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What APO should I buy this time?

Sky-Watcher Explorer 150PDS Equipment Refractors Reflectors
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Tommy Blomqvist avatar
Tommy Blomqvist avatar
I've played around with astrophotography since back in the 70:ies and have been using many different achros, apos, sct:s and newts.

My only AP-rigg right now is based on a Skywatcher 150PDS Newtonian OTA.
My last refractors were Skywatcher 72ED and 80ED but the 80 was a bit slow even with the 0,85 flattner.
I liked the 72ED field of view but the image quality was not really what I was looking for.

Most of the times the images from the 150PDS seemed much better than the 80ED.
Not only the resolution but also the focus that was better with the Newt using the same EAF (switched between the very similar focusers), filters and OSC-camera.
When I'm browsing the images on astrobin I got the feeling that it isn't only me getting this.
The ED-evostarts aren't real apochromats according to me but it wasn't the CA really worried me.

On top of that my (budget) HEQ5 seemed not to mind if I loaded it with 8 kg of scope on in (<1") so the EDs went to someone who liked them more.

But NO this is not a thread about why reflectors are the best but more about what APO I should buy now smile

I'm a bit of galaxy hunter but cannot afford the really long FL for that right now (the 750 on my 150PDS is the limit).
But sometimes I would like to image some "clouds in space" (or more likely closer to earth).

Questions:

I've been looking at Explorer Scientific AP 80/480 with FCD-100 and the "Hexafoc" focuser.
I believe that OTA is better suited for me as it is fast and has a FOV seems nice.
Does anyone has any experience or thoughts about that OTA?

( Other recommendations are welcome even if we all know that there are many billions of threads about that before smile )
Roger Nichol avatar
Roger Nichol avatar
Have you considered the Skywatcher Esprit 100ED or 120ED, or even the 150ED.  I have the 100ED (550mm, f5.5)  and find it excellent for most nebulae and not too shabby for the small stuff if you drizzle and collect enough data.
Stuart Taylor avatar
Stuart Taylor avatar
I can thoroughly recommend the Esprit 150ED APO. With the reducer it's f/5.4 and gives beautiful results. You would need a bigger mount than the HEQ5 though; mine is on an EQ8
Well Written Concise
Tommy Blomqvist avatar
Tommy Blomqvist avatar
Roger Nichol:
Have you considered the Skywatcher Esprit 100ED or 120ED, or even the 150ED.  I have the 100ED (550mm, f5.5)  and find it excellent for most nebulae and not too shabby for the small stuff if you drizzle and collect enough data.

No I've not tried the Esprit-line from Skywatcher but they seems nice.

I think the 100ED would work on my mount but it's double the price so I think I will need to consult with my CFO.
Maybee Esprit 80ED would work for me...
Around the same price as the ES-OTA and 50% less in weight and a bit faster than the 100ED.
andrea tasselli avatar
andrea tasselli avatar
None of those refractors are truly APOs, they're ED achromats.
Well Written
Tommy Blomqvist avatar
Tommy Blomqvist avatar
andrea tasselli:
None of those refractors are truly APOs, they're ED achromats.

Exactly , the 72 and 80ED are only ED achromats (as I stated earlier) but the Esprit are tripples.

But I am not going after specifications of number of lenses or exotic materials. The only real important thing for me are how well they produce good images of DSOs 😀
andrea tasselli avatar
andrea tasselli avatar
It depends on how tolerant are you of lateral colour and purple haloes.
Tommy Blomqvist avatar
Tommy Blomqvist avatar
andrea tasselli:
It depends on how tolerant are you of lateral colour and purple haloes.

True - I have realised that I'm more fund of stars without haloes than with (i don't really like diffraction spikes either)
andrea tasselli avatar
andrea tasselli avatar
Tommy Blomqvist:
True - I have realised that I'm more fund of stars without haloes than with (i don't really like diffraction spikes either)

Then it is most likely that none of the Esprit will fully statisfy you. Try your luck with either AP, Taks, Pentaxes, LZOS/Lomos and high end offering from APM.
Stuart Taylor avatar
Stuart Taylor avatar
andrea tasselli:
None of those refractors are truly APOs, they're ED achromats.

The Esprit 150 ED APO is a true apochromat. It has three elements.
Well Written
andrea tasselli avatar
andrea tasselli avatar
Stuart Taylor:
The Esprit 150 ED APO is a true apochromat. It has three elements.


Having three elements isn't necessarily suffiecient condition to meet the apochromat criterion (in the most widely accepted modern definition).
Stuart Taylor avatar
Stuart Taylor avatar
andrea tasselli:
Stuart Taylor:
The Esprit 150 ED APO is a true apochromat. It has three elements.


Having three elements isn't necessarily suffiecient condition to meet the apochromat criterion (in the most widely accepted modern definition).

Understood. But what makes you think the Esprit is not a true APO?

https://skynews.ca/review-sky-watcher-esprit-120-refractor/
andrea tasselli avatar
andrea tasselli avatar
From what I've seen they all have, to a smaller or larger degree depending on the specific model, blue-purple halos and noticeable lateral colour aberration.
Stuart Taylor avatar
Stuart Taylor avatar
andrea tasselli:
From what I've seen they all have, to a smaller or larger degree depending on the specific model, blue-purple halos and noticeable lateral colour aberration.

I've certainly not found that. In any case, surely the designation apochromat refers to the optical design? All references to the Esprit series (and not just sales pitches from dealers) refer to them as APOs
andrea tasselli avatar
andrea tasselli avatar
If you're happy with that fine by me. However, your M31 shot tells a different tale to my eyes.
Roger Nichol avatar
Roger Nichol avatar
andrea tasselli:
From what I've seen they all have, to a smaller or larger degree depending on the specific model, blue-purple halos and noticeable lateral colour aberration.

Not in my experience. I see no noticeable CA and the only halos that I have had are from filters and those are mostly gone now that I have changed from the L-eXtreme filter to the Antlia ALP-T filter.  Take a look at my recent Crescent Nebula or Cave Nebula as an example.
Tommy Blomqvist avatar
Tommy Blomqvist avatar
Sorry - It was not my intention to start an argument about the definition of what is apochromatic or not.

As I said, I am more interested in the result than the theory in this particular case.
If someone recommends me a cheap achromat that gives point-shaped stars and good resolution, I choose it even if it does not have sexy specifications.
It will hurt but I will do it

"Cheap OTA without CA ... sounds like something that needs a coma corrector" - Snake Plissken 1981
andrea tasselli avatar
andrea tasselli avatar
Roger Nichol:
Not in my experience. I see no noticeable CA and the only halos that I have had are from filters and those are mostly gone now that I have changed from the L-eXtreme filter to the Antlia ALP-T filter. Take a look at my recent Crescent Nebula or Cave Nebula as an example.


You can't seriously think of checking the CA of an image made using narrowband filters, do you? No filters whatsoever would be the way to go.