gorann

But then the filter wheel be pointing up instead of down (or vice versa), if that is supposed to matter (maybe I have to see the video).

But then, what happens to the weight balance after a meridean flip?

Yes, it does not make sense to me either - if the weight does not change (and turning the optical train will not change its weight) then balance could not change, it seems to defy physics.

That suggest that you are really running near the limits of your mount - maybe that would not be a problem with a bigger mount. Also, I still do not really understand how rotating the filter wheel could change the balance. You do not change the weight on each side of the center of gravity of your telescope. If that was the case - would you not be in trouble after a meridean flip?

PS. APM even sells it with a Riccardi as a set: https://www.apm-telescopes.de/en/telescopes/refracting-telescopes-ota/apochromates/skywatcher-esprit-120ed-triplet-apo-refractor-120-mm-f-5.25-corrector-apm-riccardi-apo-reducer-set.html

Then you need to go for the Riccardi - it has a longer distance: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p11122_Riccardi-0-75x-APO-Reducer-and-Flattener-with-M63x1-Thread.html But I am not sure why you need that camera rotator.

The stars are not out of focus - they are elongated in the corners of the image (like you get with the wrong distance between reducer and chip). I have tried with thin spacer rings in 0.5 mm steps. Unfortunately TS just says that it has to be tested out and could not give me the correct distance. There is this thread on CN where they at the end seemed to get it to work with the TSAPORED075: https://www.cloudynights.com/topic/659716-sw-esprit-100ed-focal-reducer/ This is what a simply stretched image looks like when I use a 52.5 mm distance between reducer (TSRED379) and chip, and it is the best I got so far. I also include the finally processed one where I used a few tricks in PS to kind of fix the stars.

Unfortunately SW does not make dedicated reducers for the Esprits (those for the Evostars do not work for Esprits), and the ones that people have got to work are two from TS (TSRED379, TSAPORED075) and the Riccardi reducer. With the TS reducers you need only one adapter ring while you need a whole costly bunch for the Riccardi. I have a TSRED379 and after much testing with distances I kind of got it to work with my Esprits, but for an APS-C ship I still get some annoying star elongation and chromatic abberation in the corners. It may be that with the newer and slightly more expensive TSAPORED075 you could get better results. It may also be that you need to be lucky with the particular sample you get.

I know that you should use guide-exposure times that are long enough not to chase the seeing (around 5 s), but in my experience I can never get really good guiding on nights with poor seeing and to get guiding at 0.21 "/pixel RMS would at least be impossible for me at a night with poor seeing (I am happy when I get 0.4" with my Mesu and that only happens with good seeing).

Not sure why you worry about seeing. Since you say that you have your current mount guiding at 0.21" RMS, which is almost unbelievably good, that must mean that you have very good seeing at you location (that kind of super guiding would be impossible with even slightly bad seeing), so an Esprit 120 would have no problems catching more details than an Esprit 80 if you have it on a mount that can handle it, like one of the EQ6 varieties. PS. I assume you have put in the correct focal length of your guide scope into PHD2 (or the RMS value would be wrong).

I was thinking about this thread from 2018 where FLO praised Esprits, saying "A small number have needed tweaking on the bench before they were released but I cannot recall one that was rejected outright for optical reasons. We still occasionally reject one for mechanical/cosmetic reasons, though usually before it is sent to Es Reid. Overall we, ourselves & Es, are very impressed with the Esprit series. I am not aware of any other range of triplet refractors that perform as well, certainly not at the price Esprits sell at. "

I bought both my Esprits from FLO and had them tested by Es, although I was informed by Steve at FLO that this was really not needed for the Esprits since Es never had any issues with them. So John, I would be interested to hear from from where you had the information that "Esprit scopes is a bit variable and really need checking and setting up"?

I do not think you could go wrong with an Esprit 120. I have two Esprits, 100 and 150, and I love them so I have also contemplated a 120, but then there is this one, slightly bigger and the same price, and it gets great reviews as far as I have seen: https://www.teleskop-express.de/shop/product_info.php/info/p7717_TS-Optics-PHOTOLINE-130-mm-f-7-FPL53-Triplet-Apo---3-7--Focuser.html Have a look at these on Pete's Astrobin: https://www.astrobin.com/users/pete_xl/

Great image! Like you Lee, I try to keep everything clean and I have acturally never used flats. If by chance some grains of dust have creaped in they are very easy to take care of in PS (with curves, layers and the brush tool), and that takes much less time than taking flats and calibrating. And I mainly use OSC and there flats seem to mess things up (at least the few times I have tried to use them). And the little vignetting I get with my current set ups is easy to get rid of in processing (DBE, Gradient Exterminator etc).

Interesting thread, but I expect, as someone said, that the differece between expensive and very very expensive filters may be more apparent for NB filters. I wonder if anyone has any experience with the Baader Ultra-Narrowband 4.5nm OIII Filter? It is 40% of the price of the Chroma 5nm Oiii filter. Same question could of course be asked about the Baader 3.5 nm Ha filter (I have it but have no Astrodon or Chroma to compare it to).

You can run the camera without a filter but you may get bloated stars since the camera lacks an IR/UV filter (at least my ASI071 lacks it) and your scope is probably poorely corrected outside the visual light spectrum (400-700nm). With my Esprits I noticed that it works quite well without a filter but maybe not for the less well-corrected Evostar. PS. TS also sells some filter sliders, like this one, but you will need to adjust with T2 rings to get the correct distance to the chip. https://www.teleskop-express.de/shop/product_info.php/info/p10475_TS-Optics-M48-Filter-Changer---strengthened-Design.html

I agree with Olly - my aim with processing is to exaggerate both the faint stuff and the colours. Visual astronomy is essentially a B/W experience and imaging allows us to bring out colours. Earlier today I entertained myself by putting together some HaRGB images of Sharpless object that I imaged in Feb-March. There were almost no traces of these nebulae in the RGB data - only visible in the Ha data. Ha is red to I used blend mode lighten in PS to add it to the red channel. So red is red but much more red than what our eyes could ever see, probably not even if we put an eyepiece on the biggest scopes on Earth (if there is a possibility to fit an eyepiece to them):

How do we know that Hubble got the colours right?

I echo Wim's comment!

Like Wim I have given up for the season, but then we are both at 60°N, I am sure I could still get 1-2 hours of data in a night but it would be light pulluted and I do not want that kind of data if I can get much better data in late August. So I will start digging for a new pier and obsy instead. Drewling over new equipment, which I usually do a lot in the summer, is also difficult in the present situation since delivery dates are very uncertain, especially from China (like ZWO and Sky Watcher), see for example this message https://www.pierro-astro.com/. I am still waiting for an ASI camera that I paied for in February.

I like to test out different approaches, and for galaxy hunting this spring I have been using two big SCTs (Meade 14" ACF and EdgeHD 11") but a year ago I dedicated my galaxy season to imaging with my Esprit 150 and ASI071 OSC. OK, not really <800 mm, but not that far off. The FL of the Esprit 150 is 1050mm. What I like with imaging galaxies with shorter FL scopes is that you can fit in more of them. Here is 7 hours on M100 and a few others that would not have ended up together with my SCTs. But on nights with very good seeing the SCTs will pick up a bit more detail than the smaller refractor (at least in the same amount of time).

Thanks a lot Mark! I have no idea what it would look through an eyepiece - I should try that one day when it gets dark again.

Yes, aperture rules - ESA do not put up 5" refractors on mountains in Chile.

As Olly says the Sony A7s would be a good match for a C11, especially with a 0.7x reducer. Then you would be working at 0.88"/pixel. See http://astronomy.tools/calculators/field_of_view/

Thanks Dave! Yes, astro darkness is gone so it is time to start digging for the new pier and small shed around it (just to protect the gear - not the 6 and 12 m2 ones I have now). It will initially be for a RASA8 on a NEQ6. Maybe it is borderline madness to have three obsies.....