40 replies to this topic

[Mbuna]

Im struggling with confusing information from Optolong, compared to my real-life expercience. maybe someone can give the definitive answer?

 

The problem:

I mounted my new Optolong L-Extreme into my new ZWO filter drawer. But started to wonder if i mounted it the right way. So started to search for information.

 

The info from Optolong:

On their site they tell that a simple test shows wich side should face the camera sensor. It can be found here: http://www.optolong....tXvQXurp8Mkon2c

The theory is that the 'most functional membrane' can be identified by a ghost image test. The most functional membrane blocks more light so it will show less ghosting. Seems logical to me. As a result you should face the side with the most ghosting to the camera sensor.

 

The real world test on my filter:

I did the same test (with almost the same pencil). The result was that the ghost image was most visible on the side that faces the scope?!! I added the pictures here to show the result. The threaded side is the one facing the sensor, but that seems to have to face the scope? 

 

The dilemma:

I know i could unmount the glass and turn it the other way around. But is that what Optolong wants us to do with every filter? I hope it is produced the right way, for a filter that costs $300. I also hear people say 'i don't think it matters wich side you use, i never had any problems', but that doesn't meet the Optolong explanation on their own site. And my intention is to use this filter the best way possible, and i am kind of confused right now.

 

attached pictures:

Scopeside- the test of the surface that faces my scope

sensorside - test of the surface that faces my sensor

assembled- hot the drawer is assembled, showing the scope side

optolong explanation: screenshot of the explanation on Optolong's site.

Attached Thumbnails

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Edited by Mbuna, 25 February 2022 - 10:56 AM.

[Mbuna]

And extra information; i mounted the drawer they way ZWO instructs on their site (https://astronomy-im...tions-55mm.html)

 

[Midnight Dan]

Well, this is very strange.

 

In the Optolong information you provided, the upper section with the text description and showing an unmounted filter seems to be correct.  The side of the filter with the coating on it will provide the least ghosting and should be facing the telescope.

 

But all mounted filters are designed so that the male-threaded side faces the camera and the female threaded side faces the telescope.  That way the filters can be threaded onto other devices which use the same orientations for their male and female threaded sides.

 

However your filter, and the one shown in the bottom part of the Optolong info, seem to be the opposite.  The Optolong image appears to be showing the male-threaded side on the left, and the female-threaded side on the right.  But the right image has the most ghosting meaning it should face the camera - which is backwards from the thread orientation.  And the same seems to be occuring in your filter as well.

 

So I don't have an answer for you, but I do share your confusion!

 

-Dan

Edited by Midnight Dan, 25 February 2022 - 10:13 AM.

[Mbuna]

Well, this is very strange.

 

In the Optolong information you provided, the upper section with the text description and showing an unmounted filter seems to be correct.  The side of the filter with the coating on it will provide the least ghosting and should be facing the telescope.

 

But all mounted filters are designed so that the male-threaded side faces the camera and the female threaded side faces the telescope.  That way the filters can be threaded onto other devices which use the same orientations for their male and female threaded sides.

 

However your filter, and the one shown in the bottom part of the Optolong info, seem to be the opposite.  The Optolong image appears to be showing the male-threaded side on the left, and the female-threaded side on the right.  But the right image has the most ghosting meaning it should face the camera - which is backwards from the thread orientation.  And the same seems to be occuring in your filter as well.

 

So I don't have an answer for you, but I do share your confusion!

 

-Dan

At least thank you for the shared confusion... And also: sorry! I contacted the seller (Astromarket) but they gave a strange answer like "we don't know but we don't think it should make much difference" That kind of shocked me, they don't understand that i try to squeeze everything out of my equipment. 

 

Also contacted Optolong with the same images, i wonder how long it will take them to react. And it is not difficult to turn the glass in the filter, but i'm confused that i should have to do that with a new filter...

[DirtyRod]

Interesting info. I've been just screwing the sucker in and going with it. Didn't know there was a "right" side and generally screw the filter in from the side where the filter is more centered in the drawer. I do have the drawer in reversed on one scope just because of the way the threads and spacers work. Either way the images always look good so I guess I need to read that article. 

[Midnight Dan]

Interesting info. I've been just screwing the sucker in and going with it. Didn't know there was a "right" side and generally screw the filter in from the side where the filter is more centered in the drawer. I do have the drawer in reversed on one scope just because of the way the threads and spacers work. Either way the images always look good so I guess I need to read that article. 

I have filters from another brand but to be honest, I've never done the pencil test.  Like you, I just assumed that screwing them in normally, male threads towards the camera, would be correct.  I figured the pencil test was only needed for unmounted filters.

 

Next time I have my filters out, I'll have to take a look.

 

-Dan

[Mbuna]

Interesting info. I've been just screwing the sucker in and going with it. Didn't know there was a "right" side and generally screw the filter in from the side where the filter is more centered in the drawer. I do have the drawer in reversed on one scope just because of the way the threads and spacers work. Either way the images always look good so I guess I need to read that article. 

Because of my confusion i searched for instructions. The fun part is that there are a lot of reviews, but none of them shows the actual placement in the optical train. The show a shiny filter, discuss the bandpasses and BOOM there is the image that proves how good the filter is functioning?? 

 

There are complaints about the halo's the Optolong sometimes produces. Maybe this is due to the wrong placement?

[DirtyRod]

Because of my confusion i searched for instructions. The fun part is that there are a lot of reviews, but none of them shows the actual placement in the optical train. The show a shiny filter, discuss the bandpasses and BOOM there is the image that proves how good the filter is functioning?? 

 

There are complaints about the halo's the Optolong sometimes produces. Maybe this is due to the wrong placement?

 

That is an excellent point. I just looked and my filter is installed correctly in my RedCat imaging train but I know the filter drawer is backwards in the imaging train in my SCT. I do not have halo issues with my RC so, to your point, maybe its because I have it installed correctly. 

 

If its important, I would think that Optolong would have this highlighted in the installation instructions. 

 

Thank you for the thread. 

[Mbuna]

That is an excellent point. I just looked and my filter is installed correctly in my RedCat imaging train but I know the filter drawer is backwards in the imaging train in my SCT. I do not have halo issues with my RC so, to your point, maybe its because I have it installed correctly. 

 

If its important, I would think that Optolong would have this highlighted in the installation instructions. 

 

Thank you for the thread. 

i never saw installation instructions from Optolong or ZWO (for the filter drawer). they seem to think that it all speaks for itself

[Mbuna]

Optolong reacted to me:
“ Thanks for your inquiry. I am so sorry we bring to you a big confusion .

There often received some inquiries about the about which side should face the camera sensor for unmounted filters. So we make a explaination for it on website as your link shows.

'ghost image test' is much appropriate for L-Pro，LRGB filters which with AR coatings.

The L-eXtreme with other coating technology without AR coating. So you could see there are ghosts on both sides. Just one side was most visible.

No worries, L-eXtreme facing side is correct you don't need to turn it the other way around.

Thanks for your careful attitude.”

[Midnight Dan]

Well.  There you have it. Clear as can be.    Or ... clear as Google Translate can make it.

 

I guess the main point is you don't need to turn the filter around in the filter cell.

 

-Dan

[KTAZ]

But now we are curious...

 

With the often reported "halo" problems that these filters seem to have, it would be nice if the OP could pick a nice bright star and shoot sample images of the filter facing both ways.

 

I don't think you can do it without reversing the entire filter drawer, though. Pretty sure that the drawer is not thick enough to simply thread the filter into the back side of it.

 

Time for a shoot out!

[Midnight Dan]

I don't think you can do it without reversing the entire filter drawer, though. Pretty sure that the drawer is not thick enough to simply thread the filter into the back side of it.

I'm not familiar with the ZWO drawer, but from the images above it looks like you might be able to just flip the drawer around and insert it into the holder?

 

-Dan

[Mbuna]

I actually thought about that… but I would have to dismount the filter glass from its casing, and turn it around. With the very low amount of clear skies I get here (in a bortle 8 zone in Europe) I don’t want to waste any clear sky time.

Maybe someone who has multiple rigs and more clear skies can experiment?

[Mbuna]

I'm not familiar with the ZWO drawer, but from the images above it looks like you might be able to just flip the drawer around and insert it into the holder?

-Dan

[Mbuna]

No, one-way only

[DirtyRod]

No, one-way only

Actually you can flip the entire drawer around just not the filter holder. I did not initially have the right adapter so I used to connect the M48 side to the reducer on my SCT versus connecting the camera to the M48 side as I do with my RedCat. Later I got an M48 to M42 adapter so I couple flip it and keep the filters right next to the camera in both setups. That has the filter pointed in the right direction. 

 

At the time I did not know there was a right side to the filter so I was just making it fit in the train whatever way I could. 

Edited by DirtyRod, 26 February 2022 - 02:44 PM.

[MeteorBoy]

Hi Mbuna,

 

I also have the L-Extreme filter (1.25").  Mine like yours appears to be mounted backwards (and opposite the photos published online by the manufacturer).

 

Your received Optolong text reply above only continues to confuse this issue.  Logic is that the less ghosting side faces the telescope.

 

To that end, I removed the filter holder's retaining ring, reversed the optical element then reinstalled the retaining ring.  To remove the retainer I easily made a special tool using a plastic divider from a small parts storage box.

 

I didn't have any difficulty doing this and now feel better with the less ghosting side of the filter facing the telescope.

 

Thanks for the heads-up.

[StuartT]

Well now.. this is all jolly upsetting!

 

Like all you chaps I have my L Extreme the wrong way round too! I don't have a filter drawer, but I screw the filter into the focal reducer flattener. That is with the male side of the thread facing the camera. I had no idea there were two sides to the filter, but I now see that the side with the ghosting is facing the scope. So my filter is the wrong way round too!!

 

Why do Optolong make them this way and then tell you they should be around the other way? Don't they understand how filters are fitted to equipment? Who knows whether this actually makes a real visual difference? I am very pleased with my L Extreme's performance, but maybe I will reverse it too and get even better performance! It would certainly be interesting to see a comparison (especially if this is what's causing all those halos)

Edited by StuartT, 23 March 2022 - 03:54 PM.

[StuartT]

I just reversed my filter. A very straightforward job.

 

Thanks for flagging this!

[dclt]

I'm not familiar with the ZWO drawer, but from the images above it looks like you might be able to just flip the drawer around and insert it into the holder?

-Dan

I use the same ZWO filter drawer. The way the filter drawer is constructed, there is only 1 possible filter orientation that will work when using a 2” mounted filter. If you try to flip the filter “backwards” the filter holder will not fit in the filter drawer slot.

[StuartT]

I just bought an Optolong L Pro and also wonder if I need to reverse this one too. But it doesn't look like the L Pro has the same AR surface that the L Extreme. Can anyone confirm? 

[chuckkoos]

'ghost image test' is much appropriate for L-Pro，LRGB filters which with AR coatings.

The L-eXtreme with other coating technology without AR coating. So you could see there are ghosts on both sides. Just one side was most visible.

No worries, L-eXtreme facing side is correct you don't need to turn it the other way around.

 

My interpretation of this piece of Chinglish is, L-eXtreme doesn't have an AR coating, so the test on their site isn't applicable.

[StuartT]

'ghost image test' is much appropriate for L-Pro，LRGB filters which with AR coatings.

The L-eXtreme with other coating technology without AR coating. So you could see there are ghosts on both sides. Just one side was most visible.

No worries, L-eXtreme facing side is correct you don't need to turn it the other way around.

 

My interpretation of this piece of Chinglish is, L-eXtreme doesn't have an AR coating, so the test on their site isn't applicable.

Thanks. 

 

The only thing is, my experience is the opposite. I have both the L Extreme and the L Pro. The L Extreme has very marked ghosting on one side compared to the other. But the L Pro doesn't appear to have any ghosting on either side.   

[ldipenti]

I just reversed my filter. A very straightforward job.

 

Thanks for flagging this!

Hi Stuart! Have you seen any difference with the filter in the opposite orientation?