Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Sensor size relationship to aperture and focal length

  • Please log in to reply
21 replies to this topic

#1 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 05 February 2021 - 12:40 PM

I'm relatively new to astrophotography through a telescope.  I've done some work with my Canon EOS 6D.  I finally decided to buy a good mount, I am picking up my CEM60 on Tuesday, so that is no longer a concern. I want to start concentrating finding a telescope to mount on the CEM60 and what cameras to use.  I understand that the size of pixels and sensor size affects the image through different scopes and the aperture and focal lengths play a role also.  I don't really understand those differences totally and why it is important.   Currently I own two cameras.  The EOS 6D and I also own a Sony A6000, but it has been converted to infrared (hot mirror professionally removed).  The 6D has a full frame sensor and the A6000 is a crop sensor but has more pixels.  What can I expect from these cameras, and would I be better off looking for a pure astrocamera?   


Edited by Sunpilot, 05 February 2021 - 12:41 PM.


#2 redtag

redtag

    Explorer 1

  • *****
  • Posts: 72
  • Joined: 08 Feb 2019
  • Loc: Tennessee

Posted 05 February 2021 - 12:53 PM

You can get a very good idea of Field of View (FOV) and image scale in arc-sec/pixel by putting in any sensor information and focal length information in Stellarium ( a free and easy to use planetarium program). You want to use combinations that place the image scale between 1" and 2". Just pick out some targets that interest you and see how the combinations frame the object. 


  • Sunpilot likes this

#3 Tapio

Tapio

    Aurora

  • -----
  • Posts: 4,693
  • Joined: 24 Sep 2006
  • Loc: Tampere, Finland

Posted 05 February 2021 - 12:53 PM

My opinion is this - first use what you have now.

CEM60 is a good starting point and so is the cameras you have now.

Next step could be a refractor in the range of 70-100mm.

Or if you have good camera lenses they should be utilized.



#4 imtl

imtl

    Soyuz

  • *****
  • Moderators
  • Posts: 3,897
  • Joined: 07 Jun 2016
  • Loc: Down in a hole

Posted 05 February 2021 - 01:16 PM

You can get a very good idea of Field of View (FOV) and image scale in arc-sec/pixel by putting in any sensor information and focal length information in Stellarium ( a free and easy to use planetarium program). You want to use combinations that place the image scale between 1" and 2". Just pick out some targets that interest you and see how the combinations frame the object. 

I would rephrase this as:

 

As a beginner, it would be easier for you to work with image scale of 1"-2"/pixels. 

 

The you wrote it, it gives the impression that this is some law of nature. Which of course it is not.



#5 drd715

drd715

    Viking 1

  • *****
  • Posts: 956
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 05 February 2021 - 01:35 PM

It's complicated and its not so complicated, but a lot to it.

Your camera pixel size will be what it will be. It is manufactured that way. Pixel size if optimized will complement yor maximum resolution (weakest link in the chain - lens resolution, atmospheric seeing resolution etc.) And is considered as 1/3 of the best resolution you can achieve.

Considering that seeing is most likely your limiting factor you will probably be trying to match about 1-3 arc second resolution. Telescope focal length is the variable here. Under 400mm scopes like smaller pixels. 400-800mm scopes like medium size pixels and longer scopes match better with larger pixels. Camera manufacturers are tending toward medium and smaller pixels for general use land cameras so whats available in astro cameras will reflect this. These numbers I am using are a bit loose and you can use various formulas to get a specific match, but the selection of camera pixel sizes is what it is.

There are different requirements for planetary imaging compared to wide field DSO low light subjects. Planets are bright and small often imaged in a video type mode at very high powers and long focal ratios (F-20 area) and small pixel cameras often with smaller physical size sensors. For DSO imaging longer exposures and supior tracking are needed.

Your 6D has moderately larger pixels and has been a favorite FF camera for imaging. I can not comment about the Sony other than it is a crop sensor with smaller pixel size, I have never used this model.

As time moves on the newer sensors are much better. Especially the back illuminated sensors. Now consider the cooled astro camera as a serious candidate for your imaging. Cooled cameras have several advantages over non cooled cameras. Very low electronic noise and with the newer back illuminated sensors no amp glow in the images.

One thing to consider between a FF and a crop sensor (or smaller sensor) will be the size of a "flat field " provided by the telescope usually augmented by the optical "flattener " . Full frame sensors require a larger flat circle than crop sensors.

Specific recommendation (personal) would be the asi2600 camera. Probably to start out the color version, but it does come in a mono version that may be a step too far for beginning imagery.

The best thing about a cooled camera besides low noise is that you shoot at a fixed sensor temperature so you can pre make a simple darks library to leisurely apply in your processing.



Sent from my SM-N950U using Tapatalk
  • Sunpilot likes this

#6 TOMDEY

TOMDEY

    Voyager 1

  • *****
  • Posts: 10,192
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 05 February 2021 - 01:52 PM

The two pertinent parameters that would affect sensor selection are:

 

1) F# at the image plane. The size of the Airy Disc is around the F# in microns. That is, a good F/6 scope will present a focused image of a star that is about 6 microns across. One's preferred sampling ratio, called Q, then determines the pixel pitch that one would want. Most professionals shoot for something around unity, for max information throughput, but we amateurs, who don't mind spending all night obsessing over one single target might prefer something more or less. So, in that example of a premium F/6 imager... pixel pitch somewhere between 5 and 7 microns would generally make sense.

 

2) Linear Field. Your scope presents a well-corrected linear field diameter that is characteristic of the make and model. Ideally, you would like to take advantage of that entire field, without clipping it at all. Most amateurs go smaller, only because bigger arrays are much more expensive. But it's at least worth being aware of how much field is available, if you have the commitment to fund the camera that can avail all of it.

 

That's really all there is to it.

 

PS: When I say Telescope, I mean the whole thing, including any extenders, compressors, flatteners in the chain. They become part of the telescope, as far as the sensor is concerned, changing both the F# and the linear field. Need to account for those.    Tom


  • Sunpilot likes this

#7 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 25,647
  • Joined: 27 Oct 2014

Posted 05 February 2021 - 01:54 PM

I'm relatively new to astrophotography through a telescope.  I've done some work with my Canon EOS 6D.  I finally decided to buy a good mount, I am picking up my CEM60 on Tuesday, so that is no longer a concern. I want to start concentrating finding a telescope to mount on the CEM60 and what cameras to use.  I understand that the size of pixels and sensor size affects the image through different scopes and the aperture and focal lengths play a role also.  I don't really understand those differences totally and why it is important.   Currently I own two cameras.  The EOS 6D and I also own a Sony A6000, but it has been converted to infrared (hot mirror professionally removed).  The 6D has a full frame sensor and the A6000 is a crop sensor but has more pixels.  What can I expect from these cameras, and would I be better off looking for a pure astrocamera?   

The camera/sensor deal is relatively not critical.  Don't worry, don't overthink.  But there is a clear choice here, for a reason you're probably unaware of.  At the end, it's less important.

 

These are the important points.

 

DO NOT GO TOO BIG ON THE SCOPE.  The second most common beginner problem, other than getting an inadequate mount.  You dodged that one with the CEM60, now dodge the other one.  By far the best idea is to start with a refractor in the 51-80mm range.  This would be excellent.  $489.

 

https://www.astronom...fpl-53-f-6.html

 

But you say you want a forever scope?  This is excellent also for learning DSO AP with AND is a scope you'll keep forever as your big target scope.  There are lots of big targets.

 

https://www.skywatch...t-apo-refractor

 

Can't find one of those?  This bats in the same league.

 

https://www.stellarv...m/svx080t-25ft/

 

They say these are in stock.

 

https://www.teleskop...-P-Focuser.html

 

https://www.teleskop...-Objective.html

 

This is in stock, also.  Another forever scope.

 

https://optcorp.com/...-telescope-gray

 

OK, cameras.

 

Using the Sony converted to infrared will work really well on emission nebulae.  They emit mostly right at the border of red/infrared, the Canon is somewhat blind there.  So, I'd work with that camera first, not the Canon.  You'll need an external UV-IR cut filter like this to avoid bloated stars.  An intervalometer that will let you shoot things like 30 X 60 second subexposures.

 

https://optcorp.com/...-filter-t-mount

 

Eventually you'll want a cooled astro specific camera, but there's no need for it right now.  If you do decide you want one, this is a good general purpose camera.  The field of view will be less than with your Sony, no big deal.  Sharpcap can run it well.  It sees near IR, of course.

 

https://astronomy-im...533mc-pro-color

 

You need software for calibrating/stacking/processing.  I recommend Astro Pixel Processor, an astro specific program that does all 3.  A serious advantage.

 

This book will be the best $40 you'll ever spend in DSO imaging.

 

https://www.amazon.c.../dp/0999470906/


Edited by bobzeq25, 05 February 2021 - 06:26 PM.

  • drd715 and RogerM like this

#8 sg6

sg6

    Voyager 1

  • *****
  • Posts: 10,184
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 05 February 2021 - 01:56 PM

I think you are working the wrong way.

You need to take the expected object size and calculate the final image size.

 

Fairly easy Image = Tan(Obj)*FL

 

So the 3 degrees M31 in a 600mm focal length scope give a image of:

Tan(3)*600 = 0.0525*600 = 31.5mm.

 

Might just squeeze on a full frame, but orientating the DSLR/sensor to suit would help.

 

M33 at 1 degree would be 10.5mm, more useful.

 

You likely need to determine the expected targets, that gives an idea of a focal length and remeber that you will probably want a reasonable amount of framing around an object. As ever the catch is you have objects from say M1 and M57 up to M31 and M45. How does 2 or 3 scopes sound lol.giflol.giflol.gif

 

A reducer helps, as it reduces the final image, and costs less then another scope.

 

Half guess you need to sit  and construct a basic spreadsheet of object size in 0.5 degree steps and then start entering focal lengths and compare the result to the 2 sensor sizes.

 

But the object, the focal length and the sensor size are interrelated, you need to work things out using all 3 inputs.

 

The pixel size itself is maybe a little irrelevant - you have the 2 DSLR's and you cannot change the pixel size after all. I have the same problem, the things won't alter size no matter what I ask.



#9 XM381

XM381

    Explorer 1

  • -----
  • Posts: 54
  • Joined: 01 Jan 2019
  • Loc: Oklahoma, USA

Posted 05 February 2021 - 02:29 PM

I'm a complete noob and my advice is worth what I'm charging you for it... nothing!

 

I've struggled with the same questions, read lots about field of view, pixel scale and done lots of math. 

 

I think the first thing to figure out is what kinds of things do you want to take pics of. There's a lot of variation in the sizes and brightness of all the stuff in the sky, so there's not a one-sizes-fits-all option.

 

I also think there a lot to be said with working with what you have before buying lots of equipment.... although I can't say I did a good job of following this rule!

 

Your Canon 6d is well regarded for astrophotography and is easy to computer control with lots of different kinds of software, BackyardEOS, etc. Your Sony is harder to do that with. I've got an A5000 and an intervalometer is about as good as it gets. Your A6000 has more options but nothing like your 6d.

 

And finally, look at astrobin.com to see what others can do with the equipment you're working with. Obviously lots and lots to learn about image processing, but will give you an idea of what your equipment CAN do.

 

Here's a quick Astrobin search for Canon 6d pics. Click on a pic and the text will tell you about the scopes they used and other info. 

https://www.astrobin...rch/?q=canon 6d

 

The most important part is go outside and take some pics!


  • Sunpilot likes this

#10 jonnybravo0311

jonnybravo0311

    Vanguard

  • *****
  • Posts: 2,414
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 05 February 2021 - 02:42 PM

The pixel size itself is maybe a little irrelevant - you have the 2 DSLR's and you cannot change the pixel size after all. I have the same problem, the things won't alter size no matter what I ask.

Get the ZWO ASI294MM or the QHY 294M. The pixels will magically change size for you from 4.63 to 2.315 at the flip of a virtual switch!

 

Please note - the above statement is purely facetious. The pixels themselves DO NOT change size, but rather, the drivers allow the default 2x2 bin mode to be unlocked to a 1x1 mode. The pixels on the IMX492 sensor are, in fact, 2.315 microns.


  • Sunpilot likes this

#11 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 05 February 2021 - 03:20 PM

My opinion is this - first use what you have now.

CEM60 is a good starting point and so is the cameras you have now.

Next step could be a refractor in the range of 70-100mm.

Or if you have good camera lenses they should be utilized.

I have good Canon lenses but not a long prime.  My long lens is 200mm telescopic.  I'm not going to buy any more Canon lenses, I can get a good scope for what they want for lenses. 



#12 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 05 February 2021 - 03:40 PM

I think you are working the wrong way.

You need to take the expected object size and calculate the final image size.

 

Fairly easy Image = Tan(Obj)*FL

 

So the 3 degrees M31 in a 600mm focal length scope give a image of:

Tan(3)*600 = 0.0525*600 = 31.5mm.

 

Might just squeeze on a full frame, but orientating the DSLR/sensor to suit would help.

 

M33 at 1 degree would be 10.5mm, more useful.

 

You likely need to determine the expected targets, that gives an idea of a focal length and remeber that you will probably want a reasonable amount of framing around an object. As ever the catch is you have objects from say M1 and M57 up to M31 and M45. How does 2 or 3 scopes sound lol.giflol.giflol.gif

 

A reducer helps, as it reduces the final image, and costs less then another scope.

 

Half guess you need to sit  and construct a basic spreadsheet of object size in 0.5 degree steps and then start entering focal lengths and compare the result to the 2 sensor sizes.

 

But the object, the focal length and the sensor size are interrelated, you need to work things out using all 3 inputs.

 

The pixel size itself is maybe a little irrelevant - you have the 2 DSLR's and you cannot change the pixel size after all. I have the same problem, the things won't alter size no matter what I ask.

I haven't really given a lot of thought as to exactly which DSO I will be imaging.  My expectations are probably as many as I can over time.  I fully realize that I will have more than one scope in my collection.  I'm trying to get a feel for wht scopes will complement the two cameras I already have.  I also have plans for a dedicated camera for AP and I am trying to understand the relationship between the camera, scopes, sensors, pixels, focal lengths, and all the other crazy variables that come into play.  The spread sheet idea is a good one and I will work on that.  Thanks for your input



#13 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 05 February 2021 - 03:42 PM

I'm a complete noob and my advice is worth what I'm charging you for it... nothing!

 

I've struggled with the same questions, read lots about field of view, pixel scale and done lots of math. 

 

I think the first thing to figure out is what kinds of things do you want to take pics of. There's a lot of variation in the sizes and brightness of all the stuff in the sky, so there's not a one-sizes-fits-all option.

 

I also think there a lot to be said with working with what you have before buying lots of equipment.... although I can't say I did a good job of following this rule!

 

Your Canon 6d is well regarded for astrophotography and is easy to computer control with lots of different kinds of software, BackyardEOS, etc. Your Sony is harder to do that with. I've got an A5000 and an intervalometer is about as good as it gets. Your A6000 has more options but nothing like your 6d.

 

And finally, look at astrobin.com to see what others can do with the equipment you're working with. Obviously lots and lots to learn about image processing, but will give you an idea of what your equipment CAN do.

 

Here's a quick Astrobin search for Canon 6d pics. Click on a pic and the text will tell you about the scopes they used and other info. 

https://www.astrobin...rch/?q=canon 6d

 

The most important part is go outside and take some pics!

Thanks for the input.  The learning curve is just beginning!  


  • AstroVagabond likes this

#14 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 25,647
  • Joined: 27 Oct 2014

Posted 05 February 2021 - 06:13 PM

 

 

look at astrobin.com to see what others can do with the equipment you're working with.

Any number of beginners have wasted large amounts of money and time by doing that.  _Serious_ amounts of wasted time and money.

 

What an experienced imager can do with equipment is not remotely good data on what a beginner can do with it.  It's really, really (add as many as you want) bad data.

 

What _beginners_ do with equipment is good data for a beginner.  So.

 

"I regret spending the first 6 months trying to learn imaging with an 8" Edge, with that scope it was a losing effort. Fortunately got a nice little refractor, and not only have the quality of my images improved but I'm actually enjoying the process of learning how to do it!"

 

"Of all the recommendations though, if you want to get into imaging then a short imaging refractor is probably the best one (IMHO).  I have a C8 and this was the scope I learned AP on.  It was a long, tough struggle and I have no good pictures to show for it.  I could have easily saved a year by starting with a more image-friendly scope."

 

"I made the mistake of trying to learn how to shoot with an F/10 SCT, an EdgeHD 8". I spent six months struggling with that, and then I made the switch to a William Optics Star 71 F/4.9 and I couldn't be happier with the results!

 

"I'm biased as I wasted two years starting out with a C11. After I sold it and bought a 660mm refractor I was up and running 2nd or 3rd night out."

 

"4-years into astrophotography and after making the mistake of starting with a large SW 150Pls reflector, quickly moved to a William Optics GT81 refractor, which has been much more satisfying and am still learning, big time."

 

You can find many excellent images with those scopes on astrobin.  From experienced imagers.


Edited by bobzeq25, 05 February 2021 - 06:25 PM.

  • Sunpilot likes this

#15 Alex McConahay

Alex McConahay

    Voyager 1

  • *****
  • Posts: 10,595
  • Joined: 11 Aug 2008
  • Loc: Moreno Valley, CA

Posted 05 February 2021 - 07:08 PM

I've been wondering if I have anything to add to this thread.......

 

I seem to be in a minority in that I do not really concentrate too much on arc seconds per pixel. I cannot see that as a determining factor considering the possibilities of binning, drizzling, and the vagaries of display size and cropping. I mean, why go to a lot of trouble trying to match pixel size to seeing when the recommendations for that match run anywhere from 1:1 to 1:3, or more? Why worry when one nights seeing numbers can be easily be twice or more what another's was. And does your camera become useless when one uses a reducer or even another tube. And when you throw in the fact that most of your images are displayed at about one fourth full resolution, it is quite possible to overfuss the arc seconds per pixel.  I mean, things, change. But I think any reasonable ball park for arc seconds per pixel will do. SO, I just don't fuss it too much.  

 

The issue of sensor size and scope does matter. And the answer to that is not pixel size, but image circle. The tube delivers a certain image to the focal plane. If you have a sensor too large for that image, you will get vignetting or bad performance on the corners. If you have one too small, you will be wasting photons, and getting a smaller picture (but the picture will be pretty much the same as the center of the larger sensor's frame. 

 

I would not want to buy any telescope tube that could not deliver a full frame image circle. And that frame should be fully illuminated (or close to), and fully corrected (or correctable through a flattener).

 

Whether the image circle is big enough to fill the frame is not dependent on F ratio and focal length alone. It is dependent on the overall engineering of the system. For instance, do you know the difference on your Canon between EF and EF-S lenses? The EF-S lens is built for crop sensors. If you put one on your 6D, you will get a picture, but the edges may not be all that usable. A 55 mm EF lens and a 55 mm EF-s lens delivers the same image to the central pixels. It is just that on the EF-s lenses, that usable image circle is smaller. It does not need to be bigger since it the sensor will see only that part.

 

At any rate, just be sure you get a good, clean, well lit image circle on your new tube. Whatever camera you get to go with it will love it. If you opt to get tube with an image circle that can only cover a smaller chip, that is fine, as long as you realize that you will forever be limiting yourself to cameras with a smaller chip. 

 

I hope this helps some. 

Alex


  • drd715, Sunpilot, dcaponeii and 1 other like this

#16 BQ Octantis

BQ Octantis

    Fly Me to the Moon

  • *****
  • Posts: 5,242
  • Joined: 29 Apr 2017
  • Loc: Red Centre, Oz

Posted 05 February 2021 - 08:15 PM

To Alex's point, the APS-C sensor on the A6000 will suffer less vignetting than the 6D from any aperture. And you already had it Ha modified. Seems like the obvious choice to me.

 

Since you already jumped off the deep end with the CEM60, you need a beefy scope to use up the 60-lb payload capacity. And with Mesa's reasonably dark skies, you should get a fast aperture. So you may as well go with the f/2.2 Celestron RASA-11.

 

post-257503-0-58941100-1533341433.jpg

[Source]

 

Its focal length is just 620mm, so not much of a tracking challenge. And at f/2.2, you can get away with 20 second subs on the A6000 (and 10 seconds on the 6D, at least at the center). At that flux, you could capture 2-3 targets per night vice the 1-2 targets per month with an oft-recommended f/7.5 apo.

 

Here's how the two cameras compare on that aperture:

 

cameras.png

 

With that aperture, both cameras put you in the highly coveted 1-2" per pixel range (Line 13). With 15 lb of weight margin, you could go with either. And with that much flux, you could easily upgrade to mono and do extreme narrowband.

 

Astronomics has them in stock for just US$3600 shipped:

 

https://www.astronom...tical-tube.html

 

A DSO astrophotographer with a CEM60 should settle for nothing less.

 

BQ

 

P.S. If you ever want to do planetary, you might substitute a Celestron C14 for the RASA-11. With the Fastar add-on, it's an f/2 astrograph.

 

Fastar_Cameras_DSLR.jpg

[Source]

 

Just US$5000 shipped from Astronomics.

 

https://www.astronom...y-dovetail.html

 

Made for your mount.


Edited by BQ Octantis, 06 February 2021 - 09:42 AM.

  • Sunpilot likes this

#17 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 06 February 2021 - 02:57 PM

I've been wondering if I have anything to add to this thread.......

 

I seem to be in a minority in that I do not really concentrate too much on arc seconds per pixel. I cannot see that as a determining factor considering the possibilities of binning, drizzling, and the vagaries of display size and cropping. I mean, why go to a lot of trouble trying to match pixel size to seeing when the recommendations for that match run anywhere from 1:1 to 1:3, or more? Why worry when one nights seeing numbers can be easily be twice or more what another's was. And does your camera become useless when one uses a reducer or even another tube. And when you throw in the fact that most of your images are displayed at about one fourth full resolution, it is quite possible to overfuss the arc seconds per pixel.  I mean, things, change. But I think any reasonable ball park for arc seconds per pixel will do. SO, I just don't fuss it too much.  

 

The issue of sensor size and scope does matter. And the answer to that is not pixel size, but image circle. The tube delivers a certain image to the focal plane. If you have a sensor too large for that image, you will get vignetting or bad performance on the corners. If you have one too small, you will be wasting photons, and getting a smaller picture (but the picture will be pretty much the same as the center of the larger sensor's frame. 

 

I would not want to buy any telescope tube that could not deliver a full frame image circle. And that frame should be fully illuminated (or close to), and fully corrected (or correctable through a flattener).

 

Whether the image circle is big enough to fill the frame is not dependent on F ratio and focal length alone. It is dependent on the overall engineering of the system. For instance, do you know the difference on your Canon between EF and EF-S lenses? The EF-S lens is built for crop sensors. If you put one on your 6D, you will get a picture, but the edges may not be all that usable. A 55 mm EF lens and a 55 mm EF-s lens delivers the same image to the central pixels. It is just that on the EF-s lenses, that usable image circle is smaller. It does not need to be bigger since it the sensor will see only that part.

 

At any rate, just be sure you get a good, clean, well lit image circle on your new tube. Whatever camera you get to go with it will love it. If you opt to get tube with an image circle that can only cover a smaller chip, that is fine, as long as you realize that you will forever be limiting yourself to cameras with a smaller chip. 

 

I hope this helps some. 

Alex

Alex, thanks for your advice.  I will digest it for sure. I just wanted to clear up one thing.  You mentioned the differences between crop sensor (EF-S) lenses and EF (full sensor ) lenses.  The Canon 6Ddoes not take the EF-S lenses.  They will not mount up at all.  I will consider all the other important advice about good clean image circles.  Since I have two cameras with different size chips, my choice is harder.  I might just opt to buy a new camera also.



#18 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 25,647
  • Joined: 27 Oct 2014

Posted 06 February 2021 - 03:04 PM

Alex, thanks for your advice.  I will digest it for sure. I just wanted to clear up one thing.  You mentioned the differences between crop sensor (EF-S) lenses and EF (full sensor ) lenses.  The Canon 6Ddoes not take the EF-S lenses.  They will not mount up at all.  I will consider all the other important advice about good clean image circles.  Since I have two cameras with different size chips, my choice is harder.  I might just opt to buy a new camera also.

If you do get a new camera, I recommend a cooled astro specific camera.  They're sensitive to H alpha, and low noise.



#19 Sunpilot

Sunpilot

    Explorer 1

  • -----
  • topic starter
  • Posts: 62
  • Joined: 25 Mar 2018
  • Loc: Mesa, Arizona

Posted 06 February 2021 - 03:04 PM

To Alex's point, the APS-C sensor on the A6000 will suffer less vignetting than the 6D from any aperture. And you already had it Ha modified. Seems like the obvious choice to me.

 

Since you already jumped off the deep end with the CEM60, you need a beefy scope to use up the 60-lb payload capacity. And with Mesa's reasonably dark skies, you should get a fast aperture. So you may as well go with the f/2.2 Celestron RASA-11.

 

post-257503-0-58941100-1533341433.jpg

[Source]

 

Its focal length is just 620mm, so not much of a tracking challenge. And at f/2.2, you can get away with 20 second subs on the A6000 (and 10 seconds on the 6D, at least at the center). At that flux, you could capture 2-3 targets per night vice the 1-2 targets per month with an oft-recommended f/7.5 apo.

 

Here's how the two cameras compare on that aperture:

 

attachicon.gifcameras.png

 

With that aperture, both cameras put you in the highly coveted 1-2" per pixel range (Line 13). With 15 lb of weight margin, you could go with either. And with that much flux, you could easily upgrade to mono and do extreme narrowband.

 

Astronomics has them in stock for just US$3600 shipped:

 

https://www.astronom...tical-tube.html

 

A DSO astrophotographer with a CEM60 should settle for nothing less.

 

BQ

 

P.S. If you ever want to do planetary, you might substitute a Celestron C14 for the RASA-11. With the Fastar add-on, it's an f/2 astrograph.

 

Fastar_Cameras_DSLR.jpg

[Source]

 

Just US$5000 shipped from Astronomics.

 

https://www.astronom...y-dovetail.html

 

Made for your mount.

Alex, 

 

That is  some awesome info you provided here.  It sounds like you love those scopes and the numbers certainly prove your thoughts.  I thank you for the input.  That kind of money might be a stretch for me right now, and being new to this I think maybe something a little less imposing will be better for me to start, but I can certainly see where I might head as I gain experience.

 

Thank you,

Frank



#20 Alex McConahay

Alex McConahay

    Voyager 1

  • *****
  • Posts: 10,595
  • Joined: 11 Aug 2008
  • Loc: Moreno Valley, CA

Posted 06 February 2021 - 03:16 PM

>>>>>>Since I have two cameras with different size chips, my choice is harder.  I might just opt to buy a new camera also.

 

No, not really......just get whatever tube., etc you buy big enough for the full frame. Most scopes nowadays can cover the full frame anyway I think. Look for something like "43 (or so) mm image circle." A 36 x 24 mm sensor is about 43 mm across its diagonal. Many scopes can meet this criteria. No use buying one that cannot. You can always use a crop sensor on a full size image circle. YOu cannot go the other way, however. (not without vignetting and poopy performance in the corners.) 

 

Alex


  • Sunpilot likes this

#21 BQ Octantis

BQ Octantis

    Fly Me to the Moon

  • *****
  • Posts: 5,242
  • Joined: 29 Apr 2017
  • Loc: Red Centre, Oz

Posted 06 February 2021 - 05:29 PM

That is  some awesome info you provided here.  It sounds like you love those scopes and the numbers certainly prove your thoughts.  I thank you for the input.  That kind of money might be a stretch for me right now, and being new to this I think maybe something a little less imposing will be better for me to start, but I can certainly see where I might head as I gain experience.

 

No worries at all, mate. I would love to own either of those scopes! But I'm way more budget-limited for this hobby, so my dream scope is just a 6-inch f/4 Newt astrograph (just US$300)—made for my 20-lb mount. But if someone were to gift me one of the other two…I'd find a way to afford a CEM60! laugh.gif

 

BQ


Edited by BQ Octantis, 06 February 2021 - 05:31 PM.

  • Sunpilot likes this

#22 ccs_hello

ccs_hello

    Voyager 1

  • *****
  • Posts: 10,739
  • Joined: 03 Jul 2004

Posted 10 February 2021 - 12:41 PM

Re: post #1

 

Important to note the "Image Circle" size (what the OTA or camera lens can offer in term of light output area-wise)

as well as "Image sensor size" (the real estate area on what the imager can capture).

 

See

https://www.cloudyni...6-image-circle/




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics