LRGB - which brand?

[codemonkey]

All of these claim to be parfocal, but the prices vary quite a bit. Is there a reason for this besides brand name, or are the effectively equivalent?

I can see some slight variations in bandpass between brands. I'm using an APO refractor, so I'll need to block the part of the IR spectrum that causes bloat with refractors, but I'm not sure where in the spectrum that is. Can anyone please advise?

Prostar: $195 (CLRGB)
Orion: $225 (LRGB)
Astronomik: $341.10 (LRGB)
Baader: $425 (LRGB)

Sometimes you get what you pay for, but sometimes what you pay for is merely branding. I'm happy to pay for the Astronomik filters if there's going to be a meaningful difference, but I'd rather keep it in my pocket if there's no significant difference.

[LewisM]

I believe the Orion are merely rebranded Prostar. I have used Astronomik and they are very good, as are Baader. Astrodon superb too, but mucho deniro.

[Octane]

I can only say good things about my Baader filters. At f/5 on my FSQ, I can assure you that they're not parfocal. I autofocus every 30 minutes, anyway, so, it's no big deal.

H

[Peter Ward]

Beg to differ. :)

Baaders are indeed par focal...but my FSQ isn't.

At F5 you can see the RGB focal points shift ever so slightly (some camera lenses behave the same way)
I get the same behaviour with AstroDons and Custom Scientific sets.

Same filters on my AP scopes, no refocus is required.

[Octane]

Oh, so, it's the telescope, and, not the filters? I stand corrected!

H

[LewisM]

I found what Peter said with Astronomiks in the FSQ106EDXIII. - blue was significantly off focus. In the f/6.3 FL102S, no issue at all.

The f/5 Vixen DED108ss showed only minimal blue focus shift, and always needed a tweaking.

[Amaranthus]

I'm happy with my Astronomik - have found them perfectly parfocal on my kit.

[codemonkey]

That's interesting actually; I read that somewhere else as well, but when I look at the transmission charts for the two filter sets, they're quite different.

At the moment I'm tossing up between the Orion and the Astronomik. The Baader's are too much and I've heard good things about the new Astronomiks. However the Orions are significantly cheaper and apparently parfocal... my main question there is about reflections and halos. Has anyone used the Orion filters?

I'm kind of hijacking my own thread here now, but for those of you that have have focus differences between filters (either caused by non-parfocal filters or other causes), how do you manage that? I imagine doing it by hand would result in not-quite-perfect images which could be a pain in the nether region when processing the images.

[Amaranthus]

I also use the ZWO filters, which are (I think) also the same as those badged under Orion. Fine, and parfocal, yes. I use them for my planetary cam. Only $US90 from China... http://www.zwoptical.com/Eng/Cameras/filters/index.asp

[Octane]

Les,

If automating, most image capture software allows you to use filter offsets in autofocus routines.

H

[Bassnut]

Maxim DL has a filter focus offset function.

[Amaranthus]

Humayun, you use Robofocus -- have you tried other solutions or is this the best choice? (I'm looking into automated focusing now as an upgrade to my two fingers...)

SGP, which I use, also has a focus offset option and ability to automate.

[Octane]

Barry,

I use FocusMax. It's a one-of-a-kind software.

FocusMax interfaces with any ASCOM-compliant focuser, which in my case is Robofocus. Even with the slippage in my system, I am able to nail perfect focus on every single autofocus run.

I wish I could pay for FocusMax. It really is remarkable. Check out the video for its AcquireStar function.

H

[Paul Haese]

If you can afford to buy Astrodon's do so. Even with my FSQ I have seen good focus matching from the Lum filter to the NB filters and even the colour filters are good. You don't have those on your list but I would never use anything else now. I had Astronomiks which were ok but even the new ones had some halo from reflections. Since getting the Astrodon's I really don't see that problem anymore.

[codemonkey]

Thanks for the heads up mate. I note that you're using Astronomik filters though, so why the shift? Was the upgrade worth it?





That's what I suspected... more money lol.



Thanks Paul, but I'm afraid they're out of my league.

[codemonkey]

Interestingly enough, it looks like being parfocal or not might not be that much of an issue anyway, as I'm using a refractor which from what I gather is likely not to be parfocal in itself.

I'm just about ready to pull the pin on a ZWO set which I can run in series with my Baader UV/IR cut.

[gregbradley]

I have used Baaders, Astronomiks, Astrodon. Baaders were not parfocal as advertised nor were they 1:1:1 colour combine ratios. Astronomiks are very thin and a lot of filter wheels won't mount them properly (they are 1mm and most others are 3mm thick).

Astrodon Gen 11 filters are terrific, are parfocal, mount easily, wear well, are 1:1:1 colour combines, no halo issues and make imaging a whole lot easier. Yes they cost more but work the best.

Greg.

[Amaranthus]

The ZWO filters have a UV/IR cut in the RGB - no need to run in series.

Sorry, I was unclear - I have ZWO for my LRGB set that I still use, and Astronomik for my NB filters (which I bought off Paul :D)

H., thanks for that info. So is Robofocus the mechanical focuser to be aiming for, or are there other options? (Paul also recommended FocusMax for the software)

[Octane]

Barry,

Yep, the Robofocus is the mechanics, consisting of a motor which attaches to the focuser shaft, a mounting bracket, a control box and software.

What scope would you be attempting to automate? And, what imaging rig would you be dangling off the back?

There are better options than the Robofocus (it was the staple focuser for a STL/FSQ combinations as it could take the weight and took no precious backfocus), such as the FLI Atlas/PDF and the Clement focusers. Starlight's Feathertouch and Moonlite also make great automated gear.

The better alternatives are also more expensive. The Atlas is $3,200 at BinTel. Robofocus or the newer Sharpsky are about $500.

H

[codemonkey]

Thanks Barry :-)

I pulled the pin on the ZWO. I was thinking to run it in series because I noticed in the transmission chart that their L cuts off before their R does, which led me to wonder whether shooting R alone would cause the star bloat known to happen in NIR with refractors. I also wasn't sure about AR coatings.

http://www.zwoptical.com/products/Filters/spec.gif

[Amaranthus]

H., currently it would be for an ED80T CF with a Crayford, and a C8 with a stock mirror-shift focuser - but I suspect I really need to upgrade the latter. Medium term I'm scouting out for a larger 5 inch, ~900mm FL 'frac - top on my list right now is a WO FLT132 or similar. Imager at that stage will probably be a QSI 690wsg. Time frame for this is about 6 months, so I'm currently doing the 'due diligence'!

Lee, I've not noticed star bloat in the R channel.

[kkara4]

Thanks for all your input on this thread Barry (and to everyone else too), ive been keeping an eye out for some lower cost yet still useable LRGB filter sets, and these ZWOs seem to fit the bill perfectly!

Really cant afford the likes of Baader/Astronomik/Astrodon at the moment!

[Octane]

Well, what do you know! The other day, earlier in this thread, I mentioned I wish I could pay for FocusMax. With the release of version 4, it is now a commercial product, which can be purchased through CCDware.

H