Chamonix 45N-1 Testing Procedure

[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?

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+...ient=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!"

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).