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7-9,5 Inch Telescopes for DSO Imaging?

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#26 coinboy1

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Posted 18 August 2014 - 08:33 PM

Vixen VC200L seems to match all your requirements. Flat field for full frame sensors, 200mm aperture. f/9, no coma, good 4 vane spider for diffraction effects, good focuser, light weight. Getting one soon ;)

#27 AFScienceTime

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Posted 19 August 2014 - 02:02 AM

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

 

The article on the spherochromatism was helpful. Newtonians are sadly too long and bulky to be portable, so they are not what I am looking for.



#28 AFScienceTime

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Posted 19 August 2014 - 02:03 AM

Vixen VC200L seems to match all your requirements. Flat field for full frame sensors, 200mm aperture. f/9, no coma, good 4 vane spider for diffraction effects, good focuser, light weight. Getting one soon ;)

 

Thanks. Do you know anything about the spherochromatism/aberration it displays? Also, I have heard some "problems" with it, but I don't know what exactly they are.



#29 AFScienceTime

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Posted 19 August 2014 - 02:17 AM

Also, what about the Vixen VMC260L? It is portable enough for me, but... I don't know. 3000mm focal length? f/11,6? It... doesn't... look... very good. Especially for it's money.



#30 AFScienceTime

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Posted 19 August 2014 - 03:10 AM

Additional question: Can you recommend me a sub 1500$ CCD Camera? I mean, I will probably be imaging with my DSLR, but is there any cooled, "black and white" CCD camera to use with a filter wheel? I have noticed that these produce much better images than DSLRs (who would have guessed!).



#31 orlyandico

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Posted 20 August 2014 - 12:15 AM

I wouldn't dream of doing 1500mm-range focal length, long-exposure astrophotography with a CGEM or anything in that price class, unless you also have an Adaptive Optics unit.

 

I understand the OP's requirements.  I have similar wishes. But it's not going to happen on a CGEM-class mount.  I am not even mounting a 10" on my Mach1.

 

Some issues of the OP:

 

1) covering a 35mm sensor means you'll need a more expensive scope

 

2) very few scopes of 1500mm-range focal length are going to be terribly fast

 

Given the OP's "hard" requirements, I'd probably go for an ODK10 - http://www.orionopti.../ODK/odk10.html

 

10" diameter, f/6.8, 1700mm focal length, 50mm field size, 12kg ( = 26lb) weight.  With all the extra doodads it would be pushing 40lb.  Just right for a Mach1! Unfortunately the ODK10 is $6000.  Remove about 15% (UK VAT) and you're still at $5100. Plus shipping and US taxes. Covering a 50mm image circle at f/6.8 is expensive. No two ways around it.

 

My opinion? get a standard C8 (the non-EDGE one) and add the Starizona reducer - http://starizona.com...or-P3230C0.aspx

 

You get 1500mm focal length, f7.5. You will have to deal with mirror shift. Get an OAG. And an Atlas mount (I prefer the Atlas to the CGEM, due to my poor experience with the CGEM).  Or, get the C8 EDGE (which has the advantage of having mirror locks) and the 0.7X dedicated reducer. More money.

 

I know someone imaging with a VMC260L.  He has it on a Paramount MX.  Don't even think about putting that thing on a CGEM or Atlas class mount.

 

Also, it seems the OP wants to buy everything (ref. question about CCD). To answer the question, the only decent mono camera under $1500 is a used SBIG ST8300 or STF8300. But that won't come with any filter wheel. You might find a used QHY9 with filter wheel for $1500. Filters not included. Budget another few hundred bucks at least for LRGB, more for narrowband filters and much more if they are branded "Astrodon."

 

It really all depends on the total spend. I would put most of the money on the mount. This is why I have a Mach1, but my imaging scope is a $400 newtonian and my camera is a used ST8300.


Edited by orlyandico, 20 August 2014 - 12:20 AM.


#32 orlyandico

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Posted 20 August 2014 - 12:22 AM

Oh and if the bulky-ness of the newtonian is a problem for you.. have fun hefting the 80-lb bulk of an Atlas or CGEM.

 

Atlas/CGEM head is 40lb, you'll need probably 2 x 17lb counterweights, plus the tripod is around 20lb.  The Mach1 actually weighs less than the Atlas/CGEM (30lb for the head). I still find it a chore to haul around (the tripod weighs about 25lb, plus three 9-lb counterweights and the Eagle half-pier).

 

My current favorite mount (cost $400!) -

 

 

 IMG_1169.JPG

 

Mount, scope, and tripod are around 15lb total.


Edited by orlyandico, 20 August 2014 - 12:25 AM.


#33 AFScienceTime

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Posted 20 August 2014 - 03:33 AM

Oh and if the bulky-ness of the newtonian is a problem for you.. have fun hefting the 80-lb bulk of an Atlas or CGEM.

 

Atlas/CGEM head is 40lb, you'll need probably 2 x 17lb counterweights, plus the tripod is around 20lb.  The Mach1 actually weighs less than the Atlas/CGEM (30lb for the head). I still find it a chore to haul around (the tripod weighs about 25lb, plus three 9-lb counterweights and the Eagle half-pier).

 

My current favorite mount (cost $400!) -

 

 

 IMG_1169.JPG

 

Mount, scope, and tripod are around 15lb total.

 

The problem with Newtonians is mostly  that I can't fit them in the car easily, not the weight. I have a little bit of trouble fitting a SW 10'' Collapsible Newtonian. 



#34 AFScienceTime

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Posted 20 August 2014 - 03:55 AM

I wouldn't dream of doing 1500mm-range focal length, long-exposure astrophotography with a CGEM or anything in that price class, unless you also have an Adaptive Optics unit.

 

I understand the OP's requirements.  I have similar wishes. But it's not going to happen on a CGEM-class mount.  I am not even mounting a 10" on my Mach1.

 

Some issues of the OP:

 

1) covering a 35mm sensor means you'll need a more expensive scope

 

2) very few scopes of 1500mm-range focal length are going to be terribly fast

 

Given the OP's "hard" requirements, I'd probably go for an ODK10 - http://www.orionopti.../ODK/odk10.html

 

10" diameter, f/6.8, 1700mm focal length, 50mm field size, 12kg ( = 26lb) weight.  With all the extra doodads it would be pushing 40lb.  Just right for a Mach1! Unfortunately the ODK10 is $6000.  Remove about 15% (UK VAT) and you're still at $5100. Plus shipping and US taxes. Covering a 50mm image circle at f/6.8 is expensive. No two ways around it.

 

My opinion? get a standard C8 (the non-EDGE one) and add the Starizona reducer - http://starizona.com...or-P3230C0.aspx

 

You get 1500mm focal length, f7.5. You will have to deal with mirror shift. Get an OAG. And an Atlas mount (I prefer the Atlas to the CGEM, due to my poor experience with the CGEM).  Or, get the C8 EDGE (which has the advantage of having mirror locks) and the 0.7X dedicated reducer. More money.

 

I know someone imaging with a VMC260L.  He has it on a Paramount MX.  Don't even think about putting that thing on a CGEM or Atlas class mount.

 

Also, it seems the OP wants to buy everything (ref. question about CCD). To answer the question, the only decent mono camera under $1500 is a used SBIG ST8300 or STF8300. But that won't come with any filter wheel. You might find a used QHY9 with filter wheel for $1500. Filters not included. Budget another few hundred bucks at least for LRGB, more for narrowband filters and much more if they are branded "Astrodon."

 

It really all depends on the total spend. I would put most of the money on the mount. This is why I have a Mach1, but my imaging scope is a $400 newtonian and my camera is a used ST8300.

 

For the mount: What about an iOptron CEM60 or however it is called with an 8" AT RC with a CF tube? It is only 16,5 lbs, maybe even a total 30lbs with all the equipment, and the "suggested payload" (although I do not completely trust it) is about 60lbs. I do not know anything about the mount, but if I spend more money on the mount (I think it is about 3000$ with the tripod or something?), not buy a CCD (not sure about that, as my Nikon D80 sucks a bit when it comes to low light) and use the 8" f/8 tube with a reducer/flatenner (f/5,6 which is how much it will reach with a 0,7x reducer is pretty good, although I don't know if there is a dedicated reducer or not) it will be cheap enough, and produce good results. The claimed image circle is about 40-42mm, so... I don't really know how image circle size translates to if you can or you can not use a 35mm camera, but...I guess you can't. 



#35 orlyandico

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Posted 21 August 2014 - 02:20 AM

CEM60 has a long thread in the Mounts forum.  I'd go with the CEM60 non-EC.

 

Yes the AT8RC is a good choice.   Get the Astro-Physics CCDT67 reducer, brings it down to a very decent f/5.36

 

Common problem with the AT8RC, the stock focuser is substandard. You'll have to replace it with a Feathertouch.  And even then, because the focuser is attached to the mirror cell, with a heavy load it tends to sag and dislodge the mirror.  There are various work-arounds for this.

 

I think a reduced AT8RC would also work on an Atlas or CGEM, since the focal length is now 1072mm with the AP reducer...

 

Also, I don't understand why you need 35mm coverage.  Are you going to use a full-frame DSLR? or a large-sensor CCD? (KAF-11002 or KAF-16000 chip - very pricey)


Edited by orlyandico, 21 August 2014 - 02:23 AM.


#36 orlyandico

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Posted 21 August 2014 - 02:25 AM

BTW I use an 8" f4 newtonian.  It's only 920mm focal length with a Paracorr and f4.6 - that's good enough for me that I see no benefit to getting an AT8RC (which is 1072mm reduced - not far off).

 

It fits in the trunk of my Mazda6, so no worries there..  total weight about 20-25lb with dual dovetails and a Feathertouch focuser.


Edited by orlyandico, 21 August 2014 - 02:26 AM.


#37 AFScienceTime

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Posted 21 August 2014 - 03:04 AM

BTW I use an 8" f4 newtonian.  It's only 920mm focal length with a Paracorr and f4.6 - that's good enough for me that I see no benefit to getting an AT8RC (which is 1072mm reduced - not far off).

 

It fits in the trunk of my Mazda6, so no worries there..  total weight about 20-25lb with dual dovetails and a Feathertouch focuser.

 

Well, the thing is that I have to be able to fit the telescope in the car with 3 passengers, and with little to no space in the trunk, since we have an LPG tank there. The SW 10" Collapsible Dob was the largest Newtonian I can fit there, since the length of the tube was about 80-85cm. So, any non-collapsible or similar conventional Newtonians at 8" can't fit in there, except if they are some of the Super-Newt kind (Takahashi epsilon-180 for example), and even that way, their focal length is too small.



#38 AFScienceTime

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Posted 21 August 2014 - 03:18 AM

CEM60 has a long thread in the Mounts forum.  I'd go with the CEM60 non-EC.

 

Yes the AT8RC is a good choice.   Get the Astro-Physics CCDT67 reducer, brings it down to a very decent f/5.36

 

Common problem with the AT8RC, the stock focuser is substandard. You'll have to replace it with a Feathertouch.  And even then, because the focuser is attached to the mirror cell, with a heavy load it tends to sag and dislodge the mirror.  There are various work-arounds for this.

 

I think a reduced AT8RC would also work on an Atlas or CGEM, since the focal length is now 1072mm with the AP reducer...

 

Also, I don't understand why you need 35mm coverage.  Are you going to use a full-frame DSLR? or a large-sensor CCD? (KAF-11002 or KAF-16000 chip - very pricey)

 

Thanks! Is there another reducer that reduces it less? Also, I need 35mm coverage, because I am probably going to buy a new camera (Nikon D810) shortly, and I would like to be able to use it at 35mm with a telescope. It has excellent performance at high ISO (Really, if you had to, you could use it at 1600 ISO, as long as you use a noise reduction software), and what a resolution and general image quality! 



#39 orlyandico

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Posted 21 August 2014 - 03:46 AM

The AP CCDT67 is widely considered to be the best reducer for the AT8RC even though it was not designed for it.

 

You can manipulate the spacing to reduce the amount of reduction. "Full coverage of ST10 chip" means it's only good for at most ST8300 sensor - and even there it will probably vignette.

 

The thing is if you really need 35mm coverage you're stuck with the ODK10 or similar.  Covering that large of an image circle is not something the mass-market scopes are particularly good at.



#40 orlyandico

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Posted 21 August 2014 - 03:48 AM

Like I said - 0.75X Starizona reducer http://starizona.com...or-P3230C0.aspx

 

"optimized for 35mm" notice the spot diagram looks good up to 17.5mm off-axis (35mm diameter circle).  Of course a 35mm sensor is 36x24 and thus the diagonal is 43mm.  So this reducer will still vignette on an FX camera.

 

But at least you can put it on a cheap-as-dirt C8.



#41 AFScienceTime

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Posted 21 August 2014 - 06:07 AM

CEM60 has a long thread in the Mounts forum.  I'd go with the CEM60 non-EC.

 

Yes the AT8RC is a good choice.   Get the Astro-Physics CCDT67 reducer, brings it down to a very decent f/5.36

 

Common problem with the AT8RC, the stock focuser is substandard. You'll have to replace it with a Feathertouch.  And even then, because the focuser is attached to the mirror cell, with a heavy load it tends to sag and dislodge the mirror.  There are various work-arounds for this.

 

I think a reduced AT8RC would also work on an Atlas or CGEM, since the focal length is now 1072mm with the AP reducer...

 

Also, I don't understand why you need 35mm coverage.  Are you going to use a full-frame DSLR? or a large-sensor CCD? (KAF-11002 or KAF-16000 chip - very pricey)

 

I have been reading the thread about the CEM60 for 2 days now, although I got totally lost at about page 9, too many technical details and things I have never heard of lol... Just give me an unguided 10 minute exposure at 1000mm and let me see how bad the trails are lol! Anyway, is there any other reason other than the lower cost to better buy the non-EC version? On the thread I read some things about that, but I didn't get much, because I was too dizzy with all the technical terms!



#42 orlyandico

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Posted 21 August 2014 - 08:59 AM

The EC version has an unresolved issue with errors in its encoder. Most of the boosters of the EC are guiding it.

Guiding turns off the encoder. Hence turning the EC into a non EC.

So why pay extra for the EC?

#43 AFScienceTime

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Posted 21 August 2014 - 03:51 PM

The EC version has an unresolved issue with errors in its encoder. Most of the boosters of the EC are guiding it.

Guiding turns off the encoder. Hence turning the EC into a non EC.

So why pay extra for the EC?

 

Oh, ok.



#44 orlyandico

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Posted 21 August 2014 - 09:35 PM

The "answer" is that iOptron will eventually fix the encoder problem and you'll be able to do 10 minutes unguided.  It's really your call if you want to pay the extra for a future capability that is supposed to be there today.



#45 AFScienceTime

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Posted 22 August 2014 - 03:23 AM

The "answer" is that iOptron will eventually fix the encoder problem and you'll be able to do 10 minutes unguided.  It's really your call if you want to pay the extra for a future capability that is supposed to be there today.

 

But it will still be the same with the other version with an autoguider, right? So, buying the EC version is like buying the normal one, but with a built in autoguider, only less good than a proper autoguider. So if I wanted to do unguided astrophotography, I would use the EC version. If I wanted to do unguided ap, I would buy the standard version + an autoguider. 

 

I have a question: At 1600mm, how long exposures will I be able to do with a 66mm guider scope and a cheap 200-300$ CCD camera (the autoguider Backyard Astronomer suggests)?



#46 AFScienceTime

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Posted 22 August 2014 - 03:56 AM

By the way, I found the Orion Optics CT8 Newtonian, and, since it is 86cm long, it is short enough to be portable. I generally checked all the telescopes in the Orion Optics UK page, and the AG Astrograph was to expensive as was the ODK, the OMCs had the SLOWEST. OPTICS. EVER!!! (f/20), and the VX line wasn't "good enough". The CT8 looks great, but... how bad is comma? Also, is the field flat enough by default? Because with a reducer the focal length  will be too small.


Edited by AFScienceTime, 22 August 2014 - 04:07 AM.


#47 gdd

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Posted 22 August 2014 - 08:55 AM

 

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

 

The article on the spherochromatism was helpful. Newtonians are sadly too long and bulky to be portable, so they are not what I am looking for.

 

The AT8IN is 32 inches long, the primary collimation screws protrude about a half inch. The Orion Optics CT8 Newtonian's is 34 inches long due to the slower F/4.5 optics. The Orion F/3.9 is shorter than the AT8IN  because it's tube is not extended to provide a light shield.

 

I think the MPCC Mark-III does a good job of handling coma on my AT8IN, but I am a beginner and may not be as critical as others. The coma corrector should do an even better job of correcting coma on the slower F/4.5 mirror. Take a look at full resolution uncropped images taken with AT8IN's and other imaging newts on www.astrobin.com to see how good the coma is controlled by various coma correctors (post processing may have helped too).

 

Gale



#48 AFScienceTime

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Posted 22 August 2014 - 01:23 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

 

The article on the spherochromatism was helpful. Newtonians are sadly too long and bulky to be portable, so they are not what I am looking for.

 

The AT8IN is 32 inches long, the primary collimation screws protrude about a half inch. The Orion Optics CT8 Newtonian's is 34 inches long due to the slower F/4.5 optics. The Orion F/3.9 is shorter than the AT8IN  because it's tube is not extended to provide a light shield.

 

I think the MPCC Mark-III does a good job of handling coma on my AT8IN, but I am a beginner and may not be as critical as others. The coma corrector should do an even better job of correcting coma on the slower F/4.5 mirror. Take a look at full resolution uncropped images taken with AT8IN's and other imaging newts on www.astrobin.com to see how good the coma is controlled by various coma correctors (post processing may have helped too).

 

Gale

 

 

Thanks, that is helpful. The CT8 has a longer focal length (not much longer, but...) and fantastic 1/10 PV optics. I did read some scary stuff about it though, as somebody had to drill a hole in the mirror cell to fix some problem with an alignment screw or something.



#49 AFScienceTime

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Posted 22 August 2014 - 01:44 PM

Also, AT10RC with CF tube vs AT10RC with normal tube vs AT10RC truss tube. The first two have the advantage of light baffles, although the truss one has a more durable design as far as I know. But what are the AT10RC's with CF tube advantages over the normal AT10RC?



#50 gdd

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Posted 22 August 2014 - 02:51 PM

The only advantage I see for the CF tube is better isolation from unwanted external light sources along with the baffling. The truss design can also do this with a shroud or lightweight liner.

 

Both have the focusers attached to the mirror cell, but maybe the serurrier design handles the sag.

 

The truss design has a dovetail half the length of the CF tube model. The aluminium dovetail's high thermal coefficent undoes some of the CF thermal advantage, so the shorter dovetail of the truss should be impacted only half as much.

 

Gale








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