Seawater refractometer has Halo in viewing window. | D-D The Aquarium Solution

Question:

Hello.

                            

I recently bought a brand new one of your new style refractometers to  replace/upgrade my existing refractometer (your older model). The problem  is I have to screw the focus ring out to the max position to be able to  see the graduations clearly. I did not have to do this with my old  instrument, the focus ring was somewhere near the mid point. Also when  looking through the instrument I can see two blue lines one dark line and  a fainter one slightly below it. I do not think it is my eyesight as the old one does not show this.

Any thoughts.

Regards

Mark

 

Answer:

Hi Mark

I hope i can help you.

The new optics are different to the older version due to the newer type of scale/prism box to calibrate for seawater.

My own personal copy although not quite as easy to read is still very readable but if you are looking through and seeing

two lines then this may well be due to the plastic flap not sitting perfectly flat on the glass optic below.

If the flap sits up one side the water under it isn't a uniform thickness and air can also creep under the side that is sitting

off the glass optic. As light enters the optic it will bend at slightly different angles across the optic giving a halo effect

above the line that you should be reading due to the differing film thickness of water over the glass optic. This can also

lead to erratic measurements as the film of water under the flap will not be consistent at every sampling.

To address this you need to loosen the screw holding the plastic flaps collar tight on the unit, once you have loosened this

twist the collar slightly until the flap sits absolutely flat on the glass optic when at rest.

This should be the primary cause of the halo effect , you can also make viewing a little clearer by not turning the focus ring

right out, screw it in until you get the best view of both measurement line and gauge as both are on a slightly different viewingplane. Point the unit into very bright light and i also find that opening both eyes helps the eyes adjust for depth of field.

I hope this response helps

regards Tony

 

 

Response:

 

Hello Tony.

Many thanks for your reply. I have tried what you suggested and the flap was incorrectly adjusted. I have set it properly and all is well.

Thanks again for your help.