Strange vignetting with telepinhole tube

Uncleleo · Apr 2, 2022

Can anyone help me with this strange vignetting? Why i have it?

Here is my gear.https://dfh.es/en/producto/extensible-plastic-drawing-tube-to-keep-and-transport-plans-posters-etc/

Shooted at 1250mm focal distance with 0.9mm and 3mm hole. Used different shutters, weather, focal distances. Vignette always exists.

Sirius Glass · Apr 2, 2022

The vignetting could be corrected with a few added correction lenses.

cramej · Apr 2, 2022

You already have vignetting from using a pinhole and then you have the inverse square law for light so you're compounding the issue with the meter+ distance from pinhole to film plane.

Uncleleo · Apr 2, 2022

cramej said:
You already have vignetting from using a pinhole and then you have the inverse square law for light so you're compounding the issue with the meter+ distance from pinhole to film plane.

Thanks. My сathetus on tube axis (tube length) is 720mm. Radius of the tube 55mm. Maximum hypotenuse from hole to edge of the frame is 722mm. So why this diference between light paths 722mm and 720mm makes so huge vignette?

I have same size vignette with 720mm and 1250mm focal length.

cramej · Apr 2, 2022

@Uncleleo Now the questions are beyond my knowledge . Wish I could help more!

Dan Fromm · Apr 2, 2022

Uncleleo said:
Thanks. My сathetus on tube axis (tube length) is 720mm. Radius of the tube 55mm. Maximum hypotenuse from hole to edge of the frame is 722mm. So why this diference between light paths 722mm and 720mm makes so huge vignette?

I have same size vignette with 720mm and 1250mm focal length.

Hmm. Tube length 720 mm, tube radius 55 mm, The dimensions in the product description don't match your description.

Still, accepting your description, if the pinhole is centered at the subject end of the tube the diameter of the circle covered at the end of the tube will be 110 mm. What's the size of the film you're using and how far is the film end of the tube from the film?

Light Capture · Apr 2, 2022

Uncleleo said:
Can anyone help me with this strange vignetting? Why i have it?

Here is my gear.https://dfh.es/en/producto/extensible-plastic-drawing-tube-to-keep-and-transport-plans-posters-etc/

Shooted at 1250mm focal distance with 0.9mm and 3mm hole. Used different shutters, weather, focal distances. Vignette always exists.

View attachment 302004
View attachment 302003

Looks like it could be some serious flare. Is the inside of the tube shiny and reflective?
If it is, flat paint or flocking should take care of it.
It seems that image is formed all the way to the corners of your negatives so there shouldn't be any mechanical vignetting.

NedL · Apr 2, 2022

Light Capture said:
Looks like it could be some serious flare. Is the inside of the tube shiny and reflective?
If it is, flat paint or flocking should take care of it.
It seems that image is formed all the way to the corners of your negatives so there shouldn't be any mechanical vignetting.

that's my thought too, can't think of anything else that makes sense.

DWThomas · Apr 3, 2022

What is the actual pinhole like physically -- I have seen vignetting from attempting to use a hole drilled in a thick plate. The plate containing the pinhole should be very thin, on the order of 0.1 mm or so.

Are the shutters mentioned actual camera shutters -- leaf? Focal plane? I once tracked down a problem in a pinhole rig by drawing a very precise cross section with all my mechanical parts carefully scaled to size and position, then looked at simple ray tracing. The relatively long focal length you are attempting would have a very narrow angle of view which should minimize the problem, but perhaps there is a ring or collar somewhere that constricts the light path?

Are you putting this tube on some sort of film holding back, or substituting it for a camera lens on a camera body?
How large are the film pieces we see above?
I also agree with those above that if he tube has a glossy inner surface it might provoke some serious flare.

(Yes a lot of questions, but the more we know the better the chance of someone having a moment of revelation. )

AgX · Apr 3, 2022

Dan Fromm said:
Hmm. Tube length 720 mm, tube radius 55 mm, The dimensions in the product description don't match your description.

Likely this tube comes in different sizes and the OP got a different model than linked to, which indeed can be extended to about 1,2m.

Uncleleo · Apr 3, 2022

AgX said:
Likely this tube comes in different sizes and the OP got a different model than linked to, which indeed can be extended to about 1,2m.

Yes, sorry, i checked site information. I have different tube same brand with sizes from 720mm to 1250mm.

My photos are 31x44mm (127x178 cut at half and again cut at half).

I drilled another hole at the edge of radus and now my vignette at least at the edges of the photos.

I'm using replacement holes from closing parts.

AgX · Apr 3, 2022

In your original set up no vignetting is to be expected, and I do not see it, but to be expected is lot of stray light.

I would paint a sheet of cardboard with matte black paint, or chalkboard paint, or use black cardboard, and roll such sheet and install it in that tube.

Dan Fromm · Apr 3, 2022

AgX said:
In your original set up no vignetting is to be expected, and I do not see it, but to be expected is lot of stray light.

I would paint a sheet of cardboard with matte black paint, or chalkboard paint, or use black cardboard, and roll such sheet and install it in that tube.

Given the focal length -- 1250 mm -- and film format -- 31 x 44 mm -- cos^4 fall off will be negligible. We agree on that.

If the OP is showing us negatives then the black areas are heavily overexposed. This is the opposite of vignetting and I agree that stray light is the culprit.

cramej · Apr 3, 2022

Uncleleo said:
Yes, sorry, i checked site information. I have different tube same brand with sizes from 720mm to 1250mm.

My photos are 31x44mm (127x178 cut at half and again cut at half).

I drilled another hole at the edge of radus and now my vignette at least at the edges of the photos.
View attachment 302075

I'm using replacement holes from closing parts.

View attachment 302074

This may be your problem. Ideally, as stated above, the pinhole should be very thin. I've used soda cans in the past with good results. Those grommets are really thick!

Uncleleo · Apr 4, 2022

AgX said:
In your original set up no vignetting is to be expected, and I do not see it, but to be expected is lot of stray light.

I would paint a sheet of cardboard with matte black paint, or chalkboard paint, or use black cardboard, and roll such sheet and install it in that tube.

Thank you all! After adding black sheet of paper the flare have dissapeared!

ciniframe · Apr 12, 2022

If the OP wants to experiment with very long focal length then a +1 (1000mm) close up lens could be used to improve the image quantity quite a bit. I would use a 10mm drill to make a f100 stop in a flatened out aluminum drinks can. For fixed focus you would need to rig some kind of ground glass, or a thin sheet of textured plastic to confirm focus wide open with what ever size close up lens you can obtain. When I experiment with home made rigs I usually use photo paper as a negative because it is cheap, can be handled under safelight, and is so slow, 3-6 ISO usually, that exposures are all several seconds even in sunlight.

europanorama · Jul 6, 2022

Musou darkest black paint. problems improved heavily. they also have similar velvet. google. dont expect low prices.

Strange vignetting with telepinhole tube

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