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02-11-2015, 11:04 PM   #1
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Use of ND Filters

Hi

I have just picked up 3 x Variable Neutral Density 400 filters with 52, 58 and 77 threads to suit most of my lenses. They were cheap from a well known on-line site. Perhaps I should have known better. I am experiencing a number of problems including odd metering and some uneven darkening especially on short focal lengths.

First the odd exposures. Below is a series of three shots. I would have thought the camera metering would have adjusted itself to reproduce the same exposure for all three shots. Camer had great reluctance to autofocus even on the brightest setting so focus was manual. Seems to me these filters are having an adverse effect on the K-7 metering system. I shall toss them out but before I bite the bullet and get better ones, I ask the question is there anything I am missing? For the record on M mode and using the green button to meter similar results were obtained. No need to post these photos. The unevenness on wide angles is another issue I may post some examples later as a warning to others.

[Edit] Further toying with this setup show a significant variation in the viewfinder, just by rotating the filter and keeping the ND setting constant. Keeping everything constant and rotating the whole camera body shows this effect. Reflections alter just as they would With a polarising filter. These filters are for the scrap heap

Which, if any, ND Variables should I buy? [Close edit]

Camera: K-7
Lens: SMC Pentax - DA 1:3.5-5.6 18-55mm AL WR
Mode: AV
Focus: Manual
ISO: 100
Aperture: f5.6
Shutter speed: variable according to camera metering.

Brightest setting resulted in a shutter speed of 1/160



Mid Setting - shutter speed 1/60




Towards the dark end - shutter speed 1/30




Last edited by Bruce Clark; 02-12-2015 at 12:49 AM. Reason: Update
02-12-2015, 03:11 AM   #2
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firstly those variable ND filters are not very good. Even if you go for big names like Hoya and B&W, still IQ suffers (even slightly) and you get color casts in most (if not all) of them. Fixed ND filters are the way to go. However, what I usually do when I want to take a shot with an ND filter (always in manual mode), I focus and meter without the filter on, I then proceed to screw on the filter and then I just adjust the exposure(shutter speed usually) according to the ND filter.if its a 10 stop one, I just work 10 stops backward from what my original shutter speed was without the filter. I always have a tiny printed table (2x1 inch) in my bag (http://img213.imageshack.us/img213/9885/99404882.jpg). I only use an ND800 and an ND1000 so the table is smaller than that. I also have an app on my phone which makes things easy as well.
But if you want to take quality photos of landscapes with waterfalls or cool skies etc etc... i suggest you invest in a couple of good quality ND filters (Hoya, Haida, B&W)
02-12-2015, 05:08 AM   #3
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NDs affects color, sharpness and contrast always, some filters very little and some filters much. Fixed NDs affect more little to IQ than variable NDs. Variable NDs get worse when adjusting them more darker and variable NDs can no be used with CPL filters but fixed NDs can be used with CPL filters. So fixed NDs are way to go, I not use my variable NDs much. Forget china filters, u loose ur money and get bad quality filters. My advice is newer buy anything optics that is made in china, many other cheap china made camera accessories are ok considering to very low price.
02-12-2015, 09:05 AM   #4
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rotating the filter or the camera made it get darker? Were you using a polarizer on it, too?

02-12-2015, 04:11 PM   #5
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QuoteOriginally posted by schnitzer79 Quote
firstly those variable ND filters are not very good. Even if you go for big names like Hoya and B&W, still IQ suffers (even slightly) and you get color casts in most (if not all) of them. Fixed ND filters are the way to go. However, what I usually do when I want to take a shot with an ND filter (always in manual mode), I focus and meter without the filter on, I then proceed to screw on the filter and then I just adjust the exposure(shutter speed usually) according to the ND filter.if its a 10 stop one, I just work 10 stops backward from what my original shutter speed was without the filter. I always have a tiny printed table (2x1 inch) in my bag (http://img213.imageshack.us/img213/9885/99404882.jpg). I only use an ND800 and an ND1000 so the table is smaller than that. I also have an app on my phone which makes things easy as well.
But if you want to take quality photos of landscapes with waterfalls or cool skies etc etc... i suggest you invest in a couple of good quality ND filters (Hoya, Haida, B&W)
Thanks for your excellent suggestion. Although in the case of these devices no amount of calculation would be possible as the amount of density (stops) is unknown at any given adjustment. I would have to make an exposure, check the histogram and make adjustments according. A bit long winded but may work, if I can work around the issues with wide angle lenses. Better I think to save up from some proper fixed filters.

QuoteOriginally posted by Joojoo2010 Quote
NDs affects color, sharpness and contrast always, some filters very little and some filters much. Fixed NDs affect more little to IQ than variable NDs. Variable NDs get worse when adjusting them more darker and variable NDs can no be used with CPL filters but fixed NDs can be used with CPL filters. So fixed NDs are way to go, I not use my variable NDs much. Forget china filters, u loose ur money and get bad quality filters. My advice is newer buy anything optics that is made in china, many other cheap china made camera accessories are ok considering to very low price.
These were cheap enough to take a risk. I did not expect them to be the greatest but then again I did not expect them to be so bad. Not worth the postage back for a refund. Lesson learned.

QuoteOriginally posted by narual Quote
rotating the filter or the camera made it get darker? Were you using a polarizer on it, too?
.

No not using a polariser but the filter is acting as though a polariser was fitted. Rotating the filter as intended made the scene darker. But rotating with filter in a fixed ND position (the most clear) showed the filter to be acting as a polariser and altering reflected light. Just holding the filter alone up to my computer monitor shows it to behave exactly as my CPL
02-12-2015, 04:23 PM   #6
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Variable ND filter is actually 2 polarizer together already, one cpl and one linear polarizer.
02-12-2015, 05:42 PM   #7
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QuoteOriginally posted by Joojoo2010 Quote
Variable ND filter is actually 2 polarizer together already, one cpl and one linear polarizer.
Yes that would explain some of the odd effects, I am seeing. Even some of the higher priced models (US $200+) have received scathing reviews at Adorama when used on wide angle. It is a pity that none of the information sheets or specifications or online tutorials mention any of these limitations. I have just posted a second thread shows some of the blotchy effects from wide angle lens.

My conclusions so far:
1. Cheap ones are no good.
2. Expensive ones may not be much better.
3. Do NOT use them at all on wide angle lenses <35mm on APS-C. I will let someone else work out the cut-off with FF.
4. Metering is by trial and error. It is just as well someone invented chimping.
5. If you need ND spend the money and use non-variable types even if it means 2 or 3 filters for each diameter lens.



Thanks for your reply
02-13-2015, 01:54 PM   #8
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Oh. I missed the word "variable" in your original post. That's precisely how they work. It's two polarized filters sandwiched together. When they're at a 45 degree angle from each other, it's very dark.. When they're even with each other, it's much less dark.

I really don't think it's a matter of cheap vs expensive (though I'm sure the singh ones are probably manufactured with tighter tolerances) as it is a combination of how polarized light acts, and they're sensitive to angle changes - If they're not parallel to each other, you get blotches. (If they are, you may still get a sort of star shape in the middle when it's at nearly the darkest point, on long exposures). And you may not get the same problems indoors vs under sunlight.

I have several. I use them occasionally. The only one I ever see any real problem with is one where one of the glass disks wasn't tightly glued into the filter, so when I rotate the thing, it doesn't move cleanly. That one has done some weird stuff, (sadly not in a predictable way), so I shoved it in a box somewhere. (I should get a new one. That size, I mostly used as a pair of sunglasses for my f/1.2 lens for when ISO100 was still too bright, and it was pretty darned handy)

If you need a non-variable big stopper style (ND 3.0, 1000x, 10 stop, whatever other terminology they use) filter cheap, I've been very happy with my Haida brand one. I think it was under $30 for a 49mm, and maybe 2-2.5x that by the time you hit the 77/82mm range. The only lens I tend to do exposures that long with is my 15mm ltd, so I only have the 49mm size.

02-14-2015, 02:53 AM   #9
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I imagine you are getting vignetting with wide lenses as the filter is longer than a plain filter. I use Cokin-style size P filters - the adapter ring is very short and they are big enough to use on any of my lenses. I stack them if necessary to get the shutter speed I want.
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