Home
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Help me identify lens design by reflections
View previous topic :: View next topic  


PostPosted: Sun Apr 07, 2013 12:55 pm    Post subject: Help me identify lens design by reflections Reply with quote

I have a pair of cells of unknown prescription, both show four strong equally sized reflections which indicates four air-glass surfaces in each cell. I can't see any smaller less bright reflections so I don't think there are any cemented surfaces.

So to me, that indicates there are two air spaced elements in each cell.

The two cells are probably not identical as the reflections are spaced differently, so it's likely not a symmetrical design. The front cell has the reflections in two pairs, the rear one has a closely spaced set of three then one on it's own.

The lens is marked f2.8 100mm and probably dates from the 1950s.

So, it seems to me that this lens has four elements in four groups, which sounds like a dialyte type, but probably not a symmetrical one like, for instance, the Goerz Dogmar:



Or maybe it's a double gauss type:



Anyone know what 4 element 4 group asymmetrical lens designs exist?


PostPosted: Sun Apr 07, 2013 1:04 pm    Post subject: Reply with quote

The Goerz Celor assymetrical dialyte type would seem to fit my lens:



The front pair of elements would give four evenly spaced reflections, which is what I see in my lens' front cell. The real pair would give three roughly evenly spaced reflections then one further back on it's own, which is also what I see in my lens' rear cell.

So, it seems to me I have an asymmetrical dialyte similar to a Celor.

2.8 seems awfully fast for a dialyte though. I wonder what application would require such a fast dialyte?


PostPosted: Sun Apr 07, 2013 2:01 pm    Post subject: Reply with quote


Tremendous Fun with Nex by Nesster, on Flickr

Like that? Should I take a pic of a Dogmar's reflection?


PostPosted: Sun Apr 07, 2013 2:13 pm    Post subject: Reply with quote

That's useful Jussi, cheers. I'll see if I can manage to take some pics of the reflections of my lens.


PostPosted: Sun Apr 07, 2013 2:25 pm    Post subject: Reply with quote

I'm not sure these are helpful?


DSC01353 232 by Nesster, on Flickr


#1

#2


PostPosted: Sun Apr 07, 2013 3:04 pm    Post subject: Reply with quote

I'd love that camera with the Dogmar Smile

If nothing else, they show the difference coating makes in reflectivity, just look at the difference in the reflectivity of the NEX lens and the folder ones.

Thanks Jussi.


PostPosted: Sun Apr 07, 2013 3:40 pm    Post subject: Reply with quote

Ian wrote:

Quote:
The lens is marked f2.8 100mm and probably dates from the 1950s.


This rules out dialytes and 4/4 double Gauss types. Ain't none that fast. It also rules out plasmats, for the same reason.

The most probable, given speed and focal length, is a 6/4 double Gauss type. The weak reflections from these lenses' inner cemented doublets can be very hard to see.

When counting reflections, I look at a single cell with a single light source. I look at it the cell from both ends, tilt it every which way. Looking at an entire lens, even with the diaphragm closed as far as possible, adds confusion. So does using multiple light sources.


PostPosted: Sun Apr 07, 2013 6:34 pm    Post subject: Reply with quote

Cheers Dan, I'll take another look and see if i can get some pics too.


PostPosted: Mon Apr 08, 2013 7:54 am    Post subject: Reply with quote

Quote:
Anyone know what 4 element 4 group asymmetrical lens designs exist?


Unar or Ross Xpress ? Only because ah've been reading about old lens design recently... Cool


PostPosted: Mon Apr 08, 2013 8:01 am    Post subject: Reply with quote

danfromm wrote:
Ian wrote:

Quote:
The lens is marked f2.8 100mm and probably dates from the 1950s.


This rules out dialytes and 4/4 double Gauss types. Ain't none that fast. It also rules out plasmats, for the same reason.

The most probable, given speed and focal length, is a 6/4 double Gauss type. The weak reflections from these lenses' inner cemented doublets can be very hard to see.

When counting reflections, I look at a single cell with a single light source. I look at it the cell from both ends, tilt it every which way. Looking at an entire lens, even with the diaphragm closed as far as possible, adds confusion. So does using multiple light sources.


Yes, exactly, best way to do it. I use a LED pinpoint light. Btw. a laser pointer does NOT work, due to multiple inner reflections.


PostPosted: Mon Apr 08, 2013 12:48 pm    Post subject: Reply with quote

TAo2 wrote:
Quote:
Anyone know what 4 element 4 group asymmetrical lens designs exist?


Unar or Ross Xpress ? Only because ah've been reading about old lens design recently... Cool


The Unar was 4 airspaced elements if my memory serves me correctly. The Xpres, well, it was a trade name rather than one design, some were just Tessars, some were a 5 element design similar to a Tessar, there were other types too, the f4 5 inch wide angle xpres is a 6 element plasmat. I have a few Xpres lenses and never taken one apart to figure out it's prescription, i expect I have several types, all labelled Xpres.


PostPosted: Sat Sep 07, 2013 9:05 pm    Post subject: Re: Help me identify lens design by reflections Reply with quote

iangreenhalgh1 wrote:


Anyone know what 4 element 4 group asymmetrical lens designs exist?


According to Kingslake, early Kodak Anastigmat lenses were dialyte types. Cooke triplets were used later on.

I have just acquired a Kodak Anastigmat 170mm f7.7 which is an asymmetrical dialyte type. I have not had chance to use it yet though. A quick check against a lens chart gives me the impression it is decently sharp.

Mark


PostPosted: Sat Sep 07, 2013 9:12 pm    Post subject: Reply with quote

iangreenhalgh1 wrote:

The Unar was 4 airspaced elements if my memory serves me correctly. The Xpres, well, it was a trade name rather than one design, some were just Tessars, some were a 5 element design similar to a Tessar, there were other types too, the f4 5 inch wide angle xpres is a 6 element plasmat. I have a few Xpres lenses and never taken one apart to figure out it's prescription, i expect I have several types, all labelled Xpres.


Interesting information. I have a Ross Xpres 105mm f3.8 from an Ensign Selfix folder which is "just" a triplet but is a really nice lens. It benefits from adopting unit focusing with a bellows and leaving the front element focusing set to infinity though. Then it is nice and sharp wide open. Resolution drops a lot at close focus distances if you use the front element focus. All the front element focusing element triplets that I have tried do this.

Mark


PostPosted: Sat Sep 07, 2013 9:30 pm    Post subject: Reply with quote

The Xpres 3.8/105 is a 4/3 Tessar, not a triplet. I have one on a Selfix 820, it gives the best of the Germans a run for their money. Smile


PostPosted: Sat Sep 07, 2013 10:07 pm    Post subject: Reply with quote

iangreenhalgh1 wrote:
The Xpres 3.8/105 is a 4/3 Tessar, not a triplet. I have one on a Selfix 820...


Yes, you are quite correct! The third reflection is very small and easy to miss. Mine came from a selfix 820 as well.

iangreenhalgh1 wrote:
it gives the best of the Germans a run for their money. Smile


Absolutely!

Do you have any experience of the Xpres 75mm f3.5? And what about Rosstar lenses? Are they lower or higher grade than the Xpres?

Mark


PostPosted: Sat Sep 07, 2013 10:35 pm    Post subject: Reply with quote

This is my Kodak dialyse lens.


#1


#2 Front group


#3 Rear Group


Whilst it is not entirely obvious from the reflections, the two groups have quite different optical powers.


PostPosted: Sat Sep 07, 2013 11:14 pm    Post subject: Reply with quote

The Xpress 75mm should be superb like the 105mm, but I have never tried one. The reputation of the 75mm on the MPP TLR is very high though.

The Rosstar is a triplet I think, should be a good one but will have the typical triplet weakness of curvature of field and uncorrected spherical aberration at full aperture. Stopped down, it will probably be hard to tell it from a Tessar like the Xpres.

That Kodak probably came from a 3A folder. I have the same lens on a 3A but mine is in an Ilex shutter.