Front Filter on 150 Super Symmar XL

[Scott Rosenberg]

before placing a front filter on my 110-XL i was advised to use a 67-67 step-up ring as a spacer to prevent contact between the filter and lens. should the same precautions be taken with the 150-XL?

i am planning on stepping the rear to 67mm and using my filters back there instead of using huge 95mm filters up front. besides having to focus through the filter, is there any other reason not to do this?

if you're wondering, i was asking about the front filter because i always put a protective filter on my lenses.

thanks!
scott

[Eric Leppanen]

Based strictly on superficial observation, it appears that the SS150XL has more filter clearance on the front element than the SS110XL. I have not actually tried using 95mm filters on my SS150XL, however; I always use the Schneider center filter with this lens, and apply filters on top of the center filter using a Lee press-on filter holder (FK115).

No reason why you can't use your 67mm filters on the SS150XL rear element, as long as you do final focusing with the filter in place, and you verify that no vignetting occurs with extreme movements. The only drawback is that things get awfully dark when using dense B&W filters such a Red #25, Blue #47, etc. Rear mounting won't work for a polarizer, of course.

[Lars Åke Vinberg]

My experience is the same as Eric's - CF on front, then Lee 115 mm holder. My filters are 77mm so lots of margin from vignetting on the rear side. Schneider recommends only one filter behind the lens, but that probably does not include gels.

I thought a linear polarizer would be OK even behind the lens? Or reversing the glass on a circular polarizer (since it would be mounted backwards)?

[Eric Leppanen]

Lars,

My general understanding is that there are at least two problems with placing a polarizing filter behind the lens:

1) You cannot rotate the filter while viewing through the ground glass (not an issue if you first determine the proper rotation by hand, then place the filter in the camera in the same orientation).

2) Focus shift effects can become a problem (at least in theory, especially with a WA lens) with a relatively thick filter like a polarizer. I don't really understand the theory behind this, but there are several older threads discussing this topic.

I just avoided the entire issue by going with the Lee filter system.

[William Marderness]

Read the paragraph entitled "What is the Proper Placement of the Fresnel?" in the article “Viewing Screens for Large Format Cameras” by Ron Wisner. See here: http://www.wisner.com/viewing.htm.

Wisner explains that the light is bent when glass is placed between the lens and film. He uses a filter placed behind the lens as an example. He says that a filter behind the lens results in "curvature of the image" and "erroneous focusing of the edges of the image." Focusing through the filter will not prevent this, since your plane of focus will be curved.

[Lars Åke Vinberg]

Focus shifts are manageable - just refocus after attaching filters.

What might be a bigger problem is that an additional pice of flat glass between lens and film introduces spherical aberration, which can be especially troublesome with wideangle lenses. Since a glass polarizer generally is thicker than regular filters it might be especially troublesome.

I have examined some 8x10's I shot with a Toyo linear polarizer behind the lens with the 150XL, and I must say that those sheets are razor-sharp to the corner. I wouldn't worry too much about it. Or if you do worry, perform your own tests.

[Scott Rosenberg]

thanks for setting the record straight on the use of filters behind the lens. i know that they need to be VERY clean, but my filter usually are.

could someone confirm the need to fashion some sort of spacer before putting a filter up front to prevent lens/filter contact?

thanks again, fellas,
scott

[Lars Åke Vinberg]

Scott,

There is no absolute answer to your question on the need for a spacer. It depends on the filter. With my 47XL I could not use B+W or Heliopan filters threaded all the way in, whereas Hoya works fine. What it comes down to is how far recessed in the filter ring the filter glass is. On my 150XL there seems to be about 1 mm clearance from the front of the lens barrel to the front element. I don't think Hoya is available in 95mm though.

Using a spacer will lead to vignetting problems - you paid a lot of money for that image circle, why waste it? I would suggest that you get the 95mm filter you need and do not thread it all the way in. Or seriously consider not using screw-in filters on the front of the lens.

There is another option for polarizer that will absolutely not vignet on a 150XL: Use the Cokin X-Pro system. The polarizer in that system has a glass diameter of 118 mm and mounts close to the lens.