Mike Loffland
Web Guru (Astronomics)
Reged: 09/03/04
Posts: 2080
Loc: Norman, Oklahoma
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Zhumell 2" Filter Set
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suburbanskies
sage
Reged: 12/18/04
Posts: 253
Loc: New Jersey, USA
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Nice article! I wish I had access to your testing equipment.
Would you be interested in extending your test by testing other filters? PM me if interested...
Mark
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Unknownastron
sage
Reged: 04/06/05
Posts: 209
Loc: CatsEye Observatory,Rural Sout...
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This is an outstanding review. Both scientific data and personal impressions at the eyepiece described in clear language with plenty of useful information. I hope we will read more articles from you! Clear skies and clean glass.
Mike
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"My God, it's full of stars!"
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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Original poster here. Thanks for the encouraging comments.
The symbols for wavelength (lambda), inverted comma's (used for inch measurement) look different in the online version. I do not know if it is my computer or translation error that crept up going from word to online version?
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Radiostar
sage
Reged: 10/16/08
Posts: 281
Loc: Thunder Bay, Ontario
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It sometimes depends on the character encoding and font set you have picked for your browser.
Thanks for the great article and I am wondering if the 1.25 inch set exhibits the same characteristics.
Good work!
Eddy B
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12220
Loc: Los Angeles
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Conversion of Word to html code often does the same strange translations.
As for filters, the spectrophotometer we have at work shows me the truth about filters.
The truth: there is more than one brand that stacks up well.
The best ones cost $75->$400 for a 1.25" and $120->$500 for a 2". We wish excellent filters were less. They aren't.
Something to look for:
--transmission of over 90% at the correct wavelengths (486nm for H-Beta, 496nm and 501nm for O-III and all 3 for a UHC)
--near square-wave response curves
--no reports of bad threads that don't fit eyepieces
--very little response outside the correct wavelengths--preferably zero outside of the chosen wavelengths from 450nm to 700nm.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
Edited by Starman1 (10/31/09 10:23 PM)
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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Rightly said Don. Great filters cost more for obvious reasons. I know that NASA (for Hubble) and some rooftop observatories on mountain tops use boutique filters because $500 or even $1000 are pennies compared to the millions invested.
Of late, GSO and the likes have brought decent optics within reach for the average backyard astronomer. I will be testing some better filters belonging to fellow CN'er and shall report results on how Zhumell stacks up.
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Tiny
super member
Reged: 05/02/08
Posts: 193
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Quote:
We wish excellent filters were less. They aren't.
For the value the Zhumell kit is excellent. They absolutely improve viewing on a budget and anyone who cant see spending said $100-$200 on a single filter has an alternative, i think thats the important point.
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 12220
Loc: Los Angeles
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I suggest you read the review just posted here on CN.
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Don Pensack
12.5" Truss Dob, 5" Maksutov, Fujinon Binos
Sustaining Lifetime IDA member
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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I just carried out a comparo between Zhumell, Lumicon, Televue Bandmate, Baader and Thousand Oak's OIII filters. I am preparing a scientific review for CN and shall submit in a few days. Some solid/unexpected results here with sound scientific backing.
I will be field testing these filters tomorrow on my telescope as well as a few other nicer scopes at a star party tomorrow.
Shaky
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panhard
Mongo
Reged: 01/20/08
Posts: 5191
Loc: Markham Ontario Canada
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I can hardly wait for that review. 
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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I just submitted the review to CN. Hopefully it will be online in a month, in time before fellow CN'ers put in their OIII request to Santa
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WOBentley
member
Reged: 09/16/09
Posts: 53
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Awesome, As I am hoping for some filters for my Holiday presents!
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8273
Loc: Beatrice, Nebraska
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Quote:
I just carried out a comparo between Zhumell, Lumicon, Televue Bandmate, Baader and Thousand Oak's OIII filters. I am preparing a scientific review for CN and shall submit in a few days. Some solid/unexpected results here with sound scientific backing.
I will be field testing these filters tomorrow on my telescope as well as a few other nicer scopes at a star party tomorrow.
Shaky
I have done 'rapid fire' comparisons between the Lumicon OIII, DGM Optics OIII, and Thousand Oaks OIII (used the Lumicon Multi-filter Selector to resolve any ambiguity caused by the time needed to change filters). Their performance was pretty similar, even though the DGM OIII unit I got for review was the broadest of the three with perhaps very slightly lower contrast than the other two OIII filters. Indeed, the sky background with the DGM OIII was only slightly darker than it was in DGM's fine narrowband NPB filter (a testament to the narrowness and sharpness of the NPB). With OIII filter design, the objective is to let through only the spectrum at and immediately around the two OIII emission lines and exclude everything else. To take into account things like production variation and the instrument angles hitting the filter from shorter focal length telescopes, the goal for a minimum acceptable FWHM passband I would like to see for an OIII would be roughly 96 angstroms (twice the wavelength separation of the two OIII lines). Going significantly narrower than this risks cutting into one of the two OIII lines, as happens with some of the Baader OIIIs. Wider than this, you are letting in more off-band light, but there is definitely some lee-way here. However, I kind of have to "draw the line" at "OIII" filters that have FWHM passbands of much greater than about 150 angstroms (over three times the Oxygen III line separation). For example, the Tele Vue Bandmate OIII has a FWHM passband width of around 240 angstroms, while the Astronomik OIII is at about 200 angstroms. Those are a little on the broad side for "true" OIII filters. Indeed, with that kind of bandwidth, you might be better off with a decent narrow-band unit like the NPB that at least lets through the H-Beta line without getting too broad. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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David
Your observations are exactly in line with what I observed in my lab and the data I presented in my review. Televue had a high bandwidth of 22nm (220A if you prefer) and Lumicon, Baader and Thousand Oaks had narrower bandwidths. All samples were analyzed spectroscopically under tight and controlled conditions and surfaces examined using a $60,000 Zeiss microscope.
I can PM you a separate copy of my review paper if you wish.
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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All:
I expressed my concerns about the Zhumell OIII in my feedback to telescopes.com. They readily exchanged my old Zhumell OIII with a newer Zhumell OIII from a different batch. I got my filter yesterday and subjected the filter to my spectroscopic tests. I was pleasantly surprised by the results:
1) 82.79% transmission at 500.7nm and 79.39% transmission at 495.9nm. The transmission specs are now decent and the filters transmit close to 85-90% of what the boutique filters transmit
2) The bandwidth was 17nm (not too shabby) and in between 495 and 512nm.
Incidentally, my replacement OIII performed better than Baader and way better than my older Zhumell OIII. Unfortunately, this also reflects QC issues with mass produced GSO optics. Also, my older OIII that I used in the comparo I submitted on 11/16 received a lot of flak. "Pardonnez moi, cause I own a Z10 too and have been more than happy with my telescope purchase.
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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I just noticed a chinglish transmission spectrograph (2" x 2" folded paper) in the filter box that said QC checked and 85% transmission of [OIII] lines. I dont know if the graph was mass produced too (photocopy) or if it was original transmission specs of the filter they shipped. Anyway, the new filter is a keeper and well worth the price. 
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 8273
Loc: Beatrice, Nebraska
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Quote:
All:
I expressed my concerns about the Zhumell OIII in my feedback to telescopes.com. They readily exchanged my old Zhumell OIII with a newer Zhumell OIII from a different batch. I got my filter yesterday and subjected the filter to my spectroscopic tests. I was pleasantly surprised by the results:
1) 82.79% transmission at 500.7nm and 79.39% transmission at 495.9nm. The transmission specs are now decent and the filters transmit close to 85-90% of what the boutique filters transmit
2) The bandwidth was 17nm (not too shabby) and in between 495 and 512nm.
Incidentally, my replacement OIII performed better than Baader and way better than my older Zhumell OIII. Unfortunately, this also reflects QC issues with mass produced GSO optics. Also, my older OIII that I used in the comparo I submitted on 11/16 received a lot of flak. "Pardonnez moi, cause I own a Z10 too and have been more than happy with my telescope purchase.
Again, for a decent OIII filter, these figures are not exactly what I would term as optimal. With modern interference filters, transmission of *more* than 86% at each of the OIII lines is quite achievable, and should be something to look for when considering a filter purchase. Even my old 1980's vintage Lumicon OIII managed more than 88% at the 5007 angstrom line (the new one is 92% transmission at that wavelength). A bandwidth figure of 17 nm (170 angstroms) FWHM is again perhaps a little too wide, and partially defeats the purpose of a narrowband filter (i.e. getting rid of as much non-nebular light as possible). This filter might be OK for the price, but I would probably continue my Lumicon OIII filter recommendation as a good one to get. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
Prairie Astronomy Club
http://www.prairieastronomyclub.org
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Shaky
member
Reged: 06/29/08
Posts: 24
Loc: Mason, OH, USA
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David:
Thanks for your comments
Your observations are right, the Zhumell filter is nowhere near optimal. Having said that, the replacement filter gave better readings than the original one which was a disappointment. I plan on using the Zhumell UHC filter mostly for planetary nebulae (86, 79 and 95% of 500.7, 495.9 and 486.5nm respectively) and UHC has done quite well on ring, dumbbell, NGC7000, veil, rosette and orion that I have seen through so far.
Like I mentioned in this review, I cannot recommend the Zhumell OIII and my comparo review that I submitted this week has the exact same conclusion.
A lot of factors affect transmission, the major ones being:
1. Surface smoothness
2. Glass properties and type of glass used
3. Uniformity of coatings and coating material
Of the filters I reviewed in my comparo, only 1000-oaks did >99% transmission of 500.7 line and 78% of the 495.9 line. At $69 for the Zhumell OIII filter ($37 with the kit), if it does 90% as well as a Lumicon, I'd be happy and so I am.
Clear skies to you
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suburbanskies
sage
Reged: 12/18/04
Posts: 253
Loc: New Jersey, USA
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Quote:
<snip> Even my old 1980's vintage Lumicon OIII managed more than 88% at the 5007 angstrom line (the new one is 92% transmission at that wavelength). <snip>
David, I really don't mean to be a pest but how do you know this is the truth? Back in the 1980s, many advertisers routinely touted numbers that were false. Those were the days when every other mirror maker promised 1/10th wave. They knew consumers weren't sophisticated enough to know fluff from fact. I know that Lumicon had stickers on their filter cases with "actual" test results for each individual filter but has anyone verified Lumicon's numbers?
I think this is why Shaky's report is special - he can independently put hard numbers that describe performance.
Mark
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