Lens source

[jbs054]

Has anyone tried these lenses? Any idea of the cost?

 

http://www.universeo...ens_assemblies/

 

Thanks! Jonathan

[nfoto]

Quoting the maker

 

Though they are optimized for 266nm you can see the wide range of transmission. Be advised that the lenses are NOT corrected for constant focus throughout this range. Re-focus will be required at different wavelengths.

 

In non-technical speak, you can expect a lot of chromatic aberrations. These lenses are narrow-band designs.

 

No idea about their pricing.

[Alex H]

Edmund Optics sells two of them:

 

25mm http://www.edmundoptics.com/imaging-lenses/fixed-focal-length-lenses/uv-fixed-focal-length-lenses/57542/

 

78mm http://www.edmundoptics.com/imaging-lenses/fixed-focal-length-lenses/uv-fixed-focal-length-lenses/57543/

[DaveO]

Hi Jonathon,

 

I started my UV macro work taking Australian Native Wildflowers with the 105 mm quartz lens from this agent

 

http://www.ultravioletphotography.com/content/index.php/topic/673-goodenia-blackiana-blacks-goodenia/

 

This was one of my earlier results. The UV image, when examined critically at 100% often showed a spread of false colours in the out of focus backgrounds suggesting some colour fringing effects even within the Baader U pass-band. There was a significant focus shift, as you would expect, between the visible and UV images using the Baader U filter which meant re-focussing using live view for all the UV images. Having said all that, I was happy with the UV transmission of this lens with my full spectrum Pentax K5.

 

Good luck

 

Dave

[Adrian]

I have been doing some research on quartz lenses recently, and contacted the company about these. They cost around $1300 - $1700 for the 50, 78 and 105mm versions. They sent me the technical spec for all the lenses as pdfs if you would like to see them?

Adrian

[Guest]

I have the 78mm lens from Universe Optics, and I can say from experience that chromatic shifts are definitely a problem. I wish I had known about apochromatic lenses back before I bought mine. While I am happy with the UV transmission of my lense, it can be tedious dealing with the focal shift.

[Andrea B.]

This type of non-apochromatic, industrial-use quartz lens is meant to be used with narrowband UV-pass filters. With a wideband UV-pass filter, there can be, and often are, chromatic aberrations. Rendered in either false colour or in black & white, such aberrations might be difficult to fix in an editor because they may not be in a "colour" which the editor's CA tools recognize. (I hope I've said all that correctly!!)

 

I would think, however, that mostly your UV fotos with such a lens will be OK. :D I have not worked intensively with the non-apo quartz lenses I have, else I would try to give you more information about what to watch out for and/or how to fix it. If you do encounter any problems, post the example photo and request some input. There are so many members here who know such good stuff that surely someone will have an answer.

 

Using Live View helps deal with focus shift. Mount UV-pass filter, open up lens, shine UV-LED onto subject, focus through Live View and then stop down lens. (And pray you don't experience any aperture shift, yet another pesky problem with certain lenses.)

[jbs054]

Thank you all for the information! While the price would certainly please the bean counters I'm going to recommend not since accuracy of imaging is the main goal here.

[JCDowdy]

Depending on what you need from them they can be a more affordable option. We have two of these, 25mm & 50mm. Tried the 78mm but focal length was not suited to our uses. Ditto what has been said above, great UV throughput, significant CA. That said I have encountered worse CA in the UV with some normal lenses I have played with. IMHO DaveO has demonstrated that good botanical images can be made with these. Even so, one notes he has since upgraded to a Rayfact UV 105mm.

[JCDowdy]

And pray you don't experience any aperture shift, yet another pesky problem with certain lenses.

 

What if anything can be done about it?

[Andrea B.]

It's a kind of lens aberration. So you can't "fix" the lens. You just have to compensate for it.

 

You probably won't notice it if the lens is stopped down enough because increased depth of field will cover the shift away from the original plane of focus. But, for example, if you focus at a wide-open f/1.4 to shoot at f/2.8 or f/4, the misfocus might not be compensated for because that's still rather shallow DoF. So you have to manually adjust your initial focus after stopping down. Or perform some 'focus bracketing'. Or maybe try Live View.

[JCDowdy]

It's a kind of lens aberration. So you can't "fix" the lens.

 

As I thought, thanks for confirming.

[Andrea B.]

Now I've been batting my head trying to figure out what kind of aberration it is. Spherical?

It occurs along the lens axis because the plane of focus shifts slightly?

And why would that happen just because you close the aperture blades more tightly?

 

Four minutes later: Oh duh! It happens because for some lens element shapes the light passing through the outer 'ring' of the lens doesn't focus at the same place as the light passing through the center? So when you make the aperture narrower that must cut off some of the outer ring of light and you lose the focused light? [Poor terminology here. I will try to look up the proper words later.]

 

I wonder why they make lenses like that? Not all lenses are like that.

[Bill De Jager]

Now I've been batting my head trying to figure out what kind of aberration it is. Spherical?

.....

I wonder why they make lenses like that? Not all lenses are like that.

 

Lloyd Chambers states that it's due to uncorrected spherical aberration. It seems to crop up with only some lenses, one of which is the Nikon 14-24. All I can suggest is that sometimes lens designers don't prioritize correcting or controlling that particular aberration. It can be done with lenses of this class, as was the case with the Canon 11-24 and the Tamron 15-30.

[JCDowdy]

Here is a succinct discussion entitled "What is Focus Shift?" with a good diagram.

[Andrea B.]

With auto-focus lenses focus shift would certainly be less of a design consideration I suppose. We generally do not perform the old fashioned stop-down focus method with our newer electronic auto-focus lenses.

 

John, thx for the link.

[Andrea B.]

hmmmmmm.......I think a diagram in that link are slightly off.

The wide open diagram should show focus with all rays, shouldn't it?

 

No, I'm wrong. If using a very wide open lens, then all rays do not converge precisely.

That is why we often see the "veiling" or "haze" with an f/1.2 or f/1.0 lens.