Not in the mood... :/

[clarkpm4242]

I do make a habit of trying to be prepared for a good break in the clouds.  Am a weather geek and check out forecasts and technical weather charts.

In spite of this I also struggle.  My best solution is to have a large, strong espresso well ahead of time so that I have the necessary omph to actually get set up!

Staying awake after is another problem.

Cheers

Paul

[John]

1 hour ago, Stu said:

That's not quite true John.... I doubt you'd get an APM LZOS TMB GTi 130mm f9.2 for £879, or if you did can you let me know where!!!  

Fair point Stu. I should have been more specific - the Tak and LZOS 130 did cost more than that. The other 3 cost quite a bit less though.

But I know Mike was just trying to be positive, which is appreciated

 

 

[furrysocks2]

On 28/02/2017 at 20:51, furrysocks2 said:

Put in 10 hours building a custom (squint) shed for the garden today so am pretty knackered.

Another 9 hours today. Here's the moon and Venus...

Many compound mitres - totally brain-fried. It had better not be clear again tonight... :/

[Dave In Vermont]

10 hours ago, Mr Spock said:

Psychology? Along with chemistry, optics, speleology, herpetology and a whole load of other things I can't remember off the top of my head - one wonders what you do in your spare time?

I write, of course!

See what happens when you pack a bored 12 year old off to MIT & Harvard?

Dave

[Stu]

39 minutes ago, Dave In Vermont said:

I write, of course!

See what happens when you pack a bored 12 year old off to MIT & Harvard?

Dave

MIT at 12, that's impressive Dave...

[Paz]

9 hours ago, cloudsweeper said:

Anyway - I'm back into the thrust of observing - got up at 2.30 and had a look at Jupiter - 2 bands, 4 moons.  Masking off most of the aperture in the ST120 reduced the glare and fringing, so at under x100 he was looking great.  

I then scanned some stars and wondered why they were so dim.  Dohhh - open up the aperture again!

Doug.

I've done this on occasion with my ST120 - I've also on occasion thought things looked dimmer than they should only to realise I'm still looking through my finder scope when I thought I was looking through my main scope - it's easy to forget in the dark when I'm concentrating!

[JOC]

On ‎01‎/‎03‎/‎2017 at 11:24, Grotemobile said:

https://www.firstlightoptics.com/moon-neutral-density-filters/variable-polarizing-moon-filter.html

This is what I use on Jupiter Doug. Works very well.

Ooo...this was a useful spot - as some will know Jupiter is on my radar over the next couple of months and I've just bought precisely the same filter as the one in that link from the classifieds.  I was going to use it on the moon, but will notw also try on Jupiter :-)  Not only that, but I also know it's 'parentage'!

[cloudsweeper]

8 minutes ago, JOC said:

Ooo...this was a useful spot - as some will know Jupiter is on my radar over the next couple of months and I've just bought precisely the same filter as the one in that link from the classifieds.  I was going to use it on the moon, but will not also try on Jupiter :-)  Not only that, but I also know it's 'parentage'!

JOC - presumably you meant you'd now try it on Jupiter!  Also Venus.  Good plan - get the glare down.

Doug.

[JOC]

Hi Doug - Def.  NOW!  LOL 

Incidentally I saw a video on YouTube of a chap showing one of these two part filters and I thought, usefully, he showed one part of the filter on the bottom of the EP and the other bit dropped into the eye cup so that you could still rotate it, but more easily than keep removing the EP - I thought I might try that approach.  Yes, I was going to try Venus two - she seems a prime candidate - I must admit Jupiter had not occurred to me as a target for it, I didn't get the impression from just a quick look at her that she would be bright enough for it.

[cloudsweeper]

15 minutes ago, JOC said:

Hi Doug - Def.  NOW!  LOL 

Incidentally I saw a video on YouTube of a chap showing one of these two part filters and I thought, usefully, he showed one part of the filter on the bottom of the EP and the other bit dropped into the eye cup so that you could still rotate it, but more easily than keep removing the EP - I thought I might try that approach.  Yes, I was going to try Venus two - she seems a prime candidate - I must admit Jupiter had not occurred to me as a target for it, I didn't get the impression from just a quick look at her that she would be bright enough for it.

That could work, yes - I suppose it depends on the size of the eyeguard, and of course how high you are aiming the 'scope!  Probably no good for my polarising filter, since it's a 2 incher!

I guess your 'scope has one of those "inner covers", so you can mask off most of the opening, but just leave that small inner opening.  That is another very easy way of getting the glare down.

Doug.

[JOC]

2 hours ago, cloudsweeper said:

I guess your 'scope has one of those "inner covers", so you can mask off most of the opening, but just leave that small inner opening.  That is another very easy way of getting the glare down.

Doug.

TBH I'm not sure.  The telescope has a functional plastic 'lid' that is a great fit in the top of the bottom  section of the OTA.  In the plastic lid are two purposefully formed raised circles about 3" across.  One with a removeable cap.  I've been assuming the prime function of the plastic lid is in storage to keep the dust off the primary mirror, but the purpose of the removable cap has baffled me.  Surely you couldn't leave the plastic lid in place whilst the telescope was in use even if you removed the smaller inner lid?

[furrysocks2]

33 minutes ago, JOC said:

TBH I'm not sure.  The telescope has a functional plastic 'lid' that is a great fit in the top of the bottom  section of the OTA.  In the plastic lid are two purposefully formed raised circles about 3" across.  One with a removeable cap.  I've been assuming the prime function of the plastic lid is in storage to keep the dust off the primary mirror, but the purpose of the removable cap has baffled me.  Surely you couldn't leave the plastic lid in place whilst the telescope was in use even if you removed the smaller inner lid?

It's used for "stopping down" - reducing the aperture to reduce brightness and/or not allowing light to the edges of a lens/mirror which contribute most to aberrations or scattering (think bevelled edge mirror). That's my understanding. You can also leave it open to let a dewed up mirror or lens dry out while still keeping most of the dust off it.

[JOC]

Just now, furrysocks2 said:

It's used for "stopping down" - reducing the aperture to reduce brightness and/or not allowing light to the edges of a lens/mirror which contribute most to aberrations or scattering (think bevelled edge mirror). That's my understanding. You can also leave it open to let a dewed up mirror or lens dry out while still keeping most of the dust off it.

Hi furrysocks2 - many apologies for railroading your thread, but this is interesting info.  I had no idea it was useful for more than a dustcap!  However, out of interest I've also just found this photo of it being used for solar filters too http://www.ebay.co.uk/itm/Bespoke-Engineered-Multi-Filter-Sol-Vu-Solar-Observing-Filter-For-Telescope-46-5-/262858216857?hash=item3d33921599:g:T2cAAOSwPcVVlXsj I had no idea that it could ever be used like this - in fact I am quite stunned that the 'off centre' hole can still provide an image.  However, I am quite interested in that kit in the ebay ad.  A far cheaper way of looking at the sun that buying a full 8" filter for my telescope.

[SilverAstro]

1 hour ago, JOC said:

In the plastic lid are two purposefully formed raised circles about 3" across.  One with a removeable cap.

If the hole is positioned between the spider vanes it would also remove diffraction spikes from bright stars, assuming that one had an excess of starlight ! but the imaging boys seem to make do with similar apertures !! Also it removes the central obstruction and turns a Newt into more like a frac.

Odd that the second molding is not removable, else it could have been used as a Hartmann or Scheiner focus mask.

 

[John]

It's worth remembering that stopping down your primary mirror or objective lens also reduces it's resolution to that of the size of the aperture. So the brightness does reduce but so does the amount of detail that the scope will resolve.

[JOC]

Hi SilverAstro, This is def. getting interesting so I've been and got the object in question.  Yup, one cover completely removes leaving a hole about 52mm in diameter (so not as big as my envisaged 3", but still a sizeable hole.  No thread on it, but covered by something like a close fitting camera lens cap.  No remove-able cap on the other one though - it appears to be a similar size and shape - protruding off the flat surface of the lid with a raised edge as the other one does, but the hole is covered by same plastic as the whole object and appears welded into the design.  Def. not going to come apart from the entire thing.

1 minute ago, John said:

It's worth remembering that stopping down your primary mirror or objective lens also reduces it's resolution to that of the size of the aperture. So the brightness does reduce but so does the amount of detail that the scope will resolve.

OK, so that makes sense, so then why do frac users deploy those long thin telescopes when they could be using a Dob with a huge mirror and lots of possibility to resolve detail.  Where does the Frac design score over the Dob. design? (Or does that open too many can's of worms?)

[AKB]

2 minutes ago, JOC said:

No remove-able cap on the other one though

This one is for putting the removable one on to when you've taken it from it's usual place.

[SilverAstro]

4 minutes ago, JOC said:

so then why do frac users deploy those long thin telescopes when they could be using a Dob with a huge mirror and lots of possibility to resolve detail. 

(Or does that open too many can's of worms?)

42

42

 

[AKB]

38 minutes ago, SilverAstro said:

it removes the central obstruction and turns a Newt into more like a frac

...but it will almost certainly guarantee that you have coma, since the aperture is offset from the centre of the mirror.

 

[John]

1 minute ago, JOC said:

...OK, so that makes sense, so then why do frac users deploy those long thin telescopes when they could be using a Dob with a huge mirror and lots of possibility to resolve detail.  Where does the Frac design score over the Dob. design? (Or does that open too many can's of worms?)

It's a regularly discussed subject on forums. I can only answer for myself in that I like the tightly defined and contrasty images that refractors produce. To balance this, I also like the way that a large aperture scope like a dob sucks up photons when observing the deep sky. Thats why I have both types of scope

Definitely worth starting a thread on this topic if you feel like it - the subject won't get much attention on the end of a thread about moods !

I'll get the popcorn on standby  

[JOC]

AKB - that I certainly wondered about - I am surprised with the lack of centrality that it works at all, but then I suppose there is light hitting that bit of the mirror anyway that is being passed to the EP, so why not just pass to the EP that section of light - certainly counter-intuitive when you first think about it.  NB - I love the notion of being able to store the cap on the other side - even if there is a different purpose that's so neat it could indeed be the use - made me smile as a I read and then tried it LOL!

[cloudsweeper]

Anyway - I'm still "in the mood" - new EP, new focuser, replacement GPS Module - just waiting for a gap in the clouds!

Doug.

[JOC]

You stay in the mood Doug - many apologies for thread railroad - popcorn thread started here:

 

[cloudsweeper]

No problem JOC - I don't have a problem with "thread meanderings"!

Doug.

[SilverAstro]

On 28/02/2017 at 20:51, furrysocks2 said:

custom (squint) shed for the garden today

What is squint shed please ? does it depend upon plum-bobs not being true !