Celestron EdgeHD 14" OTA on Skywatcher EQ6 Pro GOTO mount

[sixela]

plus the more aperture you have, the better the resolution.

But if you have 1300-1500mm of focal length (or less in countries with so-so seeing), the resolution you get on long exposure photographs is gated by the seeing, not the aperture. If you have 3" seeing, there's very little to be gained to make your pixels less than 0.8".

[michael.h.f.wilkinson]

Comparing the SW Mak Newt to the 11 inch Edge makes no sense at all. They are a totally different beast.

The SW scope has a focal length of just over 1000mm, and a focal reduced 11 inch edge, almost 1800mm, so you would be using them for completely different targets.

To say that aperture doesn't matter in imaging is also incorrect. The longer the focal length, the more aperture you require in order to grab the really faint targets in a reasonable amount of time, plus the more aperture you have, the better the resolution.

I have a premium large apo, and on targets that suit its focal ratio and focal length, it is unbeatable, but for fainter, smaller targets, my old (not very flat field) 14 inch LX200 knocked spots off it.

Consequently, I will be getting one of the 11 inch Edge scopes, not to replace the TMB, but in addition, specifically for faint galaxies and planetary nebulae, where long focal length and good light grasp is needed.

Cheers

Rob

Of course the MN190 and the C11 are different beasts, that is why they might complement each other: one better for planetary imaging, one better for deep sky. A C11 with focal reducer requires much tighter guiding than the EQ6 would seem to offer, hence the Mak-Newt might be better (in addition to a C11).

I also tried to make clear that it is the focal ratio that is relevant (which is what you are effectively saying too), not aperture per se. Because many say the EQ6 is good to about 1m focal length, maximizing the aperture at that maximum focal length becomes the issue (and hence minimizing the focal ratio). An MN190 fits that bill quite well (though a C14 Edge at the fastar end will do as well, but it may be too heavy). A C11 Edge does seem to offer the best of both worlds: good planetary performance and high speed imaging when needed.

[RobH]

But if you have 1300-1500mm of focal length (or less in countries with so-so seeing), the resolution you get on long exposure photographs is gated by the seeing, not the aperture. If you have 3" seeing, there's very little to be gained to make your pixels less than 0.8".

Yes, at a certain point, resolution is of course limited by seeing.

However, I have images of M101 taken with both my TMB152, and my 14 inch LX200, and the resolution is superior with the larger scope. This is practical experience, and I'll take that over theory any day

Michael....I see what you're gatting at now....on an EQ6 I would agree that the SWMN190 would be a more logical choice for DSO work.

Cheers

Rob

[MartinB]

SW rate they EQ6 at 25kg. Tak rate the EM200 at 16kg. The EQ6 is an EM200 clone with cheaper engineering. The difference in ratings has nothing to do with the mount but is down to marketing and assessment of the user base. If you are happy with a wobbly experience and visual work only then go with the 25kg limit. If you want a mount working within it's comfort zone and imaging capable (by that I mean capable of producing reasonably tight, round stars) then use stick to 16kg.

Of course, you will get exceptions. I have a dome which offers superb shelter from the wind which would, I think, allow me to go well beyond 16kg with my EM200 but I still wouldn't go anywhere near 25kg for deep sky imaging.

[Steve]

SW rate they EQ6 at 25kg. Tak rate the EM200 at 16kg. The EQ6 is an EM200 clone with cheaper engineering. The difference in ratings has nothing to do with the mount but is down to marketing and assessment of the user base. If you are happy with a wobbly experience and visual work only then go with the 25kg limit. If you want a mount working within it's comfort zone and imaging capable (by that I mean capable of producing reasonably tight, round stars) then use stick to 16kg.

That is worth reading twice, Skywatcher/Synta are rather ambitious with their maximum payloads.

[MartinB]

However, I have images of M101 taken with both my TMB152, and my 14 inch LX200, and the resolution is superior with the larger scope. This is practical experience, and I'll take that over theory any day

Both theory and practice are minefields when it comes to deciding an arguement. Craig Stark has done an excellent (to my limited brain anyway) article on Nyquists formual and maximum achievable resolution when imaging. The jist is you can go well beyond the seeing limit but there are still limits. The general thinking seems to be you can get improvements down to 1/2 the seeing limit. I'm sure that using active optic equipment you can go further still.

Like Rob, I believe my eyes before I believe a theory but it is iffy comparing images taken at different times and in different conditions.

[sixela]

Yes, at a certain point, resolution is of course limited by seeing.

However, I have images of M101 taken with both my TMB152, and my 14 inch LX200, and the resolution is superior with the larger scope.

Even if you'd increase the resolution of the smaller image by simply using a bicubic filter? It's not because the pixels are smaller that there actually is more information in the "larger" image.

[michael.h.f.wilkinson]

Even if you'd increase the resolution of the smaller image by simply using a bicubic filter? It's not because the pixels are smaller that there actually is more information in the "larger" image.

Scaling through b-spline interpolation does not increase the amount of information. To be precise: in terms of information theory, the total information does increase, but that has very little meaning. Adding noise would also increase the number of bits per pixel needed to encode it without loss. The information may be more accessible to the naked eye at a larger scale, but that does not mean we have magically created more detail by scaling the image.

[sixela]

Scaling through b-spline interpolation does not increase the amount of information.

My point is that your other image may, despite the larger resolution, not actually have more information, not that interpolation suddenly creates information. To see that, you have to compare the images at the same scale (scaling up the smaller image, as that doesn't create information but doesn't destroy it either).

Unless, of course, you actually have the seeing to support very large focal lengths with increased information in the image.

BTW, I said "focal lengths of 1300-1500mm" in my original post, so my guess is that your 152mm TMB isn't in that range (and certainly not if you image with a flattener that is also a reductor), which would mean that 3" or 2" seeing would indeed quite likely enable you to see finer details with a larger focal length scope.

[RobH]

BTW, I said "focal lengths of 1300-1500mm" in my original post, so my guess is that your 152mm TMB isn't in that range (and certainly not if you image with a flattener that is also a reductor), which would mean that 3" or 2" seeing would indeed quite likely enable you to see finer details with a larger focal length scope.

The TMB has a FL of 1200mm, and I don't use a reducer/flattener with it.

The LX was used at around F7.

I don't think, as you also say, that the TMB was at the limit of resolution, and I also don't think that the conditions ever allowed me to get the full theoretical maximum resolution from the LX. With my local conditions, I would estimate that a 10 or 11 inch scope would be about the best in terms of potential maximum resolution, and, oddly enough, I'm planning on getting an 11 inch Edge to add to my setup

I wouldn't stick a 60lb 14 inch OTA on an EQ6 and expect to get anything useable at all though :D

Cheers

Rob

[michael.h.f.wilkinson]

The TMB has a FL of 1200mm, and I don't use a reducer/flattener with it.

The LX was used at around F7.

I don't think, as you also say, that the TMB was at the limit of resolution, and I also don't think that the conditions ever allowed me to get the full theoretical maximum resolution from the LX. With my local conditions, I would estimate that a 10 or 11 inch scope would be about the best in terms of potential maximum resolution, and, oddly enough, I'm planning on getting an 11 inch Edge to add to my setup

I wouldn't stick a 60lb 14 inch OTA on an EQ6 and expect to get anything useable at all though :D:D

Cheers

Rob

Enter the EQ7 ?

[ollypenrice]

[quote

I wouldn't stick a 60lb 14 inch OTA on an EQ6 and expect to get anything useable at all though :D:D

Cheers

Rob

Nor would I and, I think, nor would anyone who has used an EQ6 for imaging... In fact finding a mount capable of making good use of a C14 (which is an attractive instrument quite popular here in France with the well heeled) is very difficult. The C14 does not require you to be seriously rich but the mount to carry it certainly does. Putting it on an EQ6 would be like using one of those 17th century refractors with the objecting hanging from a mast and collimated (ahem!) by pulling on ropes as you stood a hundred yards away while the butler held your eyepiece for you to look through.

Me, exaggerate? Never!!

Olly

[michael.h.f.wilkinson]

Nor would I and, I think, nor would anyone who has used an EQ6 for imaging... In fact finding a mount capable of making good use of a C14 (which is an attractive instrument quite popular here in France with the well heeled) is very difficult. The C14 does not require you to be seriously rich but the mount to carry it certainly does. Putting it on an EQ6 would be like using one of those 17th century refractors with the objecting hanging from a mast and collimated (ahem!) by pulling on ropes as you stood a hundred yards away while the butler held your eyepiece for you to look through.

Me, exaggerate? Never!!

Olly

:D:D How did Huygens spot those rings?

[ollypenrice]

:D How did Huygens spot those rings?

He had an almighty fine butler and was not using a CCD....

Olly