markse68

1 hour ago, Stardust1 said:

Who will get one of the new Pentax XW 30mm and 40mm?

Do these two eyepieces have a place in today's eyepiece market?

If I was really rich I think I’d probably maybe buy the full set of XWs and be happy ever after 

1 hour ago, jetstream said:

my copy is the deepest eyepiece I own.

What does this mean Jetstream? Keep hearing it but what does it mean? You can see deeper into space with it?

To stop the lens falling out? The field stop? Often the glass is stopped down as the edge performance is so distorted it’s not worth having. My Tal 25mm plossl is a case in point. It has a larger afov than is standard for plossls but the edge of field is poor compared to the centre 

30mm Delrin arrived so I’ve made the cupped Velcro standoffs originally planned- should make location and attachment of the fan unit a bit easier in the dark at the expense of possibly transmitting more vibration- if the clouds ever clear I’ll find out 🤷‍♂️

On 16/12/2019 at 12:07, Gina said:

PA Elevation adjustment.

Not sure what your total load will be but will the stepper bearings take that kind of axial load?

If it’s the thick grease getting thicker with cold temps could you maybe flush it out with lighter fluid and replace with something less viscous?

7 hours ago, CraigT82 said:

Have you seen Anthony Wesley's segmented aluminium 16" newt?  Now there's an idea... no more banging the long tube on doorways!

http://www.acquerra.com.au/astro/equipment/Nemesis-16/

Actually taking a closer look I don't really get his cooling system 🤔 He's using a sealed system by the looks of it with peltier elements on a cold plate at the end of the tube but it isn't in contact with the mirror. The outside is already cold though- I guess the peltiers would increase the temperature differential and speed up radiative cooling somewhat but there's no air movement in the tube or around the mirror- surely you need air movement to quickly move the heat away? Something like that would probably work great for a sealed tube like a Mak maybe. Perhaps he wanted to avoid blowing dust on the mirrors- perhaps it's very dusty where he lives? Be interested to learn if it worked well

Edit- this is really interesting stuff and he has documented his experiments thoroughly here http://www.acquerra.com.au/astro/cooling/

He is using fans to circulate the cold air from the Peltier cooled cold plate and is able to computer control the cooling to track the rapid ambient temp cooling where he is in Australia. Not sure I want to be lugging huge batteries around with me to power Peltiers but in an observatory this would be awesome. I might have to do some temp logging with the fan running and not to see what’s going on in there too.

1 hour ago, CraigT82 said:

Have you seen Anthony Wesley's segmented aluminium 16" newt?  Now there's an idea... no more banging the long tube on doorways!

http://www.acquerra.com.au/astro/equipment/Nemesis-16/

Thanks, I hadn’t- it’s a beautiful piece of work and that mirror blank looks amazing. 

3 hours ago, CraigT82 said:

You've probably seen these videos on the FPI protostar website shwing Schlieren tests with the mirror in an inclined tube, they demonstrate the need for the oversized tube quite well. https://www.fpi-protostar.com/bgreer/sep2000st.htm

I hadn’t seen those despite being on that site to buy my new secondary 🤦‍♂️ Will check them out after work and after looking up what Schlieren means 😉 Thanks. 

Having an oversized tube makes sense but then none of my new bits would fit very well... so if I do anything it’ll likely stay the same 10” dia as the current tube.

When I first got the scope I did think about cutting the tube in half and using something like one of the clamp rings used to seal barrels like this-

should hold the tube halves accurately enough but tbh having it one piece is a godsend really as it’s ready to use in minutes with no messing- well apart from the cooling down. I did also think about making a truss tube assembly for it - It might be my increasing age but I’m really appreciating the simplicity of this plastic tube that I can just sling in the car- even if it is a bit awkward to carry up fire escapes. 

2 hours ago, CraigT82 said:

I think the plastic will be better than aluminium for thermal management, as the alu would radiate heat quicker?  I'm not sure. 

Thanks Craig

There seem to be different schools of thought on this but to my mind having something that settles to ambient temperature as quickly as possible without offering an insulation barrier to slow that equalisation down makes some sense ? 🤔 Parallax seem to think so but then they would as that’s their product lol... http://www.parallaxinstruments.com/tubing.html

I haven’t had opportunity to test the fans yet- I’m really itching to though- if only the weather would allow... They’re “quiet” pc fans though so quite low noise and vibration. Running through the speeds with the controller there is a resonance about mid way which I’ll avoid. If vibration is an issue I’ll just run them full blast for 15mins or so for rapid cooling then drop back to minimum speed for a gentle breeze to maintain equilibrium or just switch them off. 

2 hours ago, CraigT82 said:

I find the motor focus is essential on mine, the scope is all but unusable without it.  That long glamorous grey plastic tube really vibrates!

Indeed Craig- it was your comments that convinced me it would be worth spending time to fit one. Up until then I couldn’t really see the point but having it and using it I’m very glad to have it now- so thank you very much for the inspiration 😊

Likewise the door- I couldn’t really see the point other than an aid to clearing out cobwebs but it’s proved much more useful than that this winter!

Nice bit of up-cycling! Looking forward to discovering how the adjustment works. This, the primary cell and the focuser are probably the best parts of a dobsonian  to over-engineer 😉

If you have any try a torx bit/screwdriver- you can usually find one that’s a tight fit- tap it in with a hammer if necessary- the sharp points grip the rounded hex hole 

Fitting the cooling fan unit last night revealed just how unlevel the primary mirror cell was! I suspected as much as the collimation adjuster screws were very uneven adjusted to get good collimation. So today I’m taking the opportunity to move the cell further up the tube a few mm to give a bit more clearance on the cooling fan unit, whilst reinforcing the holes with large SS washers and getting the holes better levelled. 

The unlevelness was not a surprise once the cell was removed- over the years of this scope’s life it has had many incarnations- several previous different sets of holes were evident, filled with epoxy, and the current holes were a mess!

The washers were bent to fit the tube curve better and glued with Araldite 2031- a slow cure epoxy which remains slightly flexible when cured for a very strong bond. It’s black- I think they add butyl rubber- smells like it anyway.

Old holes were masked on the inside of the tube and filled with the glue. Once cured (tomorrow probably) I’ll drill through the holes in the washers for the new mounting holes.

Pleased with how it came out. It’s a bit heavy but that nicely counters the weight added at the other end by the new focuser etc (and the huge 40mm ep I have!) The fans produce plenty of flow at max speed and can be turned down to silent temp maintenance speed once the scope has cooled properly.

Hopefully it will make a difference!

Took a friend up onto the roof of our 3 floor work building this evening for a quick and my first look at Venus. Great view from up there! Venus was a bit boring to look at but I’m glad I’ve seen it now- scope didn’t have time to cool and I knocked the collimation out clonking the spider knobs carrying it up the fire escape 🤦‍♂️ so that combined with incoming cloud/atmospherics gave a nice disk but with colour fringes- yellow on one side and green blue on the other. We found Saturn too which looked fine for its elevation-  before the clouds rolled in

New dedicated Astro snapper- white so I don’t lose it 😁 and nice and compact 

Is it really Russian? Could have a Lomo mirror which I think are highly regarded if it is? What is the strange sight thing that looks like a baby’s bottle?

There seems to be a thin silvery laminate embedded in the inner felt boot- no separate insole

3 hours ago, Alien 13 said:

The way optics work

Could someone explain this as the moon seems much brighter in my 8” scope than it was in my 4” scope which made sense to me as the way I understand it a telescope works by having a larger aperture than your eye to gather more light information to allow you to see fainter objects and or to magnify them? 🤔

Or amber? 😂

I tried my Sorels last night for the first time too. I made the mistake of thinking the thick felt liner would be adequate with just my normal thin daytime socks- it wasn’t. I was out for about 2hrs and by the end I had to stop as my toes and fingers were freezing and I couldn’t physically go on. Stopped at Decathlon this morning on way to work and picked up some merino wool hiking socks and silk liner socks. I hope there’s room for them-should be as the boots are massive. Hopefully that’ll help. On the look out for some thin cork/aluminium thermal insoles too- decathlon didn’t have any

I was right about the soles though- the mud knocked off much easier than my other boots with traditional cleated soles. And they’re much easier to put on/take off too 👍

What colour is medium? My eyes are dark bluish greenish grey at the very edges lightening towards brown fringes of the pupil 🤔

2 hours ago, johninderby said:

Apparently the lighter your eye colour the more sensative you are to brightness and are slower to adapt. Wonder if that is a factor in why some do or don’t need a moon filter? 🤔

Interesting theory John- I googled and there does seem to be something to it and it holds that people from hotter brighter climes do tend to have brown eyes- do you both? Weird thing is I’m not hypersensitive to bright sunlight and rarely feel the need for sunglasses, though I probably should and kinda wish I had in the past as they do protect from uv... If I view the moon full disk without nd and then look away it takes ages for the blind spot and purple/green embossed moon image to dissipate which is not really enjoyable. 

I guess it also depends on aperture and fov- there’s no way I can look at the moon wide field without a hefty nd with my 8”dob- like staring into headlights 😳