed anything substantially different in my negatives pre/post Chamonix purchase on my normal subject matter (small aperture landscapes with a 135mm lens).

[Peter K]

Jeremy, I can't believe this hasn't been asked before, but, isn't the better light self defeating since most of the supposed error will be in the far corners of the plate and the better light will only 'see' the center 'sweet spot'?
The 'sweet spot' of the camera or the fresnel lens? :D

Peter
(also idiotically biased in precision cameras)

[BradS]

I've already stated that I *may* which has now been turned into WILL have 2 Chamonix 45N-1 cameras to test on Friday. They were purchased separately at 2 disparate times and come from different batches. I'd test more, but only have access to these 2. I'm doing what I can here.

That's Excellent!.

Would be cool if other Chamonix owners to lend their cameras to you...:)




In what way do you want to compare one brand to another? I'm just testing Chamonix design with a fresnel installed b/w GG and lens and no fresnel at all. I don't know what testing another brand would do FOR THIS TEST.


Well, for example, if you find that the difference between with and without Chamonix Fresnel lens is say 17mm....and, then using the exact same setup, you focused another (respected?) brand of camera and found that there was a focusing error of...oh, say 15mm (I'm just pulling numbers out of the blue to illustrate the point) then, you would have something against which to compare the magnitude of the focus error allegedly introduced by the Chamonix Fresnel arrangement. In this case...the alleged fresnel focus error doesn't look too very significant.

[vinny]

If you can get a back focus chart to focus on, that will help with ease of critical focus and they way it appears on film/sensor when photographed. That's what I used in my tests with my chamonix (described in the last thread on this subject).

http://www.google.com/search?q=back+focus+chart&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

[Clement Apffel]

Okay, as my ability to focus a camera has been called into question [...]

I did not mean that. I was only anticipating nitpicking on the statistics by some random nitpicker.

Anyway, I too look forward for your results, I too find that it is a excellent thing that you have 2 chamonix to test and I too am very grateful to you for doing those tests.

regards,
CA

[Mike1234]

You go for it, Jeremy. Damn the torpedoes... full speed ahead!!

[Jeremy Moore]

That's Excellent!.

Would be cool if other Chamonix owners to lend their cameras to you...:)

I work for the guy who owns the 2nd camera I'm testing and I bet he's thinking "hey, now I don't have to test my own camera!" :D


Well, for example, if you find that the difference between with and without Chamonix Fresnel lens is say 17mm....and, then using the exact same setup, you focused another (respected?) brand of camera and found that there was a focusing error of...oh, say 15mm (I'm just pulling numbers out of the blue to illustrate the point) then, you would have something against which to compare the magnitude of the focus error allegedly introduced by the Chamonix Fresnel arrangement. In this case...the alleged fresnel focus error doesn't look too very significant.

I could compare it to a Speed graphic w/ and w/o the fresnel installed, but I don't know of any other cameras with a fresnel/ground glass combo I could test.

[BradS]

I could compare it to a Speed graphic w/ and w/o the fresnel installed, but I don't know of any other cameras with a fresnel/ground glass combo I could test.

I guess I was thinking of the control camera as being used only as intended. So for the Crown Graphic which came from the factory with a Fresnel, it would be focused with the Fresnel inplace. Any other camera could be used as the control...even one with no fresnel. The control would be focused and the focus error measured (include a ruler in the photo for example)? Not perfect by any means but, still, interesting. I have to go...maybe, more later.

[BradS]

ok, to elaborate a little bit.

Every camera has some focus error "built in". So, for example, if you focus on the model's eyebrow and she sits perfectly still, in the print you may see that the actual plane of focus was slightly in front of or behind where you focused.

It has been asserted that the Chamonix Fresnel lens introduces additional focus error. Remember even without the Fresnel, there is some focus error. The experiment you have proposed, I think, attempts to determine whether the alleged focus error introduced by the fresnel has real world significance(?). This is where the control comes in...it gives you (us) something to compare to (sloppy grammar...sorry, I'm rushing casue I have to catch the train).

[Jeremy Moore]

Okay, I get what you're steering towards, Brad. The problem here is having a control that is made to specific known standards and what is an acceptable focus error from this known standard. I can use a Cambo 4x5 camera that is used for high end large format art reproduction as a known "good" camera, but I do not have the equipment (i.e. digital calipers) to scientifically test the placement of the ground glass in relation to the plane of focus.

This still takes us further away from the simple stated goal of this experiment: to test for a focus shift caused by the fresnel being installed between lens and GG. If my tests do show a focus shift then we can investigate further tests and do more study to see how much of a focus shift is "acceptable".

[BradS]

This still takes us further away from the simple stated goal of this experiment: to test for a focus shift caused by the fresnel being installed between lens and GG. If my tests do show a focus shift then we can investigate further tests and do more study to see how much of a focus shift is "acceptable".

Yes, I think that is probably true....but...every good experiment raises more questions than it answers:) and this is a good experiment.


So, what is your hypothesis?

May I suggest that the hypothesis is that the fresnel lens does NOT introduce significant focus error (innocent until proven guilty). In this way your experiment can hope to find evidence to contradict this hypothesis. If it does, we have all learned something (as Darin B pointed out above).

[Steve Hamley]

May I suggest that the hypothesis is that the fresnel lens does NOT introduce significant focus error (innocent until proven guilty). In this way your experiment can hope to find evidence to contradict this hypothesis. If it does, we have all learned something (as Darin B pointed out above).

You may suggest that an additional lens inserted in the optical path between the image-forming surface and the taking lens doesn't introduce a (significant) focus shift, but the focus shift is there according to the laws of optics. If you don't "see" the focus shift, then it means your test is not sufficiently sensitive, or in practical terms, some other factor like focus error or depth of focus compensates for it.

And the hypothesis is contrary to several Chamonix users posted images and the manufacturer's posted information.

Cheers, Steve

[BradS]

You may suggest that an additional lens inserted in the optical path between the image-forming surface and the taking lens doesn't introduce a (significant) focus shift, but the focus shift is there according to the laws of optics. If you don't "see" the focus shift, then it means your test is not sufficiently sensitive, or in practical terms, some other factor like focus error or depth of focus compensates for it.

And the hypothesis is contrary to several Chamonix users posted images and the manufacturer's posted information.

Cheers, Steve

I am afraid you misunderstood what I wrote. I suggested a Hypothesis - not a violation of laws of physics.

This is how science works, when properly done. You start with a hypothesis which is consistent with the status-quo and conduct an experiment that will, hopefully supply evidence contrary to your hypothesis (supporting the alternative). The criminal justice system in the USA works this way too. However, in science, we often iterate, modify the hypothesis and do other experiments. Notice that in both cases, an experiment (or trial) which does not contradict the hypothesis is less informative, less powerful than one that does.




As an aside, I do not pretend to know how the results of the experiment will turn out...nor do I much care. I am encouraged that some of our numbers recognize the folly of investing too heavily in the opinions thrown casually about on internet fora and the value of careful independent testing. Finally, it is only mildly interesting to me that the Mfgr. has publicly admitted a design error...that fact does not detract from the value of independent experiment.

[stealthman_1]

I don't doubt the laws of optics, I doubt the real world issue. Besides, we're adding a 3rd lens when we look through a loupe to focus!
From a couple weeks ago...
Chamonix 45N-1 bought last fall (2008) All 100% crops of 1200dpi scans on an Epson V700 with Ilford Delta 100 film.
Schneider 90mm f5.6 @ 5'10"
http://farm3.static.flickr.com/2741/4154315743_2a9bd60f18_o.jpg

Schneider 90mm f5.6 @ 15' Note the focus problem is most likely caused by the film not being flat, which is one of the main focus issues in any view camera.
http://farm3.static.flickr.com/2700/4154325093_058f2487a0_o.jpg

Rodenstock 210mm f5.6 @ 5'10"
http://farm3.static.flickr.com/2799/4155077986_b068e0fd4e_o.jpg

Rodenstock 210mm f5.6 @ 15'
http://farm3.static.flickr.com/2743/4154316251_3ba39531fc_o.jpg
You judge.

[stealthman_1]

And for your artistic enjoyment, again, my beautiful Goerz Berlin, Doppel Anistigmat, 12 inch, f7.7:D
http://farm3.static.flickr.com/2456/4071217614_6f8c13373f_o.jpg

[Darin Boville]

>>And for your artistic enjoyment, again, my beautiful Goerz Berlin, Doppel Anistigmat, 12 inch, f7.7<<

Those old lenses sometimes don't even *look* like lenses.

--Darin

[vinny]

stealthman, we met at whitney portal last year.
Your shot with the 90mm doesn't show me much. The ruler should be at a much steeper angle for this type of test. As for the 210mm, that's not an issue since the problem is with short focal lengths. For what it's worth, my tests with my 90mm proved the need to remove the fresnel.


vinny

[Jeremy Moore]

Yes, I think that is probably true....but...every good experiment raises more questions than it answers:) and this is a good experiment.

And every good experimenter knows scope creep is the death knell of a good experiment. I want to keep this simple.



So, what is your hypothesis?

May I suggest that the hypothesis is that the fresnel lens does NOT introduce significant focus error (innocent until proven guilty). In this way your experiment can hope to find evidence to contradict this hypothesis. If it does, we have all learned something (as Darin B pointed out above).

From a scientific standpoint you're coming at this the wrong way as you go with proven theory until you falsify said theory and not the other way around. This isn't some test at the edges of science where we will rework the nature of optics, but a practical/real world experiment looking at focus shift.

Proven optical theory: a fresnel is a lens and will change the plane of focus. Fresnels have already been "proven guilty" of this so there's no reason to assume otherwise.

What we're testing is whether this shift is substantial enough to be detectable visually under the conditions I have set which are the same conditions in which the problem is said lie (wide angle lens wide open at a mid-distance). You can semantically state the hypothesis in the positive or the negative, but due to the nature of the experimental model I will have learned something--visually detectable focus shift or no visually detectable focus shift for these conditions.

[Larry Gebhardt]

What I think you are actually testing is whether the ground glass was set at the correct distance for A) use with a Fresnel in front, B) use without a fresnel in front of it, or C) some other distance.

[Jeremy Moore]

What I think you are actually testing is whether the ground glass was set at the correct distance for A) use with a Fresnel in front, B) use without a fresnel in front of it, or C) some other distance.

I'd been working off the assumption (may be an incorrect one, see below) that the GG was properly positioned at the film plane and the fresnel was added later.

I just went to Chamonix's website and the .pdf they have up states:


Based on this, I do not recommend that users of 45N-1 camera to change the position of the Fresnel lens as all cameras are tested for the accuracy of the Fresnel position before leaving our factory.

This won't change the basics of the test tomorrow--to test the amount of focus shift between with the fresnel between lens and GG and with no fresnel--but it is going to add a third test where I do not focus by eye, but by using the Betterlight's digital focus verification on a focus target: http://www.betterlight.com/viewFinder_FocusTab.html

This does come as a surprise to me, though, because if it's true then switching to an Ebony or Maxwell screen wouldn't fix the problem as the ground glass/fresnel combo would be positioned differently than the fresnel/ground glass combo factory installed on a Chamonix as the fresnel is recessed closer to the lens in a ledge at a different plane than the GG. By my understanding, an Ebony or Maxwell screen would rest on the same plane as the GG--NOT as the fresnel. Will someone with a Maxwell or Ebony screen please help illuminate this quandry.

[BradS]

From a scientific standpoint you're coming at this the wrong way as you go with proven theory until you falsify said theory and not the other way around. This isn't some test at the edges of science where we will rework the nature of optics, but a practical/real world experiment looking at focus shift.

Proven optical theory: a fresnel is a lens and will change the plane of focus. Fresnels have already been "proven guilty" of this so there's no reason to assume otherwise.

What we're testing is whether this shift is substantial enough to be detectable visually under the conditions I have set which are the same conditions in which the problem is said lie (wide angle lens wide open at a mid-distance). You can semantically state the hypothesis in the positive or the negative, but due to the nature of the experimental model I will have learned something--visually detectable focus shift or no visually detectable focus shift for these conditions.



OK. Have fun. I hope you find what you're looking for.

[kev curry]

Based on this thread (http://www.largeformatphotography.info/forum/showthread.php?t=56287) I'm going to be doing an actual test with film and a Chamonix 45N-1 camera this evening.

I will make 4 photographs. 2 with a 90mm lens and 2 with a 135mm lens.

The camera will be firmly mounted to a Majestic Tripod with 6" bed indoors and focused on a fixed subject 10-15 feet away.

I will make 1 photograph to the best of my ability with a 90mm f/5.6 Super Angulon at f/5.6. I will then remove the fresnel, refocus my camera if need be due to the fresnel being removed, and make another photograph at f/5.6.

I will then repeat this process using a 135mm f/5.6 Symmar-S.

I will light these photographs with flash and use a shutter speed of at least 1/125th of a second to avoid motion blur. I will shoot Ilford FP4+ and develop it in Pyrocat HD using a 2-bath development in a Jobo 3010 with 6 other sheets I need to develop. I will scan the resultant images and post them back to this thread.

Anyone that may have an issue with how this test is conducted and nitpick it later are given the opportunity--RIGHT NOW--to make suggestions on the testing procedure.

Jeremy, did you ever find time for the tests?

[Jeremy Moore]

Jeremy, did you ever find time for the tests?

Kev, had a concussion that has me all thrown off right now. I do have 2 Chamonix cameras sitting at my desk right now so if my headache is manageable this evening I'll do the testing tonight.

[David Karp]

Jeremy,

Feel better. Take care of that brain of yours.

[Steve Hamley]

Jeremy,

Feel better. Take care of that brain of yours.

Jeremy,

Dr. Steve recommends you stop reading the Chamonix threads and your headache will be much better. :D

Cheers, Steve

[kev curry]

Kev, had a concussion that has me all thrown off right now. I do have 2 Chamonix cameras sitting at my desk right now so if my headache is manageable this evening I'll do the testing tonight.

Sh*t sorry to hear that Jeremy....hope its mild? Sod the tests, give your brain some time out:)

Eazy does it!

[Robert A. Zeichner]

If you haven't done your test yet, a stepped target is a pretty good way to compare states of focus within one piece of film. I created one for my article on ground glass alignment back in 1996 using some foamcore and 5 sequential un-circulated dollar bills. With each bill offset by an inch from the next, you can focus on the center bill and observe the relative sharpness of the bill in front and behind. The one behind will be the next sharpest part of the target with the bill in front being the third sharpest. After development of the film, you can compare the resulting negative with the original if you leave the camera set up. I will be happy to email my article to you with photos of the set up.

[lenicolas]

jeremy, how are you doing?
has the test not happened yet because of further complications with your concussion?
you got us worried!