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Castell UHC Ultra High Contrast Deep Sky Filter, 2"

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in In stock (5)
0.30 kg
Our price:
including VAT 20.00 % ( £10.30 )

Castell UHC Deepsky Filter for 2-Inch (50.8 mm) Eyepieces

This UHC filter allows emission lines of H-alpha, H-beta, S-II and O-III where most of the light comes from in the case of emission nebulae.
On the contrary it will cut off all the light produced by Mercury and Sodium lamps that is important for astronomers in light polluted areas. The result is a darker background with higher level of contrast for our main astronomical objects such as nebulae. Deep sky objects will appear to be brighter and stars to be fainter, even though it's a visual illusion as merely the background became darker.We would recommend to buy a plastic carry case as well that is otherwise not included:
White Transparent Plastic Filter Case


Sample Images


Courtesy of Paul Hunter. Above image has been taken via a Castell 2" UHC filter by Paul Hunter with his Skywatcher Explorer-200P Newtonian telescope (f/5, 1000mm focal length), mounted on Skywatcher EQ5 mount without guiding, he also used a Baader MkIII Coma Corrector

Image details:

NGC7635 Bubble Nebula (Left) & M52 Open Star Cluster (Right), 1 hour 15 minutes total exposure. (75 x 1 minute frames), 1600 ISO, 40 Dark frames, 45 Bias frames, No Flat frames, Stacked in DSS and processed in  Photoshop. Camera used: Nikon D5300 dSLR (un-modified).


here is another wonderful image by Paul Hunter, taken by using the same equipment.

Courtesy of Paul Hunter. Click on the image for a higher resolution image at 1200px wide.

Image details:

M1 Crab Nebula, 32min 15 sec total exposure (56 frames), 1600 & 2500 ISO. Camera used: Nikon D5300 dSLR (un-modified).

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1 Most recent customer reviews (see all reviews):
Mr. Roger Snee
Oct 20, 2016
I use this filter in front of my coma corrector, when imaging emission and planetary nebulae, using a modded dslr on 130 and 254mm dia Newtonian reflectors.

It has proven to be very effective in bringing out the blue-green OIII and H-beta lines in the supernova remnants.

Advantages: Because the bandwidth passed is slightly wider than true NB filters, it means that I can get imaging OIII/H-beta/H-alpha contrast in exposure times of say 90seconds, with stacks of only 90-100 minutes.

So, for DSLR OSC imaging of appropriate targets, you are done and dusted in a single night. All this for a fraction of the cost of the narrower bandwidth UHCs.

You also get to use it as a good light pollution filter on top of the above advantages, under urban city skies

Disadvantages: Always remember that 2" filters are in fact typically 48mm in diameter, not 50.8 or 52mm.

So, when using the filter with a lens-DSLR combination, if the lens is a typical 52mm diameter then you will need a 52-48 step-down ring.

These are £2-£3 only, so no big deal, as long as you are prepped.

Like the Astronomik CLS clip, individual subs-exposures have colour tint - in the case of this product it is slightly purple in colour cast. Just take some flats to cancel out this colour cast.

It soon comes away on stacking in DSS or similar.
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