Louis D

Try a #56 green filter to block unfocused red and blue wavelengths on bright planets to see if it improves overall sharpness.  It sharpens up Venus tremendously for me.

59 minutes ago, Mark2022 said:

I noticed nobody has mentioned the Baader 495 longpass filter in this thread. I've been reading a lot about this filter and it all sounds good (except trying to find one and at a decent price). So many  are  saying that while it imparts just a shade of yellow - but apparently not too strong - it completely eliminates CA. Some have put it ahead of the Contrast Booster in fact. 

One of my scopes is the StarTravel 120 and it's that one I'm thinking of using the most for EAA when I get my entire setup up and running. I'd love to try out both, the CB and the 495 LP before deciding which I'd prefer. I'd want the 2 inch version to be 'always on' my 2 inch diagonal. Do you think someone like FLO would allow the buying of both and returning the one I didn't prefer? My bank account really doesn't like me.

If you can find a new old stock 48mm Yellow K2/#8 photographic filter local to the UK, it will have roughly the same bandpass characteristics as the Baader 495 Longpass for a lot less.  I have the Rokunar version, and it works very well with a distinct yellow cast, but not nearly as strong as a GSO Yellow #12 filter.  The 48mm photographic threads are an exact match for astronomy 2" filter threads.

When importing expensive items into the US, it can sometimes be to the buyer's benefit to break-up the purchase into sub-$800 chunks to come in under the $800 de minimis allowance per day per person to avoid import duties/tariffs.  The downside is paying multiple shipping fees.  Thus, shipping accessories separately from a new OTA can avoid fees on them.

4 hours ago, Mr Spock said:

I use a 12" StellaLyra after using a 10" Skywatcher Flextube. One thing to mention is the quality of the optics. While this only refers to the scope I have, the StellaLyra 12", I find the image quality and sharpness to be that of premium optics. The Skywatcher was quite good, but this 12" I have is outstanding. Like all premium optics, with excellent seeing conditions it just soaks up magnification without loosing sharpness or image quality.

There's no guarantee other scopes will perform the same, but, I wouldn't be surprised if they did.

The GSO mirrors (the StellaLyra Dobs are GSO made) must be quite good because Teeter Telescopes used to list them as the base option for their telescopes prior to ending production.

4 hours ago, Elp said:

The below diagram is just an indication, but I wouldn't expect a triplet to focus wavelengths of light like this:

Maybe it's trying to show something else like focus flatness across the field at all frequencies?  I'm really not sure what it's trying to show.  Perhaps @vlaiv might know?

Based on all of my "research" I really wish all companies would do like Baader and publish spectrographs/grams of each of their filters so we'd know what we're actually getting, not what we're supposed to be getting.  The #8 Yellow is a major case in point.

4 hours ago, badhex said:

Yikes, that first graphic is busy! 

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

The only reason I have the Baader Semi APO is because it came with an achromat.  It actually does quite well visually.  The previous owner said he left it on his diagonal continuously when using that scope.

4 hours ago, badhex said:

It seems to the layperson that on paper the CB and Wratten #12 are not dramatically dissimilar at the blue end of the spectrum and your images and experience confirms that. Shame you don't have a contrast booster to run through your spectrograph for a side by side with the #12!

Make that #12A.  I also have the #12 (GSO version), and it is quite aggressive at cutting out all blue as you can see from the lower right sub-image in my spectrogram composite image.  It was my second attempt to cut violet.  My first was over 20 years ago when I bought a "Minus Violet" filter, which, as you can see from the second sub-image down in the left column, is a very weak yellow filter.  Any violet reduction it might technically accomplish is not detectable to my eyes.

I then tried the #12 and found that it completely cuts all violet while imparting a very strong yellow cast to everything.  So, I set off on my journey to find the Goldilocks of yellow/minus violet filters.  The #12A and K2/Wratten #8 come closest.  The former leaves a bit of violet without adding an undue yellow cast while the latter cuts all violet while leaving a pale yellow cast that I can tolerate while picking out fine details.  For some reason, the #12A is not available in new production today, and the latter is only available in the 2"/48mm photographic size as new old stock.

The current #8 Yellows are much closer to the 1990s Minus Violet I mentioned above as you can see from the third sub-image down in the left column.  As I've said before, some of the cheap Chinese made "Yellow" filters from ebay are actually very close to the #12A as you can see from the fourth and fifth images in the left column.  However, the one I have does induce some light scatter as is visible in that artificial star image to the right of the fourth image.  Even the polyester film Rosco filters have less scatter (see R### yellows in that composite image).

Of the Rosco filters, the R312 Canary was my favorite.  It cut all visible violet while imparting only a mild yellow cast.  It turns out it is nearly identical to the K2/Wratten #8 photographic filter as is obvious from the second and third images in the right column.

On 05/08/2023 at 06:19, badhex said:

Finally got round to reading this; one of the 2" diagonals reviewed is an Astro-Tech dialectric, same as the WO, Skywatcher and various others. The below paragraph confirms what we concluded in the thread I posted above with diagonal measurements, and as @Mr Spock also mentioned regarding this specific design of diagonal. Since the maximum clear aperture of these diagonals is only 41.5mm the below results are not surprising. 

"Regardless of the diagonal used, the lateral color generated by the eyepiece remained consistent.  However, during the lateral color tests another issue became apparent.  With the Takahashi 2" Aluminum Mirror and the Astro-Tech 2" Dielectric diagonals there was significant light falloff near the field stop when a 2" eyepiece was used with a maximum field stop.  As example, when the 40mm XW was used in either of these two diagonals (approximate 46.5mm field stop size), dimming near the field stop was apparent."

I stick with the GSO dialectrics (three at last count, one being a quartz) and haven't had any issues with any of them with regards to vignetting.

12 hours ago, stormioV said:

Svbony zoom 8-3mm could be a good choice? I haven't used this but there are a lot of positive comments about this zoom.

If the OP doesn't mind tight eye relief, it is an excellent performer between 5mm and 8mm.  For the money, it would be a good buy to be able to exactly tune the magnification to the seeing conditions.

See the following post of mine below for more on SAEP vs. blackouts.  It has some nice animations of each type of blackout by @Ruud.

1 hour ago, vlaiv said:

5" is minimum usable and no wonder 130PDS is such a popular imaging scope. It is still over 600mm in FL (and does have issues with focuser draw tube).

I was thinking in terms of the GSO 6" and 8" imaging Newtonians available at various f-ratios versus the 152mm KUO achromat or even larger achromats (anyone know of any readily available?).  Weight-wise and length wise, I find the 6" f/5 GSO Newtonian much easier to mount than the 152mm f/5.9 KUO achromat.  Perhaps things change once you try to include a filter wheel and other imaging gear?

Also, I could see if you simply want to image wide fields, the refractor route handily wins out.

Would any of that outweigh simply using a fast Newtonian with coma corrector instead of a fast achromat just to avoid a central obstruction?  I can't imagine ever getting better results regardless of achromat filtering.

2 hours ago, JuergenB said:

I once owned a WO FPL-53 doublet - and yes, it showed blue colour fringes around brighter stars in LRGB images. It depends a lot on the L and B filter transmission on the blue side of the spectrum.

Nowadays, you can select beween different types of L filters, for example Astronomik offers three different ones, L1, L2 and L3. L3 opens the transmission window at higher wavelengths (>420 nm) than L2 or L1, which would be advantageous for a less than perfect ED lens.

Juergen

 

If imaging with a fast achromatic doublet like an ST80 or KUO 152, I would think you'd want an L cutoff closer to 470nm like the Yellow #12A to eliminate enough violet blurring to be useful for luminance.  This would still leave the Hβ visible.

If you want information overload, take a look at this spectrograph of multiple violet reduction filters:

I have the Hirsch 12A and find it just about the best compromise of the purely yellow violet-cut filters.  There's still a tiny bit of violet fringe, but it is hardly noticeable.  There is also very little yellow cast introduced.  It also doesn't cut into the Hβ line much, so it could be left on with nebula within bright open clusters.  The problem is, it isn't made anymore.  The closest modern equivalent are some of the generic yellow filters coming out of China (which I have).  The problem with them is that they tend to scatter more light than the older US, Japan, and newer Taiwanese filters like Meade, Hirsch, and GSO.

The modern #8 Light Yellows are similar to the Meade #8 above (which I also have).  It cuts a little bit of the far violet, but not enough to be effective.  On the plus side, there's little to no yellow cast.

The older, true Wratten #8 (Yellow K2) is very similar to the modern Baader 495 Longpass.  However, the yellow cast is strong.  It's not as strong as the modern GSO #12 Yellow, but still strong.  I tried the GSO #12 first of all my yellow filters, and find it the least usable because it cuts all blue and some green, which is massive overkill.  The Yellow K2/#8 filters are still available as new old stock 48mm (2") filters on ebay for under $20 if you want to try one.  It cuts into the Hβ line, so not appropriate for those nebula that strongly emit it.

The Baader Contrast Booster and Semi APO filters simply add a Neodymium glass base that cuts some of the yellow and yellow-orange part of the spectrum to compensate for the loss of violet.  The CB is basically a #8/K2 Yellow or 495 Longpass combined with the Neodymium glass.  The SA is somewhere between the Meade #8 and Hirsch #12A in cutting violet as you can see from the graph, and then adds the Neodymium glass.  In my experience, the SA gets rid of enough of the violet fringe without adding a nasty yellow cast.  My poor man's CB still shows some yellow cast and no violet fringe at all.  The Baader filters add violet cutting coatings to the Neodymium glass to get higher transmission.  However, this doesn't really matter all that much on the bright objects that display violet fringing the most.

There's no violet-cut benefit to the Neodymium's suppression of teal-blue to green wavelengths just above 500nm.  However, when combined with the yellow/yellow-orange cut, the Neodymium filters increase contrast by separating blue from green from red with bandgaps.  Eyeglasses for the color blind work in a similar manner to cut notches between the colors they can't separate with their retinas.

Here's some of my yellow filters run through my spectroscope.  It also includes some Rosco yellows and my attempt to photograph an artificial star through my ST80 with some of these filters.

1 hour ago, Adam J said:

It doesn't quite work as simply as that, it's not just about the focal point being different it's about spherical error changing with wavelength. Hence although you can focus for RGB at best focus B and sometimes R will not be as sharp as G and that leads to blue bloat or purple halo irrespective of you refocusing. Longitudinal chromatic error and spherochromatism are traded against each other in all lens designs so if you want to bring all colours to focus at the same point you normal end up having to trade against a reduction in focus quality for some wavelengths normally blue. Also as others point out you can't do this for Lum anyway. To avoid this design compromise you need a triplet design slower than F6, a quad design will do better and doublet worse. 

In most cases.modern processing will fix things for you but for galaxy imaging. your going to inevitably loose some resolution. 

Adam

I can verify that when using my Meade RGB interference filters with my ST80 visually, I could get a sharp image in green, a reasonably sharp image in red with a bit of refocusing, and a somewhat fuzzy image in blue no matter how much refocusing I tried.  I wrote it off to violet focusing too far from medium blue to bring them both into focus at the same time.  However, spherical aberration in blue might have been what I was seeing as well.  Regardless, I can't imagine a camera not seeing this same blue-violet fuzziness.

The other most commonly mentioned filter for planets is a variable polarizer to cut the glare.  Actually I would recommend two linear polarizers for your setup.  One would go on the front of your diagonal and the other on the bottom of your eyepiece.  Just rotate the eyepiece to vary the amount of dimming to the best level.

I don't know if you've tried binoviewing, but I've found it really takes visible detail on planets up many notches.  In particular, Mars at opposition goes from an overwhelmingly bright orange orb (haven't tried the above crossed polarizers on it yet) to loads of details in a BV.  Same goes for the full moon.

I'd recommend a #56 green filter or cheap Chinese green filter on Venus or on any planet low in the sky.  It really cuts through the red/blue color separation/scintillation due to the atmosphere.

2 hours ago, Stuart1971 said:

One thing I will add, is that it’s a lot cheaper than the rest of the Askar range, so am guessing that will be for a reason…probably the glass….👍🏻

2 hours ago, Elp said:

Always dubious when they don't declare it.

That just means it is FPL-51 equivalent glass when the term "ED element/glass" is used.  Generally figure an FPL-51 triplet will have about the same amount of chromatism visually as an FPL-53 doublet, but with longer cool down time.  I'm not sure how they would compare for astrophotography.  For visual, I would go for an FPL-53 doublet to save weight and cool down time.

Is the Bresser/Explore FirstLight/JOC Dobsonian series so bad that no one mentions them as worthwhile of a look?  I haven't tried one in person, but I like the look of those altitude trunnions and rotatable tube.  I believe the focuser can be upgraded to dual speed.

3 hours ago, GTom said:

Sure, you can "flat out" anything, but what's the point of having an 8" scope if it works like (collects light, resolves) an 6" should?

It will still have the spatial resolution of an 8" which can be important for fine details.  A central obstruction does not change this.  Think about very long baseline interferometry.  It has a huge central obstruction, and yet achieves very high spatial resolution.

58 minutes ago, John said:

Because I currently use refractors, I need to ensure that the 1.25 portion of the APM zoom's barrel clears the diagonal mirror when used in 2 inch mode. This has worked out OK in my Astro Physics and Tele Vue 2 inch diagonals. If I was to use a filter on the eyepiece barrel I think there might be problems though so any filtering of this eyepiece will be applied at the end of the diagonal barrel.

Some folks over on CN have been using a 1.25" to 2" Step Up Ring screwed onto the 1.25" filter threads of their ASZ to prevent it from smashing into their diagonal optics, especially prism ones, when used in 2" mode.  The ring's 2" outer surface will stop at the diagonal's 2" safety lip that prevents 2" eyepieces from inserting too far.  It might also be useful for other hybrid eyepieces with extraordinarily long 1.25" barrels when used in 2" mode in diagonals without a lot of excess insertion distance.

9 hours ago, Frenchastro said:

Yes this applies (VAT 20, Import 4,2...) and yes the Price is all included.

Does the seller collect VAT and remit it to the UK on international sales?  That's how sales tax works here in the US.  Sales between individuals, even internationally, don't have sales tax applied unless the seller has a sales tax permit and meets various other location and sales threshold requirements.  Technically, the buyer is supposed to remit use tax voluntarily when no sales tax is collected, but that rarely happens.  Direct international sales are only subject to federal duties, tariffs, and excise taxes when no marketplace is involved.

If you paid UK VAT, shouldn't your friend be able to get his Japan VAT refunded as a reseller?

47 minutes ago, powerlord said:

I suppose for some, it's seen as a dead end, but tbh I think that's an illusion.

Could you add Galilean wide angle or teleconverters intended for fixed lens digital cameras to the Seestar 50?  I carefully epoxied a step ring to a fixed lens camera that had no filter/accessory thread so I could mount a fisheye adapter to it.  It worked great.

Would the software get all confused by the altered angle of view?

43 minutes ago, Frenchastro said:

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Look at how far the eye lens is recessed on the 25mm!  18mm of eye relief gone to waste.  So much for any illusions of me using the 25mm with eyeglasses (low power + strong eye astigmatism = eyeglasses at the eyepiece for me).  It's almost as bad as my 26mm Sirius Plossls.  I have to really cram my eyeglasses against my face to see their meager 50 degree field of view.  Needless to say, I rarely use my pair in my BV.

I guess I'll rely on those of you with either little to no eye astigmatism or who wear contacts to give feedback on these.

As many others have said, mono versus bino viewing needn't be an all or nothing proposition.  The two forms of viewing can coexist quite happily.  As stated repeatedly by others, binoviewing works best on bright objects where putting two eyes on the target can trigger more parts of the brain's visual processing cortex; thus, revealing more subtle details.  For Mars in particular, I find it goes from being an overexposed orange orb at opposition in monoviewing to a highly detailed, normal brightness object in binoviewing.  The full moon is very similar.  Suddenly, the washed out details on the face of the full moon snap into high contrast features going from monoviewing to binoviewing.  Also, it appears sphere-like instead of circle-like.

Monoviewing shines with fields of view over 70 degrees.  You can't take in much more than about 60 degrees in a binoviewer.  Additional field beyond that is strictly in peripheral vision because you have to view on axis to merge the two images.  While it's nice for context, you simply can't scan around the field of view in a binoviewer.  You will lose one or both images, ruining the effect.  This is not an issue monoviewing.  I really enjoy viewing the neighborhood around objects, especially in star cluster rich regions.

It's also near impossible to keep two eyes aligned to a binoviewer while lazily scanning the skies in super wide to hyper wide eyepieces just to see what's up there like an aimless tourist.  This happens to be one of my favorite activities monoviewing since I like to look for new to me asterisms, associations, and multiple star systems.  I don't really care to find out what I've found, I just enjoy the moment and move on.  I find it highly relaxing and rewarding.

Using a 2" diagonal also allows for adding a TSFLAT2 ahead of the diagonal to flatten wide field views for edge to edge sharpness.  In both my 432mm and 600mm ED/APO refractors, it makes quite a difference at lowest powers.  However, I have to remove it at high powers to avoid the introduced spherical aberration from the flattener that is not visible at lower powers.