Scope choice again!

[phattanglo]

I've just posponed my specific search for a Dob as I've been reading a number of threads on imaging and I would like to explore this subject at a later date.

My question is based on a choice of two scopes, just to make things easier

Do I buy an Explorer 150pl on a 3.2 mount now, or do I buy a Skyliner 150p Dob for pure observation and save up for a more substantial mount at a later date ?

Is that an easy question or a can of worms ?

[russ]

What sort of imaging? If it's planetary, then the EQ3 and 150PL would be a good starting point. Just add dual drives, an electric focus unit and you are away.

But if it's deepsky imaging you are thinking off then the EQ3 is not really an ideal choice and certainly not with the 150PL. You would most likely change it when you began the imaging. So you may as well start with the dob now and then start from scratch with the imaging setup at a later date but still keep the dob.

That's my take.

Russ

[TheThing]

Steppenwolf does advise in his excellent book, 'Every Photon counts', that an EQ3 is the minimum requirement for getting into DS imaging (and he knows what he is talking about!) so the 150 on an EQ3-2 could certainly be a starting point if you want to get into imaging. You might want to upgrade at a later date, but it would be an excellent set up to start you off.

[ollypenrice]

I am going to disagree with The Thing, here, over the usefulness of a 150 on an EQ3. You cannot say anything about the quality of the mount needed without looking at the focal length of the imaging scope. The 150has a focal length, I believe, of 1.2 metres. I would regard that as a semi advanced focal length requiring at least an EQ5, an autoguider and excellent polar alignment. An EQ3 will be most unlikely to deliver the trackng accuracy required by this focal length.

If you go for a short focus refractor, however, you can get away with murder in terms of poor tracking. Something like a ZS66 with 0.8 reducer, readily available second hand, will give good images despite highly imperfect tracking. I would advise that you do not try to start imaging at a focal length greater than 650mm, way shorter than the 1200 of the 150.

When afflicted by wind (not that kind!) or poor seeing we forget the big scopes here and image away on widefield targets using the forgiving 328 or 450mm focal length of the Takahashi FSQ. That is the way to get going in imaging. It is the approach with which Ian King is associated and he's a body who knows what he's doing. You don't have to fork out for an FSQ, of course, since any small imaging refractor will do.

Olly

[phattanglo]

Cheers for your input, I admit I was leaning towards the Explorer for flexibility, simply because my dreamworld where I buy a super duper imaging setup is likely to stay a dreamworld.

Russ I'm interested in what you said regarding add on bits.

Is the electric focus unit a matter of convenience or is it something that is necessary for planetary imaging ?

Olly, I realise that it is always asking a lot to expect a scope to be a jack of all trades and serious imaging can take serious money, but I'm basing my choice on it being used mainly for observing with occasional planetary and DSO imaging just to dip a toe in as it were.

The Explorer 150p or the 150pl ?

I know the 750mm F5 has the better focusser but in real terms does it have any impact other than a more pleasant user experience ?

I'm thinking primarily of the F8's greater forgiveness re collimation and eyepieces.

Thing, that 8" Revelation Dob for 80 squids would have been sweet though would it not ?

[russ]

The Autofocus is a 'must buy' for that scope/mount combo.....believe me i used that exact setup for planetary imaging and the jiggles drove me mad. The Autofocus transformed the whole experience for the better.

I haven't read Steppenwolf's book so can't comment on what he said but i have used the EQ3 for imaging myself and while it worked fine as camera platform for widefield imaging, it didn't do so well with a Startravel 120 attached. And that's half the focal length of the 150PL! I concede it is a starting point for DSO imaging but not with that scope.

Russ

[NickH]

EQ6 with a 6 inch scope...I too disagree...whilst technically this may be possible, in practice, it's going to struggle heaps..

HEQ5 would work fine... and whilst Steve does know his stuff very very well..and is an exceptional astronomer. on this one we'll agree to disagree

Wind etc are key factors...quality of drives etc also.

Small refractor is a good place, and for a lot of us, is what we use for most of our imaging, even on vastly bigger and more expensive mounts

[russ]

The Explorer 150p or the 150pl ?

I know the 750mm F5 has the better focusser but in real terms does it have any impact other than a more pleasant user experience ?

I'm thinking primarily of the F8's greater forgiveness re collimation and eyepieces.

The 150P is the more all round scope. There's plenty of happy people on here with that scope. And the shorter focal length will put less pressure on the mount.

You've mentioned the downsides to the 150P. But they hold collimation well and there's reasonably priced eyepieces around that can cope with F5.

The 150PL would be my choice for planetary imaging but there's good barlows around that bring up the focal ratio of the 150P.

[NickH]

If it's for planetary, then yes, agree with Russ...deep sky...same caveats on the mount apply

[Deneb]

I am going to disagree with The Thing, here, over the usefulness of a 150 on an EQ3. You cannot say anything about the quality of the mount needed without looking at the focal length of the imaging scope. The 150has a focal length, I believe, of 1.2 metres. I would regard that as a semi advanced focal length requiring at least an EQ5, an autoguider and excellent polar alignment. An EQ3 will be most unlikely to deliver the trackng accuracy required by this focal length.

If you go for a short focus refractor, however, you can get away with murder in terms of poor tracking. Something like a ZS66 with 0.8 reducer, readily available second hand, will give good images despite highly imperfect tracking. I would advise that you do not try to start imaging at a focal length greater than 650mm, way shorter than the 1200 of the 150.

When afflicted by wind (not that kind!) or poor seeing we forget the big scopes here and image away on widefield targets using the forgiving 328 or 450mm focal length of the Takahashi FSQ. That is the way to get going in imaging. It is the approach with which Ian King is associated and he's a body who knows what he's doing. You don't have to fork out for an FSQ, of course, since any small imaging refractor will do.

Olly

I agree with Olly here, no offence to anyone - using a small decent imaging refractor with at least a EQ5/CG5 Mount can provide very acceptable images, or even cracking results if polar alignment, good seeing conditions & balancing is performed correctly, yes if there is some tracking error or a slight mis polar alignment the errors are a little more forgiving in images.

Something like a 8" or a 6" reflector may give "close up" images but I do find that they do catch the wind a bit (depending how much wind there is), resulting in more apperent Star Trailing in images.

Cheers

Nadeem.

[phattanglo]

Hmm, I'm getting the feeling that there's no such thing as dipping a toe when it comes to imaging, it needs a degree of committment scopewise that a scope for observing can't fully provide.

I'm being too ambitious by the sound of it certainly as a novice.

So if I base my needs purely on observing and assume the 3.2 is sufficiently rigid for either the 150p and 150pl can I realistically attain the same degree of magnification with the F5 for planetary observation and if so is this with a Barlow or more powerful eyepiece ?

Sorry if these are obvious questions, optics are a bit of a brain ache for me

[russ]

The beauty of the f8 150PL is you won't need to use very short focal length eyepieces to attain a desired high power. But that said, the f5 is capable of the same high power perfomance and there's plenty of eyepiece/barlow options available to attain a good useable power.

The F5 does have one distinct advantage that the 150PL cannot do anything about and thats at the other end of the magnification scale. With the 150P you have a 2" focuser and the option to use 2" widefield eyepieces for a huge widefield vista. The 150PL is going to be hampered by not only a lack of 2" focuser but also it's long focal length.

Hence why the 150P is the better allrounder. It can do all the 150PL can do plus some stuff the 150PL can't do.

[phattanglo]

Yes I see,

so with the F5 to keep eye relief at a comfortable level you would go to a 3X barlow for instance rather than a very short focal length eyepiece when planetary observing ?

Regarding a wide field view would I be looking at something like a 2" 32/36mm eyepiece ?

[TheThing]

I am going to disagree with The Thing, here, over the usefulness of a 150 on an EQ3.

Well you are, in fact, disagreeing with Steve who know's his onions!

And you're over complicating matters as well. True, it you add an auto guider or guide scope etc etc, the EQ3-2 might not be up to the task. You can, however, get reasonable results with that mount and scope combo with just a CCD or DSLR hung of the back and relatively long exposures of the brighter DSOs. Drift aligning will give a very good accuracy and tracking, sufficient for the purposes required at this stage.

Remember, the poster is only just starting out. Plenty of time later for upgrading the mount and buying lots of equipment. For starters though, the scope and mount suggested are more than adequate for visual work and for dipping a toe in the water of astrophotography.

there is dipping a toe in in - a webcam and imaging of solar system objects.

[Deneb]

..there is dipping a toe in in - a webcam and imaging of solar system objects...

Point taken.

Nadeem.

[russ]

Yes I see,

so with the F5 to keep eye relief at a comfortable level you would go to a 3X barlow for instance rather than a very short focal length eyepiece when planetary observing ?

Regarding a wide field view would I be looking at something like a 2" 32/36mm eyepiece ?

hehe some may frown upon the use of a 3x barlow but not me. I use both barlows a lot as it means i can use either the more comfortable 10.5mm Ortho or one of the widefields rather than the peep hole 6mm Ortho.

I use one of the 32mm 2" SWAN clones and it gives a large FOV in the 8" f6. In the 150P you could get away with the 26mm version and still have a 2.5deg true field of view........LARGE

They do suffer a bit at the hands of an F5 but for some reason it doesn't matter too much.

Russ

[phattanglo]

I think I'm going mad!

The gods are definitely conspiring against me.

My wife offered to top up my dwindling funds with some cash from the secret stash that apparently all women keep from their husband, as if a man would ever do a thing like that.

We then got to talking about the scope of my dreams and during the course of the conversation it became obvious that my wifes impression of a telescope is something small enough to fit on a window sill !

After describing the actual dimensions to her it became quite clear that if I want to take the scope on our regular caravanning trips in search of dark skies IT WILL NOT BE THAT BIG !

Honestly you'd have thought I'd told her I was going to make a pie out of kittens.

Bottom line I'll have to moderate my aspirations for now and look at something like an Explorer 130pm or the Heritage 130p as I think a 114mm would be just too small.

Please don't feel your help has been wasted as I am very grateful and I'll definitely get there eventually.

Right, start reading blimmin threads about Explorer 130's !

[NickH]

Pair of small refractors, and a HEQ5...she'll love it, and so will you...

[russ]

Oh that's a shame

But the 130P is still highly regarded and everything already discussed about the 150P still applies, so nothing lost.

Russ

[TheThing]

The 130 was the starting scope for many on this forum and is a very capable scope. I wish I still had mine!

[ollypenrice]

Just to complicate things, a Dob of pleasing diameter (8 or 10 inch) would probably take up less of the caravan than anything with an EQ mount. OK, no photography but the one-scope-for-all is a chimera anyway. It doesn't exist. The EQ mount is an awkward fella to stash, with bits sticking out in all directions. The Dob, however, might fit in the cupboard in which Madame stored that furtive dosh... They do lend themselves to easy stowage and quick setup. However, do things get badly shaken in moving caravans? I don't know.

Olly

[russ]

Olly, i think the 130P Heritage has been moved to front runner.......tiny little dob.

I could only get away with an ST80 on a photo tripod. The ST80 stashed away unseen in the suitcase.

Russ

[TheThing]

Just to complicate things, a Dob of pleasing diameter (8 or 10 inch) would probably take up less of the caravan than anything with an EQ mount. OK, no photography but the one-scope-for-all is a chimera anyway. It doesn't exist. The EQ mount is an awkward fella to stash, with bits sticking out in all directions. The Dob, however, might fit in the cupboard in which Madame stored that furtive dosh... They do lend themselves to easy stowage and quick setup. However, do things get badly shaken in moving caravans? I don't know.

Olly

I think you're mistaking an EQ mount for something else! The mount and tripod take up a tiny amount of space, especially when compacted down.

'bits sticking out...' by this I assume you mean the slow motion controls (which are flexible) and the weights (which can be stored almost 'flat' agaist the tripod legs).

A 5" OTA on an EQ mount will take up less room than an 8 or 10" Dob including base and is just as easy and quick to set up. In additon, a 5" scope will hold collimation better in a moving caravan than a 10" OTA.

[russ]

Yep, small EQ can be broken down quite nicely and packed away out of sight. Fold the legs and lean it in the corner of a caravan room somewhere.

[ollypenrice]

I have three EQ mounts down here racking up as much as 60 hours a week of imaging and observation time between them so I do have a vague idea of their appearance and performance!

You are quite right that they pack down small but when I was observing from a motorhome in the UK I perferred the speed of setup that came with an altaz refractor or Dob, both of which I tried as well as EQs. Surethe knock down with an EQ is no big deal but I found them a faff compared with alt az systems on those painful UK in-out, in-out nights. For a given volume a Dob has more optics and less mount, that's all. But the EQ will do the job as well.

Olly