# hide and seek with the moon



## weilin (May 5, 2014)

After mulling about for a bit, I finally decided to bite the bullet and get a telescope. After much thinking and searching I decided to get a Sky-Watcher ProED 120mm Doublet APO Refractor. I saw it as a poor man's EF 800mm. Sure, it doesn't have AF, IS, or sharpest of corners... but, I now have a 900mm lens ;D. 

I have only started this new part of my habit hobby. There's no equatorial mount... no GOTO tracker... they'll (likely) appear in due time. I've had this since last Thursday and am struggling with the Astrophotographer's curse, 30 days and 30 nights of rain (living in the Pacific NW isn't helping). Tonight was the first night I had any opportunity. For a 5 minute window, I saw a break in the clouds!

I present to you a "moonscape". Image taken with a Canon EF 2x Tele + EOS 5D3 mounted on a Arca-Swiss Z1 + Gitzo 2541 at 1/320 sec & ISO 6400. The photo has been touched up but uncropped in Lightroom 5.

For the seasoned astrophotographers lurking around, any advice? I know the ISO is a tad high for this, but I didn't have a lot of time and had to make sure I got the shot in less than 5 photos.


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## jrista (May 5, 2014)

weilin said:


> After mulling about for a bit, I finally decided to bite the bullet and get a telescope. After much thinking and searching I decided to get a Sky-Watcher ProED 120mm Doublet APO Refractor. I saw it as a poor man's EF 800mm. Sure, it doesn't have AF, or sharpest of corners... but, I now have a 900mm lens ;D.
> 
> I have only started this new part of my habit hobby. There's no equatorial mount... no GOTO tracker... they'll (likely) appear in due time. I just got the scope last Thursday and am struggling with the Astrophotographer's curse, 30 days and 30 nights of rain (living in the Pacific NW isn't helping). Today was the first night I had any opportunity and for a 5 minute window, I had a break in the clouds!
> 
> ...



First, congrats on the purchase. Good to see others getting into astrophotography.  Once you get an equatorial mount, a very wide new world will open up to you. Just make sure you get s good mount...they are the most important piece of any astrophotographers kit.

As for advice...best bit is to definitely use a lower ISO. I pretty much always use ISO 100 or 200 for the moon. It moves, but not fast enough that a 1/4 second exposure will cause blurring. You REALLY want the DR that a lower ISO offers when shooting the moon...it's an exceptionally high DR subject. 

I have lots more advice to offer...but I'll let you settle in first. ;P


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## weilin (May 5, 2014)

Thanks for the pointers. I already ordered the reducer/field flattener that goes with this scope. I think that should help the vignetting I'm seeing right now with my 2" to 1.25" adapter + t-mount adapter + t-mount to EOS adapter.

I'm looking to get the Celestron Advanced VX mount to go with this. Any thoughts on that? Any accessories I should also pick up in one shipment? I heard the GPS unit is nifty, as is a polar axis scope. Anything else I should look into?

Currently the shutter is set to 1/320 because the thing is about as stable as a sailboat on my current tripod. I probably could have dropped the ISO to 3200 because I ended up dropping the image by half a stop anyways. I'm beginning to think I need a GT3531 >.<.


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## jrista (May 5, 2014)

weilin said:


> Thanks for the pointers. I already ordered the reducer/field flattener that goes with this scope. I think that should help the vignetting I'm seeing right now with my 2" to 1.25" adapter + t-mount adapter + t-mount to EOS adapter.



Reducers/flatteners definitely help with corner performance. They do reduce focal length, though...so, if you have an f/7.5 scope, and use a 0.85x reducer, your going to end up with a 765mm scope. Wider scopes are great for nebula and imaging larger regions of the sky, they are a lot harder to use for galaxies, clusters, planetary work, etc. For those, you want something much longer, at least 1600mm, and for planetary, it's really best to have as much focal length as you can muster (regardless of the f-ratio...3000mm, 5000mm, even 9000mm is best for planetary work.)



weilin said:


> I'm looking to get the Celestron Advanced VX mount to go with this. Any thoughts on that? Any accessories I should also pick up in one shipment? I heard the GPS unit is nifty, as is a polar axis scope. Anything else I should look into?



Celestron is not really my first choice for mounts. They make some excellent scopes, and are they only source of hyperstar capable scopes, but their mounts are generally a bit wanting, and you pretty much always have to go to Celestron for any support. The EQ5/EQ6 range of mounts are actually better mounts, and the support community for them is truly vast. The Orion Sirius is an EQ5 type mount, where as the Orion Atlas is an EQ6 type mount. The Sirius is a step above the Celestron AVX, but closer to it in price. The Atlas is one of the most popular and best supported lower end mounts in the world. It's $1400, vs. the $1000 for the Sirius, but it is really the lowest entry mount you probably want to go with for astrophotography.

Mounts like the AVX are just too low end to really do a good job for astrophotography. Mount capacity is a critical factor, as is the intrinsic periodic error. The AVX has a max capacity of 30lb, and it's periodic error (PE) is around 30-50" peak-to-peak (P2P). The Orion Atlas, on the other hand, has a capacity of 40lb and a (PE) of around 15" P2P. The periodic error is what is going to determine the minimum size of your stars as you track across the sky for long exposures. At 30" or more, the AVX is just not going to handle exposures of more than about a minute or so without really good guiding. The Atlas can handle unguided exposures of a few minutes, and is easier to guide than the AVX.

Capacity is the next most important point. It's best not to load up a mount with more than about half it's capacity if you are doing astrophotography, unless your using a real high end mount. At 30lb, your 23lb scope is already over 2/3rds the weight capacity, where as it is barely over half for the Atlas. At 2/3rds capacity (and even more, once you throw on a camera, and even more once you throw on a guide scope and guide camera, which are really going to be essential for tight stars with any lower end mount), the AVX is going to be extremely difficult to control and guide out errors for. For the size and weight of your scope, especially with a camera and guider setup, you want a mount that is at the very least capable of handling 40lb. A mount capable of handling 60lb would be best...but that gets you into the territory of midrange mounts, which cost around $2500-3500. 

So, I very highly recommend the Orion Atlas. It's a very capable mount, with a phenomenal support community. It also works with EQMOD, which is a full open source, free total replacement software driver package that lets you ditch the hand controller and control your mount entirely from a laptop (once you really get into imaging, you'll learn you also need computer control software, such as BackyardEOS if your using a Canon DSLR for imaging, PHD2 for guiding, etc.) EQMOD is more capable and more flexible than the SynScan hand controller that comes with EQ5/EQ6 type mounts. The use of EQMOD also opens up the door for improving the Atlas, which is another somewhat unique feature...there is a hypertuning mod available (which cleans up the mount and gets rid of manufacturing crap left behind in the gears, which makes the PE worse, and regreases everything with high quality synthetic grease), as well as a number of belt and worm mods. Belt and worm mods can eliminate gears, reduce backlash issues, and otherwise greatly improve the performance of your mount to midrange levels for far less cost. (NOTE: To use EQMOD, you will need to get an EQDIR cable. They are about $45, but a standard USB to Serial cable costs almost that much anyway, so it is a very worth while investment.)

You really can't go wrong with the Orion Atlas (or any other EQ6 mount, like the SkyWatcher EQ6 SynScan, which is basically the same thing, just different seller.) Either way, the Atlas/EQ6 is a much better fit given that your scope already weighs 23lb, and that you are guaranteed to need to do guiding. You can pick up the Orion 50mm mini guidescope and SSAG guider for relatively cheap, and the weight of that setup is about as small as you can get for guiding. Without guiding, even with an Atlas, the 15" p2p periodic error is going to kill your chances for doing exposures longer than a couple minutes. Average seeing is 2-3", average star size is 1.5-1.8"...without guiding, your stars will eventually be around 10-15" in size...far too large.


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## weilin (May 5, 2014)

Yay! more data! Hmm your view on Celestron greatly differs from those at the local astronomy club :-\. They tend to hold the Advanced VX and CGEM mounts to a pretty high standard. I think it's sticker shock, photographers have already come to terms with $1k tripods and $2k+ lenses. The astronomers in the club haven't quite crossed that bridge yet .

The scope according to the website is about 12lb (I threw it on a scale and it's about right). The 23lb you see includes the metal case it comes with. I know it doesn't change the P2P error, but in terms of load, 120ED + 5D should be ok on the AVX?

As for not supporting EQMOD, that is of concern. I'll have to look into the Orion units...

I guess the cost difference of 900 vs 1500 is peanuts compared to everything else >.<


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## jrista (May 5, 2014)

weilin said:


> Yay! more data! Hmm your view on Celestron greatly differs from those at the local astronomy club :-\. They tend to hold the Advanced VX and CGEM mounts to a pretty high standard. I think it's sticker shock, photographers have already come to terms with $1k tripods and $2k+ lenses. The astronomers in the club haven't quite crossed that bridge yet .



Celestron equipment has a very strong religious following. I was hooked on getting a CGEM DX until I started researching, asking questions. Turns out that the CGEM and CGEM DX both have a flawed gearbox that causes what is called the 8/3 error, a non-periodic, non-integer error that is extremely difficult to guide out. I spent over two solid months researching mounts. In the grand scheme of things, my "real" mount will ultimately be the 10Micron GM2000HPS UP, a $24,000 mount which uses in-mount sky modeling and absolute encoding to allow for 20 minutes unguided exposures, and can hold up to 132lb of instrument capacity.  

In my travels around internet forums during my research, though, I found one very glaring fact: Pretty much NO ONE, EVER, complains about the Orion Atlas or EQ6 mounts. They have about as pristine a reputation as I have ever seen. They are very well loved mounts. This is in great contrast to the fact that you can find dozens, if not hundreds, of complaint threads about the CGEM mounts on astronomy forums all over the net. Mostly about gearbox issues, but not solely. Some Celestron fans and objective mount reviewers will tell you the complaints are not warranted, and perhaps not...but that does not change the fact that the CGEM mounts are widely complained about buy a LOT of people. Statistically, that has to indicate some fundamental issue.

Personally, I LOVE Celestron OTAs. Their EdgeHD scopes are amazing, although they do suffer a bit from the standard SCT problems. If you want an excellent large-aperture OTA, an EdgeHD is definitely a worth while investment. Just...put it on an Atlas, instead of a CGEM. 



weilin said:


> The scope according to the website is about 12lb (I threw it on a scale and it's about right). The 23lb you see includes the metal case it comes with. I know it doesn't change the P2P error, but in terms of load, 120ED + 5D should be ok on the AVX?



If the weight is only 12lb, then it should be OK. I'm not sure what imager your using, if it's a DSLR that could add another pound or so. The guiding setup will add another pound or so, plus don't forget to count the weight of the various cables that you'll need to control everything (cable from the camera to laptop, cable from the guidecam to the mount, cable from the guidecam to laptop, cable from mount to laptop). You might also have additional weight from an extra vixen dovetail and telescope rings (to mount the guidescope to the telescope), which also adds a couple of pounds. Even assuming the scope is 12lb, 50% capacity is only 15lb, and all these accessories are going to put you over that limit. 

The AVX is generally not considered a great mount for doing astrophotography. It's great for visual observing, but you have to understand the tolerances involved in astrophotography...if your tracking is off by arcSECONDS, your going to have problems. The AVX is the rock-bottom mount you could possibly get for AP, and it really is insufficient. That assumes that you never, ever plan to use a larger scope in the future...if you do, the $1000 on the AVX is just a waste, as you'll need a larger mount for a larger scope in the future anyway. (You will also quickly find that you'll want a longer scope, much longer, for doing anything other than nebula wide field shots...so something like the 8" EdgeHD or 8" AT8RC, both very cost effective OTAs that produce superb results, would work on an Atlas, they definitely would not work on an AVX.) You would be surprised how much better the Atlas/EQ6 is. Some astrophotographers have loaded it up with 30, 35 pounds of weight and been able to image fine...you would never be able to do that with an AVX. 

The price of the Atlas is $1500, so it's $700 more than the AVX. I know that sounds like a lot...but I honestly cannot stress enough how important the mount is for astrophotography. The difference between what is acceptable for visual observing (which is probably what most of your local astronomy club members are doing), and what is acceptable for astrophotography is quite large. You can deal with stars and nebula and planets bouncing around a bit for visual work...even the smallest amount of that is completely unacceptable for astrophotography. If you don't eventually plan on getting a really large OTA that weighs over 50lb, then the Orion Atlas or SkyWatcher EQ6 would probably be the only mount you would ever need...buy it once, never need to replace it or buy a bigger one. The same is not true of the AVX. Your already pushing it's capabilities with your ProED 120.



weilin said:


> I guess the cost difference of 900 vs 1500 is peanuts compared to everything else >.<



It really is. The mount is the centerpiece. If your mount isn't up to snuff, then it really doesn't matter what your mounting onto it...your already screwed.  Big thing to keep in mind, visual is very different, in terms of requirements and what's acceptable, from astrophotography. Local astronomy clubs tend to be based on visual observing, and less on astrophotography, so their advice is likely to be a bit biased.


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## weilin (May 5, 2014)

Ok, I'm sticking to the sticker shock theory ;D. I see what you mean about the non-periodic error that would be an problem. I'll keep looking at my options. This is a very expensive habit hobby >.<.


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## jrista (May 5, 2014)

weilin said:


> Ok, I'm sticking to the sticker shock theory ;D. I see what you mean about the non-periodic error that would be an problem. I'll keep looking at my options. This is a very expensive habit hobby >.<.



You have no idea how expensive.  I have some fairly big aspirations. Just check out the prices on these pieces of equipment:

10Micron GM2000HPS UP
PlaneWave 20" CDK
FLI ProLine PL16803 Mono CCD

That's a semi-pro setup. It's what will allow me to get magazine-quality results, assuming I can find appropriately dark skies and some land to build an observatory under. Those pieces of gear are also on the lower-midrange end of the "high end" market....there are even better mounts, larger telescopes, and even better imagers that cost three to five times more.

So yeah, ridiculously expensive, if you get really really serious.


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