Home made lens, why it glows?

[Helen B]

As I mentioned before, there are a number of different problems being shown here. I wonder what you expected to happen when you made the mod. To save time and to help pitch the discussion at the right level, could you give us a rough idea how much you know about general lens design principles, correcting for aberrations, the use and effect of tilting pupils, ray tracing, the purpose of lens coatings etc. The more you know about this stuff the easier it will be to design lens mods and troubleshoot them so that they come closer to the performance you want - they are still likely to degrade the image quality of the unmodified lens, of course.

 

[jake337]

When making a home made T/S don't you want to use a medium format lens because of the much large image circle it produces?

 

[nick_cool]

Hello Helen, thank you for the interest, your comments helps a lot.


I will try to answer.

1) I afraid I am learning about lenses. My approach is more practical than theoretical. I have no idea about correcting for aberrations, ray tracing, or the purpose of lens coatings. Where can I get a text that could help me?

2) I like to have the performance achieve with my first lens (a lens that unfortunately I sold). Here is an example:

http://www.flickr.com/photos/nick_cool2000/5962071275/in/set-72157627250905996/

I think I will try to get a Fujinon as the one I had and stick to this solution.


3) I am using a 35mm lens because it is easier to get than a medium format one. The problem is the back focus distance, that has to been larger with a divergent lens.

4) I do not think that I have reflections inside the lens, it is all black and similar to the one that used to work, but I will check again.

Thankyou again.

 

[Helen B]

Practical approaches are good, so going back to what you know works is a good plan.

Reflections occur at all air-glass surfaces (or air-plastic) not just the lens barrel. Proper single or multicoating can reduce these reflections - that plastic element may not be coated. Exactly what happens will depend partly on the interaction between the surface of the last element of the main lens and the lens you have added.

You've got distortion, coma and other things going on. Just because the extra lens works with one lens formula doesn't mean that it will work with another of similar/same aperture and focal length. The rays arriving at the image plane do not come from the 'rear nodal plane' (which is at the focal length of the lens way from the image plane when focused at infinity). They appear to come from what is called the 'exit pupil'. Two lenses of identical focal length and aperture can have very different exit pupil locations. Some lenses can even move the exit pupil with changing angle from the axis. These, and other important optical differences, will affect the performance of any element you add behind the lens.

 

[nick_cool]

Very interesting, "Two lenses of identical focal length and aperture can have very different exit pupil locations."

I get it, they will show the same image at the focal plane, but not in the way between the last lens and the focal lens (exactly were the new lens is).

Unfortunately the way the lens works internally is unknown for me, so I will keep testing and I will let you know the results.

Thank you.

 

[Helen B]

Good luck with your endeavours and experiments. Keep us in touch.

Best,
Helen

 

[nick_cool]

I got some positive results.

I changed the aperture from 2.8 to 5.6 and the glowing diminish a lot!


Here there is the comparison:

Test | Flickr - Photo Sharing!

Anyway, I can not clearly get the selective focus, I will keep testing.

 

[DennyCrane]

You should probably follow the supplied ThePhotoForum threads and post the pictures here instead of expecting people to follow links to other sites. Most people are unwilling to go elsewhere to view a picture that can easily be posted here.

 

[nick_cool]

Hello, I agree.

I tried to load the pictures from my PC and also from other web sites, but I couldn't.

It seems that it is very annoying to follow the links, so I will end up this threat here.

Thank you

 

[DennyCrane]

Just resize the pictures to something reasonable, like 800x600, go to Photobucket.com, create an account, and upload them there. Hover over the thumbnail, click on IMG Code, and it will copy the correct forum link URL. Right click here, paste, and post. Simple.

 

[RacePhoto]

I got some positive results.

I changed the aperture from 2.8 to 5.6 and the glowing diminish a lot!


Here there is the comparison:

Test | Flickr - Photo Sharing!

Anyway, I can not clearly get the selective focus, I will keep testing.

Yes you did. You didn't mention before (or I missed it?) That you were shooting wide open. Now that you stopped down and reduced the divergence you also brought the image into focus. Looks like you were at the wrong distance for the focal plane, or the point at which the lens focuses, on the second lens. This could be the distance or the curve of the lenses not being aligned.

What has happened is you have more depth of field, between the two lenses and a sharper image because it's actually in focus now. You may have had some focused points before but there was also flare and stray light at the same time.

Do you know the distance from the lens to the film plane or sensor on the front lens? You need to match that between the lenses. Also if the lens in back is curved, you have a huge problem, because film or a sensor is flat. Easier said, the front lens is producing a flat image, not a curved one.

Neat project. Good Luck!

May I ask, why two lenses, instead of just a tilt-shift extension tube? The longer tube is going to make the rear image larger, so you won't lose the edges, you will lose infinity focus if I'm thinking right? But something as simple as a rubber collar will give you the tilt shift effect? It doesn't take much to take the top and bottom out of focus and have a sharp line in the middle which is still clear.

 

[nick_cool]

Hi, nice ideas.

I put the second lens in the best place I could, i.e. trial and error until get the best result. I think it was at 17mm in this lens. 1mm variation makes a big difference at least in this case. I also tried 5 different divergent lenses.

The back focal lens is 45mm (Nikon).

The most curved face is looking at the sensor to get the sharper image.

As I used a 35mm lens in a 35mm camera, to extend 10mm the lens-sensor distance with a simple rubber collar means not be able to focus in infinity anymore, it was the first test I did
Macro photography was ok.

By the way I make a third lens and the results were very positives in terms of selective focus and speed, (Fujinon 35mm plus -8D lens at 1mm) I will publish some examples and the lens construction in my Flickr during November 2011.

Flickr: Nick_Cool2000's Photostream

As was said, one conclusion is that different lenses behave differently, no matter if they have the same focal distance and/or aperture.

Cool shots

 

[Timoris]

I can see why you want to fix the lens, although I would also have to congratulate you on making a Soft Lens! Great for artsy pictures and gives great Bokeh with differently shaped filters.

Keep this one, make another

 

[nick_cool]

I can see why you want to fix the lens, although I would also have to congratulate you on making a Soft Lens! Great for artsy pictures and give great Bokeh with differently shaped filters.

Keep this one, make another

Thank you, that was I did and I love to have both!

Nick

 

[Crollo]

I guess nick isn't so cool, after all.

Don't you get tired of going after new people? Is this forum too crowded for you, or do you just have some deep seeded self-hatred? Whatever it is, get over it already.

Don't you get tired of going after new people? Is this forum too crowded for you, or do you just have some deep seeded self-hatred? Whatever it is, get over it already.

He doesn't pick on noobs exclusively. IM-texters with no sentence structure (grammar, punctuation, capitalization, etc) as well as those without (or just ignore) spellcheck are also fair game.

Which is ironic, because his grammar and punctuation leave a lot to be desired. As for the OP, English is most likely his second language... which I'm certain he speaks much better than Keith does any other language. Typical bigot.

I guess nick isn't so cool, after all.

Useless comma splice.

Jesus guys have a sense of humor will you. It's called tongue in cheek, you should try learning it sometime.