jetstream

2 hours ago, Captain Magenta said:

Many instructions advise racking the focus-tube (and hence collimation-cap and viewing-hole) out as far as it can go, or even using an extender as I did, to allow the guaranteed-circular far end of the focus-tube and the edge of the secondary to come close together for accurate evaluation of circularity.

This adjustable sight tube works very well and very accurately. I removed the 24" spider/sec for a fiber batten tweak last night and re collimated. Sec is accurately centered and collimation is not perfect (no AC) but very very close. You can extend the tube into the focuser to get a really fine view of the sec edges. Fast, accurate, simple and expensive.

A good newt is hard to beat and I would think that you either have to splash out on an expensive SCT or get a "good" one to compete with the newt.

2 hours ago, piff said:

Millimetre for millimetre, is it considered that you get clearer images or greater magnification or both  from a refractor, or from a Schmidt-Cassegrain of equal aperture?

Which refractor? which SCT? generalizing is not the best option IMHO.

A top refactor offers such purity to the view.... and will take high mag, at a large price. However a top SCT type scope can deliver stunning views, @dweller25 might (does) have a good opinion.

Then there is the 200mm f6 newts out there that can make so many high end scope owners cringe under good seeing...

On 20/10/2019 at 12:36, estwing said:

John Nichol makes outstanding mirrors below F4...

Gerry, the bigger the dob the less ep's you use..most of my observing sessions are with the 21 and 8 mm ethos...Mapstar has plenty of nights where the 13 ethos is the only ep he uses in his 22".

Had a poor sky last night so I got around to fine tuning the 24" and tried different EP's with the Paracorr. The 21E/17E really work with the PC- TV knows what they are doing.

I can see why you guys only use a small few eyepieces now- whats your thoughts of the Delos in the bigger scopes? I'm thinking of a deep eyepiece or 2 for easy use with the Paracorr.

My Nikon HW so far wont work with the PC which is too bad, it is a superb eyepiece. The Docter is most likely out too, but I'll try TV's infocus adapter before getting the 13E.

2 hours ago, Piero said:

Still, if one spends 3K pounds in eyepieces, 500 pounds in a CC is not a big deal to me, particularly considering that the views through all the eyepieces will improve.

In my case there were a couple of issues for the wait- cost yes, with a but...I wanted to be re assured that the Paracorr would work very well, its too much money (for me) to buy and have not work.

Second, my 15" at f4.8 gives such good lunar/planetary views I didn't think it was needed, however I think an improvement will be made with the CC. I'm curious about 2 things- on axis sharpness and threshold objects with the CC.

Oddly enough I use far less eyepieces with the 24"? some might be on the chopping block, with a Delos or 2 coming (back) in. I just cant wait to try the 21E/Paracorr II on the Swan neb.... the Nikon HW might get chopped, we'll see.

Down the road I would investigate sub f4 dobs Piero, in the 16"-18" range and the corresponding need for truly engineered mirror cell design. Lockwood is one of the only makers really into this, but a couple of others can do it ie Terry O, not sure about EU. NV will add a different perspective on objects and offer much flexibility to observing.

Me, I'll slog away with a few pieces of polished glass and a dark sky lol!

10 hours ago, Piero said:

Before this, I want to reduce the currents in the tube and understand the interplay between fan and light shroud.

In my brief experience with truss dobs it seems to me they have unique likes. At times I leave my shroud pulled back at the top of the mirror box to allow any heat to rise up there. I cool with the fan-pre seacan that is- and then turn it off to observe, I find tiny blurring caused by the fan.

The white seacan keeps the 15" and 24" within 4 deg F of ambient, which is great and with no early morning dew. When its really cold I keep the shroud all the way on to combat body heat wrecking the views, this can make a big difference as does the stance taken to observe.

https://www.edmundoptics.com/resources/application-notes/optics/comparison-of-optical-aberrations/

16 minutes ago, Alan White said:

Is that Coma or
is that the Parabola of the mirror having differing focal distance centre to edge?
or is that Coma?

Sorry for such an odd question, just curious.

This link explains it simply, spherical aberration " Characterization

• Image Appears Blurred, Rays from Edge Focus at Different Point than Rays from Center
• Occurs with all Spherical Optics
• On-Axis and Off-Axis Aberration
• Third Order: W₀₄₀ = ρ^4"

Coma," Characterization

• Occurs When Magnification Changes with Respect to Location on the Image
• Two Types: Tangential (Vertical, Y Direction) and Sagittal (Horizontal, X Direction)
• Off-Axis Only
• Third Order: W₁₃₁ = Hρ³;cos(θ)"

58 minutes ago, Piero said:

Sounds great, Gerry! 

Any chance to test the Docter and Zeiss Zoom too? I've not read a comment on how those two eyepieces perform with the paracorr2. 

Thanks Piero,I will when the weather co operates - last night I had a tiny window to try it out. I wanted to see how it affected the 10BCO first but the Docter was next up but so was the moon. I hope this straightens out the Zeiss zoom, it doesn't like f4....

I can tell already the Paracorr is a winner Piero, I want to test it on those small faint averted galaxies to see any impact.

You buying one?

52 minutes ago, alan potts said:

Match made in heaven, 21mm E and the paracorr. Don't be afraid of going away from the markings for various eyepieces, I actually feel the 31mm Nagler is better a little away from where they say.

Alan

Thanks Alan, I will try this- what a difference the Paracorr makes.

The Televue Paracorr II finally arrived after almost going to the wrong address- this is life here in rural Ontario.

I'm most likely going to say what the dob mob already knows- this thing really works. It gave a super clean, textbook split of the Double Double with the 21E- edge to edge.  This set up gave what might be the best view of the Veil yet, actually Pickerings Wisp was a mass of twisted nebulosity right around that "bubble" I mentioned in other reports.

I had been told that the reduction of coma should in theory give me better contrast on nebula and the advice givers were extremely experienced optics and scope makers- if this one obs session is any indication it does.

The 30ES 82 was set up using Pensacks advice- I set up the 21E on "A" and focused, then the 30mm ES was focused using the Paracorr's adjustment on "F" roughly. This method worked well, however the 30ES did not offer the contrast the 21E did- by a long margin despite the greater illumination.  Large features or small on the Veil the 21E won handily.

The 10BCO is parfocal with the 21E and used "A" (using TV's Paracorr adapter).  NGC 7331 was observed with its bright core showing well, not all the fleas were observed but the pending moon and some very light high cloud moving in may have affected the view. Stephans Quintet needs very dark transparent skies to show well even in the 24", under the best conditions these galaxies show brightly but get down around 21 SQM mag and or avg to poor trans and the view is killed, observable yes, great view no.

The 10BCO/Paracorr showed M57's central star with ease- a very good sign.

In summary the Paracorr II in the 24" f4.1 dob worked really well. It seems to up the contrast on nebula in particular and doesn't seem to impact galaxy views but more time on this is needed. The 21E came into its own with this device, I was rocked back by the view on the Veil. BTW I have a 17E, 17 Nikon HW to compare to with no Paracorr...

The sky was 21.5 mag with avg trans that worsened with time.

13 hours ago, GavStar said:

I would say that 100 percent of my deep sky visual observing is done with nv now - I find it clearly better on nebulae, globs, galaxies and planetary nebulae.

I'm curious how NV does on some of the small unusual galaxies Gavin, ARP's and Hicksons- I viewed a strange little galaxy, kind of worm like with knots in it at high power, forget the name right now but very interesting.

have you tried observing some of these objects with NV?

I checked, it was ARP 81

On 03/10/2019 at 20:07, PeterW said:

.... can see stuff you can’t in a huge (£££) Dobs.... 

Peter

I think both technologies offer pros and cons- are there things like reflection nebula that NV suffers a bit or others?

15 hours ago, Ships and Stars said:

The Veil was also clearly visible without the OIII, but with much more 'background noise', i.e. stars competing for attention.

This is a VG sign, and seeing it no filter is a great bonus.

Congrats for a great night with the 20"!

Try that scope on IC1318 near Sadr.....

1 hour ago, scarp15 said:

Excellent, look forward to hearing about your forthcoming accounts Gerry. If that's OK so that readers who will be following your attempts, attached is some more info on this subject.  

https://observing.skyhound.com/archives/sep/Q2237+0305A.html

Perfect Iain!

Well the cats out of the bag now... this object and ones like it are a major reason I bought the 24". I'm fascinated by Einstein and other great minds like his. I want to see this classic example of light bending around the galaxy in warped spacetime and this really hits to the heart of why I'm a visual observer- I want to see it with my own eyes.

I have zero expectations to see this, I only hope I can get a glimpse of at least one image, "A" perhaps. Experienced DSO observers say 2 might be possible in the 24" and one very experienced one said "you never know, you might get them all".

Orthos are my only hope I think and I need the unusual combination of excellent seeing with excellent transparency.

This object will be my primary target for as long as its in a good position to view.

3 hours ago, scarp15 said:

What eyepiece, magnification will you anticipate for attempting this observation Gerry?

My plan is to locate the lensing galaxy, PGC 69457, 14-15 mag hopefully with the Docter 12.5mm UWA. If successful I will re align the Sky Commander on it and then try the 10mm BCO. Next will be the 10BCO/VIP @ 1.5x then 2x with both 15mm extensions. I have a VG 7mm KK ortho which will also be enlisted.

Plan B will have the Paracorr in place with a Delos possibly- sure wish I didn't sell them now...

When using the Sky Commanders realign option I can get back on target using a .14 deg tfov.

Mags will be 200x,250x,372x and 500x.

The Paracorr II should be delivered the end of next week and as Piero says I could really use the aperture stop for the Glatter laser.  An interesting thing to try is de collimating a newt in small steps to see what happens through the eyepiece.

16 hours ago, Marvin Jenkins said:

Last night was my first look at the Pleiades for quite some time. Through a low mag ep installed in a 130 newt I can only describe it as a bunch of diamonds in the sky.

What do I need to do or buy to see the reflection nebula? I am perfectly happy with how it looks (eye balls pop out) but if there is more to see I want to see it.

Marvin

How dark are your skies? The very best thing to do is get to truly dark, transparent skies- what eyepiece did you use?

Trying is a good description... all set up, the forecast good and dark adapted. The sky looks a bit strange, low extinction on the horizon, but my NELM is off? must be my eyes tonight as I was outside all day.

Yeah right..

The Sky Commander was programmed for PGC 69457 so all set to go. Warming up on Stephans Quintet showed the object very faint? not typical in the 24", hmmm

Note to self :  1-practise programming the Sky Commander before relying on it- I was massively off, messing up the Dec number

                        2- check the Aurora forecast before setting up the scope!

The Northern Lights, hiding behind trees on the ridge horizon washed everything out pretty bad, so I went the 200yds to the dock to watch them after the scope was put away.

The first try on Einsteins Cross was a learning experience lol!

44 minutes ago, John said:

Actually I think low light scatter around bright targets at medium to high magnifications is quite an important practical characteristic. Light scatter is one of the issues that can actually make seeing certain target types eg: faint planetary moons and very uneven brightness binary stars, somewhat more difficult or even impossible if it is extensive.

 

Yes, thats what I meant and corrected my post- thanks for the heads up.

@oldfruit I hope sidetracking your thread a bit is OK, I don't mean to de rail your paracorr purchase/experience.

3 minutes ago, Piero said:

I think it could lose a tiny bit on axis, but the improvement across the field should be huge at f4. You will have the whole field within diffraction limited threshold. The increase in magnification could also help you spot some other faints..

Were going to see where the Paracorr fits into Suiters wobbly stack for sure and I agree I might lose a bit on axis to induced aberration. My scopes are well above the diffraction limit so hopefully there is some wiggle room across the board.

A main interest is to see if extended objects contrast is increased near the edge of view resulting from decreased comatic smear. My experience says "you never know" lol!

A side note, but interesting : from TV's site. It seems low obstuction also helps with exit pupil flexibility.

With refractors larger pupils do waste aperture. But the magnification is so low that the wasted aperture is of little concern: both image brightness and resolution are as great as possible at that magnification. With reflectors, however, larger pupils do waste light, but primarily because the black spot in the pupil caused by the secondary obstruction becomes larger. Both light loss and field shadowing occur with reflectors, but as with refractors there is no resolution loss because of the low power.

As explained in the text, there is no practical limit to the low magnification that can be used with a refractor. But the secondary obstruction found on most reflectors does set limits, because the shadow spot it forms in the exit pupil grows as the magnification is reduced. Consider this extreme example of an exit pupil formed by an 8-inch Schmidt-Cassegrain with a central obstruction equal to 43 percent of the aperture's diameter. A telecompressor lens and long-focal-length eyepiece give 14x magnification. While the central shadow remains 43 percent of the exit pupil's diameter, it is now 6.2 millimeters in diameter and would nearly fill the 7-mm pupil diameter of the dark-adapted eye."

4 hours ago, Raph-in-the-sky said:

Have you tried all the ES82°? If I was to buy 3 or 4 which one do you recommend? Are there some that are considered weaker?

I personally like the ES 82's in mid to high focal lengths- more to do with the targets really. From around 10mm on down low scatter is high on my list and most widefields enable scatter which I dislike for lunar/planetary/ and nebula/galaxies next to bright stars. Our 6.7mm ES 82 is a great, sharp eyepiece but with the mentioned scatter.

This is a personal preference, thats all and the ES eyepieces are VG performers overall.

5 hours ago, Piero said:

Curious to know how you will find it, Gerry.

Were going find out if it "disappears" when viewing or if faint objects do when using it lol!

4 hours ago, Mark at Beaufort said:

Iain a nice reminder. I fancy having another go with my 130P Heritage - I know that Gerry @jetstreamhas been successful with this scope so when I go to our dark outreach site I will take the Heritage as well.

I can't wait to hear of your success not only on the Merope, but the whole beautiful dark lane and glowing complex all through the Pleiades.The H130 is so good here, still baffles me honestly.Ours loves the 24 ES 68, an excellent eyepiece.

The Merope itself can take a bit more mag and something like a low scatter 20mm TV plossl or the 18mm BCO can be an asset, but the 24ES 68 is my goto. I'm not an expert but this object and its area is one of my favorite, most observed targets. It is one of the most stunning in the sky.

Good luck Mark and eagerly waiting H130 reports!

I'm ordering a Paracorr myself and am happy , very happy to say that my Astrosystems dob has enough room-3 1/2"- for the Paracorr without hitting my filter slide...this is great news for me as I love the filter slide.

I'm going to try the 30ES 82 as my wide neb eyepiece and see how it is.

On 22/09/2019 at 13:54, oldfruit said:

wow, what a difference a Paracorr makes.

Great that it is working well for you Mark!