· Get a Cloudy Nights T-Shirt · Submit a Review / Article    Click here if you are having trouble logging into the forums Cloudy Nights - Official Forums of the 2009 International Year of Astronomy Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User   You are not logged in. [Login] Forum Archives · Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Astrophotography and Sketching >> Beginning and Intermediate Imaging Previous   Index   Next   Threaded   Pages: 1 Johnny5 member Reged: 03/21/09 Posts: 32 Light Pollution filter       #3353291 - 09/24/09 06:33 AM Edit   Reply   Quote Quick Reply   Does imaging through a light pollution filter like Hutech's LPS2 result in longer exposure times and would I lose detail overall for short exposures? Post Extras:       jgraham Postmaster Reged: 12/02/04 Posts: 6764 Loc: Dayton, Ohio Re: Light Pollution filter [Re: Johnny5]       #3353299 - 09/24/09 06:40 AM Edit   Reply   Quote Quick Reply   I haven't noticed a need to increase the exposure time using my LPS2, if anything they're shorter and the image shows more detail because the contrast is so much better. -------------------- -John ================================================ Homebuilt scopes from 4.25-16.5" Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130 Orion StarBlast, BinoViewers, Coronado PST Rebel XT/XTi, DSI Pro (I, II, & III), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC Tasco 60mm Refractors Post Extras:       Jerry Lodriguss Vendor Reged: 07/19/08 Posts: 576 Loc: Voorhees, NJ Re: Light Pollution filter [Re: Johnny5]       #3353420 - 09/24/09 08:57 AM Edit   Reply   Quote Quick Reply   At the wavelengths that pass through the filter, the exposure only needs to be a little bit longer. But the great advantage of a filter is that it *allows* longer exposures to reach the same level of sky background brightness. At these longer exposures, much more of the desirable "good" wavelengths pass through, GREATLY improving the signal-to-noise ratio. So, what you want to do is use the histogram to determine the correct exposure (whether you're using the filter or not). With the filter, ideally, you want to shoot about 2.5x to 3x longer than your exposures without the filter to reach the same level of sky-background brightness. You do not want the sky to be completely black. If it is, you will not be able to separate the faint detail in a nebula or galaxy from the noise in the camera. Expose long enough to get the faintest detail in the image up out of the readout noise of the camera. This occurs when the histogram is completely separated from the left wall of the histogram box. See: http://www.astropix.com/HTML/I_ASTROP/QUICK2.HTM Then, shoot a bunch of frames at this exposure, calibrate them with darks, and stack them. Jerry -------------------- A Beginner's Guide to DSLR Astrophotography http://www.astropix.com Post Extras:       woodchuck member Reged: 10/22/08 Posts: 82 Loc: Raleigh, NC Re: Light Pollution filter [Re: Jerry Lodriguss]       #3353833 - 09/24/09 12:31 PM Edit   Reply   Quote Quick Reply   I can pull 3 minute subs from my backyard without my IDAS and 5 minutes with it. Definitely a big improvement. Cheers Ian -------------------- Losmandy G11 Nikon D700, D3, D2X, D100, ... Nikkor, 500, 300, 80-200, ... Orion ED80 SSAG Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 3 registered and 0 anonymous users are browsing this forum. 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