Giles_B

16 hours ago, Stephen Waldee said:

The ONLY time I have ever heard a really elite, highly experienced deep sky observer recommend a simple colored filter for anything other than planets, is the suggestion to use a Wratten 12 (deep yellow) to see some faint details on certain galaxies. I can recall trying that a few times -- with NO significantly positive result.

So the only potentially useful filters for *extended objects* (i. e., nebulae or galaxies) will be in the following categories, according to most experts and filter marketers:

1. The LPR or light pollution rejection filter: it's a filter that cuts out the wavelengths of light generated by OLDER streetlights (high and low pressure sodium bulbs.) Since modern streetlights are often LEDs or halogen, the color balance is not yellowish, but almost bluish--and the LPR filters no longer work very effectively for VISUAL observing.  They CAN still help increase exposure times for imaging.  Now, this is the "mainstream" opinion.  I differ a bit, because I like to use the LPR or broadband type for faint objects at HIGH magnifications.  They may be ineffective at 30-50x, but try *200x* on some very faint objects, particularly planetary nebulae--even, sometimes, galaxies when you're trying to detect almost IMPOSSIBLY vague spiral arm structure.  In other ways of expressing this, use "small exit pupils" which, when you consult simple formulas for figuring this out from the eyepieces you are using in your scope, means in effect higher power.  I could expand this to about 15 pages of text at this point--neither you nor I would have the patience!

2. The other type of filter -- MUCH more effective than the above -- for "extended objects" EXCLUDING galaxies and star clusters, is the "interference line filter".  Depending on what wavelengths of light they block or admit, they are in some general types: "UHC" (ultra high contrast, which is really just a marketing term) which means in effect they are for gaseous nebulae, for the visible greenish wavelength of light known as H-beta (from atomic hydrogen.) Another type is the "O-III" filter: again, they are for nebulae but specifically ones that radiate predominantly the light waves of atomic oxygen: planetary nebulae in particular, though quite a few gaseous nebulae (like Orion's M-42) also feature the oxygen lines.  These filters work better at LARGER exit pupils than SMALL ones: i. e., at low to moderate rather than high magnification.

There are some others, including the Hydrogen-beta filter (pretty much for a handful of objects like the Horsehead and California nebulae); and the Hydrogen-alpha PHOTOGRAPHIC filter (not for visual observers.)

You can get sometimes, depending on many factors, SOME slight enhancement of contrast on star clusters, globular clusters, and galaxies with the LPR type; but it's pretty much hit-and-miss.  However, the LPR filter DOES often work well on *reflection nebulae* like the glow suffusing the star cluster M-45, the Pleiades.

I should stop here, because I've written a very large and comprehensive web paper on the entire subject of filters for deep sky observing, with internal sections that have hyperlinked observing reports of hundreds of objects with which I've used filters (mostly in scopes from 3 to 11 inches' aperture.) Let me merely state that *filters are NOT only for large scopes* (though some people think so if they have not done the correct experimentation with the right amount of magnification for the filter-type.)

There is also a general introduction, as well as some 'niche' material for more advanced users.  

http://celestialregina.x10.mx/horsehead/NebulaFilters.htm

 

I started developing this web report in 1997 and am still adding to it, refining it, and (yes, I have to admit) occasionally CORRECTING it!

In years previous to that I worked here in California USA with Orion Telescopes as the Product Development Manager and was responsible for testing and putting together the catalogue articles and user sheets for the "UltraBlock" filter; I later worked with my friend Dr. Jack Marling of Lumicon on a software program -- a "telescope/filter simulator" -- for calculating best performance ranges for his line of filters, with specific objects, scopes, and magnifications.  I have used these kinds of filters since around 1983...

Good luck--I could not IMAGINE observing without a full complement of them!  Below is my "filter case", with the specific models described on this webpage:

http://celestialregina.x10.mx/horsehead/filter/filter14-SRW-eypc-filter-case.htm

 

Steve Waldee

http://celestialregina.x10.mx

or http://reginacelestial.byethost3.com

 

 

Cripes, that's a long post, but a really informative one! Thanks Steve, I'll try experimenting with different magnification and filter combinations,which is something I've not considered before...

I came across a great resource on the web to help expand the list -

It's a website that will list the DSOs in your location according to magnitude - it classifies them into different types (Galaxies, Open Clusters etc.) - I've found it really helpful in planning viewing sessions:

https://telescopius.com/

See what you think.

Yes, those are really wise thoughts. I did laugh when you said about your 4 scopes. My other half couldn't quite believe the answer when she asked when I was getting rid of my old scope....

These are great tips. I'm also new to the world of Dobs and both nights I've been out with mine I've found a waterproof pillow and a garden chair useful. I tend to prefer to stand, so it's hard to get used to observing from a sitting position!

Thanks @mikeDnight - I do think there is a bit more thickness to the scratch that doesn't quite show on the pictures. Put I take the point - i.e. stop fussing!

The collimation was the first thing I checked after first use - the previous owner said they'd collimated it with an included laser collimator when I picked it up.

The collimation was crazily off before I had a go with my Cheshire - less than half of the primary was visible, so I guess the laser collimator is ready for the bin....

Interesting that the coma was still bad with good quality eyepieces for you @bomberbaz. I guess a coma corrector might be further up my shopping list than I thought.

Thanks for the advice on the setup right for the push to intelliscope computer - I think from your description I'm doing it correctly. My big problems were that I was unable to get warp below about 2 - but I may have been too slow to find my reference stars, or the base may have been too off level (I hadn't consider this) - plus I was scrolling through thousands of objects that were below horizon. I think if I go out with some objects in mind it will be a bit better than random pointing!

The Orthoscopics are 30mm and 6mm

Certainly I didn't go through the whole set - but went down from the 25mm to the 18mm - I probably didn't reach the lower focal lengths, so I will give them a try.

@Peter Drew I actually took a photo of the crack. It's certainly not full thickness (that is, I can't make out distortion on the mirror surface) - but I got a bit wound up by first seeing some quite hysterical posts about the aberration caused by cracking on other forums

I finally found my 'cheap enough' second hand 10" Dobsonian with a computerised star map (a Orion10XTi Intelliscope) and, after some predicable initial teething problems on the first clear night, took it out for its next spin, in my (Bortle 6) garden last night.

I found the Intelliscope hard to use, and not much help finding anything. I think this is probably a case of just going through the manual carefully, and having a better sense of what to look for in the huge database. Luckily I've attached my trusty Starsense Explorer phone mount onto a piece of 8mm acetal, screwed this to the tube rings and it works a treat at finding my way around. The bigger worry is that the optics just didn't seem to be performing as I'd expected.

As I say, the moonlit night was light and I didn't have great expectations. I found my BST explorer eyepieces had hideous coma (the scope is f4.7) - even the 18mm which I'd heard tell was fairly good in a fast scope. I fell back on a couple Baader orthoscopic eyepieces. These are never quite as twinkly as the BSTs, but I had decent views of Pleiades and the Beehive cluster. However, even given the unfavourable conditions I was very underwhelmed with the view in comparison to my 5" Celestron Starsense 130 newtonian. The Orion Nebula had a little more detail - but only a little. I couldn't even make out Bode - not unusual on a bright night for my 5", but I'd had high expectations given the extra 5" of aperture.

My fears that there may be something fundamentally shot with the optics are already heightened by the fact I spotted a small crack at the edge of the primary mirror while collimating. The jury seems out on this looking through the forums (that is, there are many voices of doom and a few saying wait and see if it is the crack is stable), and I'd decided to wait until I had better eyepieces before deciding the coma was due to this. However, I'm now wondering if the unimpressive views may be due to some degradation of the mirror.

Now, I'm a novice, and all I have to go on is the views I'd come to expect from the Celestron 5", so my question is: I am just in the process of having my high expectations of 10" performance reduced, and essentially doing the right thing patiently waiting for some high end eyepieces to be back in stock in the UK, or are there so many red flags that I should I be thinking about a new primary mirror sooner rather than later, to improve the performance with my current equipment?

Hi Jammy G,

I'm about a year in on a similar trajectory to you - I've got a Celestron 130az - so a slightly bigger reflector, but 102mm should allow you to view quite a lot. I live in the city with quite light polluted skies (Bortle 4-5). The Starsense app works well despite these conditions and will direct you to the brighter objects in the sky.

I tend to get interesting views of planets, open clusters and bright nebula. Unfortunately Saturn is pretty much too low to see now, and Jupiter is getting lower in the sky, but should be visible just after dark. Try looking at Pleiades to get a taster of open clusters and there are good views of the Orion Nebula at the moment - but there are many slightly less bright, but nonetheless fascinating, objects on the Starsense app.

One thing I'd recommend getting are some new eyepieces, because the ones supplied with the starsense scopes are terrible. I began with Baader Classic orthoscopic eyepieces, which were okay, but moved onto BST explorers, which were much more satisfactory, after advice on this forum. The eyepieces really make the experience, the view of the moon and planets is far superior and they change open clusters from dull "dots of light" to something much more structured and spellbinding.

Good luck!

Thanks for the tip on the Stellalyra. it does look very well specced, and the push to looks like an interesting option.

It sounds like a lot if the difference is about features rather than anything fundamental with the optics. I have noticed all these scopes come up on eBay from time to time, which is another way of saving cash for good eyepieces - are the optics pretty similar for all the different models if one came up at significant discount?

I'm looking for a 10" Dob to upgrade from my current beginner set up (Celestron Starsense explorer 130mm newtonian). I've narrowed the potential range down a bit, but I'm getting a bit confused between the options.

These seem to be Skywatcher 250PX https://www.rothervalleyoptics.co.uk/skywatcher-skyliner-250px-dobsonian-telescope.html

Orion XT10i https://uk.telescope.com/Telescopes/Orion-SkyQuest-XT10i-IntelliScope-Dobsonian-Telescope/rc/1306/p/109949.uts

Bresser Messier 10 https://www.bristolcameras.co.uk/p-bresser-messier-10-inch-dobsonian-telescope.htm

The technical points of difference seem to be:

Skywatcher 250PX - crayford focuser (has some recoil), teflon bearing

Orion XT10i - crayford focuser, nylon bearing, cheap base, Push-to system

Bresser Messier 10 - hexfocuser, generally better construction, upgradable to  equatorial mount, teflon bearing

The other big difference is price and availability: the Skywatcher is around £550 and everywhere, the Bresser is about the same and difficult to find in stock, and the Orion seems to be pretty rare and is nearly £1000.

-now, I am attracted to the push-to on the Orion XT10i (given I am migrating from a Celestron starsense) but I am not sure if it justifies the potential lead time and huge cost difference (I am anyway planning to adapt the starsense explorer phone adapter to the new scope): are there technical differences I am missing?

Any advice gratefully received

Our understairs cupboard is overflowing, so it's the shed or nothing, for now anyway (I may get rid of the Celestron at some time depending on the ability of the Dob to travel). The added bonus is that a scope in the shed raises will be easier for my partner to ignore. She's already made it clear she isn't on board with me turning the place into the next Greenwich Observatory... sigh.

Is it worth getting a special cover like this https://www.firstlightoptics.com/telegizmos-telescope-covers/telegizmos_tg2d.html ?

Any desiccant packs you'd recommend?

I'm considering my telescope upgrade having reached the limits of my current Celestron 130mm newtonian. I'm thinking a Dobsonian is the most affordable route, although not yet quite decided on the make and size. Our house is pretty crowded and so I'd plan to store this in our garden shed (which is dusty but dry). I wondered if there was any downside to doing this, for example, do the bearings and focuser get rusty or stiff, does the mirror get mouldy etc. etc.?

If there are issues, I'm not beyond some routine maintenance (i.e. cleaning, greasing and oiling, but are there any special steps I should be taking to keep a shed stored scope in good condition?

One final thought is about security. Thefts are uncommon, but not entirely unknown where I live. I'm assuming a reasonable sized Dob would not be an attractive proposition to a thief (heavy to shift and difficult to sell), but I'd be interested to hear your thoughts and wisdom.

2 hours ago, pete_l said:

In that case why not make one from wood?

If you know someone with a table saw they can cut the angles correctly and you can have the bar whatever length you desire. Plus mounting holes (untapped) where ever you please.

If you worry that it will get indentations from fixing screws being too tight, put some sheet metal sides on it. Or use a hardwood such as oak.

Thank you, but if you saw my standard of carpentry you'd think twice about the advice. If I can get away with £15 for a bar, that will save a lot of grief!

Thanks - that's the sort of reassurance I needed!

I agree. I'm not quite a year into observing, but it just gets better and better. Part of this is getting the right equipment, for me, part of it was calibrating my expectations: once I realised the limits of what I can see I could stop trying to recreate the hubble telescope in my back garden.

I bought my scope wanting to see the planets, but I more and more I've found myself drawn to the DSOs and Open clusters. The latter get a lot better with good eyepieces, you can see a lot of intricacy that isn't present otherwise. DSO are just so mysterious they draw me in. Also have a look at the emission nebula in Orion. There is so much to see, so don't give up.

Pleiades is fantastic - find it in Taurus - and the beehive cluster in Cancer was a nice find for me last week.

Great to have some clear nights again after all the cloud over Christmas.

Excuse the stupid question, but is dovetail bar the same all over? I'm astounded that it can vary in price so much. Dovetail bar seems to range from just over a tenner for something generic, to £70 or more for something exotic. Am I okay getting cheap bar or is the cheap stuff is cheap for a reason... Has anyone advice or cautionary tales?

If it's helpful, the bar only needs to hold about 600g in weight - I'm thinking about moving up and on from my Celestron Starsense Explorer 130az, Inspired by descriptions on this forum and elsewhere I'm looking for dovetail bar to help fashion something to attach the Starsense phone dock to a setup (not sure what scope, still thinking about my options there, so this is kind of a 'proof of concept stage'!).

Really glad you are enjoying it - sadly a combination of a heavy work schedule and the constant rain has meant I've been out less than I would have liked over the past week, but I agree the app and the portability factor are real marks in the Celestron Starsense's favour. I think the only thing I don't enjoy about the scope is its rather wobbly nature - it always takes a good 30 seconds to settle down if I adjust it - so you can just imagine the problems when I tried to show my 5-year old Saturn a few weeks ago - she just couldn't look without grabbing the tube and told me Saturn looked like a "wobbly dot"!

Thank-you very much for these responses and apologies for my delay in replying - I guess picking up my scope and getting out of town is the best, and maybe I'm just getting over influenced by catburglar's recommendation, but I think I may start to seek out some emission nebulae with a view to getting an OIII if I can get a reasonable view (i.e. not obstructed by trees and houses from my garden) - there's nothing like the convenience of observing the sky from my backyard

It was a wonderful clear night in Bristol last night. I got some great - really great - views of Jupiter and Saturn - the atmosphere seemed crystal clear and they were probably the best I've managed since getting my scope, a 130mm Newtonian (Celestron starsense explorer 130AZ ).

Once again I was also draw to deep sky objects which I find fascinating (despite the light pollution of a big city). You can't see much from my garden, but I spent a good time looking at the Andromeda and the Hercules cluster. The view is very faint, and it is difficult to make out structure. I understand, thanks to discussions on SGL, that this is normal for visual astronomy and not helped by the limitations of my location and equipment.

While I'm content to persevere, I wondered if it would be worth getting any (more) filters for my set up. I have a moonlight/city light filter, which doesn't seem to do much to the view when I combine them with my 25mm BST explorer eyepiece, but I have read (I think) that some coloured filters can improve the view of DSOs.

Is it a pointless waste of my money to add filters when I could get a much better effect by driving 20 miles outside town to somewhere with less light, or would filters be worth it?

If so, can anyone recommend 1.25" filters that won't break the bank?

18 minutes ago, russ said:

It really gets on my nerves. It was worse last year with Mars. Not just the Beeb but all the daily rags too. 

Indeed, this suggests the "interview" quote was probably from a press release (standard practice for science reporting) - so the Royal Observatory rather than BBC is probably the institution to get annoyed with / complain to....

@Louis D It sounds like an advance on an Ikea bag and a couple of towels wrapped around the tube, which is what gets me by

There might be a cheap solution that is a step up from duffell bags and bubble wrap if you don't see a special advantage in spending £££ on a bespoke case. If any padded bag of the right dimensions should do the job - a quick google for "padded bag" using the dimensions of my scope (a Celestron 130mm admittedly much smaller than yours) showed this might just do the job: https://www.terralec.co.uk/padded_bags_and_covers/padded_equipment_bag_762_x_356_x_356mm/28075_p.html - I just wondered if there might be something similar that would suit you, that could be found with a bit of searching?

13 minutes ago, John said:

Bristol Astronomical Society have an rurally located observatory to the west of the city which provides reasonably dark skies. When we can meet up again I'm sure open public observing sessions will begin again

https://bristolastrosoc.org.uk/observing/

Thanks John, I'll be looking out for these sessions!

Tiny Clanger - you may be right, my experience of DSOs may be a repeat of my initial "isn't Saturn small" experience... I'll check out the guide