annular anomaly!

echomedia · Post by **echomedia** » Thu Feb 05, 2015 8:56 pm

Hi Folks-

Please take a look at the attached photos. I have an annular shaped light flare or reflection of some sort that is messing up my effort to get good quality photos and video. I can't tell where this is coming from or how to get rid of it. I've tried placing a piece of diffusion material over my microscope's light source but it still occurs (and it cuts back too much light to be practical anyway).

You may notice that the hydra's arm seems to create a shadow over part of it- so maybe that's a clue. I'm hoping some of you experienced microscopists may have seen this phenomenon before and can tell me how to solve it- or at least point me in a few likely directions.

Please note- Although this is a phase contrast image, the annular anomaly also occurs with bright field images, and also dark field although it's less noticeable.

zzffnn · Post by **zzffnn** » Fri Feb 06, 2015 5:59 am

That may be tube reflection. Depending how you mount your camera, it may be eyepiece tube, camera tube or/and camera adapted tube. Please try attach some light absorbing material into the tube(s), for example a piece of folded paper.

Also try adjusting condenser height and diaphragm.

I read your previous threads too. Are you shooting afocally through an eyepiece in eyepiece tube? If not, I suggest trying that (it may remove reflection and increase resolution).

You may start with a ~60mm full frame equivalent (~45mm on APSC sensor) camera lens and use a digiscoping adapter (e.g., Google "Orion SteadyPix Deluxe" or "Orion SteadyPix Pro") to mount to microscope eyepiece (the adapter will clamp camera onto an eyepiece). This afocal set-up can be replaced and re-attached in less than a minute, if you have one extra eyepiece (original eyepiece can stay attached to camera / adapter assembly, you just swap in an extra eyepiece).

Pau · Post by **Pau** » Fri Feb 06, 2015 6:29 am

Because it may have several causes, you need to isolate the problem
- Do you see the same halo trough the eyepieces? If not, very likelly it's from the photo coupling, and my vote is for zzffnn's hypothesis or from similar reflection in the photoadapter. Detailed info and pictures of your microscope and photoadapter could help.
Try shotting a picture (even with a mobile phone) afocally through the eyepieces

- Try closing the field diaphragm: if it dissapears (not just goes darker) it could be from the filter holder or condenser walls ...

- Rotate the microscope head and then the condernser to see if it rotates with the eyepiece (and wihole image) or just over the specimen image...

and so.. just move, rotate, change, test all parts to find the cause

echomedia · Post by **echomedia** » Fri Feb 06, 2015 7:07 am

Thanks- I'll try these suggestions out. (I'm shooting through a Konus photo adaptor tube thru the scope's photo port.)

echomedia · Post by **echomedia** » Sat Feb 07, 2015 4:30 pm

I lined the inside of the photo tube with a black velvet coated paper and the results are much better. There's still a circular highlight, but I may have to live with that. Even though the black velvet is very matte and light absorbing, there's still a fair amount of light bouncing off the tube interior toward the stage end.

If any further suggestions come to mind, please let me know. Thanks!

Pau · Post by **Pau** » Sun Feb 08, 2015 2:47 am

echomedia wrote:Even though the black velvet is very matte and light absorbing, there's still a fair amount of light bouncing off the tube interior toward the stage end.

You can also try putting a black ring (fixed diaphragm) over the objective or at the objective end of the microscope tube to cut lateral light, or to avoid reflections if the objective or nosepiece have a reflective ring

Again,

Pau wrote:Detailed info and pictures of your microscope and photoadapter could help.

echomedia · Post by **echomedia** » Sun Feb 08, 2015 1:14 pm

Pau- OK thanks. I'll try to get some decent photos of my set-up together.

Is this fixed diaphragm something I'd need to make myself, or are there places that sell them?

Pau · Post by **Pau** » Sun Feb 08, 2015 4:09 pm

echomedia wrote:Is this fixed diaphragm something I'd need to make myself, or are there places that sell them?

You can make it with black cardboard or flocking material.
A compass cutter is a very useful tool for the task

But best find before the origin of glare

echomedia · Post by **echomedia** » Fri Feb 13, 2015 11:41 am

OK- so here's some photos of my set-up and some tests I did with a fixed diaphragm. The diaphragm is rough but this was just a test to see if the concept would work. I tried making the annulus wider but it started to occult the image rather than just limit stray light bouncing off the inside of the photo tube.

BTW- I tested the various components such as the nose piece, condenser and light source and it's my conclusion that the stray light is the result of light bouncing off the lower inner sides of the phototube.

Any general suggestions or comments are welcome. Any suggestions as to a superior material to use to absorb stray light inside the tube would be especially welcome. I am using a black velvet or black flocked coated paper.

Pau · Post by **Pau** » Fri Feb 13, 2015 12:20 pm

You got the idea about the fixed diaphragm, you can make some more of them with black cardboard and test the best diameter and position (maybe inside the phototube or closer to the camera) just wide enough to do not get vignette

Flocking the interior of the tube seems the easier way if as you say the reflection comes from it.

About flocking materials take a look:
http://www.photomacrography.net/forum/v ... 912#113912
I use Protostar and it's very good

You could also get some glare from reflections on the (pol?) filter on the phototube base, you can try putting it inside the nosepiece head (just over the objectives) and even a bit tilted

zzffnn · Post by **zzffnn** » Fri Feb 13, 2015 2:27 pm

You can try to use blutak putty to line lower part of your photo tube. It is not difficult to remove and you can alter coating thickness yourself. I used it on my $50 toy scope and it worked perfectly. Just don't get blutak on your glass components.

echomedia · Post by **echomedia** » Fri Feb 13, 2015 3:57 pm

Awesome- thanks for the tips!

zzffnn · Post by **zzffnn** » Sat Feb 14, 2015 1:44 pm

I forgot to mention 2 things:

1, the light reflection that I had was not as severe as yours; I suspect your phase contrast may exaggerate the reflection.

2, as you might already know, Pau's recommendation should theoretically work better and seems to be a more elegant solution. Putting that material on and off may not be as easy as blutak putty though.

echomedia · Post by **echomedia** » Sat Feb 14, 2015 4:28 pm

zzffnn-

The phase contrast is definitely making it more noticeable. In fact, I'd say it isn't a problem at all except with phase contrast.

Truthfully, I'm having a hard time imagining what type of light absorbing material could work better than the black velvet paper I'm using. And the fixed aperture solution doesn't seem workable either- the best I could hope for would be to make the bright spot smaller but not eliminate it completely before it starts to occult the image. The stray light is hitting the lower, skinnier part of the inside of the phototube.

rjlittlefield · Post by **rjlittlefield** » Sat Feb 14, 2015 7:35 pm

echomedia wrote:The stray light is hitting the lower, skinnier part of the inside of the phototube.

This sort of problem should be solvable by inserting one or more paper baffles into the tube to block reflections from the sides of the tube. The ones that I use with camera extension tubes are a ring of black paper with tabs that fold to press against the sides of the tubes.

When baffles are properly sized and placed, they can be far more effective than flocking. This is because flocking actually leaves quite a few small surfaces for stray light to reflect from. See http://www.photomacrography.net/forum/v ... hp?t=17917, especially the Protostar. Baffles, on the other hand, can be sized and placed to allow single-bounce reflections only from the edges of the baffle material. Using black paper, that can be a very small area compared with the entire surface of the phototube.

Design and placement of the baffles will depends on details that I can't tell about from what's posted here. In general, between one circular lens and another, the baffles should be circles that are sized to fit snugly around the cylindrical or conical volume between the two circular lenses. Between a circular lens and a rectangular sensor, the ideal baffles will have openings that are rectangular with quarter-circle corners, again to fit snugly around the volume between the circular lens and the rectangular sensor. The latter design is summarized HERE, and the rest of that thread contains a lot of discussion about baffles in general.

--Rik