parallaxerr

1 minute ago, vlaiv said:

43mm 82 degrees eyepiece will be 3" - max 2" can offer is something like 40mm 70degrees (or maybe closer to 38mm).

Haha good point, so again it all comes down to the practicalities of reaching maximum TFoV. 

So only really a deciding factor if chasing the wide fields.

It seems that my thinking was logical then. Using different FL EP's, one can match the FoV, magnification and image brightness between scopes, up to the point where practical issues such as the slower scopes requirement for very long FL EP's may come into play.

So, as far as the view at the EP is concerned, the faster scope offers the ability for larger TFoV, but all other considerations are more "practical".

42 minutes ago, andrew s said:

Lighter weight and  more compact. 

On the down side stresses the eyepiece more as it presents more oblique rays to it.

Regards Andrew 

That's a good practical point, though my question is more about the view in the EP I suppose.

37 minutes ago, John said:

I'll just give one example.

I have two 4 inch refractors - a Vixen ED102 with a focal ratio of F/6.5 and a Tak FC100-DL with a focal ratio of F/9.

With my Nagler 31mm eyepiece the Vixen will show a true field of view of 3.8 degrees. With the F/9 the true field with the same eyepiece is a degree smaller.

When I want to see the whole of the Veil Nebula in a single field of view, the F/6.5 will do that comfortably but the F/9 won't get near it.

 

 

I suppose this is similar to my example John and as Andrew says, by using a Nagler of a longer focal length you could achieve the same view.

28 minutes ago, andrew s said:

But, what if you used a 43mm eyepiece (assuming I did the sums right) with the F/9 to match the magnification? 

Regards Andrew 

Agreed!

15 minutes ago, vlaiv said:

I would say that illuminated field has something to do with it as well.

Most fast scopes are built to illuminate larger field? They can for this reason display wider true field of view than slower counterpart.

Faster scopes are therefore - "richer field" telescopes - able to put more stars into single field of view and also able to put really large objects into FOV with enough context to make them stand out better.

There is another factor - faster scopes can produce max exit pupil with reasonable eyepieces. Take F/10 scope, in order to have 7mm exit pupil - you would need 70mm eyepiece. You'll have hard time trying to get one. With F/5 scope - that is 35mm EP - easy (but not cheap if you want good correction all the way to the edge).

 

Another practical consideration with respect to the EP's there Vlaiv.

When weighing up new scope options, inevitably there is a choice to be made over focal ratio. I have read in numerous posts over the years how faster scopes are more beneficial for deep sky observation and I've always assumed this is simply down to the brighter image presented in any given EP vs that when used in a slower scope.

However, we can of course control image brightness by adjusting the exit pupil with different focal length eyepieces. I know for example that from my home observing location, an exit pupil of 3.2mm is perfect for the majority of DSO objects (quite small some may think, but it works well for me given the sky background brightness). I discovered this using a ES16mm 68° in my ST120 and have chosen EPs for subsequent scopes based on this value, give or take a little. The 24mm 68° in the 4" F7 served up a similar image with comparable contrast at 3.4mm exit pupil, albeit with slightly less magnification.

Take the following for example though - two 6" scopes, one at F6 the other at F8.  By using different eyepieces (with same aFoV) the exit pupil, magnification and FoV can be matched as near as makes no difference.

So what exactly is the faster scope offering over and above the slower scope? 

Just the other day I was thinking the ability to track with the AZ100 would be good. With a loosely aligned EQ mount of course, you only need to track in RA at a constant speed for visual, but the AZ100 would have to be variable in both axis and reverse itself on the Alt axis when crossing the meridian. I can only see this working as a full goto system so the mount knows when to perform such changes in rate and direction. 

Your experience with the 102ed-r mirrors my own Paz. It was incredibly easy to set up due to it's light weight and size and worked extremely well on the AZ4. It was a fine scope but compared to the ST120 it just didn't go deep enough for me. I spent weeks observing the Veil with it through an OIII filter, but ultimately I couldn't tease out the fainter detail that the cheaper achro could.

You have the luxury of several scopes though and I was trying to find a one scope does all solution at the time...a foolish quest.

I'm back to a 120mm F8 achro for the time being, but have my sights firmly set on the 150EDF 😬 Hardly grab 'n' go admittedly!

That's the paint job sorted. Just need clear skies for first light now.....Not happening anytime soon judging by the forecast though!

Got the EQ6 top plate machined down today to match the Orion pillar and AZ100 O.D. of 100mm. Just needs a lick of paint now.

Also replaced the socket cap screws with some knobs to make assembly/disassembly easier. Turning out nice I think.

Well I managed to counterbore the dovetail with a cone drill and drop some socket caps in to get the scope mounted

The slow motion  cable length is perfect, placing the knobs right next to the focuser.

9 minutes ago, johninderby said:

Welcome to the club. 🙂

Chunky littlr beast isn’t it.  You need to ger some low profile head bolts now for the counterweight flange. 

Chunky indeed John. Took me by surprise when I opened the package, researching all the dimensions and even looking at pictures doesn't give you an appreciation for the heft of the AZ100.

8 minutes ago, John said:

What, no wood ??????

 

Not yet John, the savings account is still in shock, plus now I need a new dovetail so may as well go Losmandy and CNC rings! I'll be machining the top plate down and painting black so it's all one diameter, should be pretty sleek. A Berlebach may come in time.

6 minutes ago, Alan White said:

Now that's nice @parallaxerr, I knew you would blink.
Please let us all know how you get on with it.
 

You know me well Alan, the matchsticks stood no chance!!!

Postie had to flex some muscles to deliver this heavy load today...I've paid my fees, can I enter the AZ100 owners club lounge now?

Thanks to @Stu for the AZ6 top plate too, perfect post timing. 

Shame I can't mount my scope. Silly cheap SW/Celestron dovetail with sticky outy bolts wont go in the saddle. Back to Flo for more £££

Ah those pics help a lot, thanks Stu.

If the base is 100mm diameter then it appears the step/protrusion is about 65mm OD. Though it's not possible to determine the height of it.

It look like the stepped down diameter of ~65mm would sit in the recess of my top plate, but with only minimal land.

Gents,

I wonder if any of you would happen to have a photo of the bottom face of the AZ100 and know the outer diameter at the base? Is the base machined flat or does it have any steps/shoulders and if so what diameter are the shoulders?

Basically trying to figure out if I can fit it to my pier extension which is for the Orion SVP, same as EQ5 I believe. It's 100mm OD and fortunately there is ~17mm through hole so the required M12 bolt wont be a problem, just want to check that it will sit flat because there's a small step in it with a diameter of about 85mm. So, the AZ100 would ideally be flat bottomed and either less than or a good bit larger than 85mm OD (looks quite a bit larger).

The north peg is removable so no problem there.

Thanks.

Oh, and if anyone has any other recommendations for a solid mount that will fit the SW/Orion EQ5 pier, I'd love to hear about it. Let's keep it sub £500 for now! 

I'm very much enjoying my Celestron Omni XLT 120mm refractor. In combination with my AZ4 on top of a 1.75" tripod and 16" pier extension, it makes for a great low to medium power sweeper and DSO setup.

However, there's no getting around the vibrations at high Mag. Some lunar action a few nights ago with stable views up to X400 mag proved a little frustrating on the focusing front. Combined with 55° EP's and no tracking, I barely had time to observe between vibrations dying down and the next nudge, so a new mount may be on the horizon specifically for planetary and lunar work.

I love the 1.75" tripod/16" extension combination and so I had settled on the idea of an Orion SkyView Pro EQ mount (EQ5 class) with manual slow motion controls. In manual config I see EQ as preferable due to only having to track in one axis vs a manual alt/az.

BUT...….An iOptron AZ Mount Pro has become available, locally and at a very decent price. I hadn't planned on going back to a powered mount but given it's in-built battery and simple setup procedure, it looks pretty good. Also a little research confirms it will fit on my pier thus overcoming the tripod clashing issues with longer scopes (a little research also suggests they had/have a few problems too, so no warranty on this potential purchase).

There are pros and cons to both and a fair difference in purchase price, but for me the deciding factor comes down to....

Which of these two mounts will handle the scope the best, specifically with respect to vibrations?

What do you reckon!? Can anyone give first hand experience advice on an EQ5 class mount vs the AZ Mount Pro?

2 hours ago, mark81 said:

@parallaxerr sounds like a decent first session - especially with the use of those filters... How did you get on with the AZ4?

Mark

Hi Mark, the AZ4 is absolutely fine for low to medium power stuff, it makes a nice combo with the 120 for DSO work. It's only above about X150 where the damping time takes a bit too long, so I'm considering an EQ5 head or equivalent to go on my pier extension for planetary work, but there's no rush given that they're all hiding at the moment!

I had a rather pleasant observing session this evening. My mount has been setup and strapped down in the garden for a good week or so now, but the presence of the full Moon, high winds and some cloudier nights prevented me from going out. Tonight though I was presented with clear, steady skies and the Moon is late to rise, so I put the new Omni XLT 120 out to cool after dinner.

Went out to observe about 9.45pm with poorly adjusted eyes so started off just focusing in on a few bright stars at low power. I used the opportunity to try out some of my filters to see what effect they had on controlling the (minimal) CA in the achro. After a bit of to and fro, I decided to stack the Baader semi-apo and a #8 light yellow and to my surprise found they nearly completely eliminated CA, even at X200 mag on Vega with only a very slight yellow cast. So slight I believe because the un-filtered views through this scope are particularly cool.

After 10 minutes or so visiting Arcturus & Vega I could start to feel my eyes adapting and seeing fainter stars and by about 10.30pm I was surprised at just how much I could see with the naked eye. I was expecting a bit of a wash out given Stellariums estimation of my atmosphere & LP.

As I cruised around the Eastern extremity of my observable skies at X50 using a humble 20mm plossl, I stumbled in to the glob M92. I was not expecting to pick out anything faint this evening but it really popped into view. I decided to try the Great Cluster in Hercules just next door and was rewarded with a very nice view indeed. Changing to the 9mm LER yielding X110, I could resolve individual stars albeit very faint, seemingly quite deep into the core. This is the resolution I missed in the 4" scope and tonights view very much reminded me of the view through my C8 a few years ago. 

Seeing as I was in the neighbourhood, I panned across to Lyra to pick out the double double. Very clean split at X200.

To finish off I located the Ring Nebula with the 20mm, then with a UHC filter pushed the mag up to X110 again. I was rewarded with a very nice contrasty view with subtle hints of what looked like a twist in the ring.

Given that I was in two minds tonight, that was most enjoyable!

7 minutes ago, jock1958 said:

Question whats that little silver bracket on the bottom of your AZ4 mount for?

TADA.. they say a picture paints a thousand words! It's a mobile phone holder so I can use stellarium to pull up alt-az cords and find the fuzzies using the az ring and a wixey angle finder

10 minutes ago, dweller25 said:

Strap is a very good idea - I’m guessing you have a big metal screw in the ground ?

Yes, that's right. It's a ground anchor, cant remember what the original use for it was but it's about 12" long. It's been there for about 18 months now, never budges.

1 hour ago, John said:

I reckon your pillar adds a bit of stability though, and the strap from the central tray to the ground helps as well. These things might make all the difference.

Agreed. I found if I tap the pillar there was next to no vibration, but tapping the scope there was. This suggests the flex is in the mount head itself and the pillar and tripod are sturdy enough.

1 hour ago, John said:

I tried my ED120 on my AZ-4 a few times but overall I found that combination did not work for me other than at low to medium powers.

I should have mentioned the weight. The Omni with Crayford and finder weighs in at 6kg. Do you know what your ED120 weighs John?

I have, for a long time, restricted myself to the use of a Sky-Watcher AZ4 mount and for good reason. There’s no two ways about it, I like refractors. I’ve had quite a few over the last few years and the pick of the bunch was a lovely Sky-watcher Equinox 120ED. I picked the Equinox up at a bargain price and very much regret letting go of it, but it wasn’t getting the use it deserved. The mounting requirements were significant and to enable the scope to perform at its best I mounted it on a Giro Ercole atop a 16” steel pier extension and a CG5 2” stainless steel tripod. Having spent a lot of money arriving at this setup, I stopped using it. Why? Size & weight.

The whole mount assembly was very heavy. Combined with the required journey through the house to get to the garden (resulting in many door frame dings), followed by the many steps to set it up on the top level of our tiered garden, it just became too cumbersome and I stopped bothering.

Shortly after selling that setup I discovered the AZ4 and it was a bit of a revelation for me. With a bit of tuning I found I have a great Alt-Az mount with smooth motion that handled a 4” scope with ease. One of the features I particularly like is the fact that the scope rotates around the Az axis, whereas with Giro style mounts the scope is mounted out on an arm and the throw and motion of the scope at the eyepiece end felt a little un-natural to me. For a while I used a 102mm ED with the AZ4 which was a perfect match, but that scope didn’t really float my boat. Then I picked up an 80mm F11 Vixen achro which is a great performer, but of course all the while I’ve been suffering aperture fever knowing what a 120mm scope can pull in from my location.

So, I started researching how the AZ4 would handle a 120mm refractor, I read many posts and spoke directly via PM with several other owners. There were mixed opinions that ranged from “unusable” to “rock-solid” but of course there are variables such as the tripod used, the weight and focal length of the scope etc. I am confident that my AZ4, again mounted on top of a steel pier but this time on a 1.75” steel legged tripod is as sturdy as an AZ4 can get. This mount weighs considerably less than the Giro and 2” legged version and is far easier to handle. When I found a batch of new Celestron Omni XLT120 F8.3 achros for sale, I pulled the trigger.

First impressions of the scope on the mount were that it looked perfectly acceptable and everything balanced up nicely. The Axes remained smooth in operation giving me some confidence that it would all be OK. First light came at the end of last week. The forecast was not great with gusty winds and scattered cloud, but I setup anyway. The moon presented itself in the perfect pre-dusk position, nice and high just past the meridian and at approximately 50% phase.

The lighting was near perfect for observing one of my favourite lunar features – the Apennine Mountains and the Apollo 15 landing site at Mons Hadley. I decided I’d have a bash at Hadley Rille and set about testing the scopes performance at a range of magnifications right down to my shortest 5mm EP, yielding a mag of X200. The scope held up VERY well, far better than I had imagined it would. I noted that the view was particularly cool, compared to me previous ED scopes. CA was present of course, but only really became distracting at the higher mags. I tried the Baader semi-apo filter but didn’t really get on with it this time, instead opting for a #8 light yellow filter which suppressed the CA more than satisfactorily and only gave a very light cast to the image. The shadows of the Apennine Mountains were a deep dark black with fantastic resolution. The 5mm LER eyepiece presented a very sharp image which I was pleased about considering the image starting breaking down in my 80mm scope with this EP, obviously a function of the scopes aperture. In fact, so sharp was the image I pushed further using the 9mm LER barlowed to approximately 4.5mm yielding X222 and Hadley Rille was there in all its glory. Clearly defined at its Southern end with the Northern end a little harder to define, but it came and went with the seeing. The resolution of the image with this 120mm glass was notably superior to the 80mm.

When reasonable darkness set in I slewed the scope around to the East, away from bright moon and inserted the 32mm plossl, this time un-filtered. I scanned around waiting for my eye to adjust after the bright moon, taking in the very sharp pinpoint stars displaying no discernible CA at this low mag. I decided to carry out a star test and with my limited horizons, Arcturus presented itself well. The star test was all that I had hoped for. Very nice concentric rings inside of focus and slightly softer outside of focus suggesting slight under-correction. I am aware though that the spread of colour due to being an achro can cause the softness so would need a green filter to test properly. Most importantly though, the lens cell is collimated well so I know at least it’s performing at its best and I am more than happy with the result.

So far so good then. Very happy with the scope but how did the AZ4 perform?

I would say that the 120mm F8 frac has the AZ4 at its limit for high mag work. There was some wobble when the wind picked up, however I would not normally observe in such winds. Pre-empting vibration during focusing, I had already fitted the scope with a Sky-Watcher dual speed Crayford focuser which worked very well. The light touch required to focus with the fine knob did not impart excessive vibration, it was a level I can certainly live with. The limitation comes when manually tracking while observing. The 55° FoV of my short FL EP’s results in lots of manual correction at high mag with the associated vibration. A wider apparent FoV EP would be better suited here, or a tracking mount. Placing the target in the upper right of the FoV and allowing it to drift was the best option, allowing enough dwell time to make out fine detail, though at X222 the target moves fast!

My desire for more aperture though comes from improving DSO observations, and for this, at lower magnifications this setup will be AOK. With a 25mm EP giving me close to my known preferred exit pupil, vibration is not an issue and I’m really looking forward to seeing what can be pulled in come the Autumn when the skies darken and more interesting objects come in to my view. I am particularly looking forward to viewing the Veil Nebula considering the success I had with the 4” ED using an Astronomk OIII filter.

All in all, a positive first test of the scope and how the mount handles it. Hopefully I’ve put a bit more meat on the bones on the subject of how the AZ4 handles a 120mm refractor and this will help someone considering a similar setup to make an informed decision. If you give the AZ4 a solid foundation it can work well, depending on the type of observation you want to do. My setup is very sturdy and any residual  vibration comes from the mount head itself as opposed to the tripod, I think I’d be inclined to agree that this wouldn’t work on the aluminium legged version!

 Cheers,

Jon

I've laid this idea to rest now, t's an unknown scope and too expensive to take a risk on. I think it would have been a good fit for the AZ4, but as you say Mike, given it's short focal length it may not have been the best all-rounder anyway.

2 hours ago, mikeDnight said:

I'll still talk to you Jon.

See, I knew the "Tak pack" were friendly really 😆

Bringing the thread back down to earth with a bump, sorry, here's my latest frac. I always liked the look of the Omni XLT120 but it was never available as an OTA alone in the UK (at least that I could find). It's out of production now so I was surprised to find a batch of them for sale by Altair Astro recently, apparently they had the last "old new" stock from Celestron UK who finally broke out the mounts and OTAs to sell separately. Not a bad deal really at £199 versus the £269 of the equivalent Skywatcher Evostar and the Celestron has a collimatable cell to boot.

I immediately adorned it with a Skywatcher Crayford focuser (which is a far better, more snug fit than the standard R&P), Altair finder shoe which went straight on with the supplied screws and red dot finder. It comes in just over twice the weight of my 80mm Vixen @ 6kg, so time will tell if the AZ4 will cope. There are so many mixed opinions on this, I decided I just had to try myself.