Lukehurst-Nichol classic dobsonian modifications

[niallk]

A beaut of a scope Piero!!  Enjoy + clear skies - looking fwd to reports

[jetstream]

2 hours ago, Piero said:

We can talk in more detail if you like.

Sounds good- and it might be informative for others to banter here a bit- such as...

Can you tell me the measurement from the center of the sec to the focal plane (roughly)? or to the top of focuser? I'm always curious as to where makers set the fully illuminated field vs central obstruction %. I'll run Mels calculator, both my 15" and 24" have nicely illuminated fields and run 20% and 19% roughly.

[Piero]

6 hours ago, jetstream said:

Sounds good- and it might be informative for others to banter here a bit- such as...

Can you tell me the measurement from the center of the sec to the focal plane (roughly)? or to the top of focuser? I'm always curious as to where makers set the fully illuminated field vs central obstruction %. I'll run Mels calculator, both my 15" and 24" have nicely illuminated fields and run 20% and 19% roughly.

I can measure this this evening when back from work. 

For the time being, I can say that CO is 20.3%.

When talking with David about altitude bearings, we opted for a diameter of 15" which was about the diameter of the UTA. Therefore, the distance from the centre of secondary to the plane where the Moonlite is installed should roughly be 7.5" plus about 1" due to a) the UTA side (which is thicker on the focuser side), b) short Moonlite spacer, and c) metal plane to attach/detach the focuser+finder.

To this distance the focuser travel is added.

 

[JOC]

That's a bit of a stonker.  Hope you get the wheels dirty soon 😉

[Tzitzis]

Wow that's a beast. I'm trust that you put it in a good use.  

[Stu]

4 minutes ago, Tzitzis said:

Wow that's a beast. I'm trust that you put it in a good use.  

Given Piero's observing ability with even a 60m scope, I'm sure he will see some amazing objects with this new dob 👍👍👍

[Piero]

2 hours ago, Stu said:

Given Piero's observing ability with even a 60m scope, I'm sure he will see some amazing objects with this new dob 👍👍👍

Thank you, Stu! Too kind!

About the observing, I hope so!

[barkis]

I can only echo the accolades all the other thread contributers have written.  I would just like to add that when quality scopes contain  quality wooden structures as mount and support mechanisms, it makes me very happy. Wood is a wonderful medium to include in a large telescope,  and this instrument is a very fine example.   I'm sure you will get a great deal of pleasure using your  new acquisition. 

I wish you clear skies so you can get the results this scope is capable of.

Ron.

 

 

Edited June 25, 2019 by barkis

[Piero]

I'd like to thank everyone for the very kind comments. 

I am lucky to be able to afford a telescope like this. David Lukehurst did a great job and I'm looking forward to giving this scope a first light. 

[John]

22 hours ago, Piero said:

 

Anyway, I only plan to use the above eps with this telescope, therefore no 1.25" eps...

 

You might find that you want to be able go higher than 270x with a good mirror like that in the scope. Over the past few years that I've had my 12 inch F/5.3 I've found myself using 300x - 400x more often than I ever thought I would. This sort of magnification helps to tease out faint point sources such as planetary moons around Uranus and Neptune, central stars of planetary nebulae etc, etc.

I've also found 320x (Pentax 5mm XW) really useful for picking out the finest lunar details such as Plato cratelets beyond the "big 4" and the central rille in the Vallis Alpes.

Obviously the seeing needs to co-operate as well but its useful to be able to "go to 11" sometimes

 

 

[Paz]

That's a great looking scope, you ought to set it up in the living room as an ornament when you're not observing with it.

[Piero]

7 minutes ago, John said:

You might find that you want to be able go higher than 270x with a good mirror like that in the scope. Over the past few years that I've had my 12 inch F/5.3 I've found myself using 300x - 400x more often than I ever thought I would. This sort of magnification helps to tease out faint point sources such as planetary moons around Uranus and Neptune, central stars of planetary nebulae etc, etc.

I've also found 320x (Pentax 5mm XW) really useful for picking out the finest lunar details such as Plato cratelets beyond the "big 4" and the central rille in the Vallis Alpes.

Obviously the seeing needs to co-operate as well but its useful to be able to "go to 11" sometimes

Thank you, John! 

I realise my lack of clarity . What I meant was those 4 eyepieces plus the VIP barlow. Absolutely, I want to go beyond 270x, seeing permitting! 

The docter plus VIP will give slightly more than 300x, similarly to your Pentax xw. 

[Piero]

2 minutes ago, Paz said:

That's a great looking scope, you ought to set it up in the living room as an ornament when you're not observing with it.

Thanks, Paz. Yes, it is stored in the living room, although dismantled, as this is easier to take it out. Plus, the whole gem is almost 2m tall!

[FenlandPaul]

2 hours ago, Piero said:

Thank you, John! 

I realise my lack of clarity . What I meant was those 4 eyepieces plus the VIP barlow. Absolutely, I want to go beyond 270x, seeing permitting! 

The docter plus VIP will give slightly more than 300x, similarly to your Pentax xw. 

Happy to lend you my Nagler Zoom on nights of good seeing! 😀

[Piero]

16 minutes ago, FenlandPaul said:

Happy to lend you my Nagler Zoom on nights of good seeing! 😀

Thanks, Paul!

I should be okay at high powers. My zoom plus VIP can go to more than 570x. Then there is the HR 2.4mm (755x) and in the most extreme case I could VIP barlow the two HRs and go above 1000x.

Will need to practice with tracking on the moon, first.

[John]

I have used my 2-4mm Nagler zoom quite often with my 12 inch dob, which I didn't really anticipate when I bought the zoom - I thought it would be in the refractor focusers mainly. I can't say that I've used the 2.5mm and 2mm settings that often though with the 12 - apart from the seeing, my floaters tend to hog the field of view with that exit pupil !

[maw lod qan]

Very beautiful scope! I hope it gives you many years of enjoyable viewing.

[Piero]

On 25/06/2019 at 08:25, Piero said:

I can measure this this evening when back from work. 

For the time being, I can say that CO is 20.3%.

When talking with David about altitude bearings, we opted for a diameter of 15" which was about the diameter of the UTA. Therefore, the distance from the centre of secondary to the plane where the Moonlite is installed should roughly be 7.5" plus about 1" due to a) the UTA side (which is thicker on the focuser side), b) short Moonlite spacer, and c) metal plane to attach/detach the focuser+finder.

To this distance the focuser travel is added.

 

@jetstream here are more accurate measurements.

Altitude bearing diameter: 15 in

UTA external diameter: 14 in

Approx distance between Sec Mirror centre and back of the focuser is 6.5 in. Note that there is .5 inch of moonlight spacer too.

Sec mirror MA is 62mm

Edited June 28, 2019 by Piero

[jetstream]

Excellent!

These true numbers give a fantastic illumination:

" Remember that illumination may drop to 70 % for visual use.

---

Off-Axis	Illum.	Light Loss
0.00 mm	100.0%	0.00 mag
2.00 mm	100.0%	0.00 mag
4.00 mm	100.0%	0.00 mag
6.00 mm	100.0%	0.00 mag
8.00 mm	100.0%	0.00 mag
10.0 mm	100.0%	0.00 mag
12.0 mm	100.0%	0.00 mag
14.0 mm	100.0%	0.00 mag
16.0 mm	100.0%	0.00 mag
18.0 mm	99.88%	0.00 mag
20.0 mm	96.18%	0.04 mag
22.0 mm	90.50%	0.10 mag
24.0 mm	83.85%	0.19 mag
26.0 mm	76.64%	0.28 mag"

 

What a great set of numbers Piero!

[jetstream]

6 hours ago, Piero said:

here are more accurate measurements. 

Piero, here is the 24"- opticians including Mel tell me that as long as bit of the field is fully illuminated and the edge is above 70% all is good espc if it allows low central obstruction- the trade off is worth it. In my experience this is very true. I'm not a fan of central obstructions over 30% for sure, less than 25% is better and yet some highly obstructed SCT's give super views...

thoughts?

" Remember that illumination may drop to 70 % for visual use.

---

Off-Axis	Illum.	Light Loss
0.00 in	100.0%	0.00 mag
0.10 in	100.0%	0.00 mag
0.20 in	100.0%	0.00 mag
0.30 in	99.93%	0.00 mag
0.40 in	98.42%	0.01 mag
0.50 in	96.29%	0.04 mag
0.60 in	93.93%	0.06 mag
0.70 in	91.44%	0.09 mag
0.80 in	88.89%	0.12 mag
0.90 in	86.30%	0.15 mag
1.00 in	83.69%	0.19 mag"

[Piero]

1 hour ago, jetstream said:

Piero, here is the 24"- opticians including Mel tell me that as long as bit of the field is fully illuminated and the edge is above 70% all is good espc if it allows low central obstruction- the trade off is worth it. In my experience this is very true. I'm not a fan of central obstructions over 30% for sure, less than 25% is better and yet some highly obstructed SCT's give super views...

thoughts?

" Remember that illumination may drop to 70 % for visual use.

---

Off-Axis	Illum.	Light Loss
0.00 in	100.0%	0.00 mag
0.10 in	100.0%	0.00 mag
0.20 in	100.0%	0.00 mag
0.30 in	99.93%	0.00 mag
0.40 in	98.42%	0.01 mag
0.50 in	96.29%	0.04 mag
0.60 in	93.93%	0.06 mag
0.70 in	91.44%	0.09 mag
0.80 in	88.89%	0.12 mag
0.90 in	86.30%	0.15 mag
1.00 in	83.69%	0.19 mag"

Thanks Gerry!

what is the CO of your 24" dobson?

[John]

Mine is 21%

[Piero]

5 minutes ago, John said:

Mine is 21%

Pretty much like mine: 20.3%

Edited June 28, 2019 by Piero

[jetstream]

29 minutes ago, Piero said:

Thanks Gerry!

what is the CO of your 24" dobson?

I'm at 19% with the 24" and if I remember 21% with the 15". My playing around tells me 37% I don't like, 30% is better but 25% and less is where its at , for me anyway.

[Piero]

It's a bit windy, but the dob is ready for tonight!