Nikon Fluophot Test Shots

rjlittlefield · Post by **rjlittlefield** » Sat Nov 20, 2010 11:42 am

Mitch, I'm puzzled. The description for Field Diaphragm in the manual agrees with the Köhler definition, but I don't see how it relates to your earlier description:

It adjusts from almost black to bright enough to make you see spots all day.

I had assumed you were describing what you see through the eyepieces. But now I'm thinking you were describing what you see coming straight out of the illuminator. Through the eyepieces, a field diaphragm will affect flare but not brightness. On the other hand, it can definitely change the total amount of light coming out of the illuminator.

I generally have been opening it till things look good. What better way to do it?

None better. In fact there is an old story about a college instructor teaching his students about these controls. He carefully explained the standard advice about closing the aperture to 70%. Then he asked each student to adjust his or her own scope and report what the best setting was. Answers ranged from 10 to 100. "Exactly," said the instructor. "The best setting depends on what you want to see. The standard advice is just a guideline."

--Rik

Mitch640 · Post by **Mitch640** » Sat Nov 20, 2010 12:12 pm

I was describing what I see in the eyepieces. You can't see anything coming out of the illuminator itself, it's attached to the rear of the scope on a dovetail slot. Here's a pic of what I have.

Inside the black box at the rear of the base, is a 12V 100W halogen bulb. I can attest that that thing is enough to really hurt your eyes if you were to look at it with the rheostat turned up. The light comes from the box into the back of the base, through the base to the base of the Field Lens, then up to hit the bottom of the condenser. You control the field diaphragm with that dial on the base beside the field lens. It's all inside the base, you can't see it or get to it, but you can hear and feel it moving when you adjust it.

It does not control the brightness as a rheostat would, but it certainly does act as the iris on a condenser does, lowering the quantity of light in the same way, right down to almost black.