• Ultraviolet Photography

Broadening Your Horizons (with SvBony et al.)

Lens TriColour Macro
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#1 Bernard Foot

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Posted 01 April 2021 - 17:16

In the post at https://www.ultravio...__fromsearch__1 David describes how he fits an SvBony meniscus lens behind his main lens to get a wider angle of view and a brighter image on his M4/3 camera. (This is a home-made, dumbed-down version of the focal reducers sold to allow SLR full-frame lenses to be used on mirrorless cameras with smaller sensors while retaining their full-frame angle of view. These devices start at £80: they have more sophisticated optics which should give better image quality but will almost certainly reduce UV transmission.)

This was an interesting and potentially useful development, and I wanted to see if David’s invention would work on the slightly larger APS-C sensor.

At the same time I thought I’d try out another solution for widening the angle of view – wideangle converters that screw into the front of the prime lens. I had one in the back of a drawer from my Hollywood days when I used 8mm cine cameras. This multiplied the prime lens focal length by a modest 0.7x. I also got a Lazer Titanium 0.42x version off ebay for the grand sum of £1 (although postage cost several times as much). These devices have “macro” in the name because you can unscrew them and use the rear lens as powerful close-up lens. You just know these devices are going to be great performers because they are engraved with terms like “High Definition” and “Professional”, are from brands famous for optical excellence (like Opteka, Sunagor, Kepcor, Seimar, …), cost as little as £10 new, and are intended for use on camcorders. (There are some exceptions – Schneider Kreuznach produce some costing up to multi-£000s.)

Here is a review of these three devices. All testing (unless stated otherwise) was done using a Baader U. Lenses used were the Focotar-2 50mm f/4.5, IgorOriginal 35mm f/3.5, and Lithagon 28mm f/3.5, all at f/11.

Angle of View

The following images illustrate the increased angles of view when using a Focotar-2 with the three devices. The angle of view of the Focotar-2 on its own is indicated by the red box.

What is also immediately apparent is the barrel distortion introduced by these devices.

The angle of view using the SvBony is similar to that using the Sunagor.

Attached Image: Coverage SvBony.jpg

Attached Image: Coverage Sunagor.jpg

Lazer Titanium:
Attached Image: Coverage Lazer.jpg

Image Quality

In these images, the ruler was laid diagonally across the frame from frame centre to extreme corner. Image cut-off can be seen in some images – this is discussed later.

The reduction in image quality is obvious, and as a result I don’t expect to be using any of these devices in real life. Interestingly David’s experience was that the SvBony improved the image quality of the Cassar S.

Focotar-2 50mm:
Attached Image: Resolution Focotar.jpg

IgorOriginal 35mm:
Attached Image: Resolution IgorOriginal.jpg

Lithagon 28mm (Edited: original post had a repeat of the IgorOriginal image):
Attached Image: Resolution Lithagon.jpg

UV Reach

UV reach was tested by measuring exposure factors for each device on the Focotar-2 using three UV bandpass filters. The lower the exposure factor, the better.

Attached Image: UV Reach.jpg

All of these devices will be fine with a broadband UV filter like the Baader U.

The SvBony performance with the 315BP20 is adequate for it to be used with applications such as TriColour. The (Lazer) Titanium could be used at a push, if enough light is available. The Sunagor, on the other hand, would be totally unusable.

Effect on Exposure

David’s experience with the SvBony indicated that up to 2 stops could be gained. I did not see this benefit, although there was some speed gain using the SvBony on the Focotar. I also did a quick check using the Lithagon lens, and here the speed gain was almost negligible.

The screw-in wideangle adapters had a negative impact on exposure – presumably simply because of absorption by the additional glass.

Attached Image: Exposure.jpg

Image Cut-off/Vignetting

None of the devices caused any image cut-off when used with the Focotar-2.

With the wider angle lenses, the cut-off is on a knife-edge. For example, if you use the 28mm Lithagon with no filters attached, there is no cut-off using the SvBony, and very little when using the Titanium. However, when you add the Baader U you get significant cut-off.

Even focussing for different distances can cause cut-off to appear.

My environment probably makes this situation worse. I have 48mm-49mm stepping rings on each side of the Bader U, making it quite deep. And with the Sunagor and Titanium (where the filter fits between the device and the prime lens), there is an additional 52mm-49mm stepping ring in front of the filter and, in the case of the Lithagon, a 49mm-52mm stepping ring behind the filter. The impact of these can be seen in the ruler images earlier on.

To illustrate this further, here are comparisons for the Lithagon with the SvBony and Titanium:

Lithagon + SvBony, Baader U:
Attached Image: Lithagon SvBony.jpg

Lithagon + SvBony, No Filter:
Attached Image: Lithagon SvBony No Filter.jpg

Lithagon + Titanium, Baader U:
Attached Image: Lithagon Titanium.jpg

Lithagon + Titanium, No Filter:
Attached Image: Lithagon Titanium No Filter.jpg

"Macro" Capability

Here is what you get from the "macro" function of the Titanium and Sunagor, by unscrewing them and using the rear element as a strong close-up lens. These images were made using the Focotar-2 focused on infinity. No need for any comment!

Attached Image: Focotar Sunagor.JPG

Attached Image: Focotar Titanium.JPG

Edited by Bernard Foot, 03 April 2021 - 20:13.

Bernard Foot

#2 dabateman

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Posted 02 April 2021 - 06:15

So the SvBony with a dual adapter will cover the Sony 1.5x crop APS-c sensor. Thats great to know.
You do seem to have an increase in sharpness and contrast with SvBony and igoriginal at the center of the frame for the ruler. But this is at a significant penalty for the corner sharpness.

This maybe due to distance from sensor or alignment of the lens. Distance matters a lot for the SvBony. The further away it is the more light will be focused on to the sensor. I assumed the C-mount in the dual adapters would be equal distance from the sensor to give you 17.5mm for C-mount lenses. But that may not be the case. If you have an other empty 25mm ring see if spacing the SvBony further away makes the image worse or better.

Anyway the SvBony may still be useful for focusing your attention on center subject or if its focusing in a curve for your lens, may want to test field curvature, than might help get corner subjects at a different distance in focus.

#3 dabateman

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Posted 02 April 2021 - 06:37

Also check with a zoom lens what your field of view change to equal.
I have 4 SvBony 0.5x lenses. 1 is flipped (concave to sensor) in original 1.25 inch holder. It used with my Nikkor 80mm f5.6 EL lens with a C-mount to 1.25" adapter. Its would be about 30ish mm away from the sensor and it changes the EL80 to a 43mm lens.

One is in a 25.5mm filter ring I got from Cadmium, (concave to sensor) and screwed in the C-mount of dual adapter. Used with my 35mm igoriginal lens and it changes to a 23mm view. Not sure exact distance from sensor.

The other is in slimmer 25mm ring and used behind my soft Steinheil 50mm EDIXA lens. That one improved image quality the most.

#4 Bernard Foot

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Posted 02 April 2021 - 08:38

David - you made a few points:
  • Curvature of field: I did try angling the ruler to get different distances betwen centre and edge, but the edge resolution was so poor it was difficult to determine which was the best (or, rather, least bad) image.
  • Using a zoom lens - I don't have any M42 zoom lenses, unfortunately.
  • Changing the position of the SvBony - I don't think I have the parts to do this elegantly, but I may try to put together a kludge using Blu-Tac or whatever.
BTW - it's interesting to see what impact reversing the SvBony has (i.e. having the convex surface towards the sensor). I think resolution was slightly better with the wider angle lenses. Cut-off was less. And I was able to get infinity focussing using a 17-31mm helicoid (while awaiting the 12-17mm helicoid).
Bernard Foot

#5 dabateman

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Posted 08 April 2021 - 07:09

Sorry Bernard I wasn't clear.
Take an image with your lens that has been modified with the reverse mounted SvBony focal reducer.
Then remove the lens. Add a zoom lens to the camera and try your best to match up the exact same frame. Then read off the focal length from the zoom.

Now you will know what that distance from sensor, the SvBony gives you for focal reduction. As in if your 35mm is equivalent to 17.5mm on zoom. You have full 0.5x reduction. But most likely based on your exposure you may only be at 0.8x. So I am guessing your igoriginal 35mm lens looks like a 28mm lens.

Edited by dabateman, 08 April 2021 - 07:11.

#6 dabateman

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Posted 11 April 2021 - 08:02

Your sharpness images changed. Now the Lithagon 28mm looks the best with SvBony even out to the edge.
So that lens seems to need some SvBony correction.

#7 Bernard Foot

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Posted 11 April 2021 - 08:09

View Postdabateman, on 11 April 2021 - 08:02, said:

Your sharpness images changed. Now the Lithagon 28mm looks the best with SvBony even out to the edge.
So that lens seems to need some SvBony correction.

Yes - I'd originally screwed things up - I had one of the other sharpness images duplicated and omitted the Lithagon image (actually, it appeard at the end of the post as I hadn't referenced it in the relevamnt position).

And you're right - it doesn't look oo bad with the SvBony (where does that name come from?) reversed.
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#8 dabateman

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Posted 11 April 2021 - 13:00

Bernard I have never cared about the name of stuff. Just as long as it works well and is cheap.
However, their name is actually an acronym and stand for the following, I must say I think its a little unusual for a Chinese company.

The meaning of SVBONY is:
S means support, we will provide the maximum technical support for each purchased customer,
V stands for sound, we will listen to the voice from the customer so as to better improve the product quality.
B means bring, we hope to bring high quality products to customers at cheaper prices.
O means obtain,We hope that every customer who buys from us can get a very good customer experience.
N means new,We pursue constant innovation, Looking forward to a newer self
Y means young,The company has just started, as a young brand, the staff are also relatively young, we look forward to this younger enthusiasm to fight for a better self
The above is the meaning of our name.

#9 Stefano


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Posted 11 April 2021 - 13:07

View Postdabateman, on 11 April 2021 - 13:00, said:

V stands for sound
Are you sure? (I know it is a joke)

#10 dabateman

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Posted 11 April 2021 - 13:54

View PostStefano, on 11 April 2021 - 13:07, said:

Are you sure? (I know it is a joke)

I don't think thats a joke, unless internal to the company.
I get e-mails from them with the subject line "How is your life going". Then there will be a sale or discount. I think the people behind this distribution company have an odd sense of humor.