7x9in Pinhole camera test

[marciofs]

It seems the borders wasn't exposed. Could it be because it is too wide? Or maybe too short exposure?

It has 0.350mm Pinhole Diameter and 88mm focal length.

 

[Dave Wooten]

The image is not evenly circular? Look for an "obstruction"
Burr etc at the bottom and around lens. ?

 

[marciofs]

I got it! I seems to be the tape around the hole. I think because it is so wide angle that the tape is blocking the borders.

I Just gave more room and I am doing a last test today because the sun is going away (30min. exposure ouside).

I show the result later on tonight.

 

[DWThomas]

As you get into really wide angles, it's amazing how many bits of mechanics can obstruct the light path. A pinhole is strictly a ray tracing situation, there is no retrofocus or other tricks like might be done with lenses.

In another thread, one about converting a Brownie camera to a pinhole, I (there was a url link here which no longer exists) of how one might do a scale layout to determine what will or won't vignette. It was tailored to a 6x6 format, but the method could be adapted to any situation. The biggest problem is making accurate measurements if there is a an aperture at the bottom of a hole or some other stuff in the way of using normal measuring tools.

 

[marciofs]

Thank you DWThomas,

I made the tape wide but it didn't changed much. I will check Thomas link:

 

[Joe VanCleave]

Another useful way to test a camera's angle of view for vignetting is to use a red laser pointer, aimed into the pinhole from outside the camera. You should be able to project the laser all the way into the corners of the image area at the film plane.

~Joe

 

[NormanV]

It is not vignetting due to an obstruction it is because the distance from the pinhole to the film surface is greater at the edges than from the pinhole to the centre and the edges are underexposed. If you curved the film plane or made a centre filter you could reduce the problem. Or it could be done with careful dodging when printing.

 

[DWThomas]

It is not vignetting due to an obstruction it is because the distance from the pinhole to the film surface is greater at the edges than from the pinhole to the centre and the edges are underexposed. If you curved the film plane or made a centre filter you could reduce the problem. Or it could be done with careful dodging when printing.

Enh, it's true there is noticeable fall-off at wide angles off-axis, but to my eyes the images above show shadows of an irregular "edge" of some sort. The situation you're describing is more subtle and graduated (in my experience).

 

[Jim Jones]

The soft edges of the image circle and the non-circular shape suggest a pinhole with the edges too thick. The dimple, punch, and sand method usually does a good job of thinning this edge. Also, there will be several stops less exposure at the corners of a pinhole image with such a wide angle.

 

[marciofs]

There was a tape near the pinhole that was making this edge not circular.
But the problem is that the box is too narrow which places the filme too near the hole.

I am looking for a box which I can have 7x9in but I can't find any that will be deep enough to avoid vignetting. When I find it is too bit.

Maybe I will have to make a box with woods.

 

[ronlamarsh]

coverage

I used the online pinhole calculator and for that focal length and pinhole diameter coverage at the film plane will only be 6.65in. The only way to get more coverage would be to move the film plane back.

 

[NedL]

There was a tape near the pinhole that was making this edge not circular.
But the problem is that the box is too narrow which places the filme too near the hole.

I am looking for a box which I can have 7x9in but I can't find any that will be deep enough to avoid vignetting. When I find it is too bit.

Maybe I will have to make a box with woods.

This happened to me. I spent too much time looking for the right box and then finally I just made one out of matboard. It seemed a little silly to be making a cardboard box, but once I sat down and went at it, it did not take very long and I ended up with what I wanted.

 

[SMBooth]

But to compare, Jimmy over at f295 has built a 8x10 /70mm and gets full coverage. Perhaps the thickness of your front face is creating the vignetting.

Check it out http://www.f295.org/main/showthread.php?19185-8x10-in-Nantes

 

[DWThomas]

I used the online pinhole calculator and for that focal length and pinhole diameter coverage at the film plane will only be 6.65in. The only way to get more coverage would be to move the film plane back.

I assume this is from "Mr. Pinhole." There's a lot of info at that site, so maybe it tells us somewhere, but my complaint is that there are assumptions behind those calculations and I don't see what criteria he uses. Presumably the coverage is based on some level of exposure fall-off, but it doesn't say what.


In a quick pass i get the (diagonal) field of view of the OP's camera as 117º. That is quite wide, and yes, there will be fall-off. But here's one on paper from my 4x5 with a 103º FOV:


(Scanned and inverted)

Mr. Pinhole seems to think this should be 4.69 inch coverage but what you see is actually over six inches. The camera has a 0.30 mm pinhole at 62 mm from the film/paper.

(Further edit):
I've not seen what the OP's pinhole plate actually is. The shot I show here is a hole done by dimple-and-sand in 1 mil brass shim stock -- that's almost a knife edge to begin with. If the hole is made in much thicker stock, the image begins to look like a tunnel view just from the sides of the hole interfering.

 

[marciofs]

I found a deep box today (180mm) and it is a bit larger than 7x9, which is perfect.

I have being using coca-cola can aluminium to make the pinhole, but in this case I made the pinhole on the box cover and it may be thicker. I will make a bigger hole and place a pinhole made with cola can aluminium to see if it works.

I really like Jimmy's idea to put 5 pinholes. I may try it later on.

 

[marciofs]

A made an other camera easier to load and now it image seems almost perfect.

I just have to make holdes for the sides bothers because the paper is following off.

It has a little bit vignetting but after cropping the edges it will be not very evident.



It has a 0.410mm pihhole
F-stop: 366
Focal Length: 140mm

I load a 9,5x7in paper in the camera but after crop I guess it will be 6x8in. Not bad.

 

[TheToadMen]

Congratulations: I think you've got it.
And I don't mind vignetting in pinhole images. It's often a good part of the image, so don't crop to quick.
Is it possible to show us the image not cropped also?

You could also pre-flash the photo paper to control the contrast en lessen the effect of vignetting and get more details in the shadow parts. I haven't done it yet myself, but will with the new Ilford Direct Positive Paper I got from Ilford. Here is more info:
http://www.lesmcleanphotography.com/articles.php?page=full&article=27 ,
(there was a url link here which no longer exists) ,
http://www.ilfordphoto.com/aboutus/page.asp?n=125 ,
(there was a url link here which no longer exists).

Have fun!
Bert from Holland

 

[DWThomas]

Yes! I agree with TheToadMen, you've got it. And yes, sometimes a bit of vignetting helps emphasize the primary subject; it's not necessarily a bad thing. After all, if one wants absolute sharpness and perfection, one would probably go to a lens!

 

[marciofs]

TheToadMen,

I only cropped where the paper holder appear. I didn't crop the vignetting.

DWThomas,

I think I am enjoying more the soft look of the pinhole than the sharp look of my lens cameras.


About pre flashing, does it make difference if I pre flash the paper I will do the final (contact) print instead pre flashing the paper negative? Because the first option is easier for me.

 

[TheToadMen]

About pre flashing, does it make difference if I pre flash the paper I will do the final (contact) print instead pre flashing the paper negative? Because the first option is easier for me.

It does make a difference. What isn't in the negative, will never be in the print. Make sure the negative is optimal, then decide what kind of print you'll make. Preflashing the print also is a possibility, but I would do the negative at first.

 

[marciofs]

Ok,
Thank you very much for all the help.

I shot this two today. But I still have to fix the paper holder. It is taking too much of the paper.

 

[Jim Jones]

That second one is a very well composed and exposed shot!

 

[TheToadMen]

That second one is a very well composed and exposed shot!

+1

 

[NedL]

That second one is a very well composed and exposed shot!

+2!
It's a very nice photograph!

 

[marciofs]

Thank you very much.

When I was trying with the first camera I made I was using Ilford RC multigrade paper. Now I am using Tetenal RC Variable contrast (which I guess means the same as multigrade). I don't know why but I like better Ilford than Tetenal.

Is there any paper you would recommend?