SW 150pl and focal reducer?

[gazza63]

Hi everyone

I would like to know if i would benefit from using a 0.5x focal reducer on my sw 150pl for DSO'S?

(wider FOV). Or am i better off using a wide field eyepiece. Being a 1200mm long f8, would a reducer also make it faster....f4 or 5 possibly (tighter collimation)?

any help would be appreciated

gazza

[John]

I reckon a wide field eyepiece would be better. A 1.25" 32mm plossl will show 1.4 degrees of true sky with your scope. If you can use 2" eyepieces then you can get up to 2.2 degrees with a 2" wide field eyepiece.

Buying an F/5 6" optical tube is not very expensive on the used market though and might be another option worth thinking about.

[michael.h.f.wilkinson]

A reducer would not affect collimation requirements (that depends on the mirror), but as John says, a wide field, 2" EP is better for visual.

[gazza63]

I reckon a wide field eyepiece would be better. A 1.25" 32mm plossl will show 1.4 degrees of true sky with your scope. If you can use 2" eyepieces then you can get up to 2.2 degrees with a 2" wide field eyepiece.

Buying an F/5 6" optical tube is not very expensive on the used market though and might be another option worth thinking about.

thanks John.... i would prefer to buy the right eyepiece as mentioned...as opposed to buying another scope, I like the 150 i have at the moment, just want to get its full potential.

any information i get.... helps.

[cotterless45]

Seeing deep sky objects depends on aperture, suitable magnification and seeing conditions. I believe that focal reducers are used by imagers .

A widefield eyepiece shows deep sky objects in the background star field. I use a 15mm Skywatcher Panorama with good effect.

This gives x80 in a 1200 mm tube. The 82 degree view gives a space walk feel.

A 6" f8 is optimal as is an 8" f6.

Of more effect are seeing conditions, any light pollution will affect your view and require you to use greater magnification to blast through.

If you get to a dark site , then aperture is less important as the contrast with the background is greater. Many nebulae , galaxies and clusters can be seen by eyes ,which will have an aperture of 5-7mm.

For finding dso's I use a 25mm Bst giving x48, then a 12mm to study and for the brighter planetary nebulae an 8mm or a 5mm to push magnification to x240.

Hope this helps to squeeze a bit more out of your scope, it keeps collimation well and being f6 is very forgiving with eyepieces,

Nick.

[gazza63]

Seeing deep sky objects depends on aperture, suitable magnification and seeing conditions. I believe that focal reducers are used by imagers .

A widefield eyepiece shows deep sky objects in the background star field. I use a 15mm Skywatcher Panorama with good effect.

This gives x80 in a 1200 mm tube. The 82 degree view gives a space walk feel.

A 6" f8 is optimal as is an 8" f6.

Of more effect are seeing conditions, any light pollution will affect your view and require you to use greater magnification to blast through.

If you get to a dark site , then aperture is less important as the contrast with the background is greater. Many nebulae , galaxies and clusters can be seen by eyes ,which will have an aperture of 5-7mm.

For finding dso's I use a 25mm Bst giving x48, then a 12mm to study and for the brighter planetary nebulae an 8mm or a 5mm to push magnification to x240.

Hope this helps to squeeze a bit more out of your scope, it keeps collimation well and being f6 is very forgiving with eyepieces,

Nick.

Great advice... thanks nick

[John]

thanks John.... i would prefer to buy the right eyepiece as mentioned...as opposed to buying another scope, I like the 150 i have at the moment, just want to get its full potential.

any information i get.... helps.

No problem - it's just that I've seen a number of 150mm F/5 newtonians recently (Skywatcher and Celestron) that were for sale, used, for less than a decent wide field eyepiece would cost. My proposal involved you owning 2 optical tubes, one for wide field use and the other for higher power viewing.

Lots of folks end up with more than one scope for these sorts of reasons.

[michael.h.f.wilkinson]

No problem - it's just that I've seen a number of 150mm F/5 newtonians recently (Skywatcher and Celestron) that were for sale, used, for less than a decent wide field eyepiece would cost. My proposal involved you owning 2 optical tubes, one for wide field use and the other for higher power viewing.

Lots of folks end up with more than one scope for these sorts of reasons.

You mean, you can do astronomy with just one scope?

Don't tell me missus!!

More seriously: the 6" F/8 is quite tolerant for lower quality EPs, so a modestly priced 2" 40mm wide field (5mm exit pupil, so you will be fine) is OK (if your focuser can handle it)

[gazza63]

thanks for everybody's advice. looks like a wide 32 to 40mm ep it is then.

[John]

thanks for everybody's advice. looks like a wide 32 to 40mm ep it is then.

Can your scope use 2" eyepieces ?.

If so, great, go for a 40mm 2" wide field. If not, stick with a 32mm as longer focal length eyepieces in the 1.25" size won't show any more sky.

[gazza63]

No john it does'nt take 2" ep's (unless i buy an adapter?). Think i'll take you're advice and get a 1.25" 32mm plossl. I will eventually in the future buy a shorter focal length f5 scope. i've only had this scope for a month, (got it half price). It was a toss between sw 150/1200 f8 or the cheaper sw 150/750 f5. The f8 won me over coz of the price reduction. But i think i made the right choice as for planetary viewing it blows me away.

[John]

..... But i think i made the right choice as for planetary viewing it blows me away....

I agree. 6" F/8 newts are very potent lunar and planetary scopes.

The vast majority of deep sky objects would fit into the field of view given by a 32mm plossl in an F/8 scope so you should be fine.

[gazza63]

Did you see my first ever webcam photo i took this week. I was surprised how well it came out

[moriniboy]

No john it does'nt take 2" ep's (unless i buy an adapter?).

Or you could swap the 1.25" focuser over for a 2" double speed one by increasing the size of the focuser hole.

I did this with my TAL 2

[gazza63]

Nice scope you have there. I dont fancy drilling the only scope i have at the moment. But it's a thought...... thanks

[michael.h.f.wilkinson]

To adapt the scope to a 2" focuser you would really need to change the secondary mirror to avoid vignetting. A larger secondary reducer the planetary and lunar views (and reduces the amount of light for the vast majority of DSOs slightly). Having said that, I still got some pretty good views of DSOs with a 25mm Ortho in my old 6" F/8 with its 1.25" focuser. At just 48x you got nearly a full degree in the FOV, allowing many pairs and triplets of galaxies to fit in one FOV. There are very few DSOs that require more FOV. For those cases, a rich-field scope like the 6" F/5 with 2" focuser and larger secondary (2.84 deg FOV with a 26mm Nagler) would be better.

[gazza63]

hi michael

thanks for the information. I fully intend to keep my scope as it was made. A low powered lens seems the right way to go. I'm new to this, with so many setups and right and wrongs it is a little confusing sometimes.

thanks

gary

[Stargazer_00]

Or you could swap the 1.25" focuser over for a 2" double speed one by increasing the size of the focuser hole.

I did this with my TAL 2

That looks really weird on the wrong side of the scope usually the focuser is on the other side, means you have to use the finder with left eye if its set up that way. Is that true of all TALs?

[Stargazer_00]

hi michael

thanks for the information. I fully intend to keep my scope as it was made. A low powered lens seems the right way to go. I'm new to this, with so many setups and right and wrongs it is a little confusing sometimes.

thanks

gary

then the best you can do is a 32mm 50degree AFOV in terms of minimum magnification at acceptable AFOV. You could go lower but it would compromise the AFOV below the 50 degree minimum standard for non speciaist eyepieces (such as BGOs which operate around 40 degrees).

If you increase the AFOV you need to increase the magnficiation too, the TFOV remaining more or less constant. So perhaps a 24mm with 72degrees would be OK, like a TV panoptic or some such (didnt do the math but im sure that's probably about right) showing the same amount of sky as a 32mm plossl but with more panache and style!

The BST Starguiders are all 60 degree AFOV and the maximum eyepiece is a 25mm in that range. They are a good set to get.

There are also many 68 degree AFOV sets you could look at. I believe Explore Scientific offer a range of these. Other sets may be more readily available as well.