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 Post subject: Light pollution filter
PostPosted: Sun Sep 23, 2012 8:14 pm 
Hi all,
What light pollution filter do I need to fit onto my Pentax 50 & 135mm lenses?
Probably a dumb question but I've no idea. I've seen them on astro boot but they appear to be for EPs.
Cheers
Andy


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 Post subject: Re: Light pollution filter
PostPosted: Sun Sep 23, 2012 10:05 pm 
You are best using an Astronomik CLS Clip Filter. These fit into the body of the camera and you then fit the lens to the camera as normal. You would need to check with the vendor as I know that the Canon EF-S lenses do not fit as they connect with the filter when it is in place.

They are not cheap - Appox £100.

See link to one vendor:-

http://www.astronomik.com/en/clip-filter-system.html


Ian


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 Post subject: Re: Light pollution filter
PostPosted: Mon Sep 24, 2012 7:36 am 
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Joined: Mon Oct 12, 2009 6:47 pm
Posts: 1247
Location: Bolton
A lower-cost option is to get a broadband filter to fit a 2" eyepiece:
http://www.rothervalleyoptics.co.uk/skywatcher-light-pollution-filter-2-quot_d2936.html
http://www.scopesnskies.com/prod/filters/anti-light-pollution/2inchLPR.html
or even a UHC version: http://www.scopesnskies.com/prod/filters/narrowband/2and1.25inchUHC.html

and then Brian made me an adaptor-ring to the filter-thread on the front of the Pentax lenses.

It's also a good idea to fit a lens-hood (it helps as a dew-shield too) - get one of the folding rubber types which have a filter thread on the inside, so that you can still fit the LPR filter with the hood in place.
And I wrap a heater-tape around the outside of the lens to keep the dew off, but Gerald finds that keeping a gentle draught of (cold) air over the camera using a domestic fan is also effective.


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 Post subject: Re: Light pollution filter
PostPosted: Mon Sep 24, 2012 8:55 am 
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Joined: Mon Oct 12, 2009 8:27 pm
Posts: 370
Location: Adlington
Andy,
With the clip filters you will need to snip off the projecting bits/pins on the back of the Pentax lenses to stop them hitting the filter. This probably destroys any value the lenses my have but they will work fine on the Canons. I have snipped several Pentax lenses (20mm to 300mm) and as they are only used on Canons it is no big deal.
As regards which LPR filter then the UHC filter is by far the best - certainly with modded cameras and should still work with an un-modded one. I now use an Astronomik UHC clip filter here in Lancashire.

For the lenses you mention a (cheaper) alternative to the clip filter is the Baader 2-inch (48mm thread) UHC filter - the Baader has the two important band-passes, blue/green and red. You would need a step ring to screw it onto the front of the lenses - Pentax usually take 49mm filters so you would need the 49/48 (or is it 48/49?) step ring. Front mounted LPR filters don't work with wide angle lenses but would with 50mm and 135mm.


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 Post subject: Re: Light pollution filter
PostPosted: Wed Nov 21, 2012 2:14 pm 
Just ordered my 2 baader filter. After speaking to the guy in the shop for a bit more advice as i was torn between the UHC S or UHC S L. He advised that the Neodymium was a far less focused filter & was excellent for the moon, planets & deep sky while retaining the LP filtration properties that we suffer so much from.
He also said that the UHC S & UHC S L are both very focused for nebulae.

Anyway, here it is & can someone villify whether ive been duped or not!!!
http://www.harrisontelescopes.co.uk/aca ... #a2458334A
Cheers
Andy


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