Chamonix camera 45N-1 focusing error

[Peter K]

But at some point you have to see that this precision is not achieved on any view cameras available today. why ? because we do not need such a precision.

How do you know this? Or is it only a guess to help to ignore that not all cameras have the precision a LF-camera needs. Possible not needed by you. But if a camera will be used as a tool for taking high-quality images, measuring, photogrammetry etc. and not only for leisure.

BTW the tolerances shown here are for filmholders. For cameras the tolerances must be much smaller as mentioned by others before too.

And why discuss in e. g. the lens section of this forum resolution-power, MTF-curves of lenses etc. if this lenses will be used with misaglined cameras?

[Clement Apffel]

Just saying that the absolute 0 alignment is not very important for general use.
And that viewcamera factories do not aim this absolute 0 for GG alignment. it is not rocketery science.
Of course if you throw in microphotography or photogrammetry or any other scientific application of photography, you'll need precision accordingly to the exigencies of experience.

But that is not what we are talking about here, sorry.

I'm just saying that measuring the GG alignment with laser is totally overkill for general use.
My standards of sharpness are very demanding for my prints, believe me. And those are fulfilled by both of my misaligned cameras: therefore they are in my standards.
Just sharing this opinion to balance the over-measuring previous posters.

Apply the precision you REALLY need. That’s the bottom line.

I was reacting to some previous poster who started to worry about their GG alignment reading all this thread without having themselves noticed a sharpness issue on their prints.

Regards,

[Marko]

How do you know this? Or is it only a guess to help to ignore that not all cameras have the precision a LF-camera needs. Possible not needed by you. But if a camera will be used as a tool for taking high-quality images, measuring, photogrammetry etc. and not only for leisure.

BTW the tolerances shown here are for filmholders. For cameras the tolerances must be much smaller as mentioned by others before too.

And why discuss in e. g. the lens section of this forum resolution-power, MTF-curves of lenses etc. if this lenses will be used with misaglined cameras?

Peter, I don't want to sound argumentative, but I don't think any wood field camera could ever be used as a tool for taking the type of high precision images you are mentioning. And we are not even talking about the likes of Ebony but a cheap(er) wood field camera here.

While you are certainly right in the technical sense, most of these cameras will have bigger slop in the movements than the precision required for the back. I think that's what Clement is trying to say and I think that he also has it right in practice and within the scope of this discussion.

On a general note, I will agree with some other posters - this has been a great thread for learning. I will particularly remember it whenever someone mentions pixel-peeping.

[Peter K]

And that viewcamera factories do not aim this absolute 0 for GG alignment. it is not rocketery science.

Again, how do you know? Of course that the maker of the camera in question doesn't care about could be the impression if one reads not only this thread.

Apply the precision you REALLY need. That’s the bottom line.

But what happens if the standards are not parellel if wanted, the gg is misaligned, the filmholder takes not the position of the gg-holder and the film itself lacks of flatness? You will always get unsharp pictures because after Murphy's law, tolerances will always cast up in the wrong direction.

Peter K

[Clement Apffel]

What I mean with "absolute 0 for GG alignment" is nanometric alignment, theoretically perfect alignment.
Absolute alignment in a word.
Do you really think viewcamera makers aim that precision?
Do you realise the cost of production this precision would involve?

Concerning the second point, again, you misunderstood what I mean.
“Apply the real precision you need” doesn’t mean: do not care about precision.

I know the misalignment of my holder / GG device to all 4 corners and center and its rough value, the direction of the potential derivation due to film not being flat.
And knowing all this, accordingly to some basic optics calculations and to some field tests under my condition of use, I know and I see that I am currently under my IQ standards:

I apply the precision I really need.

regards,
CA

[kev curry]

Well it does get you thinking and learning. So I just done the test outlined in the book ''Way Beyond Monochrome'' to determine if the gg and film plane are in proper alignment. The test was pretty simple and doesnt require special equipment.

Its done with a ruler a toothpick and a bulldog clip.

1. Take the back off the camera and load it with a film holder with the dark slide removed. The holder must have a sheet of film in the holder.

2. Lay the back of the camera flat on a table so that the inside of the holder containing the film is facing you.

3.Place the ruler on its edge across the holder . Place the toothpick vertically against the ruler (180*) and lower it until it makes contact with the film, then clamp it in place with the bulldog clip. This identifies the film plane location.

''After doing this with all film holders (both sides) leave the toothpick positioned for an average holder''.
(4).''Now remove any film holder from the camera back, and compare the average film plane with the ground glass location (see 2nd photo). If the toothpick just touches the gg, then no adjustments are required. Knowing that a sheet of regular writing paper is about 0.1mm/0.004'' thick provides a tool to quantify any offsets. If the toothpick touches before the ruler, then you could shim the gg with paper, but if there is an unacceptably large gap between toothpick and gg then professional machining of the camera back is required.'' (W.B.M)

Btw... this was with (my) gg changed to nearest the lens with fresnel on the viewers side. My gg needs a little shimming!... maybe the equivalent of 3 layers of writing paper. But its a vast improvement over the factory configured placement of the gg/fresnel combination!


Who's gonna be first to fry me for copy-write infringement

[Darin Boville]

I apply the precision I really need.

Indeed. Some of these tolerances bandied about are down in the thousandths of an inch, sometimes smaller.

Are we still talking about lightweight, wooden field cameras?

It would seem that a light wind would deform the camera alignment enough to swamp standards such as these. It would seem the pressure of the loupe against the ground glass would negate much of this precision. I never realized that my little 4x5 was such a fragile instrument!

In any event, those who favor measurement over experimentation have not uttered a word about magnitude or significance, or whatever term is preferred. There will always be error--but how much is too much?

Me? I'm still waiting for images (very few have been posted despite the fervor with which this topic has been debated). Perhaps we should move the discussion to dpreview in the interim?

--Darin

[Bob Salomon]

Now for the next problem, film isn't flat (digital sensors are) film sags. So how would you compensate for the average sagging of a sheet of film in the film holder under all conditions? Camera level, camera vertical, high humidity and heat, freezing cold, etc?

Just before Kodak introduced their first film holder for their original instant film they contacted us, as the Linhof distributor, as well as all of the then current USA view camera suppliers or manufacturers. Kodak's engineers wanted to know the film position settings of the different companies while they developed their holder. Some of you might remember that the original holder had problems maintaining sharpness in different cameras.

We contacted the factory and, like the other companies, supplied Kodak with the specifications. After a few months the Kodak engineers came back to us after they finished their project with some of the results. Of all of the cameras available at that time only two had a "0" position ground glass per Kodak's specifications. Neither was Linhof or Sinar. But the film holder made from these "0" specs would not supply optimal sharpness as film sags and the film sag was not factored into the holder. So it was re-designed.

The proof of the concept is that film is sharp where it is focused on, especially on an inclined plane. What is especially critical is that the film is positioned within the depth of focus of the lens and the more accurately this is done the better the overall sharrpness will be and as shorter lenses have less depth of focus the more critical this positioning becomes for people using shorter then normal lenses. So the average film sag most lie within the depth of focus of the shortest lenses you will use and the gg position has to be placed accordingly.

[Mike1234]

Ahh jeez... now we've gotta make vacuum backs to keep the film flat. Hey, Sandy!!! Wanna do the prototype??

[Steve Hamley]

Interesting Bob, thank you for posting. What is the average film sag, say for standard 7 mil film like Tri-X?

If one is checking backs, then the GG would need to be further than the "ideally flat" emulsion by the film sag if I understand your post correctly.

I'd also assume that sag is very small in 4x5 with relatively stiff 7-mil film, and more in larger formats since we all know the dangers of pointing ULF downward!

Cheers, Steve