Eye piece advise for 300p

[JOC]

3 minutes ago, Barry-W-Fenner said:

Being inexperienced I assumed that it was down to the scope resolving them larger.

No, I don't think so, in fact I don't think there is any scope out there size wise that makes stars look like discs (the only exception being Sirius which the atmosphere often renders as a monster raving party star light show).  The jump from what I've got to what you have scope wise  is very slight.  It might permit slightly more magnification of something like a true planet, but it is marginal and would require decent conditions to improve hugely on the x200 or x250 which is the ultimate maximum I get from my scope.   What your larger mirror has purchased over mine is the ability to catch a bit more light to render DSO's more clearly - which might be why you have succeeded with the cats eye nebula, you might just have tweaked that into better focus too - you will be able to push very slightly more magnification of objects that I can, but it won't be huge.  Though if that's the best you can manage on Arcturus and Vega I'd surprised if you got sufficient focus to get the best views of the cats eye nebula and maybe you have been impressed with a less than ideal view of that too.   I doubt you will get much use out of and EP smaller than around 4mm in UK conditions - I top out at around 5mm on a good night.

I guess it might be worth checking the collimation of the scope http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/ Follow the linked to guide to the letter no matter how odd the instruction and you won't go wrong.  I can't advise on the focusser set-up, but there will be folks here that will know if it looks correct.  You certainly are not getting the best view your scope or EP's can offer if you can't improve on the shots of the stars above - you absolutely need to resolve those bright pinpoints of light.

 

[Geoff Barnes]

I know what @Barry-W-Fenner means regarding bright stars with a 300mm Dob, I get the same affect with mine. It is only noticeable with the very brightest stars like Sirius, Arcturus, Vega etc. which do show a kind of bloated form, even with perfect collimation. All the dimmer stars do exhibit as pinpoints of light. It is just the nature of the beast with a 300mm SW Dob.  

[Barry-W-Fenner]

45 minutes ago, Geoff Barnes said:

I know what @Barry-W-Fenner means regarding bright stars with a 300mm Dob, I get the same affect with mine. It is only noticeable with the very brightest stars like Sirius, Arcturus, Vega etc. which do show a kind of bloated form, even with perfect collimation. All the dimmer stars do exhibit as pinpoints of light. It is just the nature of the beast with a 300mm SW Dob.  

Hi Geoff,

Thanks for the confirmation. Your description is exactly what I am experiencing.  Only the brightest stars show as per my pic. And to be honest my pics dont really do much justice. They are very clear bright orbs?!

Have you changed your focuser on your 300p? If so did you use the spacer that came with it. I only ask as I do feel I am using quite a large amount of the back focus currently as per my pic.

 

Cheers

 

Barry

[Barry-W-Fenner]

12 hours ago, niallk said:

The Cat's Eye is a treat 8-9mm and 12-13mm should be good choices, and pushing the mag higher can be worth it too.

I was going to ask if you have an O-III filter?  With a 300mm mirror it could be a good call for planetary nebs.

Afternoon Niallk

Sorry I missed your post!

I do have an O-III filter, I havent used it on planetary nebula yet. Perhaps I should give it a go to see if I can bring out anymore detail. So far my best views of the Cats Eye have been with my 12mm at x125 mag. The detail at this power is very good. the central star shows constant and the nebula has a small amount of structure to it. Very impressive.

I tried my 8mm x 187 mag but lost quite a bit of detail and it started to look fuzzy.

Thank you

Barry

[Alan White]

On 15/06/2020 at 13:08, Barry-W-Fenner said:

Long term I am going to do my best to purchase 3-4 high end eye pieces and stick with them, As you have mentioned though this is a very slippery slope 🙂

Good luck on that one Barry, many before you have said the very same......... and many know where it ends 

[John]

Personally I don't find filters make a big difference to the Cat's Eye or Blinking planetary nebulae. They can make the central star in those nebulae harder to see though !

The Veil Nebula is becoming better and better placed now and that's where the O-III will really earn it's keep.

 

[Louis D]

2 hours ago, JOC said:

No, I don't think so, in fact I don't think there is any scope out there size wise that makes stars look like discs (the only exception being Sirius which the atmosphere often renders as a monster raving party star light show).

Betelgeuse has been resolved by several large observatory telescopes such as the  European Southern Observatory's Very Large Telescope as in the images below highlighted on APOD earlier this year.

[Barry-W-Fenner]

12 minutes ago, John said:

Personally I don't find filters make a big difference to the Cat's Eye or Blinking planetary nebulae. They can make the central star in those nebulae harder to see though !

The Veil Nebula is becoming better and better placed now and that's where the O-III will really earn it's keep.

That the view I had on the O-III, Useful for The Veil and the North American nebula. I look forward to my 1st views of them.  As the Cats eye shows very nicely without a filter I assumed the O-III  would worsen the View. I will give it a try though!

Don't get me started on the Blinking planetary! I tried to hunt it down for quite some time last night but had no joy.

 

[JOC]

13 minutes ago, Louis D said:

Betelgeuse has been resolved by several large observatory telescopes such as the  European Southern Observatory's Very Large Telescope as in the images below highlighted on APOD earlier this year.

Interesting........but I bet they still have a bit more under their belts than a 300P!

[Geoff Barnes]

2 hours ago, Barry-W-Fenner said:

 

Have you changed your focuser on your 300p

Yes I have, I replaced it with this dual speed upgrade kit and am pleased with it, good solid quality and simple to fix...

https://www.365astronomy.com/Lacerta-Dual-Speed-1-10-Microfocus-Upgrade-Kit-for-Skywatcher-Crayford-Focusers.html

[Guest]

Sorry Barry, but I couldn't resist! 🤣

https://youtu.be/mGq-jqy6-AM

[Don Pensack]

5 hours ago, Barry-W-Fenner said:

Morning Andy,

For reference this is what Arcturus & Vega look like at focus for me.

The 4 bright short diffraction spikes are from the spider holding the secondary mirror, and are normal.

The other long spike is of more concern, however, and you gave a clue of its cause--the focuser.

You mentioned the focuser was nearly all the way in when focus was achieved, and it seems logical to conclude it is sticking into the light path to the mirror and causing a massive spike.

If the focuser is at approximately that angle relative to the spider vanes, that would cinch the identification as caused by the focuser.

So how to get it out of the light path to remove the diffraction?  Well, it would focus farther out if it were shortened, and I think I have a way:

--get rid of the 1.25" adapter that you now use and instead use a tall 1.25" adapter like the Baader Click-Lock, or an Antares Twist-Lock, or something with at least 10mm of height above the focuser.

This would move the eyepiece in quite a bit, and require the focuser be moved out to compensate.  That might be enough to get the focuser out of the light path.

You can check to see how much it intrudes into the tube when you're in focus.  You want the focuser to not be inside the tube at all when the eyepiece is focused.

Chances are there is not a lot of clearance between the mirror and the tube.  If the inside diameter of your upper tube assembly is less than, say, 40mm larger than the mirror, the tight clearance

could easily lead to having the focuser intrude into the light path.

 

You also have the possibility of simply dropping the UTA toward the primary by 10-20mm to experiment with seeing whether the focuser is at fault.  That would require moving the focuser out by the same amount.  If the long extra diffraction spike disappears, then you know what causes it and what you have to do to eliminate it.

 

Edited June 16, 2020 by Don Pensack

[Pixies]

6 minutes ago, Don Pensack said:

--get rid of the 1.25" adapter that you now use and instead use a tall 1.25" adapter like the Baader Click-Lock, or an Antares Twist-Lock, or something with at least 10mm of height above the focuser.

Baader Click-Lock on sale in the For Sale section just now. Spooky!

[bomberbaz]

26 minutes ago, Don Pensack said:

The 4 bright short diffraction spikes are from the spider holding the secondary mirror, and are normal.

The other long spike is of more concern, however, and you gave a clue of its cause--the focuser.

You mentioned the focuser was nearly all the way in when focus was achieved, and it seems logical to conclude it is sticking into the light path to the mirror and causing a massive spike.

If the focuser is at approximately that angle relative to the spider vanes, that would cinch the identification as caused by the focuser.

So how to get it out of the light path to remove the diffraction?  Well, it would focus farther out if it were shortened, and I think I have a way:

--get rid of the 1.25" adapter that you now use and instead use a tall 1.25" adapter like the Baader Click-Lock, or an Antares Twist-Lock, or something with at least 10mm of height above the focuser.

This would move the eyepiece in quite a bit, and require the focuser be moved out to compensate.  That might be enough to get the focuser out of the light path.

You can check to see how much it intrudes into the tube when you're in focus.  You want the focuser to not be inside the tube at all when the eyepiece is focused.

Chances are there is not a lot of clearance between the mirror and the tube.  If the inside diameter of your upper tube assembly is less than, say, 40mm larger than the mirror, the tight clearance

could easily lead to having the focuser intrude into the light path.

 

You also have the possibility of simply dropping the UTA toward the primary by 10-20mm to experiment with seeing whether the focuser is at fault.  That would require moving the focuser out by the same amount.  If the long extra diffraction spike disappears, then you know what causes it and what you have to do to eliminate it.

 

Sorry @Don Pensack surely if you add height to the focuser you are then having to wind the focuser in further to compensate or did I misunderstand what you meant?

Would pushing pushing your primary mirror up 5mm not be another option assuming that is there is enough travel!

Steve

[Barry-W-Fenner]

45 minutes ago, Don Pensack said:

You mentioned the focuser was nearly all the way in when focus was achieved, and it seems logical to conclude it is sticking into the light path to the mirror and causing a massive spike.

Afternoon Don,

Thank you for your informative posts, They have been of great help.

It actually the other way around. My focuser is pretty much all the way out to gain focus. I used the term back focus so hopefully that is correct. Anyhow, The blow pic is the position my focuser is in to achieve focus. In my opinion it seems to far out, There is hardly any of the focuser in the tube to obstruct the mirror.

When I put on my DS focuser there was a spacer between the standard focuser and the tube, As seen in the pic. I put this on to my DS focuser as I assumed it was required to fit the 300p? I am now wondering if this is having an effect?

Thank you

 

Barry

[Guest]

Barry, you said in another thread that you had collimated the new scope with a laser collimator. Could this have caused you problems? 

[Pixies]

I've seen that extra diagonal spike when the tube hasn't cooled completely.

[Barry-W-Fenner]

41 minutes ago, merlin100 said:

Barry, you said in another thread that you had collimated the new scope with a laser collimator. Could this have caused you problems? 

Hi Merlin,

I did a collimation but there wasn't a huge amount of adjustment.  I was going to check my collimation last night after setting up, However I couldn't find my laser anywhere, Naturally it jumped out in front of me this morning and was looking at me the whole time!

I will double check it next time i set up the 300p

The sky is clearing a bit here now after a mega downpour, I might get the 200p out tonight!

 

Baz

[Barry-W-Fenner]

2 minutes ago, Pixies said:

I've seen that extra diagonal spike when the tube hasn't cooled completely.

That's interesting.  The scope was out for about 30mins approx cooling before I started viewing, Perhaps it wasn't quite at the optimal temperature.

 

[Barry-W-Fenner]

I am pretty happy with the view so far. They have been very good all around and sometimes exceptional.

 

My main concern is to find out if the focuser is out to far as I have very little outward focus left available currently.

 

Cheers

[Pixies]

2 minutes ago, Barry-W-Fenner said:

That's interesting.  The scope was out for about 30mins approx cooling before I started viewing, Perhaps it wasn't quite at the optimal temperature.

 

I have seen that spike on my 8" dob after 30 minutes, but gone at 60.

[John]

43 minutes ago, Barry-W-Fenner said:

..My main concern is to find out if the focuser is out to far as I have very little outward focus left available currently.

 

 

My guess is that it might be something to do with the focuser upgrade. If the replacement unit is lower in profile than the one that it replaced, the drawtube will need to be racked out further to get eyepieces to focus.

I've marked the key distance on the image below. If this was a bit longer when the original focuser was installed, that would explain what is happening.

 

 

[Barry-W-Fenner]

7 minutes ago, John said:

I've marked the key distance on the image below. If this was a bit longer when the original focuser was installed, that would explain what is happening.

Thank you John. Im outside now setting up the 200p to cool. I will check the height of the standard 300p focuser aswell.

I won't be using the 300p tonight. Its just started to brighten up after a downpour. I am not confident that it is going to stay dry, I need something I can put away quickly 😁

[Barry-W-Fenner]

49 minutes ago, John said:

My guess is that it might be something to do with the focuser upgrade. If the replacement unit is lower in profile than the one that it replaced, the drawtube will need to be racked out further to get eyepieces to focus.

I've marked the key distance on the image below. If this was a bit longer when the original focuser was installed, that would explain what is happening.

 

 

I have had a look at the stock 300p focuser and my skywatcher DS model. They are both measuring 65-70mm the marked areas above. I would go as far as to say the actual focuser bodyis identical and it's just the gears, nobs that are replaced to create the 10.1 speeds.

I could be being ott but I do feel something is not quite right with the 300p focuser area.

🤔🤔🤔

🤔🤔🤔

[bomberbaz]

have you collimated it since you got it Baz, how far in is the primary. Perhaps this is screwed in quite a way and is pushing your focuser to far out.