Mike_S

Yes. I hear some people bought maks as beginners and regretted it l. I can imagine them being tough to locate dso’s. I understand that shorter focul length may be useful to compliment a longer focul length scope in your collection.

has anyone actually bought a big dob then sold it because the focul length was too long/field of view too narrow? It sounds like focul ratio is the practical limit to aperture size. 

Just another question. I hear a lot of neutral density filters. Is the Baader neodymium a neutral density filter? Or is the cheap Sky-Watcher moon filter one?

https://www.harrisontelescopes.co.uk/acatalog/skywatcher-moon-filter-1.25.html

these are the filters I have as well as some 2 inch ones that won’t fit some of my planetary eyepieces. 

For some reason Jupiter wasn’t as sharp for me tonight as last night. Had sharpest view yesterday at X 133

Hi,

just tried looking for DSO’s today. 10 inch F4.7 dob. 30mm ES 82 degrees eyepiece. Tried looking for ring nebula, dumbbell nebula and some of the globs. Couldn’t find them. Using the skyview app on my phone. I am in north west uk so the skies weren’t very dark and it’s a Bortle 6.

the only DSO I have seen so far is Orions Nebula in March. Are the DSO’s this time of year as bright and easy to find as that?

Thinking more for DSO’s on this one to be honest. I’m having difficulty finding them so I’m using a 30mm eyepiece currently. If I see a used 12 inch F5 solid tube come up I might get it. 

I see some just go all the way from a 10 to a 16 inch but they’re usually 1800mm long. I’m enjoying finding my way about anyway. It was just a thought that popped into my head. 

Seeing as most big dobs appear to be around F4-F5. Have you ever bought one and thought the focul length was too much? Too narrow field of view? If so, what size was it and what did you go back to?

music to my ears. I really want a 12” dob 😂

Right so perhaps a smaller aperture reflector would also have been good? Is there a downside to the actual mirror over a lens besides the central obstruction?

John why exactly do you think you sometimes get better views with your refractors over your 12 inch dob? Are they 4 or 5 inch or what? 

Is there a calculation for determining at what point a reflector aperture size beats the contrast of a refractor of a given size? So say a 100mm refractor. Considering typical central obstruction in the most common Chinese reflectors, what would the required aperture size be to match the contrast of the refractor? Is there a rule of thumb? Obviously don’t want to go too big as field of view comes into it.

So I have learned quite a bit here. When it comes to the bright planets, it seems that light gathering is not important but aperture is for resolution which brings out the detail. 

I’m a bit confused on contrast. How to improve contrast with a reflector? Can they ever beat refractors for contrast? 

Also this article.

https://medium.com/@phpdevster/help-i-cant-see-detail-on-the-planets-ac27ee82800

so it seems my main issue was actually atmospheric disturbance as it really looked like the example he shown with poor atmosphere. It was higher when I viewed it tonight so that explains things.

it would be interesting to try a refractor sometime but even more aperture with a larger dob would help instead. 

This article has just blown my mind. Right I tried a 9mm eyepiece tonight (X 133, 1.9mm exit pupil) and I got my best view of the bands. It was just very small. I will try a 7mm eyepiece when I get one.

anyway so it seems that exit pupil is a lot more important than I realised. So if I had a 12 inch F5 dob instead I could see the same detail perhaps with a 1.8mm exit pupil but it would be at X 166. 

But people are still getting better views with a 100mm apochromatic refractor?

 https://medium.com/@phpdevster/how-telescope-aperture-affects-your-view-24507147d7fc

Never seen good quality AZ mounts before besides on dobs. Will check them out thanks.

It’s the mounts that are putting me off a refractor especially as I don’t really do astrophotgraphy. I do like the dob mount. I’m going to order another filter just to try. Perhaps a variable polarising one. I will get a 7mm eyepiece as well. Also a Cheshire collimator and maybe a new focuser as the rack and pinion thing is awful. Got lots to try to get the best our of this scope first. Thanks everyone for the replies. I will let you know if I get to look through a refractor or if improve my view with the dob. 

Thanks, yes the moon is incredibly sharp with it even with my highest power eyepieces. I might try get to an astronomy club this weekend to look through others.

Also seen a Celestron Nexstar 102 GT for £135. Tempting but could wait and get a 100-102mm apo for £400 used. 

At the moment I want to spend as little as I can to rule out problems. I want to try a Pentax XW7mm but can’t see any second hand or can get a SW Evostar 102 F9.8 on an EQ3 mount and use my 5mm eyepiece for X200 magnification. Next month maybe. Will probably go with the lower power eyepiece first or even a cheaper one if a decent one comes up second hand.

4 hours ago, jetstream said:

My 10" f4.8 dob gives much much better views than those images...

Cooling, collimation and dealing with local thermals are where to concentrate efforts IMHO.

Is this from northern hemisphere and this time of the year? What magnification please?

It’s okay I like the science part even though can’t take it all in that quick. A bit better viewing tonight. Could make out some faint orange bands on Jupiter. Saturn was pretty sharp too. On the sticky thread “what can you expect to see”. The images it shows for a 4 inch frac are better than what I am getting from my 10 inch dob. Do you expect to see as clear as this through the eyepiece? 

I was looking at that but can’t get down to Essex anytime soon. 

15 hours ago, Stu said:

This is the f11 achro which is a very nice scope.

https://www.teleskop-express.de/shop/product_info.php/info/p1958_TS-Optics-102-mm-f-11-Fraunhofer-Refractor---Optical-Tube-Assembly.html

There is an ED version which is interesting, but perhaps missing the point.

https://www.teleskop-express.de/shop/product_info.php/info/p11262_TS-Optics-102-mm-f-11-ED-Refractor-with-2-5--RAP-Focuser.html

Had a look at these and another look myself and came to the conclusion that you picked the best value! Maybe later in the year. The achromatic is only £492 here

https://www.astroshop.eu/telescopes/ts-optics-telescope-ac-102-1100-ota/p,58274#tab_bar_1_select

there are still some Celestron Astromaster 90/1000’s around too for under £200 or this looks better even 

https://www.firstlightoptics.com/evostar/skywatcher-evostar-102-eq3-2.html

1 hour ago, John said:

Now I use the same as I use for observing all targets - alt-azimuth, manually driven. A Skytee II (bottom pic) and a Giro Ercole (top pic). I did have a couple of driven equatorial mounts for a while but I prefer using the alt-az mounts so the eq's were gathering dust.

What scope is this please John?

Thanks for the brilliant replies. I think I’ve got enough to take this in now. Keep going with further thoughts if you wish 

John what mount do you use on your refractor for viewing planets?