Retooling for new year. A6000 and Baader U?

[KaJashey]

I'm thinking of retooling for the new year. Thinking of picking up an A6000 full spectrum from life pixel and a Badder U possibly from B&H.

 

I know the camera is low end but I'm hoping it's a step up from my really low end Nex 5n. I've seen a user or two on here with the A6000 so it seems to work. Anyone use this or have any comment? 

 

I'm also hoping the Baader U is a step up in transmission. I have a La La U by UVIROptics but I think its best transmission is like 30% at 360nm or something. Where is the best place to get a Baader U? For photography I read here that it works best threads first. How thick is the Baader U with it's brass body?

 

Thanks

[ulf]

27 minutes ago, KaJashey said:

I'm thinking of retooling for the new year. Thinking of picking up an A6000 full spectrum from life pixel and a Badder U possibly from B&H.

 

I'm also hoping the Baader U is a step up in transmission. I have a La La U by UVIROptics but I think its best transmission is like 30% at 360nm or something. Where is the best place to get a Baader U? For photography I read here that it works best threads first. How thick is the Baader U with it's brass body?

 

Thanks

I think you will be a bit disappointed about the speed gain you get from a Baader U.

The La La U is not that bad, with a transmission much better than 30%.

 

Here below is Steves theoretical transmission graph.

It do not include the surface reflection losses so I would guess the real transmission is 8-9% lower.

The peak would then still reach a rather good 55-58%.

 

If you compare that to the transmission of Baader U,  around 75% + , the speed gain will be around half a stop.

I predict that if you have an exposure time of 10s with the current filter, a Baader U will give you between 6 and 8s.

 

The gain you get by the flat top peak of Baader U, deeper into UV a is almost completely cancelled by the camera sensor's steep sensitivity drop against shorter wavelengths.

 

 

There are advantages and disadvantages with a dichroic filter like the BaaderU

On the plus side:

• This filter is produced with a super quality with properties that are very valuable for astronomy usage. There other filters in the same Planetarium-line with common properties making them suitable for changing on a telescope without affecting the telescopes settings. To get that, the filter material is rather thin. (ca 1mm?)
• The filter is optimised for telescopes where the passing light rays are rather parallell.
• Due to the coating the surface is immune to the dreaded glass corrosion caused by high humidity, that is often seen on raw optical U-glass materials.
• The dichroic design gives a high transmission pass band.

On the minus side:

• The cost. The BaaderU is expensive
• The thin material is more easy to break, and if you do, there is a replacement cost that is high.
• The IR rejection is limited to around OD4. In some situations that might be visible
• The transmission and IR rejection is sensitive to the angle of the passing light beams. 
• The dichroic design is more sensitive to light hitting the filter from the side outside the image area. It is more important to use a lens hood. 
• There have been cases with less IR rejection than OD4. It might be old stock or newer batches. The high OD might not be as important for astronomy usage as it is for us.

I have a Baader U that I bought five years ago, but I use it rather seldom.

 

FYI the Baader U is mounted in a filter cell with threads that are not found on camera lenses. I think it is 48mm x 0.75mm

 

The filter cell's total length is 8.08mm including the threads. The outer surface without threads is 6.00mm

Some of us has remounted the filter glass from a Baader U in different filter ring/(s) with 52mm threads.

 

 

[KaJashey]

20 minutes ago, ulf said:

I think you will be a bit disappointed about the speed gain you get from a Baader U.

The La La U is not that bad, with a transmission much better than 30%...

 

...FYI the Baader U is mounted in a filter cell with threads that are not found on camera lenses. I think it is 48mm x 0.75mm

 

The filter cell's total length is 8.08mm including the threads. The outer surface without threads is 6.00mm

Some of us has remounted the filter glass from a Baader U in different filter ring/(s) with 52mm threads.

 

 

 

Thank you. Very enlightening. All my La La U documentation had been erased by eBay cleaning out old posts/photos/records and I was working from fallible memory. 

 

I was aware of the 48mm threads but the other physical characteristics of the Baader U don't sound easy to work with. May carry on with the La La U

[ulf]

One of the reasons I do not use my Baader U much is that I like to experiment with many different filter glass types.

Then I have to work with a separate IR blocking filter, like my S8612 2mm, stacked with different filters.

In my setup I have surface losses from four surfaces, getting less transmission, but stillI find it acceptable.

 

Exposure time is affected by many other things that half a stop more or less transmission.

There are many possible paths for improvement and sometimes getting a new filter is not the best one.

[Andy Perrin]

The one thing I really like about the Baader (from the comparisons Andrea has done on here) is the contrast and the false colors compared to other single-filter options and filter glass. Obviously one needs a lens with good transmission and sharpness also, to take advantage of these.

[lonesome_dave]

FYI here is my Kolari Vision converted Sony A6000 with a quartz Sirchie lens and a 1.25" Baader-U that I remounted into a 30.5MM filter ring. Lens hood from an old Rollei 35GS added.

 

The smaller Baader-U is less expensive than the 2 inch version and is adequate for the C-mount lenses you should consider using for their low cost and decent UV transmission. The smaller sensor size of the A6000 allows for the use of rather inexpensive C-mount lenses with little multi-coating which can allow for a good UV pass. The lens pictured here is not cheap but I have also used this setup with $30 C-mount 25mm f/1.4 lenses with decent results.

 

But as has been said even the smaller Baader-U is expensive (look for used ones on ebay). The standard UV-pass/IR block filter stack is much cheaper and yields just as good result in my opinion unless you also want to spring for a quartz lens.

[Andy Perrin]

How is the chromatic aberration, Dave? I have that lens but I found it was giving me a lot of aberration near the edges even on APS-C NEX-7, however that may not be an issue with a much smaller sensor.

[lonesome_dave]

Andy, I haven't noticed chromatic aberration but that's probably because I only use it for UV and IR pics. I'll check some of the early VIS images I took when I first got it. We should note that the Sirchie 60mm f/3.5 lens we are discussing here is a macro lens intended for forensic imaging. On the original Sirchie electronic imager you can get to infinity focus but on most camera mounts you will need to modify the lens by removing the slide-in filter holder to use it as a general purpose lens.

 

For those wondering, this lens is from the Sirchie Krimesite imager you can sometimes find on ebay for a few hundred dollars or more. I've obtained several of those kits over time and re-packaged them for educational use as both UV and IR live imagers. There is also a smaller quartz lens they make (25mm f/2.8) for the Scan & Find version. That lens I don't recommend for photographic use as it has significant barrel distortion.

 

To clarify my advice for the original poster... If you get a mirrorless camera with a smaller sensor like the APS-C or micro 4/3rds you might consider getting a C-mount adapter ($15) and try an inexpensive C-mount lens ($30-$50) or two for UVA photography with a UV-pass/IR block filter stack ($30-$40). Depending on the lens you may get some image cropping but photoshop will take care of it and you'll still have thousands of pixels each way. You can spend several hundred or more on a quartz or fused silica lens and then more yet on a Badder-U type filter to try to get deeper into UV but I don't think you will find much difference. For the most part stuff that looks darker in UVA vs VIS will just look a bit more dark in UVB. The big bang for the buck is getting a decent UVA image (350-380nm for example) which will look very different from a standard VIS image.

 

To be clear I'm talking about a low-cost entry into UV photography here and not the high-end setups many folks on this forum use.

[Andy Perrin]

13 minutes ago, lonesome_dave said:

Andy, I haven't noticed chromatic aberration but that's probably because I only use it for UV and IR pics. I'll check some of the early VIS images I took when I first got it. We should note that the Sirchie 60mm f/3.5 lens we are discussing here is a macro lens intended for forensic imaging.

I am referring to chromatic aberration in the UV false colors (after white balance against PTFE or similar procedure). For instance, look at this photo. This is a 1-1 crop to show the issue, but you can see the yellow fringe of C.A. in this UV false color picture.

[lonesome_dave]

Ah yes, I understand. I guess my first take is to say that I am a bit less picky than some about this level of defect.

I presume this is only observed when using a setup that gets you down into or near the UVB spectrum. My knowledge of false colors from a photo sensor in UV is limited but I believe you need to get down to around 320nm or so to see the yellow-green?

 

Is there another UVB-capable lens you would recommend?

[Andy Perrin]

Nah, this is definitely UV-A. My filter was a 330WB80, and the lens is quartz, but the camera sensitivity goes down very fast so the true peak is probably still in the 350's or something. Yellows start showing by 365nm. 

 

Anyway, my point is that this lens might be okay as long as you use it with the 1/2" sensors or maybe micro-4/3, but on larger sensors it's going to get aberrations near the corners, even on APS-C sensors like the above pic.

 

Quote

Is there another UVB-capable lens you would recommend?

I don't think the original poster really wants a UV-B capable lens, if they are planning to take normal UV photos like the majority of the forum. Only a very few posters (Lukas, dabateman, Jonathan, maybe a few more) have attempted UV-B, mostly with monochrome cameras. It's EXTREMELY difficult and costly.  

 

A good UV-A capable lens that's affordable with excellent bandpass is the EL-Nikkor 80mm/5.6 metal rim version, which everyone on this forum ought to own. It's wicked sharp and well-corrected, and it passes all the UV-A that one would want. 

[lonesome_dave]

Cool. I see the EL-Nikkor 80/5.6 can be had for about $125. Not sure if it's the metal rim version. Is that important?

[Andy Perrin]

Yes, the metal rim version is a different lens (in UV) from the plastic one. That price seems high but I haven't been keeping track recently.

[dabateman]

The EL 80mm f5.6 metal also transmits more UVA light than my Quartz Pentax UAT 85mm lens at the same F-stop. The UAT wins for UVB and UVC transmission. The EL 80mm doesn't transmit any UVC light.

 

But would agree with Andy in that the El 80mm is probably the best starting lens for UVA. $100 might not be too far off for it as we have been talking about it too much here, which seems to raise the cost. 

I got a mint new in the box metal El 105mm f5.6 last year for around $125. Also a good lens. I have never seen the original box or dome before.  Its also a nice lens.

 

The A6000 Sony also seems to be an excellent UV camera.  One of the few cameras with great UVB sensitivity and might also be sensitive to UVC, if you use enough light in a ventilated area. It was Bernard's favorite. 

 

@KaJasheythe Baader venus u filter is my favorite for its contrast.  But it Does have its limitations and tricks.  Its not too different than a stack with coated S8612 with U340. The best stack for UVA transmission might still be 2mm coated S8612 with 2mm U360. You can cheap out with ZWB2 for U360 or ZWB1 for U340. 

 

[lonesome_dave]

Glad to hear the Sony A6000 (full-spectrum converted) might be good for UVB (with quartz lens). I was planning on getting a narrow bandpass filter around 310-320nm to try to photograph something down there to look for any changes from UVA. If it doesn't work with the camera I can use it on the electronic imagers I have. So far I haven't seen much difference in subjects appearance vs UVA even when using the electronic imager in UVC. The darkening of materials just gets darker.

 

The Baader-U is the only wideband UV filter I plan to own as I'm not much interested in UV false-color. My main interest in UV imaging is for forensic and educational applications and the color (and wider band) just complicates comparison with other spectrum images. I've done a lot of false-color IR back in the film days but hadn't thought about doing it in UV until seeing what you guys have done here on UVP. The artistry may yet draw me into it.

[Andy Perrin]

It requires a ton of blocking to reach UVB. A single filter won’t do it without leaks. Please review what Lukas went through here before you start buying things. Read the WHOLE thread. We went through quite a lot to verify what was being photographed and I don’t want to go through it all again with someone else if they haven’t learned the lessons of the last person. 

 

[Stefano]

Regarding UVB, my full-spectrum Canon EOS-M with original coverglass, CFA and microlenses can record UVB, at least down to 310 nm, given enough blocking and exposure.

 

I use two Chinese 310 nm bandpass filters stacked together, each rated at about 50% transmission and OD 5 blocking. A single filter was not enough to block UVA at ~340 nm, red and IR. Only using two stacked I had enough blocking (OD 10) to take UVB photos under sunlight. Under bright sunlight in a sunny day, this usually requires at least 8-15 s of exposure at ISO 25600 at an aperture of about f/4, using lenses with good transmission there (SvBony 0.5x focal reducer or fused silica). In an overcast day, the exposure may be 30 s or one minute. The only things I can see in live view are the Sun and 310 nm LEDs.

 

I was even able to use a halogen lamp for illumination, but this required 23 exposures at ISO 25600 and 30 s.

So it is possible with the right equipment, but quite challenging. Provided your camera can see UVB at all (I think Andy's camera can't, for example), you probably need at least OD 8-9 of blocking. As Andy said, one filter (usually rated between OD 4 and 6) is not enough.

[lonesome_dave]

Thanks Andy and Stefano. Yes I have read your threads and checked them again now. The work you and the others have done there is impressive.

I was going to try a 25nm bandpass around 315nm and stack 2 Baader-Us for more blocking. I already have those and want the UVB filter for my electronic imagers anyway. IR pollution is a concern and at least for the electronic imagers the IR falloff is earlier than the camera so maybe it will work better on the imagers. Like you say I may need more blocking.

 

My purpose is not to prove I am getting all UVB but to look for differences in subjects that can be useful forensically. That means I also have the ability to adjust the imaged spectrum a bit by controlling the light source.

[Andy Perrin]

I strongly suggest that you do what I did at the end of that thread and simulate the entire thing (including light spectrum and sensor response if you can) ahead of time, before buying filters and spending money. If you don't know what you are really seeing, then you have nothing, especially for a scientific purpose like forensics. Work that isn't reproducible is not good work. Out-of-band leakage is very very easy to get.

 

Quote

stack 2 Baader-Us for more blocking

See, this is the kind of idea that is characteristic of people who haven't done the work to simulate the end-to-end response. Because if you had, then you would have realized that the Baader cuts to zero at 330nm, so you would be cutting your signal!

 

This is from Jonathan's thread here:

https://www.ultravioletphotography.com/content/index.php?/topic/2375-baader-u-and-invisible-vision-308nm-filter-comparison-for-skin-imaging/#comment-17160

 

If you had gone ahead with that plan, it would have cost you a LOT of money for two Baader U's and you would also have defeated your own purpose. I hope this convinces you of the need to do your homework before you start, beginning with the light source spectrum. You can at least maximize your chances of getting a good result if you do the work ahead of time.

[lonesome_dave]

Yes Andy, you are correct that I should have looked forward a bit before pondering. However I think you missed that I said I was looking at 315nm, not 308nm and that I already had the 2 Baader-U's. I can see that my pass spectrum would still be quite limited though and I should adjust up a bit to maybe 320 or 325nm if I want to use the camera. The electronic imager uses a photomultiplier so it might be usable with a 315nm bandpass with a good light source and a Baader-U. There is the option of just recording the phosphor screen on the imager like you have to with UVC.

 

I wanted to use the Baader-U's I already have so I'll start from there and the light source (was thinking about building with 315nm LEDs) to figure out the best bandpass filter to get. This would be in an enclosure to protect everyone from UVB exposure.

 

I'm trying to find something interesting for a forensics lab idea in a class I'm trying to help with, not doing research. Based on what I've seen of UVB so far on this site my expectations are low and I may end up just sticking with the UVA, Near-IR, and thermal-IR stuff.

 

Thanks for putting this together. It helps me figure this out.

[Andy Perrin]

No, the 308nm was just from Jonathan’s old work (however see next paragraph). It was not the point of my post, which was to show that using any Baader U’s is a poor idea. Getting some Hoya glass would be a better choice, even if you already have a Baader. You are fighting the sensor curve also.  
 

When Lukas used a 308nm he ended up with an actual peak near 317nm when all effects were accounted for, so it is probably better to pick a bandpass filter on  the short side of where you are aiming for. 

UV LEDs are very weak and also pricey. Might be okay for relatively closeup or macro work, however.

 

Please do your homework and actually multiply out light source, filters, and camera sensitivity to find the curve, and design rationally rather than by guessing. 

[lonesome_dave]

Yeah I've gotten lazy in my old age and like to do things empirically instead of trying to calculate everything beforehand with uncertain data. I guess it's my way of keeping my charitable work fun without consuming all my time.
 
All the stuff I buy gets donated or lent out semi-permanently so I don't worry too much about wasting a little money on sloppy planning now and then. I have a regular supply of components to donate to school science programs! It's my excuse for buying cool techie stuff to play with while I'm still able to enjoy it. But yes, mine is not the best method.

 

Thanks again for your help on this one Andy.

[Andy Perrin]

All data are uncertain, that’s never a reason not to calculate things. But I guess now I know not to help you any further!

[lukaszgryglicki]

UV-B is quite hard, I believe I was able to record it in 310-330 range with:

- Mono converted, full spectrum, quartz cover glass Fuji 50R.

- UV-Nikkor.

- Invisible Vision 308nm filter.

- Hoya U-340 4mm thick.

We come to conclusion that my peak is around the edge between UV-B and UV-A about 317nm or probably somewhere around 310-320.

LOT of sunglight is needed, very long exposures, in range of around 1 minute or more.

 

EDIT: and I'm going to stay with this setup as my fav one. I will also try witj my new ZWB 8mm. I also think about buying one more IV 308nm - that would make a best UV-B only stack IMHO.

 

EDIT2: can I have a link to "chinease 310nm filter" ?? Anybody did any measurement of such a filter? UV-B filters are (IMHO) almost impossible to get and ultiomately have leaks, if there is a cheap chinease UV-B 310nm filter then *I want it!* - but I need to know if this is something that is really UV-B or just anything, like almost everything you can imagine from aliexpress.