Is there interest in a New Rapid Rectilinear lens?

[Nodda Duma]

Check out the samples on the Petzvar Kickstarter page (AFAIK it's a "true petzval" to the original design).

Tangential. Makes me want to shift a lens.

 

[LJH]

IMO, Petzval swirl is fairly 2008... Time we moved on. A silly effect , much like digital images that have film borders superimposed on to them. Gimmick at best

A true soft focus lens leaves a swirly Petzval for dead.

Again, wide angles for ULF are my preference. They can be used for smaller formats where coverage is required (eg. architecture, product shooting etc), opening up more sales opportunities.

 

[Nodda Duma]

What kind of performance specifications are you guys used to seeing? MTF? Spot size? lp/mm? Ray fans?

 

[Dan Fromm]

What kind of performance specifications are you guys used to seeing? MTF? Spot size? lp/mm? Ray fans?

Tim, wander over to dioptrique.info and look at Eric Beltrando's calculated performance for many classic designs.

Re MTFs, take a look at the Rodenstock propaganda here: https://skydrive.live.com/redir?resid=8D71BC33C77D1008!324

 

[Nodda Duma]

Tim, wander over to dioptrique.info and look at Eric Beltrando's calculated performance for many classic designs.

Whoa. Reminds me of the LensView database, but I haven't had access to a copy for years.

You just contributed to a significant lack of sleep I will experience this weekend going through those.

-Jason (not Tim )

 

[alanrockwood]

Nodda,

What Software are you using?

I am not an optical designer, but I have played around with Winlens quite a bit.

 

[Nodda Duma]

I use ZEMAX, both at home (I have my own key) and at work. I've used Code V in the past as well.

 

[massimodec]

Everything is very nice !
.... and what about build a low priced Pinkham & Smith or Struss replica ?

 

[Dr Croubie]

There are already lenses around 150 mm that cover more than 90 degrees and that don't have severe distortion. For example, the 155/6.8 Grandagon-N. Now discontinued and I have no idea how many were sold, how often used ones come to market, or how much they've sold for.

More seriously, formats up to 8x10 are fairly well supplied (come on, all pile on now) with lenses from around .4x to 3-4x normal focal length. Larger formats (but which one to address?) aren't so well served.

Well, what I wrote before regarding wides for 8x10 wasn't so much about being available, but also including the fact that they're affordable too.

I've got a few minutes so I'll go do some fleabay searching on the more common >90 degree lenses, all condition unknown:

Super Symmar XL 150mm: none for sale, two sold recently for $2300 each.
Nikkor SW 150mm: none for sale, four recently sold $1100-1800.
Grandagon-N 155m: none for sale, three recently sold $1200-1400.
Angulon 165mm: two for sale $430 and $580, one sold at $280 (does this decently-resolve 8x10, or just illuminate?)
Super Angulon 165mm: one auction starting at $930, BINs at $2000-2900, three recent sales from $900-1100.
Grandagon 200mm: none for sale, two sold for $3000 and $4600.
Angulon 210mm: two BIN for $340, none sold.
Super Angulon 210mm: two BIN for $4000 and $4800.
Super Symmar XL 210mm: one for sale for $5300, none recently sold.

So it's pretty much the relatively ancient Angulons unless you can afford a grand or four, I know I can't. But true, there's even more a dearth of these at longer lengths for larger formats, most of these examples are the longest in their series. And they're mostly damn huge except the Angulons and SSXL. 200mm Grandagon is 2.6kg, 210mm Super Angulon is over 3kg!

Going down to ~80 degrees they do become a bit more affordable and available. There's the old single-coated Fujinon W series at 210/250/300/360 which seem to be the best value and most common, plus the 250mm Wide Field Ektar and probably a whole bunch more that I don't know much about (I'll stay out of the debate of whether a Dagor covers 80 degrees or not). Apo-Sironar W and Super Symmar HM also start around the $1k mark and I wouldn't really call affordable.

Below them at the 70 degree mark there's a whole bunch of older designs like regular Symmars, Sironars, W and CM-W, in longer lengths and a lot cheaper too, so I wouldn't waste too much time competing with them.

So where I'd aim for is something about 90-100 degrees in a simple design with 4-6 elements, assuming that's possible (I don't think you'd get much over 100 degrees without adding extra elements, weight or cost). Make it with a relatively small max aperture (like f/9-12) to keep size and cost down. Start one at 150-200mm to keep the 8x10 shooters happy (ie me), and just replicate it a few times in longer lengths, eg 180/270/360/450/600/900 or something.
If you can get themat under $600 and 1kg a piece then all you're really competing against in that price range are the older Angulons at the shorter end, and there's not much to compete with at the large end at all.

Ultra-low distortion really isn't high on my list of must-haves, especially if it's going to be a huge Biogon-esque design, I'd rather something that I can lift with one hand. This inverted-telephoto double-gauss non-biogon thingy sounds good...

 

[Dan Fromm]

Croubie, I think that the OP's w/a design is a variation on the Super Angulon.

Useful rule of thumb: extreme (long, short) lenses have extreme prices.

 

[Nodda Duma]

The Super Angulon and the Angulon designs have a pair of triplets at the center. I'm avoiding those because I don't like them as a general rule. 3 singlets or a doublet and a singlet are always better than a triplet from a cost / weight / tolerance (typical performance) perspective.

The lens is hammering out. I'm running a 4 lens (two doublets two singlets) version and a 6-lens (4 singlets 2 doublets) version. These are inexpensive glass types so cost should be manageable. I haven't aspherized any surfaces yet but I could if needed.


165 mm f/5.6. So far it is very sharp at center 50% of area with softening towards edges at wide open (f/5.6). Close it down two stops and it's diffraction-limited over the central 50% of the 8x10 image area and sharp at the edge. There is slight focus shift due to spherical, but I'm controlling that in the optimization to keep it low. Glass weight is about 600 grams (about 1 3/8 lbs). Back focal length (from last glass surface to the film plane) is about 115 mm, or 4 1/3".

How's that sound so far?

 

[AgX]

Terminology:

The Super Angulon and the Angulon designs have a pair of triplets at the center.

I thought the term "triplet" was only used for that Taylor design and its successors.

 

[LJH]

Any idea on coverage? Thanks.

 

[Dr Croubie]

The Super Angulon and the Angulon designs have a pair of triplets at the center. I'm avoiding those because I don't like them as a general rule. 3 singlets or a doublet and a singlet are always better than a triplet from a cost / weight / tolerance (typical performance) perspective.

The lens is hammering out. I'm running a 4 lens (two doublets two singlets) version and a 6-lens (4 singlets 2 doublets) version. These are inexpensive glass types so cost should be manageable. I haven't aspherized any surfaces yet but I could if needed.

165 mm f/5.6. So far it is very sharp at center 50% of area with softening towards edges at wide open (f/5.6). Close it down two stops and it's diffraction-limited over the central 50% of the 8x10 image area and sharp at the edge. There is slight focus shift due to spherical, but I'm controlling that in the optimization to keep it low. Glass weight is about 600 grams (about 1 3/8 lbs). Back focal length (from last glass surface to the film plane) is about 115 mm, or 4 1/3".

How's that sound so far?

Sounds like a beast if it's already got 600g of glass, add enough support and a shutter and it'll touch 1kg or so.
It also gives an aperture of 29.4mm, which will just barely fit in a #1 (max 30mm according to Grimes), but more than likely is best in a #3 if nothing else for rigidity.
What can you save in size and weight by making it f/8 or even f/11? Composition will still be possible (esp for people like me who shoot landscapes f/32-64 and contact-print), it'll fit a #1 easier, could it bring a lot of the weight down?

If this design gets rehashed in longer lengths for more ULF shooters, size will become even more important (imagine the size of one of these in 500mm!) and sharpness less important as the chances of contact-printing instead of enlarging become greater.

Just on the Super Angulons, from the diagrams I've seen, the newer f/5.6 versions are 8/4 with 1-3-3-1, the older f/8 were 6/4 with 1-2-2-1, is your design similar to the older f/8s?

The original Angulons were more like asymmetrical convertible anastigmats, just 6/2 in 3-3. They claimed 105 degrees in the 1934 catalogue, but even if 90 degrees is more realistic that's totally suitable. Could you maybe update the original Angulon design with more modern glass and sharpen the corners a bit, even split it to 1-2-2-1 if it's hard to cement triples? (or is that what you've done anyway?)

 

[Nodda Duma]

I'm designing for an 8x10 format, so it would be good for a 325 mm diameter image circle. That'll give you 80 degrees across a 325 mm diameter film with minimal distortion. It will cover out beyond that (barring whatever the mechanical design ends up being) but I am not correcting beyond there.

Terminology:


I thought the term "triplet" was only used for that Taylor design and its successors.

My apologies...It is a difference in jargon. In lens design world the term "triplet" is used for "cemented triplet".. ie 3 glasses bonded together much like a cemented doublet.

For the Taylor design, we say Cooke Triplet.

 

[Nodda Duma]

Sounds like a beast if it's already got 600g of glass, add enough support and a shutter and it'll touch 1kg or so.
It also gives an aperture of 29.4mm, which will just barely fit in a #1 (max 30mm according to Grimes), but more than likely is best in a #3 if nothing else for rigidity.
What can you save in size and weight by making it f/8 or even f/11? Composition will still be possible (esp for people like me who shoot landscapes f/32-64 and contact-print), it'll fit a #1 easier, could it bring a lot of the weight down?

If this design gets rehashed in longer lengths for more ULF shooters, size will become even more important (imagine the size of one of these in 500mm!) and sharpness less important as the chances of contact-printing instead of enlarging become greater.

Just on the Super Angulons, from the diagrams I've seen, the newer f/5.6 versions are 8/4 with 1-3-3-1, the older f/8 were 6/4 with 1-2-2-1, is your design similar to the older f/8s?




The original Angulons were more like asymmetrical convertible anastigmats, just 6/2 in 3-3. They claimed 105 degrees in the 1934 catalogue, but even if 90 degrees is more realistic that's totally suitable. Could you maybe update the original Angulon design with more modern glass and sharpen the corners a bit, even split it to 1-2-2-1 if it's hard to cement triples? (or is that what you've done anyway?)

For ULF at longer focal lengths I'd work from a different design family specifically to address the weight.

For this version I can stop it down

That's pretty much what I've done for the first configuration (which is turning out to be the sharper). That's a 1-2-2-1 which weighs in at about a pound of glass (I think.. I don't have the design in front of me). The second configuration -- which I show the layout for below -- is a 1-1-2-2-1-1 as an attempt to split the power in the first / last elements and reduce the curvature on those surfaces. It's being stubborn like that but the performance is pretty good. As you can see a lot of weight is taken up in the first lens. I'm working to reduce the size of the first element but it's a fight against performance.

The performance (spot sizes or lp/mm) is comparable to the original 8x10 format Schneider Super Angulon design if you are familiar with that lens .... but the Super Angulon I looked at in Zemax is flipping heavy.

The layout looks ugly but it is progressing. Without fail, in my experience a good-performing lens has a good looking layout.

 

[LJH]

For ULF at longer focal lengths I'd work from a different design family...

Are you considering ULF "stuff" at this stage or just working on the 8x10 (which still interests me, FWIW)?

 

[Nodda Duma]

Absolutely. I'll certainly look at ULF stuff. If there's demand for it then why not?

I joined the Large Format Photography forum, so it might be easier to sort out what's wanted over there.

 

[Nodda Duma]

Continuing progress. Not sure how interesting the details of lens design is but here it is anyways.

I'm focusing on the f/5.6 version and making room for a Copal 1 shutter in the middle. This is marginally difficult because the center lenses want to be close. But I've made about 20mm of room, which is just enough to fit one in (based on available dimensional drawings). Now I'm optimizing glass types.

Also shaved glass weight to ~450g (about a pound). This is without putting much thought into mounting diameter of the lenses...just adding 4% to the diameter of the clear aperture (common practice).

Once I have it squared away, I'll trim it down to f/6.3 or f/8 to cut weight further and improve wide open performance. When I look at mounting I will shave every ounce possible. Been there, done that

I will save the f/5.6 design...perhaps there will be future interest.

The lens scales down in focal length (for smaller formats) really well.

In any case, at f/16 it is incredibly sharp.



For the original rapid rectilinear, I find myself wondering what matching aspheric doublets would do for performance.

 

[Dan Fromm]

I'm focusing on the f/5.6 version and making room for a Copal 1 shutter in the middle. This is marginally difficult because the center lenses want to be close.

What are the inner cells' ODs, including mount? I ask because (a) the #1's diaphragm opens to 30 mm and (b) the front and rear inner threads are M40x0.75 and M36x0.75. This leaves room for moderately large pieces of glass.

Remember, the well-known alternatives, mostly 6/4 and 8/4 Super Angulon types, have inner groups that nearly touch the diaphragm and shutter blades.

 

[Nodda Duma]

Hi Dan,

This is the first of two approaches: first pull the center lenses out past the thread flange and allow them to be wider.



Second, pull them in tight to the diaphragm to clear the ID of the flanges like in the Super Angulon.

The second approach creates more vignetting than the first.

 

[Lachlan Young]

A small, lightweight lens in the 180-200mm range with good coverage for 8x10 would be good - ideally not in a massive shutter.

A 350mm lens with ULF (600mm?) coverage stopped down that isn't bulky & heavy would also be quite attractive. For both these designs sharpness & low weight would ideally come ahead of speed.

Perhaps we should also be considering 21st century shutter solutions too - it surely shouldn't be too hard to design a simple electronic shutter that can be fired from a smartphone...

 

[Nodda Duma]

Lachlan that is an interesting thought. I can look into that as well. It would not be difficult to do.

But as a separate project

 

[David A. Goldfarb]

A small, lightweight lens in the 180-200mm range with good coverage for 8x10 would be good - ideally not in a massive shutter.

There are Dagors that fit that description. I have an 8.25" f:6.8 in an Ilex 3 shutter, and I've seen a 180mm.

 

[Lachlan Young]

There are Dagors that fit that description. I have an 8.25" f:6.8 in an Ilex 3 shutter, and I've seen a 180mm.

I'd quite like a new multicoated lens that doesn't have the dagor tax on it...