How to Troubleshoot a Lens Focusing Issue with a DIY DSLR Lens

[S15]

Hello all
As an experiment I tried to make a lens for my dslr with plastic lens of a Kodak Funsaver disposable camera. The lens in this camera is convex-concave and is a 30 mm lens.
Problem is: My lens can only show items in focus if they are at about 1-2 cm away from it. Nothing past 2 cm will be focused. While the lens functioned in the disposable camera.
I have tested by looking through it and on a dslr. Same results.
What could be wrong? There are dozens of videos on youtube showing how the same lens and procedure has worked for others.

thanks in advance
ps The photo shows how these lenses are made.

 

[BvU]

Hi,


Sounds impossible: a 30 mm lens can not form a real image of anything within 30 mm.
You have the well-known $${1\over o}+{1\over i}={1\over f}$$(object distance, image distance, focal point distance)
to deal with.
So you want to check a few things (manually, with lens only):
focal distance
image distance
is the image upside down when e.g. o=i=2f?

$\$

 

[S15]

Hello
Thanks for your reply and welcome, nice forum this is. I am sure I can learn a lot here.

This is what's puzzling me also. The only things that I can see clearly are very close to the lens (less than 5 cm) and they are NOT upside down which is another strange thing. I took physics in high school so I am familiar with the formula and also the ray of light rules and drawings. None the less this is how it is.

I tried reversing the lens, it did not help anything. I even mounted the lens on a movable cylinder so I can adjust the distance to the sensor. That did not work either. I do not think there is anything wrong with the lens itself since it came out of a woodworking camera. I am just puzzled. Can you suggest any tests or experiments?

I posted this question in a photography forum also. Few people said that they have made it and it worked and a few said that it did not work for them. They were all using the same type of cameras (Olympus micro 4/3), which have the same distance from lens to sensor.

I think I have to explain also that with this lens it is possible to take picture. It forms a picture but it is all blurry no matter at what distance, while in 5 cm everything is super sharp (and not upside down).

 

[BvU]

The only things that I can see clearly are very close to the lens (less than 5 cm)

This formulation worries me:
Are you looking through the lens ? In that case you are looking at an upright virtual image.

Or are you looking at a preview screen on the dslr ? In that case the electronics turn the image upright.

With the lens only (plus a light bulb or something as object and a piece of paper as screen) you should be able to confirm the 3 cm focal distance and a linear magnification of -1 at o = 2f. To check, you can do the same with the camera lens only.

The latter should not act as simple as a single thin lens, but as a thick lens.

[edit] Don't have a 4/3, but a 55 mm toy lens and ancient Pentax do the trick as expected ... and a grandfather magnifier can serve as a telephoto lens

$\$

 

[S15]

I look through the lens and it is very sharp almost like a macro lens at 4-5 cm (and not reversed). I took photos with it at that distance also very sharp. I tried taking photos at objects at varying distances not everything is out of focus. These disposable cameras are supposed to be in focus from 1 meters to infinity. I have kept the lens in the same housing as the disposable camera so the diaphragm is the same (must be f10). This is a very interesting problem since it is so illogical.
I have been trying to find a diagram that shows passage of light through such a lens and see how objects at different distances should look (attached). I can't figure out anything from it.

BvU I would greatly appreciate if you can attach a diagram that shows how an arrow supposed to look like through such a lens at say 2 m distance.

 

[BvU]

I look through the lens

Again ! With your eye ? In that case you are looking at an upright virtual image.
Question: does that link work for you and do you understand it ?

BvU I would greatly appreciate if you can attach a diagram that shows how an arrow supposed to look like through such a lens at say 2 m distance.

was answered:

With the lens only (plus a light bulb or something as object and a piece of paper as screen) you should be able to confirm the 3 cm focal distance and a linear magnification of -1 at o = 2f.

mutandi: set i = 30.45 mm. With f = 30 you get o = 2000. Magnification -30.15/2000 = -0.015
So a 200 mm arrow will yield an inverted real image of 3 mm on the sensor

You don't even have to do the calculation yourself :

$\$

 

[Drakkith]

I look through the lens and it is very sharp almost like a macro lens at 4-5 cm (and not reversed).

Looking through the lens with your eye will tell you little about it since you are adding an entirely separate optical system, that being your eye. What you see in-focus when looking through the lens with your eye will NOT be the same as what is brought to focus on the sensor/film.

I took photos with it at that distance also very sharp. I tried taking photos at objects at varying distances not everything is out of focus.

Was the lens attached directly to the DSLR without any other lenses in between the disposable lens and the sensor?

 

[S15]

BuV I mentioned that this is a covex-concave lens which does not look like the lens in the link. It's been a while since my high school days but I think the two lenses are different. Thanks anyways.
Darkkit lens in its original housing with the original diaphragm (f10) is mounted in a camera body cap that I drill a hole (#16) to pass the housing through. There is nothing in between lens and sensor.
Here is Youtube video explaining how it is made :

WARNING: in case you want to duplicate this experiment. The flash capacitor in the disposable camera can give a very serious electric shock, resulting in burns. First make sure the flash is not charged and capacitor is empty. Do at your own risk.

 

[Drakkith]

Okay, that's much more clear on what you're doing. If you're only getting objects within a few cm of the lens in focus, then that suggests that your spacing between the lens and the sensor is off. I'd suggest trying to incorporate some spacers in between the lens and the lens cap (which is what is holding this lens) to move the lens backwards towards the sensor. That should bring the distance into better focus.

You can also directly measure the distance you need by placing a piece of paper behind the lens, move the paper until something in the distance is in focus, and then measuring the distance between the lens and the paper. That distance should be the same distance you want between the lens and the camera sensor. This may or may not be useful, as you may not know how far it is between the lens attachment point and the sensor.

 

[S15]

Thanks a million Drakkith (sorry for misspelling last time) I did as you suggested and now the lens is significantly improved. It is sharp and usable.

 

[sophiecentaur]

IF you only have fixed spacers then you may need thinner ones to build up just the right thickness. A threaded system could be too fiddly. You might fix the lens and adjust the circuit board position with screws(?) just an idea.