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#26 jhk3

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Posted 25 August 2013 - 09:36 AM

I ordered the DGM filter and received it and my final piece (the mount and tripod) came in Friday, but unfortunately Friday night was cloudy. So yesterday (Saturday) was clear sky in the late afternoon and evening which was great. However, I set everything up right before sunset for a test, but was unable to see anything. I'm fairly certain I installed everything correctly and checked it multiple times. I collimated the tube right before I began and everything seemed aligned. I removed the Paracorr and eyepiece (13mm Ethos) and looked through both they work find, but when I assemble it all together, I can't see anything or get anything into focus. I slowly adjusted the focuser all the way through, even with the fine adjuster only and nothing. I didn't install the filter yet as I was just trying to get everything working. I'm sure it's a typical beginner issue and something simple I missed. Any thoughts?

Orion 8" f/3.9 Newtonian Astrograph Reflector
Tele Vue Paracorr Type 2
Tele Vue 13mm Ethos eyepiece
Atlas EQ-G mount and tripod

Thanks,

John

#27 Kraus

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Posted 25 August 2013 - 09:42 AM


What's the paracorr thing? Sounds obscene.

#28 jhk3

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Posted 25 August 2013 - 10:08 AM

It's the coma corrector. I've tried without it also and still the same.

#29 David Knisely

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Posted 25 August 2013 - 12:40 PM

The Paracorr requires a little inward focus travel. It is possible that your scope does not have enough of that. Try during the day with the scope pointed at some terrestrial target and start with the focuser wracked all the way in. Clear skies to you.

#30 jhk3

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Posted 26 August 2013 - 07:38 PM

David,

That worked. Thanks. I had to pull the Paracorr almost completely out of the focuser to get my object (a terrestrial target) into focus. Now, I can't leave it like that as it's a little scary having the Paracorr barely attached to the focuser. I'm guessing I will have to find an extension or something.

So, when you say "inward focus travel", does that mean the eyepiece moves toward the secondary mirror or away from the secondary mirror? I ask because I had to pull it away from the secondary mirror.

I can't believe it, why does it have to rain when I get my new telescope?

Thanks again and clear skies to you too.

John

#31 David Knisely

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Posted 27 August 2013 - 12:39 AM

David,

That worked. Thanks. I had to pull the Paracorr almost completely out of the focuser to get my object (a terrestrial target) into focus. Now, I can't leave it like that as it's a little scary having the Paracorr barely attached to the focuser. I'm guessing I will have to find an extension or something.

So, when you say "inward focus travel", does that mean the eyepiece moves toward the secondary mirror or away from the secondary mirror? I ask because I had to pull it away from the secondary mirror.

I can't believe it, why does it have to rain when I get my new telescope?

Thanks again and clear skies to you too.

John


It sounds like you may have a focal point of the telescope that is a little too far *out* rather than too far in. You may either need to move the primary mirror back slightly in the tube (farther away from the front of the scope) or use an extension tube to get the longer focal length eyepieces to focus with the Paracorr. Clear skies to you.

#32 SkyGibbon

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Posted 27 August 2013 - 01:11 AM

David,

That worked. Thanks. I had to pull the Paracorr almost completely out of the focuser to get my object (a terrestrial target) into focus. Now, I can't leave it like that as it's a little scary having the Paracorr barely attached to the focuser. I'm guessing I will have to find an extension or something.

So, when you say "inward focus travel", does that mean the eyepiece moves toward the secondary mirror or away from the secondary mirror? I ask because I had to pull it away from the secondary mirror.

I can't believe it, why does it have to rain when I get my new telescope?

Thanks again and clear skies to you too.

John


Is that with the drawtube all the way out? You have a low profile focuser it seems by the specs. I have the same issues with some eyepieces on my low profiles. Extension tube will solve it. The shorter, the better on the extension tube though. Believe it or not, you will not get enough in-focus if the extension tube is too long.

#33 jhk3

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Posted 27 August 2013 - 06:38 AM

The telescope came with an extension tube for the focuser which now works great. I'll try it out once the skies clear up. Learning a lot.

I really appreciate everyones input. Thanks.

#34 Jon Isaacs

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Posted 27 August 2013 - 09:16 AM

I appreciate David sharing his observing experience. As a real scientist for 30 years and with far too many research Psychologist friends over the years I also appreciate that to quantify subjective measurements you need double blind tests, lots of data and statistics.



One way or the other, I have been a "real" scientist for most of my life and was raised in a family of "real scientists." Science begins with observation, careful observation. This is something a trained scientist can do and something that is at the heart of amateur astronomy, learning to see, seeing differences.

In comparing filters for example, one notes a specific feature/detail and then works back and forth between them, noting differences. In terms of evaluating filters, this is not a difficult task because the differences can be quite noticeable.

Rather than discussing the accuracy of David's evaluations and his body of work, maybe you could share your own experiences with the variety of filters you have used.

My own comparisons are rather limited, I own the filters I own, I use them. On one occasion I did spend an hour comparing two Celestron O-III filters and TV Bandmate viewing the Veil Nebula from a Dark Sky location with a 17.5 inch Dob looking through a 31mm Nagler. What was most striking was that one of the Celestron filters was very effective at increasing the contrast while the other was not, showing the Veil barely better than no filter. The TV Bandmate was in the middle.

On other nights I have compared my 2 inch Celestron O-III (the better of the two in the comparison) with my 1.25 inch Orion O-III using a variety of scopes and eyepieces (always 1.25 inch) and noticed very little difference.

But....

The most important thing about using filters is choosing the right filter for the task. An O-III is a great filter for the Veil but a poor choice for the California nebula. The original poster is interested in filters for both galaxies and nebulae, the bulk of this thread has addressed nebulae.

Basically there is not much that can be done to increase the contrast of galaxies because like light pollution, the light from a galaxy covers a broad spectrum. Notch filters and narrow band filters are effective for that small class of objects whose emissions are mostly in a very narrow band. By only passing the narrow part of the spectrum, the contrast in greatly increased because only the background sky light (including pollution) is allowed to pass.

Jon Isaacs

#35 Jon Isaacs

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Posted 27 August 2013 - 09:22 AM

That worked. Thanks. I had to pull the Paracorr almost completely out of the focuser to get my object (a terrestrial target) into focus.



How far away was the object? The closer an object is, the further back the focal plane. It is possible that when viewing the night sky, there will be no trouble.

However, the Orion 8 inch F/4 is designed for astrophotography, cameras generally require more inward focuser travel than eyepieces so scopes designed for AP will often require an extension tube to come to focus with an eyepiece.

Jon

#36 David Knisely

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Posted 27 August 2013 - 03:59 PM

MrJones wrote:

As a real scientist for 30 years and with far too many research Psychologist friends over the years I also appreciate that to quantify subjective measurements you need double blind tests, lots of data and statistics. If David had found outliers from his observations, in particular filters that were so much worse than the others that you probably shouldn't even consider them that might be somewhat useful. But one person's observations are still statistically meaningless.


One does not necessarily have to be a practicing "scientist" to do useful and meaningful research, although extensive experience (and perhaps a little formal training) does help somewhat. I do have a little of that training (B.S. in Physics with the "Astronomy" option from the University of Nebraska), and that has proved useful a number of times over the years. As for "outliers", I am not sure what you are referring to, but with filters, I have found a few of those (mostly the "no-name" filters from various retailers, especially during the period where Lumicon filters were absent). They are generally in the line filter class where manufacturing specifications need to be followed more critically if consistent performance is to be achieved. In those cases, it was more of a random effect of some filters being good and others not. The review of the Zhumell narrow-band and OIII filters here on Cloudynights demonstrates that a little, as the OIII the reviewer termed "disappointing". Even Lumicon in their early days had two quality classes of filters: regular and "premium". The regular filters (basically "seconds") were some that would work, but not with the kind of consistent quality that might be found with some that were "hand-picked" from the lot to have very high transmission at the desired wavelengths. Eventually from the demand, Lumicon just dropped the "regular" line and stayed with selling only the premium ones, presumably rejecting the rest. This does increase the cost, since some of the filters produced basically have to be thrown away, but it did mean that what one got with the filters tended to be of a more consistent optical quality. Some of the "Brand-X" filter outlets may be selling both the "OK" filters as well as some really good units but not classing them as Lumicon did. However, Lumicon was not completely without fault, as even they screwed up a little on occasion (just not very often). With the regular narrow-band nebula filters, the requirements on quality are not quite as high, so in those cases, you can often buy on just price alone and still get a useful filter.

As for my survey (which you may be referring to), as is mentioned in its introduction, it was done using multiple observations with multiple instruments at multiple observing sites. The observations were done with a single set of Lumicon filters and at what I would consider true "dark-sky" sites to provide some consistency in the study. The primary instruments used were a 10 inch f/5.6 Newtonian, an 80mm f/5 refractor, a 100mm f/6 refractor, and a 9.25 inch f/10 SCT, although a large number of the observations were with just the 10 inch Newtonian and the 100 mm refractor. The Lumicon multi-filter selector was used to allow instant comparisons between filters to reduced the observational "memory" errors. As mentioned in the introduction, the project remains an on-going one, so I still go back and revisit the objects using the various filters, especially now that I have a 14 inch Newtonian in my telescope "stable". There were (and are) some statistics involved (as well as some input from other people), although as I clearly stated in the introduction, the actual results will be somewhat subjective due to the nature of a visual evaluation and personal observing preferences. However, to the extent that is possible with personal observations of this type, the survey is statistically meaningful, as others who have done similar observations often report somewhat similar results.


Also hard factual observations such as "Orion put out many 2" filters with non-standard threads over the past several years that could sometimes be forced on but still fall on your mirror" and the current state of their threads would be useful. You sure don't want to take a chance on a used one.


Orion (and other filter retailers) generally have the right filter threads, but the consistency of the manufacturing thread quality has varied. Sometimes the filters don't fit a specific eyepiece, and the blame for that can go both ways. I had one old 1.25" Lumicon H-Beta filter that would *only* thread fully into my old Meade 14mm Ultrawide and one other eyepiece (would only go on part ways in my other eyepieces), so one has to consider whether it was the filter threads or those on the eyepiece were to blame. If a filter won't fit a majority of your eyepieces, it is time to send it back for a replacement.

As I said what we need to see in any filter comparison is first and foremost, transmittance spectra and secondly some ASTM testing on the durability of the coatings. Kind of a Consumers Reports on filters or say DxOMark.com for camera lenses. The transmittance spectra will tell you all you need to know about the filters and then you could have fun trying to correlate the data with observations.


This has been done on a number of web pages, although again, precise spectral response of filters can vary considerably from one filter batch to another batch. Orion at least provides a spectrum scan output for their filters, although again, it is not clear whether this is a "generic" scan or one for the precise filter the consumer receives. In any case, a simple hand-held spectroscope available for less than $30 can help for quick visual comparisons of filters, so one may not necessarily need a multi-thousand dollar spectrophotometer to make a somewhat useful evaluation. The "truth" is in what the filter will show on the sky on a given target, and in the end, that is all that really matters.

Clear skies to you.

#37 lamplight

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Posted 28 August 2013 - 08:11 AM

Well this has been interesting and informative. I have not been able to see the eastern or western veil nebula from my backyard. I have three filters, Orion ultrab lock, sky glow, and an O-III. II tried all three on this target recently with no luck. More than once, but I can't recallif I've tried the bigger dob so that will need to be done. I intend to do the same testing at a darker site this weekend with the 10", which should give me some more information. These filters have been essentially useless to me.. I haven't done enough testing to determine if its the filters, my skies or my eyes, but I'm leaning towards the filters at this point. The only noticeable experience I've had was I think the O-III on the dumbbell nebula. I saw it at home in the 16" and it was very bright and well defined, at a dark(er) site with a smaller 10" it wasn't as defined, used the filter And it helped. That's the ONLY usefulness I've gotten out of all three unfortunately. I haven't even attempted to thoroughly evaluate these on multiple objects /scopes, don't get me wrong.. My main point of posting was to mention I've never seen the veil nebulae yet , and I'd like to!! With darker skies that should give me an indication of the helpfulness of the filters

#38 csrlice12

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Posted 28 August 2013 - 08:30 AM

Best overall filter is the gas filter....getting to darker skies.....even your other filters will work better there......Wasn't really a filter fan till I tried the Lumicon OIII on the Lagoon Nebula at the dark site....

#39 REC

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Posted 28 August 2013 - 10:08 AM

Matt; interesting comments! What zone would you say your backyard is in? For me, it's a Red zone with maximum 4.5 Magnitude on a good night. Once in a while with great transparency and low humidity it goes to Mag.5 I use the stars in the constellation Corona which us high in the sky now.

I just got a 2" DGM NPB filter that has been highly recommended here the other day. I tried finding the Veil in my 8" SCT the other night and could not see it? I was on it as my scope is a goto, so I know I was there with 52cgy. in the EP. I did sew a notable difference in the Dumbbell as you mention and not too much in M8. Perhaps my transparency was not the best and no doubt the LP has an effect.

Clear Skies to you!

Bob
I am very interested in your next report from a darker observing spot.

#40 David Knisely

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Posted 28 August 2013 - 10:49 AM

Well this has been interesting and informative. I have not been able to see the eastern or western veil nebula from my backyard. I have three filters, Orion ultrab lock, sky glow, and an O-III. II tried all three on this target recently with no luck. More than once, but I can't recallif I've tried the bigger dob so that will need to be done. I intend to do the same testing at a darker site this weekend with the 10", which should give me some more information. These filters have been essentially useless to me.. I haven't done enough testing to determine if its the filters, my skies or my eyes, but I'm leaning towards the filters at this point. The only noticeable experience I've had was I think the O-III on the dumbbell nebula. I saw it at home in the 16" and it was very bright and well defined, at a dark(er) site with a smaller 10" it wasn't as defined, used the filter And it helped. That's the ONLY usefulness I've gotten out of all three unfortunately. I haven't even attempted to thoroughly evaluate these on multiple objects /scopes, don't get me wrong.. My main point of posting was to mention I've never seen the veil nebulae yet , and I'd like to!! With darker skies that should give me an indication of the helpfulness of the filters


Well, the OIII is the filter to use on the Veil, especially in-town. However, filters tend to work somewhat better under darker skies, so you should keep that in mind. In urban or suburban settings, it can be difficult to impossible to get dark adapted enough for the human eye to see some objects, filtered or not. This (along with using a little too much magnification) is the primary reason for failures using filters. If you cannot get to a location that has little to no light falling directly on you (i.e. some light shielding in your immediate area), you will probably fail to get dark adapted in the first place. If you haven't spent at least 20 minutes in that darkness (and take steps to stay dark adapted, like using a *dim* red flashlight and shielding your observing eye), you will not be properly dark adapted. If you are not using fairly low power (3.5x per inch to 9x per inch of aperture) and make full use of averted vision, you may not have much luck with the Veil under urban or suburban conditions even when using filters. That having been said, with my Lumicon OIII filter and my 10 inch f/5.6 Newtonian at 47x using a dark shroud over my head, I have managed to see the brighter arc of the Veil (NGC 6992) from my front yard *with the full moon in the sky*. It was just barely there (appearing as a faint ghostly arc), but it was there, despite the fact that the limiting magnitude at best was 4.0 to 4.5. It *can* be done with filters, but one has to have done the proper prep-work before hand.

I do recall one night at the Nebraska Star Party's Beginner's Field School help session (zenith limiting magnitude was fainter than 7.5) where a gentleman with an 8 inch Go-To SCT came up to me and complained that he couldn't see the Veil. I went over to his scope (which had an OIII filter in it) and looked in. Running right down through the center of the field was a portion of the main arc, so he just couldn't see it in the first place even though the scope was correctly pointed by the telescope's computer. It would have helped to have him use a little lower power so to take in a little more of the object, but I don't think he was prepared for exactly what it would look like or how to see it. It was a case of someone who just needed a little more experience on exactly how to observe. The Veil is not an easy target to view in-town (without a filter, it is impossible), but with a filter (preferably a *good* OIII filter), it is definitely doable. Clear skies to you.

#41 lamplight

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Posted 28 August 2013 - 11:07 AM

Bob
We'll see. Yes I can usually make out Corona Borealis curve on a decent night. It varies as you say .. On the map I'm orange.. Sometimes it feels like red sometimes it feels like closer to yellow ;) there has a been a LOT of poor nights all spring and summer.. But the last few weeks have had a better percentage.

I've learned to properly dark adapt David, been a big fan of that since I first learned of the advantages , 60 minutes! my tablet is rubylith filmed and its very low light output when also turned down. and I seem to always be at relatively low magnification I always backlit off when the stars get blurry and so rarely can't push it up. Looking forward to another clear night and darker skies.

I was so impressed with the lagoon nebula at a green zone recently I never even thought to try to filter it. Hmm..

#42 lamplight

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Posted 28 August 2013 - 11:15 AM

Here's another thought: was looking for NGC 7006 recently (i think it was near the nova in delphinus), and couldn't find it with my zoom eyepiece at the lowest mag (24mm). Switched to a modest astro tech paradigm ED (12mm), and there it was. That was the last straw. Anybody want to buy a zoom eyepiece cheap?

#43 AstroTatDad

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Posted 28 August 2013 - 05:22 PM

Bob,you have a awesome filter before you go out again go over David's list and write some targets down that scored good with the use of the UHC filter. The Veil is a tricky one in higher LP, the OIII filter is the best for me for the Veil. I have tried my UHC filter on it, I can see it with it. it's kinda hard to explain but I get different detail of the Veil with the UHC. It's not bright but it's there, near by lights is the killer. If I don't block the lights near me and put something over my head too. I can't see it, but with dark adapted eyes, using light blockers, something over my head I can even see it with no filter but of course it's very faint. Next time try putting 52 Cyg just a little out of view but close to the edge. Give yourself so time to get use to the filter. I have noticed over time using the OIII filter I'm seeing better and better.
When I first got my OIII my girlfriend could hardly make out any detail using the filter. Now that her eyes have more experience she is seeing a lot better with it now.

But yeah check out David's list there is a lot of goodies that your DGM filter will kick but on. :)






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