Filter placement - front or back

[Eric Rose]

I was wondering (I do a lot of that) if the hassle wasn't an issue, would it be better (ie: sharper) to place the filter on the back element of the lens or is it better to put them on the front?

Most LF lens have a threaded rear element so I think this is possible.

I'm being alturistic here, I know it would be a bother to do it, so that is not the issue. I am looking for maximum sharpness, contrast etc. We are assuming we have the best filters money can buy as well.

Has anyone ever tried this?

Eric

 

[David A. Goldfarb]

Putting the filter in back introduces focus shift, so you have to be sure to focus with the filter in place. Dirt or scratches will also have a greater effect behind the lens than in front.

On the other hand, you don't have to worry about shading the filter, if you put it behind the lens.

In an ideal world, I'd always use filters with a compendium bellows in front of the lens, but in the real world, I've got too many weird old lenses with odd filter sizes for this to be practical. I also have a few ultrawides that just can't take a filter in front without vignetting, because even a step-up ring for a larger filter will vignette. So for those lenses, I have 3x3" filter holders epoxied to the back of the lensboard, and I put the filter behind the lens.

 

[lee]

I use gels and have for several years placed the filter in the rear of the lens and I see no difference in the the sharpness or any loss of contrast. You should try it and see if it works for you and your equipment.

lee\c

 

[Eric Rose]

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (lee @ Jan 10 2003, 03:07 PM)</td></tr><tr><td id='QUOTE'> I use gels and have for several years placed the filter in the rear of the lens and I see no difference in the the sharpness or any loss of contrast. You should try it and see if it works for you and your equipment.

lee\c </td></tr></table><span class='postcolor'>
Lee, if there is no apparent difference, I would assume that means there is no advantage to using the filters behind the lens. For sharpness and contrast anyway. Since you go the extra step to put them behind the lens, what is the advantage from your experience? Also how do you attach the gels?

Eric

 

[glbeas]

One advantage I can see for gels behind the lens is it gets the filter assembly out of the way for getting to the shutter and aperture controls. It's also a cleaner environment so would be much less likely to collect any stray dust, especially if you were working outside.

 

[lee]

Those are important considerations. The main reason is simplicity. I use a double sticky tape and place it on the back of the lens rim. This stuff is really malable and you can form it into strings. The filter is pressed into the tape. Care is taken to make sure I don't use the center of the filter. Then I attach the lens board to the camera. You understand that this is nearly the last step in taking the shot. All the prelim work (composition and focus) have been done. But the main reason is it gets the filter out of the way and won't blow off and get trashed as quickly. I do have to replace filters every so often. I have several lenses that do not share a common thread size. So, lthis is what I came up with. It works for me and I am happy with it.

lee\c

 

[lee]

one other thing you might do is there are some card board squares that serve as frames for the filters and you could slide the filter into that and then use the double sided tape to attach the whole thing to the back of the lens.

lee\c

 

[Eric Rose]

Is there any worries about the filter not being 100% parallel to the back element? If it is not totally square would this serve to add some distortion to the final image. I guess not since you find it successful. Have you done any A/B studies with the filter on the front, then back then no filter to see if there is any degradation? I suppose I'm getting to nit picky, something I try to avoid when it comes to my photography. I find some get more obsessed with techie kinds of things and not enough with the "art".

Eric

 

[lee]

As far as I can tell, there is no problem. All you are doing is coloring the light. Those techie things are somewhat necessary but they do become the devil's workshop. =[8^)

lee\c

 

[John Luke]

I place grads and polarizers up front. They will induce focus shift on the rear. Sure, you could put them on the rear and then focus, but I have found it difficult to focus through anything that has any measurable density. I used to put Wratten CC gels on the rear, but if using 2 filters, that was prone to a ghosting, or double images in highlight areas. After reading the photonet posts, I don't think I will ever put anything on the rear again. Here are some links from photonet that dealt with this:

http://www.photo.net/bboard/q-and-a-fetch-...g?msg_id=0033SN
http://www.photo.net/bboard/q-and-a-fetch-...g?msg_id=0039TF
http://www.photo.net/bboard/q-and-a-fetch-...g?msg_id=00392R
http://www.photo.net/bboard/q-and-a-fetch-...g?msg_id=003FaN

John Luke
APA/ASMP

 

[Joe Lipka]

Fred Picker recommended that the thin gelatin filters were best used behind the lens. The thinness of the gelatin was negible with regards to focus shift. I tried this for a while, but I found it maddening. Went back to the screw in filters. Like everything else, you can make it work if you either want to or have to.

 

[michael9793]

Most of the LF people I have discussed this with all say filters behind the lens seems to be the best for sharpness. But you must refocus after placing the filter do to refractions of light from he color you are using. At least that was what I was told.

 

[William Levitt]

I use filters behind the lens for the simple reason that a good number of my lenses have front elements that are just plain too large for my standard 3X3" filter. Even my 100mmX100mm Sinar filters don't cover the entire front element of my Schneider 5,6 360mm lens. So, intead of carriy several sets of filters, depending on the lens size, I have one set that covers everything from my 250mm WF Ektar down to my 210mm Schneider Angulon behind the lens.

I do my focusing and comoposing without the filter, then place the filter on the back ofg the lens using rolled up tape, replace the GG and then refocus. it's always worked for me.

 

[lee]

I agree.

lee\c