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View Full Version : 150XL and Rear Filters - Who is doing this?



turtle
15-Mar-2012, 04:15
Can anyone tell me whether one needs to use wide angle filters on the rear of the 150XL in order to avoid vignetting/a reduced image circle?

Have any of you had problems with focus shift?

I am considering the use of polyester filters on the rear, as they are thinner so should not result in any real focus shift, but will have to see if the holder will fit OK. Has anyone used gels/polyester filters on the rear?

Bob Salomon
15-Mar-2012, 04:37
Real? Put anything back there and there is a focus shift. And image degradation since the lens did its job on the image when the rays came out the back. Now any marks, smudges, imperfections, distortions, lack of flatness of the filter will effect the image before it reaches the image plane.

Filters belong in front of the lens unless they are designed by the lens manufacurer to be part of the optic.

Helen Bach
15-Mar-2012, 05:12
You don't need a holder to use filters behind the lens. You can attach them with tape. One way is to tear off a strip of camera tape about 10 mm wide, then fold it over lengthwise, sticky side out, before wrapping it round the outside of the back of the lens, fold to the rear of the lens and slightly proud - thus forming a sticky circle onto which you place the filter. Easier to demonstrate than to describe. You can also use little rolls of 'snot tape' - Scotch ATG tape.

I don't usually use behind-the-lens filters with LF, but I have used gelatin and sometimes thin polyester filters behind the lens for motion picture. A friend and colleague of mine, who has way more status as a commercial LF photographer than I do, uses Cokin resin filters behind his LF lenses and you can't tell the difference between his shots and mine in terms of resolution and sharpness until you print larger than 16x20 - but I use 'better' lenses than he does, so who knows. There's no point in me trying to persuade him that one shouldn't use Cokin filters behind the lens when he has had so much success when using them - he often tells me how many millions each of his ancient lenses have made for him, and he always uses an 81A. I think that experience should be your guide. How much does it cost to find out if using a filter behind the lens will make a difference with your lenses, your method, your print size, your standards?

turtle
15-Mar-2012, 05:41
Yes Bob, I am considering it! I know the theory, but focus shift is not a game changer as one can easily focus through the filter. Image degradation would be a concern, but there is theory and practice. In short, I am looking at the options for filters with the 150XL. The large front diameter means more expenditure and bulk, whereas I already have almost all of what I need were I to mount filters behind the lens. Polyester filters are so thin that I very much doubt that they will cause focus shift of note.

Worst case scenario I could mount filters in front, but this will entail compromises of its own. At this stage I am looking for info.

Noah A
15-Mar-2012, 05:50
Of course it's ideal to use the filters in front, but the 150XL uses huge filters!

There will be focus shift, but as long as you focus with the filter in place it shouldn't matter.

It really comes down to what you're doing. If you're contact-printing 8x10 then I'd be willing to bet you'll see no difference in sharpness. If you're drum scanning and printing huge, then, well, you may see a tiny bit. But in that case it's worth your trouble to do a test shot, scan and some test print sections just to be sure.

I think it'll be fine.

In terms of needing a slim or wideangle filter, I doubt it, but all you need to do is slap a normal filter on the back and check for vignetting on the camera.

Helen Bach
15-Mar-2012, 06:50
I know that we have covered this a few times before, but remember that the focus shift is not constant: it depends on the angle of incidence, so it causes spherical aberration as well as field curvature. This may or may not matter, and the thinner the filter the less the difference.

turtle
15-Mar-2012, 06:56
I cannot imagine that Schneider would have put a rear thread on there if it was likely to be a disaster and it is interesting to note that they did not put a rear filter on the 72 XL, which shares the same front diameter. I guess I will have to find out. I only use Lee polyester filters on LF at the moment, because they are very small and light. Considering that they are something less than 100mm (they are in a plastic mount) vignetting might be an issue with full movement. Certainly, carting about a selection of large filters that would cover the even bigger CF is not exactly appealing!

Helen Bach
15-Mar-2012, 07:17
Here's the tape method, in this case with a 165 mm Super Angulon and an old resin filter for illustrative purposes.

http://i215.photobucket.com/albums/cc155/hbphotobucket/backfilter165sa-SIDE.jpg

http://i215.photobucket.com/albums/cc155/hbphotobucket/backfilter165sa-TOP.jpg

E. von Hoegh
15-Mar-2012, 07:41
Yes Bob, I am considering it! I know the theory, but focus shift is not a game changer as one can easily focus through the filter. Image degradation would be a concern, but there is theory and practice. In short, I am looking at the options for filters with the 150XL. The large front diameter means more expenditure and bulk, whereas I already have almost all of what I need were I to mount filters behind the lens. Polyester filters are so thin that I very much doubt that they will cause focus shift of note.

Worst case scenario I could mount filters in front, but this will entail compromises of its own. At this stage I am looking for info.

Assuming a spotlessly clean filter, the image degradation will depend on the thickness of the filter and the refractive index of the filter material.

Eric Leppanen
15-Mar-2012, 14:57
It is possible to do front filtration with the SS150XL without mechanical vignetting issues. There are a variety of threads covering this subject, here is one:

http://www.largeformatphotography.info/forum/showthread.php?39322-Need-filter-holder-solution-for-Schneider-150mm-SSXL&highlight=ss150xl+filters

aporodagon
16-Mar-2012, 12:45
I'm using a 150XL with the centre filter and gels on the back of the lens. I cut a small square of black foam core and used an Olfa circle cutter ($5 - $10) to cut out a circle the same diameter as the rear of the lens. The gel is taped to the foam core and then pushed on to the back of the lens. Since you'll probably have a lot of foam core left over, you could cut several pieces and dedicate a filter to each piece.

turtle
16-Mar-2012, 14:11
thanks for the info everyone. V useful link Eric and what a good idea aporodagon. It would work as a nice cheap adaptor for the front too. The problem with the Lee is that you need the 115mm push on holder with the CF and the 100 without and buying both is fairly outrageously expensive considering what it entailed. If I do go down this route, I would most likely go for the 115 adaptor and use the foam core and tape solution for when not using the CF.

Old-N-Feeble
16-Mar-2012, 18:18
I'll not use a CF on the back of any lens because that's definitely not optimal... they're just not designed for use behind the rear element. However, I'll certainly use gel filters on the back because they're optically neutral.

John NYC
16-Mar-2012, 19:02
I think I have had this argument on this forum before... my advice as a former 150mm SS XL owner is to buy a proper center filter. People who say you don't need it must prefer the significantly vignetted look, which I agree can look good but is not for every shot. It is a fantastic lens if you like that focal length on 8x10. Sharp. Very good color rendition -- perhaps the best of any lens I have owned in this regard.

turtle
16-Mar-2012, 23:59
I don't think anyone suggested using a centre filter on the rear. In fact, I don't think you can even do that. There was only mention of gels/polyester/resin filters on the back. It seems like the Lee 115 holder is best as this works with the CF on the front and an improvised solution should suffice to hold filters on the front if I do not wish to use the CF. At least this way one is not spending $400 on bits of plastic to hold filters in place!



I'll not use a CF on the back of any lens because that's definitely not optimal... they're just not designed for use behind the rear element. However, I'll certainly use gel filters on the back because they're optically neutral.

Old-N-Feeble
17-Mar-2012, 05:57
Sorry, turtle. I must have misunderstood what you were trying to convey in post #12. I'm easily kunfyoozed these days.


I don't think anyone suggested using a centre filter on the rear. In fact, I don't think you can even do that. <snip>!

Hugo Zhang
17-Mar-2012, 09:10
I do and I only contact print and I can use my 150mm ssxl to cover 7x17. Front filter will not do if I use the lens with filter for 7x17.

frotog
18-Mar-2012, 07:53
Tape filters on the rear element at your own risk. If rear filtration is your thing try to locate a horseman behind the lens filter gizmo. Can't be beat.

If you choose to go with a c.f. for the 150xl rear filtration will be your only option unless you can shell out the cash for the nearly unobtainable Lee custom 115 front filter holder.

Extreme vignetting, the costly c.f. with the two stop loss in speed and the two year wait for the Lee 115 were all deal breakers for me. I sold my 150xl and now use a rodenstock apo 150mm W - lots of coverage for my 5x7, just as sharp as the xl and little to no vignetting.

Helen Bach
18-Mar-2012, 10:06
Tape filters on the rear element at your own risk.

Who is suggesting that you tape filters to the rear element?