Sky-Watcher 150PL, Rev Astro 2.5x Barlow and 10mm EP...unable to focus...help?

[Nastyness]

As the title suggests, I am finding it impossible to get any king of focus with that setup...I calculate that to be 300x mag, which admittedly is the limit of my OTA, but it was a very clear night last night and we have practically no light pollution where we live...so what's the issue? Even at 120x mag, I'm achieving pretty crisp focus but not perfect... so could it be a collimation issue?

[Chris H]

The mag is too high, the atmosphere dictates the max usable power rather than the limiting mag of the scope. Don't usually use more than x200 and often much less.

[Parus major]

A couple of things, are you able to focus on things during the day? And are you able to almost focus but go past and not run out of travel?

[DOBBY]

try easing it out of the focuser as you view...if it comes into focus...you need a small extension piece... First Light Optics - Two-inch Focus Extension tubes

or similar

[Nastyness]

A couple of things, are you able to focus on things during the day? And are you able to almost focus but go past and not run out of travel?

Havn't tried during the day...I'll give it a go. With regards running out of travel, no...I'm able to nearly focus but go past.

I'm surprised that even when using the 10mm EP alone, I'm still not able to get a perfect focus?

[Nastyness]

try easing it out of the focuser as you view...if it comes into focus...you need a small extension piece... First Light Optics - Two-inch Focus Extension tubes

or similar

Thanks Dobby, I'll give this a go too.

[Nastyness]

The mag is too high, the atmosphere dictates the max usable power rather than the limiting mag of the scope. Don't usually use more than x200 and often much less.

So should I invest in a 12mm EP then? or get rid of the 2.5x barlow and buy a 2x? The Rev Astro 2.5x barlow gets great reviews, so I'd rather hang on to it if possible...

[Parus major]

Havn't tried during the day...I'll give it a go. With regards running out of travel, no...I'm able to nearly focus but go past.

I'm surprised that even when using the 10mm EP alone, I'm still not able to get a perfect focus?

The supplied 10mm is pretty poor in my 150PL to the point where it doesn't even live in the same place as the rest of my eyepieces, off which I have very few decent ones, so it's likely to do with it being guff. I'm sure you'd have got a 25mm in there? Try that in the 2.5x, should be the same mag as the 10mm on it's own. I bet that's a lot better.

You are of course right, this could be collimation based, a startest will tell you. I believe this is detailed in the manual that came with the tube.

[Nastyness]

The supplied 10mm is pretty poor in my 150PL to the point where it doesn't even live in the same place as the rest of my eyepieces, off which I have very few decent ones, so it's likely to do with it being guff. I'm sure you'd have got a 25mm in there? Try that in the 2.5x, should be the same mag as the 10mm on it's own. I bet that's a lot better.

Yes, I have the supplied 25mm EP...I'll give that a go with the barlow as you suggest.

What's the maximum useable mag you've achieved with your 150PL then? Am I wrong to expect decent results at anything over 200x?

[Chris H]

If the 10mm won't come to focus then check the collimation.

[Parus major]

Yes, I have the supplied 25mm EP...I'll give that a go with the barlow as you suggest.

What's the maximum useable mag you've achieved with your 150PL then? Am I wrong to expect decent results at anything over 200x?

I've got a 6mm Celestron Omni which gives pleasing results consistently, usually very sharp in most conditions. I've stuck it in the low quality supplied 2x barlow and it looks ropey but it is a rubbish barlow and 400x is far, far to high but you can make out detail you couldn't really see before. At that mag Jupiter looks about the same size in the eyepiece as the naked eye moon.

Good seeing and a decent eyepiece and barlow 300x+ should be possible. Not ideal but possible. Generally I find the 6mm on it's own to be the most pleasing on planets in all conditions.

[Nastyness]

I've got a 6mm Celestron Omni which gives pleasing results consistently, usually very sharp in most conditions. I've stuck it in the low quality supplied 2x barlow and it looks ropey but it is a rubbish barlow and 400x is far, far to high but you can make out detail you couldn't really see before. At that mag Jupiter looks about the same size in the eyepiece as the naked eye moon.

Good seeing and a decent eyepiece and barlow 300x+ should be possible. Not ideal but possible. Generally I find the 6mm on it's own to be the most pleasing on planets in all conditions.

So the 6mm will give you a mag. of 200x...in theory then, if I invest in a decent 12mm EP and combine with my 2.5x Barlow, that should give the same mag. but offer a little more eye relief?

[Moonshane]

I have a 6" f11 so similar to your scope.

Cooling - are you allowing the scope to cool down? About an hour for higher magnification but you can observe at low powers almost straight away.

Collimation - you should really check this at least, before every single session. Often there will not be an adjustment needed but I feel you should always check it - takes about 1 minute max. even if an adjustment is needed. I usually check after the scope has cooled.

Magnification - with Jupiter I often find that the seeing will not allow more than 150x but sometimes more, often less. I don't think I have ever used 300x on Jupiter. I have however used a lot more than 300x on the moon and double stars on a regular basis. The higher the magnification, the better your collimation, cooling, focusing, tracking, eyepiece quality and observing skills need to be.

Seeing - seeing is the effect of the atmosphere on the visibility. In the UK this is affected by weather systems and we rarely if ever get the lovely solid air above deserts etc. Local seeing (like chimneys, central heating vents and even warm paving stones) can also affect your own site. When observing at higher powers, it's normal for the view to go 'in and out' of sharpness. My method is get to the point where it seems sharpest and then wait. It is likely the image will be soft and then sharp intermittently. This is normal and you have to 'grab' the image with your eye as it goes sharp. This takes practice but when you understand how it works you'll start to see more detail. Also, looking at planets and lunar detail for longer allows your eyes to acclimatise to the brightness and again detail then starts to 'pop out'. This is why you will often see experienced observers go quiet in mid conversation and then mutter something like 'ahhhh, there you are.....' or similar. Don't worry about this as it's also normal

Transparency - basically, how clear it is. Ironically, the clearest nights are often the worst for seeing and the nights with a little wisp of cloud offer more stable conditions for higher power. Therefore, many choose targets on such nights that are appropriate to the conditions. Sometimes you just have to forget planets and look for lower power targets like open clusters and if the transparency and darkness are good, the fainter objects which are usually harder to see.

Hope this helps.

[Nastyness]

Cooling - are you allowing the scope to cool down? About an hour for higher magnification but you can observe at low powers almost straight away.

I had been allowing time to cool, not an hour, but a couple of hours viewing it's still not focussing...

Collimation - you should really check this at least, before every single session. Often there will not be an adjustment needed but I feel you should always check it - takes about 1 minute max. even if an adjustment is needed. I usually check after the scope has cooled.

I have a collimation laser, but it's in dire need of callibration...I just need to prepare some kind of rig to do it on...any ideas?

[Moonshane]

use your barlow with the laser in it. no need to worry about whether it's aligned (the laser) or not then. google 'barlowed laser collimation'.

[Parus major]

A block of wood and nail hammered in to make two 'V''s. You then sit it on a table on a concrete floor or outdoors and point it at a wall. Stick a bit of masking tape on there and point the laser at it. Turn the laser and mark the point on the tape, doing this a few times will give you a rough center point. As long as you don't move your jig you'll manage.

Once you've done that move the whole thing farther away from the wall and start again to get the last bit out.

[Nastyness]

So the 6mm will give you a mag. of 200x...in theory then, if I invest in a decent 12mm EP and combine with my 2.5x Barlow, that should give the same mag. but offer a little more eye relief?

Realised that it would be a 15mm that would give 200x magnification with a 2.5x barlow on my scope, but am I fundamentally right? A larger focal length combined with a barlow to achieve the same magnification as using a smaller focal length alone, offers better eye relief?

[Stephen]

Realised that it would be a 15mm that would give 200x magnification with a 2.5x barlow on my scope, but am I fundamentally right? A larger focal length combined with a barlow to achieve the same magnification as using a smaller focal length alone, offers better eye relief?

In theory yes, but may come at cost of optical degradation.