uv/ir cut filter for rookie

[dancingcat]

Howdy all and Happy Thanksgiving to those in US…

 

I am a rookie here and my Olympus Em1mk2 full spectrum conversion is on its way back to me from Kolarvision.

The advice here seems to be to use a stack of Hoya U360 2mm + Schott S8612 2mm for UV.   Need to verify with you if that’s right - this is for botanicals.

 

Also what do you recommend for cutting out the UV and IR so I can do work in just the visible?

 

I plan to start with the Olympus lenses I have now, but will probably need to go lens searching down the road.

 

Thanks for everyone’s help to a noob.

 

 

 

 

[Andy Perrin]

The best UVIR cut choice on the IR end of things is Schott BG38 2mm, and on the UV end of things the Zeiss T* UV cut filter. These must be stacked together to cut both ends. Of the two, the BG38 is more important to the color balance, and the Zeiss just reduces flare with the coatings and takes away some of the UV haze effect. (It would also be important if you are doing any fluorescence work.) So if you are picking just a single filter, the BG38 2mm should be your choice, but ideally you use both. 

 

That said, every camera is slightly different and some need more or less IR blocking, so Cadmium has suggested BG40 as an alternative to BG38 if the latter isn't pleasing enough.

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You should AVOID the Hoya UVIR cut filters, because they let a lot of UV through and don't cut IR enough either. I think Kolari's filter is okay but it's basically just BG38 - it will let a lot of UV through.

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Quote

The advice here seems to be to use a stack of Hoya U360 2mm + Schott S8612 2mm for UV.   Need to verify with you if that’s right - this is for botanicals.

That is right.

[Fandyus]

If you're a rookie, you could just get a BG39 2mm and a ZWB2 2mm from Tangsinuo as your stack. I use it and there's no leakage, worked very well for me so far.

As a starter UV lens I recommend the Industar 50-2, it's very cheap, reasonably sharp, and has a reasonable reach.

[Andy Perrin]

Fandyus, she’s a scientist, she needs good equipment, not hobbyist level stuff that can’t be reproduced by others. Rookie is beginner, but I think in this case it’s best to just buy the right thing and not cut corners. 
 

Sue: Chinese glass like Tangsinuo is a first class ticket to the Journal of Irreproducible Results. 

[dabateman]

Yes a S8612/U360 stack will be great as your first starter set.

To get back the visible,  for Olympus micro four thirds camera I like the BG40 at 2mm. Its very close to what the sensor has. Then as Andy said getting something to remove the UV, like a Zeiss T* or a Tiffen 2A filter.  

 

[ulf]

There might be a reason to temporarily cut corners with Tangsinuo glass, availability.

Sometimes the quality glasses are not available and as Tangsinuo glass is not expensive they could be used while waiting for the Schott/Hoya glass.

 

When funding is not a problem a Hoya U360 2mm + Schott S8612 2mm for UV stack is optimal for flexibility and IR rejection.

An expensive alternative with less IR rejection, but slightly higher transmission is the Baader U. That filter also have some issues due to the dichroic design.

[Andy Perrin]

Ulf, I disagree regarding the Tangsinuo. If you are trying to make archival quality photos of a collection of specimens, which I think is the intent (Sue will correct me if this is not the case), you don’t want to change equipment in the middle because then the previous images cannot be compared to the ones after the filter is switched. (Remember how Mark tied himself down to a shooting routine in just this way and couldn’t adapt his routine later on because he would have had to reshoot the earlier flowers?)
 

Regarding UV filters, the Baader would also work well here - we know Andrea and Birna have used it successfully for flower photos for years now without dichroic issues since they are using slightly telephoto lenses. 

[ulf]

9 hours ago, Andy Perrin said:

Ulf, I disagree regarding the Tangsinuo. If you are trying to make archival quality photos of a collection of specimens, which I think is the intent (Sue will correct me if this is not the case), you don’t want to change equipment in the middle because then the previous images cannot be compared to the ones after the filter is switched. (Remember how Mark tied himself down to a shooting routine in just this way and couldn’t adapt his routine later on because he would have had to reshoot the earlier flowers?)
 

Regarding UV filters, the Baader would also work well here - we know Andrea and Birna have used it successfully for flower photos for years now without dichroic issues since they are using slightly telephoto lenses. 

Andy, actually I fully agree with you about all you are saying about the need for proper filters.

 

My point is that if there are enough funds the extra cost if any time is gained by beginning with chinese filters is not that big, if you want to practice working with the equipment in UV before getting the proper filters.

 

Filters from Tangsinuo might be a reasonable way to do just that.

You have to be aware of that the transmission of the chinese filters are not correct compared to the quality filter materials.

 

If you really need to be sure of the transmission of a filter you have to invest in getting it measured.

Even filters from Schott and Hoya Glass have batch variations and are only guaranteed at a few wavelength points.

[aphalo]

I do not think that even for research is crucial to use Schott or Hoya filters, as long as the glass is from a good batch and you can measure the transmission spectrum and report it. More important if you are planning long-term consistency, I think would be to have back up filters from the same batch in case of their accidental damage or destruction, and possibly even filters of different sizes all from the same batch of glass (achieving this is easier and affordable when buying from Tangsinuo and contacting Mr. Jason Li, the compromise is that it is unlikely that in the future filters matching these will be available). At the moment Tangsinuo has a batch of QB21 2mm glass that is anti-reflection coated, which I think is interesting (I posted in another thread at this site about it only yesterday). I received one of these some days ago, and seems to work extremely well for restoring the normal white balance of my full spectrum converted Olympus E-M1 ("Mk I"). I have now ordered two more from the same batch in other sizes, as they are affordable enough. Of-the-shelf Olympus cameras are responsive to UV-A, their built-in filters do not have a cut-off at 400 mn as other camera brands but at somehow shorter wavelengths.

 

For UV induced visible fluorescence, the best blocking filter for the UV-A excitation is the Tiffen 2A. If using a stack, keep the 2A as outermost. The reason is that ionic glass filters (yellow, orange, red, etc.) fluoresce strongly under UV-A. The Tiffen 2A filter is not based on absorptive glass, but on some kind of gelatin or similar film sadwiched between optical glass. The Zeiss UV T* is dichroic and does not fluoresce either, and works as long as the light source does not emit past 400 nm. I looked at the Kolari filters' page, they sell the cheaper Kolari Vision UV/IR Cut Color Correcting Hot Mirror Filter which seems to be currently antireflection-coated BG38 (or equivalent) and Kolari Vision UV/IR Cut Hot Mirror Pro 2 that looks like BG38 (or similar) combined with a dichroic coating cutting off wavelengths shorter than 400 nm, which should be roughly equivalent to stacking a BG38 and the Zeiss UV T* filter.

 

There is one MFT objective that works well in UV-A: Sigma 30 mm 1:2.8 DN (there is a photo at https://www.photo-spectrum.info/2019/07/digital-uva-photography-with-m43-equipment/ and some photographs taken with it at https://www.photo-spectrum.info/pages-content/lenses-notebook.nb.html that are unsharp because of movement in the wind; and some more at https://www.photo-spectrum.info/2019/06/measuring-campaign-in-the-alps/ although this page sometimes takes very long to load because photographs are served from Flickr). I have been mostly using a Baader U or an StraightEdgeU filter with the Sigma objectives. With bright enough light autofocus and auto-exposure (with a slight manual compensation) work. This lens can be combined with auto-extension tubes for macro (those from Kenko are quite good, while most of the Chinese ones are let down by their reflective internal surface. When testing them I was shocked at how bad some of them can be https://www.photo-spectrum.info/2017/09/macro-extension-tubes-for-mft-glare/). As for adapted manual objectives I find the Nikon Nikkor 24mm 1:2.8 A-IS to be the best I have for MFT (I do not remember who recommended it in a post here). It is sharp in UV-A even at relatively large apertures and well corrected at close focusing distance. Even if the Soligor/Hanimex/etc. family of objectives which I also have has higher UVA transmittance they work well only at small appertures (http://www.savazzi.net/photography/35soligor.html). I do like the ergonomics of the "newer" Soligor's preset apperture ring  but I find myself using the Nikkor more frequently. I have had to shim adapters to be able to achieve infity focus or to make the focusing scale markings show something close to real distances. For consistency in rendering outdoors and to freeze movement in the wind you will most likely need to use a flash. 

 

This is a summary of a few years' of using an E-M1 camera. Much of what I describe above I learnt by reading posts written by other members of this site, but I haven't been able to find all those older posts to link them here. I learnt about the Sigma MFT objectives form Enrico Savazzi's post.  I see now, that I am repeating to some extent what dbateman wrote in a different thread... so I will only add that the Sigma 30 mm 1:1.4 DN works well for UV-induced fluorescence with its larger aperture. I do have the Sigma 60 mm 1:2.8 DN and its UV-A transmittance is lower than for the Sigma 30 mm 1:2.8 DN and I do not find it very usefull for UV.

 

Pedro.

 

p.s.: If it stops raining during the weekend, I will compare the AR coated QB21 vs the AR coated QB21 stacked with a Zeiss UV T*.

[Andy Perrin]

Quote

I do not think that even for research is crucial to use Schott or Hoya filters, as long as the glass is from a good batch and you can measure the transmission spectrum and report it. More important if you are planning long-term consistency, I think would be to have back up filters from the same batch in case of their accidental damage or destruction,

Ok, if you can MEASURE the spectrum, that definitely changes the equation, and I would agree with Aphalo in that case. I was forgetting that sometimes people do have access to spectrometers and can get some idea of whether the spectrum is within tolerances. (This would also be true for Schott and Hoya incidentally.) I have no such capability and am reduced to trusting the manufacturers. That said, I think the message I wanted to send was that in a large project, consistency is an important factor that must be taken into account.

[aphalo]

10 hours ago, Andy Perrin said:

Ok, if you can MEASURE the spectrum, that definitely changes the equation, and I would agree with Aphalo in that case. I was forgetting that sometimes people do have access to spectrometers and can get some idea of whether the spectrum is within tolerances. (This would also be true for Schott and Hoya incidentally.) I have no such capability and am reduced to trusting the manufacturers. That said, I think the message I wanted to send was that in a large project, consistency is an important factor that must be taken into account.

I fully agree with the need for consistency. This may also require using the same lens, camera, light sources and raw-conversion software for the whole study. At least thorough checking for possible biases would be needed. I also agree that if funding is available, Hoya or Schott glass would help ensure long-term reproducibility and be preferable. For those of us in Europe, easiest to find is Heliopan BG38 which is available in multiple sizes and is Schott glass as far as I know. Importing filters from the US is more expensive because of high shipping rates and less convenient than using AliExpress which charges EU taxes at source as well as handling of EU customs clearance. For, Sue, being in the US, things are diferent in this respect, I assume.

[dancingcat]

Thank you all for great help... I'll certainly report back on results.

 

Just for scientific info (I am also a scientist.. most of the time.. :-))... what spectrometer do folks use to measure transmission?

I can probably track one down at local universities to borrow time on.  Physics isn't my thing, botany is, so no clue about how to do these measurements but would like to learn.

 

Sue

[dabateman]

Would be best for you to ask the people at your university: 

"I have a bunch of filters I would like to know the spectrum for, does anyone have an available suitable instrument? "

 

Because what we recommend,  you might not be able to find. But your engineering or physics department might have built the perfect in house system and we wouldn't know. 

 

[Andy Perrin]

Yeah, Sue, I think you probably would have resources we don't. Most people on the board with spectrometers are using very low end devices due to the cost issues, but universities will have better things.

[Fandyus]

 

On 11/25/2021 at 3:58 AM, Andy Perrin said:

Fandyus, she’s a scientist, she needs good equipment, not hobbyist level stuff that can’t be reproduced by others. Rookie is beginner, but I think in this case it’s best to just buy the right thing and not cut corners. 
 

Sue: Chinese glass like Tangsinuo is a first class ticket to the Journal of Irreproducible Results. 

Standardization in UV feels a little futile to me. Unless you're precisely making trichromes the likes of what Bernard did, and even then it would be questionable. Why? I mean isn't it known that different cameras respond differently to UV? Maybe if the images are converted to monochrome but even then the images might a be a bit different. Plus we have asserted you can't determine wavelengths off of the typical UV images we take. So it feels to me like the only thing you're reliably gonna know is the change in texture, and that should show up about the same everywhere where the reach isn't severely limited. So long as there are no leaks, and you can easily test for those. My Tangsinuo ZWB2 setup has no leaks. I think the only time I got weird colors off of it was when imagining a candle flame, and it's understandable some leak would happen there without extra thickness to the filters.

I'm not arguing against buying the premium filters, by all means, if you have the money go off. But I feel like some people here are really hung up on thinking that cheap = bad. I've bought numerous cheap items off of Ali and eBay in the last year and I can only say I've burnt myself maybe two times. One filter had striations and one 365nm bulb I ordered was laughably weak. That's about it. I also have ordered a few cheap color filters which ended up being unusable due to striations but those are literally just pieces of plastic so I don't even count those.

[Andy Perrin]

Fandyus, I'm going to reply in DM. This thread is Sue's, and I don't want to drag it further off-topic.

 

I do think if the glass spectra can be measured, then it won't matter as much which exact filter because then you know what you're seeing in the images.