Jump to content
UltravioletPhotography

Bushnell 21mm vs Nikkor 18mm UV Transmission Test Comparison


Cadmium

Recommended Posts

My experience is that the 21/4.5 has a significant focus shift visible to UV, so LiveView (or EVF) is highly recommended.

 

I'm using the 21 with a rear-mounted Baader U (last generation) on my Panasonic GH-2. The Baader sits inside the lens mount adapter. With the Nikon D3200 the similar Baader is inside the camera and although I can focus through the finder in a normal manner, checking focus via Liveview is again desirable.

 

As this is not a "fast" lens, there has to be sufficient UV illuminating the scene for the LV/EVF to show anything at all. In fact, using a Zacuto finder attached to the rear panel of the D3200 is the better option as the eye can accommodate to the low brightness. The EVF frequently degenerates into static and precise focusing might be hard to obtain. In bright light, the difference in focusing efficiency is much reduced but the unnatural brightness of the EVF - again -does cause more strain on the eyes.

Link to comment

By the way Bjorn, unreal photo, very nice indeed, nice blue in the background also.

I don't have a UV stack made for this yet, but I made an RG830 rear filter for it today, 2mm thick, with a 1mm thick custom O-ring to give clearance space between the filter glass and the rear lens element dome. This worked well.

Not sure yet if I can fit the UG11+S8612 2.75mm thick stack in the same space yet. I don't have the UG11 cut yet.

Here are the pics with the RG830 2mm rear mounted filter. This was a dark day, overcast skies with some intermittent light rain.

I shot this on two cameras, not sure about the difference, I used the same settings, but I am not as familiar with the D7200 yet.

I used Aperture Priority with both cameras.

D7200 shots also seem more grainy than the D7000 shots with close inspection.

Focus is not the same with the rear mounted filter, I had originally set it to infinity focus, and had to change that in live view. I use the Zacuto live view finder/loupe also.

 

Using D7000 (ISO 200, f/8, 1/80s)

post-87-0-43302300-1461470543.jpg

 

Using D7200 (ISO 200, f/8, 1/120s)

post-87-0-16843900-1461470834.jpg

Link to comment
  • 2 weeks later...

Here are two shots using the Bushnell/Tamron 21mm lens with a rear mounted UG11 1mm + S8612 1.75mm laminated stack.

This fits in the holding ring with a 1mm O-ring between the filter and the rear element holding ring, necessary to prevent filter from touching rear element dome.

I used f/11 for these shots.

Full size images.

post-87-0-42989400-1462644806.jpg

 

post-87-0-80638500-1462644842.jpg

Link to comment

I was trying to do a Bjorn pic here... :-)

Settings: f/8, 2s, AP, 0EV, Center-Weighted, ISO 250, D7000, Bushnell 21mm, UG+BG stack rear mounted (BG forward facing).

post-87-0-71153900-1462853992.jpg

 

Actual Pixels Crop of above shot:

post-87-0-73573700-1463411713.jpg

 

This one has a dandelion:

post-87-0-13575900-1462853898.jpg

 

Actual Pixels Crop of above shot:

post-87-0-69259300-1463465530.jpg

 

post-87-0-75392700-1462854163.jpg

 

Actual Pixels Crop of above shot:

post-87-0-65147900-1463411704.jpg

Link to comment
Andy Perrin

I really like the last one Steve

Me too! What I like about it is how the UV-colored trim stands out.

Link to comment
  • 2 years later...
SteveCampbell
Quick note on the Bushnell 21mm f3.8 - lets in approx 2.5 stops less light than the Takumar 35/3.5 at comparable apertures on informal testing. Suggests to me that it's not a fantastic performer.
Link to comment

Steve, "Bushnell 21mm f3.8"?

It is one of the best performers for that focal length range. Many 35mm lenses would out perform UV transmission of 365nm, as shown in the first post comparing the Nikon 18/4 and the Bushnell 21/4.5.

But if you want a wider angle lens than 35mm, UV transmission is hard to find much better.

The 21mm transmits UV slightly better than the 18mm, a bit stronger it seems, not enough to worry about.

Have you tried an 18/4?

Link to comment
SteveCampbell

Steve, "Bushnell 21mm f3.8"?

It is one of the best performers for that focal length range. Many 35mm lenses would out perform UV transmission of 365nm, as shown in the first post comparing the Nikon 18/4 and the Bushnell 21/4.5.

But if you want a wider angle lens than 35mm, UV transmission is hard to find much better.

The 21mm transmits UV slightly better than the 18mm, a bit stronger it seems, not enough to worry about.

Have you tried an 18/4?

 

I noticed for the 21/4.5 the trick is removing the rear element. Is there a similar procedure for the 21/3.8? Which of the two has better transmission?

 

Haven't tried the Nikkor 18/4 on account of the cost, but will keep an eye open for bargins

Link to comment

I nave no experience with a 21/3.8. So I can't answer that question.

Yes, the 18/4 was expensive last I looked.

Alex was the person who I first saw show how the Bushnell 21/4.5 worked for UV.

If you have questions about that lens, you might ask him, because he may have more knowledge about it than me,

and he may know about the 21/3.8 you are talking about also, perhaps. Alex is very smart about lenses.

 

The good thing about the 18/4 is that is it probably the best combination of widest and best UV.

The best thing about the Bushnell 21/4.5 is that it is a little better UV, but a little less wide.

I don't know if Alex ever got an 18/4 yet. :)

However, I do think the Bushnell 21/4.5 is definitely one of the best very wide lenses for UV that I have tried.

I don't know of any lens that wide that transmits UV any better.

If anyone knows of a lens that transmits UV that well, and is that wide please let us know.

Link to comment
  • 2 weeks later...

Very interesting topic. For me the best "affordable" wide-angle lens so practice UV photography is the Tokina 21mm F/3.8. I also own the Tamron 21mm F/4.5, and even if the UV transmission is a bit better, the corners are not so sharp. And taking into account that I need tripod to shoot at F/11 and iso100 with both, the few difference in exposure time does not justify to prefer the Tamron over the Tokina regarding the picture global quality.

 

Here is an example taken with the Tokina at F/11, 100iso, 3s on a Canon 6D full-spectrum body. Filter used is a stack of Hoya U-360 2mm and Schott S8612 2mm.

 

post-112-0-68799300-1530443630.jpg

Link to comment
SteveCampbell

Very interesting topic. For me the best "affordable" wide-angle lens so practice UV photography is the Tokina 21mm F/3.8. I also own the Tamron 21mm F/4.5, and even if the UV transmission is a bit better, the corners are not so sharp. And taking into account that I need tripod to shoot at F/11 and iso100 with both, the few difference in exposure time does not justify to prefer the Tamron over the Tokina regarding the picture global quality.

 

Here is an example taken with the Tokina at F/11, 100iso, 3s on a Canon 6D full-spectrum body. Filter used is a stack of Hoya U-360 2mm and Schott S8612 2mm.

 

post-112-0-68799300-1530443630.jpg

 

Thanks Don, good to know I don't need to keep searching for a better wide-angle. I would love to know which of the elements of the 21/3.8 are most highly coated. I'm in the process of getting together equipment to experimentally remove lens coatings (a roughed-up takumar preset 105/2.8 might be my first taget). With the 21/4.5 it's apparently that removable back element that's most responsible coatings-wise. With the 21/3.8, who knows. Perhaps if I compare element UV color rendering against a PTFE background...

 

Note: I just realized that the color of specular highlights (is there a more precise optical term?) in the lens elements will probably give some hints. For the preset 2.8/105 it's predominantly the rear element that gives a blue color.

Link to comment

With the 21/4.5 it's apparently that removable back element that's most responsible coatings-wise. With the 21/3.8, who knows. Perhaps if I compare element UV color rendering against a PTFE background...

 

Note: I just realized that the color of specular highlights (is there is more precise optical term?) in the lens elements will probably give some hints. For the preset 2.8/105 it's predominantly the rear element that gives a blue color.

 

I assume that you already know that it is not only the coatings that attenuate the UV-light.

Some optical glass types and cements are also possible offenders.

 

Are you sure it was the coating and not the glass in the back element that caused the attenuation?

At least at the time the lens was designed, I think it would have been easier and cheeper to use a filter-glass to cut UV.

 

I think someone mentioned the back element had a faint yellow tint.

That is how to describe the looks of a Schott GG420, especially if it is thin.

Schott has several different filter glass types cutting UV, and so has Hoya.

 

Your experiment removing lens coatings is interesting, but it might not always work UV-wise.

Looking forward to hearing about the results.

Link to comment

 

Here is an example taken with the Tokina at F/11, 100iso, 3s on a Canon 6D full-spectrum body. Filter used is a stack of Hoya U-360 2mm and Schott S8612 2mm.

 

 

Was the stack front- or rear-mounted?

Link to comment
SteveCampbell

I assume that you already know that it is not only the coatings that attenuate the UV-light.

Some optical glass types and cements are also possible offenders.

 

Are you sure it was the coating and not the glass in the back element that caused the attenuation?

At least at the time the lens was designed, I think it would have been easier and cheeper to use a filter-glass to cut UV.

 

I think someone mentioned the back element had a faint yellow tint.

That is how to describe the looks of a Schott GG420, especially if it is thin.

Schott has several different filter glass types cutting UV, and so has Hoya.

 

Your experiment removing lens coatings is interesting, but it might not always work UV-wise.

Looking forward to hearing about the results.

 

This is good to know, I had assumed that the majority of the effect was via coatings and the UV-attenuating effects of all standard types of glass. I chose the Takumar 105/2.8 as my first attempt because of the 4e/4g arrangement, allowing me to avoid the complexities of cements. I have a a couple projector lenses in the mail that I would imagine are unlikely to use UV-cutting glass - if anyone can show specialized attenuating glass in the 105/2.8, I'll have my hand at the projector lenses instead.

 

I'm currently using my Bushnell 21/3.8 with a 72->77 step up to UG-11 + BG39.

Link to comment

There are many types of glass used for lens design.

They are combined too cancel out different optical errors to make a well corrected lens.

More exotic materials than glass are sometimes used like quartz and calciumfluorite.

Here is a thread about different optical glass types:

http://www.ultraviol...ous-lens-glass/

 

Here is an example of an optical design with different glass types:

https://www.synopsys...ass-expert.html

 

The GG420 I mentioned before is a glass type specially designed for filtering, just as your UG11 or BG39

The GG395 look crystal clear to us, but cut UV at 395nm at a certain glass thickness.

Link to comment

I'm currently using my Bushnell 21/3.8 with a 72->77 step up to UG-11 + BG39.

 

Are you using this combination on a full frame camera, and if so, do you have any problems with vignetting?

Link to comment

 

 

Was the stack front- or rear-mounted?

I use both 82mm filters stacked in front of the lens, using a 72mm to 82mm filter.

Link to comment

As shown in post #1 of this topic, for the 21mm there is a small filter type glass that should be removed in the rear, because it cuts UV.

I think it is GG420 or the like, so it cuts all UV.

I have a few older telephoto lenses with similar rear filters. They work the same way, and like Ulf says, yellow glass (GG### type), cuts UV.

 

I remember Bjorn had a page (probably still does) that talks about removing the front coating on the Nikon 35mm E lens.

I have the E, but I have never tried removing the coating, would probably be easy enough to try and compare, just use some cerium oxide.

Link to comment
SteveCampbell

 

 

Are you using this combination on a full frame camera, and if so, do you have any problems with vignetting?

 

FF 5D mark II with spectrosil conversion. No noticable problems with vignetting noted so far

Link to comment
SteveCampbell

As shown in post #1 of this topic, for the 21mm there is a small filter type glass that should be removed in the rear, because it cuts UV.

I think it is GG420 or the like, so it cuts all UV.

I have a few older telephoto lenses with similar rear filters. They work the same way, and like Ulf says, yellow glass (GG### type), cuts UV.

 

I remember Bjorn had a page (probably still does) that talks about removing the front coating on the Nikon 35mm E lens.

I have the E, but I have never tried removing the coating, would probably be easy enough to try and compare, just use some cerium oxide.

 

Yes, the 3.8/21 has a similar element to the 4.5/21, but optical performance is hugely compromised with it removed.

 

I'll be using either cerium oxide or 0.25 micron water-based diamond abrasive paste, depending on how the diamond paste performs on my first attempt.

Link to comment

Yes, the 3.8/21 has a similar element to the 4.5/21, but optical performance is hugely compromised with it removed.

 

This rear element on the 3.8/21 might be shaped like a lens, making its removal more significant.

 

Even a flat window or filter have some impact on the optical performance of a lens system as it can be a part of the optical design, not only for filtering.

 

One example of this are high magnification microscope lenses that are designed for the specific thickness of the cover glass covering the specimen on the microscope slide.

There is least impact on the system if all light beams passing the element are parallell.

Link to comment
SteveCampbell

 

 

This rear element on the 3.8/21 might be shaped like a lens, making its removal more significant.

 

Even a flat window or filter have some impact on the optical performance of a lens system as it can be a part of the optical design, not only for filtering.

 

One example of this are high magnification microscope lenses that are designed for the specific thickness of the cover glass covering the specimen on the microscope slide.

There is least impact on the system if all light beams passing the element are parallell.

 

Yes, it's more lens-shaped. With it removed the image has more chromatic abberation, softness, profound peripheral softness, and narrower angle of view. It's a cool effect though.

Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...