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Technical solutions for filters inside and behind the lens


Bill_D

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I'm posting this in the main technical discussions forum because while my inquiry is motivated primarily by invisible spectrum efforts, people doing only visible light photography might assist with these equipment questions or benefit from answers that may be provided.

In learning about Nikon lenses I've found that a certain proportion have unusual filter arrangements. These include internal filters on a wheel (several fisheyes), internal but exchangeable filters in a holder (various long lenses), rear-mounted filters (the mirror lenses among others), and rear gel filters (14mm f/2.8).

The rear-mounted and holder-mounted filters are special Nikon filters with external threads and a unique thread pitch. Other makes of filter won't fit these threads, and the filter holders have limited clearance in any case.  Thus you are limited to using the filters Nikon made, if you can find them. This limited selection of filters presented only modest issues when I was shooting 35mm film, as I seldom used these lenses. Now this situation has reared its head again due to my new photographic efforts.

Additional issues I'm faced with are that certain specialty filters such as the Baader astronomical filters are only available in 1.25" and 2" sizes, making them too small to go in front of some lenses. Due to the Nikon thread, they also won't fit in the filter holders or on the back of lenses with rear-mounted filters.

So here I am plotting ways of trying to use certain lenses for astronomical uses and for UV on converted wide-spectrum cameras. Currently I have a wide-spectrum Panasonic GX1 and a wide-spectrum D5100; IR is taken care of with dedicated IR cameras.

 

Here are the specifics:

1. Sometimes lenses will go on a M4/3 camera via a mount adapter. I want to glue an adapter ring inside the mount adapter which could receive various 1.25" filters such as the Baader Venus, H-alpha, or others. This looks doable in at least some cases, though I have yet to find a suitable adapter ring to use for this project. Before I ruin a mount adapter or find unexpected optical issues, are there any things I need to be aware of when I pursue this modification? Is there a better way to go about this concept other than a custom filter box / mount adapter?

2. I'd like to be able to place similar filters on the rear end of lenses having a filter mount there. This might work (given careful attention to mirror clearance) if anyone makes or has made an adapter to the special Nikon thread. I have not found any such thing yet.

3. I'd like to be able to place similar filters in the filter holder of suitable Nikon lenses. It looks like this would require custom-modified filters, either placing the filter glass into the Nikon filter ring (with a filler ring due to the difference in diameter) or else finding an adapter to connect the special Nikon thread on the filter holder to custom-made slim-line filters.  (The effects of the undersized filter diameter, 33mm vs. 39mm, hopefully would be addressed by the DX format of the camera.)

4. It looks like I could use slimline 48mm filters in my Canon FD 800/5.6, though I have not tried yet since I don't have any in that size. My Baader Venus filter (supposedly 2" but really 48mm, and serving as a proxy for all the other Baader filter types), does more or less fit the screwthread but is too wide to allow the filter holder to go back into the lens. Sounds like custom filter-ring fabrication is needed.

At some point dealing with numbers 2 through 4 might get so expensive that I'd be better off just getting an internal-filter UV camera, or maybe a wide-spectrum NEX with filters in the adapter as per #1.  However, for now I'm trying to avoid more conversions. Lenses and supporting equipment are good essentially indefinitely if properly cared for, while digital cameras and conversions thereof have a definite half-life. Alternately, I could just stick with M4/3 cameras for these lenses, but I'd like to have more choices in format.

I'd greatly appreciate any information or suggestions on these issues!

Thanks,
Bill

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I do on occasion use a filter box with dedicated holders you can slide in from the side. The German company Teleskop-Service makes nice sets. The box is designed for astrnomical use so has the ubiquitous 48 mm threads (male/female) on either end. It's easy to rebuild to have say 39/42 mm thread, F, or m43 mount on one side and what you require on the other end. Great for situations where you require extension, and in the case of m43, you often can reach infinity focus when the box is used insterad of the usual mount adapter.

In case of m43 or similar, put the filter inside the mount adapter. This works nicely with Baader and similar filters and you all of a sudden can use rear-mounted filters on all your lenses. This is my normal solution for using the Coastal 60 mm f/4 APO lens on a broad-spectrum Panasonic GH-2. These mount adapters are cheap so you cna have individual modified adapters so say UV or IR usage.

Knocking out the native glass and replacing with your own filter is a good solution for long lenses which filter drawers. Purchase an oversize filter and let an optician cut it down to the required size.

Most convenient, but also most expensive, approach is having camera(s) with perrmanently mounted filters on the inside.

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Thanks, Bjørn!  The key here is flexibility to allow experimentation.  Baader claims you can stack their filters but we'll have to see when I get to that point.  Meanwhile, I have three extra Nikon filters on their way.  They will be available for sacrifice should I go that route which I expect to do.

 

I photographed the annular eclipse and Venus transit last year in visible using a solar filter, and the next step is to try other wavelengths!

 

 

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Filter quick changers (boxes) and extra filter drawers, at Teleskop-Service http://www.teleskop-express.de/shop/advanced_search_result.php?keywords=TS+Filter+Quick+Changer&suchdas=OK and at Amazon UK http://www.amazon.co.uk/s/ref=sr_nr_i_0?rh=k%3ATS-Optics+ultra-slim+filter+drawer%2Ci%3Aelectronics&keywords=TS-Optics+ultra-slim+filter+drawer&ie=UTF8&qid=1386826772 .

 

One problem I noted is that with these items one loses automated communications between the camera and the lens.  This would generally be the case anyway when using a cross-format adapter, but it is something to keep in mind if you're planning on photographing something that changes fast enough that you'd want auto-exposure working. 

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Think of this as using an old-fashioned bellows device. Some functionality is lost some is gained. Nothing prevents you from putting a CPU into the filter box (or bellows) to recoup some of the automation you lost. I do this with the expressed purpose of keeping track of exposure variables since hand-written notes tend to be forgotten or go astray later. Knowing the gear set-up is paramount when you do a lot of experimentation and want to be able to replicate results later.

 

However, as most of the time with such contraptions involved you shoot under controlled conditions, the problem is less severe than you might think. Plus, auto-exposure and say UV is not a viable combination.

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