4 x 5 focus problem

[Pere Casals]

The nodal point is usually close to the diaphragm regardless of the lens board position, and telephoto lenses can have it not a bit, but far in front of the first (front) element.
.

First is that there is not a single Nodal Point in a real glass, but two, but this is not much significative for that calculation as it is related to a 3000mm magnitude for the case, and distance D and bellows' draw B resists a measuring error of 10mm. This may affect the calculated correction of 1/20 mm that cannot anyway be fine adjusted with the standard's gearing.

For the Tele points displacement, I'm not sure how the formula must be applied, yes ...Fuji 300T needs only 195mm at infinity, so a 105mm displacement is there...

[Pere Casals]

If the Shen Hao was originally provided with a correctly installed Fresnel between the ground glass and frame, and the Fresnel has been removed, the ground glass will be displaced forward by about 2/3 the thickness of the Fresnel due to the index of refraction.

This would be possible, but it looks that Shen Hao fresnel are after market, 3rd party, to be placed in the exterior. So it would be rare...

[DrTang]

is it in the neg ?

maybe the scanning is the problem

[LotusEsp]

I took some measurements with the lens out. From the ground glass to the lens board, and then the same measurement with a burnt negative in a holder. The film is 2mm further back from the lens than the ground glass.

could this be the source of my problems?

[Pere Casals]

I took some measurements with the lens out. From the ground glass to the lens board, and then the same measurement with a burnt negative in a holder. The film is 2mm further back from the lens than the ground glass.

could this be the source of my problems?

It is, I think it's a lot, but effect depends on the lens focal and the selected aperture.

Easy to know...

Take the loupe and fine adjust focus to your subject's eyes, then move the back 2mm away and see what happens.

For the moment (until you solve it) you can focus as always and once you place el film holder you have to move the "camera rear" excactly 2mm, that's to place the film where the GG was when you were focussing.

These 2 mm cannot be a manufacturing error, may be a fresnel was between glass and wood frame.

Just make a 2mm frame that fits in the wood frame with a 4x5 square hole inside, this will move the ground glass to the same plane the film lays, and solved, check again. (you can also glue 4 wood strips on the original wood frame (2mm thick) to make that spacer frame)

The other thing you can do is to place a fresnel, in the middle, but it should match the thikness and the optic effect... So to nail the solution just make that 2mm thick frame. If you later want a fresnel place it in the outside, it works nearly the same in practice, and no complication.


And, again, to check the solution, take that shot of the metering tape on the floor to be sure, film vs GG matching is critical, too many things can go wrong in LF, so not being sure about film/GG matching is not an option.

[R.K]

Simon,
It is hard to believe that you got a camera with manufacturer defect.
For you information. The Shen –Hao cameras designed the way that the Fresnel lens, if it is made for those cameras shall be installed below the ground glass with the grooved side facing the ground glass. With Shen-Hao cameras the ground glass will not be shifted from its original position no matter the Fresnel installed or not (of course if it is a Fresnel made for this camera). If you like to have a bit more information on the subject see this two treads:
http://www.largeformatphotography.in...esnel-Question

http://www.apug.org/forum/index.php?...l-lens.102276/

The size of the 4x5 Shen-Hao ground glass shall be about 101mm x 127.5mm or very close to this, let say 100mm x 126mm. if you ground glass not original and having at list one dimension about 5mm smaller that the problem. In that situation ground glass may slip deeper in to the wooden frame and take a place what manufacturer originally allocate for the Fresnel lens. And as a result the ground glass will be on about 2mm closer to the lensboard then the film. But if ground glass original, I can’t imagine that it may happens.

Another famous deferens between Shan-Hao and other cameras is a very strong springs. It takes a much more effort to shift the film holder in place on the Shen-Hao then on any other cameras I used. So check it again if you pushing the film holder in its place in full. On the Shen-Hao you will hear the click when the folder will get in place.

[Bill_1856]

I took some measurements with the lens out. From the ground glass to the lens board, and then the same measurement with a burnt negative in a holder. The film is 2mm further back from the lens than the ground glass.

could this be the source of my problems?

Probably yes. It would have my my first thought.

[rdenney]

Loupes should not even be necessary except in very low light or with a really slow lens.

You must either be young or near-sighted.

I use a 6x tilting loupe made by Seagull, I think. It is focusable and it's easy to focus it on the ground surface of the ground glass.

Without loupe, even with trifocals, I can't get close enough to ground glass to focus the lens.

Rick "neither young nor near-sighted" Denney

[Jac@stafford.net]

Speaking to brouwerkent: You must either be young or near-sighted. [...]

Oh, I'm so glad that you wrote that. I'll be several of us had the same thought. Good for brouwerkent.

To add something, as a tri-focal guy, I'm thinking of experimenting with one of those loupes that swings down from my glasses frame, over the dominant eye. My optometrist is willing to work with me, but gads he's expensive. I suspect he's a Leica junkie.

Has anyone tried such a thing?

[rdenney]

I tried it but the dark cloth and the camera kept bumping them and pushing them out of alignment. I've stopped using them for my clock and watch hobby, too, except casually, in favor of proper eye loupes, like these:



But eye loupes tend to fog up in steamy conditions.

Rick "resigned to having to remove his glasses to focus" Denney