Is there interest in a New Rapid Rectilinear lens?

[E. von Hoegh]

The two outer elements are the same on each side of the stop, and made out of inexpensive glass. Only the doublets are asymmetrical. After letting the optimization run over the weekend, the performance is about as good as an entirely non-symmetrical lens would be. This will help cut cost further.

I made a couple more tweaks to the optimization inputs, and I'll let it run unattended for several days. While that's going I'll put together some information on the performance to give you a better idea of what it can do. When I'm satisfied that it's been tweaked as best it can, I'll generate drawings to get the optics quoted.

I also need to cross-post to the large format photography forum. I wanted to wait until I could get closer to getting quotes.

I tried to cut out the doublets and replace with singlets but wasn't as satisfied with the results.

-Jason

You know, those outermost elements look to be 'one to a block' for both the concave and convex surfaces.

 

[Nodda Duma]

Yes. The design wanted either those curvatures on the outer elements or make them achromatic doublets to control color. I could pull back on the curvature but I think it would blow up.

 

[TheToadMen]

Yes. The design wanted either those curvatures on the outer elements or make them achromatic doublets to control color. I could pull back on the curvature but I think it would blow up.

"... to control colour": does that mean it would be easier to design a lens for B&W use only?

 

[StoneNYC]

"... to control colour": does that mean it would be easier to design a lens for B&W use only?

Of course, because you're not worrying about lining up all the spectrum as perfectly as is needed for color. (I'm probably saying this wrong, but I hope my meaning is understood). Different colors have a different "bend" to them so when they pass through the lenses they don't all line up in the same place, so the color lenses that are corrected for this commonly called APO, our little more complex to design because they have to redirect different wavelengths of color to slightly different directions so that they all lined up together on top of each other on the film plane.

Did that make sense? And of course am I wrong? lol

 

[StoneNYC]

Yes Michael, sorry, you're right about that.

 

[Nodda Duma]

"... to control colour": does that mean it would be easier to design a lens for B&W use only?

No: color means color spectrum...that is, the range of wavelengths which the film is sensitive to. As you know, different colors have different wavelengths, and the angle of refraction through glass is dependent on wavelength. B&W film is sensitive to a range of wavelengths, so you have to correct for all the colors (bring them all to the same focus) within that range. Otherwise what would be color fringes or halos in a color print would be a larger fuzzy blob in B&W.

 

[TheToadMen]

No: color means color spectrum...that is, the range of wavelengths which the film is sensitive to. As you know, different colors have different wavelengths, and the angle of refraction through glass is dependent on wavelength. B&W film is sensitive to a range of wavelengths, so you have to correct for all the colors (bring them all to the same focus) within that range. Otherwise what would be color fringes or halos in a color print would be a larger fuzzy blob in B&W.

I understand that, but isn't the range for B&W film smaller than for colour film, thus easier to handle?
And hence the discussion for single coated (SC) lenses for B&W and multi coated (MC) for colour?
Or am I mixing up the wrong ingredients?

 

[Dr Croubie]

Colour fringing is a problem on B+W film, both yes and no.
Yes, as stated the colour fringes on Panchromatic film would just result in 'fuzzy edges'.
But no, as in if you put a single-colour filter in front of the lens then that one single colour is perfectly focussed and nothing's fuzzy (same as with Ortho film).
That's a fairly well-known thing with one of my lenses, a Gundlach Turner Reich Convertible Anastigmat. Pretty much anything you google says that if you use it with single-element-only then colours aren't corrected, so don't shoot colour film and put on a filter for shooting B+W.

For a lens this big, and even moreso the future longer lengths that will be pretty well aimed at ULF, that's more likely to be B+W, so you can 'get away with' less colour correction as it'll be less noticeable unless someone uses Pan film with no filter (or finds some 7x17" RVP). Plus being ULF there's less chance of making enlargements and smaller factors if they do, so all other errors are less noticeable than when making a 16x20 from 135 film.
But then again, I've got that 9.5" roll of Ektachrome to do something with one day, that'd look great as a 9x20" panorama, so I'd want at least a little colour correction with that...

 

[Nodda Duma]

A follow-up question on the asphere question (actually I suppose this could apply to any shape): why is a ground element considered to be superior in quality to a molded element? I'm also intrigued by your mentioning non-moldable glass.

It's not...at least from my point of view as the designer / optical engineer. It is my responsibility to ensure that the parts that come in from the shop meet the performance specification when assembled. If my design doesn't support manufacturing tolerances then I didn't do my job right. Assuming I did, then if the parts coming in aren't meeting the specifications, then I have to go talk to the vendor and see what they're having trouble with. But honestly I try to design optics which are easy to produce...ground, molded, whatever. Wait..let me clarify: I try to design optics which are easy for the vendor I get quotes from to make...I do that up front and then get feedback during the quote process so if the design can be tweaked to reduce risk then I can do that. That way I avoid quality issues and keep costs down. If the tolerance requirements are tighter, then I go to a different shop (chosen from a list of shops the capabilities of which I am very familiar with due to past experience).

Sometimes a designer will "abuse" the molded optic capability. Even if you're going to use a molded asphere, that doesn't mean you can get away with a crazy wonky surface. But then again, you can get into trouble even without aspheres if you don't know what you're doing.

 

[Nodda Duma]

I understand that, but isn't the range for B&W film smaller than for colour film, thus easier to handle?
And hence the discussion for single coated (SC) lenses for B&W and multi coated (MC) for colour?
Or am I mixing up the wrong ingredients?

No I still correct because I cannot know what film the end user is going to have. Besides, you don't gain much for correcting the narrower spectral band of traditional B&W emulsions vs the whole visible spectrum. Might as well just do the whole range and avoid potential trouble.


Btw for an integrated system (digital imager) I do know exactly what spectral band and response of the imager is. Usually it's much wider than just Visible (like VIS and near infrared or even into the SWIR band, or multiple infrared bands), so there I must be more careful about selection of the design wavelengths.

 

[Dan Fromm]

Bert, the Boyer Opale is a de-achromatized Boyer Saphir (tessar type). It uses chromatic aberration to get its soft focus effect. Berthiot's Color is much the same. Chromatic aberration is a killer with black/white.

Similarly the big difference between the KOMZ Uran-10 and -25 is that the -25 is better achromatized. The -10 should be used only with strong filtration.

Way back when when emulsions were sensitive only to red using badly achromatized lenses was relatively safe, except for focusing issues. Think of the difference between visual and chemical focus.

Jason has the right of it.

 

[Nodda Duma]

I took a look at reducing the curvature of the outside elements and it shredded the performance like I thought it would... just grisly... Huge spot sizes everywhere. The optical design equivalent of the big German guy in the Raiders of the Lost Ark airplane fight scene...

 

[Dr Croubie]

I took a look at reducing the curvature of the outside elements and it shredded the performance like I thought it would... just grisly... Huge spot sizes everywhere. The optical design equivalent of the big German guy in the Raiders of the Lost Ark airplane fight scene...

Hehehe, such descriptive words...
So what does that mean for the size of the filter ring, to make sure it protrudes far enough to protect the outer element from damage and doesn't vignette?

 

[Nodda Duma]

Probably the 77 mentioned in post #112. I'm almost certain.

Or maybe use the Cokin P system.

 

[E. von Hoegh]

Of course, because you're not worrying about lining up all the spectrum as perfectly as is needed for color. (I'm probably saying this wrong, but I hope my meaning is understood). Different colors have a different "bend" to them so when they pass through the lenses they don't all line up in the same place, so the color lenses that are corrected for this commonly called APO, our little more complex to design because they have to redirect different wavelengths of color to slightly different directions so that they all lined up together on top of each other on the film plane.

Did that make sense? And of course am I wrong? lol

Panchromatic = sensitive to all colors. This means a lens needs to be color corrected, period, since B&W film records colors as greyscale.

 

[E. von Hoegh]

I took a look at reducing the curvature of the outside elements and it shredded the performance like I thought it would... just grisly... Huge spot sizes everywhere. The optical design equivalent of the big German guy in the Raiders of the Lost Ark airplane fight scene...

Slice & dice??

 

[Nodda Duma]

Probably the 77 mentioned in post #112. I'm almost certain.

Or maybe use the Cokin P system.

82mm filters will be required out front, so that means the Cokin P system.

 

[Dr Croubie]

82mm filters will be required out front, so that means the Cokin P system.

That's perfect for me actually, my 90mm SWD has 82mm filters, as does my 45mm Takumar for P67, plus my 50mm Flektogon and 180mm Sonnar for P6 have 86mm, so already I've got a decent set of Cokin Z grads plus a few other coloured screw-ins and step rings.
I know others would probably prefer the filter rings smaller if possible though.

Here's a fun question, what's the fall-off like? You said something like it not having much mechanical vignetting, but what about the other few cos-terms?
I've got a Schneider Centre Filter IV, 82-105mm (originally for 90/5.6 Super-Angulon I think) that I use on my SWD, how would that fare on this lens?

 

[Nodda Duma]

I think I calculated you'll lose about 1 1/3 stop at the corners from falloff when stopped down. Wide open it's more like 1 2/3 stop, the additional loss due to vignetting.

 

[StoneNYC]

82mm filters will be required out front, so that means the Cokin P system.

Hey Question,

Can you put a rear filter thread and make sure the rear lens element is no bigger than 77mm? That would enable us non-Cokin users to still add filters on the back of the lens at least? That's what I can do with my 150 SS XL which is why I chose it over a nikon with a rear barrel that was too big.

 

[Nodda Duma]

No. 77 mm will vignette as well. (See the layout). But I would hope the cost of the lens and a Cokin P system will be less than the 150 SS XL.

 

[StoneNYC]

No. 77 mm will vignette as well. (See the layout). But I would hope the cost of the lens and a Cokin P system will be less than the 150 SS XL.

Yes, 67mm would be ideal then, common and still large enough. But you get the idea.

 

[Nodda Duma]

Hi Jason - thanks again for the answers you've given so far to my questions. In relation to falloff, I wonder if you can comment on the "tilting pupil/pupil distortion trick" used by Rodenstock and Schneider in the Grandagon-N and Super Angulon series respectively. As I understand it, this optical trick causes the entrance or exit pupil to "tilt" as it is viewed off-axis, retaining its circular shape and effectively reduces the falloff progression to Cos^3 theta.

Michael

Hi Michael,

You can allow distortion to compensate for the changing aspect of the pupil and keep it round when viewed off-axis as done in a fisheye, or in superwides it's possible to do the same but very carefully keep distortion low.

You can eliminate 3 of the cosines by curving the film so that all areas of the film are equidistant from the exit pupil. You lose cos^2 from variation in distance between the film and pupil, and another cos from the incident angles of the rays on the film.

 

[Nodda Duma]

Drawings are done. When power's restored I'll be able to send them off for quotes.

Also noticed that moving the first lens away from the rest of the groups increases "soft focus", ie sph aberration. I can put the first lens in its own threaded cell so you can move it out from nominal position for increased soft focus, but there will be one additional mechanical part (adds to cost).

 

[TheToadMen]

Also noticed that moving the first lens away from the rest of the groups increases "soft focus", ie sph aberration. I can put the first lens in its own threaded cell so you can move it out from nominal position for increased soft focus, but there will be one additional mechanical part (adds to cost).

Please do!! It will help convincing me to get one!

Bert from Holland
http://thetoadmen.blogspot.nl