Want a Cassar S lens?

[bvf]

I reckon the Cassar S 50mm f/2.8 is probably the best non-specialised UV-capable lens (although the Kuribayashi fans might take issue with that). Just noticed there is one being auctioned on ebay, with the current latest bid at about $5 + $25 postage - see https://www.ebay.co....jkAAOSwHVFegeFA

 

If the price doesn't go up much, that's a real bargain. But there is an element of risk - there appears to be a bit of dirt at the edge of the rear element on the inside, and although it claims that the optics are in good condition the lens hasn't been tested (so there could be an issue with focussing movement or aperture movement).

 

Serial No. 2068084.

 

The sale finishes on 4th April at about 19.38 BST (18.38 GMT).

[bvf]

Well, I couldn't resist bidding for this Cassar S, and got it for 45 Euros (half of which was postage from Germany). A real bargain - there is another one for sale on ebay for about £300 + £50 postage (from Australia).

 

I don't need the lens, as I already have one of them - but I couldn't bear to see it being lost to the UV community. I'll check it out and compare it against my existing Cassar S.

 

So if you want a Cassar S, PM me.

[nfoto]

I already have one. A pristine sample directly from Japan, at a very affordable price (even less than you paid). However, as it is indeed a good UV performer, the idea that a member of our small community could have use for it is a very nice thought.

[bvf]

Well, the lens arrived and it was a dud. The aperture didn't work, full-open only. So it's going back to the seller for a refund. The seller said he hadn't realised - but it's hard to believe he didn't know because the aperture ring was loose and turned without any resistance and without doing anything.

[nfoto]

If i may ask, for what range of magnifications have you used the Cassar? The UV-Nikkor, whilst being a tremendous performer, is not easy to handle in my stacking setups at much larger than life-size 1X, as the package tends to be long and thereby prone to wobbliness. I presume the lens is used in a reversed position?

[nfoto]

To answer my own question, a quickly hobbled-up combination of Cassar (reversed) plus a short bellows gives around 2.5X. Which is within my target range of 2-5X. I can add more extension to approach 3X or slightly higher without the setup becoming unwieldy. Thanks for the pointer towards using the Cassar for macro work. Now, I do have to test whether the output quality suffices although judged by the images you have posted that should not be too big a problem?

[bvf]

Hi, Birna.

 

Yes, I reverse the lens when I get to true macro scale.

 

My view of the Cassar S as a macro lens is that it is only so-so - after all, it's only a 1960s triplet. And you need to be stopped down to about f/8 to get reasonable quality. If you've got a proper UV lens then you're going to get far better results. But the Cassar does seem to be better that then El Nik 105 because the El Nik has significant focal shift by 345nm (and serious focal shift at 315nm) and because it does not seem to be able to create a good image at 345nm even if you have re-focussed it for that wavelength.

 

The Cassar has a small focal shift between 380 and 345nm, and you may be able to get away without refocussing. By 315nm the focal shift is significant: for example if the lens focussing scale is at infinity for a 380nm exposure I turn it to 5 feet for a 315nm exposure when the distance from front of lens to subject is 11 cm. For subject distances from 1 metre to infinity the lens focussing ring is set to 12 feet for the 315nm shot. (The focussing for 380nm is achieved using the helicoid with the lens focussing ring set at infinity).

 

As you indicate, you can get 2.5x with the Cassar and extension tubes. With long bellows, I can get about 10x, but image quality is not great.

 

I would prefer to use the El Nik (or some other) 105mm lens because it gives more working space between lens and subject - e.g. to get 4 flashguns up close and to change filter without touching the subject. But from the point of view of image quality I think I'm going to have to use the Cassar for close-up and macro work.

 

BTW - are you using extension tubes? If so, beware the cheap-from-China tubes. I bought a couple of these M42 extension tube sets, but my images lacked contrast (in visible as well as UV). So I got some vintage M42 sets (inc. a Mamiya Sekor set) and these were much better. The coating inside the cheap-from-China tubes is obviously too reflective.

[nfoto]

Hmm. Perhaps I shall be experimenting with a reversed Coastal 60 APO instead? It might show the dreaded UV hot spot in the required range of magnification though. I have to devise a bespoke lens shade for it, which should hopefully help.

 

I always examine extension, whether bellows or rings, for their behaviour in UV/IR. It is true otherwise impeccably operating stuff simply will not work well outside the visible range due to unwanted reflection, or in case of bellows, material leakage.

 

I have issues using a long focal lens (UV-Nikkor) because I do the macro work with floating duckweeds and thus cannot shoot them from the side, only from above. Hence the setup needs to be as compact as possible as I do work indoors. Illumination is no problem as I use powerful studio flashes and they can be put at a conveniently long distance to the subject.

 

Before I give up on the Cassar, I'll test it against the CO 60.

[bvf]

You mentioned hot spots. I experienced those with the Cassar S at magnifications approaching 1:1.

 

In the visible range you can see the hotspot in LiveView as you stop down - generally not visible at full aperture. Sometimes a lens hood helps, and its generally not a problem in the final image when I am using flash.

 

I've not noticed the hotspot when using the Baader U, but I definitely get it when doing tri-colour UV. The 380BP20 and 315BP25 filters seem to be the most susceptible, the 345BP25 less so. Sometimes moving the flashguns (even slightly) helps.

[nfoto]

I ran a quick test and confirmed the Coastal 60 APO is the better option for me.

 

Hot spot and loss of contrast in macro work often are caused by flare from surrounding areas since the reversed lens itself only covers an small image circle, yet due to its design passes a lot more non-image-forming light. Thus making a tiny and very narrow hood to mount on the exposed rear end of the lens tends to improve final quality.

[bvf]

I ran a quick test and confirmed the Coastal 60 APO is the better option for me.

 

Hot spot and loss of contrast in macro work often are caused by flare from surrounding areas since the reversed lens itself only covers an small image circle, yet due to its design passes a lot more non-image-forming light. Thus making a tiny and very narrow hood to mount on the exposed rear end of the lens tends to improve final quality.

 

Ha! You've solved my problem! I was getting UV hot spots with the lens non-reversed and magnifications from about 0.5 to 0.7. Tried an ordinary lens hood, but that didn't work. Then I screwed a 3cm m42 extension tube in front of the filter, and that worked wonderfully. Example (quick and dirty test at ISO 5,000 using 315BP25 filter):

 

[nfoto]

Glad to be of any help ....

 

I learned that trick in the old days when a reversed 24mm gave hopeless flare, whilst a 25mm Cine lens (for 16mm film) did not. Made a narrow lens hood for the reversed 24mm and all of a sudden the flare was gone. Apparently, I have to refresh my own routines once in a while!!