Nd filters versus stopping down

[Doremus Scudder]

Thank you all for your views.

Therefore, my understanding is :-
1] Given the optimal (recommended/preferred) aperture for large format images seems to be f16 or f22
2] Given a lens with a large aperture but no diaphragm.
Then I could use ND filtration on the lens to give an effective f16/f22 setting and use the appropriate speed for that pseudo f16/f22 lens aperture.
[Again I'm ignoring the effects of the ND filtration on the image due to its manufacturing characteristics, and the difficulties of focusing through high ND filtration]
Right or wrong???????
Regards
Tony

Tony,

Stopping down the lens makes the hole the light is passing through on the way to the film smaller. This has two important optical effects besides reducing the amount of light getting to the film: 1. the smaller the hole, the greater the depth-of-field. 2. the smaller the hole, the more (image-degrading) diffraction there is. Further to this latter: there is a "sweet spot" in most lens designs where stopping down eliminates lens-design flaws and aberrations, but where the image-degrading effects of diffraction are not yet enough to really reduce image quality. Any larger aperture and there would be more degradation due to aberrations; any smaller and diffraction would degrade the image more. This point is different for different formats; for large format it is approximately f/22.

Neutral-density filters reduce the amount of light getting to the film by absorbing some of it on the way through the filter. This is independent of the effects of stopping down. Using an ND filter to get the same exposure at f/5.6 as you would get by stopping down to f/22 retains all the optical characteristics of an f/5.6 aperture, i.e., shallower depth-of-field and possible degradation due to lens aberrations (which would be corrected at f/22).

So, you can use an ND filter to get the right exposure with an aperture-less f/5.6 lens, but you'll have to live with the optical effects of the larger f/5.6 aperture.

BTW, you don't have to focus with the ND filter in place...

Hope this helps,

Doremus

[Pere Casals]

Well, also rather than using a ND filter we always can use a lower ISO film, even ISO 25, so we may get a technically better result from the lower ISO.

What I can say it is that my DIY dry plates won't usually require NDs

[tonyowen]

[QUOTE=Doremus Scudder;1429863]So, you can use an ND filter to get the right exposure with an aperture-less f/5.6 lens, but you'll have to live with the optical effects of the larger f/5.6 aperture./QUOTE]
Thank you, that answers my query without issue
regards
Tony

[ic-racer]

Thank you all for your views.

Therefore, my understanding is :-
1] Given the optimal (recommended/preferred) aperture for large format images seems to be f16 or f22
2] Given a lens with a large aperture but no diaphragm.
Then I could use ND filtration on the lens to give an effective f16/f22 setting and use the appropriate speed for that pseudo f16/f22 lens aperture.
[Again I'm ignoring the effects of the ND filtration on the image due to its manufacturing characteristics, and the difficulties of focusing through high ND filtration]
Right or wrong???????
Regards
Tony

Best to forget about the lens. It's aperture or effective aperture or shutter efficiency do not change at all with addition or subtraction of ND to the light path!
I teach that ND affects the ISO or Exposure Index of the film. It is as if you have a dense ISO trimmer coating on the emulsion. Nothing to do with the lens or shutter.

[andrewch59]

http://www.bwvision.com/complete-gui...-2016-edition/

Try this link, was very useful when I started dabbling in long exposures using nd filters, and some great examples.

[consummate_fritterer]

STOPPING DOWN...
1. Increases depth-of-field
2. Allows for a slower shutter speed
3. Decreases lens defects (chromatic aberrations)
4. Increases diffraction effects

ND FILTER...
1. Can decrease Depth-Of-Field (wider aperture)
2. Can allow for a slower shutter speed
3. Can be too dense demanding too wide an aperture (lens defects more pronounced)
4. Can allow for a wider aperture (less lens diffraction)
*** This is essentially similar to using a slower speed film!! Given the choice, I'd rather just use slower film but this isn't always practicable especially when the speed decrease desired is very substantial.

COMBINING BOTH (along with film speed choice)...
1. Allows finding the best combination for the lens, film and final image look

[William Whitaker]

Another consideration regarding ND filters germane to this forum and the netizens who frequent here is the type of lens you're using.

Some Portrait/Pictorial lenses, e.g., the Wollensak Verito (as a prime example), change the character of their image as they're stopped down due to the restriction of marginal rays which show a great deal of spherical aberration. So if you're working in a situation where the lighting may not be within your direct control, such as outside with a model, an ND filter will allow you to shoot with the lens aperture set to your desired level of diffusion, yet providing a shutter speed within the range of whatever shutter you're using.
In fact, speaking from experience, a robust ND filter large enough to cover the lens aperture is a necessary accessory for a Verito. Of course, there are any number of other portrait lenses which are diffuse wide open, then sharpen significantly as they're stopped down. It's just that most of my experience is with the Verito.

[consummate_fritterer]

Good point, Will, and this is why most (or many) Imagon lenses were supplied with a ND filter.

[Jody_S]

But stars are very bright point sources, it's that pesky atmosphere and light pollution that's the problem...

Where's contrast when 'ya need it!?!!!

Steve K

So use a film with bad reciprocity failure characteristics. That will significantly darken the landscape and light pollution.

[Jody_S]

I find I'm now using ND and grad filters for maybe 75% of my outdoor shots, sometimes more if I'm using barrel lenses with a Packard or Galli shutter. I also find the designations confusing, not to mention a 0.9ND might not be exactly 3 stops. I've solved this rather easily by spot metering through the filter.