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Post by Rick in NWArk on Mar 4, 2015 20:31:30 GMT
As most of you know, the final effective focal length of your setup (telescope plus spacers / extenders / focal reducers / Barlows / etc.) determines the field of view on the chip of your camera. If you cant get your focal length down, the Andromeda Galaxy will look like a fuzzy patch because you're zoomed in to the core. Likewise, we all likely agree that we can never get a small enough field of view to get a big enough Saturn! You can look up the formula and put it in Excel, or you can use some nice online tools to do the calculations for you. I use David Cambell's here: www.12dstring.me.uk/fov.htmI like David's because not only does he have a nice list of different cameras and scopes, you can also enter in custom settings for any he does not have in the list. Now, mind you, the camera's specifications also play a role in the field of view. In this case I put in my MallinCam Jr Pro settings : 8.4 micron pixel size and 768x494 pixels. Binning was left at 1x1. So using David's app, I looked up several planets and many Messier objects, got them to fill the field of view, then grouped them into some standard focal lengths. Attached are my results. I have also put together equipment combinations to hit those focal lengths, but I have not been able to test anything yet. I didn't include those combinations because everyone has different scopes and equipment. I'm pretty sure the sensor size on the Jr Pro is the same for the Extreme and Extreme2... I'm not sure about the Exterminator. Anyway, I hope this is useful for folks. --Rick
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Post by Deleted on Mar 5, 2015 4:38:39 GMT
Hi Rick,
Why would you want to fill the fov? Images look better nicely framed, and seeing will never be good enough to support doing so on smaller objects. Also exposure times will go way up and detail will go down. Now if your observatory is parked next to HST ignore me. I live in an area of decent seeing, and rarely can I use 525x on Jupiter (1/3" chip = 6mm eyepiece image scale) in my 8" f15.5. and see more detail than at 350x. Once in perfect conditions I got good results using a 3.8mm for 827x which would be 4962mm fl for a 1/3" chip. But that was for about 2 hours in over 13 years.
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Post by Dragon Man on Mar 5, 2015 12:25:31 GMT
Sounds like a cool program Rick. But I can also see Richard's point of View. I have the good fortune of being friends with 2 quite famous Planetary Imagers (Paul Haese and Anthony Wesley) and I have stood next to them on many occasions watching them at work on their imaging runs, and they never get what we would call a good Live image of the planets on their monitors. It's all in the stacking and processing that makes their Solar System Goodies look nice. But as for Live, the closer they get (narrow FOV) with Planets the crappier they look, to the point of a bubbling boiling mess. And these were in still skies on perfect nights. A slightly wider FOV on planets does help them in a Live Video situation. Just have to put up with them looking a bit smaller than hoped. I always found Planetary imaging far harder than DSO imaging because of the long focal lengths and huge magnifications involved.
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Post by Rick in NWArk on Mar 5, 2015 18:32:41 GMT
Hi Rick, Why would you want to fill the fov? Images look better nicely framed, and seeing will never be good enough to support doing so on smaller objects. Also exposure times will go way up and detail will go down. Now if your observatory is parked next to HST ignore me. I live in an area of decent seeing, and rarely can I use 525x on Jupiter (1/3" chip = 6mm eyepiece image scale) in my 8" f15.5. and see more detail than at 350x. Once in perfect conditions I got good results using a 3.8mm for 827x which would be 4962mm fl for a 1/3" chip. But that was for about 2 hours in over 13 years. Because you can obviously work your way down from there. What would it look like from a theoretical limit? How close can you get? What are tradeoffs? The biggest win for me in this exercise is getting groupings of like-sized items that I can go after with the same equipment setup to achieve a specific field of view. I get the primary field fillers, and I get those in neighboring groups that all would have enough size to be appreciated. From a planetary perspective, I am hoping to work on eyepiece projection this Spring to deliver a larger image size. --Rick
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Post by Rick in NWArk on Mar 5, 2015 18:37:21 GMT
Sounds like a cool program Rick. But I can also see Richard's point of View. I have the good fortune of being friends with 2 quite famous Planetary Imagers (Paul Haese and Anthony Wesley) and I have stood next to them on many occasions watching them at work on their imaging runs, and they never get what we would call a good Live image of the planets on their monitors. It's all in the stacking and processing that makes their Solar System Goodies look nice. But as for Live, the closer they get (narrow FOV) with Planets the crappier they look, to the point of a bubbling boiling mess. And these were in still skies on perfect nights. A slightly wider FOV on planets does help them in a Live Video situation. Just have to put up with them looking a bit smaller than hoped. I always found Planetary imaging far harder than DSO imaging because of the long focal lengths and huge magnifications involved. At some point you definitely hit the limits of resolving power and atmospheric turbulence etc. etc. Doesn't mean you cant take a shot on the theoretical side. It is going to be fun exercise to push some of those limits and see what the actual results are. --Rick
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Post by Deleted on Mar 5, 2015 19:39:30 GMT
Thanks for the link, Rick. I added it to my home screen. Knowing the FOV with your setup is critical, especially when trying to view large nebulae. I recently viewed Eta Carinae with my Lodestar and had to use a FL of 162mm and still could have used a little more FOV. The calculator will help a lot with planning a viewing session. Don
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Post by Dragon Man on Mar 6, 2015 2:52:45 GMT
Sounds like a cool program Rick. But I can also see Richard's point of View. I have the good fortune of being friends with 2 quite famous Planetary Imagers (Paul Haese and Anthony Wesley) and I have stood next to them on many occasions watching them at work on their imaging runs, and they never get what we would call a good Live image of the planets on their monitors. It's all in the stacking and processing that makes their Solar System Goodies look nice. But as for Live, the closer they get (narrow FOV) with Planets the crappier they look, to the point of a bubbling boiling mess. And these were in still skies on perfect nights. A slightly wider FOV on planets does help them in a Live Video situation. Just have to put up with them looking a bit smaller than hoped. I always found Planetary imaging far harder than DSO imaging because of the long focal lengths and huge magnifications involved. At some point you definitely hit the limits of resolving power and atmospheric turbulence etc. etc. Doesn't mean you cant take a shot on the theoretical side. It is going to be fun exercise to push some of those limits and see what the actual results are. --Rick Yep, been there Rick At one Astro Camp the sky was absolutely perfect so we Barlowed a Barlow and put them in another Barlow and we got Saturn to completely fill the eyepiece, and the rings were outside the FOV Was fun at the time, but wow it looked terrible. It had to be tried
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Post by Rick in NWArk on Mar 6, 2015 3:46:35 GMT
Glad it could help, Don! That's a real nice image!
Ken, I agree - you learn so much more by trying. Another learning for me is getting more familiar with object sizes. I suppose someone has already written observing session planning software based upon focal configurations and object sizes.
--Rick
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Post by Deleted on Mar 6, 2015 16:13:29 GMT
Hi Ken,
Done that too! Stuck 2 barlows in my 15.5 for 12584mm fl with a 3.8mm Pentax. Aimed at a insulator on a light pole at sunset, surprising sharp image. Then pointed to Jupiter, just a huge blob of light. Could not even tell what it was. Seems 99.9% of the time 600x is the most the atmosphere allows no matter the scope. The objects I find best at high power are Planetary Nebula like the Ghost of Jupiter, the Ring etc.
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Post by Deleted on Mar 23, 2015 17:33:01 GMT
Here is a single raw image of Jupiter at 3146mm taken with my 8" 1/60 exposure using a DSO-1 with no post processing. Also M57 same just longer exposure. Last is Trap in M42. Richard
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Post by Deleted on Mar 23, 2015 17:47:27 GMT
I think for most objects other than planets, the loss of effective aperture can be a killer using small chip video camera's. If I am thinking right, my 8" with a 32mm baffle would need .20 reduction to use all the light coming into the scope using a 1/3" 6mm chip. While resolution would be the same, brightness would not.So I think my 8" at 15.5 is actually showing the brightness of a much smaller scope and 80% of the light is not hitting the chip? I would need a camera with a 32mm chip to be 100% effective? I may be way off base here, but I don't see this discussed much.
Richard
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Post by Rick in NWArk on Mar 23, 2015 17:52:45 GMT
That is a fantastic Jupiter, Richard! Love how you got the central star in the Ring too - its magnitude 14.8!
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Post by Rick in NWArk on Mar 23, 2015 17:59:50 GMT
I think for most objects other than planets, the loss of effective aperture can be a killer using small chip video camera's. If I am thinking right, my 8" with a 32mm baffle would need .20 reduction to use all the light coming into the scope using a 1/3" 6mm chip. While resolution would be the same, brightness would not.So I think my 8" at 15.5 is actually showing the brightness of a much smaller scope and 80% of the light is not hitting the chip? I would need a camera with a 32mm chip to be 100% effective? I may be way off base here, but I don't see this discussed much. Richard I'm definitely interested in understanding and discussing this. Obviously, telescope geometry plays a factor here, but once you've taken obstructions into account in the calculation of "light coming into the scope", where are there additional losses? I agree that for 8", your Ring seems dim compared to what I've gotten in just a few seconds exposure with my MallinCam Jr Pro and my 8" RC scope (also getting the central star).
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Post by davy on Mar 23, 2015 18:00:50 GMT
Jupiter looks brilliant..cream if the crop ..great capture richard
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Post by Deleted on Mar 23, 2015 20:46:52 GMT
Hi Davy & Rick, Thanks for the comments. Rick, it's the same as when using most eyepieces, more power = dimmer view. Your 8" RC is what, f8? and using a 1/2" chip it should be a brighter if smaller image scale. If I used a .2 reducer I would be getting max image brightness. 32x.2=6mm 1/3" chip size. When I have a 32mm cone of light and only a 6mm chip or eyepiece it's not going to pick up but a fraction of the light, just to small.Now it's probably not quite that bad as the cone is getting smaller as it gets closer to focus, but in a long fl scope it can be a lot. Shorter fl scopes have stepper cone angles I would think, so may be less effected yet? I guess the thing to do is try many eyepieces with different field stops, see which is brightest without vignetting. Then you can see what reduction you need to get maximum brightness and shortest exposure given the size of your chip. Since they don't make round chips, your going to have vignetting at the corners to some degree depending on chip layout. If it is square 6mm x 6mm should be even at the corners. If it is something like 6x8mm it will be more on 2 corners. We have got used to seeing images in a square or rectangular format as film and chips come in that format. Wish they made round chips :-). I guess we could clip the vignetted areas of square chips on the image in a circle, and get a better looking image? Every optical device I know creates a circle, yet we image them with squares. And then we have the problem of coma etc using reducers.So I guess it is better to have a camera with a bigger chip to be able to use less reduction for less coma, but then larger area requires flatter fov. So every scope design will be different and no hard and fast rules or formula works for everything. Here is an image of M57, same night and scope, using focal reduction. Brighter image but still not getting 100% of the light. Richard
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Post by Rick in NWArk on Mar 23, 2015 21:37:49 GMT
I think I follow what you are saying.
As we change the focal length to get a specific image scale, a different section (%) of the total light cone (field of view) hits the chip -- and therefore, fewer photons total will hit the chip during the same exposure times.
But, all the photons for the Ring Nebula would still get onto the chip ... so we have those photons hitting a different number of pixels (photocells). Since they are spread out, they are not filling up the well of an individual pixel which means less intensity when the chip is read. This is like an eyepiece where the same photons are spread out over a different number of rods/cones in our retina. More photons = more intensity = brighter.
Who's going to step up and invent Miloslick for our eyeballs, haha?!
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