Flywing using reflected darkfield

peterkinchington · Post by **peterkinchington** » Fri Jun 06, 2014 2:29 pm

Hi,
I am almost satisfied with this image of a fly's wing - although I do not like the out of focus/blurred areas on the Left hand side of the image. Do I need a deeper stack? Can Rik, Charles or another skilled photomicrographer fill me in on this. I used reflected darkfield with a lomo 9x epi objective.
Cheers Peter

rjlittlefield · Post by **rjlittlefield** » Fri Jun 06, 2014 7:06 pm

This is coming along nicely.

Yes, that looks like an area that just never got focused. I get the feeling that it's foreground, on the theory that ridges and not grooves would be giving those bright reflections.

I notice also that in the center of the image there seems to be some glare -- the contrast looks lower and there's only darker gray instead of anything approaching crisp black. Have you checked for any reflecting elements along the sides of the optical path that might be causing that?

--Rik

peterkinchington · Post by **peterkinchington** » Fri Jun 06, 2014 11:28 pm

Hi Rik,
Thanks for the feedback. Yes there would be glare that I need to address - I built my epi-illuminator out of plumbing fittings and led lights. I need to put in a light baffle tube from the centre of the epi-objective to the exit tube going to the camera. I will also try combining crossed linear polarisers to help eliminate glare.
Cheers Peter

rjlittlefield · Post by **rjlittlefield** » Sat Jun 07, 2014 10:34 am

peterkinchington wrote:Hi Rik,
Thanks for the feedback. Yes there would be glare that I need to address - I built my epi-illuminator out of plumbing fittings and led lights. I need to put in a light baffle tube from the centre of the epi-objective to the exit tube going to the camera. I will also try combining crossed linear polarisers to help eliminate glare.

I'm unclear exactly what your setup is. Normally the phrase "reflected darkfield" or "episcopic darkfield" means that the illumination comes from around the imaging lens, so that if you look at a flat mirror you see a dark field -- no reflections from the illuminators. Crossed linear polarizers can help eliminate reflections, but in the image shown here that would lose quite a lot of modeling from those ridge reflections. Crossing polarizers can be a great help with episcopic brightfield, where illumination goes out through the same lens that imaging light comes in. But I don't think that's the case here.

Can you clarify?

As for the light baffle tube, I don't have a good imagination about what that would be doing. Do you have illumination going out through a hollow barrel of the objective, and then concerns about leaks letting some of it get loose and get bounced up into the camera, avoiding the lens altogether?

--Rik

peterkinchington · Post by **peterkinchington** » Sat Jun 07, 2014 4:23 pm

Hi Rik,
Yes Rik I was unwittingly thinking of brightfield when I mentioned the crossed polarisers. However my epi illuminator the way that I have built it only gives darkfield. The leds direct light down the outer barrel of the epi objective. At the moment there is a slight gap behind the back element of the central lens of the epi-objective - I believe this is where light from the leds is contaminating the reflected light from the fly wing/subject. A tube of matt black paper surrounding the back of the lens (central area) of the objective and going past the led light source to would enable the reflected light to reach the camera sensor uncontaminated by light coming directly from the leds. This hopefully should give me "crisper" blacks.
Cheers Peter

peterkinchington · Post by **peterkinchington** » Mon Jun 09, 2014 3:01 am

Tried using the tube of black paper as a baffle. However still have the glare issue. I'll have to keep at it! At least the stack is deep enough.