Filter stack order

[bsas]

So, I finally got my 52mm set from UVIR Optics (U-360 52mm x 2mm + S8612 52mm x 2mm) and I was wondering. Does it make any difference the order of the filters?

 

For example: lens -> S8612 -> U-360 or lens -> U-360 -> S8612?

 

I imagine that it shouldn't make any difference in the results, but does it make any difference in the exposure?

 

Thanks all!

[Andy Perrin]

I've never noticed an actual difference. In theory if they have different refractive indexes, then it could make a difference to the reflectivity factor, but again, any such difference probably needs a spectrometer to notice, not a camera!

[dabateman]

These are both ionic glass types not dichroic. Its shouldn't matter which is first or last. I will sometimes have S8612 on the lens first, just so I can flip through my other filters.

 

Some believe that the face side of the Baader venus filter matters. So many including my self have flipped the filter over in the holder. But I think Andrea did a study and found that it makes no difference.

 

For polarizers there was some arguement that filter order matters. I think Lee has a diagram indicating the order. But its so confusing that everyone argued either way. I did a quick test and didn't see any effect, one way or the other. Polarizer will cut 50% of the light by definition. Then your filter cuts the rest. So do you want to filter from 50% or do you want 50% of your filtered light? Still not sure why one way would be better than the other. If your filter is special than maybe it needs to be first to avoid odd chiral effects.

 

For stacking 2 dichroic filters it may matter as the angle of light matters. I will place 313bp25 then 330WB80 improved filter then camera lens. So filter the light, then clean it. But I am also forced to stack this way based on the way I made the filters. I don't have front threads on most of my dichroic bandpass filters.

 

But based on the sensitivity of our cameras, being really poor, it mostly doesn't matter.

[Cadmium]

Only for the sake of hocus pocus, I put the S8612 in the front, no tested reason for it, it should make no difference, I just like blocking the IR first.

But like Andy and David said, I don't think it should matter, and I have never heard anyone say it would or might, and I have never seen any difference.

The Baader U I have never seen any difference in the direction it is mounted either. I have tried it both ways, and see no difference.

Theoretically, I think the reason people said to reverse the direction was because it was designed to be mounted behind a telescope, and we are mounting it in front of a lens,

but I forget the theory. Regardless, I never used it behind a lens, only in front and could not see a difference when reversing it,

so I just left it mounted in the direction that was suggested for us terrestrial camera people that front mount the filters.

I can see why some might want to mount the S8612 closer to the lens, so they can change from U-360 to (say) UG5 (U-330) or other U filters without removing the S8612 also.

Makes sense. Test it both ways and decide.

 

What will you take UV pics of mostly? Landscapes? People? Flowers?

[Andrea B.]

The thing to look out for in stacked separate filters is unwanted reflections caused by some light bounce between layers. I haven't seen much of it, but I have definitely seen some. So it is good to be aware of it.

Please excuse my lack of proper terminology for this side effect. "Light bounce between layers" may not be the correct description. Anyway, I once had an odd blurring of small detail caused by reflection when using filter layered with glass to prevent oxidation. I had to return it to have the that removed. I've also seen some reflections when stacking on wider angle lenses. Moving around and re-framing helps with that.

 

The thing to look out for in very shiny, hard-coated filters like the BaaderU or other dichroic filters is -- yes, again -- unwanted reflections. The advice for the BaaderU was always to place the shiny pink side outwardly facing the subject. Of course, the transmittance of the BaaderU or other filters is not affected by which side faces the subject. I've never seen anything too bad with the BaaderU pink side in. But it is important to be aware that it can happen. BTW, these days the "pink" side of the BaaderU might be another colour? I think it is more golden in recent BUs?

Example of unwanted reflections: https://www.ultravioletphotography.com/content/index.php/topic/2882-filter-test-seu-gen2-8-dichroic-reflection-detour/

 

The reflection problem in either case can manifest itself as a hotspotty king of thing or as a washed out area or as concentric rings. And there is also the flare type of reflection which are discoloured blobs along a diagonal usually brought on by shooting contrajour. With my much lamented doubly dichroic Edmund Optics 340/10, I get 3 kinds of problems at once - ringed hotspotty washouts. La!

 

I'm very scientific today --> discoloured blobs.

[Andy Perrin]

I have some issues with my dichroic UVIR cut filter where it produces nasty flare or duplicate images of the light source. It doesn’t seem affected by what order I stack it however.

[Andrea B.]

Andy, is that over a wide angle lens? Or over any lens length? Just curious.

Who makes that cutter?

[Andy Perrin]

Hoya makes the cutter, and it’s any lens.

[Andrea B.]

Do you think it might be faultily constructed?

[Andy Perrin]

I don’t think so? I figured it was just shiny dichroic filter and camera facing light source are not a felicitous combination? I think they need to add an anti reflective visible coating also. That would help.

[Andrea B.]

I wonder if there is some clear anti-reflective filter you could stack over it. At the risk, of course, of further inducing more unwanted reflections. But ghosting is slightly different from reflecting off internal lens parts, so maybe it could work???

[Alaun]

Isn't it simply to keep out e.g. fluorescense, if you have a glass sensitive for that, or to keep out heat, e.g. with the Baader (the red side in front keeps out the heat, the red side at the back the IR will heat the glass) ?

[Andy Perrin]

I don't know why you would want to keep out near IR using a camera filter! It's kinda small for that. Usually in applications where heating is important, you use a cheap plastic film over a much larger area? No, Hoya UVIR cut filters are intended for photography, probably mainly to fix leakage in the built-in filter of unmodified cameras.

[Alaun]

Well, the Baader is originaly intended for telescopes. Looking at the sky, at a sunny day, might put quite some heat to a filter.

[dabateman]

Andy,

I think there maybe a small language issue.

What Alaun is referring to is the order of blocking in a dichroic filter. If the IR blocking part is further in, than it will block the IR, but will need to pass back through the filter, which can cause issues. So best to try both ways, either IR coating side on outside or inside, to see if there is an effect of passing through the glass.

I hope that makes it clear. Some filter types work best to filter your wavelength out first then follow up with a cleaning filter. But not all will work that way. If Omega tested it and found an optimum orientation it will be marked on the filter.

[Andy Perrin]

No, he clarified. He really did mean heating, I did not consider that the Baader were originally intended for telescopes where you actually could get significant heating of the sensor due to the “magnifying glass frying ants” effect. I do think my Hoya filter was not meant for astronomy purposes. It’s an ordinary 52mm filter not like the Baader’s odd size.

[Alaun]

Andy, dabateman is right, that is exactly, what I had in mind.

[Andy Perrin]

I am totally baffled here. Are we talking about Baader UVIR cut filters or my Hoya UVIR cut filter? Mine is not astronomical. Flipping the filter isn't going to do much of anything because the reflection is a VISIBLE light reflection.

 

Here is the filter:

https://hoyafilterusa.com/product/hoya-hmc-uv-ir/