Upgrades for 250PX

[warpi]

Hello,

I borrowed a Celestron AstroMaster 130EQ and I am now stuck on visual observation of space. After reading hundreds of posts on this forum I have decided to very soon purchase the Skyliner 250PX (solid tube). But I am already now thinking about what eyepieces to use for this. I have further read hundreds of posts regarding eyepieces for 250PX and have been thinking about the following setup.

- Explore Scientific  68° 28mm Eyepiece

- Explore Scientific  68° 20mm Eyepiece

- Explore Scientific  82° 6.7mm Eyepiece (equvalent of 8,08 if you consider 68 fov).

But I would also like to have a 2X barlow for getting 14-10-4,04 from the above eyepieces.

1. What do you think about the setup above?

2. Do you have any recommenations of 2x barlow which would work well with this setup? (or shall I choose another barlow ratio?)

Thanks in advance

warpi

[swamp thing]

looks good to me.

In my 10" I use 

31mm 82˚  (very, very occasionally)

20mm 82˚

12mm 82˚ 

2" 2x powermate.

Thats it. I don't see the need for any more. 

[YKSE]

I'd think the 11mm and 8.8mm 82 deg are slightly better fit for your scope than 20mm and 6.7mm, and can be barlowed well for high power view.

[warpi]

The thing is that 8,8 equals to 10,61 (when considering it is 82 degree fov instead of 68), therefore the 20mm barlowed 2x will equal 10mm and therefore this step becomes redundant?

2x powermate is like 310 EUR which is very much. I do not think the barlow needs to be super quality since I will mostly use without barlow 28-20-8,1 but when something inbetween is needed or going further zoom it would be nice to have. What is next step down in price from powermate?

[Paul73]

Looks like a good range. I would pop in a 12mm rather than a barlow. That gives you great range. You may want to add a 5mm at some stage (but not essential).

Paul

[YKSE]

The thing is that 8,8 equals to 10,61 (when considering it is 82 degree fov instead of 68),

I would prefer to think in terms of exit pupil instead of FOV, human eyes' acuity is around 2mm exit pupil, eyepieces proudce exit pupil around 2mm is most suitable for finding faint DSO (galaxies or nebulae) when they're magnified to recognizable size to our eyes. Thinking in terms of exit pupil is much easier when you have mutiple scopes of different focal ratio.

This is my thoughts about the choice for your scope:

28mm (5.9 exit pupil):  suitable as finder eyepiece and viewing large nebulae and galaxies.

11mm(2.3): median size (>2'?) faint DSO

8.8mm(1.9) together barlow 11mm and 8.8mm should be good for planetary, and stellar size galaxies and nebular, also brighter or small globular.

Here's a link I can warm recommend:

http://starizona.com/acb/basics/observing_theory.aspx

[Paul73]

In my 250px. The highest contrast seems to be at 20mm or 24mm dependent on how much light is around.

Paul

[YKSE]

Here's an excellent link about human eyes posted by other site member:

http://www.telescope-optics.net/combined_eye_aberrations.htm

I'd not be surprised though there're variations among our eyes, to me, 2mm exit pupil is a good guideline for any telescope, of course it'll miss if our eyes deviate much from that, and as we usually say, YMMV - your mileage may vary.

[bish]

looks good to me.

In my 10" I use 

31mm 82˚  (very, very occasionally)

20mm 82˚

12mm 82˚ 

2" 2x powermate.

Thats it. I don't see the need for any more.

That's interesting. There was a time when I just used a 26mm (not often), 11mm nag, 8mm rad and 2x barlow. Do you use these same 3 for the 20" or have you got others?

[warpi]

Now I have ordered the 250PX

After talking with my local astronomy shop it seems that anything else than a very high quality barlow will not make any use. And a high quality barlow cost €270 (powermate 2x 2") and then it is cheaper to buy eyepieces instead.

After reading the
http://starizona.com/acb/basics/observing_theory.aspx
it seems that optimal is 24 or 28mm, 11 or 8.8 and 4.7 from the Explore scientific inventory.
Therefore Im thinking

28mm for diffuse nebulae and general navigation (€110)
11mm for galaxies (€149)
4.7mm for planetary nebulae (€139)

Total €398

What do you think?

[DannyH]

Hello Warpi,

I have the same scope as you and after much deliberation went for Maxvision 28, 24, 20 & 16, ES 8.8 & ES 2x focal extender.

Maybe a little overkill on the Maxvisions, but after a few hours with the 16 and 24mm I wanted to try the 28 and 20 too. As others have said MV's really are a bit of a steal.

[warpi]

Hello DannyH,

So you are using the 8.8 with focal extender to reach 4.4?

Do you think still it is needed to have all these steps or could I reduce this inventory to 28, 11 and 4.7 only?

[DannyH]

Hello DannyH,

So you are using the 8.8 with focal extender to reach 4.4?

Do you think still it is needed to have all these steps or could I reduce this inventory to 28, 11 and 4.7 only?

I'm by no means an expert with the ideal ranges, I suppose it's an individual thing - but that's definitely the plan with the 8.8 - a magnification of 136 & 272, which for me made more sense than a 4.7 alone. I would say something like 24 or 28, 16/14 & 11/8.8 and a 2x barlow would probably be good to start. 

The 16mm Maxvision is the eyepiece I used most, so far.

[swamp thing]

That's interesting. There was a time when I just used a 26mm (not often), 11mm nag, 8mm rad and 2x barlow. Do you use these same 3 for the 20" or have you got others?

Hi Bish

Yep same ones. The 31mm gets a lot more focuser time in the big scope though.

I'm still deliberating eyepiece choice with the big scope ATM. So many choices............So little cash right now

Could be looking at 21mm and 8mm 100˚ eyepieces + Powermate for that scope. We'll see. 

[spaceboy]

I have owned a skyliner 250PX and found focal lengths around 9mm, 13mm, and 22mm 82° eyepieces got used a lot.

[jetstream]

Now I have ordered the 250PX

After talking with my local astronomy shop it seems that anything else than a very high quality barlow will not make any use. And a high quality barlow cost €270 (powermate 2x 2") and then it is cheaper to buy eyepieces instead.

After reading the

http://starizona.com/acb/basics/observing_theory.aspx

it seems that optimal is 24 or 28mm, 11 or 8.8 and 4.7 from the Explore scientific inventory.

Therefore Im thinking

28mm for diffuse nebulae and general navigation (€110)

11mm for galaxies (€149)

4.7mm for planetary nebulae (€139)

Total €398

What do you think?

Those 3 choices you list are excellent, consider a nice OIII too, which will be fantastic with the 28mm. Very well thought out.

[warpi]

One alternative would be to swop the 11mm against 8.8 and 16 (since I read that many people are happy with 16mm and 8.8 would be more spot on the nominal exit-pupil 2mm and the 13x the aperture in inches)

This would then result in

28/68 (43x exit-pupil 5.93mm)

16/68 (75x)

8.8/82 (136x, exit-pupil 1.86mm)

4.7/82 (255x)

Is the price range of eur 110-149 for these eyepieces reasonable for european customer, or is it possible to find them cheaper?

[John]

On the focal lengths, personally I'd feel happier with something around 180x now and then plan to add the higher power when funds allow. I think you might find the 136x - 255x jump too large and frustrating on nights / targets which won't support a max power of 255x. Jupiter is a good example of this.

[YKSE]

I'd think both of your choice are good starting point, you may find the gap(s) later on after using them on different objects for some time.

Buying used is a good way to save some moeny, there comex regularly ES/MV eyepices for sale on ABS, actually almost a full set of them now:

http://www.astrobuysell.com/uk/propview.php

[warpi]

Ok, probably the 6.7mm is nice to have as well then.

For now, I think I will start with 28, 8.8 and 4.7 in order to check what my newly scope is capable to deliver. Then for convinence I might purchase 6.7 and 16 in future.

[warpi]

Last night was my first ovservation with my newly bought 250PX with stock eyepieces and I was amazed This together with SkyMap in the telephone and Stellarium in the laptop, I could navigate nicely, accuratly and stabile in the whole sky.

But now I wonder. I undestand why the 6.7mm could be good as a ocular if seeing conditions does not allow for 4.7mm magnification. But why is it needed with anything between 8.8 and 28? The 8.8 will show all the darkest nebulas/galaxies best and all other sizes (6.7mm, 16mm, 20mm...) will just make them less visible?

[YKSE]

Last night was my first ovservation with my newly bought 250PX with stock eyepieces and I was amazed This together with SkyMap in the telephone and Stellarium in the laptop, I could navigate nicely, accuratly and stabile in the whole sky.

But now I wonder. I undestand why the 6.7mm could be good as a ocular if seeing conditions does not allow for 4.7mm magnification. But why is it needed with anything between 8.8 and 28? The 8.8 will show all the darkest nebulas/galaxies best and all other sizes (6.7mm, 16mm, 20mm...) will just make them less visible?

I'd glad that you tried the stock eyepieces, it's a good way to train your eye and find out a couple of things about operating a scope and finding objects.

8.8mm maybe show your the darkest nebulae/galaxies in magnitude, but only those with high surface brightness and very small in size, for those somewhat extented benulae/galasies with low surface brightness, you'll not be able to see them with 8.8mm, even in good seeing, because the higher magnification dim the objects too much, it's for these DSO(and they are quite a lot) eyepieces between 8.8 and 28mm are needed.

The link to starizona page worth reading many times to get a good understanding.

[warpi]

Hello,

Thanks for your feedback, then I understand better. Difference of magnification between 28mm and 8,8 is 218%. Introducing 16mm will give magnificationsteps of ~80%. Introducing 14mm, 20mm will make ~50% of magnificationsteps. What steps are needed in order to get reasonable image quality? Is 80% steps sufficient for this?

[YKSE]

I'd think a 14mm/82 is a better compromise than 16mm/68, my guess is that you'd seldom feel gap from 28mm to14mm being too large in that scope

[warpi]

Ok, so then it all cooks up to 28/68, 14/82, 8,8/82 and 4,7/82... For optimum magnification versus brightness I do not feel that any more steps are needed when looking at the below homepage

[1] http://www.clarkvision.com/imagedetail/visastro/m51-mag/index.html

Regarding the 6,7mm, I think I will skip this. For me it is better to wait for good seeing conditions to be able to use the 4,7. It is basically only planets that will be shown with 6,7 anyways.

If I go with 18/82 (old model) instead of 14/82 (new model) I will save about €43. Or do you think it is worth to put this €43 to get the new 14mm instead?