# What (nd) filter to put in the 17-40L back filter holder?



## Marsu42 (Sep 20, 2013)

I recently realized my 17-40L has this back filter holder  and I now even have though of a use for it: With my 10x glass screw-in nd filter I don't get long enough shutter times for cloud blur in bright daylight, so I'd like to add another gel nd filter.

Question: What nd gels do I get to put behind the 17-40L?


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## Eli (Sep 20, 2013)

What?...


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## Marsu42 (Sep 20, 2013)

Eli said:


> What?...



What what? Did my elaborate English skills fail me? Are you familiar with the 17-40L?


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## Canon1 (Sep 20, 2013)

I've got a nice b+w drop in gel I don't use with my 17-40 anymore. Willing to trade for a screw on front element filter for my 500 f4is.


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## Rat (Sep 20, 2013)

Well, I'll be damned - I got a lens with a rear filter holder. Thanks for sharing, I'm curious what this will bring us


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## Marsu42 (Sep 20, 2013)

Rat said:


> Well, I'll be damned - I got a lens with a rear filter holder. Thanks for sharing



Don't be ashamed, I also wondered for some time what these four edgy things are for 

But I'm still open to any useful advice as for what gels work best for the back holder...


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## tiger82 (Sep 20, 2013)

I did just fine with cloud blur using a screw-in B&W ND3.0 77mm on my 17-40L. I got 30s and longer exposures with small apertures and low ISO.


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## Marsu42 (Sep 20, 2013)

tiger82 said:


> I did just fine with cloud blur using a screw-in B&W ND3.0 77mm on my 17-40L. I got 30s and longer exposures with small apertures and low ISO.



I also tried/did that but a) 30s isn't much to blur slow moving clouds significantly, ymmv in a tornado, b) to get the longest exposure you have to max. close the aperture which means iq loss and will show every single speck of dust on your sensor.

So a+b = putting another 3 stop gel behind the lens shouldn't hurt if it's cheap and iq is ok... the question still is: which?


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## tiger82 (Sep 20, 2013)

Try the Marumi 16.5 stop ND filter. I haven't had much luck stacking ND filters but the LEE 4x4 seems promising if I could ever get my hands on one.


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## Marsu42 (Sep 20, 2013)

tiger82 said:


> Try the Marumi 16.5 stop ND filter.



Well, my budget is already maxed out with the Heliopan 10x nd, I only want a quick/cheap gel nd addon for some shots - for water blur & people removal 10x is fine. 

Btw also adding an ir blocker to the gel holder would make sense in any case to avoid the color cast.


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## surapon (Sep 20, 2013)

Marsu42 said:


> I recently realized my 17-40L has this back filter holder  and I now even have though of a use for it: With my 10x glass screw-in nd filter I don't get long enough shutter times for cloud blur in bright daylight, so I'd like to add another gel nd filter.
> 
> Question: What nd gels do I get to put behind the 17-40L?



Dear Marsu42.
Per the Photos below---My DIY, The Cheapo one, I just cut the Milar or Clear Thin Plastic Box, and Paint with the Pink color Permanent Magic Felt Tip pen, and use for take the Photo in the Fluorescent light room---to get the Redish color of the Green/ Blue Picture from the Flu. Light------Yes Cheap and with out move the UV. protective filter in front of Lens. 
Enjoy
Surapon


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## surapon (Sep 20, 2013)

My DIY, The Cheapo one, I just cut the Milar or Clear Thin Plastic Box


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## surapon (Sep 20, 2013)

My DIY, The Cheapo one, I just cut the Milar or Clear Thin Plastic Box to use as the back of lens filter.
Yes, You can buy the Ready made plastic sheet color filters to cut and fit too.
Enjoy
Surapon


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## tiger82 (Sep 20, 2013)

I just dug out a test 25 second exposure with a B&W 10x shot with my 17-40 at f/4 ISO 100. I lengthened the exposure to 138s at f/4 and ISO 100 to get more light in and more blur.


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## fugu82 (Sep 20, 2013)

For the best optical quality, you can use Kodak Wratten gels. Their #96 ND gels work well, and come in various densities. You have to cut them to size to fit your holder, and handle them with gloves or tweezers to prevent fingerprints.


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## Marsu42 (Sep 20, 2013)

tiger82 said:


> I just dug out a test 25 second exposure with a B&W 10x shot with my 17-40 at f/4 ISO 100. I lengthened the exposure to 138s at f/4 and ISO 100 to get more light in and more blur.



Second one looks nice, though the first one is the reason why for me 10x isn't enough - to me it looks kind of a boring/broken and "in the middle" between sharp and blurry.



fugu82 said:


> and handle them with gloves or tweezers to prevent fingerprints.



Doh, that doesn't sound like me  and/or outdoor shooting, so it won't be a replacement for a glass filter - but thanks for the answer, I now have an idea of what to buy.


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## tiger82 (Sep 20, 2013)

My point is both were shot with a 10 stop ND3.0. I've shot up to 30 minutes with an ND3 filter. I recall the hot pixels became an issue.


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