Re: My finanl Report: Artefacts in digital photographic images. (Coolpix-problem)

Gordon Couger schrieb:
> Good work.

Thank you - feels good to read such an appreciation from an expert!

> My investigations come to the same practical conclusions yours do. I feel
> that by using the shortest focal length and maximum aperture my CoolPix 995
> has no artifacts I can find using 0.9 n.a. Koehler illumination with a
> Nachet 60x 1.0 DIC objective. This is the most critical setup I have. Ted
> Clark has had similar results on Zeiss and Olympus optics. I have not tried
> full oil immersion over 0.9 n.a. Ted is able to fill the frame with no
> artifacts with a Olympus 8X WHK eyepiece and a high eyepoint 10x Zeiss Kpl
> 20 mm FN eyepiece

> http://www.couger.com/microscope/Ted-Clarke/camera%20adapter/adapter.htm.

I did not know this interesting page. I will mail the Link to all
recipients of my report. -- Many amateurs do not care about vignetting
and "hot spots", and they use doityourself-adapters keeping the pupils
of the mic and the camera-objective far apart. They are glad to get
any image on the chip, and then put their scrap-photographs on their
homepages. My son and I sometimes have difficulties trying to explain
proud homepage-owners, why we refuse to link their sites on
www.mikroskopie-muenchen.de. Nowadays, I think, one must be glad to
find a professional scientific magazine without such scrap-photos.

> The artifacts of a CoolPix 990 are much less noticeable and limited to faint
> rings that are over whelmed by most images other than clear background
> making it a much more versatile camera than the later models.
> 
> I agree with Ted Clarke's observation that the rings appear to look more
> like tool marks than that spin casting artifacts. 

I can understand this opinion. Having considered the possibility of
tool marks very carefully, I now prefer to think that there are no
marks at all. In this case the rings would point to circled areas of
different density, perhaps caused by the ongoing polymerization
process, or the cooling process, one or both of which may cause those
areas of inhomogenity in the lens-body. (I remember the spin-casting
method first having been developed for the production of
eye-contact-lenses, which are very thin, and small in diameter,
compared with an objective lens.) But, regardless of what really
causes those structures, on or in the lens, my intention rather was to
explain, why the chip can see and receive them in a camera adapted on
a microscope.

I don't think Nikon has
> put much investigation into the problem and just wrote it off since they had
> no plans of resolving and they aready knew the end of the product was near
> due to the shrinking size of the competition.

> What you call bubbles I call blobs are located in similar places among
> multiple cameras leading me to believe that they may be wear in in the lens
> mold or some other of the lens parts molds.

After a look into my English-German dictionary I agree that this is a
good idea.

> I also suspect internal reflections and improper edging of the lenses may
> show up in a coherent beam of light. These get worse as the lens gets more
> complex between the 950 and the 995.

That could explain, why - obviously depending on the adjustment of the
microscope illumination - sometimes the "rings" show
interference-lines all over the image.

> There is also a central artifact that varies with the focal length that
> appears very much like a bubble but changes rapidly at short focal lengths.
> 
> I have a 995 lens I may sacrifice if I go ahead and rebuild the camera using
> 1/4 x Nikon eyepice in place of the lens. I have already removed the
> infrared blocking filter. I bought the camera very inexpensively when it
> came back from Japan from a paid repair and didn't focus at infinity. That
> would settle a lot of questions about the lens.

I you decide to sacrifice the lens, you certainly will publish your
findings right here in the NG, do you?
> 
> I tried my son's CoolPix 5400 and it will take a relay lens to make it work
> with a microscope if the lens can be clamped in an adapter and the camera
> allowed to move up and down as it zooms. I could not find an eyepiece that
> would put a full image on the CCD though the camera lens. So it looks like
> Nikon is out of the microscope camera business for the near future.

Not only Nikon, I fear.

Greetings from overseas!
Klaus Henkel