Nikon 8mm f/2.8 Ai - filter carousel

[Kuri]

I often photograph using infrared (and ultraviolet), so I am interested in the filters and possibility of replacing some of the filters in the 8mm filter carousel.

The Nikon 8mm f/2.8 AI Fisheye lens has a built in rear filter carousel containing 5 filters.
L1A - Clear Skylight
Y48 - Medium Yellow
Y42 - Deep Yellow
O56 - Orange
R60 - Red

These tests were shot using a full spectrum DX conversion, so the full circle of this fisheye is cropped by the DX sensor.
These shots are white balanced from RAW in NX-D.

From looking at the 8mm f/2.8 repair manual it doesn't appear that the filter carousel can be removed without taking apart most of the rest of the lens.

Here is what I learned from removing the 'filter cover' (part 40-1):
1) The filters can't be removed by removing the 'filter cover', because there is not enough clearance to lift them out, and also
2) The filters seem to be glued into the 'filter revolver' plate (part 41). Note: The line of residual glue on the 'filter revolver' plate.
To remove and/or replace these filters you would need to dismantle the front end of the lens, focus ring, etc., to get the filter revolver plate removed.
It is unknown to me how easily the filter glass could be removed given the glue used to hold them in place.
The filters are 20mm in diameter, and they look like about 2mm thick.

[brent_e]

thanks for posting this.
I'd love to see larger versions of your photos! 

[Erik Lund]

I have the repair manual, and yes it's a total disassembly as far as I can see,,,

also you would need more or less exactly the right thickness filter or you will loose infinity or focus range.

Filters in front of the camera sensor is preferred with these fishy lenses

[Kuri]

Erik, Thank you. Both Andrea and Bob recommended you as 'the person to ask' about this. I am glad you have the repair manual also.
It looks fairly involved to get access to the filters...

Brent, here is a larger version of the red filter shot. I didn't even focus those shots, so...?

[Erik Lund]

Sorry not much help.
Focus is quite critical for the 8mm, even the 6mm demands it!

[bobfriedman]

unfortunate that it is not easier... would be quite nice to change those filters..

interesting shot.. you need a full frame cam!

[Kuri]

Erik, You are quite helpful actually. Thanks again.

Yes, those I shot just to see how even filter would white balance. I 'may' have focused it to infinity? But I doubt I focused it.
I don't have a full frame full spectrum converted camera yet, so that is why I used the converted DX, just to see how the existing filters worked in full spectrum.
I will make sure I focus next time. ;-)

[Kuri]

The 8mm f/2.8 lens filter revolver removed.
Filter glass is all 20mm diameter x 1.8mm thick.
Glue holding filters in revolver is relentless. I don't know yet how to remove the filters or loosen the glue. 
The revolver is NOT easy to access. I advise getting the service manual and digesting it a few days first.
This lens transmits UV very poorly. The front elements are very dark blue in UV, add to that the lesser dark blue of the rear elements and L1A clear filter.

[bobfriedman]

you did it!... disassembled the lens!?

[Akira]

Wow, this is a formidable project!!!

[Thomas G]

Wow, this is a formidable project!!!

Following with increasing interest 

[longzoom]

To the OP: you may try 20mm filters for Microscope collections. I did find there 20mm Pola filters, as well as many more, 30 years(about!) ago, for the same needs. Only the problem there, most of them are 2.5 and more mm thick. You have to spend time try to find ones of 1.6 - 1.8mm thick. If not, you may find square ones, they are about 1.4 mm thick, and cut it out, not a big deal. Good luck, it really worth it!  LZ

[Kuri]

Thomas, I make filters, any size, any thickness, so that is no problem, but I am not sure how to remove the glue, without also removing the paint, etc..
One possible idea would be to mount gel filters over some of the colored longpass filters.
For example, mount a Wratten 89B (720nm) or Wratten 87C (850nm) over one of the colored filters. There is enough clearance to do that (I think).
Those glass revolver filters are all just longpass filters and transmit IR, so stacking IR gel filters will cut out the visual and still transmit the IR that the gel filter transmits.
Not sure how that would work optically compared to the visual results using this lens, but a test of this idea would be interesting.
This idea can also leave the clear filter available for visual stock camera shots, and any of the other filters that one might want to use.
I would still like to find a way to remove the glue, but... for now... ?

[Akira]

Kuri, if you are not particular about this Fisheye Nikkor, there are possible alternatives.  Sigma makes circular and rectangular fisheye lenses both for FX and DX, and all have holders on their rear ends for the gelatine filter.

I'm not sure if they offer the image quality in IR to suit your need, though...

[longzoom]

Kuri, somehow I believe you are answering to my post. I do not think to use the gel filter is such a good idea. The gel can't be perfectly flat, to some degree. So it may contact the glass, and those contact points will produce a Fresnel effect, less or more. Yes, glue. It is a problem. I removed it with the knife, with the paint, simultaneously, but did paint the new filters sides to the black deep matte. Never had any reflections! LZ