Adam J

Thinking about it further another well suited option may be a astro-modified Canon 6D MK1, with its large pixels and huge sensor. Those can be picked up for about £350 used and if self modified is well within budget.

From above FOV simulator image I would say that for someone starting out the 533mc on even a reduced 100ED is going to give too small a FOV. To get the whole of M31 you would need to take 3-4 images and as opposed to 1-2 with the QHY8L. Also 1arcsecond resolution imaging will just not be supported by a 100mm aperture the physiscs will not allow it irrespective of pixel size, daws limit / guiding errors / seeing will prevent it. I dont see it as likely that a beginner to AP is going to get sub arcsecond guiding from a long scope like a 100ED on a HEQ5pro, its just asking too much. Of the suggestions you make all are out of the OPs stated budget and the only one that makes sense to me without needing a change of scope is the ASI071mc pro as it will at least get close to the FOV of the QHY8L. But even second hand you are looking at a minimum of £850 for one of those. So within his budget with some left over even for a duel narrow band filter like an L-extream, I really do think the QHY8L at £400 is a killer option for this scope. https://astronomy.tools/calculators/field_of_view/?fov[]=46||9791||0.85|1|0&fov[]=46||3106||0.85|1|0&fov[]=46||66||0.85|1|0&messier=42 https://astronomy.tools/calculators/field_of_view/?fov[]=46||9791||0.85|1|0&fov[]=46||3106||0.85|1|0&fov[]=46||66||0.85|1|0&messier=31 Above we see that even the all time beginer classic M42 will not fit into the FOV of a reduced 100ED with a IMX533 sensor. Of course the other option for OP would be to go with a shorter focal length scope 300-400mm and then a DSLR or a small sensor camera like the IMX585 but that would again be way over his stated budget. More QHY8L examples below: https://www.astrobin.com/spz642/?q=QHY8L https://www.astrobin.com/317799/?q=QHY8L https://www.astrobin.com/68954/B/?q=QHY8L https://www.astrobin.com/414958/?q=QHY8L https://www.astrobin.com/235662/B/?q=QHY8L I also note that OP may not even have a guide camera / scope as a beginner and doent not mention one above, so again sub arcsecond is not going to happen and the big pixel of the 8L are the way to go. More money left over for a guide camera in future if he is not stretching to £800+ for a newer generation dedicated camera and the 8L will far outperform the DSLR options within budget, especially none modifed units off ebay. Adam

Those are also good options but the issue is that with a 900mm scope at F9 even reduced 2.9-3.75um pixels are small and the field of view tiny. So my view remains that the larger sensor above with large pixels will serve him much better.

https://www.astrobuysell.com/uk/propview.php?view=187929 Would match well with the 100ED due to large pixels and will out perform the DSLR you mentioned. £400 and coupled with a modern filter it's a bargain and still very capable of you can get some longer exposures in. HEQ5 will allow that in theory. https://www.astrobin.com/utxyxp/?q=QHYCCD QHY8L Close to 2 arcseconds per pixel which in my view is ideal. In terms of the DSLR option you mention remember this will not be an astro-modified camera off ebay and so will not be sensitive to the essential Ha wavelength like any dedicated camera would be and will not have cooling like the QHY8L mentioned above either. As a USB camera you will be able to control either the DSLR or the 8L from the house via a remote PC. But as a beginner dont underestimate the challenges involved in remote imaging, it will be hard work getting it all up and running but in the end you will see the benefits. What I would say is that the 100ED is a slow long focal length scope to be starting with something like a SW72ED is a better option for use with a DSLR as it has faster optics, but only if you modify the DSLR by removing the IR filter (depends on your skill level and confidence with electronics). Adam

Dedicated cameras will frequently come up on the used marked for around £500 keep an eye out on astrobuysell and this forum and eventually something will turn up. I would recommend to that over a DSLR with your budget.

You may yet get away with it as 135mm is a wide frame relative to potential pointing errors, its not like your trying to align two esprit 120s or something. Adam

will be interested to learn how well your frames line up between the two without the ability to adjust the pointing of at least one of the two imaging trains. Adam

Its not just the CA in itself, yes you can remove that during processing but in the end it makes the Luminescence channel less sharp because blue photons are not going exactly where you want the to go, same is true for OSC imaging when you cant refocus between RGB filters. Less important for wide field nebula work especially in narrow band, but as the OP has stated small targets (galaxies most likely) then sharpness is going to be a factor in picking up detail and if you don't have to use the L3 you are going to get allot more of those nice blues we want to see in spiral arms. I have a FPL-51 equivalent scope in the form of the FMA180 but that is very much a wide field instrument and using a L3 filter is valid. The often quoted "a good FPL-51 scope will outperform a poor FPL-53 scope" scenario basically relies on someone making a poor FPL-53 design, in this day and age of computer lens design and improved polishing methods you would have to try pretty hard to find such a scope. Hence, given the choice for imaging FPL-53 / FPL-55 / FCD-100 is the way to go. Moreover we know that the Starfield 102 is a good design in this case and that the above argument doesn't apply are a result. The other nice thing about a 4 inch F7 is that they reduce nicely to F5.5 for wider field use also. A 102mm F7 scope with access to both flatterer and reducer is a versatile imaging tool. Adam

I dont see that as being an imaging scope more wide feild visual. You are going to see significant blue bloat from a 110mm FPL-51 doublet at F6 Adam

If you are specifically wanting something for smaller targets and you can afford a stellamira 80mm F10 then if it was me I would honesty be looking at a 150mm F5 Newtonian. Maybe one of the TS optics ones. But if you want a refractor in your price range then that's more difficult. https://www.firstlightoptics.com/starfield-telescopes/starfield-102mm-f7-ed-doublet-refractor.html The starfield 102 F7 would be my choice. Adam

F10 is generally too slow optically to make a good imaging scope.

yes that is normal for this scope, what you will find is that if you move focus in and out then it will centre itself. But if you then move it with your hand you will see some wiggle across the helical focuser. In that situation you have caused an issue by wiggling it and if you then imaged with it colimation would be a long way out. Just move the focus back and forth and it will recenter itself. Maybe something to do before you use it if you have transported it. It will wiggle more the further the focus is pushed outwards. So basically mine does the exact same and if I don't mess with it then it seems to work fine regardless of this "feature". However, having said all this I cant see how bad your wiggle is so one thing to check is this. If you remove the objective you will see three small screws on the focuser ring that hold the thread for the objective onto the focuser. Make sure that they are not loose. They are only small so dont strip them, they just need to not be loose, they should not need to be super tight. Honestly I know the type of program you mean and I have never gotten along with them. My recommendation is that you bit the bullet and do a proper start test its the only thing I have ever found to help me really diagnose these type of issues. Adam

The TS115mm triplet FPL-51 is a great scope to consider as its better than either doublet option you mention above.

Just remember that the maximum batter size you are allowed (in a single unit) to carry onboard a airliner is 100WH. Adam

most important thing is does it slew with the handset? Adam

The 62ED seems a little overkill to me, I would not have thought that you would need more than a 50mm guide scope to be honest. Maybe even a ASKAR FMA180. If you really want to go bigger then how about this: https://www.firstlightoptics.com/telescopes-in-stock/william-optics-guidestar-61.html Adam

Looks like a processing artefact to me. You should not see an Airy disk in prime focus imaging so long as you are in good focus, seeing / guiding errors would normally blur out the first diffraction ring in any case in long exposures. You would normally have to use eyepiece projection to image it. Adam

Hi you are too far out of focus, you should have only about 5 rings visible. If you get too far outside focus the test becomes less sensitive as the errors blend into each other. Not sure what your using but you dont want to auto stretch the image as it will ruin the detail. You want to set exposure so that you can see the rings correctly with autostretch turned off in something like NINA. I tend to do this with a mono camera so not sure how well it works with OSC, the problem being that the different wavelengths may blure the result, I tended to use a green filter for best results. This is an example star test from a friends scope, I did not have any of my own saved. Green filter on a mono camera three rings seen. What you are looking for is that little dot in the middle to be dead in the centre of the outermost ring. As you have less rings the effects of seeing on the star test will be increased and in these temperatures I really doubt you will get good seeing, so defo use an artificial star, 5 meters of atmosphere is much more stable than 10km.

Pegasus focus cube, works really well, I have two.

Depends on actual ambient temperature. But I would say that in the majority of cases if you exposing less than 60s at less than 20c you don't need cooling.

Thinking about it I do think the whole cant include a wedge as standard in the whole range thing when your paying 500+ is very very ribbish of ioptron. Main thing pusing me to the skywatcher. Adam

am also interested in the skywatcher base. Will you post some guiding charts and commend on dithering / backlash if possible? Adam

No not quite, its not how circular the stars are that you are looking for. You want to defocus the star so that you get a ring with a bright centre just on the outside of focus, this is undercorrection in a bright APO. It best to do this with a mono sensor but you can do it with a OSC its just harder. Once you have that then you need to make sure that the brighter central dot is in the centre of the outer rings. This must be done with the star dead centre in the FOV. With such a short focal length you can have it very close (relatively speaking) 20 x focal length is the minimum. So I would think 5 metres is a safe bet. If you find the defocused star is concentric in the centre of the FOV then you can be reasonably sure that it is tilt and not colimation. In this case you can move the star to each corner and focus on it. If you have an auto focuser you can read off the movement relative to the centre focus position, that way you know which direction you are out in. Post images of what you see here and ill help if I can. Adam

could be tilt but also could be colimation, the only way I would be able to tell is with a star test. The fact that your RGB channels look out of alignment pushes me towards it being colimation though. This is how its performing for me with a ASI1600mm pro and a L3 filter to cut down the blue. But I did need to tune the colimation as described to get to this result. I show you this so as you dont feel its just the scope design itself. Another possibility with latteral CA is that of a de-centered lens element on the objective and thats not something that can be cured yourself. The issue with amature scopes and amature astronomy equiptment in general accross the board is that of smaple to sample variation. Its unfrotunate, but not all of it is even the responsibility of the manufacturer with fast apos as all it takes is a jolt in transportation. All I can say is get a artificial star, they are useful things to own in anycase. Adam

True but in that case is it eqmod comparable?