IR/UV Filters

[AstroAdam]

Hi All,

I'm looking for a 1.25" IR filter for my new Sammy and was wondering if the following would be suitable (the QHY one)...

http://modernastronomy.com/filtersOther.htm

Doesn't specify UV also, so I was wondering how important blocking the UV end is for Video astronomy?  

If not, would something like the following be more suitable?  This is specified as a UV-IR filter....

http://www.ebay.co.uk/itm/Skys-the-Limit-1-25-UV-IR-Cut-Premium-High-Transmission-filter-with-data-/381096225871?pt=LH_DefaultDomain_3&hash=item58bb1aec4f

Thanks,

Adam

[NickK]

It depends on the sensor and if it has filters as part of the sensor and camera.

A bare sensor will pick up UV and IR as valid signal. The problem is that most scopes (anything with lenses including coma correctors) have been designed to converge visible light in a specific range - i.e. Achromatic and Apochromatic. So anything out of that range (i.e. UV and IR) is usually out of focus and leads to bloated stars and blurring of details.

Now cameras with bayer matrices and IR filters already in that will still pick up some UV - depending on the bayer matrix attenuation of UV in the blue filter. The reason most cameras have IR is that the sensor QE sensitivity is higher for IR than it is for UV (again depends on camera and sensor).

I always use a UV/IR as I use a refractor (although a rather good one) - regardless of the camera or filters in use. If you're scope can focus it (and that means any reducers, flatteners or coma correctors too with reflectors) then you could make use of the UV and IR..

Never heard of "the skys the limit" before.. not sure how good it is. Just look at the Sammy's sensor response curve and the filter's blocking curves.

[AstroAdam]

Sky's the limit are the company that sell the BST starguider eyepieces. I've had quite a bit off them and it's always good quality. Free postage too

[AstroAdam]

So by the look of things, an IR/UV filter is probably the best bet to use with the refractors, and remove it when using the reflector.  
 

Cheers for the help - will get hold of one and experiment

[Dragon Man]

Adam, don't go cheap on UV/IR filters!

I made that mistake and regretted it.

One of the cheaper ones I bought made everything green 

I finally bit the bullet and went for the best, an Astronomik 'L' UV/IR filter.

I use it on all my refractors for Video Astronomy.

This one. Look at the Graph and the data: http://www.astronomik.com/en/photographic-filters/l-filter.html

Price is here:  http://www.astronomik.com/en/photographic-filters/l-filter/astronomik-l-filter-uv-ir-sperr-1-25.html

[NickK]

I have a 1.25" and 2" versions of the Baader UV/IR (and the Neodymium). It gets as much use as the 2" version!

[stash_old]

for the sammy perhaps you could use this method http://stargazerslounge.com/topic/238736-c-thread-ir-uv-filters/ ?

[Dragon Man]

for the sammy perhaps you could use this method http://stargazerslounge.com/topic/238736-c-thread-ir-uv-filters/ ?

Those C/CS threaded filters are a great idea. Only problem I see with that method is if you want to use the filter on other cameras like a ToUcam, SPC900NC, and any other camera that doesn't use C/CS mount.

With the standard filter thread it can go onto any nose-piece, or eyepiece too for visual in Achros. With the C/CS thread you are limited to only C/CS cameras.

The trick with our gear is to make our accessories as versatile as possible. Astro goodies are just too expensive to limit their use.

The only brands I trust for UV/IR filters or IR Filters are Astronomik, Baader, Hutech, and Mallincam.

I have had bad results with other brands, from colour tingeing, or being un-focusable, through to not working at all.

[stash_old]

"The trick with our gear is to make our accessories as versatile as possible. Astro goodies are just too expensive to limit their use." I couldn't agree more - Buying Atro stuff is like buying a car without wheels,engine and gearbox to get it running how you thought it would "out of the box" is never straight forward there is always - "then you will need this"