Second Time Around

Quite a few  2x Barlows can also be used at 1.5x.

On these dual 1.5x/2x Barlows the black lens cell at the bottom of the Barlow can be unscrewed from the body and then screwed into the filter thread at the bottom of an eyepiece to give approx 1.5x.

US retailer Agenda Astro say in the specification section of each Barlow they offer whether the lens cell can be removed.  Go to https://agenaastro.c...-extenders.htm

FLO do a good own brand such 1.5x/2x Barlow that also has a T" camera fitting at the eyepiece end.  Go to https://www.firstlightoptics.com/barlows/astro-essentials-125-2x-barlow-with-t-thread.html

There's also the Baader 1.3x/2x Barlow Q Barlow, but this can't be used with all eyepieces.  This is because if there's a lens near the bottom of the eyepiece there may not be room for the Barlow cell to be inserted.

Whether or not a Dioptrx will help depends on  the degree of astigmatism you have in your observing eye.  You can find this on your prescription under cylinder, often abbreviated to CYL.  Note that your left eye appears on the right hand side of the prescription and vice versa.  The higher the number, the greater the astigmatism.

It also depends on the exit pupil of the scope with a given eyepiece.  I assume that your Starfield refractor is an f/7, in which case a 5mm eyepiece will give an exit pupil of 5/7, i.e. less than 0.75.

As Don has pointed out, with such a small exit pupil your astigmatism would have to be fairly bad to need correction.  The graph on the link below will quantify this.  From this you'll see that your astigmatism would have to be about 3 dioptres or worse for a Dioptrx to be any use to you with an exit pupil of 0.75.

https://www.televue.com/engine/TV3b_page.asp?id=54&Tab=_Choose

At bigger exit pupils/lower magnifications you may benefit from a Dioptrx even if your astigmatism isn't very bad. Again the above graph will help here.

I'd add that it's not just Televue eyepieces that accept a Dioptrx.  Quite a few others do as well such as the Pentax 70 Deg XW and Baader Morpheus ranges.  However, that really needs a separate topic.

The same applies to whether to observe with glasses or a Dioptrx, for which there are pros and cons.  Don prefers the former while I prefer the latter.  A search (certainly on Cloudy Nights, but possibly here on SGL as well) should show our reasons and that of others.

Cheers.  Will post tomorrow when back home.

10 hours ago, Franklin said:

An active night vision eyepiece, something like a Quark that just plugs into a regular scope but allows you to see in NV.

Many NV devices already do just that!

That's interesting!

Support for the latest 32mm series, that's based on new technology, is being withdrawn in 2026.

Yet all the current versions of the older 36, 42 and 50mm models are still being supported.

I wonder what that tells us? 

I'm certainly glad that for other reasons I decided to go for the 12x36 III rather than one of the 32mm models.

Allow me to present an alternative view.  It's not better or worse than Jules's, just different 

Firstly, I have a genetic condition that badly affects my muscles.  In fact, on bad days I don't even have the strength to lift a mug of tea. 

On good days though I have almost full strength.  However, even then my back and neck are badly shot to pieces.  Like Jules, if I lift the scope or mount in the wrong way I'm out of action for 10-14 days.

I wasn't able to attend star parties but instead whilst in Germany visited several telescope shops.  There I was able to directly compare a large number of makes, models and sizes.

The first thing I decided was that Go-To wasn't for me because of the extra weight.  It meant that I'd have to go down a size.

I also found that it wasn't just the weight that was important but the footprint of the mount.  Having a less bulky mount meant that I could hold it closer to my body, meaning less leverage and less pain.

By far the best DOB mounting was the OOUK one.  Being made of aluminium it's a lot lighter, plus the footprint is much smaller.

Additionally, they have large circular altitude bearings in a ring shape.  These make an excellent handle, and I found that I could cope with a mount one size bigger as a result.  The Bresser (Explore Scientific in the US) is similar, but not so light as it's not aluminium.  This design of bearings also make these two makes particularly smooth.

The VX series of Dobs from OOUK also have aluminium tubes, so are lighter than the normal steel.  

The conclusion I came to was with OOUK Dobs, and to a lesser extent Bresser, I could cope with one size up compared to Skywatcher and GSO (the latter manufacture many of the generic makes on the market).

I ended up deciding on a 10 inch OOUK Dob, but couldn't justify a new one.  Used models in this size proved very hard to find, but I did get hold of an 8 inch f/6 very quickly.  However, it took me over a year to find a 10 inch f/4.8.

Since then I've had plenty of opportunity to compare the two sizes.  On the planets there's not been much between them because poor seeing in the UK is usually the limiting factor rather than the size of the scope.  Only on the rare steady nights has there been much difference.

It's on DSOs where the extra aperture really scores.  The difference isn't hugely marked though in my Bortle 4 skies, except that is on one class of object.  Here there's a very definite improvement with globular clusters - my favourite objects.

As a result I wondered whether to go up to a 12 inch.  So I asked OOUK to bring a 12 inch f/4 to a show last month. 

I found the jump in weight from 10 to 12 inches much harder to cope with than from 8 to 10.  Additionally, the mount was much bulkier. 

What I like with the OOUK 10 inch mount is that it fits just over my hips and thus it doesn't move around.  I find that this extra steadiness makes a huge difference when walking with the mount rather than just lifting it. 

I certainly couldn't carry even an OOUK 12 inch very far at all.

So for me 10-in is the optimum size.

I fell on the eyepiece end of my OOUK 10inch f/4.8 and dented it.  The end cap was also badly buckled.

The local body shop soon fixed the tube for a cost of £50.  Spare parts from OOUK are very expensive and a single end cap was £54 + about £6 carriage if I recall correctly.

Better than a complete new tube though that would have been £180 + £54 for each end cap + about £34 carriage.

Hope that helps.

Signed and multi-shared.

Wow to the pics!

And thanks for the tips.

On 13/03/2023 at 22:43, Stu said:

There is also a Bresser 8” dob in there at £380 which has some nice features

https://www.firstlightoptics.com/offers/offer_bresser-messier-8-dobsonian-telescope_359285.html

This is the one that I'd choose because it has a better, smoother mount.  In fact I'd choose this even at full price. So this return is a bargain.  Additionally, the tube rings make it easier to carry. 

Indeed, I find I can carry one size bigger tube with a Bresser than a Skywatcher or GSO.  The latter make a lot of scopes that are rebadged. 

However, there's no difference with carrying the bases.  Here you'd exceed your budget unless you can find a used Orion Optics UK Dobsonian that have both tubes and a very compact mount made of aluminium 

You can easily upgrade almost anything on a Dobsonian, but the mount is more difficult and expensive to upgrade unless you make your own.

On 13/03/2023 at 12:45, LDW1 said:

Yes about the APM and even moreso the new Svbony equivalent but many, many, many observers want more range for their $ than what they offer. Thats why I personally didn't buy either, we aren't all moon / planetary focussed ! As for the others, we all have our experiences.

Whilst I take your point about the zoom range, the shorter the range the easier it is to make a high quality zoom at a given price point.

Also, the smaller field of view at the low power end of zooms has to be taken into account.  For instance, with my Baader zoom I used it almost entirely at 8-16mm, then skipped over the other focal lengths to 24mm just to get the widest field of view. 

With the 7.7-15.4mm APM I have almost the same focal lengths as the Baader but a much wider apparent field of view at low powers.  As I posted above, the true FOV of the APM at 15.4mm is wider than that of the Baader at 24mm.  Plus the magnification is higher meaning a darker sky background and so almost always more stars visible.

There's a market for zooms at various price points of course.  I'm lucky that I can now at last afford the APM, but appreciate that many members will be in the same boat as I was not so long ago when my budget was tight.  On the other hand, the quality and wide field of the APM zoom means I need less fixed focal length eyepieces now as Stu posted.

Here are some updated thoughts on the zooms I've used so far, including the new APM Superzoom:

Hyperflex 9-27mm.

I compared it with my Baader during the day on my shed. Even though the focal lengths are lower, the actual field of view at 27mm is about the same as the Baader 8-24mm at 24mm. Nor was it as sharp as the Baader in my f/6 refractor. I was planning to try it with my Quark, but there were no sunny days or clear nights before I passed it on to two of my grandkids to use with the 70mm f/10 I bought them for Xmas. Not surprisingly, it was better at f/10. Not Dioptrx compatible.

Svbony 7-21mm.

I tested it on a very low down Saturn, and surprisingly found that on my f/6 refractor it was as good as the Baader on axis. Sharpness fell off somewhat off axis though, plus the field of view was quite a bit smaller. However, trying it on prominences at f/26 with my Quark it was way, way behind the Baader, seemingly because of lower contrast. I bought this for outreach rather than risking my expensive zooms and have kept it for this. It's very small and light, even compared to other Svbony models, so would be useful in binoviewers.  Dioptrx compatible with O-ring.

Celestron 8-24mm.

The version I bought was the spotting scope one, so it might be different to the astro model, but I believe that optically they're identical. The first thing I noticed was that it was even less parfocal than my Baader. In fact, no zooms I've tried are parfocal to my aged eyes, but might be to someone younger. The field of view was also smaller than the Baader. What disqualified it completely though was that it wasn't threaded for filters or screw in Barlows, although I think the astro version is. I therefore returned it without further testing. Dioptrx compatible with O-ring.

Baader 8-24mm.

This is more expensive than those above, and not surprisingly outclassed all of them, both in sharpness/contrast and field of view.  Until I bought an even better but more expensive APM Superzoom it used to be by far my most used eyepiece, although I also own a selection of quality fixed focal length ones. Can be used as a 1.25 or 2 inch eyepiece.  Dioptrx compatible with O-ring. The only downside, that's really important only for binoviewing with a Dioptrx, is that unlike most zooms the eyelens rotates when zooming.

APM 7.7-15.4mm.

The best zoom I've ever used, although not cheap.  As sharp as the Baader but with somewhat better contrast.  Wide 66 degree field of view throughout the entire zoom range.  Indeed, the APM has a wider actual FOV at 15.4 mm than the Baader does at 24mm!  Can be used as a 1.25 or 2 inch eyepiece, but needs extra infocus with 1.25 inch.  Dioptrx compatible with inexpensive M43 to T-thread adapter.

2 hours ago, Telescope40 said:

Hello. Think I ran across this guy last year via an advert I was running on ABS at the time.  I was selling a scope and basically he came at me asking for my "rock bottom" price.  Had to confirm the price was on the advert.   I didn't take offense in any way as he wasn't meeting my price. Just fishing and everyone wants a bargain don't they.

Lately, anything I sell seems to get a " would you take so much for it"  e mail on any adverts I post.  I do try and price fairly but it doesn't seem to  work anymore. Personally I don't do this.  If I 'm happy with the price on the advert I'll pay it in full. If not, I move on. I think most sellers try and price accordingly.       The way of the world I guess.  Sigh !! 

John

Mods - if this post against forum rules, I apologize. Please remove if you see fit.  Thx 

Like John I never haggle over the price.  If the price is too high I just move on. 

I don't accept offers at all at first.  I give SGL members first crack of the whip.  If the item doesn't sell here then it goes on UK Astro Buy/Sell.

If not sold after a while only then will I readvertise at a lower price, again on SGL first.

1 minute ago, iantaylor2uk said:

 

I know people say price at around 2/3 of new, but now inflation is high, retail prices are going up, so you could argue why is my second hand telescope now worth more than a year before. 

 

3 minutes ago, Mr Magoo said:

Kit sold on SGL should be sold for the benefit of a members observing experience, not their bank balance. If you don't need it once you've bought it, put it back up for sale on the same site for the same price.

I price my kit at about 2/3rds if in good condition, less if it's not. Most of my items sell pretty quickly at that level.

However, this is 2/3rds of the current price. 

I consider what I paid to be immaterial.  I often don't remember anyway. However, I never buy to trade but to use.  

Inflation does has to be taken into account. After all, nobody would sell a house for what they paid for it 25 years ago!

So it's replacement cost that's relevant.

We can lose as well.  For instance my fishing book collection has crashed in value in line with its replacement cost.  As I need the space, I'm currently selling a lot of fishing books for a small fraction of what I paid for them.

You may not be able to actually see the high cloud but if it is there it'll reduce the number of stars that you can see.

My first time around from the age of 12 I had no instruments so had to learn my way around the sky just with my naked eyes.  That helped when I eventually got a small scope, and in those days the only option with it was manual starhopping.

Fast forward several decades to my second time around and those early experiences held me in good stead.  I could still find my way around the sky even when only a few stars were visible because of cloud, and could still find many of the brighter DSOs without a star atlas.

Nowadays because of poor health my observing sessions are much shorter.  Occasionally I still starhop and still do enjoy the thrill of the chase.  However, the vast majority of the time I use a push to system.

This is simply because by doing so I can see way more objects in these short sessions.

Initially, I used a Nexus push to with encoders, but have now switched to Celestron's Starsense Explorer.  I've since adapted the latter to fit into a standard Synta finder shoe and so it can be used with all my scopes.  A search on the forum will show lots of ways to do this.

Two reasons why I prefer Starsense Explorer to the Nexus (and for that matter to a Go-To) is that the former can be moved around my garden without needing realignment.  I also find I can set up Starsense Explorer quicker in the first place, especially in part cloudy skies.

What I don't agree with is that unless you starhop you're cheating.  As I said earlier I can indeed starhop, but most of the time I prefer not to.

Just measured mine at 38mm. 🙁

Will dig them out and check. 

However, these should fit https://www.baader-planetarium.co.uk/shop/baader-42-43mm-winged-rubber-eyecup-for-baader-hyperion-and-aspheric-eyepieces/

Here you go, Ray.

https://www.firstlightoptics.com/adapters/stellamira-m48-adapter-for-stellamira-reducers-and-field-flatteners.html

I think I have some spare Field Optics Research eyecups sonewhere. What size do you need?

I have the StellaMira 0.6x reducer/flattener which probably has the same thread.  Mine is M54 (54x0.75mm).  

Hope that helps.

A truly excellent review!  More please.

Nice to meet you Carole, and half a dozen others.

Only thing I bought was a spare part for my OOUK 10 inch Dob.  Decided that their displayed 12 inch was too heavy to manage, so in a way the trip paid for itself!

My wife and I will be there. You can see what I look like from the photo in my avatar.  We'll both be using folding chair sticks.

Hope to see some of you there.

2 hours ago, Don Pensack said:

Human vision has a sharp center of 2-5° wide.

With an apparent field up to 68° or so, you can simply move the eye to look at the field, providing the image forms far enough away from the eye.

With anything wider, moving the eye sufficiently to look at the edge will move the pupil of your eye off the exit pupil of the eyepiece.

You have to roll your head over a bit to use direct vision to look at the edge.

And, the wider the apparent field, the more you have to roll the head to look at the edge.

If you stop to think of it, the edge of the field in a 100-120° eyepiece is closer to parallel to the scope than it is to perpendicular.

Some people don't mind moving the head (I'm one), while others simply hate it (maybe they have arthritis in their necks?).

 

Now, your peripheral vision extends to about 145° horizontal and 125° vertical, so seeing the edge of the field with peripheral vision when staring at the center of the field is easy.

It's looking at the edge with direct vision where you have to roll your head.

I have a damaged neck and, having tried wider field eyepieces, find I much prefer 60 to 70 degree AFOVs.

My favourite eyepiece of all is the 7.7-15.4 mm APM Superzoom.  Unlike most medium power zooms this has an almost constant AFOV.  This is 66-67 degrees, that I find ideal.  If I want shorter focal lengths I Barlow the zoom and so keep the same AFOV.