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Considering 9.25 Edge HD...

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#1 bazookaman

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Posted 13 April 2021 - 10:22 AM

Check my head on this... I'm a visual observer getting into AP with a primary interest in lunar and globs. I want great quality prints up to 38"x50" (120dpi minimum). I use a Canon 5dsr for terrestrial and have used it with a 400mm for AP on my EQ6r pro mount.

 

Inspired by Tom Glenn's lunar photo from January, I'd like to create a very high quality photograph (multi-frame composite) of the moon.

 

If I pick up a 9.25 edge hd, I'd like to, for now, use my Canon 5dsr and the eq6r. This would be oversampled at .36 as/p. I also have a 5d mk2 which has a larger pixel and would decrease the sampling to .56 as/p. (Would that be better?) At some point, I'd likely get an ap camera.

 

I would also be using this scope for lunar juxtapositions against the landscape so I'd likely pick up a (lighter, more portable) alt-az mount as I wouldn't need tracking for these shots, but would possibly need to move the tripod quickly from one place to another to compensate for some azimuth error. I might also use this set up for visual. If I prefer this over my 10" dob (I understand the only significant difference is the fov and dew), I might consider selling it.

 

Does this sound like the best value path for what I'd like to do? I know everyone says to start with a short FL refractor, but I have my 300 and 400mm lenses for that, and I don't have much interest in wide field. I've done a few so far and have had enough success with my tests, that I feel I'm ready to take the next step.


Edited by bazookaman, 13 April 2021 - 10:28 AM.


#2 Tom Glenn

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Posted 14 April 2021 - 07:47 PM

Thanks for the comments in reference to my images.  If you are interested in creating large, detailed images of the Moon, then the C9.25 Edge HD is a good telescope to do this with.  There are, however, a lot of technical details that go into generating a large image suitable to print at the sizes you are contemplating.  To make large prints, you need a very high quality image, which is determined predominately by the atmospheric seeing conditions coupled with your technique and your gear.  The concept of oversampled is quite a bit different when talking about high resolution telescopic imaging.  You are not oversampled with your Canon 5dsr at 0.36"/px.  I'm shooting with an astronomy camera with 2.4um pixels (ASI183mm), and the image scale is 0.21"/px, which is about perfect for this scope.  I'm also collecting some 4000 frames per panel and stacking 500-1000 frames.  In your case, the entire Moon will fit into frame, which is convenient (see below for FOV), although I don't know how feasible it will be to collect thousands of frames with this setup.  Nevertheless, you should be able to create nice images.  

 

FOV.jpg

 

The Edge HD optics are suitable for wide field shots of the Moon, as the field curvature and coma are minimized.  In the context of high resolution imaging, wide field doesn't mean the same thing it means in terrestrial photography.  Anything more than about 5mm sensor size may be considered "wide", depending on the context.  However, I'm not fully understanding your intended dual purpose of landscape juxtapositions.  As you can see from the FOV above, you will only be imaging the Moon, without any room for landscapes.  I'm thinking of images such as lighthouses or other structures (mountains, rocks, etc), with the Moon in the background when I think of landscape juxtapositions.  This FOV doesn't make much sense for this imaging.  Also, while the C9.25 is certainly very light and portable for its powerful optics and long focal length, it is not the type of scope you would quickly pick up and sprint across a field chasing a fleeting image.  From your description of landscape images, and desired rapid portability, I would think a long telephoto lens or short refractor telescope would be suitable for those types of images.  But, for high resolution shots of the Moon, the C9.25 Edge HD is excellent.  For visual, however, it will not be better than your 10" dobsonian.  The dob has more aperture, smaller secondary obstruction, and better cooling.  The dob will, however, be worse than the C9.25 Edge HD for imaging the Moon with large camera sensors, because of the coma, as well as difficulty tracking.  


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#3 bazookaman

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Posted 14 April 2021 - 08:15 PM

Tom, thanks so much for your input. Your thoughts are basically what I concluded from all of my reading over the past few days. I'm glad that you have verified it.

 

As far as lunar/terrestrial juxtapositions, this would be at moonrise/moonset. I have a photograph I've been wanting to create for years... I don't want to share details, as I've not seen it done (it probably has, but as a landscape artist that sells my work, I like to be as original as possible), but it will be a certain distant object on the horizon, miles away, juxtaposed with the rising moon. It's size should allow it to fit inside the disc of the moon. I've done similar lunar juxtaposition photographs, but not at this focal length. Max 400-560mm on full frame. I know the moon quality will be poor due to atmosphere, and I will need to focus stack, but for my purposes, I think it will work well enough. There are other similar photographs that I would like to do as well, but this one has been on my mind for a long time. Whenever I get it done, I'll try to remember to send you a print. smile.gif


Edited by bazookaman, 14 April 2021 - 08:16 PM.


#4 Tom Glenn

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Posted 14 April 2021 - 08:29 PM

Cool, I'll be interested to see the work when you can pull it off.  Good luck.  I would say that on the horizon, the Moon will be boiling in atmosphere, and so photographing at 2350mm will not lead to a sharp image.  However, if there is no incentive to have any extra field of view, because the object will be completely contained within the Moon, then I suppose it can't hurt to use a C9.25.  However, I would worry somewhat about the portability issue, because as I said, this isn't  the setup to quickly sprint 100 yards with once you realize the ephemeris prediction was slightly off.  However, with enough research, and double checking using multiple ephemeris programs, you could overcome this, although personally I'd rather have something I could run with if needed.  Also, double check the apparent size of the Moon at the time of your planned image, because the FOV simulator above is just an average, but the Moon changes apparent size according to its distance from Earth, and that FOV isn't leaving you much room to spare.  Also, SCT style scopes have variable focal lengths depending on the back focus, and you would hate to find that that Moon didn't fully fit in your FOV, but had the edge shaved off.  You can, however, also buy a focal reducer for the C9.25 Edge HD, which would probably be ideal for your landscape shot, although they are about 360 dollars.  


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#5 bazookaman

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Posted 15 April 2021 - 08:55 AM

Ok, that's good to know. The 8" is a shorter focal length, lighter weight, less expensive, and shorter backorder. Would that be something to consider, or would I be sacrificing too much detail? The downside is it's 1.25" focuser. I guess that's a deal breaker eh?


Edited by bazookaman, 15 April 2021 - 08:55 AM.


#6 Borodog

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Posted 15 April 2021 - 06:48 PM

The focuser is internal; has nothing to do with the Visual Back. Buy a 2" VB, or an SCT threaded camera adapter, or both.


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#7 John_Moore

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Posted 15 April 2021 - 09:56 PM

On upgrading to a 9.25" scope, it might be worth taking in to account Ed Ting's wonderful advice -- "examine what your life style is, and buy the telescope that fits in to it".

 

John - gone through 13" and 8" reflector setups in permanent housing, let alone a 6" refractor that later dictated the in and out lugs' a waste of time, if not on my back lol.gif .


Edited by John_Moore, 16 April 2021 - 05:23 AM.

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#8 bazookaman

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Posted 16 April 2021 - 10:18 AM

Thanks for the input, I've still not gotten the courage to get on the queue for a new one. That's a chunk of change plus a 6 month wait unless I can snag a used one, and from what I understand, for DSO I'll need to use OAG due to the long FL which will add a significant cost. If it was about half the price, I'd be more comfortable. :)



#9 Borodog

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Posted 16 April 2021 - 11:54 AM

Unless you are an enthusiast who is driven to image very small objects like the Crab Nebula, planetary nebulae, or the smaller galaxies, you may be frustrated and disappointed with trying to image DSOs with that long of a focal length. Even if you spend hundreds more dollars to get a special focal reducer for an EdgeHD scope, you will still be a many times the focal length you'd want to be at to image the most popular, larger, brighter DSOs like M42, M31, the Pleiades, the Orion Nebula, the Rosette, North America, California, etc. These objects are huge; larger than the full Moon and some of them much larger. The Andromeda Galaxy is roughly 6 times wider than the full Moon, for example.

 

It's subjective, but you want to be in the range of probably 250 - 500mm focal length to image these objects, and that's with a large sensor camera. A 0.63 reducer on a C8 will put you at around 1300mm. A 925 will be another 25% longer still.


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#10 Tom Glenn

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Posted 16 April 2021 - 01:10 PM

The advice above is good.  Ed Ting's video summarizes the situation well.  

 

You can't do everything with one scope, so you shouldn't rush any purchase, especially if you are attempting to do something with the scope that is not ideal.  If your goal is primarily lunar "close ups", high resolution images of the Moon, primarily with an astronomy specific camera, then the C9.25 Edge HD is a great option, and allows for larger sensors to be used without worrying about field curvature or coma.  But in the world of astronomy cameras, "wide" would include cameras such as my ASI183, which has a sensor that is still much smaller than an APS-C sensor.  However, if your goal is landscape photography with the Moon included, the C9.25 Edge, and indeed any of the moderately large SCTs, is a particularly bad choice.  In addition to the portability issues I raised above, they are somewhat fussy about collimation if they are moved, and usually require thermal equilibration to achieve optimal results.  And the long focal lengths will prove unsuitable for images taken on the horizon, with no advantage over something with  <1000mm focal length.  Similarly, if you are just getting starting with DSO imaging, a ~2000mm focal length will be a poor choice.  So, you have to decide upon the primary use, and your tolerance for size/weight/budget, and let that guide your decision.  


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#11 bazookaman

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Posted 16 April 2021 - 01:17 PM

Unless you are an enthusiast who is driven to image very small objects like the Crab Nebula, planetary nebulae, or the smaller galaxies, you may be frustrated and disappointed with trying to image DSOs with that long of a focal length. Even if you spend hundreds more dollars to get a special focal reducer for an EdgeHD scope, you will still be a many times the focal length you'd want to be at to image the most popular, larger, brighter DSOs like M42, M31, the Pleiades, the Orion Nebula, the Rosette, North America, California, etc. These objects are huge; larger than the full Moon and some of them much larger. The Andromeda Galaxy is roughly 6 times wider than the full Moon, for example.

 

It's subjective, but you want to be in the range of probably 250 - 500mm focal length to image these objects, and that's with a large sensor camera. A 0.63 reducer on a C8 will put you at around 1300mm. A 925 will be another 25% longer still.

So is there a good alternative? Something that will allow me get the full lunar disc on a full frame sensor while also allowing me to do some larger FoV imaging? Is using a barlow a normal practice in imaging? Basically, what would be the difference in using a 4x barlow on a 500mm scope for the moon... slower ratio, but the moon is bright so shutter speeds should still be adequate. Or am I missing something.


Edited by bazookaman, 16 April 2021 - 01:20 PM.


#12 Tom Glenn

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Posted 16 April 2021 - 05:08 PM

So is there a good alternative? Something that will allow me get the full lunar disc on a full frame sensor while also allowing me to do some larger FoV imaging? Is using a barlow a normal practice in imaging? Basically, what would be the difference in using a 4x barlow on a 500mm scope for the moon... slower ratio, but the moon is bright so shutter speeds should still be adequate. Or am I missing something.

What is the primary goal?  If it's imaging the Moon such that the Moon fills the entire frame, then this won't be compatible with anything considered "wide field" in deep sky astrophotography.  You can absolutely use a barlow lens when imaging the Moon, although this is not done in deep sky imaging.  Don't allow your focal ratio to exceed 5x your pixel value in microns however, or else you are just sampling diffraction without any additional detail, to the detriment of your images.  Most people that are imaging the Moon are not worried about filling a full frame camera, and instead resort to mosaics.  Alternatively, you can use small pixel astro cameras with shorter focal length telescopes to image the Moon.  I routinely do this with my 916mm focal length scope, see images below.  

 

https://www.cloudyni...ive-6newtonian/

 

Swapping out the astro camera for a standard DSLR increases the field of view, suitable for lunar eclipses and the like.  

 

https://www.cloudyni...-in-the-clouds/

 

This is probably about as much focal length as I would attempt to use for a landscape on the horizon.  Although if I was serious about doing a lot of landscapes, I would probably opt for something even smaller, simply so I could use a standard tripod and walk around with the setup easily to change my perspective.  But ultimately, you'll have to decide what niche you want the scope to occupy.  


Edited by Tom Glenn, 16 April 2021 - 05:10 PM.

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#13 bazookaman

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Posted 16 April 2021 - 06:14 PM

The primary goal is to do everything and not spend a fortune! laugh.gif But seriously, I have a few different goals as mentioned in my first post....

 

1. I want a high quality first-quarter/third-quarter and/or crescent lunar print with "excellent" detail (as I would see it through my 10" dob for example) up to 40"x40". This comes out to needing at least 4000x4000px.

 

2. I want to be able to photograph moonrises and moonsets on the "horizon" (not necessarily true horizon, but in some cases yes) at reasonably long FL's in the neighborhood of 1200mm (assuming I'm using the 5dsr). I realize there will be little detail, but the point is the juxtaposition, not the detail. And if I'm down in a valley shooting up 30 degrees or even higher, then much of the detail returns.

 

3. I want to photograph smaller DSO's, particularly Globs... for the larger DSO's that everyone photographs don't interest me too much and I already have a 400mm lens I can use for the time being.

 

 

For now, I think I can accomplish #1 well enough with my current set up. At least, I'm going to try. I can hand-track the dob and get a few hundred exposures in a reasonable amount of time. Here is my first attempt with 8 exposures. I was shooting at 1/30 which I think is a bit too slow as I think there is some motion blur. 2400mm.

 

022021-lunar.jpg

 

022021-lunar_crop.jpg

 

If I get rid of the motion blur, I think I'll be happy with the detail, at least for now.




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