Eyepieces (8.5" f/7 and 3" f/4.5 dobs)

[furrysocks]

Hi, folks.

This forum is not short of threads looking for advice on selecting eyepieces and I've read dozens of them. I have a few thoughts running through my head and would appreciate a bit of help. I popped down to a local astronomy group meeting tonight to find nobody there.

I recently bought a cheap Aldi 76/350 dobs which came with an SR6, an H20 and a 2x barlow. These are all of very poor quality and collimation of the scope is limited to the secondary.

I am in the process of designing and building (and not necessarily in that order!) an 8.5" f/7 dobs. The Crayford-style focuser is built around a length of PVC pipe into which the Aldi barlow will friction-fit perfectly to serve as a lens holder, so I am losing the cheapo barlow housing from the set and restricting myself to 1.25" (for now).

I don't know the sky very well at all which was partly the reason for getting the Aldi scope - to play around with while I'm building the 8.5". With the H20, I can fit Orion's sword in the FOV but would like to go wider if I can. The mirrors on the Aldi scope may not be first rate but I expect to see better performance on the whole with a better quality EP.

I've had a look on astrobuysell.com and have picked out two listings...

- Set of 5 Revelation eyepieces - £50

(http://www.astrobuys....php?view=63308)

- Skywatcher Deluxe 2x Barlow - £20

(http://www.astrobuys....php?view=61299)

The set contains 9, 12, 15, 20 and 32mm EPs and have been taken from a Photo-Visual kit bought a couple of years ago. The Barlow I believe to have come bundled with a new Skywatcher 200 dobs and is unopened.

Making these two purchases would certainly get me going and both prices seem very reasonable to me. However...

Much of the advice on here is to but the best EPs you can afford at the time and often to avoid kit EPs. The Revelations do seem to get good reviews and as a cut down set (no barlow, filters of case) are available at fairly low cost. The Skywatcher Deluxe 2x Barlow can be bought new for £30 - £20 is £10 off.

Before I found these two listings (and they may well get sold before I make my mind up), I had reasoned that I'd start with a 30mm Vixen NPL (or a 32mm Skywatcher SP, Meade 4000, Antares or TS-Optics plossl) to get better views in the Aldi scope now and have something well worth using on the 8.5" later. My current preference would be the Vixen. Any of these is going to give me a 6.5-7mm exit pupil with ~4deg AFOV on the Aldi scope and about 4.5mm with ~1deg AFOV on the 8.5". I'll admit I've not worked out any more re: suitability than that.

I don't think I'd be likely to be able to use such a lens comfortably with a barlow, so I'd then put myself back in the market for something like a 10mm + barlow, and so on... I don't know if the Skywatcher Deluxe would then be the barlow I would choose or not.

All that said, the secondhand listings I've picked out would probably do me just fine for years and I wouldn't set myself up for having to spend more.

On the other hand, I know that I probably would keep spending anyway so perhaps its a false economy to buy it all up front.

What do you think I should do?

[nephilim]

Personally, I'd go for a decent quality 25mm & 9-10mm, I'm new to this to but i've read a few threads stating as u said, dont get a set. A good eyepiece can do wonders for a cheaper scope. There are plenty of knowlegable people on here who will be able to help you out & hopefully someone with a bit more experience than me will answer ur post soon. As for me I got a decent skywatcher 25mm that came with my scope & then added a Meade 5000 HD-60 9mm to replace the 10mm that also came with it, the meade was £86 but money very well spent. Good luck & clear skies.

Steve.

[furrysocks]

Cheers, Steve.

Because the one I'm building is f/7, I'm thinking 30mm or 32mm over 25mm for just that bit lower magnification and greater true FOV. I may not get any more FOV from the Aldi scope, I've not actually worked that out yet but should be ok on the bigger one.

So, +1 for buying better EPs at a slower rate...

(PS. "AFOV" in my first post should have read "true FOV")

[Capricorn]

For the f/7 dob build I would say the Revelation set would serve you pretty well, until you look through something better and decide a change is required. The lengths stated would be reasonable also.

The Barlow, I have no idea as I tend to use single eyepieces, I have collected enough.

The Aldi scope is the problem, the Revelation's should improve over the ones you have, however f/4.5 is going to test most eyepieces and the Revelations should be an improvement but they may not be great. Equally at f/4.5 the ones that do operate well there are TV plossl's and they are sort of £80-100 a piece. So sensibly they can be ignored.

The other op0tion you gave - the Vixen plossl's - are certainly a good choice. They work well and you could simply slowly collect all the 1.25" ones one at a time. Price is good at £30 each as well. The Vixens have an 8mm which I suspect would be good on the future build giving around 188x.

I suspect that you would be "safer" with the Vixens, however at £50 for the 5 Revelations it is certainly worth going for, especially at this time when you mainly have the Aldi scope for use.

Once you have the f/7 you can see if the Revelations deliver what you expect and then possibly consider trying a Vixen, BST, Celestron or whatever appears to be worth considerating.

[wookie1965]

http://www.swindonstargazers.com/beginners/eyepieces.htm

Have a read of these i would go for a low medium and high power eyepiece the best you can afford that will be best in your scope to get the best out of it.

[furrysocks]

Wookie - thanks for those two links. There's a lot of experience, thought and careful words in both of those guides. I'd read both of them before and will read them again as my thoughts crystallise further.

Capricorn - The Aldi scope is never going to be great - hence the idea of just using it to get to know the sky with a wide field view for now (30/32mm). As I get shorter EPs, I can rediscover what view the Aldi scope gives. Or my son can save up for an EP himself. Only having that scope to play just now with I don't think is justification in itself to get the 5-piece set. I could see myself chopping and changing lenses in it and saying things like "yep - still disappointing..." (As an aside, the benefit of a scope over binoculars for familiarisation is that I can show my four year old the same views and keep pretending like it was bought for him. If he has to save up for his own EP(s) then that would be a good thing, anyway.)

The 30mm Vixen is £40 at FLO, with the shorter FLs £35 or £30. So the cost of a single 30mm Vixen is still a bit of a kicker compared with the Revelations set. The 25mm/10mm Vixens at £65/pair stands up well against £50 for the Revelations.

Another thing then is I guess to seek confirmation on what I'm thinking re: FOV and mag. An f/7 is slightly longer than most reflectors that come bundled with the 25/10+barlow combination. Wider field, lower mag = more light, quality EP = better contrast and bigger "wow"... is this about right? In the new build, a 30mm will give 50x, whereas a 25mm is 60x. Not a huge difference, really but a 25mm bundled in something like the Skywatcher 130 is giving 36x or even 26x mag, so a much wider true FOV than I will ever get out of my relatively slow 8.5". I could look at it this way, though... if I buy the 30mm now, I'll buy the 25mm later. And vice-versa.

[furrysocks]

I could look at it this way, though... if I buy the 30mm now, I'll buy the 25mm later. And vice-versa.

Which is the point at which the Revelations set begins to look attractive again, with a 32 and a 20. Arg!

Really, I think slowly does it and the Vixens NPLs do get good reviews for contrast.

[nephilim]

Cheers, Steve.

Because the one I'm building is f/7, I'm thinking 30mm or 32mm over 25mm for just that bit lower magnification and greater true FOV. I may not get any more FOV from the Aldi scope, I've not actually worked that out yet but should be ok on the bigger one.

So, +1 for buying better EPs at a slower rate...

(PS. "AFOV" in my first post should have read "true FOV")

Ahh sorry, well in that case a good quality 30-32mm would be my preference, again i'm quite biased because of the Meade I bought, I was in 2 minds due to its price but the quality is amazing so I thinks its a case of you really do get what u pay for & a good quality 30-32mm would be great in your future build. I wouldnt like to offer any good ones tho as im still very new myself, but as I did with the Meade, research & reviews pays off.

[furrysocks]

Thanks for the thoughts, folks.

I may wish that I had gone with the used Revelations set and Skywatcher barlow as these did represent good value for money, but I have now bitten the bullet and started a collection of Vixen NPLs with an order into FLO for a 30mm and an 8mm, at a little over £70 delivered for the pair. I will be very interested to see the difference they make to the views through cheapo 3" Aldi scope and I look forward to using them on the 8.5" in due course.

I suspect the 20mm will be next and possibly the Baader Classic 2.25x/1.3x barlow.

[furrysocks]

Had a quick peer through the Aldi scope with the new eyepieces at a cobweb on the neighbours' shed. Greater AFOV from the new ones, contrast seems greater though 30mm vs 20mm and 8mm vs 6mm may not quite be fair comparisons. Very encouraged by the true FOV with the 30mm.

think the Aldi scope is now exactly what I want it to be - a wide-field, small portable scope to let my kid look through after tea, or when we go camping. Looking forward to Pleaides and Orion next time they're out. Might Barlow the 8mm at Jupiter if it's good seeing. Printed out some star charts, got my planisphere thing to hand - time to learn the sky and build the big dob. Nearly bought a 900m 4.5" on a motorised EQ1 this week, but it's just not what I want - I'd rather have the FOV and portability of the Aldi scope, despite only 3" primary.