Need help with filter sizing.

[Bob Salomon]

Interesting post Bob... As I recall Sinar recommended placing filters behind the lens. They even included a filter holder on the back of their Sinar Copal shutter (which I frequently use). Obviously Polarizers and gradated ND filters have to be used in front of the lens.

Placing filters behind the lens makes the filter part of the lens. That will always cause a focus shift = to 1/3rd the thickness of whatever you place there. More importantly any defects, scratches, dust, fingerprints, etc. will also have far more detrimental effect then with placement in front where the filter does not effect what the lens does.

[Eric Woodbury]

Bob, we're going to need a reference on your last statement.

[Bob Salomon]

Bob, we're going to need a reference on your last statement.

Check any photographic optical text book.
Filters only go behind or in a lens if they are part of the design of the lens. Otherwise they will effect the image.

[Xia_Ke]

Thanks again everyone for the input

Send an email to Heliopan and ask them if they have any 84mm filters or adapters left. Ideally you would want an 84 to 86mm adapter. But you would need to know the thread pitch of your lens as well as the thread size.

Thanks Bob I'll give them a call on Monday.

[Tracy Storer]

Check any photographic optical text book.
Filters only go behind or in a lens if they are part of the design of the lens. Otherwise they will effect the image.

I learned this way. Thin wratten gels behind the lens, ok if you must, glass = nono.

[Keith Fleming]

Another option would be to contact S. K. Grimes and have them make an adapter to take the screw-in filters of your choice. They would need the lens itself to verify the lens threads and then for checking the fit of the final product. For example, for my 355 mm Schneider Dagor the Grimes company made an adapter that adapts a 67 mm filter to the lens' 60 mm diamerter. I found it much easier to find 67 mm filters than 60 mm ones.

Keith

[Jerry Bodine]

...Filters only go behind or in a lens if they are part of the design of the lens. Otherwise they will effect the image.

Even if the lens produces a blurry, swirly image?

[Greg]

Placing filters behind the lens makes the filter part of the lens. That will always cause a focus shift = to 1/3rd the thickness of whatever you place there. More importantly any defects, scratches, dust, fingerprints, etc. will also have far more detrimental effect then with placement in front where the filter does not effect what the lens does.

Thickness of Kodak gel filters is 0.08mm. So now will have to compensate for that 0.0266666mm focus shift. Unfortunately my Sinar standards are not calibrated in one one hundreds of a mm so will just have to live with knowing my focus is 0.0266666mm off.... I can live with that.

[Xia_Ke]

Another option would be to contact S. K. Grimes and have them make an adapter to take the screw-in filters of your choice. They would need the lens itself to verify the lens threads and then for checking the fit of the final product. For example, for my 355 mm Schneider Dagor the Grimes company made an adapter that adapts a 67 mm filter to the lens' 60 mm diamerter. I found it much easier to find 67 mm filters than 60 mm ones.

Keith

Thanks Keith If a call to Heliopan doesn't pan out, I may try going that route. Do you mind if I ask what the cost was when you had one made?

[Keith Fleming]

The filter adapter--a step-up ring-- from Grimes was made roughly 15 years ago, so the current price is likely higher. As I recall, the price I paid was about $80.00. I should add that some research on the Internet may turn up a cheaper commercial 60-67 step-up ring. At the time, I did not find a commercial version of what I wanted, but that may not be the case today.

Keith