New Scope - an 'in between' scope

[Mr Spock]

I am happy with the scopes I have, the 4" apo and 12" Dob. Each has it's purpose which it does well.

• 4". Very light and portable. Excellent quality; perfect for planetary and doubles.
• 12". For when I need resolving power and high magnification lunar.

The negatives for these are the 4" doesn't really go faint and the 12" isn't moveable from the patio where its storage is. Both are subject to the horrible LED light pollution I have here.

There seemed to be a gap between the two. I set out my specification as follows:

• Light enough to fit on an EQ5
• The largest aperture possible
• Wide field, coma free
• Portable to a dark sky site

Once I had produced my statement of needs, and mulled over the results, I decided on the StellaLyra 8" f4 with matching coma corrector. With my 30mm UFF it gives a 2.39° fov at an admittedly high 6.9mm exit pupil. I've also ordered a 'mild' 2" OIII filter (I have a 1.25" stronger filter) and a Baader RDF. The RDF will replace the 9x50 finder and save a bit of weight. With the scope's 8.4kg, less finder, plus CC and eyepiece, it should still be below the weight limit of the EQ5. The short 730mm length helps with stability too.

The only negatives are: it probably has the usual GSO weak primary springs, and, they won't help with the the expected f4 issues around collimation. I'll have to keep on top of collimation throughout each session, it's just something you have to expect at f4. The large secondary means it won't be so good for planetary - but that's not what it's for.

Compared to my back garden, having 8" wide field in darks skies will be an eye opener. I'm looking forward to faint fuzzies and comets among other things. I'll have to see how it goes from home too and what else it can do.

[Mandy D]

I started the other way, with the 8 inch first (ignoring the 10 inch which is elsewhere), then added the 4(ish) inch and now the 12 inch. OK, so my 8 inch is f/5.9, but I'm more interested in the Moon, so that suits me. Now, we both have the same quandary, having filled the gap between 4 nd 12 inch, we have two new gaps to fill! I think it is a good mix, at least for me.

Oh, hang on ... I already have a 6 inch, so with the remote 10 inch, I think my set is complete! 🤣

Edited September 17, 2023 by Mandy D
Old age and memory problems ...

[RobertI]

Nice choice. My initial reaction was an 8” SCT or Classical Cassegrain might fit the bill for you, but the F4 newt sounds like a very capable alternative and cheaper too I imagine. I’m guessing that collimation isn’t such an issue for most DSOs. Very interested to see how you get on with it. 

[Ratlet]

It will probably do in a pinch for planetary.  I used the 130pds for a year with its oversized secondary and whilst it wasn't great out of the box a contrast booster filter helped massively and might help in your case.  Since it's not what it is for it's not much of an issue, but a stacked yellow and moonglow filter did the trick for me and might do for you in a pinch if you found the seeing warranted a quick peek.

What's your thoughts around the eyepiece position?  I only tried mine on an EQ mount a couple times before giving up due to the eyepiece ending up at weird positions requiring rotating the scope and contortions to get my eyeball to the eyepiece.

Will be interested to see how you get on with the coma corrector.  Is it the Stellalyra one with the 75mm back focus and 1.1 X magnification?

[Mr Spock]

1 hour ago, Ratlet said:

What's your thoughts around the eyepiece position?  I only tried mine on an EQ mount a couple times before giving up due to the eyepiece ending up at weird positions requiring rotating the scope and contortions to get my eyeball to the eyepiece.

Will be interested to see how you get on with the coma corrector.  Is it the Stellalyra one with the 75mm back focus and 1.1 X magnification?

Rotating the scope doesn't bother me.

That's the CC. The top comes off if ever I want to do imaging.

[Elp]

Considering what you already had, I would have thought you'd go the other way and get something truly widefield like a 300-400mm refractor. You must have some excellent skies to take advantage of the apertures.

[Mr Spock]

21 minutes ago, Elp said:

like a 300-400mm refractor

I have a FS-60 - 355mm and 7.7°  I need faint and dark skies. Home is Bortle 6-7.
Here's my dark sky location. On top of the moors with a spot sheltered from the wind.

It's about 16 miles and 30 minutes away.

[Elp]

It's nice to be near a dark sky, think mine is an hour however so has to be completely clear forecast for me to consider, which usually means some cloud tends to stick around.

[Mr Spock]

There's light domes (big ones) from Sheffield North East and Manchester North West, but in between is black enough to pick up M33 naked eye 

[Mr Spock]

Here it is. Small and compact and well built. It's right on the limit for the EQ5 though despite being under the 9.1kg quoted maximum.

One thing I really like is I can get the eyepiece in the right position for standing, so no back strain. It may, depending on results, become my most used scope. I'm not sure if it can do planets - that remains to be seen - but I'll give it a go on doubles.

[Mr Spock]

I did note out of the box it didn't need collimating 

[Mandy D]

I'm wondering why you think it might not do planets. I have no problem observing Jupiter and Saturn with my 200P (f/5.9) and 250PX (f/4.7). Admittedly, they are both 1200 mm FL, but I would have thought shorter focal length eyepieces or Barlows would make up the difference. What am I missing?

[dweller25]

You are around 35% central obstruction Michael so not too bad and certainly worth pointing it at Jupiter in the Autumn,

[Mr Spock]

What I'm expecting is a low MTF due to large central obstruction similar to an SCT. It's f4. My 12" f5 is exceptional on planets, but, has a small central obstruction. 

What a poor MTF does is make things like Jupiter's belts 'fade' compared to an apo for example. It doesn't change the resolving power, so it will, if it has good optics, see fine detail. 

[Ratlet]

10 minutes ago, Mr Spock said:

What I'm expecting is a low MTF due to large central obstruction similar to an SCT. It's f4. My 12" f5 is exceptional on planets, but, has a small central obstruction. 

What a poor MTF does is make things like Jupiter's belts 'fade' compared to an apo for example. It doesn't change the resolving power, so it will, if it has good optics, see fine detail. 

That ties in with what I observed (or rather didn't) with the 130PDS (also has an oversized secondary) on planetary.

[Mr Spock]

It needs better springs. I've just spent nearly an hour trying to fine tune the collimation and it's a no go. Conditions are a bit too 'fuzzy' anyway - even the Tak is fuzzy.

[Mr Spock]

So, new springs fitted 👍It's surprising how weak the supplied springs are. Why have they never sorted this? 

Anyway, FLO didn't have them in stock so get next day delivery from RVO. A couple of minutes to fit the springs and a few seconds to collimate and we are good to go 👍

[John]

4 hours ago, Mr Spock said:

So, new springs fitted 👍It's surprising how weak the supplied springs are. Why have they never sorted this? 

 

GSO made scope ? - weak springs have been reported for around 15 years as I recall.

Why indeed on otherwise good telescopes 🙄

Judging by the comments on here, the one issue that folks are concerned about with newtonians is collimation !

Glad you have got it sorted 🙂

 

Edited September 23, 2023 by John

[Mr Spock]

1 minute ago, John said:

Judging by the comments on here, the one issue that folks are concerned about with newtonians is collimation !

It's not difficult, but it is critical to good image quality 

[John]

Just now, Mr Spock said:

It's not difficult, but it is critical to good image quality 

And the manufacturer must know this and especially so at F/4. And yet .........

[Mr Spock]

Indeed. My 12" creaked and groaned every time it moved around. New stronger springs fixed that and now it holds collimation perfectly.

Really poor from GSO. It's so easily fixed.

[John]

With car suspension springs you can uprate them for towing by fitting rubber inserts into the springs. I wonder if something similar but on a much smaller scale could be used for newtonian primary springs to make the upgrade easier ?

 

Edited September 23, 2023 by John