first eyepieces/barlow to get

[zhgutas]

dadaaam! since I have already grabbed my firstscope (helios startravel 102 EQ1) i'm looking for few more accesories to complete first kit:) the first thing i;m thinking about is a barlow. but the question rises: should i go for x2 or x3? plus, i have only a 25mm plossl now, and i guess i need at least one more for a start. i was looking at 10mm plossl , but i'f i'll go for an x2 barrlow, it just doesn't make any sense:)

any advices welcome:)

thank u

marius

[GordonCopestake]

I would go for a 32mm and a 2x barlow. This gives you with a 4" f/5:

32mm 16x magnification

25mm 20x magnification

16mm (32mm with 2x barlow) 31x magnification

12.5mm (25mm with 2x barlow) 40x magnification

A nice spread leaving a small gap at the short end. Perhaps an 8mm which would also give you a 4mm with the barlow. Although the image will get dim at these mags.

8mm 63x magnification

4mm 128x magnification

Note that as this is a fast (short) 'scope it's not ideal for planetary use or high mags.

Going this route means you need 3 eyepieces (32, 25, 8 ) and a 2x barlow

[zhgutas]

cheers for an advice Gordon.but what 'bout 3x barlow? Is it practical at all? btw, I can increase my FL to f/10 by using half of the dust cap. that makes it a bit better lets say, on moon.

[GordonCopestake]

Perhaps for bright objects like the moon and planets. But your 4" 'scope has a maximum useable magnification of 200x and at that magnification things will get dim plus you will have lots of false colour as you have an f/5 'scope. As you have a 510mm focal length you can reach 200x mag with a 2.5mm eyepiece, or a 5mm 2x barlowed, or a 7.5mm 3x barlowed.

The 3x might not be such a bad idea if you want high magnifications and it would give you the following mags:

32mm 16x mag

25mm 20x mag

10.5mm (32mm with 3x barlow) 48x mag

8.3mm (25 with 3x barlow) 61x mag

Perhaps add a 6mm to give 85x mag

barlowed 3x would give you 2mm which is 250x mag (too high)

Hmmm seems a shame to buy an 8mm as the 25mm 3x barlowed is 8mm too. Personally I would stick with the 2x barlow as at these very short focal lengths the cheaper plossls become almost unusable. Stick with the widefield stuff for now and think about your next 'scope for high mags (maybe a mak or sct)