9 replies to this topic

[M16SEAL]

Can I do DSO astrophotography under light pollution, is there any filter will help ..

[Jon Rista]

You can indeed to DSO imaging under LP. I image under a red zone myself. Sometimes it's better, most of the time it's pretty solid red. Anyway, I use an IDAS LPS-P2 with an unmodded Canon 5D III. I get some pretty good results. Definitely not as good as those from my dark site, but you can check out my astrobin (signature) for examples.

 

For the record, I'm a multi-night imager. Even with a light pollution filter, you still get additional light, and that light adds noise (it's additional signal, and noise is SQRT(signal)). To counteract that additional noise, I like to get as many subs as I possibly can, so I will usually image the same targets across many nights to get as much object SNR as I can. My integrations these days are usually around 200 subs, exposures between 180-240 seconds, with an f/4 scope. My total integration time is usually 9-11 hours lately, although it's inching up towards 12 hours the more time I spend on any given target. I will usually start processing once I have a couple nights worth of data, but I frequently don't consider my images done until I have at least 10 hours of integration time.

 

The IDAS LPS-P2 or IDAS LPS-D1 are great filters for color-balanced imaging. They pass more light, and only block the most egregious LP offenders: mercury and sodium vapor lamp emission lines. (And, really, only those from low pressure lamps...high pressure lamps emit more bands that are not blocked by these filters.) They might help you by getting you a magnitude darker (in terms of mag/sq", relative to a true dark site), but you do need to take a lot more subs to deal with the noise from skyfog. These are good for any target, but better or galaxies than other LP filters, as they pass more light in the greens and yellows.

 

The IDAS LPS-V4 is a nebular filter. It has two bandpasses, a narrow one in the reds around Ha and NII, and a broader one in the blues and blue-greens. It's similar to the Astronomik CLS filters, which have a broader bandpass in the reds. These filters will get you better contrast on emission nebula DSOs, but will produce poor star color/quality, and usually imbalanced color for galaxies.

 

There are also UHC filters, or ultra high contrast filters. These are similar to the V4 and CLS, but usually with narrower bandpasses. These give you higher contrast on emission nebula, allowing you to expose even longer, but exacerbate the problems with the V4 and CLS. I would still opt for a UHC if I was able to expose for longer...10 minutes and up should give you some pretty nice, deep exposure on nebula. 

 

You can always combine stars from unfiltered images or P2/D1 images with nebula from a V4/CLS/UHC. That can correct the star color issue, while giving you the better contrast on the nebula. For galaxies, I would stick with the P2/D1 or just unfiltered (and LOTS of subs, at least 200 to 400...which may be out of the realm of practicality for some imagers.)

[bobzeq25]

Jon's telling you how to do it right, if you're experienced.  I believe you're just starting out in AP.  Here's how to get by for now, until you learn more.

 

Forget about it.  The filters will increase your exposure time, and make tracking harder.  They work well on emission nebula, but are of more limited use on things like galaxies, clusters, and reflection nebula.

 

Take bright subjects that can rise above skyfog.  Like M42, my avatar, shot in a Bortle 7 zone, without a filter.  Star clusters, like M35.  The website below shows the Beehive, with a chunk of rock going past it.  Yes, you can do DSOs in light pollution, at least to Bortle 7.  I've shot the Leo trio of galaxies, but the image is lousy, because my guiding was off.  That and focus are likely to be the real problem areas for any beginner.

 

https://www.youtube....h?v=-eSQLL3L8Gw

 

When you can take some pictures where you see skyfog is holding you back, try filters.  In preparation:

 

You might want to measure your skies like this:

 

http://www.pbase.com...37608572&exif=Y

 

and check out his filter recommendations here, at the bottom of the page.  People can debate these, but they're not bad.

 

http://www.samirkhar...et/filters.html

 

Narrowband is the real cure.  But expensive, and hard in any number of ways.

 

Leave all of it alone for now.  Go out and take some pictures.  Trust me, your equipment is unlikely to be what's in between you and those for some time (except the long focal length scope).  I've been at this for five months, and I haven't come close to getting the best out of about the most basic setup, ZEQ25, C80ED, Sony NEX 5.  Just now starting to work on autoguiding, a necessity if you want to use filters.  I did use a light pollution filter (CLS) to capture the Horsehead with a mono camera.  Other than that, it sits.

 

Go take some pictures.  Process the data, which is a place where you can remove some of the effects of light pollution, by fair means and foul.  See where you're at.  If you haven't already, get and read this.  I got a lot out of it the first time I read it, and more rereading it after I took some pictures.

 

http://www.amazon.co...rd_i=113877684X

Edited by bobzeq25, 12 March 2015 - 04:54 PM.

[M16SEAL]

Thank you all

[CharlesW]

Pixinsight goes a long way towards making light polluted images look pretty good. I haven't been able to pick up my LP filters yet but I'm pretty happy with my stuff so far and I shoot from a red zone.

[jgraham]

I do all of my imaging from my red-zone backyard and I have found that there are two ways to deal with light pollution. The best is to get a good imaging light pollution filter. I've used the Hutech IDAS LPS-2 and the Orion imaging skyglow filter with excellent results. You can also just use a custom white balance using an image of a relatively blank section of sky as the reference frame. This works surprisingly well, but you lose a bit of contrast since you are not actually removing any of the light pollution. Personally, I use both; a good imaging light pollution filter and a custom white balance using a sky reference frame. The sky reference frame is easy to take (60 seconds at ISO 1600) and you can use the same reference over and over again unless your sky conditions change.

[Wouter D'hoye]

Hi,

 

I too image from heavily light polluted skies. It is certainly doable but as indicated above long integration times are required for best results. The use of a monochrome camera in conjunction with a decent LPR or UHC filter certainly helps a lot. But on a color camera these filters have a bad tendency to screw with the with the white balance.

 

Software tools to compensate for background gradients might be very helpful especially if you have a relatively large field of view. the smaller your field of view the less trouble with gradients you will have.

 

Cear skies,

 

Wouter.

[SKYGZR]

So, the best option for a "clip in" filter, using a clear glass modded cam, for galaxies, and or, wide fields w/ a lens would be?

[bobzeq25]

So, the best option for a "clip in" filter, using a clear glass modded cam, for galaxies, and or, wide fields w/ a lens would be?

Hotly debated.  <grin>  And it depends on many things, your particular skies, your particular target, to a lesser degree, your particular camera.

 

But, one thing that is not hotly debated is that their benefit for galaxies, a broadband source, is much less than it is for emission nebula, with more discrete light output.

 

Post #2 is very expert advice, the best here.

 

The third website referenced in post #3, is also good.

 

Those two both represent substantial experience and testing of various filters, which beats opinion.  With no IR/UV filter on your camera, one thing you'll want to be careful about, is suitable IR blocking.  Discussed and shown in detail on that third website.

Edited by bobzeq25, 14 March 2015 - 02:59 PM.

[M16SEAL]

Please check this filter from Orion , but how can i thread this filter to my canon T-adapter 

 

http://www.amazon.co...tography filter

 

the same filter features from orion website :

http://www.telescope...5561.uts#tabs-1