Ilford MC filters, above or below lens.

[markbau]

Does anyone know the difference between the filter sets that Ilford make that are labelled "below" and "above" lens apart from the size? Is there any optical difference between them? I want to use them for below the lens burning.

Thanks for any help.

Mark

 

[PKM-25]

The only thing I can think of is that the below the lens versions are held flat by plastic frames where as the above lens one are not, so you would have to construct some type of holder that would keep them totally flat or else they could droop and cause optical defects.

When I used them, I needed larger ones for my 150 Apo N so I made a holder out of a Cokin gel holder and it worked great with the small above the lens set. I now no longer use them because I replaced that enlarger with an LPL 4550XLG with the variable contrast head...

 

[Bob Carnie]

Above the negative stage is where I use them.

 

[tkamiya]

Comparing between commonly available 3.5x3.5 and 6x6 AND the below lens type, they are all the same material. I actually took one of the below type apart and compared the filter itself against the former. They were identical.

 

[markbau]

Thanks TKamiya, I sort of suspected that they are the same material. Bob, I wont be using them above the lens, as I said in my original post I will be using them to dodge with a hard filter, and anyhow, I have a colour head

 

[BMbikerider]

Ideally the above lens filters are to be the preferred type so the light path via the lens is not compromised, however in practise it will make very little or no difference. The Ilford below lens filter outfit comes with a 'cage' (The best way of describing it) which has an open end with no plastic and the other end is circular and will fit between the 39mm lens screw thread and the lens mount.

Another reason why I used to prefer below the lens filters is the ease of changing filters if I was doing a print which required a number of different grades. If you have the type that fit in a filter drawer then there is a chance that when changing the filter you may just knock the enlarging head out of alignment.

As I use a colour head for all my prints I have never experienced this problem.

 

[grahamp]

Provided they are kept clean you can use 'above' filters below the lens. I used to do this with my old Durst F30 as the negative carrier was disturbed by removing the condenser/filter drawer unit. I still do it for odd burning in jobs, even though I have a colour head. You can drop the filter over the aperture of a burning card which is convenient. It's a trade-off. Putting anything below the lens risks image degradation, but fiddling with the enlarger can throw the focus off with some models. I need a step to change the settings on my colour head at maximum enlargement, so I sometimes don't bother Under lenses sets and large above lens sets can be expensive.

Use what you can get now, and get a better solution when and if you can.