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Small refractor and Barlow question

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#1 Biggen

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Posted 16 February 2019 - 04:55 PM

Been doing a bit of reading and was thinking about possibly putting together an EAA rig in the future. Was looking at a small APO refractor like an AT72ED paired with a ZWO ASI294MC. Even with no reducer, M31 fits inside the frame nicely with this setup.

 

But am I totally without planetary viewing with this setup? Would a 4x or 5x Barlow allow any planetary viewing or am I building a strictly DSO setup here? Playing around with the FOV tool at astronomy.tools, Jupiter does show up with a 5x Barlow. But only a bit... Is a 5x Barlow even a possibility or does that need pristine skies?

 

 


Edited by Biggen, 16 February 2019 - 04:56 PM.


#2 Gary Z

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Posted 16 February 2019 - 06:48 PM

I'd like to bring your attention to the astronomy tools web site where you can choose your scope, camera, or eyepiece, barlow to get an idea what you will see, but remember you also need to look at the AT72's max useful magnification as well.  These calucations also do not take in atmospheric conditions either.

 

Some useful information from the user manual:

Lowest Usable Power........ 11x (with 40mm eyepiece)
Highest Terrestrial Power ... 72x (with 6mm eyepiece)
Highest Practical Power.... 108x (with 4mm eyepiece)
Theoretical Maximum........ 143x (with 3mm eyepiece

 

The first link is the fov for Jupiter, a 4x Barlow, the ASI294 camera, and the AT72 ED:

https://goo.gl/kWUugr

 

The second link is the site where you can input your gear for visual and imaging:

https://astronomy.to.../field_of_view/

 

Now, all this aside, I have done some initial imaging of M31, M81/M82, and M103 and was quite pleased with the outcome.  I also have the ZWO ASI294 camera.

 

Gary



#3 Howie1

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Posted 16 February 2019 - 07:20 PM

With that setup, yes ... Jupiter is tiny, But don't forget software such as SharpCap do have a zoom button. But of course, software zoom and you get pixellation.

 

I see folk going pretty long exposure times with 294's on NSN broadcasts. If you're going to use Alt Az I'd also ask folk / check on the forum if that camera has enough sensitivity to work nicely with AltAz short exposure times. Not such a problem if going to use Eq mount. 

 

Personally, having used 224's and an Infinity on ST80 and ED80 with all manner of reduction (0.83x, 0.5x, 0.3x) I think you'd be much better off with a 224 on that scope plus adding a 0.5 reducer.

 

Why? Well it gets you .....

 

1. More sensitive camera for faster exposures. Especially necessary to have that better sensitivity if you are going to use Alt Az. Are you?

2. Faster f/3 F Ratio with 0.5x reducer (and even lower if you get a 2nd hand Mallincam MFR5 reducer) ..... so again much shorter exposures for those (dim) nebs, galaxies and clusters.

3. Faster f/3 F Ratio with 0.5x reducer (and even lower if you get a 2nd hand Mallincam MFR5 reducer) .....for getting the wider field objects. M31 is just a tad too big. But IMHO you have to put exposure time and sensitivity ahead of seeing absolutely everything. Everything else fits well including M45.

4. Smaller chip of the 224 gives you much better magnification on planets with or even without using barlows on the 72ED (dont need reducer on for planets ... just barlows). 


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#4 Eddgie

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Posted 16 February 2019 - 07:51 PM

Been doing a bit of reading and was thinking about possibly putting together an EAA rig in the future. Was looking at a small APO refractor like an AT72ED paired with a ZWO ASI294MC. Even with no reducer, M31 fits inside the frame nicely with this setup.

 

But am I totally without planetary viewing with this setup? Would a 4x or 5x Barlow allow any planetary viewing or am I building a strictly DSO setup here? Playing around with the FOV tool at astronomy.tools, Jupiter does show up with a 5x Barlow. But only a bit... Is a 5x Barlow even a possibility or does that need pristine skies?

It is unlikely that this would be very useful for planets because by the time you got to 120x, if floaters were not a serious problem by this power, the dimming caused by the tiny exit pupil might be.

 

Probably OK for the moon, and you might be able to see Saturn's rings, but this is not an aperture that is going to give much in the way of planet detail when used visually.

 

But hey, this is CN, and someone will just as likely say that they have done amazing planetary views with a 60mm scope, so my opinion is just one of many, and if you are patient, someone will tell you that it is a great idea.


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#5 roelb

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Posted 16 February 2019 - 08:02 PM

About planetary, ask it here: https://www.cloudyni...ing-processing/



#6 Biggen

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Posted 16 February 2019 - 08:28 PM

Thanks for the replies guys. Yeah, it confirms what I was thinking.

 

Honestly, I’m ok with a DSO only setup. I enjoy finding and looking at those.

 

 

With that setup, yes ... Jupiter is tiny, But don't forget software such as SharpCap do have a zoom button. But of course, software zoom and you get pixellation.

 

I see folk going pretty long exposure times with 294's on NSN broadcasts. If you're going to use Alt Az I'd also ask folk / check on the forum if that camera has enough sensitivity to work nicely with AltAz short exposure times. Not such a problem if going to use Eq mount. 

 

Personally, having used 224's and an Infinity on ST80 and ED80 with all manner of reduction (0.83x, 0.5x, 0.3x) I think you'd be much better off with a 224 on that scope plus adding a 0.5 reducer.

 

Why? Well it gets you .....

 

1. More sensitive camera for faster exposures. Especially necessary to have that better sensitivity if you are going to use Alt Az. Are you?

2. Faster f/3 F Ratio with 0.5x reducer (and even lower if you get a 2nd hand Mallincam MFR5 reducer) ..... so again much shorter exposures for those (dim) nebs, galaxies and clusters.

3. Faster f/3 F Ratio with 0.5x reducer (and even lower if you get a 2nd hand Mallincam MFR5 reducer) .....for getting the wider field objects. M31 is just a tad too big. But IMHO you have to put exposure time and sensitivity ahead of seeing absolutely everything. Everything else fits well including M45.

4. Smaller chip of the 224 gives you much better magnification on planets with or even without using barlows on the 72ED (dont need reducer on for planets ... just barlows). 

 

So if I want to focus on DSO, you’d still recommend a 224 over a 294? Yes, I’d imagine I’d start with Alt/Az. Probably the Sky Watcher Az GTi mount.



#7 Howie1

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Posted 17 February 2019 - 03:39 PM

I searched on the forum and found the sensitivity of the 294 is almost as good as the 224 and 385 cameras. That's good news! The 224 and 385 are usually mentioned in threads where folks want to use small refractors on Alt Az for EAA. Just like you do. So, the 294, being almost as sensitive, will work for you. But it's still going to be wider than the 224 or 385 options. Whether that is acceptable to you, or not, is up to you to work out.

 

How do I do that you may well ask! Here's a short vid showing you all that. (Pictures are worth a thousand words 'n all!). To protect us all I put that vid up as non-pubic ... only available to view if you click the link below.

 

https://youtu.be/rSDX9wb-Psk


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#8 Biggen

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Posted 17 February 2019 - 05:50 PM

Wow, that video was great! I really appreciate the time you put into it.

 

Im torn between the 294 vs 224. The 294 allows me to image/see just about everything that is large. The FOV is massive with a 60 or 80mm refractor.  I’m just concerned small DSOs like the Ring or Crab Nebula will be too small to see very well. Sure, I can zoom via Sharpcap, but will I be able to zoom to a level that shows me detail without becoming pixelated?

 

On the other hand, the 224 has a very small FOV using the same scopes. I can reduce down to .8x -.5x which helps. M45 nearly fits perfectly with a .5x flattener with a 224 and said scope.  However, how bad is curvature/vignetting using a .5x flattener?


Edited by Biggen, 17 February 2019 - 05:51 PM.


#9 Howie1

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Posted 17 February 2019 - 08:27 PM

Up to you .... everything is a compromise which only you can work out what suits.

 

Zoom will definitely pixelate ... how many of those small objects are you willing to give up in order to get all the big ones?

 

Crab nebula doesnt look bad / too small IMO. Did you go to that site and check it out for yourself? That site shows the 'view' in a small rectangle ... But on a pc running sharpcap it will be a large 'viewing' window occupying about two thirds of the size of the pc screen. 

 

224 or 385 very small FOV ...  they are definitely to be used with 0.5 reducer. Not only for the wider FOV but also the 4x faster exposures which will greatly help on AltAz (where you are limited to under 15 or 20 secs as an average exp time).  I've used 224 with 0.5x on ST80 f/5 scope ... no vignetting. Maybe someone else has used same size sensor and 0.5x on the ED72 who can say for sure about vignetting on the ED72?

 

The elephant in the room BTW .... have you ever used a camera in full manual mode? And used photo editing software with sliders for saturation, color balance, and a histogram with black point and white point and gamma sliders? Many think you put the camera into the scope and click a button to take the image, and then just like a point and shoot fully auto DSLR or smartphone, the image appears on the screen. It doesn't. Strongly suggest to search on this forum for the beginners sharpcap guide written by HiTen. Download the sharpcap guide and have a read. 

 

Found it ... here's the thread with the sharpcap guide .... https://www.cloudyni...ck-start-guide/


Edited by Howie1, 17 February 2019 - 08:28 PM.

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#10 Biggen

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Posted 18 February 2019 - 07:26 AM

Thanks for the detailed response. I think I’ll go with the 224. It’s cheaper and should help me get my feet wet with EAA and beginner imaging. I can always move to a 294 at a later time if I decide I want to pursue it.

 

I was thinking about either a Sky Watcher AZ GTi or a the newer iExos 100 which is a GEM. Any thoughts?



#11 davidparks

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Posted 18 February 2019 - 09:42 AM

As others have indicated, the Astronomy.Tools FOV Calculator is a great resource.  I use the WO Z73 which has the same focal length as the AT72ED (430mm) with both the ZWO 294 and 224.

The 294 is great paired with this scope/focal length for the larger DSO's.  It also provides a very pleasing field for Solar and Lunar, however, it probably would not please you with Jup/Sat/Mars.

 

The 224 is great for many DSO's, Nebula like Trifid, Eagle - Galaxies and Globs - Planetary Nebulas, again you can use any FOV calculator and many Planetarium type programs (like SkySafari) to detail out lists of DSO's that are suitable.  The 224 will do better on Jup/Sat/Mars because it has smaller pixels, which will show a bit more detail than the 294.  However, you will still need to use something like a 5x Powermate to really see much detail.  With a 5x Powermate, the 224's 3.75um pixels will resolve 0.36" per pixel, while the 294's 4.63um pixels will resolve 0.44" per pixel, and you will be cropping out (ROI) a large part of the sensor to get frame read rates high enough for lucky imaging with the 294.

 

Honestly I love having both cameras, each has it's strengths, however, the 224 is a great camera to start with that will keep you busy with ALOT of targets waytogo.gif and between the two is the one I would choose if you want to try for planets.

 

The AT72ED will be great for DSO's with either camera, and can do a nice job with Jup/Sat/Mars if you can really stretch out the focal length, and the seeing that night is great... really you want optimal conditions.

The bottom line really is that planetary really needs longer focal lengths.


Edited by davidparks, 19 February 2019 - 08:56 AM.

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#12 davidparks

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Posted 18 February 2019 - 11:30 AM

I was thinking about either a Sky Watcher AZ GTi or a the newer iExos 100 which is a GEM. Any thoughts?

 

I think either of those mounts will work for you, and seem very comparable in many ways.

 

Here are a few thoughts:

 

EQ mount/mounting is generally used for guiding and longer exposures.  EAA is typically exposures < 60 seconds, and live stacking on Alt/Az works great, and is much simpler.

Having said that, I love guiding even short exposures on EQ mounting, for long integrations without field rotation.

 

The AZGTi seems to be a smaller mount, can be used in AZ mode (great for terrestrial too), or EQ mode with additional purchase of an EQ base  (I use iOptrons)

In AZ mode, the AZGTi has a very simple North-Level alignment routine.

The AZGTi tripod comes with a pier, great for both AZ and EQ modes.

SynScan is a fully developed mature product that runs on iOS/Android/Windows, and tried and true ASCOM compatible.

 

The iExos 100 might be able to handle a little more payload weight (3 or 4 lbs more?), not that you will need it with the AT72ED and accessories.

EQ only mounting, works with both longer exposure AP, and shorter exposure EAA.

EQ alignment requires a bit more effort, with either the AZGTi or iExos100, but it really is simple and quick once you do it a few times.

According to this thread, the ExploreStars interface is still under development, but seems to work with ASCOM just fine.

 

I really think either mount would work great with your proposed scope and intent to use it for EAA

 

I have a definite BIAS for the AZGTi, so please take my advice with a grain of salt, however, I love being able to quickly setup in AZ Mode with it's simplicity, doing a quick North-Level alignment, and viewing 30 second exposures in a 5 minute live stack with Sharpcap.  Mount/Scope/Cam/Laptop only.  -  And having the option to EQ Mount, load on the guidescope, and take up to 20 minute guided exposures.  Best of both worlds (EA/AP)

 

Hopefully a BIAS'd iExos 100 owner can give opinion too waytogo.gif


Edited by davidparks, 18 February 2019 - 11:32 AM.

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#13 Biggen

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Posted 18 February 2019 - 11:48 AM

David, that is excellent information.  I really think I am leaning towards the 224.  I think the information I have gathered is pushing me that way.  As I said, I can always move to a large sensor size camera in the future if I decide I really enjoy EAA/Astrophotography.  The 224 will keep me loads busy in the meantime.

 

Where those pictures you linked all livestacked on an Alt/AZ mount or where they long duration photo session imaging on a GEM?

 

I'm also leaning towards the AZ GTi.  I can always buy a cheap wedge and play around with the AZ GTi GEM function at a later date.  I also want to keep it as simple as possible with just starting out, and having to polar align every time I want to view doesn't sound like a ton of fun.  I can't see Polaris due to a neighbors house in to my north either, so there will be some frustrating times ahead trying to polar align.  I see Sharpcap has a polar align feature, but needs a FOV of at least 1.  Using an AT72ED with the .8 reducer/flattener, that still only gives me a view of .8 x .6 degrees.  So I'd have to use a larger reducer (e.g. 5x) or a guide scope in order to polar align using Sharpcap.

 

Have you used any of the .5x flatteners with either the AT60ED or AT72ED?  I see that Astrotech makes an "official" .8x flattener/reducer for these scopes.  I then see the many knockoff .5x flatteners out there as well.  Is vignetting really apparent using the .5x flatteners with these scopes?


Edited by Biggen, 18 February 2019 - 11:48 AM.


#14 davidparks

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Posted 18 February 2019 - 01:44 PM

The 294 DSO pictures are longer integrations, typically 1 minute exposures, stacked for 30 minutes in the case of Orion objects, 1 hour for Andromeda, and 2 hours for the Soul Neb.  However, it is amazing what you can see in only 5 minutes.  (You can click the pictures to see the details).  The AZGTi in Alt/Az can handle similar exposures (<=1m) but you will get field rotation noticeable in the corners the longer you stack, which is generally acceptable in EAA, and may not even show up in 5 minute stacks.  Sharpcap automatically de-rotates the image during stacking, but this leaves the edges, particularly the corners "less integrated".

 

EDIT:  Just to be clear, the DSO images above are longer integrations and post processed, so are not representative of what you will get with just 5 minuets of live stacking.  Look elsewhere here in the EAA forums for more applicable samples, however, you'll be amazed at what 5 minutes and no post processing can do.

 

Sharpcap's polar align would work fine with the AT72 and 294, probably not with the 224, and you need to have clear sky within 5 degrees of the pole.  The AZGTi uses the Synscan app on iOS/Android/Windows and has a Polar Alignment routine that can use any star, which is very useful when you can't see the Pole area, and only requires that you be able to center a star, using whatever means you have, mainscope, finderscope, red-dot finder, whatever.  I don't know if the iExos 100 and ExploreStars has an ASPA routine or not (All Star Polar Align).   I think Polar Alignment will preset the same challenges and use the same solutions with either mount if/when you can see the Pole area, but when you can't see the Pole area, i know the AZGTi can still be aligned with ASPA.

 

I use the Flattener (no reduction) built specifically for the WO Z73 made by William Optics, and have no experience with reducers on the AT models.  The chip size of the 224 will be sampling just a small area in the center of the total imaging circle offered by the AT72, so vignetting will be very minimal i should think, however, you may see more vignetting when using a small 1.25" accessory (reducer/filter/nosepiece) compared to just mounting the 224 onto the 42mm threads of .8/Flattener (you may need spacers).   In any case, dealing with vignetting (and dust bunnies) can be quick and simple with Flat calibration frames  (easy to do in Sharpcap)


Edited by davidparks, 18 February 2019 - 01:49 PM.

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#15 Biggen

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Posted 18 February 2019 - 06:52 PM

Thanks again David. That certainly helps. I’ll start looking around for used deals and see if I can stretch my dollar some. I think I’m sold on the AZ GTi and the ASI224. I just have to decide on either a 60mm or 72mm scope. I suppose whatever deals come up in the classifieds will suffice.



#16 Howie1

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Posted 18 February 2019 - 09:31 PM

Lovely images David! Interesting to also see your signature block ... not only do we seem to agree on the benefits / compromises between 294 and 224 and strengths and weaknesses ... but lo and behold same scopes selections. Well, I've sold those combos but I most certainly started out very happily with those combo's. 

 

Biggen, when deciding on either of those scopes ... dont forget to check with FOV calculators first ... just to check FOV, F ratio (faster is faster shots necessary on AltAz), etc.

 

I don't have a video on SharpCap as for ages I've used other software. But, I can say for sure many people struggle learning it. The tip / easy way is to do the following ....

 

* Setup the scope about an hour or two before it gets dark. Being daylight you can use sharpcap to set gamma, exposure time and gain to AUTO, meaning you only have to worry about finding the focus point of the camera, and learn color balance.

* Point the scope at something way out on the horizon, with a few colors in the scene. IE green grass/tree, brown tree trunk, blue sky. IE to be able to find the infinity focal point of the camera, and to learn the color balance process.

* Sharpcap view probably won't show anything at first ... set those gamma, exp time and gain to AUTO and first focus the camera.

* When you have focus, measure (tape measure) or cut a 'template' (card or plastic) which will be the length between the camera front and the focus tube. You'll end up using this in the dark when you take out your eyepieces after doing your alignment process ... slip the camera in and use the tape/template to adjust the focuser to that where the camera should be close to correct focus.

* BUT stay doing the following steps also in the day after you have found focus ... the colors in the image from the camera may be a bit 'odd'. Even if they look correct ... open up the sharpcap menu where you find the RGB (Red Green Blue) color sliders. Learn what they do to the image as you move them to adjust the colors. Color balance becomes important to know about when you eventually get to looking at stuff in the dark!

* Then look for a 'histogram' button on the sharpcap top menu bar ... just to the right hand side of the Zoom field on the menu bar and it looks like a green curve with horizontal and vertical chart axis. 

* Click the histogram button and a histogram chart will open up within the sharpcap menu on the right hand side.

* You'll see a white curve (the overall white balance), as well as a button to turn on the Red Green and Blue curves ... as white light is made up of those three primary colours. My version of sharpcap is old and maybe new ones you dont have to turn on the RGB curves ... dunno?

* Again move the Red Green Blue sliders around and see how the RGB curves move. Notice by moving the sliders around, that when you use them to align the peaks of the RGB curves over the top of each other ... so R peak overlies G peak overlies B peak ... that the view in sharpcap will show fairly natural looking green grass, siding color, roof color and blue sky color. This process of aligning the color peaks is one of the main ways we color balance the images we shoot in the dark. It is very important to learn to use. 

* So now you have easily learnt the focus point of the camera, and how to easily color balance, by now it should be getting dark in your neighbourhood. This is where you uncheck the auto exposure and gain and gamma buttons. Your aim is to learn how to adjust the gain and exposure using the sliders so that the image of that far away scene stays pretty bright..

* You should be able to keep adjusting those sliders for gain and exposure and keep the distant scene showing in sharpcap right up to when it is getting pretty dark! That's the aim!

* So now you have learnt enough to be able to use the mounts GoTo and goto some bright target objects ... and start with just single frames. Do NOT worry about stacking to start with. Your aim is to try to get the brightest/contrasty single images. Why? Stacking needs / works best with nice bright contrast single image. Otherwise you often get stacking failures.

* Also download and read Hitens excellent Beginners SharpCap guide ... search on cloudynights for it. Good read for you. It tells you more about all the individual controls and settings for the night and how to stack. 


Edited by Howie1, 18 February 2019 - 09:55 PM.

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