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Post by Deleted on Sept 27, 2015 20:00:59 GMT
Well about to order the OTA that I want to use with my AV system, whatever that turns out to be (that is another discussion), MallinCam or Astro Video System. I wonder if I could get you folks opinion on a Celestron 8" EdgeHD OTA. Aperture of 203.2mm at F/10, focal length of 2032mm. I plan on this being dedicated for video astronomy with some small amount of visual thrown in from time to time. Anyone see any glaring problem with the OTA or maybe a poor choice on my part as a total novice in AV. It will be on a EQ GoTo mount, more than likely the Advanced VX. OTA weight is 13 lbs, Advanced VX capacity is 30 lbs. Link if you like: www.celestron.com/browse-shop/astronomy/telescopes/advanced-vx-8-edgehd-telescopeI plan on remote control since it gets a tad nippy here in Wisconsin during the winter and thus the other reason for AV. Maybe someone here is using that set up.................? Aperture reducers I imagine are in the cards. Thanks, Chuck
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Post by Deleted on Sept 27, 2015 22:13:41 GMT
Chuck, The C8 is a nice scope but for video astronomy you need faster optics. At F10 you will need a significant focal reduction to get down to F5 or less, or else you will require long exposures. Your VX mount should be capable, but you may find that you need an autoguider. As for focal reducers, there a many to choose from, just factor that into your buying decision. Alternatively you might look a faster OTA, such as the Mallincam VRC 8, which is F8.
Tim
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Post by Deleted on Sept 27, 2015 23:18:57 GMT
Hi Tim, Good point on the F/10. I had that in my brain, I guess I did not consider the long time I might be waiting for the image. I was also looking at a reflector the Explore Scientific AR152 ( which I refer to as the Elephant Gun!)but I think with that unit Chromatic Aberrations might rear its ugly head although some folks say its not too bad. Its at a F/6.5.
I guess I could look at some Reflectors, but during visual viewing with the EQ mount gets at a EP crazy angle once in a while. No free lunch is there?
Took a quick look at the VRC 8, very nice looking unit...going back for a closer look. I did not knows that Mallincam built OTA's.
Thanks for your input,
Chuck
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Post by davy on Sept 28, 2015 0:17:01 GMT
hi chuck, totally agree with tim, f10 is very slow for video astronomy we usually go for short fast scopes, scope I use is the skywatcher ed80 around f6 but can be made faster with the dedicated focal reducer/flatner.lots of astrophotographers and video astronomers go for this in the uk bats well above its price range. davy
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Post by Deleted on Sept 28, 2015 1:18:09 GMT
Ok........would you say that the Explore Scientific AR152, F/6.5, Acromat refractor, 988 focal length, be one of the acceptable ones? Edit: ah!! its too heavy...23 pounds..need 40lb rated mount I guess. Now that gets too heavy for me to handle, back to looking at the ED80. Think I am on track now, yeah, right! Chuck
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Post by Dragon Man on Sept 28, 2015 12:21:42 GMT
G'day Chuck. I'm glad you asked before purchasing. The above 2 comments are spot on. f/10 is way to slow for Video unless you pair it up with a Fastar or Hyperstar. They bring an SCT down to around f/2. But they are also very expensive. Reflectors aren't always a great choice either. Even though they sound fast with focal ratios like f/5, their focal ' length' is still too long. There are some exceptions in the Reflector range like the little Comet Catcher. But if you really want to get great results with a really pleasing Field of View, get a short tube Refractor. There are soooo many that are fantastic for Video Astronomy. If you have a look at my website you will see my results from an ED80, an ED100, a 120mm f/5 Achromat, and a 6" f/5 Achromat. All have short focal lengths and are suitable for Video Astronomy. ballaratman.wix.com/mallincamDon't worry about Chromatic Aberrations or Violet Fringing from Achromats. I help solve that problem too: astrovideoforum.proboards.com/thread/1079/using-achromats-video
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Post by Deleted on Sept 28, 2015 13:03:15 GMT
I just had a feeling it was right to sign up with this forum! Good info for sure. Continuing my search.
Ken, when I go to your site the drop down menus will not work, i.e. I go to ED scopes the white menu drops down, but nothing appears when I select it. Should that action direct to somewhere else?
Chuck
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Post by Dragon Man on Sept 28, 2015 13:18:21 GMT
Chuck, when you mouse over 'ACHROMATS' or 'ED SCOPES' the little drop down appears and you click on which one you want to look at. I just checked and it works fine. If not, here are the direct links to each drop down: Achromat - 120mm f/5Achromat - 6" f/5ED80 ED100
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Post by Rick in NWArk on Sept 28, 2015 14:21:59 GMT
Jumping in here with my two pence... First off, Chuck, remember the phrase "everything is relative". The combination of focal length and focal ratio does have an impact on video astronomy, but its not impossible to use an 8" F/10 SCT either. Natively (without focal reduction etc.) the combination of focal length and the camera sensor will likely give you a very small part of the sky (field of view) and will make smaller objects quite large (image scale). While that may be good for planets and some planetary nebula, its not good for most things because you wont be able to fit it all in the field of view. Check out www.12dstring.me.uk/fov.htm which is a field of view calculator that shows you how objects would look in the eyepiece - at least from a size perspective. Speaking of small parts of the sky, the smaller your field of view, the more precise your alignment and tracking have to be. Especially if you have to have longer exposures of 20 seconds or more or if you are doing live stacking or if your camera uses interlacing technology... I have the AVX. I did not have experience with GEMs prior to going into video astronomy, only alt-az. They are a different creature. I'm still not used to them. There are some nights where I just give up because my AVX and I are not getting along. I make it sleep on the couch. Don't get me wrong - its a good mount and I have a lot of good experiences with it - but its MUCH better for wider fields of view where tracking doesnt have to be spot on. I'm going to give guiding a try here pretty soon which I hope to help with smaller fields of view. From everything I've heard, the Edge HDs have great optics. I have the Mallincam 8" VRC. I think its the perfect size. Not too heavy (mine's the carbon fiber model) and F/8 is not too hard to get lower. It has 1600mm of focal length, tho and so I do have problems from time to time getting the image scale down (wider field of view) for larger objects. I imagine it to be worse with over 2000mm. One idea you might consider is getting a small refractor to start. I wish I had done this. About 18 months ago is when I started getting heavy into Video Astronomy. I thought I would just go gang-busters and get my ultimate scope etc. etc. Long story short, I should have bought my 80EDT first and learned through that. I would not have struggled so much with focus/focal plane/focal reduction. And getting that small refractor is not a throw away - its great for grab and go and also it can be used as a guidescope. I hope this post helps your decision process! --Rick
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Post by Dragon Man on Sept 28, 2015 14:46:01 GMT
Rick, sorry to interupt on the theme of this thread, but I have PM'd you. Please reply to it. Davy and I are waiting for your response I will delete this post after the PM's are sorted
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Post by Deleted on Sept 28, 2015 14:52:03 GMT
Ken, I used your links and it worked fine. Once I got there from your above link I could select the others from your page. Strange, but it works so no worries. Nice shots, gives me hope! I have reconsidered and also taken Rick's small refractor comment to heart along with yours. Tentatively I am looking the the AR127 (the achromat)by Explore Scientific, F/6.5. Think it will do to get me started and can have a few bucks left over for the AV equipment. I like the physical aspects of it also, especially the handle on top.
Rick, Thanks for your thoughts also. I did look at the VRC, found it to be a nice looking/working unit but like you said I might want to start a bit smaller first. Probably going with the Celestron AV-X mount along with the ES AR127, the AVX should be a good fit weight wise and somewhat wide field of view of the 127 hopefully will allow me to properly align/track. Don't think it comes with the polar scope, so will add that to the mix.
Thanks again folks,
Chuck
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Post by Dragon Man on Sept 28, 2015 15:23:40 GMT
All good Chuck.
The AR127 should give you some really top views through a Video camera. When used with a Focal Reducer it should be great.
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Post by Deleted on Sept 28, 2015 20:56:49 GMT
Ok guys you have spent my money, probably be in the end of the week. ES AR127 (free Besser 25mm lens with it), Clestron AVX goto mount, polar scope and power supply. Then the wife says...."whatcha gonna do when its 10 deg F outside, hmmmmm?" Well darn I guess I better buy the Wi-Fi control for the mount don't ya think? Yep she says. So following instructions as a dutiful husband I add the Wi-Fi (Sky Portal) to the order.
Now we shop for the AV system....Another thread for sure. I hate to ask what is the best here, kinda got my mind made up though, but more reading to do. Anyway, thanks all you guys for your input, I am pleased and excited. The shopping journey is half the fun.
73 (Regards, as we say in my other hobby - HamRadio)
Chuck
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Post by Rick in NWArk on Sept 28, 2015 21:06:40 GMT
Chuck, I run my AVX from my computer and use a serial/USB adapter which allows me to have a long run of USB so I can at least be in the garage if not in the warmth of the house!
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Post by Deleted on Sept 28, 2015 21:32:16 GMT
I thought about doing that Rick, as I have GUC232A Serial/USB adapter but I am kinda running out of USB ports. Could of run a Hub I suppose. The long term plan is having full mount/AV control in the warmth of the house. Step outside to setup and tear down, so there still will be some cold weather work. But if its super cold and windy, I just turn on the hamradio and talk to the guys in Florida. They can listen to me complain!!
Ok on the AVX, might have some questions for you from time to time if that is ok.
Chuck
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Post by davy on Sept 28, 2015 21:47:38 GMT
hi chuck,,10 f ,,tell the mrs to bring you out a jersey and a cuppa tea lol
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Post by Rick in NWArk on Sept 29, 2015 14:41:25 GMT
I'll be glad to help, Chuck.
I'll also add that you'll want a powered USB hub at some point. If not for the expanded number of ports then for making sure you have proper power going to a future USB camera, etc. etc. Some PCs dont give enough juice to their USBs.
--Rick
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