Thinking about a lifelong telescope?

[gorann]

22 hours ago, DaveS said:

Start with the mount. I have my doubts about the CGX, as one of us here @Datalord had all kinds of woe with his and ended up buying one of the last two ASA DDM85s available (I have the other), a £12k mount. As you're in the US possibly a Paramount or AP might be a better bet, though over here the Mesu 200 (Note the Mesu is now in Mk2) is a firm favourite with 100 kg capacity and under £6k, as is the 10micron.

Regarding one 'scope for all? Don't try it as you'll spend more time chopping and changing between imaging and visual to do either effectively. The CPC1100 sounds a great 'scope for planetary visual and imaging, but forget about wedges, as you'll be laying yourself open to even more woe, @ollypenrice has a thing or two to say about those, as he has for Hyperstar. If you want a damn good imaging 'scope the TEC140FL ticks all the right boxes, and is made in the USA to boot.

With DSO imaging the fine tuning to get the best results is so finicky that once you've got everything playing nicely together LEAVE IT ALONE until you start seeing problems.

What camera are you planning on? This will affect the field of view, and the plate scale, which will also impact on how well you can guide, I assume that if you're planning to image with a SC that you'll be using an OAG, as mirror flop will (Not can) be a problem. Trying to get much below 1"/pixel is tricky and depends heavily on your seeing (Not sky darkness)

@gorann has started imaging with a 14" Meade, but his is on a damn good mount (Mesu 200 I thin), he may have something to say about long FL imaging

And just to show I'm not anti big aperture, I have an ODK12 incoming, but that's a relatively manageable 2040 mm FL and will go on the DDM85.

As Dave says I have started imaging with a 14" Meade ACF but it is not on my Mesu but on the EQ8. I bought it more as an impulse since I found it cheaply (2500 GBP) near where I live and thought I could give it a try on my EQ8 that was not in use after I bought the Mesu200. I have to say I have been very positively surprised by how relatively easy it has been to get decent images out of it. With a ZWO OAG and Lodestar X2 I have on good nights had 0.4 "/pix RMS. Here is the first image I caught with it (NGC7331) using a Canon 60Da for RGB and an ASI1600MMpro for lum, totally 5 hours over two nights. I used a Lepus 0.62x reducer so FL=2.2 meters f/6.2. One important point: I also built a second obsy to house this thing - I would never try to set it up each night - just the tube weighs 37 kg (I believe that Celestron is a bit lighter as they use thinner metal.).

Edited September 17, 2019 by gorann

[Datalord]

On 16/09/2019 at 11:44, jinchuriki said:

Just to point out for the mount, were you referring to the CGX, or CGX-L? As it has a fairly big difference between the 55 LBS for CGX and 75 LBS for the CGX-L.

Late to the party, but as DaveS pointed out, I have been a CGX user. Not CGX-L, true, but the difference between those two is a bit of size, not actual mechanic ability. Stay FAR away from Celestron if you want "a lifelong setup".

As to what others point out, the difference between long FL DSO and short (I have a RASA as well as a 12" RC) is unbelievably big. Everything is different. Deciding one night to change from hyperstar to long FL means recalibrating balance, new polar alignment, flats have to be done all over again, camera changed, unless you use CMOS colour, image processing is different. I could go on and on. DaveS had the wisest words:

On 16/09/2019 at 11:25, DaveS said:

With DSO imaging the fine tuning to get the best results is so finicky that once you've got everything playing nicely together LEAVE IT ALONE until you start seeing problems.

As has been said elsewhere in this thread, you seem to have your heart set on this Celestron setup, but lifelong it is not. You will learn a ton of stuff, you will have some good photos and it might be just great. But you will become annoyed over time and you will upgrade. That is my prediction. I can only hope you don't get Post Traumatic Mount Disorder with that CGX.

[pete_l]

10 hours ago, Datalord said:

Deciding one night to change from hyperstar to long FL means recalibrating balance, new polar alignment, flats have to be done all over again, camera changed, unless you use CMOS colour, image processing is different. I could go on and on.

I don't think it works like that 😀 People understand (or quickly learn) that the a reconfiguration on that scale involves a lot of work. So they would tend to make the change-over once a season or once every few months depending on how many observing sessions they have. Unless they have another OTA permanently set up.

But an SCT provides far more options. Apart from the native focal length, it is quick and easy to bolt on a reducer. So an F/10 SCT can easily become F/7 or F/6.3. And using a Night Owl can be brought down to F/4 (though that limits a user to OSC due to shortened distance behind the reducer).
And while the mount was an abhorrence from day #1, my Celestron U2K is still optically and mechanically sound - it will be 20 years old in November.

[Datalord]

3 hours ago, pete_l said:

I don't think it works like that

I would argue it is exactly like that, but the choice of changing is a matter of deciding how often you are willing to go through these motions. 

As someone who went through the motions of cheaper gear and pain, I will advice anyone to buy dedicated equipment for each purpose. Accept limitations, learn strengths and later expand to more setups. The fewer moving parts, the better. 

[william123]

On 15/09/2019 at 18:20, jinchuriki said:

Hello, I've had 2 setups so far, which are the Explore Scientific ED102 and Skywatcher 150p, both on EQ5 mount.

I really feel like I'm ready to take my gear up to the next level, and I really like both observing and imaging, the thing is I'm not really sure how far I'd like to go with this.

Since the EQ5 is not a very sturdy mount for imaging, I'd really like to upgrade it, and I'd also like to upgrade my aperture for both observing and imaging, the most suitable scope for that to me seems to be the celestron SCT so far, I believe with an SCT scope I'll be able to use it for both observing and imaging, the question is really how far I'd like to go with that.

Ideally, I'd say the C11 edge would do the best job for both worlds, it's a really nice scope, fairly big aperture, very sharp for imaging, and that will surely satisfy me.

The issue I'm having with that is I might want to upgrade again in the future, and anything bigger than the C11 is a lot of money....BUT, possibly instead of investing around 4000-6000$ for the C11, it might just be worth spending some more(the C14 edge with CGX-L is sold for 8700$)  and eventually getting the C14 edge, which will probably won't require me to upgrade my gear ever again. It is a thought that needs to be taken very seriously, both money-wise and size/weight-wise, it surely isn't an easy task, but spending 6000$ now, and in 2, 4, maybe even 6 years later spend another 8700$ feels like a waste to me.

A few very important things, first of all, I'm extremely aware of the C11 and obviously the C14 weight and size, it's HUGE AND HEAVY, but I've seen friends with both the C11 and C14, I've also set it up myself, and I don't think it's something I won't be able to handle, and at times, I could still always use my refractor for a small trip if I wanted to.

My imaging goal is mainly DSO, which is why I'm intrested in getting a hyperstar for whatever scope I'll purchase, obviously RASA is what comes to mind first, but since I'd also want to do planetary observing/imaging, I don't think the RASA setup will be very suitable for me, even though it's amazing for DSO.

So after all of this, do you guys have any suggestions for me? One of the reasons I'm coming with this now, is that I'm currently in a place which I can pretty much allow myself to do it, I got a great job, I don't have much responsibilities or bills to pay at the moment, so I can save up very nicely without having to worry all that much about spending such amount of money, which I really can't tell if that will be the case in the future. Thanks for the help.

 

One telescope for everything?  A TEC 140FL or 160FL.  Brilliant for visual or imaging.

[ollypenrice]

7 hours ago, william123 said:

 

One telescope for everything?  A TEC 140FL or 160FL.  Brilliant for visual or imaging.

And capable, with a change of camera, of doing semi-widefield...

or high resolution...

Certainly as far as imaging goes I think a 6 inch class refractor is as close as it gets to 'one scope for everything.'

Olly

 

Edited September 30, 2019 by ollypenrice
Typo

[ollypenrice]

On 16/09/2019 at 22:21, DaveS said:

Of course, if you have a big enough telescope you don't need hyperstar. This is 2 mins exposure at f/10

The catch? A 2 m aperture on la Palma, the Liverpool Telescope.

 

The best proof of the F ratio myth I've ever seen!

Olly

[Ags]

Yeah, but how big were the photosites? I'm guessing you could land a helicopter on them... 😀

[DaveS]

15 um, binned 2x2  so 30 um square. Yep, a pretty good landing pad for helicopters. Or photons.

[Adam J]

On 16/09/2019 at 21:21, DaveS said:

Of course, if you have a big enough telescope you don't need hyperstar. This is 2 mins exposure at f/10

The catch? A 2 m aperture on la Palma, the Liverpool Telescope.

 

Everyone uses this example and every time I say it's a huge sensor with pixels the size of dinner plates better QE than any mature sensor on the market and cryogenic cooling. That's why it overcomes F10. If you stick a asi1600 on it do you really think you would get this result with 2min subs? 

[DaveS]

Nope.

[Datalord]

46 minutes ago, Adam J said:

That's why it overcomes F10. If you stick a asi1600 on it do you really think you would get this result with 2min subs? 

I don't understand the fuss. I shoot at f/8 with my RC. Even at very modest 12" I have to pace my subs from blowing out with a G3-16200, so f/10 can't be that different. 

[ollypenrice]

14 hours ago, Adam J said:

Everyone uses this example and every time I say it's a huge sensor with pixels the size of dinner plates better QE than any mature sensor on the market and cryogenic cooling. That's why it overcomes F10. If you stick a asi1600 on it do you really think you would get this result with 2min subs? 

Sure, but pixels matched to telescope is the key point. And there really is an addiction to the notion of F ratio in isolation in some imaging circles, which is what makes Dave's point valid. Is it right to think in terms of 'overcoming' F10? How did Julian Shaw 'overcome' F15 in the Sombrero posted earlier?

Olly

[niallk]

On 16/09/2019 at 12:20, jinchuriki said:

...and I might just get a big dobsonian later on in the future if I feel like it.

Ya, just go for a real nice dob

[Adam J]

8 hours ago, ollypenrice said:

Sure, but pixels matched to telescope is the key point. And there really is an addiction to the notion of F ratio in isolation in some imaging circles, which is what makes Dave's point valid. Is it right to think in terms of 'overcoming' F10? How did Julian Shaw 'overcome' F15 in the Sombrero posted earlier?

Olly

The sombrero is a very very bright galaxy. I think I actually did the full calculation for you on that telescope once before ill look to link it tonight.

The problem is that in the community we tend to  decide on our camera first and our scope second, that is normally because the choice of camera is constrained even more than the choice of scope by financial considerations.  Or if we do have a scope already then we just bung the sensor that we can afford onto it as opposed to the one that best matches the scope and the desired FOV.  People cant generally afford a large sensor and a large aperture fast F-ratio scope to match it to  and to cover the sensor with a flat field. What that results in is compromise on either the sensor the scope or more likely both. 

So lots of the time when people discuss wanting faster f-ratio scopes to reduce imaging time then its under the assumption that they will be forced down the path of using the sensor they have with it as opposed to the sensor that matches it best trading image scale for FOV and speed.  As such with that fixed sensor type you will always image faster with a lower f-ratio scope as larger optics at a higher f-ratio will just result in increasingly sub optimal image scale.

As you note looking instead at achieving a fixed image scale independently of focal length, in that case and assuming that your read noise is fixed at a per pixel level you will end up with the imaging rig being faster independent of f-ratio.  The problem is that its not possible to do  as we don't have access to a infinite range of sensor types in the same way as we have access to scopes that cover all focal lengths.  Although you can bin in software and or hardware it all becomes impractical because the sensor has gotten no bigger and you cant afford a bigger sensor with larger pixels to go hand in hand with you cheap 120mm F9 doublet and allow you to continue to fit the whole of M31 into your FOV at a fixed image scale.

With the "affordable" cameras having relatively small pixels and small sensor area these days trading image scale for increased Signal to noise and FOV via a focal reducer is a good trade. Are you better off having the same FOV with a larger sensor and larger and bigger pixels to maintain image scale irrespective, coupled to a larger aperture higher F-ratio scope....of course you are....can people afford to do that, no.     

The sombrero is a fantastic top quality image, but I seem to remember from previous discussion that I dont believe that on very close inspection detail is being resolved down to the pixel level, as such it was my previous conclusion that its was slightly over sampled for the seeing and that as such a similar result could have been achieved in less time if the Barlow had not been used. But even regardless of that the argument here is not that it could not be accomplished at F15 its that the same SNR would have been achieved in less time if it had been taken at F9. Finally as above the Sombrero is very bright, not sure I would want to try that with even something like M101. 

 

Adam  

Edited October 1, 2019 by Adam J

[Limerick John]

The C11 is a good all round instrument. Get a decent mount though, something like a Losmandy G11 or better. Be careful with Celestron mounts if you intend to hold onto them for a long time as spare parts can dry up on them once Celestron stops supporting them. I find myself using the smaller instruments most of the time, largely due to time limitations and the crappy weather here. I can't remember the last time I set up my C11.