IDAS LPS-P2 Performance

[dasams]

I live in an urban area and I acquired an IDAS LPS-P2 filter to cut down on the light pollution.

In this first test, I shot 30 sec with a Nikon D800 and 24 1.4 lens at f2 and ISO 400. The focus was a bit off and the lens suffers from coma but is the light suppresion as expected?

The shots were taken last week at 10 PM and are raws straight out of the camera except the WB was set at 4,000K and tint on zero.

The gradient is strong and linear on the first shot and but looks horrible on the LPS shot and has a donut shape. Dave

 

[rgibbons]

...I acquired an IDAS LPS-P2 ...raws straight out of the camera except the WB was set at 4,000K... looks horrible on the LPS shot and has a donut shape.

The 4,000K WB setting might cause part of the color tint. The Sun (and most stars in the sky) are around 5700K, Light pollution filters tend to kill more of the yellow spectrum for Sodium vapor lamp light pollution (where stars are also the brightest), leaving more red and blue (which your picture shows).

If your city uses high pressure Sodium Vapor (yellowish) or Mercury lamps (pinkish), then the light pollution filters do a good job, but if your city is moving toward florescent or LED lighting (as mine is), than the filters become less effective, and the colors become strange. Colors can look different in each direction (different cities use different lighting in my area).

I have two LPS-P2 filters (48mm for my telescopes of 1100mm to 2200mm, and 77 mm filter for my 300mm lens). I've never seen the doughnut, but I'm only doing telephoto, and my field of view would be in the center of your wide angle doughnut.

Russ G.

 

[sharkmelley]

Assuming the filter is mounted on the front of your lens, then the 24mm lens on a full frame sensor (35mm) will be accepting light from a very wide cone. At the extremes, the angle of incidence of the light rays hitting the filter will shift the frequencies of the light being transmitted/filtered. This could give rise to the donut shape you are seeing

You need to find out (from the manufacturer's specs) what angular cone can be sensibly filtered without causing noticeable shift in frequencies of the light being filtered.

[Later edit: I've found relevant off-axis transmission shift data here: http://www.sciencecenter.net/hutech/idas/filtplt.htm ]

The only other alternative is to somehow mount the filter between the lens and the sensor, clip-in style: http://www.sciencecenter.net/hutech/filters/ffilter.htm Then you would get a light cone of F2 which is much narrower than the wide angles of incidence when mounted on the front of the lens.

Filtering is surprisingly complex, with many pitfalls

Mark

 

[swimswithtrout]

Assuming the filter is mounted on the front of your lens, then the 24mm lens on a full frame sensor (35mm) will be accepting light from a very wide cone. At the extremes, the angle of incidence of the light rays hitting the filter will shift the frequencies of the light being transmitted/filtered. This could give rise to the donut shape you are seeing

You need to find out (from the manufacturer's specs) what angular cone can be sensibly filtered without causing noticeable shift in frequencies of the light being filtered.

[Later edit: I've found relevant off-axis transmission shift data here: http://www.sciencecenter.net/hutech/idas/filtplt.htm ]

The only other alternative is to somehow mount the filter between the lens and the sensor, clip-in style: http://www.sciencecenter.net/hutech/filters/ffilter.htm Then you would get a light cone of F2 which is much narrower than the wide angles of incidence when mounted on the front of the lens.

Filtering is surprisingly complex, with many pitfalls

Mark

Ding Ding Ding !!!!! You can't use an LP filter in front of wide angle lens, they are designed to be screwed onto the T-ring of a camera used for prime focus photography through a telescope, and their more parallel rays.. There are the clip in styles, but they are only manufactured for Canon cameras.

 

[D L Fischer]

IPAS filter for installation internal to camera is available for some Nikon bodies.

I have LPS-D1-N4 installed in my D7100 body.

-- David F.

 

[sharkmelley]

I'm only guessing that the original poster might be using it on the front of the lens - I could be wrong.

For longer focal length lenses (e.g. 70mm lens or more on a 35mm sensor or 50mm lens or more on a 24mm sensor) there shouldn't be any issues using it front mounted. But for a wide angle lens it is a definite no-no.

From this link: http://www.sciencecenter.net/hutech/filters/ffilter.htm it appears that they are available as clip-in for some Nikon cameras as well as Canon.

Mark

 

[dasams]

Ding Ding Ding !!!!! You can't use an LP filter in front of wide angle lens, they are designed to be screwed onto the T-ring of a camera used for prime focus photography through a telescope, and their more parallel rays..

Ding Ding Ding !!! you are right <slaps forehead>

 

[dasams]

I'm only guessing that the original poster might be using it on the front of the lens - I could be wrong.

Mark - You were right. I also have an 85mm lens with 77mm threads and I'll give it a try but most likely this will end up in a For Sale listing. Dave

 

[sharkmelley]

It's an informative thread though - it's the first time I've seen this effect so dramatically.

Mark

 

[Tristimulus]

IDAS have ordinary screw in LPR filters from 52 mm and up to 77 mm (search for Hutech). They also have standard astro sizes and the DSLR clip filter for some Canon cameras.

Can be used as front filters? Sure.

With no color change? Not completely if using wide leses, normal or telephoto lenses works fine.

Too much Ding here?

 

[dasams]

We had clear skies last night so I ran a new test using my Nikon D800 and Nikon 85 lens. Both shots at 8 sec, f 1.4 and ISO 800. The first without filter and the second with the 77mm filter screwed onto the front of the lens. The exp difference was about 1 stop as the histogram of the 4 sec shot without filter (not shown) was similar to the 8 sec shot below (with filter).

These shots are raws converted in LR and the only adjustment was the WB that was set to Daylight so that they were the same for both.

My conclusion is that this filter works great for 85 mm lenses and should also work great for longer focal lengths. Dave


Nikon D 800, 85mm lens 8 sec, ISO 800, f1.4, no filter


Nikon D 800, 85mm lens 8 sec, ISO 800, f1.4, LPS filter screwed to front of lens