Filters in Front of a Long Lens

[Pawel Achtel]

We know that filters degrade image. The longer the focal length and the bigger the aperture of the lens, the more degradation. Filter quality (flatness) plays big role. If a filter is used in front of say 400mm lens, then even a supposedly high quality Hoya HMC Pro will cause very significant (unaccaptable) image degradation. This is because the filter needs to be flat to something like 1/2 light wavelength, so even placing a filter in a frame will buckle it beyond that! Scarry stuff! :scared:

My questions:

1. What filters (in particular NDs) are the best quality?

Pancro, Schneider, Formatt,... they all say they are "flat" but how flat is flat?

2. What is the maximum focal length and aperture one would use a filter in front of the lens for 4k acquisition?

Of course internal filters are the answer, but show me a lens with 3 internal filter frames....

 

[Elsie N]

Pawel, glad you started this thread. Hope you can clarify if all filters (uv, poli's etc.) have an effect on a long lens. And lastly, is there any filter that will lessen the effects of atmospherics on an image?

 

[Pawel Achtel]

Hmmm...no thoughts anyone?

OK, consider the results in this article before you put a filter in front of your expensive lens. Warning: the images may offend and can be very disturbing to filter manufacturers. :blushing:

http://www.clarkvision.com/articles/evaluating_filter_quality/index.html

My results of using HOYA HMC UV filter were very similar, if not worse. I used Canon 70-200 2.8 L and, at first, I thought the lens was faulty because all of the pictures at the long end were so soft. I thought it was the autofocus, but the problem was that nothing was in focus! So, it couldn't have been focusing problem. It ended up to be the "high quality" Hoya HMC Pro you beaut filter.

Anyone with some thoughts? Surely someone set up a test or has some experience using long lenses.

 

[ericyoung]

Interesting - of course, before dismissing Hoya filters, it'd be interesting to know the flatness figures for other more expensive filters from Tiffen, Schneider, Formatt, Panchro et al, not to mention coatings.

In my opinion, it's still good practice to leave at least one protection filter on, but in the light of these test results, it may be worth leaving it off for specific shots.

 

[Stephen Williams]

There is a reason that film is produced with different ISO ratings & color balances.

 

[Pawel Achtel]

What's the reason?

Edit: Can/Should one use filters in front of long lenses, which filters and which lenses?

 

[Hans von Sonntag]

What's the reason?

Stephen is saying that a 50 ASA film needs less ND filtration than a RedOne with approx. 200 ASA.

With the new sensor, officially rated at 800 ASA, heavy ND filtration is even more needed.

Hans

 

[Hans von Sonntag]

In my opinion, it's still good practice to leave at least one protection filter on...

We only use a clear filter if the environment calls for it. Any glass in front of the lens degrades the picture, especially if the shot is prone of flares (hot window, etc...)

Hans

 

[Elsie N]

Stephen is saying that a 50 ASA film needs less ND filtration than a RedOne with approx. 200 ASA.

With the new sensor, officially rated at 800 ASA, heavy ND filtration is even more needed.

Hans

Hans, I think I remember reading on one of the RECON threads that the greater sensitivity in the M-X means that the noise floor will be lowered, and not that the highlights will clip sooner.

Don't remember if this was someone from RED who stated this or a poster.

 

[Harry Clark]

Pawel,
In my experience, the Nikon 200mm T2 and 300mm T2 (PL versions) can take a standard Tiffen or Schneider filter on the front. The corresponding Canon T.2.8 PL-mount conversions can not. I would never put a filter on the front of the 150-600. I do not know why I have had problems with the Canons. Maybe I was working with DPs in the 1980's who planted that seed in my head, and I have just accepted it as fact...
I filter Optimo and HR long zooms from the front all the time, with no problems. Same with the Panavision 24-275. I have not used their new 70-200 T.3 zoom.
I cannot speak to the Hoya line of filters, as that's less common in my world, nor to the various lines of still camera lenses.
For the long lenses that I own (200mm Nikon T2, 300mm Nikon T.2, 300mm Zeiss T.3) I keep a full set of the appropriate sized 85's and ND's for rear in the case of each lens. This way I can put the basic correction in the rear and the effect filter up front.
I have not put more than one filter on the front of the primes... typically you are doing an ND or an 85ND combo, right? Or perhaps an 85Pola combo for water reflections? Grads sometimes come into play, yes. Then I would typically use a rear ND (or 85ND combo) and put the grad up front. But I cannot recall ever having to put more than one in front in the case of the super long primes. Not saying it cannot be done, or does not need to be done. I just have never needed to. I have, however, stacked multiple filters on the long zooms, so it should be OK.
I would test.
Based on many years as a working AC, and shooting my own stuff as well...
Cheers,
Harry

 

[Steve G]

In my experience, schneider filters seem to be best. Less colour shift in nd grads.

If going for tiffen, water white glass is best.

 

[Pawel Achtel]

Clearly, this could not have been settled without a proper test.

The Setup:

• Van Diemen Leica Apo Telyt-R 580mm at f/4.0 (the biggest caliber I could find)
• Schneider 6.6" x 6.6" 85+PL Combo filter
• Schneider 6.6" x 6.6" Coral Grad #1 Filter
• EOS 50D with PL mount

Now, you guys have to guess the results :hand:

 

[Sam Taylor]

Pawel what were you testing? They are both schneider filters. Maybe you were testing with filter and without? Thanks,

 

[Pawel Achtel]

Yes, tested with and without filters in front of a long lens with a large aperture.

 

[David Rasberry]

Thanks for posting the article Pawel. Useful info indeed.

 

[Sam Taylor]

Please tell us Pawel!

I expect that there will be a loss in image quality, but that "noticeable" difference in the final shots/footage will depend on the size you are viewing at, and also the nature of the footage. With stills viewed on a large screen yes it will be quite obvious, but for a lot of moving footage viewed on the tv or web much less obvious. Eg if you shot a clip of a car speeding towards you in daylight with the ND on, versus not then the overall better image resulting from using the ND would outweigh the loss of sharpness, which would be less of a problem due to the moving subject. However if you are filming a stationary figure for a long distant shot, then yes.

 

[Pawel Achtel]

Scientifically speaking the result of putting a (high quality) filter in front of a long (580mm), fast (f/4.0) high quality lens lens WFO is equivalent to smearing a layer of Vaseline over the front element, basically. :emote_headwall:

In the next few days I'm going to do some tests at f/5.6 and f/8 but, I think, I will get the idea of using filters in front of long lenses out of my head.

 

[David Rasberry]

Is this perhaps why some big long lenses have filter slots at the rear? (Other than front element size being too big)
How does a rear mounted filter behave by comparison?

 

[Pawel Achtel]

Is this perhaps why some big long lenses have filter slots at the rear? (Other than front element size being to big)

Right! And it has one. That's right: ONE! :emote_headwall:

 

[Pawel Achtel]

How does a rear mounted filter behave by comparison?

You can't remove the rear filter. It is part of the optical design. The lens won't focus properly without it. You can insert different filters, including clear, which is present in both crops.