Focotar 50mm f1/4.5 from first year to last. Transmission difference.

[ulf]

I have three Focotar 50mm f1/4.5 in my lens collection.

They have production years spanning from the first year to the last. 1952, 1964, 1969.

The first is marked DOOCQ on the barrel, the second is marked 16781R and the last has no type marking.

All are identified by a tiny serial numbers engraved at the mounting end.

https://www.l-camera...1_1:4.5_/_50_mm

 

I have not yet used any of them in the field, and cannot show ortell anything about any visual- or UV-photo results.

I have so far mainly used my favourite UV-lens, an old metal type El-Nikkor 80/5.6.

 

When I measured the transmission of the three lenses I found that the latest two from 1964 and 1969 have a quite god UV-range.

They have a UV limit close to the results from my SOLIGOR 35mm/3.5 Kuribayashi-clone.

 

I have normalised the different spectra to simplify comparisons.

 

As a comparison I also added spectra obtained from my old EL-Nikkor 80/5.6 and a STAEBLE-LINEOGON 1/3,5/35mm.

The STAEBLE-LINOGON is supposed to have the same optics as the Novoflexar 35/3.5.

[bobfriedman]

which curve represents the lens marked DOOCQ.. turns out i have one of these. my serial number is 1611163

[Cadmium]

I am a bit confused. I went to the link that has all the serial numbers listed,

and the list doesn't seem to match up with the two lenses you have that have side markings:

 

From the link list:

DOOCQ: 1883001 ^ 1884000 50 mm f/1.4 Summilux ^ (DOOCQ) 1961 [1000]

16781R: 2090801 2091500 50 mm f/4.5 Focotar (16781R) 1965 700

No marking: ?

 

Your lens SN's:

2384744 (black)

2030597 (green)

997834 (blue)

 

PS:

Just went to look at mine, but mine is a FOCATAR-2 (with higher SN than end of list)

I 'thought' the FOCATAR-2 lenses transmitted UV deeper, however two of yours look quite deep and deeper than I thought the FOCATAR-2 is.

So I don't know, more confused now. :-)

[ulf]

Well, I rechecked the numbers and markings. They are as in my first post.

I'm a little bit dyslectic and could easily have mixed up the data, but I have not this time. :)

 

The blue curve is the lens marked DOOCQ.

The lenses measured is listed in the top left of the spectrogram picture.

 

When the map and the reality disagree, the reality often wins.

I have three pieces of reality here! :) :) :)

 

I think there must be some error in the list.

The link list say "Serial numbers compiled from Puts Pocket Pod.pdf" at the top.

After a very quick search at this source, I could not find anything about the side markings like DOOCQ.

 

I do not think there is much problem with my wavelength measurements.

I checked it against a reference HgAg-lamp yesterday.

The spectrometer is quite well wavelength-calibrated, better than 1nm at the 27 peaks I used for calibration.

 

It looks like Leitz changed the design of the FOCOTAR sometime between 1952 and 1964.

 

I have also read someone thought that the FOCOTAR-2 should be better, but but without any proof.

Mayby this statement wasn't about UV-range or based on a comparison to an older FOCOTAR lens.

 

It would be interesting to measure a FOCOTAR-2 and compare.

However, for the moment my FOCOTAR-level has reached saturation.

[Alex H]

Klaus compared transmission curves of different models and versions of Focotar lenses and concluded that Focotar-2 50mm was better than predecessors.

[ulf]

Do you have any more information about Klaus's findings, like a link...?

[Alex H]

He stated this in one of his posts on NikonGear (now Fotozones) forum many years ago (25 January 2010). I have seen transmission curves to confirm the statement, but these are not published.

[Cadmium]

UlfW, thank you for publishing your graphs.

They look good, and even better than the collection of unpublished graphs to me.

I understand that there is a difference when comparing graphs made by two different people, with two different sets of equipment.

Also, as you show, there can be quite a difference between serial numbers.

Your graphs show that the transmission of two your Focotar lenses are much better than I have seen presented before.

Only one of your Focotar lenses crosses the 365nm line below 80%.

The only way to actually compare is to test a Focotar-2 along side the others with the same equipment at the same time.

[ulf]

Thank you for the reference.

I have read that post at Fotozones.

I just searched for FOCOTAR

 

There I also found some closeup pictures from one of our members, bobfriedman, of a Geranium maculatum taken with a FOCOTAR.

Very nice pictures and enough sharpness for me!!

 

OK, then it might be possible that Klaus's curves was from an older FOCOTAR like the one giving the blue line in the spectrogram picture above.

I do not think he tested many versions of FOCOTARs produced over the years.

 

Sometimes he tend to omit information and are not that specific about exactly what lens is tested.

 

There is another example of this, where he stated that Soligor 35/3.5 was inferior for UV, but he stated what type he measured.

There are several versions of that lens, both good and less good for UV.

 

The FOCOTAR-II can absolutely be a better lens, as it has a more modern design.

It is expensive and, at least on eBay, less frequent than the older version.

 

The FOCOTAR seams quite good for UV too, if you get one with the right age.

[Alex H]

I've been shooting FOCOTAR-II (both 50mm and 100mm) for past few years and did not find a better lens in terms of sharpness and transmission among the optics not specifically designed for UV-imaging.

[Cadmium]

OK, then it might be possible that Klaus's curves was from an older FOCOTAR like the one giving the blue line in the spectrogram picture above.

I do not think he tested many versions of FOCOTARs produced over the years.

 

That actually could be true, because you are showing a substantial difference in transmission between some serial numbers.

Your Focotar SN 997834 (blue line) transmission looks more like the Focotar (-1) lenses of the unpublished graphs.

 

Sometimes he tend to omit information and are not that specific about exactly what lens is tested.

 

This is why your published graph is worth a whole lot more than an unpublished graph. ;)

[Cadmium]

If you would like, perhaps we could arrange for me to loan you my Focotar-2 50mm for a short period of time so you can do a shared publicly posted direct comparison.

[ulf]

I would really like to do that test and comparison, but I think it will be too expensive and/or complicated as I am in Sweden.

 

There would probably be customs and VAT costs on top of the freight costs that would be complicated to recover.

I think the paperwork for import and re-export can also be quite complex.

[ulf]

When I read the old Fotozones posts about FOCOTAR, I saw a statement by Klaus that made me order yet another enlarger lens.

 

He wrote:

"Another excellent candidate for UV and a tack sharp lens, yet never been cheap, is the Leica 2.8/50mm Focotar-2 (Focotar II) enlarger lens

(ONLY that one, not the older types) as well as its even more expensive brother, the Focotar II 5.6/100mm. .

Identical to the latter is the Schneider Componon-S 5.6/100mm, yet much cheaper (since most people don't know that).

All three have some focus shift, but reach about 315-320nm."

 

I found and bought a Schneider Componon-S 5.6/100mm and hope that it is the same type as the one Klaus referred to.

When it has arrived I will publish the spectrogram here.

 

How many enlarger lenses can you own before it is too much?

[Alex H]

Sorry to disappoint you but later on it was found that 100mm Componon-S is not the same as Focotar-II.

[ulf]

OK, it wasn't that expensive.

It was a calculated risk.

I do not trust all statements from Klaus.

 

How bad is it?

[Alex H]

Can not answer this, all I know is that it is different design.

[ulf]

OK, I'll post result when I have measured it.

[Alaun]

Ulf, you wrote: I have normalised the different spectra to simplify comparisons.

 

One of your curve shows at some point a transmission slightly beyond 100%

 

How much does the normalisation influence the comparison?

[ulf]

The normalisation is done for an average value to be 100% over a selected range of wavelenghts, ca. 440-480nm.

 

The curve slightly beyond 100% is the oldest FOCOTAR that will look very slightly better than it is.

 

As the steepness of the transition range is reasonably high, a small amplitude difference do not cause a big significant wavelength shift.

I would estimate that less than 0.4nm per percent of amplitude error could be reasonable.

 

Compare at the slopes how much the wavelength changes for a given amplitude change.

Blue curve 20% - 40% => ca 8nm difference

[Alaun]

Ulf, thanks for the clarification.

[ulf]

My Focotar 4.5/50-family just got two younger members.

 

The first is one of the type DOOHF, 17581A known as LFE ~ Large Front Element, made by Schneider. (green curve below)

https://www.l-camera..._1:4.5_/_50_mm.

 

The second is a Focotar-2, produced 1975. (magenta curve below)

https://www.l-camera...2_1:4.5_/_50_mm

 

I have quickly measured these two new lenses together with one of the better old Focotars in post #1 of this thread.

(black curve in both spectrograms)

 

This new diagram show the first part of the wavelength selection for normalisation as a grey area, beginning at ca 435nm.

(ending at 500nm)

The waviness near 100% is due to noise caused by a short integration time without any averaging.

 

The alignment and setup of the optical structure is not optimised causing some deviations from the spectrogram in post #1.

The old Focotar has a better transmission than this latest result show.

 

To do: Redo this measurement with a better alignment... I´ll be back!

 

It is interesting that the slopes of the two newer lenses are more steep.

I wonder what can cause this difference. Could be the sloppy setup.

 

By the way I got the Componon-S 5.6/100 a few weeks ago too. (post #14) It is not usable for UV! :(

I will not publish the spectrogram unless someone really want to see it and ask me to show it.

 

-----

How should the level for a cutoff-wavelength be defined for lenses?

What attenuation should be used?

50% of maximum transmission often is is used for optical filters.

Is this level correct for lenses too?

 

This is analog to how cutoff frequencies are defined in electronics and seam natural for me.

(50% of the power-level in the passband (-3dB))

[nfoto]

The 50% point should be useful, I think.

[bobfriedman]

do you have any Rodagon spectrums?

 

any of the following would help?

 

Rodenstock Rodagon 80mm f/4

Rodenstock Rodagon 105mm f/5.6

Rodenstock Rodagon 105mm f/5.6 (zebra)

Rodenstock Rodagon 135mm f/5.6

Rodenstock Rodagon 135mm f/5.6 (zebra)

Rodenstock Rodagon 150mm f/5.6 (M50 mount, 58mm filter)

[ulf]

do you have any Rodagon spectrums?

 

Hi Bob,

 

Sorry but the only Rodagon I have is a Apo-Rodagon N 50mm 2,8.

It has a cutoff wavelength of around 370nm

 

I have two Rodenstock Apo Gerogon lenses 150/9 and 240/9, that might be slightly better.

TBD