Baader Fringe Killer

[baggywrinkle]

I am looking at buying this for my ST120 frac....anyone used one and how good are they?

[rwilkey]

Hi Baggy, they do help, but do not eliminate CA altogether, if it is for visual, you probably don't need it, however, I think the Semi-apo filter is better, but again, if for visual consider carefully how much of a problem CA is for you personally.  If it doesn't bother you very much, I wouldn't spend the money.

[jgs001]

They work, and are effective on the blue halo's (at least on my ST80 clone)... however, I didn't like the heavy yellow tint imparted by it. I ended up using a Semi APO filter... it worked, although not as effect as the fringe killer at removing the CA... the colour was far more 'normal', and I much preferred using it.

Have a look at http://stargazerslounge.com/topic/30187-baader-ca-filter-comparison/ for my findings and some tests..

[Mark at Beaufort]

I bought an Opticstar 80mm f5 Achro frac to use as a travel scope. Its okay up to 30x then becomes very soft and in fact quite poor. I bought a Baader Fringe Killer to try and improve things. It is slightly better but as John stated it adds a yellow tint to the view. I found its best to stop down the aperture which improves things quite a lot.

[baggywrinkle]

Thank everyone..now cogitating

[michael.h.f.wilkinson]

I have not used such filters, but please note that results on an 80mm F/5 do not translate directly to a 120 F/5. The latter has FAR more CA than the former.

[nicoscy]

I don't use a CA filter on my ST120mm, simply because this scope is not meant to be a planetary scope and there are not that many stars in the sky that would need filtering to avoid CA or where CA would be really intrusive.

However if you would like to use it on the moon for example, and you don't mind a yellow cheesy moon, a #8 Yellow filter removes CA and improves contrast.

[Dave In Vermont]

Being a Filter-Nut, I have quite a few filters for dimming CA in a fast refractor - and I have an ST80. While the Baader Fringe Killer will add a bit of yellow, I find it to be the best one for not making things too yellow, or darkening the objects you seek. It's my filter of choice and lived mounted in the diagonal on the scope. Though I do remove it when I'm doing something else with the scope - like spectrographic viewing. Those ST80's are nice little scopes. It's my grab&go choice for community outreach down in the park. That and an 8mm - 24mm Zoom EP and my green-laser.

Clear Skies,

Dave

[John]

I used a William Optics VR-1 filter with a 150mm F/8 achromat and it reduced the extent of violet fringing around the lunar limb and other bright objects by around 50%. Like others I was not keen on the yellowish tint that the filter added so I did not persist with it. I think it's best to accept that the F/5 achromats are not intended for high power use and let them shine where they are best - low to medium power star fields and deep sky viewing.

[cotterless45]

Try the Baader semi apo filter. It really works , greatly reducing ca.

Nick.

[happy-kat]

If looking at the moon only remove the smaller lens cap supposed to cut ca down.

I find ca is worse the cheaper the eyepeice in my st80.

[John]

If looking at the moon only remove the smaller lens cap supposed to cut ca down.

I find ca is worse the cheaper the eyepeice in my st80.

Yes it would. It reduces the effective aperture of the scope to around 50mm but the focal length of the scope remains the same. So you now have a 50mm scope with a 600mm focal length so the focal ratio has become F/12 and very little CA should be visible. The downside is that the lightgrasp and resolution of the scope is now that of a 50mm so there is no "free lunch" unfortunately.

[Macavity]

Maybe go the *whole hog* and get the Contrast Booster filter?

Incorporates similar "minus violet" filtering *plus* the Neodymium

RGB selection and rejection of Na / Hg line etc. light pollution...

I just found it a rather more interesting addition to a collection! 

[michael.h.f.wilkinson]

A Neodymium filter is a very nice versatile filter, and I have heard people mention it reduces CA a bit as well.

(BTW, Chris: what double post )

[D4N]

The UHC-S is a very harsh filter, if you want to use it visually you will find it cuts out a lot of light, of course it is cutting out the right light though so if your after nebula it's great. The neodymium lets a lot wider spectrum through.

I generally leave the UHC-S attached to my camera.

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