E/P selection advice

[Troy.k]

Hi, I have a bintel 8" Dobson and have recently bough an explore scientific 82 degree 8.8 e/p from a member here, I want to keep growing my collection so I am after something with higher mag for planets.
Is there enough visual difference between the 8.8 and a 6.7 or should I get the 4.7 and skip the 6.7.
I can do the math to work out the difference on paper myself but am interested in visual observing differences any input/advice would be appreciated
Thanks Troy

[brian nordstrom]

:thumbsup: Hi Troy and welcome , nice scope you have there .
Simple maths says your 8.8 gives 136x , ( 1200 divided by 8.8 = 136 ) .
Personally I would get the 6.7 giving 180x ( 1200 divided by 6.7 = 180 ) as the 4.7 giving 255x will be a bit much as the seeing rarely allows that much magnification .

The ES eyepieces are very good ain't they ;) .

You will see plenty at 180x also give a good GSO 2x barlow a thought this will give you 270x with the ES8.8 and a whooping :eyepop: 360x with the 6.7 .

What did the 8 inch come with ? the 10 and 25mm plossls ? if so the 6.7 and 2x Barlow will round out a good magnification spread of 48x , 96x , 120x , 136x , 180x , 240x , 270x and 360x :eyepop: .
One more thing that 360x is getting to the max an 8 inch will be able to use , the formula for any scope is about 50x per inch so 50 x 8 = 400x , laws of physics mate .

Brian.

[Troy.k]

Thanks for the quick reply Brian it came with a 9, 15 plossl and I think a 25? 2".
Having never used any other e/p when I got the explore 8.8 it blew me away absolute worlds apart. I was wondering if a 4.7 would get much use so thanks for your input. So will the difference between a 8.8 and 6.7 be very apparent visually?

[grimsay]

Hey Troy,

I have the same scope and use a 5mm (200x) and 6mm (240x) regularly. There is a noticeable difference between the two. Not significant but useful. Maybe a $1 vs 0.20c coin?

240x is only intermittently worth it where I am.

Hope that helps, Iain

[Wavytone]

General rule from one eyepiece to the next, choose a factor between 1.4X and 2X on focal length. I'd say skip the 6.7 unless you plan on buying the full set - go straight to the 4.7 mm, which will be close to the limit on magnification.

For a dob a set of 3-4 eyepieces is enough to span the useful magnification range.

Resist the temptation to buy a suitcase full of big fat lumps of glass. They are unnecessarily heavy, big and fat.

[fbk]

I have the 6.7, 11 and 18 in the ES82°, they are awesome. I agree on sticking to 3 or 4 EP's and keeping the steps between them consistent. Like you I also have a handful of plossls that are a bit disappointing after the ES so I haven't looked through them since. I also have a 30mm SV so roughly 1.65x steps. SkySafari lets you simulate FoV with various EP's which is useful in deciding.

In my 12" the 6.7 gives me 225x which mostly sees use on planets and tight globulars etc. On good seeing it is fricken amazing, on the weekend just gone the seeing was particularly good and I got the best views of Jupiter I've ever had. I barlowed it to push it a bit further but it wasn't really worth the gain going to 450x. I generally avoid using barlows and really wish I had a 4.7 just for that!

In your case the 6.7 is pretty close to the 8.8 and 180x might leave you wanting on planets, but the 4.7 @ 255x might get limited use some nights due to seeing. Tough call!

[brian nordstrom]

:thumbsup: Spot on Fraser ! , I second the SV 30mm , I had and loved one for years , great eyepiece for the money .
Brian.

[Wavytone]

Agreed 4.7mm might be a tad short.

You could split the difference and go instead for a Meade Series 5000 Ultra Wide Angle 5.5mm. Not overkill magnification-wise, but more likely to be used and distinctly more power than 6.7 will give.

There are several choices at 6mm.

[fbk]

While I prefer to avoid using them Barlow suggestion is a good one. GSO (and others) make one that is 2.0x or 1.5x if you unscrew the lens end. On your ES 8.8 it would give you equivalent of 5.9 and 4.4 for really good nights. You still get the nice wide 82° AFoV and same eye relief but let you try out those shorter lengths before you splash out on a EP that might not see much use.

And yes Brian, the GSO 30mm SV is a very nice EP considering it came with the scope. I'd love the ES30mm to round out my 82's and I'm sure it does even better but for the price I always talk myself out of it!

[bigjoe]

Hi Troy .
Also make sure if you can, to observe your chosen object when it is well above the horizon .
You'll be amazed by how much more power your scope will take, and the image quality if you do so under good seeing.
Cheers bigjoe.

[bigjoe]

HI Brian; this has to be the best bang for your buck 2" El Cheapo EP out there IMO
bigjoe

[Troy.k]

Thanks everyone for the input I was bidding on an eBay auction on a couple tonight missed an 18 that went for $120ish I know I should of bid more was at work and missed the end of the auction:doh: but I got a 6.7 for a fantastic price so couldn't resist.
And I agree Fraser I was thinking 4 e/p would be the perfect number to have i was thinking maybe the 18 next? Getting ahead of myself need to look through the 6.7 first:D

[fbk]

They were a steal at those prices! 8.8 to 18 leaves a bit of a gap but the 18 is a really nice 2" EP. 14mm and 24mm (68°) would also be good steps up in your scope to keep it to four.

[gaseous]

You'd lose a bit of FOV compared to the ES eyepieces, but you could also consider an 8-24 Baader Zoom - I've found this to be a really good eyepiece if you want to keep a lid on your eyepiece numbers/frequency of swapping. And thumbs up to the GSO 30mm SV also - fantastic EP, as is the 42mm in the same range.

[yoda776]

If you are a member if an astro club it may be an idea to try before you buy. There is a limit to magnification as brian jas pointed out. I personally like my meade uwa 82 degree set. I have found the meade uwa 18mm is great. I also agree with the fact a 4.7mm in the scope would be stretching the limit and the best view would towards zenith and not the horizon ( thicker atmosphere to look through). I have smaller eyepieces at 2.5mm and 4.7mm and they work well in apo refractors but in other scopes are difficult to attain focus. You also need a good viewing night when you magnify (i.e. little to no wind or atmospheric disturbance) otherwise the mahnification is lost. With friends who have just started i have suggssted the same of starting with a good 3 or 4 eyepieces. With my 16" dob i struggle anything below a 9mm and have to have a good viewing night. Not syre hiw your dob will go but a meade telextender 2x i found has been useful at halving eyepiece sizes from 8.8 to 4.4mm. Plus you can use the telextender on other eyepieces ro do the same.

Wide angle eyepieces are definiteky worth it, especially at the smaller end imho.

[N1]

FWIW, I have the same dob (GSO branded), and I'm glad I've got short FL EPs for it. While the 6mm is probably used most often in that scope for hi power (giving 200x), the 5mm and 4mm, sometimes even the 2.5mm, come out when conditions allow, and the views are great when they do. No, those very short EPs don't get used as much as other EPs, but lots of use wasn't what I got them for.

[AEAJR]

I have an Orion XT8i, probably very similar to your bintel Dob.

I have the EX 82 8.8 and 6.7. Use them a lot. I also have a Meade HD60 4.5 mm which gives me 266X. I don't use it very often as the seeing is usually not good enough for that much mag.