Should Optolong filters be installed in a certain orientation? 

source:Optolong popularity:10713Release Time:2022-04-18

Should Optolong filters be installed in a certain orientation?  


We received the queries about Optolong filters whether they maybe installed in a certain orientation like below said:

"I bought 36mm unmounted LRGB & narrow band filters of your company. I have a question. Is there a front and back of the filter when attached to the filter wheel?"

"Should Optolong filters be installed in a certain orientation?"

"Should the male thread side be toward the camera or can it be facing toward the scope?"



Tecnicially, there are two type of filters here: naked fiilters like 31mm, 36mm, and mounted filters like 1.25", 2".  How do we distinguish the orientation issues of the both type of filters?


Naked Filters


Testing method is very simple and can be identified with our eyes. The tool what we used is the usual gel pen with the background of A4 blank paper under fluorescent lamp. 

Graphic 1. tool and checking method




Let's take Optolong 36mm LRGB for example to identify which side toward camera or sensor, and which side toward Sky or Scope. 

From Graphic 2, there are two graphs for each L, R, G, B separately, the left side is toward Camera or Sensor, while the right side is unified toward the Sky or Scope (light source). 

Do not look at the color, look at the reflected intensity, and you'll find difference of both sides. Strong refection side (the right side) towards Sky/Scope.

For 31mm unmounted L, R, G, B, you can also use this way to identify which side toward Camera or Sensor. 

Graphic 2 LRGB 36mm




Standard Mounted Filters

We say 1.25" and 2".

In our SOP(standard operation procedure), the rule of the way to determine assembly sequences and assembly directions are stipulated in detial. 

When we assembled filters, there is a fixed assembly direction according to the properties of the film layers. So we suggest that the samll calibre or filter threaded side toward Camera/ Sensor, while the heavy calibre toward Sky/Scope.

Graphic 3 is taking Optolong 2" L-eXtreme for example. 

By analogy, 1.25" can also be identitied in this way. 

Graphic 3 L-eXtreme 2inches





Usage Scenarios of Optolong Mounted Filters.


From Graphic 4, you'll find three commonly used installation methods, all show the heavy calibre toward Sky/Scope, and the small calibre or filter threaded side toward Camera/Sensor. 

Graphic 4 Optolong Mounted Filters ApplicationsX3; thanks to Mr. Andrea Maggi(Italy)'s image


1. The outer diameter of the cell/frame/filter is less than 50.5mm, nomatter how about the thickness, it can be screwed on the eyepiece tube and insterted into the standard barrel lens tube for sure. 

2. Only when th eheight of the filter is less than 5mm so that it can be installed on the filters wheel/disk, then the filters can be switched freely. 

3. The filter is used as a adapter rign, connect with the telescope in front and the CCD in the back. Due to the limit of the height of Optolong filters, which can not be used in this application. More improtant is not safe enough in this application, so not recommended. 



The Forth Application- Filter Drawer



From above two graphs, you may find that the drawer can be installed forward or backward, either way can be connected. However, when you installed Optolong filters in right way, the left figure is correct way. 

So, you'd better put the drawer right way like Graphic 7 showed so that you can guarantee the small calibre of the filter is facing down and toward Camera/ Sensor. 

Graphic 7 right drawer way





Hope that can help a little. If ohter opinions, let's discuss. We always thank you for your support and feedback. Your opinion and suggestion make Optolong filters better and better. 

Really appreciate for contacting us if any query! We will update the desciptions if any findings. 

Welcome always. Thanks for your attention.