Reassurance required!

[stebai]

Hi folks,

I bought my wife a BT202 Dob last year for X-Mas and we have had some fun with it. She in particular was excited by viewing Jupiter and Saturn for the first times, and we have spent much time enjoying the wonders out there. Well i for one hate late X-Mas shopping so i start early, infact today.
As mentioned already planetary viewing is the most exciting astronomy for us both but our Dob doesn't quite cut the mustard when it comes to viewing the rings on Jupiter. We can just about make them out but they are kind of vague. She thought a higher powered eyepiece might be the answer (we have a 9mm that came as standard) and a bit of research revealed a 6mm existed.
However on visiting my local Bintel we were told that a Barlow lens would be preferable as the 6mm generally were very difficult to use (infact i was told they no longer are stocking them.) So i took advice and bought the Bintel Barlow 2x ED (2"). I also bought a Nebula filter (which i think is the same as a light pollution filter???) and 4 coloured filters (Yellow, Orange, Med Blue and Green).
My main problem is that i won't be able to use them until X-Mas and i wanted to know if the items i have bought will make a useful difference to the size and clarity of the planets mentioned.
I know this is dumb but will using the 2x Barlow make the image twice as large?:screwy:
Also can you use a coloured filter with the Nebula filter? (i forgot to ask instore.)
Many thanks to any who reply.

[Lumen Miner]

You should be fine, the barlow will indeed make the image twice as large, yet that maybe to high magnification with a 9mm. As in you may be now be only viewing the rings of jupitier, not a more clarified view of the planet.

I would be under the assumption, that a more expensive 9mm might be more appropriate.
Do you know what brand the eyepiece is? I believe a $200 9mm would bring out the rings.


Then again, I am only new to this, so I would wait for someone more experienced to reply. :thumbsup:

[Mike21]

In my opinion, you have been given sound advice wrt Barlow instead of a 6mm EP. Standard EP's are not bad, but they are not much chop either. The closer you get to the very short end of the EP scale, the bigger the problems of inexpensive EP's. I gather a BT202 is 200mm? If so you should not have any problems seeing Jupiter's bands or the Great Red Spot even on rather ordinary nights. Far be it from me to spend your money for you, but since Jupiter is such good viewing now, you could give her the Barlow (just 'cause you love her) and get her a nice wide field, 2" EP for Chrissy. Wide field EP's tend to be longer and therefore magnify far less, but they show alot of the sky at once and make you feel like you're swimming in space.

[Mike21]

check your collimation if you're having trouble with Jupiter

[astro744]

With your 'scope you probably got a 26mm (46x), 15mm (80x) & 9mm (133x) eyepiece. With a 2x Barlow you'll effectively get 13mm (92x), 7.5mm (160x) and 4.5mm (266x).

A 6mm would give you 200x which would just about be an ideal upper magnification limit. The 160x of the 15mm Barlowed would also be very useful. The 9mm barlowed would only be useful on nights of exceptional seeing.

There is a basic 12mm Plossl available to give you 100x & 200x when Barlowed and that is the lowest cost option and not a lot of extra cost.

Not sure how much you want to spend but a 12 or 13mm wide or ultra wide field (eg 12 or 13mm Nagler) would be an absolute stunner on deep sky (Omega Centauri) with your 'scope and when Barlowed would give you a wide 6mm with comfortable eye relief for extended viewing of planets.

The reason a standard 6mm Plossl is not recommended is that the eye lens is very small (peep hole) and the eye relief is very short, ie. eye right up close to the lens. Basically it is uncomfortable for extended viewing.

The coloured filters are for planets only and they to enhance contrast of certain colour features on planets. eg. Jupiter's red spot looks darker with a light blue filter (80A). Do not use the colour filters with your nebula filter or you will just lose light throughput. The nebular filter would be best with your 26mm eyepiece on things like M42 (sword of orion but wait until summer), M8 & M20 (Lagoon & Trifid, up high in the evening) and any other gaseous nebula. M17, the Swan nebula is very nice and up high in the evening.

[mental4astro]

Hi Stebai,

There is alot to talk about! Wow.

First, there is no chance of viewing the rings around Jupiter. Not unless you have access to the King Kong of all professional telescopes, and then just. Its ring system is really only a token ring. Faint & thin. Even space probe photos have trouble detecting them unless they specifically look for them.

Your telescope is a fine instrument. It should be able to give a max. magnification of 400X without breaking a sweat. However, the atmosphere has more to do with how clearly you will see. In fact, rarely does it allow more than 350X, regardless of the size of the telescope or the quality of the eyepiece. To give you an idea, I've viewed Jupiter with my 17.5" scope, say, ten times in the last two months. Only once have conditions been good enough to see well at 350X. Usually only 100X to 150X is all that can be routinely used. 350X is a rare & special beast.

A barlow will double the magnification, but a precautionary note. If the barlow you are using isn't a quality unit & combined with an EP of the same rank, you won't improve things. The one you bought is very good though. Just be aware that it also makes the dob top heavy with the extra weight. I don't really like barlows, that's me though. They put too much glass between me & the universe. I rather a good quality, shorter focal length EP.

The filters you have serve different purposes. Lets start with the nebula filter. It is also called a light pollution filter because it filters out nearlly all wavelengths of light except for those at which nebulae are seen at. You may have noticed that nebulae are either red in colour or blue. The reason why is not important here, but what is is that it is these particular wavelengths that the filter transmits. When you use them in an urban or dark sky site, they allow the nebulae to be seen more easily. The darker the sky conditions are in the first place, the better they are seen.

These filters don't work on galaxies, however, because the light from galaxies is formed from the entire spectrum, & only a tiny amount from the wavelengths nebulae glow at.

The specific coloured filters you have will allow specific features to be more pronounced on all the planets. What features they will reveal is best sought from a specific listing on the topic. Someone else here in IIS may be able to give a link to such a list. Blue, especially would allow the Great Red Spot be be more clearly visible on Jupiter.

Using these coloured filters with the nebula filter is not necessary & a useless. The specific wavelengths transmitted by nebula filters does not match that of the coloured ones, & only makes the whole image darker.

Mental

[Wavytone]

Methinks the OP meant the rings around Saturn - not Jupiter !

[PCH]

... or the bands around Jupiter is what i thought he might mean. Anyways, one or the other.

[Lumen Miner]

I was taking that for granted. :thumbsup:

[Blue Skies]

Well they wont be seeing any rings around Saturn at the moment either - remember they are edge on to both earth and the sun at the moment. They'll just have to wait until next year now.

[mental4astro]

Here is a link to filter use, thanks astro744:

http://www.lumicon.com/astronomy-accessories.php?cid=1&cn=Filters

Info on nebular filters top half, planetary info lower half.

[chunkylad]

Your barlow lens will double your image scale (make things twice as large) by effectively turning your 9mm into a 4.5mm.

As others have said, you need to optimise your set-up first to get best results. Collimate your 'scope first, then look again with the 9mm. The clarity of what you see will be determined by the 'seeing' conditions. Now that you have a barlow, do a search for the barlow method of collimation. I find it's easier.

Those coloured filters are used to bring out certain details, especially when you are observing planets. I would advise that you get the basics right before you experiment though.

You and your wife will have lots of fun with that 200mm dob. Enjoy the learning process, and remember everyone of us started in a similar way - so there are no really dumb questions.

[stebai]

Thanks folks.

Doh.. i did mean the bands around Jupiter (although we have seen the wafer thin ring around Saturn too!).
Thanks for all your replies, as always you guys are a font of knowledge.
I have always been a bit concerned re the collimation of our scope though. We bought it second hand off a disillusioned teen who was more interested in Playstations, and although it came with manuals, i couldn't really fathom out if it was setup properly. Is there a good and easy to understand guide anywhere? Do i have to re-collimate after fitting the Barlow?
When we view Jupiter (for instance) it appears about the size of a small pea with quite vague banding - it is very bright and tends to "soften" the image at the edges. Is this about what we can expect from a 202 dob with a 9mm eyepiece with no filter?
Anyway as always cheers and many thanks for any replies.

[RobF]

You may already be aware of much of this Steve, but to get your best planetary views:

- Ensure jupiter is above 60 degrees from the horizon
- Decent "seeing" helps - not much you can do about it - you have to take what you get
- Ensure the scope is properly cooled - at least a couple of hours, and fan on if you have one
- Collimation very important - plenty of good references to sites with pics etc on Ice In Space you can hunt down

6mm or a barlowed 13 should give nice scale without pushing it too much. I'd hope/expect to see plenty of banding, some swirls in moments of good seeing, the Great Red Spot when visible (check web or Sky and Telescope) and plenty of moons. Would be good to make sure you have the points above sorted before getting too carried away with filters.

You really do have to keep watching for quite a while to catch those rare moments when all the swirling air above us settles for a moment or two. All the best with your barlow. You're both bound to have fun with it, and always handy to have such a versatile accessory available. :thumbsup:

[Blackant]

Hi Steve and Hayley,

Congratulations on your 'scope I've only recently got one exactly like yours, and i'm having an awesome time with it :thumbsup:

Regarding collimation, here is a link to an article that really helped me:
http://www.iceinspace.com.au/63-390-0-0-1-0.html (http://www.iceinspace.com.au/forum/../63-390-0-0-1-0.html)


Another thing you might want to think about if you don't have one already is to buy some kind of collimation tool, they make the job 100% easier. I ended up getting an orion collimating tool from bintel, and it has been great. I bought it after advice from others on this forum, and the following link leads to that thread. It also contains lots of great general information and other links to collimation in general:

http://www.iceinspace.com.au/forum/showthread.php?t=46205

apologies if you already have this info, and I hope you have as much fun with your telescope as I'm having with mine :)

Kind regards

Ant