Quote:
Originally Posted by Monstar
I got up early again only to be met by total cloud cover so I thought I'd read up on some filters and the links Astro744 provided.
I think I'll go with Astro's UHC recommendation, but have also read some things that suggest a UHC-s is more suited to smaller apertures. Can anyone spread any light on this?
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YES!!!!
Remember, filters act by cutting out light we don't want. UHC and OIII let a very small amount of light through to restrict it to a very specific bandwidth. These bandwidths are very narrow and on the most part to an area where our eyes are not great in when light levels are low. These filters are then better suited to LARGER apertures as they gather more light to make these filters effective. They do work with small apertures, but smaller apertures render an image that is dim to be really effective.
If you have a small aperture, you require a wider bandwidth through put. Something like the Lumicon Deep Sky filter. These are very good filters to use in the big smoke with novices as they allow more light through. It is a good first filter.
Look carefully through the Lumicon filter selection guide. It explains what each filter does and what they are best for. Astro744 mentioned this guide first but it requires you to click on a poorly marked link:
http://www.lumicon.com/pdf/3filterspec_prnt.pdf
Now, there is another problem with filters, in the way they are marketed. As there is no universal standard on nomenclature, some filters are not what they are labelled as being. The Celestron one mentioned & the Baader UHC-s are not true UHC type. They work, but the band through-put is more of a wide band Light Pollution Filter. You will not see the Horse Head Nebula with this Celestron or Baader filter, where with a true UHC type you will (using a minimum aperture of 8" too). The objects that make the most out of UHC filters are very dim from the first instance, like the Horsie. True UHC type work very well with brighter objects, but their main purpose is to detect these very faint objects.
There are are also hybrid filters that cross over different bandwidths. Omega Optical, the parent company of DGM, make an OIII + Hbeta filter that for me is probably the best all round filter if you only want to purchase the one filter. Not only is it effective in the OIII range, but it also allows the Hbeta to be transmitted where the Horsie nebula glows in. Yes the overall image is a little brighter than a native UHC or OIII, but it is a great compromise. I've seen the Horse Head Nebula with this filter too, which you won't see in a dedicated OIII filter. You'll find this filter on the Omega Optical's ebay site:
http://www.ebay.com.au/itm/Filter-48...bd1f88d&_uhb=1
Omega Optical makes the filters for some high profile brands - you just won't hear about it too much. They make their own prestige line of filters under the DGM banner. Having two outlets, and their own manufacturing facilities, they can be very creative with the filters they produce. Their UHC type filter called the NPB, is considered to be as good as it gets for this type of filter. Their OIII is flaming brilliant too. But, puritans just can't swallow hybrid filters, so the OIII+Hb filter is marketed under the parent company's brand.
I also have an NPB filter. It is terrific. But I still use the OIII+Hb filter a whole lot more...
