markse68

Perhaps it is an eyeball reflection but then I don’t know why I’d not see it with the others. Can you get multi coated contact lenses? 😁

That’s a nice pic John- id have that on my wall 😉

It must be that big curved lens that the 7, 10 and 14 have I reckon- high brightness objects cause internal reflection that beams out as secondary image moving faster through optical gearing in opposite direction. For some reason the 14 isn’t as noticeable but I bet the 10 will do the same or similar. That’s frustrating.

9 hours ago, bomberbaz said:

strange you should say that and you have just prompted me. My session tonight I got the same thing on Jupiter using a nagler. What OTA were you using mark?

 

That’s interesting Steve- It’s an 8” f8 dob I’m using. I suppose it could be just a case of the beam size and concentration overwhelming the anti reflective coatings or something- I’ve not noticed it on other targets 

I’ve not noticed that Louis but I’ll check next time. Are you using it with a refractor? I’m using it with a longish newt. What I’m seeing is a bit like but not really the reflected double image I get with a Nagler 4.8 with something bright like Sirius. In that case though I think it’s an internal reflection- it moves the opposite way to the star image and doesn’t seem to interact with my eye- it’s contained within the ep. This though really feels like it’s projecting out of the ep and sweeping across my eye. All the XWs apart from the 2” ones seem to have identical upper optical assemblies so it must be some strange interaction with my scope I guess. 

I recently picked up a s/h but supposedly  unused XW7mm but it seems to have a problem. Or maybe not... 

when I observe Jupiter with it the image is excellent- I’m getting just about as much sharpness and detail as a 7mm ortho I think but it does this strange and quite irritating thing. It’s hard to describe but it’s like Jupiter is forming a beam of light that swishes across my eye as the disk moves across the fov and if I move my eye it kind of dances around. The 5 doesn’t do it nor the 14 or any of the others I have (I don’t have the 10 yet) I’m wondering what could be the cause? The eye lens is clean and like I say the image it produces is excellent. Anybody own the XW7 noticed something similar? I guess it could be an interaction with my scope 🤷‍♂️ Maybe it’s a reflection off my eyeball? It’s fine with less bright objects and I didn’t notice it on the moon when I first tried the ep.

6 Ser is a nice double- found it quite easily after finding M5 which is a lovely glob! With M5 in lower left of 20mm ep and 5 Ser top right moving scope up and tight along the line between the 2 about double the distance and there it was. With a 5mm it wasn’t terribly tight but the secondary is tiny and faint and easy to miss. Quite satisfying 😉

ooh Lambda Cyg is tight isn’t it! 

34 minutes ago, Stu said:

A reminder of how much I miss seeing John’s posts and images on the forum. Some amazing planetary images if you search.

I just had a look at his flickr- some amazing images- Mars 😳!. Didn’t realise he was in Oz- I think Antares might be a bit easier from there?

Reviving this thread as it’s such an amazing image and I’ve been enjoying the challenge again this summer. I didn’t think to try a UHC but I will now- thanks for the tip. Antares feels close to splitting right now and I hope the clearer covid skies will help- other targets have really benefitted. Last night I kept imagining I saw a greenish haze leading the boiling red mass of Antares A and looking at SkySafari indeed that’s where the B star should be- leading the pair. Perseverance is the order of the day though a dose of luck would help! 🤞

3 minutes ago, sputniksteve said:

Thanks for your comments. The seller currently wants £230, having reduced from £250.

I paid 200 for mine but it had some issues. They don’t come up that often. You need to think how you’re going to use it as it is a beast of a thing. I hardly used mine at all as shortly after bought my 8” dob. Bizarrely the 8” f8 dob is far more portable and usable than the Tal was- I can sling it in the car and drive to my regular site with ease- the Tal would have been a mare. Like others have said if you have somewhere to store it assembled and wheel it out to use it or a proper observatory then it’s a lovely scope and will give fine views. It’s a very different beast to what you could get for that amount new in terms of engineering! 

Mark

Really nice scope and that finder is desirable on its own (when pointing right way but check optics are good- finder and ep lenses known to delaminate. And it’s a beast to move- built like a tank!  so much bigger and heavier than the Tal-1 (my first proper scope). Has the nice clock drive too  if that’s working. 

I always get a little thrill when one shoots through the fov 😬😉

Hi Ian, welcome! It’s amazing what you can see and frustrating what you can’t from our light polluted skies ( I’m in SE London) but this place is great for inspiration for things to look for and it’s full of really helpful friendly folk   Took me ages to find M13 last year but it’s a firm favourite now. 
Mark

Amazing work Chris!

Had a look last night and it’s surprisingly tight but nice split comfortably with my 5mm @ 320x. Thanks for the suggestion John. This is fun!  Will check out 6 Ser tonight and nearby M5 which I don’t think I’ve looked at before 👍 Antares felt so close to splitting last night but still no go for me here...

22 hours ago, John said:

You need dark skies though - these filters are not "magic bullets" if there is much light pollution about.

I’ve been trying every clear night we have lately for the Veil with oiii / uhc with my 8” and not a whisper 😞 But I did try the Dumbbell and Ring last night with oiii as per discussion here and found it really beneficial  Lots more detail and structure visible. So I’m glad I have them and just need to get somewhere darker for the Veil I guess.

Some prisms 😊

Sounds like a wonderful evening you had  The pawprint- yes! So distinctive! Many new targets of interest will now be added to my list- thanks!  

14 minutes ago, jetstream said:

My coater says to clean regularly as any organic material on the surface in conjunction with moisture (dew etc) will cause etching of the surface. I only use de mineralized water and Sunlight(mild) dish soap.

That’s another interesting take on it- I don’t get why we worry about the fraction of a wavelength accuracy of the figure but then aren’t concerned about a layer of much larger dust particles🤷‍♂️ Is there some physics which explains that? 
 

Water of course also reacts with aluminium and salty water pretty fast and the fairy liquid I use contains salt I think (they warn you not to use it for car windscreen washing for that reason I think) and de-mineralised water is more reactive too- agh! 😳

Lockwood has his own take 😄

http://www.loptics.com/articles/mirrorcare/mirrorcare.html

John had me paranoid about isopropyl for a moment there but now I feel a bit better 😉

1 minute ago, John said:

I'm not a chemist either but I believe that isopropyl does react with aluminum. Which is why I wondered if this mirror did not have overcoating, or had poor quality overcoating.

 

 

Well shows what I know- from wiki “ Like most alcohols, isopropyl alcohol reacts with active metals such as potassium to form alkoxides that can be called isopropoxides. The reaction with aluminium (initiated by a trace of mercury) is used to prepare the catalyst aluminium isopropoxide.[14]“ but that’s apparently colourless but maybe 🤔

3 minutes ago, John said:

I agree - my point was that some mirrors don't have an overcoating (quartz or otherwise) I was wondering if those would be affected by the isopropanol.

 

I’m not a chemist John but I’m pretty sure aluminium is fairly safe in alcohol too. But if it was contaminated with some caustic chemicals then that would be bad!

25 minutes ago, johnturley said:

Personally I don't agree with this, obviously it is best to try to avoid the mirror getting dirty in the first place and reduce the need for cleaning to a minimum, but Newtonians or scopes where there isn't a corrector plate or optical window sealing the tube, will eventually need cleaning at some point, unless one is prepared to put up with significantly reduced performance.

I wash mine fairly regularly and I think it does make a difference- maybe my flat is particularly dusty but it quickly gets a dullness from dust deposits. I start with isopropanol then fairy and fast running water then de-ionised water and a hairdryer set on cold to blow the droplets off at the end. Don’t touch it with anything  other than air and liquid.

i very much doubt the op’s green film was the mirror coating- it’s a mineral coating similar to that used on lenses etc -silicon dioxide (quartz) usually I think, and won’t be dissolved by alcohol. They don’t varnish mirrors or at least I’d hope they didn’t! More likely it had built up a film of something in the air where it was stored or my bet the isopropanol was contaminated with something?

 

Really interesting indeed.  It basically says nobody will ever fully benefits its newton without a very active cooling?   Wow and almost 2 decades later we still think about solutions😬

Yes I saw his site before- worth clicking through the links to his other pages if you didn’t- he’s done some pretty cool stuff with sealed peltier cooling 

http://www.acquerra.com.au/astro/cooling/version3/

Doesn’t it depend what you’re looking at though? I mean a 20mm gives me a lovely full moon disk but if I want to see crater details something shorter is needed? And Jupiter is pretty small in a 20. Perfectly formed and super contrasty but a bit small to see much detail

You bring up a very valid point- John’s fan looks like it’s only going to have any effect cooling the back of the mirror and like has been mentioned- is that really the issue? Mine makes a semi seal at that bottom of the tube and shifts quite some air though that tube- if I leave the top cap on the tube and remove the eyepiece it’s like a hair dryer air flow out of the focuser on full blast 😉 I’ve found that very beneficial and I can see it from star testing but maybe my ota material made this more of an issue that needed solving than a metal ota tube would 🤷‍♂️
 

The fans are noctua quiet pc fans that run at a lower speed than average and I fitted a noctua speed controller. I usually just leave it running full blast but if I’m out a long time I’ll drop the speed to where I can barely hear them at all. With hand on ota I can detect they’re running but haven’t been able to see anything through ep. The plexiglass disk is somewhat isolated by Velcro attachment pads which likely helps too. The ota is no lightweight either at ~16kg which likely helps damp out vibration too

The other nice thing about the fans is when I bring the scope home from a night outside. I store it indoors and coming in from the cold the mirror instantly dews up and everything gets dripping wet. I run the fans for half an hour or so to quickly warm it all up again and clear the moist air from the tube to help prevent corrosion 👍

I have no idea if your air diverter will help- seems logical that it would but maybe it’ll impede airflow and that will outweigh the benefits? I think air flowing up past the mirror edge will tend to pull the air from the front of the mirror anyway by Venturi effect? Like you say the outcomes of these sort of experiments are very hard to measure 

2 minutes ago, DaveL59 said:

interesting experiment Mark, not sure I'll pull any of my TAL plossl's apart tho  I've yet to try the new TAL 2x Barlow I recently acquired tho I expect it'll perform nicely when I do get the chance.

Hi Dave, I like my Tal barlow- it’s very compact and optically I haven’t noticed any issue. I compared it to a more modern 3 element “apo” barlow from AE and it compared well though did suffer some slight warm sepia colouration but I only really notice that when doing a direct comparison like that.