What Filters to Buy??

[acropolite]

I have a Meade 8 inch LX90 and want to buy some filters. Given that everyone comments on rarely using most of their filters I would appreciate any suggestions.

From information I have already read (Houghy's post) a DGM NPB filter is at the top of the list. Would this filter be suited to my 8 inch or is it suited to larger aperture scopes. DGM also make a VHT filter which they claim is suited to smaller scopes. Would this be a better option?

Moon Filter. Recommendation and Brand, ND or polarised.
Something to bring out more detail on Jupiter (e.g filter number and brand).
Something to Bring out more detail on Mars.


Thanks in advance. :confuse3:

[Striker]

1.25" or 2"

I don't have the experience to comment on filters but the 2" filters I picked up from Photo continental Brisbane for $7 each are a bargain....all made in japan eg...Hoya....I don't know if they still have any on special...Mark Hodson picked up about 8 or 9 the same as me all different colors.

[asimov]

The moon......I dont look at.
For jupiter, I use a cardboard aperture reducer. Or a hartmann works good too.

The only filter I may use once in a blue moon is the baader fringe killer on jupiter if using the refractor.

You would be suprised how well a pair of sunnies work, in different curcumstances too!

[Starkler]

Only filter I use is a Lumicon UHC nebula filter which improves contrast on emission and planetary nebs.
I have also tried the standard moon filter and have an Antares variable polarising filter, but for me those light reducing filters just degrade the view.

[ving]

I have heard that A light (really light that is) blue filter works well on jupiter for bring out the bands and such.
and as asimov said an aperture stop works well on jupiter, saturn and the moon. It also reduces glare for splitting bright doubles :)

[ausastronomer]

Phil,

My colleague in the US tested 25 different filters on 4 different scopes ranging from 4" to 18" aperture. This review will appear in a leading US astronomy magazine in the near future, for this reason I can't give too much away.

Of the 25 filters tested he rated the DGM NPB filter as the best all round filter as it offered a benefit on the largest number of targets and offered a greater benefit than most other filters on targets where all the tested filters provided a benefit. The DGM VHT filter performed reasonably well but by comparison it scored 22 points as against the NPB which scored 28 points. The 2nd best performing filter scored 26 points. The DGM VHT filter is a cross between a broadband (LPR) and a narrowband filter. You really need a narrowband filter to offer the most benefit in observing DSO's under most types of sky conditions from semi light polluted to dark.

My recommendation would be to try the DGM NPB filter as it currently represents good value for money. If you wish to buy something local I would go for either the Astronomiks or Lumicon UHC.



I generally prefer to view the moon unfiltered. If you find it too bright the best filter IMO is the Orion variable polariser. Neutral density filters dim the image but also wash out a lot of detail that would otherwise be visable.

Given your using an 8" scope the best filter for planetary observation may be 1 of the specialist planetary filters. I have the Sirius Optics Planetary contrast filter and it does a fair job, although I rarely use it, I rarely use any filters for planetary observation unless I am trying to tease out some specific detail. In this regard the best all round coulour filters would probably be an #82A light blue and a #21 orange. #23A (Red) and #25A (Dark Red) also work well on Mars but in scopes under 8" aperture I find the #21 Orange works better on Mars than the Red filters, but thats a pretty judgemental thing.

CS-John B

[acropolite]

Thanks Guys, that's the sort of feedback I was after. I am going to order the DGM NPB from the US, the rest I'll try to purchase locally. The reason for filters is that I don't seem to get much detail, especially with jupiter, I only seem to get the most prominent equatorial belts. I might try a mask as well.:D

[iceman]

Have you checked your collimation? And what has the seeing been like?

Also it might just take more time - when I first started observing Jupiter, all I could see were the 2 darkest belts. But with more experience, proper collimation, and fixing the pinched secondary, I can now make out much more detail.. assuming the seeing is good.

[ausastronomer]

Phil,

I don't know that planetary filters are going to be the answer, maybe there are issues with your scope ? SCT design are inherently not the best instruments for planetary observation due to the large central obstruction, that having been said, a good SCT is still a pretty fair planetary instrument and an 8" should show more detail than that.

A couple of things you should check with your scope before you buy planetary filters:-

1. Has it cooled properly? an 8" SCT "can" take over 2 hours to cool properly.

2. Is the scope collimated properly? Poor collimation leads to poor planetary views with a SCT.

3. Most of the detail on Jupiter is "low contrast" hence it does not take magnification that well. With an 8" SCT on most "average" nights the image will break down somewhere between 180X and 240X. It will be rare nights indeed that you can use more than 240X on it. How much power are you using on it ?

CS-John B

[acropolite]

John, I haven't had it out enough to know whether it's a scope problem, cooling or maybe just bad seeing. Cooling may be the issue but I've noticed that when still warm there's noticeable distortion of the image but once it settles down the image seems sharp enough, just not much definition. That's with a 14mm EP (s5000 meade) which is sharper and has more contrast than the standard 26mm EP. 14mm gives approximately 140x, maybe the answer is a little more magnification, or a longer cooldown time. Collimation is OK; I have collimated a couple of times and stars are nice pinpoints. I am however a little concerned with secondary mirror alignment. I have suspicions that the secondary isn't concentric with the corrector/primary, but I have yet to investigate that.