246 replies to this topic

[Fongky]

Hi,
Two of my friends have recently bought a set of Optolong narrowband filters: Ha (7nm), SII (6.5nm), and OIII (6.5nm). When one of them tested by taking pictures around his house using a modified DSLR (IR-cut filter removed) mounted with either Ha or SII filter, he noticed that there are other colors besides red. He was curious and requested me to do some testing with my Baader Ha (7nm) and SII (8nm) filter. I noticed that I only have red but no other colors in my images. We decided to do a simple comparison between Optolong and Baader filters.
 

We use a RGB color template as the test subject. The template is displayed on a LED screen. Then using a modified Pentax K-5 (IR-cut removed) camera to image the color chart.

 

Figure 1: Test Setup

Figure 2: Color Template

Here is the comparison between Optolong Ha (7nm) and Baader Ha (7nm):



Here is the comparison between Optolong SII (6.5nm) and Baader SII (8nm)



According to the spectral curve on Optolong's website, the Ha filter has 80% transmission of Ha (centered around 656nm) and only 0.1% off-band transmission. Here is the official spectral curve:


The Optolong SII filter has 80% transmission of SII (centered around 672nm) and only 0.1% off-band transmission. Here is the official spectral curve:


From our rudimentary tests, the Optolong filters seem to have extremely high off-band transmission as compare to Baader filters. Both the Ha and SII should only appear as red while most green and blue should be cut off as in the Baader filters.

Is our method of testing wrong or something is wrong with the Optolong filters? Can anyone conduct independent tests with similar filters?

 

Edited by Fongky, 17 December 2017 - 11:27 AM.

[petert913]

Very interesting test.  Thanks for sharing.  I'd select the Baader.

[gatsbyiv]

Wow.  It's a simple test, but the evidence is damning.  There is no way they match the spectral curves shown.  It would be great if someone had access to a spectrograph to test them precisely.  I'd bet a simple red Wratten filter would do almost as well.  

[StarMike8SE]

That is rather disappointing with the Optolong filters.

[keithlt]

interesting test, I do wonder if the color template being displayed on an LED screen makes a difference compared to how the filters behave in natural light.

Edited by keithlt, 18 December 2017 - 08:43 AM.

[Bart Declercq]

interesting test, I do wonder if the color template being displayed on an LED screen makes a difference compared to how the filters behave in natural light.

How could it? Light is light, regardless of its source.

[keithlt]

 

interesting test, I do wonder if the color template being displayed on an LED screen makes a difference compared to how the filters behave in natural light.

How could it? Light is light, regardless of its source.

 

well the badder ha filter just made a sea of red even including the white background

[jimthompson]

Hi Fongky,

 

I very interesting test.  Some times the simplest of tests are the most useful.  It would appear that the Optolong filters are passing a lot of blue, quite unlike what the manufacturer spectral response plots say.  That is odd as the filters I tested all matched their quoted spectrums closely when I measured them.  I have a USB spectrometer, and would be happy to measure the spectrums of your friends' Optolong filters.  Unfortunately I am far away in Ottawa, Canada.  Maybe somebody reading this thread located in North America would be willing to loan me their filters to test.  I do have a 7nm Halpha filter from them that I have not measured...maybe I should take a closer look at it.

 

Best Regards,

 

Jim T.

[Fongky]

Hi Fongky,

 

I very interesting test.  Some times the simplest of tests are the most useful.  It would appear that the Optolong filters are passing a lot of blue, quite unlike what the manufacturer spectral response plots say.  That is odd as the filters I tested all matched their quoted spectrums closely when I measured them.  I have a USB spectrometer, and would be happy to measure the spectrums of your friends' Optolong filters.  Unfortunately I am far away in Ottawa, Canada.  Maybe somebody reading this thread located in North America would be willing to loan me their filters to test.  I do have a 7nm Halpha filter from them that I have not measured...maybe I should take a closer look at it.

 

Best Regards,

 

Jim T.

Thanks, Jim. I will be curious to know your test results.

I have another user to his Optolong filters with the same method. He reported no problem with them. His filters were purchased in 2016.

Optolong in China has responded to my report and contacted me. According to their representative, they are conducting an internal investigation. I will update this thread when I have more information.

Edited by Fongky, 18 December 2017 - 12:13 PM.

[Alien Observatory]

 

Hi Fongky,

 

I very interesting test.  Some times the simplest of tests are the most useful.  It would appear that the Optolong filters are passing a lot of blue, quite unlike what the manufacturer spectral response plots say.  That is odd as the filters I tested all matched their quoted spectrums closely when I measured them.  I have a USB spectrometer, and would be happy to measure the spectrums of your friends' Optolong filters.  Unfortunately I am far away in Ottawa, Canada.  Maybe somebody reading this thread located in North America would be willing to loan me their filters to test.  I do have a 7nm Halpha filter from them that I have not measured...maybe I should take a closer look at it.

 

Best Regards,

 

Jim T.

Thanks, Jim. I will be curious to know your test results.

I have another user to his Optolong filters with the same method. He reported no problem with them. His filters were purchased in 2016.

Optolong in China has responded to my report and contacted me. According to their representative, they are conducting an internal investigation. I will update this thread when I have more information.

 

Fongky,  I did a non scientific (eyeball) test with your color chart today using my 7nm ZWO Ha (it looks almost like your Optolong Ha), and then with my Lumicon Ha (it looks the same as your Baader Ha)....  Interesting stuff...   Pat Utah   

[jimthompson]

Hi Fongky,

 

It is promising to hear that Optolong has responded to your report so quickly.  I have had only positive experiences with the company, so it is good to hear from someone else that they are similarly committed to standing behind their product.  Indeed, please keep us updated with what you find out.

 

Best Regards,

 

Jim T.

[StarMike8SE]

_{I also am glad Optolong responded.  looking forward to seeing their response}

[Bart Declercq]

 

 

interesting test, I do wonder if the color template being displayed on an LED screen makes a difference compared to how the filters behave in natural light.

How could it? Light is light, regardless of its source.

 

well the badder ha filter just made a sea of red even including the white background

 

A computer screen has pixels in three colours, Red, Green and Blue - to produce Red, it lights up the red pixels, to produce white, it lights up Red, Green and Blue pixels - if a filter blocks all the green and blue light, "white" will look exactly the same as red, which is precisely what the Baader filter shows.

[jammeymc]

uhhhh....that doesn't look good for Optolong.  I've got a set of their LRGB filters and am now curious, and would like to see, a similar test done on those...

[SandyHouTex]

 

 

interesting test, I do wonder if the color template being displayed on an LED screen makes a difference compared to how the filters behave in natural light.

How could it? Light is light, regardless of its source.

 

well the badder ha filter just made a sea of red even including the white background

 

That would be because white contains all of the colors.  The Baader just allowed the red component through.

[Alien Observatory]

uhhhh....that doesn't look good for Optolong.  I've got a set of their LRGB filters and am now curious, and would like to see, a similar test done on those...

Use this image on your computer screen and hold the various filters to one eye (cover the other eye) and see how it looks  (non scientific eyeball test) and /or take a screen shot / iPhone image and share your results... Pat Utah  

 

here is a link to a full size image...

 

https://upload.wikim...veColor.svg.png

Attached Thumbnails

• 

Edited by Alien Observatory, 18 December 2017 - 10:22 PM.

[andysea]

FWIW I had to return the 2” lrgb optlong because they were causing very strong reflections with my 10” DSi/RCOS scope.

[Mike Lockwood]

I had a friend's Optolong filters on loan (for use with nightvision equipment) and saw something very similar - my test image is attached.  These are photos of my monitor displaying a stock color wheel image that is available online.

 

Image is here:  https://www.canstock...l-14648450.html

Attached Thumbnails

• 

Edited by Mike Lockwood, 18 December 2017 - 11:01 PM.

[Alien Observatory]

Mike if you would kindly post the Link for the color wheel, life would be much easier to make a quick comparison...  Pat Utah  

[Mike Lockwood]

Mike if you would kindly post the Link for the color wheel, life would be much easier to make a quick comparison...  Pat Utah  

Sorry, added it to my post above.

[Alien Observatory]

TY Sir...Pat Utah... 

[rockstarbill]

Heh, guess I wont be buying any optolong filters anytime soon.

 

Would be interesting to see the AstroDon filters in this same test. 

[andysea]

I have a set of 3nm astrodon filters that I can test, however the camera is going to be mono, so I'm not sure how do the test, 

 

[yuriy oseyev]

So interest test. How about the same test for Optolong-OIII?

[Fongky]

So interest test. How about the same test for Optolong-OIII?

Hi Yuriy,

I have tested both Optolong 6.5nm OIII and Baader 8.5nm OIII. No significant off-band failure has been detected. But Mike did another test and showed there is some red leaking through https://www.cloudyni...lter/?p=8282207.

He are my tests:
 

Regards,

Edited by Fongky, 19 December 2017 - 06:10 AM.