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7-9,5 Inch Telescopes for DSO Imaging?

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#1 AFScienceTime

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Posted 16 August 2014 - 04:04 AM

I am looking for a high level, but sub 3800$ telescope for DSO imaging. My criteria:

 

  • It has to have a focal length larger than 800mm. 
  • It HAS to be portable. That is, it CAN'T be longer than 85cm (preferably shorter than that), and CAN'T be heavier than 18 kilos.
  • As I have already stated, it has to be 180-250mm in aperture, preferably 7-9,5 inches.
  • It HAS HAS HAS to be cheaper than 4000$, and preferably cheaper than 3500$.
  • It has to have very little or no chromatic aberration/spherochromatism, so that it can be later (probably) used for spectroscopy.
  • MUCH preferably faster than f/10, but if it matches all other criteria, I would probably not mind too much if it was f/12, but not slower.
  • It has to be very good for DSO astrophotography with 35mm chips, that is, it has to have a flat field. I don't care for larger than 35mm.
  • Diffraction spikes don't annoy me, I actually find them very nice.
  • Good contrast is welcome.
  • Point like stars are very welcome.
  • Coma is NOT welcome.
  • It doesn't HAVE to be a catadioptric, I am just posting it here because most of them will probably be. It can be what ever optical design you want, as long as it matches the criteria (say, it can't be a common newtonian, since that would be way too large, and would probably have coma. There are some shorter "super-newts" though, although most of them are really expensive and have 500mm of focal length (yes, I am talking about you, epsilon 180ED))

Am I asking for too much?


Edited by AFScienceTime, 16 August 2014 - 04:10 AM.


#2 dotnet

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Posted 16 August 2014 - 04:14 AM

If it didn't have to be 180mm or larger the WO FLT132 would fit the bill nicely.

 

Other OTAs that fit the dimensions would be the Intes Micro Alter M706 or M806 astrographs, but I doubt very much that you'd get them for $4000.

 

Cheers

Steffen.


Edited by dotnet, 16 August 2014 - 04:19 AM.


#3 Cotts

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Posted 16 August 2014 - 06:18 AM

$2600 on the 'other' site...

 

http://www.astromart...ified_id=863297

 

Sounds like a Ritchey - Chretien is your best bet....

 

Dave



#4 AFScienceTime

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Posted 16 August 2014 - 06:20 AM

If it didn't have to be 180mm or larger the WO FLT132 would fit the bill nicely.

 

Other OTAs that fit the dimensions would be the Intes Micro Alter M706 or M806 astrographs, but I doubt very much that you'd get them for $4000.

 

Cheers

Steffen.

 

Hmmm... The WO FLT132 isn't what I am looking for. The Intes Micro Alter M706 seems very interesting, but since it is a Maksutov-Cassegrain, I am not sure about how flat the field will be, and it might have some spherochromatism/chromatic aberration. I have to learn some more stuff about it.

 

Anyway, any other suggestions? If there was some good 8'' f/8 Ritchey Chretien with a flat field at 3500$ it would be perfect.

 

Thank you anyway.



#5 Cotts

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Posted 16 August 2014 - 06:23 AM

Lots of choices here:

 

http://www.optcorp.c...lescopes-1.html

 

 

dave



#6 AFScienceTime

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Posted 16 August 2014 - 06:23 AM

$2600 on the 'other' site...

 

http://www.astromart...ified_id=863297

 

Sounds like a Ritchey - Chretien is your best bet....

 

Dave

 

This looks nice! It is not perfect, but with a field flattener it will be. The coolest part is that this telescope is available in a nearby astronomy shop. The portability might be an issue though (10''). 

 

I am still open to any suggestions.


Edited by AFScienceTime, 16 August 2014 - 06:28 AM.


#7 AFScienceTime

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Posted 16 August 2014 - 06:31 AM

Um... the 10'' RC seems to have a huge central obstruction, so the contrast will be degraded. Not too bad though.



#8 GJJim

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Posted 16 August 2014 - 07:17 AM

At the f-ratios of typical RCs you are looking at long sub exposures for DSOs and performance of the mount becomes important. What mount are you planning to use?



#9 AFScienceTime

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Posted 16 August 2014 - 07:52 AM

At the f-ratios of typical RCs you are looking at long sub exposures for DSOs and performance of the mount becomes important. What mount are you planning to use?

 

Not quite sure yet. I might use the Celestron Cgem DX, most probably with an autoguider, but since the 10'' CF one is really light, the Cgem DX might be good enough to take acceptable unguided photos, I have heard very good things about it's tracking. But do you have any suggestions for a mount at about the same price range? 



#10 elwaine

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Posted 16 August 2014 - 08:22 AM

 

At the f-ratios of typical RCs you are looking at long sub exposures for DSOs and performance of the mount becomes important. What mount are you planning to use?

 

Not quite sure yet. I might use the Celestron Cgem DX, most probably with an autoguider, but since the 10'' CF one is really light, the Cgem DX might be good enough to take acceptable unguided photos, I have heard very good things about it's tracking. But do you have any suggestions for a mount at about the same price range? 

 

 

IMHO, you are working backwards. Decide on your mount and tripod first, and understand their capabilities and limitations. Then chose a 'scope to match the mount. E.g., how much instrument weight can it carry and how well does it track (guided and unguided) under a given instrument load. It is a lot more satisfying, and a lot less frustrating, taking long exposure subs with a good mount (e.g., one that has an inherent PE of +/- 10 arc seconds) than it is to try to get nice round, un-bloated stars, using short subs on a mount with a PE of +/- 35 arc seconds and wiggles in a breeze or vibrates when anyone walks near the mount.

 

If you're serious about astrophotography, your choice of a mount is more important than your choice of a telescope - especially if you plan on using rather long focal length instruments. On the other hand, if all you want are OK photos (and even just OK photos can be loads of fun and very satisfying), then you will have more leeway with your choice of a mount... but it's still very important.



#11 elwaine

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Posted 16 August 2014 - 08:26 AM

Um... the 10'' RC seems to have a huge central obstruction, so the contrast will be degraded. Not too bad though.

 

Not so. That statement holds for visual astronomy, but for astrophotography the final product of your stacked images undergoes post-processing steps that enhance the contrast and sharpens the final image. 



#12 AFScienceTime

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Posted 16 August 2014 - 11:33 AM

 

 

At the f-ratios of typical RCs you are looking at long sub exposures for DSOs and performance of the mount becomes important. What mount are you planning to use?

 

Not quite sure yet. I might use the Celestron Cgem DX, most probably with an autoguider, but since the 10'' CF one is really light, the Cgem DX might be good enough to take acceptable unguided photos, I have heard very good things about it's tracking. But do you have any suggestions for a mount at about the same price range? 

 

 

IMHO, you are working backwards. Decide on your mount and tripod first, and understand their capabilities and limitations. Then chose a 'scope to match the mount. E.g., how much instrument weight can it carry and how well does it track (guided and unguided) under a given instrument load. It is a lot more satisfying, and a lot less frustrating, taking long exposure subs with a good mount (e.g., one that has an inherent PE of +/- 10 arc seconds) than it is to try to get nice round, un-bloated stars, using short subs on a mount with a PE of +/- 35 arc seconds and wiggles in a breeze or vibrates when anyone walks near the mount.

 

If you're serious about astrophotography, your choice of a mount is more important than your choice of a telescope - especially if you plan on using rather long focal length instruments. On the other hand, if all you want are OK photos (and even just OK photos can be loads of fun and very satisfying), then you will have more leeway with your choice of a mount... but it's still very important.

 

Well, mounts confuse me a little bit. Can you suggest me one that is portable, not much more expensive than the cgem  dx, has the load capacity needed for some 10" scopes (if it works perfectly well with 16 kilos then it is probably OK) and has little PE? I have heard good things about the cgem dx, people say that the tracking is very good and has very little PE, but I don't know exactly how little. 



#13 AFScienceTime

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Posted 16 August 2014 - 11:46 AM

Speaking of wobbly mounts, my first telescope ever was a Celestron NexStar 130SLT. I enjoyed using it very much, but I had to hold my breath while observing! Man, it was wobbly! And what a bad focuser... Ok optics though.



#14 AFScienceTime

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Posted 16 August 2014 - 12:12 PM

Also, I noticed a truss tube Astro Tech RC. Anyone know about that?



#15 Dom543

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Posted 16 August 2014 - 12:14 PM

Hypertuned CGEM's are used by many successful astrophotographers. The trick is not to extend the legs and possibly get a spreader shelf. The CGEM DX is the same mount on a heavier tripod.

I am surprised that no one has suggested an Edge HD 9.25. The 9.25 has the reputation of being the best of the SCT's and the HD's are optimized for flat field and full-size sensors. All that they need is an aftermarket Tempest fan.

AstroTech RC's have the reputation of being high maintenance tubes that are not easy to work with. They need additional investment in an adequate focuser and are difficult to collimate. Could be a frustrating first immersion into astrophotography.

--Dom

#16 AFScienceTime

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Posted 16 August 2014 - 12:23 PM

Hypertuned CGEM's are used by many successful astrophotographers. The trick is not to extend the legs and possibly get a spreader shelf. The CGEM DX is the same mount on a heavier tripod.

I am surprised that no one has suggested an Edge HD 9.25. The 9.25 has the reputation of being the best of the SCT's and the HD's are optimized for flat field and full-size sensors. All that they need is an aftermarket Tempest fan.

AstroTech RC's have the reputation of being high maintenance tubes that are not easy to work with. They need additional investment in an adequate focuser and are difficult to collimate. Could be a frustrating first immersion into astrophotography.

--Dom

 

"Hypertuned"? What does that mean? Also, yeah, the Edge HD is great and has a very flat field, but sadly it does have spherochromatism and some chromatic aberration. If I decide to do spectroscopy, the Edge won't be very good I think. I know that the Astro Tech RC's are hard to collimate, but I don't mind, because I know some experts relatively near my house, so they could help me with that. 



#17 elwaine

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Posted 16 August 2014 - 02:15 PM

Well, mounts confuse me a little bit.

 

 

:) You're not alone. I've been doing astrophotography for more than 20 years, and I've been an amateur astronomer for over 30 years, and mounts still confuse me too.

 

it would be presumptuous of me to suggest a mount as I don't want to spend your money. So let me say this: astrophotography is A LOT OF FUN!!!  You don't have to take a publishable quality astro-image to fall completely in love with the hobby. My first one was terrible (in retrospect), but it was an absolute thrill.

 

My suggestion is to start that hobby with a small refractor - something in the 80 to 90 mm aperture range and not with a 180 - 250mm telescope. There are many mounts that will support such a telescope and result is very beautiful photographs. 

 

Astrophotography is a hobby one has to "grow into."

 

Here is the best advice I can give you: call our friends (and sponsors of Cloudy Nights) at Astronomics. Tell them what you want to accomplish and how much you can afford to spend - including mount, telescope, and camera. They won't steer you wrong.

 

Go for it, friend. Astrophotography is a wonderful hobby!


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#18 mark379

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Posted 16 August 2014 - 03:18 PM

I think a celestron edge HD 8" or 9.25" with the .7 focal reducer would fit your requirements nicely....



#19 AFScienceTime

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Posted 16 August 2014 - 03:35 PM

 

Well, mounts confuse me a little bit.

 

 

:) You're not alone. I've been doing astrophotography for more than 20 years, and I've been an amateur astronomer for over 30 years, and mounts still confuse me too.

 

it would be presumptuous of me to suggest a mount as I don't want to spend your money. So let me say this: astrophotography is A LOT OF FUN!!!  You don't have to take a publishable quality astro-image to fall completely in love with the hobby. My first one was terrible (in retrospect), but it was an absolute thrill.

 

My suggestion is to start that hobby with a small refractor - something in the 80 to 90 mm aperture range and not with a 180 - 250mm telescope. There are many mounts that will support such a telescope and result is very beautiful photographs. 

 

Astrophotography is a hobby one has to "grow into."

 

Here is the best advice I can give you: call our friends (and sponsors of Cloudy Nights) at Astronomics. Tell them what you want to accomplish and how much you can afford to spend - including mount, telescope, and camera. They won't steer you wrong.

 

Go for it, friend. Astrophotography is a wonderful hobby!

 

Thank you! I have to say that I am not planning to take up astrophotography or buy any of these telescopes/mounts yet, as I don't have the money yet, but I want to learn what is available and all the options! I have heard the thing about starting out with a small refractor and then moving on to the "big guns", and I have considered it seriously, BUT I thought that a "large" but portable catadioptric or similar would suit me better, as if I take the (steep) learning curve, I will have the telescope I really needed anyway, and I won't have to upgrade and spend even more money. I know, small refractors can capture stunning wide field images, but I am more interested in taking close-ups of planetary nebulas, galaxies, and generally smaller objects. Eventually, I might decide that it would be better to buy a small APO first, but the information about catadioptrics from this thread will still be useful, when I decide to upgrade. 

 

Anyway, thanks!



#20 Dom543

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Posted 16 August 2014 - 05:31 PM

Hypertuning is a service offered by DeepSpaceProducts for mid-grade mass-produced mounts. They also sell a DIY kit with an instructions video.
They disassemble the mount, replace some bearings with better ceramic ones, polish some shafts, lubricate and reassemble the mount.
The consensus is that hypertuned mounts run much smoother. For an Astro=Physics mount you don't need hypertuning.
Here is the URL http://www.deepspace..._4226_8661.html

On a separate subject, PEC doesn't matter, if you use autoguiding. And you should use autoguiding.

--Dom

#21 AFScienceTime

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Posted 17 August 2014 - 02:44 AM

Hypertuning is a service offered by DeepSpaceProducts for mid-grade mass-produced mounts. They also sell a DIY kit with an instructions video.
They disassemble the mount, replace some bearings with better ceramic ones, polish some shafts, lubricate and reassemble the mount.
The consensus is that hypertuned mounts run much smoother. For an Astro=Physics mount you don't need hypertuning.
Here is the URL http://www.deepspace..._4226_8661.html

On a separate subject, PEC doesn't matter, if you use autoguiding. And you should use autoguiding.

--Dom

 

So, hypertuning a CGEM will be better than a non-hypertuned CGEM DX? If yes, it is a very good deal. But I don't know if I want to use auto-guiders, since they add more weight and they do cost quite a lot.



#22 astroricardo

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Posted 17 August 2014 - 09:56 AM

I hate to break it to you but there's no way you will be doing any long exposure photography, especially with a long focal length instrument and mass produced mount, without auto guiding. A CGEM and CGEM DX are basically the same mount.  A DX handles more weight because of the heavy duty tripod and ability to use larger counterweights.  If you're not going to be using a heavy instrument then yes you may be able to get a CGEM and hyper tune it for the same money it takes to buy a CGEM DX.  

 

You will save yourself a lot of headaches by taking everyone's advice by starting with a short, inexpensive refractor.  Some of those big SCT's don't end up in the classifieds because people are buying bigger ones.



#23 elwaine

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Posted 17 August 2014 - 12:38 PM

I thought that a "large" but portable catadioptric or similar would suit me better, as if I take the (steep) learning curve, I will have the telescope I really needed anyway, and I won't have to upgrade and spend even more money.

 

 

OK. Now I understand what you are asking and I think we are on the same page. By all means, start with an aperture in the size range you are exploring (7" - 9.25"). 

 

There is a reason that an 8" SCT is so popular. It has enough aperture to be a very satisfying 'scope: not only for beginners, but for folks who have enjoyed amateur astronomy for decades. I have had a few 8" SCTs over the years. I have also had a Celestron 9.25 Edge. The 8" is lighter weight, can be used on a lighter (and less expensive) mount, and is easier to transport. The 9.25" allows you to see a bit more and a bit brighter views at comparable magnifications - but the difference minimal, and probably not nearly as much as you might think. As a general rule, the benefits of portability and ease of use tend to trump those of aperture - especially in the long run. Ease of transportation, ease of setting up and taking down (in the dark), translates into ease of use which, in turn, means you will use it more. But personally speaking, I never had any trouble with my C9.25 Edge.

 

I am going to recommend an 8" Celestron on an Evolution mount - or, because you do not want coma, something unconventional: buy a new Evolution mount with a 6" SCT, sell the 6" and then buy and mount an 8" Edge on the Evolution mount. (Celestron does not currently sell the Evolution mount with Edge series telescopes).

 

Another possibility is an 8" Edge on an AVX mount, but that set up will be at least 2 - 3 Kg above your weight limit; and transporting a mount with counterweights is a bit of a PITA. The Evolution mount will be easier to transport and much easier to set up and use: especially for visual astronomy.

 

So let's examine your list:

- It has to have a focal length larger than 800mm. The 8" SCT has a FL of 2032, but you can buy a .7 x focal reducer for the 8" Edge about $300. It will result in an f/7 scope with a FL of 1422mm

 

- It HAS to be portable. That is, it CAN'T be longer than 85cm (preferably shorter than that), and CAN'T be heavier than 18 kilos. The 8" Edge is only 17" long. The Evolution mount, plus tripod, weighs about 26 lbs. Total weight of the 8" Edge on an Evolution mount, plus the tripod that comes with it, weighs just a bit over 40 lbs (... a bit over 18 Kg).

 

- it has to be 180-250mm in aperture, preferably 7-9,5 inches. The 8" Edge fits right in the middle.

 

- It HAS HAS HAS to be cheaper than 4000$, and preferably cheaper than 3500$. The 8" Edge on an evolution mount will cost about $1,800. - I know the Evolution mount with an 8" SCT costs only $1,600; but if you follow my suggestion and buy an Evolution mount with a 6" SCT, sell that 'scope and the buy an 8" Edge to put on the Evolution mount, you will incur an additional cost of about $200 - $300 as you will have to take a loss on the lale of the 6". Still, the cost is way below your limits.

 

- It has to have very little or no chromatic aberration/spherochromatism, so that it can be later (probably) used for spectroscopy. I've done spectroscopy with an 8" SCT (non-edge) using an SBIG Spectrophotometer. I do not know if the Schott glass corrector lenses in the Edge scopes effect spectroscopy... but I tend to think not.

 

- MUCH preferably faster than f/10  The 8" SCT is a native f/10, but for $300 you can buy a .7x focal reducer for the 8" Edge. You'll then be able to use it at f/7 with a FL of 1422 mm.

 

- It has to be very good for DSO astrophotography with 35mm chips, that is, it has to have a flat field. Very good for DSO astrophotography? Yes, and no. The Edge series have a flat field. The Evolution Mount can be used successfully for short exposure AP, so you can certainly use it on the Moon and on Planets. For DSOs, you be best off buying an Hyperstar adapter. It will convert the scope to an f/2. That will allow you to take very nice APs of DSOs with short exposure times. However, the FL will be reduced to about 400 mm. - Tools are often best at performing specific jobs. In Astronomy, there is no "one size fits all." -  BTW, Since you want to explore AP, I do not recommend the 9.25" SCT on the Evolution mount. Add a camera and the weight will be too much to allow the mount to track well enough for AP. You'd be pushing it with the 8".

 

- Diffraction spikes don't annoy me, I actually find them very nice. If you like diffraction spikes, you can always add s simple cross made of heavy wire, or thin strips of balsa wood (painted flat black) to the front of the SCT... although I don't know why anyone would want to do that (other than to use it temporarily in order to use the diffraction spikes as an aide for focusing). 

 

- Good contrast is welcome. The contrast is good with an SCT. Not as good as with a refractor, but everything is relative. And, btw, contrast is something we are concerned about for visual use. For AP, one enhances the contrast and the sharpness via image post-processing. So the contrast of SCTs is not an issue when it comes to AP.

 

- Point like stars are very welcome. Stars will look very good - again, not quite as pinpoint as with a refractor, but very good indeed.

 

- Coma is NOT welcome. No coma with the Edge 'scopes. It is this requirement of yours that made me suggest you swap out the SCT that comes with the Evolution mounts and get an Edge scope.

 

Note: while I think Meade also makes very good SCTs, I did not recommend them for two reasons: They are heavier than Celestron scopes, so they will exceed your stated weight limit requirement. Second, while they have no coma, they do not have a flat field (which is another of your requirements.

 

There are, of course, other solutions to fill your needs (wants). But since an 8" SCT is such a good, all around scope - for beginners and advanced hobbyists alike (even for Consumers), it's a pretty safe bet that the above recommendation will make you very happy. And if not, I'll be happy to buy it from from you  - at a slight discount, of course.  ;)

 

Hope that helps....


Edited by elwaine, 17 August 2014 - 12:42 PM.


#24 AFScienceTime

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Posted 17 August 2014 - 04:23 PM

 

I thought that a "large" but portable catadioptric or similar would suit me better, as if I take the (steep) learning curve, I will have the telescope I really needed anyway, and I won't have to upgrade and spend even more money.

 

 

OK. Now I understand what you are asking and I think we are on the same page. By all means, start with an aperture in the size range you are exploring (7" - 9.25"). 

 

There is a reason that an 8" SCT is so popular. It has enough aperture to be a very satisfying 'scope: not only for beginners, but for folks who have enjoyed amateur astronomy for decades. I have had a few 8" SCTs over the years. I have also had a Celestron 9.25 Edge. The 8" is lighter weight, can be used on a lighter (and less expensive) mount, and is easier to transport. The 9.25" allows you to see a bit more and a bit brighter views at comparable magnifications - but the difference minimal, and probably not nearly as much as you might think. As a general rule, the benefits of portability and ease of use tend to trump those of aperture - especially in the long run. Ease of transportation, ease of setting up and taking down (in the dark), translates into ease of use which, in turn, means you will use it more. But personally speaking, I never had any trouble with my C9.25 Edge.

 

I am going to recommend an 8" Celestron on an Evolution mount - or, because you do not want coma, something unconventional: buy a new Evolution mount with a 6" SCT, sell the 6" and then buy and mount an 8" Edge on the Evolution mount. (Celestron does not currently sell the Evolution mount with Edge series telescopes).

 

Another possibility is an 8" Edge on an AVX mount, but that set up will be at least 2 - 3 Kg above your weight limit; and transporting a mount with counterweights is a bit of a PITA. The Evolution mount will be easier to transport and much easier to set up and use: especially for visual astronomy.

 

So let's examine your list:

- It has to have a focal length larger than 800mm. The 8" SCT has a FL of 2032, but you can buy a .7 x focal reducer for the 8" Edge about $300. It will result in an f/7 scope with a FL of 1422mm

 

- It HAS to be portable. That is, it CAN'T be longer than 85cm (preferably shorter than that), and CAN'T be heavier than 18 kilos. The 8" Edge is only 17" long. The Evolution mount, plus tripod, weighs about 26 lbs. Total weight of the 8" Edge on an Evolution mount, plus the tripod that comes with it, weighs just a bit over 40 lbs (... a bit over 18 Kg).

 

- it has to be 180-250mm in aperture, preferably 7-9,5 inches. The 8" Edge fits right in the middle.

 

- It HAS HAS HAS to be cheaper than 4000$, and preferably cheaper than 3500$. The 8" Edge on an evolution mount will cost about $1,800. - I know the Evolution mount with an 8" SCT costs only $1,600; but if you follow my suggestion and buy an Evolution mount with a 6" SCT, sell that 'scope and the buy an 8" Edge to put on the Evolution mount, you will incur an additional cost of about $200 - $300 as you will have to take a loss on the lale of the 6". Still, the cost is way below your limits.

 

- It has to have very little or no chromatic aberration/spherochromatism, so that it can be later (probably) used for spectroscopy. I've done spectroscopy with an 8" SCT (non-edge) using an SBIG Spectrophotometer. I do not know if the Schott glass corrector lenses in the Edge scopes effect spectroscopy... but I tend to think not.

 

- MUCH preferably faster than f/10  The 8" SCT is a native f/10, but for $300 you can buy a .7x focal reducer for the 8" Edge. You'll then be able to use it at f/7 with a FL of 1422 mm.

 

- It has to be very good for DSO astrophotography with 35mm chips, that is, it has to have a flat field. Very good for DSO astrophotography? Yes, and no. The Edge series have a flat field. The Evolution Mount can be used successfully for short exposure AP, so you can certainly use it on the Moon and on Planets. For DSOs, you be best off buying an Hyperstar adapter. It will convert the scope to an f/2. That will allow you to take very nice APs of DSOs with short exposure times. However, the FL will be reduced to about 400 mm. - Tools are often best at performing specific jobs. In Astronomy, there is no "one size fits all." -  BTW, Since you want to explore AP, I do not recommend the 9.25" SCT on the Evolution mount. Add a camera and the weight will be too much to allow the mount to track well enough for AP. You'd be pushing it with the 8".

 

- Diffraction spikes don't annoy me, I actually find them very nice. If you like diffraction spikes, you can always add s simple cross made of heavy wire, or thin strips of balsa wood (painted flat black) to the front of the SCT... although I don't know why anyone would want to do that (other than to use it temporarily in order to use the diffraction spikes as an aide for focusing). 

 

- Good contrast is welcome. The contrast is good with an SCT. Not as good as with a refractor, but everything is relative. And, btw, contrast is something we are concerned about for visual use. For AP, one enhances the contrast and the sharpness via image post-processing. So the contrast of SCTs is not an issue when it comes to AP.

 

- Point like stars are very welcome. Stars will look very good - again, not quite as pinpoint as with a refractor, but very good indeed.

 

- Coma is NOT welcome. No coma with the Edge 'scopes. It is this requirement of yours that made me suggest you swap out the SCT that comes with the Evolution mounts and get an Edge scope.

 

Note: while I think Meade also makes very good SCTs, I did not recommend them for two reasons: They are heavier than Celestron scopes, so they will exceed your stated weight limit requirement. Second, while they have no coma, they do not have a flat field (which is another of your requirements.

 

There are, of course, other solutions to fill your needs (wants). But since an 8" SCT is such a good, all around scope - for beginners and advanced hobbyists alike (even for Consumers), it's a pretty safe bet that the above recommendation will make you very happy. And if not, I'll be happy to buy it from from you  - at a slight discount, of course.  ;)

 

Hope that helps....

 

 

Thanks!



#25 gdd

gdd

    Apollo

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Posted 18 August 2014 - 07:23 PM

An article describing how much spherochromatism is introduced by the SCT corrector plate:

http://www.telescope...ics.net/SCT.htm

 

 

You said you were not interested in newtonians because of coma, this is corrected to full size 35mm frame by the MPCC mkIII according to Baader. This inserted into a AT8IN or similar F/4 imaging newtonian also meets all of your size and weight requirements. It is not just faster than F/10, but "much faster" as you specdified. At 800mm FL it is the minimum you require. This can be extended to F/6 or F/8 with a barlow. For work were you cannot have additional optics you can omit the correctors and barlows and work the center of the field.

 

Gale








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