digital lens, image circle using roll film ?

[archivue]

i know that manufacturers are sometimes quite conservative about the image circle they published...
Digital lens, are the sharper lens available, but the IC seems too small for roll film (6x8 and arca Fline, subject : architecture)... so i'm looking for real world expérience with this type of lens... and maybe a source with usable IC with roll film...

Thanks

[JW Dewdney]

You'd be surprised. Most that I've tried (that's three now) are QUITE comparable with their same-focal-length cousins in the film world, if not BETTER in this regard. And, promising something on the order of 200 lp/mm, they're pretty intriguing.

That you may actually see real-world gains, using real-world apertures however - is another question entirely.

[Bob Salomon]

i know that manufacturers are sometimes quite conservative about the image circle they published...
Digital lens, are the sharper lens available, but the IC seems too small for roll film (6x8 and arca Fline, subject : architecture)... so i'm looking for real world expérience with this type of lens... and maybe a source with usable IC with roll film...

Thanks

You are using too wide a brush with this statement.

Rodenstock Apo Sironar Digital lenses have image circles of 125 to 150mm which are fine for roll film. They are available in 35mm, 45mm, 55mm, 70mm, 90mm, 205mm, 120 macro, 135mm, 150mm, 180mm.

Apo Sironar Digital HR lenses have image circles of 70 to 80mm. Might those be the ones you are referring to? They are available in 28mm, 35mm, 60mm, 100mm 180mm.

There are twice as many digital lenses in Rodenstock's case that cover any roll film size then that don't.

[archivue]

You'd be surprised. Most that I've tried (that's three now) are QUITE comparable with their same-focal-length cousins in the film world

have you tried one around 38-47-55 ?

[JW Dewdney]

Yes... a 55.. mind you - I never shot film with them.. but played with them on my sinar... just to check out the image circle. The only one I had any extensive play with was a rodenstock 135mm. It covers 4x5 with TONS of room for generous movements. The 55 seemed like it would cover 6x9 pretty easily. Not 4x5 though, quite.

[archivue]

i allready know that i should avoid the HR serie for roll film use.
i will probably buy a lens around 47, and to prepare the future, i think it can be a good idea to buy a digital lens instead of a 47xl... but i need movements with my 6x8 films...

[JW Dewdney]

6x8??? what is it - a fuji?? I think the image circles are all published somewhere - aren't they? I'd still imagine it would be pretty important to know how much you can rise, say, on a digital studio setup.

[Bob Salomon]

i allready know that i should avoid the HR serie for roll film use.
i will probably buy a lens around 47, and to prepare the future, i think it can be a good idea to buy a digital lens instead of a 47xl... but i need movements with my 6x8 films...

The HR are excellent for roll film as long as they adequatly cover the format in use. But to use them properly with any film format a screw-in corrector plate is required on the rear of the lens to compensate for the lack of the cover plate normally on a digital sensor. That cover plate is the final element in the HR lens.

[archivue]

6x8??? what is it - a fuji??
no, mamiya motor drive 6x8 back on an arca swiss Fline69... much better than the arca/horseman back !

a screw-in corrector plate is required on the rear of the lens... rodenstock sold them ?

[Bob Salomon]

6x8??? what is it - a fuji??
no, mamiya motor drive 6x8 back on an arca swiss Fline69... much better than the arca/horseman back !

a screw-in corrector plate is required on the rear of the lens... rodenstock sold them ?

Yes Rodenstock sells them for the HR series only. The Apo Sironar Digital series does not require them.

[JW Dewdney]

6x8??? what is it - a fuji??
no, mamiya motor drive 6x8 back on an arca swiss Fline69... much better than the arca/horseman back !

a screw-in corrector plate is required on the rear of the lens... rodenstock sold them ?

Bob will certainly beg to differ on this and try to find an argument for getting you to purchase a corrector plate... but if you're shooting at f/8 and beyond... it really won't matter. It probably wouldn't matter at any aperture - when you consider the tiny differences in field curvature it would make. But the proof is really in the pudding, and you should test for yourself. Worst case scenario - and you really wanted to shoot flat-field type stuff wide open (most photographic subjects are NOT flat-field anyway) - then you could always make-do with a UV filter screwed onto the rear of the lens. Just make sure you focus with it in place, etc..

[Bob Salomon]

"then you could always make-do with a UV filter screwed onto the rear of the lens. Just make sure you focus with it in place, etc.."

No that would not work as the UV filter glass is much thicker then the corrector plate.

" but if you're shooting at f/8 and beyond... it really won't matter. It probably wouldn't matter at any aperture - when you consider the tiny differences in field curvature it would make"

What the corrector plate does is modify the point where the rays come to focus on the film.

Stopping down will change the depth of field. The corrector plate changes the depth of focus and the depth of focus does not change with the aperture..

[JW Dewdney]

See? Told you Bob would find an alternative argument. Anyway try it and see.

Depth of field, Depth of Focus? Depends on which end of the lens your looking through, it seems to me.

[Bob Salomon]

See? Told you Bob would find an alternative argument. Anyway try it and see.

Depth of field, Depth of Focus? Depends on which end of the lens your looking through, it seems to me.

What "alternative argument"?

If you don't know the difference between depth of focus and depth of field you better look it up.

While depth of field is easily adjusted depth of focus isn't. If the depth of focus is not properly adjusted your images just will njot be sharp.

[JW Dewdney]

Bob - alternative to MY argument.

Depth of Field assumes a certain tolerance of 'circles of confusion', varying subject distance, with a fixed distance to the film plane. Depth of Focus assumes a certain tolerance of 'circles of confusion', fixed subject distance (normally flat), with a variable distance to the film plane (meaning, that for a certain size C.O.C., there is SOME play in the nodal point-to-film distance.

I can't really think of a better living metaphor of 'two sides of the same coin'.

My point was that the resulting curvature in NOT using the corrector plate is somewhat moot, due to;

1. it being completely absorbed by 'depth of focus'.
2. the fact that all subjects in the real world don't exist on a flat plane (the only condition under which your argument would be truly meaningful).

Sorry - I'm not trying to erode your sales quotas... just trying to help a brother out.

[Oren Grad]

It probably wouldn't matter at any aperture - when you consider the tiny differences in field curvature it would make.

You're right about depth of field/depth of focus being two sides of the same coin, of course.

But do we know that what the corrector plate is correcting for is field curvature? The Linos literature doesn't have anything to say on this beyond the nonspecific claim that the characteristics of the CCD cover glass "were taken into the equation of the optical correction".

[JW Dewdney]

Oren - it was established in the thread below - that the effect of placing a plane of glass of a specific thickness behind a lens (pretty much any lens) that, the result would be (EFFECTIVELY) a spherical aberration, as well as a focus shift of ALMOST 1/3 glass thickness, depending totally on reproduction ratio/magnification. Thus, I think it is reasonable and quite defensible to extrapolate that the result of removing such a plate from an optical system designed for a flat-field WITH it, would be field curvature. i.e. - the system would no longer be PERFECTLY flat-field corrected. But still enough, IMO, for EXCEPTIONAL quality film photography under 'normal' (scenes with varying distance relationships) circumstances.

http://www.largeformatphotography.info/forum/showthread.php?t=24489

I think it was Helen's post (with the graph) that actually established this fact most convincingly.... though I was (less convincingly apparently) arguing this would happen, in different words.

[Oren Grad]

Ahhh, got it - thanks for the link, I'd missed that thread. Very interesting.

Bob's comment makes sense if one interprets it as referring to the focus shift.

Anybody have a clue as to the thickness of a typical CCD cover glass?

[JW Dewdney]

yes, except you wouldn't get ANY shift if you're using the lens without the plate in the first place. it's only between the state of 'with plate' and 'without plate'. On a view camera - you just focus on the GG... and that's all there is to it.

[Oren Grad]

WYSIWYG! But then if you're being ultra-critical using it in a digital application, you'd better be focusing off the acquired digital image, unless your focus analog has a corrector too.

[JW Dewdney]

I'm not sure I follow, Oren - the original discussion centered around being able to use a digital lens (since they're going pretty cheap on the 'bay right now) in place of a standard view camera lens for a FILM CAMERA, since they're pretty highly-corrected affairs. I was saying that it would be great to use for that application... Bob came in and suggested that they shouldn't be used without the corrector plate... to which I responded the above, and that it would probably just fine, and still probably give you marginally better results than a stock viewcam lens - at large apertures, anyway.

[Oren Grad]

Understood. I'm just extending the logic the other way, to make sure I understand what's going on: suppose you use the HR-type lens as intended, to image on a CCD with a cover plate. What are you focusing on?

[JW Dewdney]

WITH a CCD - the situation is no different, really. Since the corrector plate is a clear, presumably EXTREMELY flat piece of glass - you're focusing on the CCD, just as you would be without the plate. The plate simply changes the location at which the rays converge, ever so slightly.

[Oren Grad]

Ah, but if you're focusing on a ground glass, say on a slider back, and then moving the CCD into place, your focusing analog doesn't have a cover glass, while your imaging sensor does. That's all I was getting at. Unless the ground glasses on slider backs intended for digital use are, or can be, fitted with corrector plates to make the analog true.

[JW Dewdney]

I'd assume that - for that application - you'd use 'digital' focusing. I have no idea what the arrangement is with the sliders. I suppose Bob would be the one to answer that one.

But in that very specific case - I really don't see why you couldn't use a thickness of glass of an appropriate species to give you the same amount of focus shift (i'm assuming the amount of focus shift to be sub-millimeter, btw).

[Bob Salomon]

"Bob came in and suggested that they shouldn't be used without the corrector plate"

No I di not. I said that with the Apo Sironar Digital HR series you need the corrector plate with film.

I said that with the Apo Sironar Digital series that you do not need the corrector plate.

On the HR series the plate is needed to correct the position where the rays come to focus. It makes a focus shift. I mentioned nothing about curvature or other optical defects. Only plane of focus.

[JW Dewdney]

Bob - yes, we were discussing the HR specifically. Well, that was my understanding. I believe this was also Oren's understanding. I know you mentioned nothing about field curvature. If you look back, it was my conjecture, based on what was established about similar effects with filters in the optical system. This was in a previous post (the one where you were trying to suggest that focus shift was exactly 1/3 filter thickness).

[Narcissist]

I'm looking at getting a 100mm digital lens for use with 6x7 film. Which lenses should I be looking at that will cover this?

Will the performance at say f/11 be much better than my schneider 110mm XL?

[JW Dewdney]

I'm looking at getting a 100mm digital lens for use with 6x7 film. Which lenses should I be looking at that will cover this?

Will the performance at say f/11 be much better than my schneider 110mm XL?

I would say that, beyond, say, f/8 any differences in lens design are going to be pretty minimal if not utterly insignificant. Even a good schneider from the 60s, say, will be pretty close, especially at f/11. I've seen some posts from someone who suggested that one of the newest apo-digitars or what-have-you was sharper than another one-earlier generation digital lens at f/16. I'd say that person probably had a pretty serious case of "i don't know what I'm talkin' about"!!