Again TS 152 F5.9- does it worth over ST 120 achro? I am using bino or ultrawides

[Emperor!Takahashi!]

1 minute ago, Marian M said:

I love refractors; but reflectors seems winning on the benefits. Here it is my internal debate- one part of the mind is pushing against the rationale towards a bigger, heavier, colorful scope, while the logic part keep pushing back- largest aperture, similar effort to get out. Well, maybe the easiest way is to buy both 

I hear you! I love refractors, too, but I think that 8"-12" fast reflectors don't receive as much attention as they deserve as relatively portable rich-field telescopes. I can't think of another telescope that would match the bright, wide, pristine views that, say, a 10" f/4 with a coma corrector will provide without being far more expensive and/or heavy. But perhaps others would disagree?

[Marian M]

On 25/07/2023 at 15:35, Louis D said:

At low to medium powers on dimmer stars and DSOs, both the 6" achro and 6" fast Newt show similar views.  The Newt doesn't show diffraction spikes on dimmer objects, so that advantage of the refractor is lost.  The unfocused light in the frac is hard to detect, so that advantage of the Newt is lost.

I like having the eyepiece up nice and high on the Newt.  I refuse to extend the legs on my tripod due to the inherent shakiness in so doing, so the refractor's eyepiece ends up a foot or two off the ground which is really uncomfortable.

On DSOs in particular, I see no advantage to the frac over the Newt when you figure in cost, weight, and cool down time (the frac has more glass to cool).

Louis, if I were to give one more chance to the refractor (DSO only), your subjective opinion- which is the aprox magnification where the Newton is becoming crisper than the 152?

Is the 152 yet sharp at 100x? Many thanks again!

[Louis D]

5 minutes ago, The60mmKid said:

I hear you! I love refractors, too, but I think that 8"-12" fast reflectors don't receive as much attention as they deserve as relatively portable rich-field telescopes. I can't think of another telescope that would match the bright, wide, pristine views that, say, a 10" f/4 with a coma corrector will provide without being far more expensive and/or heavy. But perhaps others would disagree?

I totally agree.  Even a 6" or 8" f/4 or f/5 Newt with CC yields fantastic wide field views.  You just want to avoid going so large in exit pupil that secondary shadow becomes an issue.  I find my 6" f/5 GSO Newt a joy to use on an alt-az mount.  It's light, holds collimation well, and has sharp, color free images.

[Mr Spock]

I tell you, I'm fancying this setup as a perfect wide field filler for between my 4" Tak and 12" dob. An 8" f4 with coma corrector:
https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f-4-m-lrn-newtonian-reflector-with-2-focuser.html
https://www.firstlightoptics.com/coma-correctors/stellalyra-2-4-element-photo-visual-coma-corrector-for-newtonian-telescopes.html

I think that would go well on my EQ5 just for wide field visual. It would suit a simple alt-az too.

[Louis D]

18 minutes ago, Marian M said:

Louis, if I were to give one more chance to the refractor (DSO only), your subjective opinion- which is the aprox magnification where the Newton is becoming crisper than the 152?

Is the 152 yet sharp at 100x? Many thanks again!

On dim DSOs or bright objects?  I'd say on dim objects, it's fine up to 100x.  For example, I recall the Trapezium looking good at that sort of power.  On bright objects, it needs green filtering to achieve sharpness at any power.  By way of comparison, the 6" f/5 Newt looks good at any power and brightness of object.  If secondary spider diffraction spikes are showing in the Newt, violet and red are showing in the achromat, so there's always a trade off between these two on brighter objects.  However, the Newt is sharp while the achromat is a blurry mess needing green filtration.

Edited July 27, 2023 by Louis D

[Louis D]

5 minutes ago, Mr Spock said:

I tell you, I'm fancying this setup as a perfect wide field filler for between my 4" Tak and 12" dob. A 8" f4 with coma corrector:
https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f-4-m-lrn-newtonian-reflector-with-2-focuser.html
https://www.firstlightoptics.com/coma-correctors/stellalyra-2-4-element-photo-visual-coma-corrector-for-newtonian-telescopes.html

I think that would go well on my EQ5 just for wide field visual. It would suit a simple alt-az too.

Swap in the 6" f/5 and it's the same setup I have.  You have to be careful with that dual speed focuser to not reduce tension too far.  If you do, the draw tube drops to the bottom of the focuser.  It's a known issue with it because it has no separate pre-loading tensioner.

I rides fine on my DSV-2B mount while the 152 achro is clearly overloading it.

[Mr Spock]

Just now, Louis D said:

You have to be careful with that dual speed focuser to not reduce tension too far.  If you do, the draw tube drops to the bottom of the focuser.  It's a known issue with it because it has no separate pre-loading tensioner.

It's the same focuser as on my 12" and that works perfectly.

[Louis D]

16 minutes ago, Mr Spock said:

It's the same focuser as on my 12" and that works perfectly.

I thought the StellaLyra 12" f/5 Dobsonian comes with the standard GSO 2" Crayford Focuser for Reflectors:

  While the GSO OTA Newts come with a cheapened version of the GSO 2" Linear Bearing Crayford Focuser for Reflectors:

Notice that the pre-tensioning set/grub screws were removed from the GSO LB focuser that is available for purchase separately:

This leads to the problem I mentioned.

Notice that your focuser has at least one pretensioning set/grub screw, so it avoids this issue.

You're right, the standard GSO focuser works fine while the GSO LB packaged with their OTA Newts has the issue I mentioned.

[Mr Spock]

This isn't a discussion about GSO focusers though 

[Marian M]

Happy to discuss the focusers as well here, I am at the beginning of the Newtons curve learning 😄

 

Now, the big question- most of the observations I am using either heavy bino (MB + 2 Morpheus) or large eyepieces (APM XWAs) 

Is this suitable for the above Newton, what about the back focus required for Bino. For all my refractors I did changes that all are accommodating the bino without GPCs, for largest FOV possible. Would that work with the newton? Would be a pity to have a design for large FOV which is destroyed by the GPC

 

Also, being so fast (F/4), I presume the second mirror is large. Would that affect the view through a large 2" 40mm eyepiece like Lacerta/ Paragon (secondary being somehow visible?)

[Louis D]

6 minutes ago, Marian M said:

Happy to discuss the focusers as well here, I am at the beginning of the Newtons curve learning 😄

 

Now, the big question- most of the observations I am using either heavy bino (MB + 2 Morpheus) or large eyepieces (APM XWAs) 

Is this suitable for the above Newton, what about the back focus required for Bino. For all my refractors I did changes that all are accommodating the bino without GPCs, for largest FOV possible. Would that work with the newton? Would be a pity to have a design for large FOV which is destroyed by the GPC

 

Also, being so fast (F/4), I presume the second mirror is large. Would that affect the view through a large 2" 40mm eyepiece like Lacerta/ Paragon (secondary being somehow visible?)

If you tension the cheapened GSO LB focuser enough, it will easily lift heavy loads, just with a bit of stiffness in the action.  I've used it with the GSO CC and a 2 pound eyepiece (40mm Meade 5000 SWA) without issues.

I have the original V1 version of the focuser on my KUO 152 achromat.  It's a beast.  I've not noticed any tendency of it to slip and it is buttery smooth.  It's practically over-engineered.  I have no idea what their current V3 focuser is like, though.  While the V1 focuser has plenty of focuser travel, I'm not sure it would accommodate a BV's needs.

Even on my f/5 GSO Newt, the secondary is fairly large to avoid vignetting because it is intended for imaging.  I've used it with my 40mm SWA mentioned above, and I haven't noticed secondary shadow being an issue.  I can't speak to the f/4, though.  It is one of the reasons I went with the 6" f/5.  I had also read balance is a concern with the 8" f/4 due to difficulty getting the rings and associated dovetail bar in the correct position due to the focuser's location on the stubby tube.

[Emperor!Takahashi!]

I realized I should add a qualifier to my previous posts. The 10" f/4 I owned was a dob built for visual observing. A wonderful instrument. I'm not sure whether newtonians specced for imaging would perform the same because I haven't looked into them much.

I consider 5-6" to be a tipping point when considering the practicality of refractors and reflectors. I would prefer a 5" refractor over a 6" reflector because the former, in my opinion, is a more versatile instrument and yet still portable. But the equation changes when it's 6" refractor vs 8" dob. I would take the latter due to the ease of portability and deployment, plus the greater aperture and lack of CA. As we size up, the portability advantage of refractors starts to disappear, and the aperture advantage of reflectors starts to compound.

[Louis D]

22 hours ago, Marian M said:

Also, being so fast (F/4), I presume the second mirror is large. Would that affect the view through a large 2" 40mm eyepiece like Lacerta/ Paragon (secondary being somehow visible?)

I tried out my 40mm Lacerta ED in my 150 f/5 Newt last night on the moon.  While I could detect a slight secondary shadow dimple on the face of the moon, I had to go looking for it.  I wouldn't consider it intrusive at all.

[Louis D]

On 27/07/2023 at 07:54, Marian M said:

Louis, if I were to give one more chance to the refractor (DSO only), your subjective opinion- which is the aprox magnification where the Newton is becoming crisper than the 152?

Is the 152 yet sharp at 100x? Many thanks again!

Here's a quick comparison I did last night with the KUO 152 achromat (top row images) against the GSO 150 f/5 Newt (bottom row image).  The upper left image is unfiltered while the upper right image is filtered with a Baader Semi-APO filter.  The single Newtonian image is completely unfiltered.  I adjusted the refractor gamma to bring them into alignment exposure-wise with the Newtonian since they were a bit overexposed.  Please disregard the blown out highlights in the upper row as they are simply artifacts of my poor ability to handhold the phone, align it properly, and adjust exposure for afocal projection.

All images were taken with my 12.5mm APM Hi-FW eyepiece using afocal projection with my Galaxy S7 phone's camera.  The upper images work out to 72x while the lower image works out to 60x.  I thought it more important to use the same eyepiece than try to match magnifications.

The violet fringing in the upper left was actually stronger to the eye than what the image shows.  I don't think phone cameras are very sensitive to far violet light.  The Semi-APO image fairly closely resembles reality except for the yellow fringe.  It appeared to be a faint violet fringe to the eye.  I think it's due to the different sensitivities of the eye versus the camera to various wavelengths of light.  The lower left image is accurate except for the brown color cast.  That was due to having issues matching exit and entry pupils handheld.  The absolute lack of color fringing is accurate.

The Newtonian image to the eye was sharp and etched.  The achromat images to the eye were slightly fuzzy edged even filtered.  The violet cast was mostly distracting on high contrast features.  Unfortunately, those are the very things most worth looking at on the moon.  I will say that the Semi-APO filter tamed the extreme violet fringing enough without adding much color cast that I found the image pleasant to view.

I'll try again tonight if I get the chance to see if I can improve on the results.  No guarantees.

 

Edited August 4, 2023 by Louis D

[Louis D]

@Marian M Here's some more comparison images from last night using the same setup except with a Parks GS 2x Shorty Barlow, so roughly 144x (achromat) and 120x (Newtonian):

Top Row, Left to Right: GSO 150 f/5 Newtonian unfiltered, KUO 152 Achromat unfiltered, KUO 152 Achromat with Baader Semi-APO filter

Bottom Row, Left to Right: KUO 152 Achromat with Yellow K2 filter (Wratten #8), KUO 152 Achromat with Green X1 (Wratten #11), KUO 152 Achromat with Hirsch #12A Light Yellow (Wratten #4) and Hirsch #82B Light Blue (Light Cyan)

This shows that filtering the unfocused violet and red ends of the visible spectrum can help to sharpen up the achromat's image.  However, I stand by my original assertion that the 150 Newtonian stomps all over the 152 Achromat for image sharpness, contrast, and color fidelity on bright objects.

I'll try and get out tonight to see if I can improve on the achromat's performance any.

Edited August 4, 2023 by Louis D

[Marian M]

@Louis D , @The60mmKid , many many thanks for your patience and advices! Having also an APO close to my 120 achro, I see the difference between the 2 designs and also I acknowledge the mass added for a refractor (both for the device itself, as well as for the corresponding mount) for each single inch added. 

I spend the whole afternoon here browsing from other users experience on 152 achro, as well looking for Newton/ Dobson with binoviewer. The single major drawback of the Newton is the lack of bino-friendliness against the refractor; with some short adapters, the 152 may accommodate binoviewer without GPCs.

As I learn from my own mistakes, better to spend more time with comparing my achro and apo, together with my budies Dobsons and experiment when possible my concern on bino. I become bino addicted after discovering the perfect match of MB2 and Morpheus 17.5, for wide view- only the 100 degree eyepieces will be close as visual experience for me

Will keep you posted once I will decide and share here my experience

 

Thank you!

[Louis D]

As promised, I went out last night and took more comparison images of the moon.  This time, it occurred to me, how close would a 2x Barlowed smaller, but higher quality, scope show relative to the big KUO 152mm Achromat.  I brought out my Astro-Tech 72ED and TS-Optics 90mm FPL-53 Triplet APO for comparison at both native and 2x magnification.  I did the same with the GSO 150mm Newtonian as well.  I skipped Barlowing the KUO 152m Achromat because it did so badly in that mode the night before.

Here is a composited comparison image, this time with labels (ST152 = KUO 152mm Achromat).  Make sure to click it open for a high resolution view.

My impression at the eyepiece was that the 90 APO showed the sharpest, contrastiest views, even when Barlowed.  The 72ED was a bit behind thanks to being an FPL-51 doublet.  The 150 Newt was showing incredible detail, sharpness, and contrast as expected.  However, the APO had more WOW factor due to the high contrast.  All three Barlowed extremely well.

The ST152 was just sad to look through.  The Baader SemiApo filter helped it a bit, but there's just nothing that will make it a compelling bright object scope.  The views were blurred, low contrast, and awash in false color.  I included the "Typical Violet Fringe" image because it best captured how the view looks to the eye at the eyepiece.

I will say that bright star fields looked decent in the ST152 with my 40mm XW despite there being some violet fringing on brighter stars.  I'll have to do a comparison in that mode at some point.  Perhaps it might "shine" for wide field sweeping.

[Louis D]

Here's a composite of the KUO 152mm Achromat with no filtering and 8 filter variations to try to both cut violet and sometime red fringing in an effort to increase sharpness and contrast:

The SemiApo is the Baader SemiAPO filter in 2" format.

It's too bad the Hirsch filters are only available used because they had a bunch of unusual colors such as their Light Yellow #12A (Wratten #4) and Light Blue #82B (Light Cyan).

The Green X1 (Wratten #11) and Yellow K2 (Wratten #8) filters are both 48mm Rokunar photographic filters.  Both are still available as new old stock on ebay in 48mm size.

The Cheap Yellow and Green filters came in a set of 6 colors from China for $13.  They tend to cause a bit of light scatter and loss of image fidelity.

The 600nm Shortpass filter (Minus-Red) is an uncut dielectric filter from China.

As in my previous post, the Baader SemiAPO does a very good job at cutting most of the objectionable violet fringing while avoiding adding a harsh yellow cast.

The Hirsch #12A does a good job cutting violet while adding very little yellow cast to the image.

The Yellow K2 is a bit heavy handed.  However, it cuts all but a tiny bit of violet fringing.  I should try pairing it with my 48mm Moon & Sky Glow filter to make a poor man's Baader Contrast Booster and reduce the yellow cast.

The Green X1 is a good compromise to cut both violet and red at a reasonable cost.

The Yellow/Cyan and Yellow/Minus-Red filter combinations do a bit better than the Green X1 by having higher transmission over a broader passband while still cutting almost all violet and red fringing.  However, the components are difficult to find.

[Emperor!Takahashi!]

@Marian M, I know that you mentioned needing to spend time assessing your options, but I also wanted to throw another idea in for consideration. A 100mm binocular telescope is a brilliant rich-field instrument. With the "binocular summation factor" in mind, the brightness of the views it provides is on par with a ~160mm instrument. If I was after a reasonably portable rich-field instrument for binoviewing, something like that would be my first choice. I'd recommend Teleskop Express due to their outstanding customer service.

[bosun21]

On 27/07/2023 at 14:49, Louis D said:

I thought the StellaLyra 12" f/5 Dobsonian comes with the standard GSO 2" Crayford Focuser for Reflectors:

  While the GSO OTA Newts come with a cheapened version of the GSO 2" Linear Bearing Crayford Focuser for Reflectors:

Notice that the pre-tensioning set/grub screws were removed from the GSO LB focuser that is available for purchase separately:

This leads to the problem I mentioned.

Notice that your focuser has at least one pretensioning set/grub screw, so it avoids this issue.

You're right, the standard GSO focuser works fine while the GSO LB packaged with their OTA Newts has the issue I mentioned.

This is the focuser on the SL 12”.

 

[Marian M]

On 31/07/2023 at 16:07, The60mmKid said:

@Marian M, I know that you mentioned needing to spend time assessing your options, but I also wanted to throw another idea in for consideration. A 100mm binocular telescope is a brilliant rich-field instrument. With the "binocular summation factor" in mind, the brightness of the views it provides is on par with a ~160mm instrument. If I was after a reasonably portable rich-field instrument for binoviewing, something like that would be my first choice. I'd recommend Teleskop Express due to their outstanding customer service.

@The60mmKid- I already have a Celestron 20x80 binocular, but I am not using it anymore due to the much better optics in the MB2 and APO (even in the 120/600 achro)/ larger flexibility on eyepieces + more convenient view to zenith. Anyway, with the 90 degree binoculars, this is a fair idea and will give some reading on forums how to they compare + mount requirements. Thank you!

[Marian M]

On 30/07/2023 at 02:51, Louis D said:

Here's a composite of the KUO 152mm Achromat with no filtering and 8 filter variations to try to both cut violet and sometime red fringing in an effort to increase sharpness and contrast:

The SemiApo is the Baader SemiAPO filter in 2" format.

It's too bad the Hirsch filters are only available used because they had a bunch of unusual colors such as their Light Yellow #12A (Wratten #4) and Light Blue #82B (Light Cyan).

The Green X1 (Wratten #11) and Yellow K2 (Wratten #8) filters are both 48mm Rokunar photographic filters.  Both are still available as new old stock on ebay in 48mm size.

The Cheap Yellow and Green filters came in a set of 6 colors from China for $13.  They tend to cause a bit of light scatter and loss of image fidelity.

The 600nm Shortpass filter (Minus-Red) is an uncut dielectric filter from China.

As in my previous post, the Baader SemiAPO does a very good job at cutting most of the objectionable violet fringing while avoiding adding a harsh yellow cast.

The Hirsch #12A does a good job cutting violet while adding very little yellow cast to the image.

The Yellow K2 is a bit heavy handed.  However, it cuts all but a tiny bit of violet fringing.  I should try pairing it with my 48mm Moon & Sky Glow filter to make a poor man's Baader Contrast Booster and reduce the yellow cast.

The Green X1 is a good compromise to cut both violet and red at a reasonable cost.

The Yellow/Cyan and Yellow/Minus-Red filter combinations do a bit better than the Green X1 by having higher transmission over a broader passband while still cutting almost all violet and red fringing.  However, the components are difficult to find.

Dear @Louis D,

 

Many many thanks for your time and patience to come back with so many details. It is very visible that there is no comparison between the 152 and the APOs or the Newton. I have compared directly my 102 APO with the 120/600 achro on Moon and, in fact, there is no comparison. Despite the fac that I have few instruments and eyepieces, you make me curious reading about filters- so far I don’t have any filter in my collection

 

Would help if, at some point of time, you succeed to compare the 2- Newton and 152 achro, for some DSO at different magnifications. At least in theory the 152 should provide better and more pleasant views up to 50x (if DSO is not so shiny- I read somewhere that it was a little violet in Orion nebula 😀), comparable up to 100x and worse after

 

From my initial collection of eyepieces and scopes, I kept so far only the 120/600. Rest I have sold and acquire other stuff, because I realized that is not delivering to the expectations, hence no hurry now with 152 or other design- still learning...

 

Thank you!

[Marian M]

Hi friends!

 

Trying to resurrect this topic, I found that there is another option for a RFT- APM 100mm ED 90 deg binocular. Many thanks @The60mmKid for the idea, somehow I did not pay the proper attentions from the beginning.

From binocular summation theory could be similar with an 140 refractor with binoviewer, or more. I had the chance to look through an Omegon 100mm 90 deg binocular today with 9mm Morpheus (around 60x magnification), but plenty of colors. I presume this one is the same with APM SA (plain achro), so the APM ED should be better. Attaching here a picture with my hand held phone.

• Second image, for the sake of comparison, is another building with high black/ white contrast,  same eyepiece but 120/600 achro, full of colors but maybe better.

 

Just wondering if someone here had the chance to compare a larger refractor with binoviewer with a true binocular

 

Thank you!

[Marian M]

Forgot to add, same magnification and similar eyepieces

[Marian M]

Hi friends!

 

End of the story (at least for the moment)- after a disappointing experience with a new APM 100 SD 90 degrees, I decided to go with an used Omegon Brightsky true binocular (achro, 70mm, 45 degrees) and a branded new TS doublet FPL53

 

Extremely happy with the Omegon true binocular, at low/ low-medium power, through binocular summation factor, shows the same as my 102 with bino, but has the advantage of going to lower power and easier to setup. For medium to high/ high power, for sure 102 is better. I went to observations already many times with it, it is phenomenal with Morpheus 17.5 and 9, probably I should add to my collection the Morpheus 12 as well. Also very nice with APM 24 UFF. It is very natural and easy to setup with a phot tripod and video head. Even if it is an achro, stars looks great, without annoying chromatic aberration. During daylights, the colors are there, but image is very bright and sharp for an achro.

 

The TS 125 just come and I have to test it more times, so far the weather was bad here. It came extremely well collimated from TS (great services from them!) and, at first sight, seems closer to 150 vs 102, where I did some comparisons, as overall planetary performance. Surprisingly, on a short comparison with 120ED SW, the 0.5cm more shows a little bit more- some stars close to Polaris where a little easier to be seen than with 120.

 

Wish you clear sky!