Back to forums

Clear Filter or No Filter

ZWO EFW 5 x 2" Filter Wheel UV/IR Cut
15 replies•328 views
Jerry Gerber avatar
Jerry Gerber avatar
Hi!

I have a ZWO 5x2" filter wheel for an OSC camera.

I put a UV/IR filter in one of the slots not realizing my camera , the ASI2600MC already has that filter built into it. 

My question is, should I remove the UV/IR filter from the slot and have no filter in that slot or should I get a clear filter and replace the UV/IR filter with that?  In other words, is it better for weight/balance to have a filter in each slot or does it not matter?

Thanks,
Jerry
Well Written Engaging
Dale Penkala avatar
Dale Penkala avatar
Jerry Gerber:
Hi!

I have a ZWO 5x2" filter wheel for an OSC camera.

I put a UV/IR filter in one of the slots not realizing my camera , the ASI2600MC already has that filter built into it. 

My question is, should I remove the UV/IR filter from the slot and have no filter in that slot or should I get a clear filter and replace the UV/IR filter with that?  In other words, is it better for weight/balance to have a filter in each slot or does it not matter?

Thanks,
Jerry

Hello Jerry,
I have the same setup and I use a UV/IR Cut filter in my EFW as well. I have the UV/IR, L-Pro & NBZ. I bought 2 of the Starizona’s “blackout” to put in the other 2 spaces and have not had a problem at all.
Personally I wouldn’t worry about the 2x uv/ir but I just didn’t like the fact that I had 2 open slots where dust etc…. Could make its way to the cameras sensor window. Plus I can take darks easily as well!

Dale
Helpful Supportive
Christian Großmann avatar
Christian Großmann avatar
From my experience every unnecessary surface in the light path decreases quality a bit. But it might be negligiable. Leaving the filter in might stop some additional light that passed the first filter although it should not. But it may or may not be an issue.

But there is one thing that might be worth thinking about. With a set of filters from the same manufacturer, the focus distance usually does not change much. I don't know what this is called in english. But the glass of the filter effects the focus distance and staying within the products of one maker, all filters may change it by nearly the same amount. So if you are using and OAG, this might help keeping the guiding camera in focus. But I can't guess, how much this effects the sharpness, because a lack of experience. It's just a thought…

CS
Christian
Charles Hagen avatar
Charles Hagen avatar
My question is, should I remove the UV/IR filter from the slot and have no filter in that slot or should I get a clear filter and replace the UV/IR filter with that?  In other words, is it better for weight/balance to have a filter in each slot or does it not matter?

You should not remove the UV/IR filter there for a couple reasons, paramount of which is the back focal issues that it will cause. Filters take up a certain amount of optical back focus, as a rule of thumb by 1/3rd of the filters physical thickness. Therefore, completely removing the piece of glass will drastically change your focal point and your back focal correction without a filter. This means you won't be able to optimize your systems back focal distance between all filters. Additionally, the integrated UV/IR sensor window (which I cannot find any information on, if it exists at all. most of the time they are only AR-coated windows) is likely not to be as restrictive as you may want for the extraneous UV/IR signal. Adding an extra layer of filtering there will reduce star bloat, out of band chromatic aberration, and microlensing artifacts on bright stars. 

CS,
Charlie
Helpful Insightful Respectful
Jerry Gerber avatar
Jerry Gerber avatar
Dale Penkala:
Jerry Gerber:
Hi!

I have a ZWO 5x2" filter wheel for an OSC camera.

I put a UV/IR filter in one of the slots not realizing my camera , the ASI2600MC already has that filter built into it. 

My question is, should I remove the UV/IR filter from the slot and have no filter in that slot or should I get a clear filter and replace the UV/IR filter with that?  In other words, is it better for weight/balance to have a filter in each slot or does it not matter?

Thanks,
Jerry

Hello Jerry,
I have the same setup and I use a UV/IR Cut filter in my EFW as well. I have the UV/IR, L-Pro & NBZ. I bought 2 of the Starizona’s “blackout” to put in the other 2 spaces and have not had a problem at all.
Personally I wouldn’t worry about the 2x uv/ir but I just didn’t like the fact that I had 2 open slots where dust etc…. Could make its way to the cameras sensor window. Plus I can take darks easily as well!

Dale

That's pretty much what I did.  I am shooting with an OSC so the 5 filters I use are  the UV/IR cut, L-Ultimate, the Ha-Oiii, Sii-Oiii and a dark filter for shooting darks.
Oscar Echeverri avatar
Oscar Echeverri avatar
Maintaining a UV/IR/Clear filter in your filter wheel ensures that each slot in your filter wheel remains near parfocal, given that all your filters are parfocal. However, if there’s an unoccupied space in the filter wheel, the focus at that particular spot will be different from the other spots.
Well Written Concise
Imran Badr avatar
Imran Badr avatar
What scope do you have? Some are forgiving for a small 1-2mm. I have esprit100ed with 2600mc pro and efw with L-ultimate, L-enhance and askar color magic filters. I have a slot open for broadband. I have another setup with 2600mcpro with askar300 and dual band filters. I have a slot open there as well. Haven't run into backfocus issues.
Jerry Gerber avatar
Jerry Gerber avatar
What scope do you have? Some are forgiving for a small 1-2mm. I have esprit100ed with 2600mc pro and efw with L-ultimate, L-enhance and askar color magic filters. I have a slot open for broadband. I have another setup with 2600mcpro with askar300 and dual band filters. I have a slot open there as well. Haven't run into backfocus issues.

I have an Askar 130 PHQ at a remote site.  No worries about backfocus as the scope is a quadruplet with the flattener inside the scope.  i am going with the advice of Charlie and keep the filter array the way it is.
Byron Miller avatar
Byron Miller avatar
If you use an off axis guider you want a clear filter as parfocal as can be otherwise with no filter it will be out of focus.
Imran Badr avatar
Imran Badr avatar
Byron Miller:
If you use an off axis guider you want a clear filter as parfocal as can be otherwise with no filter it will be out of focus.

That is a great point, Byron! Might explain my occasional issue with guide camera focus when I switch between no filter and dual band. I do use OAG.
Well Written Respectful
Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
Oscar Echeverri:
Maintaining a UV/IR/Clear filter in your filter wheel ensures that each slot in your filter wheel remains near parfocal, given that all your filters are parfocal. However, if there’s an unoccupied space in the filter wheel, the focus at that particular spot will be different from the other spots.



This is only true if the filters are all the same thickness. Having a 3mm thick uv/ir filter with the others being 1mm filters would make it worse than not having that uv filter.   

In general, I agree with others. It's best to have filters in those slots. You can benefit from the AR coatings and if all filters are the same thickness, retain focus for your OAG across your filter choices.
Helpful Insightful Respectful
Jerry Gerber avatar
Jerry Gerber avatar
Byron Miller:
If you use an off axis guider you want a clear filter as parfocal as can be otherwise with no filter it will be out of focus.

There's an OAG but it's located in the image train before the EFW so the filter will not affect the light that's picked off for the guide camera.  It's already parfocal but may need to be adjusted.  The gear hasn't seen first light yet as it just got set up last week and it's at a remote location.
Chris White- Overcast Observatory avatar
Chris White- Overcast Observatory avatar
Jerry Gerber:
Byron Miller:
If you use an off axis guider you want a clear filter as parfocal as can be otherwise with no filter it will be out of focus.

There's an OAG but it's located in the image train before the EFW so the filter will not affect the light that's picked off for the guide camera.  It's already parfocal but may need to be adjusted.  The gear hasn't seen first light yet as it just got set up last week and it's at a remote location.



hes talking about whether the guidecamera and main camera maintain focus between filters.

Filters shift the focal plane, so if you no longer have a filter in the light path, you will need to refocus the main camera, and the guidecamera will lose perfect focus. 

That's why you want the same thickness filters in all your fw slots.
Helpful Insightful Concise
Oscar Echeverri avatar
Oscar Echeverri avatar
Chris White- Overcast Observatory:
Oscar Echeverri:
Maintaining a UV/IR/Clear filter in your filter wheel ensures that each slot in your filter wheel remains near parfocal, given that all your filters are parfocal. However, if there’s an unoccupied space in the filter wheel, the focus at that particular spot will be different from the other spots.



This is only true if the filters are all the same thickness. Having a 3mm thick uv/ir filter with the others being 1mm filters would make it worse than not having that uv filter.   

In general, I agree with others. It's best to have filters in those slots. You can benefit from the AR coatings and if all filters are the same thickness, retain focus for your OAG across your filter choices.

Hence why I said "given that all your filters are par focal"
Jerry Gerber avatar
Jerry Gerber avatar
Chris White- Overcast Observatory:
Jerry Gerber:
Byron Miller:
If you use an off axis guider you want a clear filter as parfocal as can be otherwise with no filter it will be out of focus.

There's an OAG but it's located in the image train before the EFW so the filter will not affect the light that's picked off for the guide camera.  It's already parfocal but may need to be adjusted.  The gear hasn't seen first light yet as it just got set up last week and it's at a remote location.



hes talking about whether the guidecamera and main camera maintain focus between filters.

Filters shift the focal plane, so if you no longer have a filter in the light path, you will need to refocus the main camera, and the guidecamera will lose perfect focus. 

That's why you want the same thickness filters in all your fw slots.

I understand. One of the several reasons I chose to image in color is to avoid some of the complexity of using different filters for every (or nearly) every image. 

I'll change filters but rarely, to image in narrowband, Ha-Oiii, Sii-Oiii or a UV/IR filter. 

​​​​​​The guide camera needs to be in focus, but the imaging camera needs to be in better focus. My understanding of guide star detection is that even if not in perfect focus, it can still guide successfully within the limits of the mount and sky conditions. That's been my experience. But it's possible that I may have to refocus the guide camera to find the best possible compromise between any deviation between filter thicknesses.

Glad you pointed that out, thanks.
Helpful
Marc-Antonio Fischer avatar
Marc-Antonio Fischer avatar
Allways use a full set of filters in the filterwheel. Reasons are like someone said you want to have the quite same focusposition and more important, the filterwheel can be out of balance and worst case is that the filterwheel cant drive to the exact same position again and your flats wont work. Had this experience with your filterwheel in the past.