Focusing idea Chamonix 45N-1 [Archive] - Large Format Photography Forum

Jfnphotography

7-Oct-2009, 06:56

Have a fall colors trip next week. This will be the first big test of my new camera. Want to use my 90mm lens for the trip. Don’t want to remove the fresnel lens that’s one of the reasons I purchased the camera. I have read some of the other suggestions. Here is my idea.

Seen another e-mail that said

But did note the false focal point at about 25 feet (fresnel in place between gg & lens). This then focused about 30% closer with the fresnel removed (about 17 feet).

So I measured out 25ft from the camera and focused on something. I then put an object 17 feet away and focused on that. I found that the rail moved 2mm back wards to focus at 17ft. (fresnel in place between gg & lens)

I than made a line on the focusing knob and found that the different from 25ft to 17ft is ¼ turn counter clock wise.

If I’m taking a photograph with no camera movement and focus on something like a fence at 25ft then move the focus knob ¼ turn counter clock wise would I be in focus?

Could I use some movement if things were at a distance from the camera? I think any thing close would be out of focus from moving the rail.

It would be a pain to do this for every photograph. I would still need to remove the fresnel to test my idea out. I think I’m going to see if I can order a back with just ground glass, so I can switch them out when I use my 90mm.

BarryS

7-Oct-2009, 07:14

I suggest you test your camera before go on your trip. My 45N-1 focuses correctly. I can tell because I shoot a lot with fast Petzval lenses wide open and the negatives are sharp at my focus point.

Lachlan 717

7-Oct-2009, 14:26

You could drill a hole in the centre of the Freznel (10-12mm should suffice). That way, you can use a loupe to check the brightest part of the GG to corroborate the Freznel focus.

This, of course, will not be of much use if you're swinging/tilting/shifting as it will only show the middle of the shot to be in focus...

Lachlan.

Robert A. Zeichner

7-Oct-2009, 15:31

Jacob, the designers of any camera that was meant to be used with a Fresnel between the GG and the lens should have taken that fact into account when arriving at the plane for the frosted side of that GG. From all that I have read on this forum, this is not the case with the Chamonix unless this has changed very recently. That said, I would test the camera very carefully. I would do this with and without the Fresnel installed at distance of less than 6 feet and with a lens fully open at f 5.6 and compare your results. I'm guessing that you will see a very noticeable difference. Be aware that with shorter lenses, ground glass/film plane coincidence is even more critical. I'll email my article on this topic to you as it may be of help.

jb7

7-Oct-2009, 15:45

That seems like a big problem with that camera-
I'm quite surprised that people seem to be willing to work around it-

If the correct plane of focus is on the gg without a fresnel, then surely removing the fresnel is the only way to work?
That, or replacing the gg on the outside of the camera...

GPS

8-Oct-2009, 02:10

Absolutely amazing! Chamonix is probably the only modern camera manufacturer producing some cameras that cannot be focused properly! Now, when it is known in amateur circles, I wonder how long it will take for them to correct the problem or if they will persevere with their explication (published in a different post) that it doesn't matter as pictures are usually taken at smaller apertures than they are being focused at! Amazingly brazen stupidity!

eddie

8-Oct-2009, 03:13

mine works fine......hhhhmmmm

Larry Gebhardt

8-Oct-2009, 06:47

Mine works fine as well. I tested it at close distances wide open with some old Polaroid film. Focus seemed dead on.

This is the first I have heard of this issue. Do you have any more info on this issue?

Darin Boville

8-Oct-2009, 09:28

Mine is fine as well. I posted my Polaroid in the other thread.

--Darin

Darin Boville

8-Oct-2009, 09:30

Just another thought...

Why don't the people who bought the bad ones list when they bought the unit and which dealer they bought it from--it may turn out to be a bad batch vs an ongoing quality control issue.

--Darin

Jfnphotography

8-Oct-2009, 10:04

The people that have Chamonix that work fine, what lens are you using. From my understanding the problem is with 90mm lens, wide open. I did some test today hope to process the film tonight.
Jacob

Larry Gebhardt

8-Oct-2009, 10:46

I tested mine with a 210mm lens from several feet away from a ruler. I did this because the longer lens should show focus errors better than a short one.

I have used my 90mm in the field and have not seen any issues, but it was stopped down. I have a few sheets of gunky polaroid left. I'll try the 90mm tonight.

BarryS

8-Oct-2009, 10:58

The people that have Chamonix that work fine, what lens are you using. From my understanding the problem is with 90mm lens, wide open. I did some test today hope to process the film tonight.
Jacob

I'm using a variety of lenses, including a 90mm Nikkor SW f/8 at f/11 and f/16. The negatives from shots with the 90mm are very sharp. I'd think any focus shift would be more noticeable with longer lenses at large apertures--because of the small depth of field. I went back and looked at a lot of my Petzval shots (many with a 120mm lens @ f/3.2) and the focus looks right on the mark where I focused. I'll see if I can shoot a precious Polaroid or a slightly-less-precious sheet of TMX of an angled rule to check the focus. Maybe I'm consistently misfocusing and the camera is correcting. :)

Edit: Something I wondered about was the fact the smooth side of the fresnel is in direct contact with the ground side of the glass. From my reading of Stroebel, I understood that the fresnel surface should be against the ground side of the glass. Maybe I'm mixed up, but I wonder if that's a factor in this issue?

GPS

8-Oct-2009, 11:01

Guys, the focusing error is a well known reality, known to the Chamonix designer and owner. Search for the "focusing error" thread...

Larry Gebhardt

8-Oct-2009, 13:32

I'm leaving on a trip in a few days, so the thought of a focusing error with some lenses concerns me. I just used 3 of my last 4 sheets of type 54 polaroid to test with the 90 f/6.8 Caltar (Rodentock I believe). The first test sheet was inconclusive because of the large depth of field. The second setup I put the camera at a very shallow angle and focused on the 32cm mark. The Polaroid shows perfect focus on the 32 mark, and the 31 and 33 are both very blurry. So in this setup the focus is right on.

Now I question if the problem could be masked because of the large bellows extension, effectively making the lens work more like a longer lens. I'm not sure how to test critical focus at non macro distances with wide angle lenses.

However it doesn't look like this is a design flaw with my Chamonix. Looking at the relatively few sheets of film I have put through the camera (less than 100), and these tests I am confident I don't have a major problem.

The camera I have is #0295. I bought it used, so I don't know the original purchase date.

Jfnphotography

8-Oct-2009, 18:54

Tested my Rodenstock 180mm at f5.6 and it was sharp. Tested my Fuji 90mm at f45 and it was good. Tested the 90mm at f8 it looked a little soft so I'm going to test it again. My camera is 865.
Jacob

Clement Apffel

12-Oct-2009, 04:27

My 45N1 is number 293.
From the second batch I think.

I noticed the focus problem like 5 months ago.
I was doing wide open portraits with a f/4.5 150mm.

Before that, I never experienced focus errors with standard use of my lenses :
65, 90 and 150mm. My standard use is landscape and architecture at f/16 or f/22 mostly.

When I noticed the problem on those portraits, I immediately made my own test on the fresnel. (i.e. same shot with and without the fresnel lens)
My conclusion was that the fresnel was causing the focus shift.
I instantly removed it and I used my camera without it from this point.

I don't miss it at all.
The fresnel was for me a bonus gimmick anyway.

GPS

12-Oct-2009, 05:44

My 45N1 is number 293.
From the second batch I think.

I noticed the focus problem like 5 months ago.
...
My conclusion was that the fresnel was causing the focus shift.
I instantly removed it and I used my camera without it from this point.

I don't miss it at all.
The fresnel was for me a bonus gimmick anyway.

Well done, Clement! Wouldn't it be honest and useful if the Chinese manufacturer of this Chamonix camera had at least the common sense if not honesty to put a note on the camera saying - "User beware! This camera has an inbuilt focusing error well visible at open apertures. Remove the fresnell lens if you need proper focusing"..?

Clement Apffel

12-Oct-2009, 06:08

Wouldn't it be honest and useful if the Chinese manufacturer of this Chamonix camera had at least the common sense if not honesty to put a note on the camera saying - "User beware! This camera has an inbuilt focusing error well visible at open apertures. Remove the fresnell lens if you need proper focusing"..?

Maybe.

Actually (and please understand that by that I mean no offence) I kinda don't care.
I don't feel scammed. I just fixed an issue of my camera by removing an item that I didn't have so much use anyway.

The camera is still worth the bucks. At least to me.
And I'm not the raise-a-scandal kind of guy.

But yeah, I guess you are right. They should notify it to current user of the affected batches.
And they should work on a solution to fix the issue.

That said, I’m not aware of their reaction to all this. I mean I don’t read the “Large format scandal sheets”. ;-)

GPS

12-Oct-2009, 07:49

I understand you, after all, I don't read those sheets either...;-). I just think that the LF community should be well aware of the Chinese Chamonix camera manufacturer's reaction when he realized that users now know about this inbuilt focusing error (something along the line - "it doesn't matter because the pictures are taken at small apertures anyway so the error is lost...") As I said, it's this brazen stupidity that is the cherry on the top of the cream... ;-)
And no, it's not a question of some affected batches -it's a question of the construction itself. Incredible as it is from the technical point of view and incredible from the ethical point of view. As if milling the wooden frame correctly for the fresnell were more difficult than milling it correctly just for the gg alone!

Brian Ellis

12-Oct-2009, 07:57

I second Barry's suggestion. I didn't use my Chamonix very much but when I did there were no problems with the focus. IIRC mine came from the second batch that was made.

mandoman7

13-Oct-2009, 07:30

After reading this and the other threads about this issue, I took some measurements on my 45n-1 (built earlier this year). Like most others I've been quite happy with its use and haven't noticed a focus problem in the negatives. But I had an Arca Swiss that had the fresnel mounted incorrectly which I did a lot of work with before I realized the problem and wanted to avoid that frustration.

First I took readings off a holder and got 0.19" of depth from the surface of the holder to the back edge where the film lays, the industry standard, roughly.
Then measuring the wood only that holds the gg and fresnel and I got a width of 0.12", with a width of .006" measured for the thickness of the fresnel lens by itself.
So with the gg on the outside, set with the rough edge facing the fresnel, the surface of the rough edge of the gg is quite close to where the film will lay when inserted.

However, the fresnel was positioned with the rough surface away from the gg however (at the factory), and I don't think that is the right arrangement (in effect providing 2 different focussing surfaces?). I don't really know but my intuition suggests that putting the 2 rough surfaces together where they sit at 0.18" might be all that needs to be changed. A simple reversal of the direction of the fresnel so that both focussing surfaces are at the prescibed depth.

I'll be testing later today with a sharp lens that supposed to be arriving...

Clement Apffel

13-Oct-2009, 07:51

I'm confused.
Did your 45n-1 suffer from the focus shift ?
Or did you only experienced that on the arca ?

Anyway, I'll stay tuned for your tests results.

Stefan Geysen

14-Oct-2009, 03:47

There's an announcement about the problem on the Chamonix website:
http://www.chamonixviewcamera.com/Announcement.html

Clement Apffel

14-Oct-2009, 09:06

yeah, actually, I didn't mention it cause I forgot about it. but I remember reading this announcement quite some time ago.
Something like a month or 2 after I removed my own fresnel.
Early July IIRC.

GPS

14-Oct-2009, 11:03

Unfortunately, the announcement is not complete. It seems that Chamonix cameras in all formats that use the gg+fresnell combination suffer from the same focus error - so it has been reported on this LF forum. If Hugo announces the bad news on the site only to the 45n-1 users what about all those that buy the other formats cameras??

Darin Boville

14-Oct-2009, 11:34

Some people are seeing errors, others aren't. But we are all using different testing methods.

Could someone who is seeing a focus error detail a testing procedure that reveals the problem--so we can all use the same test method?

--Darin

Steve Hamley

14-Oct-2009, 12:19

Why not just measure - it's a standard number? That's what the factory does. That eliminates any testing method error.

I assume that's what Chamonix did before making this announcement:

http://www.chamonixviewcamera.com/Announcement.html

BTW, Richard Ritter and a few other folks will measure the T-distance and adjust the screen as needed.

Cheers, Steve

GPS

14-Oct-2009, 12:50

Steve Hamley

14-Oct-2009, 14:51

O.K. I’ll take a stab at it.

First of all you need the “thickness" of the camera’s GG frame. I measured mine as shown in the attached jpeg. It was 0.192” (average) and that’s where the image forming surface of my GG is. The spec for holders is 0.1875 or 0.188 rounded.

Then I measured a Riteway Holder see jpeg #2. I measured the total thickness being sure not to be in any grooved surface, then the platen thickness – you’ll need a witness mark on the knob if you use external calipers like I did, otherwise you can’t get them off. Subtract one from the other and divide by 2 (there are 2 sides). I got 0.189, so the platen is within 0.003 of the image forming surface of the GG.

Now assuming I had a non-image forming Fresnel in front of the GG and the Fresnel is 0.62” thick and the Fresnel shifts focus by 1/3 of the distance (about 0.020), then the frame needs to be 0.169 for the Riteway’s platen to be where the image forming surface behind the fresnel is. (0.189 – 0.020).

Someone check the math please. Comments?

Cheers, Steve

GPS

14-Oct-2009, 15:08

O.K. I’ll take a stab at it.

....

Now assuming I had a non-image forming Fresnel in front of the GG and the Fresnel is 0.62” thick and the Fresnel shifts focus by 1/3 of the distance (about 0.020), then the frame needs to be 0.169 for the Riteway’s platen to be where the image forming surface behind the fresnel is. (0.189 – 0.020).

Someone check the math please. Comments?

Cheers, Steve

If I get it correctly, 1/3 of 0.62" is not 0.020...
But this is not how they do it in a factory. The fresnell combination must be measured optically to take into account the mechanical + optical combination of factors. That's probably the reason (my guess) why the Chamonix manufacturer wanted to cut the corner and made no correction at all for their gg/fresnell combo. Easier than the optical measuring, isn't it...

Steve Hamley

14-Oct-2009, 15:20

Darin Boville

14-Oct-2009, 15:23

Wouldn't Polaroids get to the point more directly? :)

--Darin

GPS

14-Oct-2009, 15:30

Actually I said "about 0.020", and the 1/3 figure came from Ron Wisner's old site which I believe is no longer up. But either way the point is that if there's a fresnel in front of the image forming GG, it makes a considerable difference in how deep the GG frame needs to be.

Cheers, Steve

Actually your "about" is 10x less than the correct 1/3...;)
The 1/3 figure is valid for a flat piece of glass which is not the case of a fresnell lens (flat +grooves in its profile).
There is no doubt that a fresnel in front of the gg makes a considerable difference in the gg correct placement - that's what the whole thread is about, isn't it...:)

Steve Hamley

14-Oct-2009, 15:53

Ah yes, that's why I asked for a math check... :D But what's a factor of ten among friends? Thanks GPS!

But there's a few things we can conclude from the math. One is that if your GG frame is 0.187 or 0.188 deep, the platen of a spec-made film holder is going to be very close to the image forming surface of a regular GG, an Ebony or Ebony-type Maxwell fresnel with the frosted side facing the lens.

Which also suggests fixes as Chamonix suggests; you need the image forming surface against the GG frame.

Can someone measure their Chamonix frame just for info?

The place you HAVE to start is determining if everything is in the place it's supposed to be according to the design criteria. I think film is not a good test because there are a lot of variables to be controlled depending on the photographer and camera. Ones that come to mind is how good the photographer's eyes are (the third lens in the system), how accurate your eyeglasses are (if you have them, the 4th lens in the system) how your loupe is adjusted or made (the 5th lens in the system), how accurately the camera holds focus when locked, the lens focal length, play in the standards, the slop in the film holder hold-down rails, film base thickness, and so on.

A friend had some holders made for an older format, observed focus issues, and he measured the T-distance to be off, and compensated by calibrating the focusing knob. But he measured to determine what he needed to do and how much to compensate for and in what direction based on the rack and pinon focusing gears. If you don't measure, you don't know how to compensate or by how much.

But he eventually sold the holders because it was a lot of trouble and stuff not made to specification is just plain irritating as evidenced by this thread as GPS noted.

Cheers, Steve

Actually your "about" is 10x less than the correct 1/3...;)
The 1/3 figure is valid for a flat piece of glass which is not the case of a fresnell lens (flat +grooves in its profile).
There is no doubt that a fresnel in front of the gg makes a considerable difference in the gg correct placement - that's what the whole thread is about, isn't it...:)

GPS

14-Oct-2009, 16:07

Ah yes, that's why I asked for a math check... :D But what's a factor of ten among friends? Thanks GPS!

...Cheers, Steve
I wholeheartedly agree...:D

jb7

14-Oct-2009, 16:23

A friend had some holders made for an older format, observed focus issues, and he measured the T-distance to be off, and compensated by calibrating the focusing knob.

I suppose that'd be acceptable if you always worked at the same magnification,
landscapes for example-

As magnification increases, so does focus spread-
if the calibration on the focus knob is significant at landscape distances,
it'll be literally off the scale at head and shoulder distances-

Steve Hamley

14-Oct-2009, 17:28

mandoman7

14-Oct-2009, 18:26

I'm confused.
Did your 45n-1 suffer from the focus shift ?
Or did you only experienced that on the arca ?

Anyway, I'll stay tuned for your tests results.

I got my Arca used and was shooting a lot of paintings for artists (10 yrs ago) and knew that I had checked all the corners with the loupe but was finding discrepancies in the transparencies. I took measurements like we've been describing and found that the depth of the ground glass was .05" or so less than the depth of my average holder. So inserting a a fresnel solved that problem, and I sandwiched them with the rough edges together.

So I've had a chance to look at the negatives that were shot with my fresnel reversed in my 45n-1 and they look fine. I was using a 120mm that needed testing, not the 90 that seems to be where people are having problems. My tests were not clinical, just several different shots with the loupe used to note the point where the focus should be.

I'm not clear on the focus shift that some are saying is produced by the fresnel. If that's the case then simply turning it around wouldn't help, of course. But it doesn't seem right to me that the fresnel's rough side would be away from the gg's rough side, as factory installed, and my initial tests seem to agree. I'm not one who noticed a problem I should mention, although I've shot many 90mm negatives. Usually stopped down though. I'm only acting after having read these threads :rolleyes:

My point in bringing up the Arca experience though was to say that I've had past experience with realizing that my focus was off after having shot a lot of film with it. Who needs another variable like that?

jb7

15-Oct-2009, 01:58

jb7,

Actually no. All he did after noticing focus aberrations was to measure the T-distance difference between the original vintage holders and the new ones, and calibrate the focus knob to compensate.

So he focused on the GG of the reference (vintage) camera at whatever magnification, then inserted the "new" holder and turned the focus knob so that the film plane was in the same position as the reference holder.

So it was just like using a reference holder; the difference in holders is the same regardless of magnification.

Cheers, Steve

Well Steve, it obviously works for him, so that's fine-
However, he'll also be augmenting that by doing other sensible things, such as stopping down...

As has been mentioned earlier in the context of the original post, it's another unwanted variable-

I still reckon that the focus adjustment is not linear,
that the compensation required at infinity is not the same as the compensation required close up, for critical focus,
though perhaps somebody could convince me that I'm wrong, using math...

GPS

15-Oct-2009, 02:38

jb7,

Actually no. All he did after noticing focus aberrations was to measure the T-distance difference between the original vintage holders and the new ones, and calibrate the focus knob to compensate.

So he focused on the GG of the reference (vintage) camera at whatever magnification, then inserted the "new" holder and turned the focus knob so that the film plane was in the same position as the reference holder.

So it was just like using a reference holder; the difference in holders is the same regardless of magnification.

Cheers, Steve

Steve, what jb7 meant (correct me if I'm wrong) was the difference in close up photography between focusing by moving the back standard or the front standard. In one case you don't change the lens to subject distance and the other you do. That change is not significant if focused at infinity but is relatively more significant in close up photography. If I understood both you, not sure...